ABSTRACT. Given a set of inelastic material models, a microstructure, a macroscopic structural geometry, and a set of boundary conditions, one can in principle always solve the governing equations to determine the system’s mechanical response. However, for large systems this procedure can quickly become computationally overwhelming, especially in three-dimensions when the microstructure is locally complex. In such settings multiscale modeling offers a route to a more efficient model by holding out the promise of a framework with fewer degrees of freedom, which at the same time faithfully represents, up to a certain scale, the behavior of the system. In this paper, we present a methodology that produces such models for inelastic systems upon the basis of a variation scheme. The essence of the scheme is the construction of a variation statement for the free energy as well as the dissipation potential for a coarse scale model in terms of the free energy and dissipation functions of the fine scale model. From the coarse scale energy and dissipation we can then generate coarse scale material models that are computationally far more efficient than either directly solving the fine scale model or by resorting to FE2 type modeling. Moreover, the coarse scale model preserves the essential mathematical structure of the fine scale model. A crucial feature for such schemes is the proper definition of the coarse scale inelastic variables. By way of concrete examples, we illustrate the needed steps to generate successful models via application to problems in classical plasticity, included are comparisons to direct numerical simulations of the microstructure to illustrate the accuracy of the proposed methodology.

ABSTRACT. In Vietnam and many other countries, commercial drones are commonly known as flycams—flying cameras used mainly for imaging and video. While this reflects their most visible application, it also underscores a limitation: current drones remain largely passive sensing platforms. The next generation—flyrobots—seeks to move beyond this role by becoming physically capable systems that can actively interact with and shape their environments.

This talk will explore how recent advances in mechanics and control are driving this transition. We will examine the fundamental challenges of empowering aerial vehicles with physical capabilities, working on floating-base systems with complex dynamics. Case studies from my recent research and collaborations will demonstrate how such systems can perform tasks beyond passive observation, including perching, payload transportation, and cooperative manipulation.

Looking ahead, the talk will highlight how the fusion of mechanics, control, and recent advances in AI is enabling a new generation of physically capable aerial robots—versatile flying machines designed not only to observe the world, but to act within it, performing complex tasks in challenging real-world environments.

ABSTRACT. In many practical engineering applications, complicated fracture phenomena in functionally graded materials induced by thermo-mechanical loading are challenging for the engineering design process. Consequently, the ability to model such fractures is desired for computational simulations. From that motivation, the authors introduce an effective smoothing gradient-enhanced thermo-mechanical damage model to capture complex thermal crack patterns. To describe the adiabatic property of the damage zones (crack patterns), a scalar variable indicating the degradation of material, which is usually called damage variable, is integrated into the heat conduction balance equation. In detail, the local heat flux and heat capacity are modified to present a decrease in heat flow at the location of cracks. The governing equation system is composed of the equilibrium, evolution, and heat conduction equations to account for the thermal effect (e.g., thermal shock) on damage initiation and propagation. Formulations of the developed damage model for transient heat transfer are given. The efficiency of the coupled smoothing gradient damage model is illustrated through the numerical test, where the predicted crack patterns induced by thermo-mechanical loading for transient heat transfer case show potential to extend developed damage model to more complex fracture problems in functionally graded materials.

ABSTRACT. Flat slabs are widely used for their quick construction, cost-effectiveness, and space flexibility . However, they are prone to punching shear failure, especially when openings increase shear stresses at slab-column connections. In this study, a numerical model was developed using the finite element method to investigate the punching shear behavior of flat slabs with openings. The model was validated against experimental data, showing strong agreement in terms of the load-displacement curve and failure mode. Additionally, the effects of key parameters, including the location, shape, and size of openings, slab height, and reinforcement ratio, were analyzed. The findings provide valuable insights for improving the design of flat slabs.

ABSTRACT. An effective explicit time integration scheme for simulating dynamic crack growth governed by a physics-based energy limiter nonlocal damage model is presented in this work. The present gradient damage framework incorporates both an energy limiter and a damage threshold, enabling natural crack evolution while significantly reducing spurious damage. To ensure computational efficiency under dynamic loading with complex crack patterns, an explicit fracture algorithm is developed based on the central difference method. Key components of the implementation include the row-sum technique for mass lumping and a consistent procedure for updating damage-related variables. Additionally, a practical criterion is proposed for determining the critical time step for low-order elements in both 2D and 3D simulations. Representative numerical examples demonstrate the robustness and effectiveness of the proposed method in capturing dynamic fracture behavior.

ABSTRACT. Concrete, a primary material in urban infrastructure projects, is known for its high compressive strength and durability; however, it is susceptible to time-dependent deformation (creep) under sustained loading. Creep leads to gradual strain accumulation, which can reduce the load-bearing capacity and shorten the service life of structures. To characterize and better understand this behavior, the present study focuses on quantifying key mechanical properties through laboratory testing. Uniaxial Compressive Strength (UCS) tests were conducted to determine the compressive strength, while Brazilian creep tests were performed to assess creep behavior. The experimental creep data were subsequently fitted using the Burgers rheological model to derive creep parameters representative of the concrete’s long-term deformation characteristics.

ABSTRACT. Numerous phenomena in mechanics, physics, chemistry, and plasma physics lead to the Duffing-type nonlinear equation of motion. Traditionally, the properties of this equation's solutions have been investigated in the real domain, revealing several distinctive phenomena in Newtonian mechanics. However, research into the solutions of this equation in the complex domain remains limited. The Duffing equation, being strongly nonlinear, possesses complex-valued solutions that should not be overlooked. This paper applies the Coupling Successive Approximation Method (CSAM), an iterative procedure for solving nonlinear differential equations, which was previously published and validated for its accuracy and convergence in the Vietnam Journal of Mechanics (Nos. 2 & 3, 2014). The results yield complex-valued solutions exhibiting chaotic characteristics in a three-dimensional phase space. The chaotic nature is verified using Poincaré sections. The problem is solved for various sets of parameters, revealing several distinctive properties of the solutions. This solution and analysis method can be applied to study the dynamics of flying objects such as rockets and spacecraft.

ABSTRACT. In the damage analysis of material with complex microstructures, a direct numerical simulation (DNS) could produce huge computational costs. Alternatively, the multiscale modeling is a more effective method by using less degrees of freedom to balance the computational accuracy and cost. In this paper, a new multiscale method for damage analysis is proposed based on the framework of the variational effective model for elastoplastic problems originally presented in author’s previous work. The key idea is to construct variational statement for the free energy and the dissipation potential of a coarse scale model by relating the free energy and the dissipation potential of a fine scale model. In this way, the damage analysis can be directly simulated at the coarse scale solution, resulting in significantly higher computational efficiency compared to the DNS in fine scale. In addition, the relaxation damage model is used to effectively avoid ill-posed boundary value problems in damage analysis without use of gradients or integration techniques. Three numerical examples are provided to demonstrate the effectiveness of the proposed method, by comparing the computational accuracy and cost of the proposed method with reference solutions provided by DNS and FE2 algorithm.

ABSTRACT. This study develops a novel locking-free numerical method for pseudo-static limit-state analysis of structures. In the proposed formulation, each quadrilateral element is first enriched with a single bubble node (Q5-element); the smoothed formulation is then constructed over cell partitions. Numerical investigations on two-dimensional plane-strain benchmarks demonstrate that volumetric locking, which typically persists in pseudo-static formulations, is effectively eliminated by the proposed approach, resulting in locking-free responses. The resulting optimization problem is expressed as second-order cone programming (SOCP) and solved efficiently with state-of-the-art conic solvers (e.g., MOSEK). Accuracy and convergence are demonstrated through systematic numerical studies and mesh refinement, with results consistent with reference solutions and baseline implementations.

ABSTRACT. The presence of surface-active agents (surfactants) can critically alter the dynamics of interfacial flows by changing surface tension. Surfactants are widely used to manipulate interfacial flows in various industrial, biomedical, and microfluidic applications. A front-tracking method is used to track the interfacial flow with insoluble surfactants. A surfactant concentration evolution equation on the interface will be solved together with the incompressible Navier-Stokes equations using a linear equation of state that relates interfacial surface tension with surfactant concentration at the interface. Verification tests are performed to check the accuracy and computational results of the deformation and movement of a droplet rising in a liquid column in the presence of an insoluble surfactant. The results are in good agreement with analytical solutions and other simulations. In all the cases considered, the role of surfactants in the dynamic behavior of droplets was investigated. It is observed that, the insoluble surfactant reduces the surface tension on the interface of the droplets.

ABSTRACT. Microfluidic devices with complex geometries and obstacles have attracted significant attention in the fields of biomedical engineering and chemical analysis. This study examines the dynamics of multi-core compound droplets in microchannels. Two cylindrical obstructions were arranged within the microchannel to assess their impact on droplet behavior. Using numerical simulations based on the front-tracking method, the study demonstrates that the presence of obstacles significantly alters the motion dynamics of the droplets. The simulation results identify three distinct movement modes: “Passing-Nonmerger” (P-NM), “Passing-Merger” (P-M), and “Trap” (T). These modes depend on the obstacle size, and flow property parameters. The findings offer critical insights that contribute to the development of more efficient microfluidic systems.

ABSTRACT. The solidification of suspended hollow droplets is a phenomenon commonly encountered in both natural systems and industrial applications. In this study, we investigate the containerless solidification process of hollow droplets subjected to forcing flows, utilizing the front-tracking method - a robust method for simulating multi-phase flow dynamics. Our findings indicate that key parameters, such as the Weber number (We), the solid-to-liquid thermal conductivity ratio (ksl), and the gas-to-solid viscosity ratio (μgl), have a impact on both the solidification rate of the advancing front and the final geometric characteristics of the droplets. The inner (Ari) and outer (Aro) aspect ratios of the droplets are strongly influenced by these parameters during the solidification process. The study covers a wide range of parameter values, with We varying from 0.125 to 4, ksl ranging from 0.125 to 4, and μgl spanning from 0.0125 to 0.4. By analyzing the effects of these parameters, we provide deeper insights into the complex interplay of thermal and flow properties that govern the solidification process. These results not only enhance our understanding of phase change mechanisms in containerless environments but also offer valuable implications for material processing and the development of advanced manufacturing technologies.

ABSTRACT. The roof is the element of a building that contacts directly and most with storm wind. Actual observations show that most of the roofs are often blown-off immediately after gusts, in which the storm wind suddenly accelerates in a very short period (approximately 0.3 - 0.5 seconds), and the blown-off areas are mostly crosswind and downwind roof slopes. It is only suitable to investigate this process during one period of fluctuation of wind speed, ie, T = 1/frequency, and the correlative average speed of wind during the fluctuation period, which can be called “frequency speed”. Based on that, applying the equation connecting Boyle's and Bernoulli's laws to the outside wind field around the building while the airflow was passing, the authors presented the changes in atmospheric pressure during gusts and calculated the pressure difference between the inside and outside of the building with vents on the roof. This pressure difference is exactly the loading causing damage to the roof. For the 3-second gusts that affect the building (with the vents), the graph of the maximum differential pressures depending on the area of the vents/building volume ratio has been established.

ABSTRACT. This work explores the transient development of Crow instability in a pair of counter-rotating vortices of equal strength descending toward a flat no-slip wall under mutual induction at a Reynolds number (Re = 4000). Direct numerical simulations are performed for two initial vortex heights, h/r₀ = 5.0 and 10.0, where h denotes the initial distance from the vortex cores to the wall and r₀ is the spacing between the two primary cores. This setup allows for a detailed examination of instability evolution and serves as a representative model of aircraft wake vortex behavior in ground-effect conditions. As the vortex pair moves closer to the wall, flow separation occurs, giving rise to secondary and tertiary vortices rotating opposite to the primary pair. This interaction produces a rebound effect, in which the primary vortices are deflected upward away from the wall. For the h/r₀ = 5.0 case, strong wall interaction leads to the formation of secondary vortices prior to vortex reconnection. Vortex tongues emerging from these secondary vortices are observed, along with rapid kinetic energy decay and a sharp increase in enstrophy. Conversely, at h/r₀ = 10.0, the primary vortices undergo long-wavelength Crow instability, reconnecting to form vortex rings. These rings then descend and interact with the wall, producing secondary vortices at a later stage compared with the h/r₀ = 5.0 configuration. The evolution of vortex structures, together with variations in kinetic energy, enstrophy, and helicity, underscores the complex multiscale dynamics inherent in vortex–wall interactions. The results provide valuable insights into near-wall vortex dynamics with important aerodynamic relevance.

ABSTRACT. A numerical study employing the Vortex-in-cell method examined the turbulent energy cascade and vortex topology modifications arising from a vortex ring collision with a wavy solid sphere at Re_Г = 2000 and 6000. The research elucidated the influence of parameters, including wavenumber (n_w) at 0, 5, and 9; wave amplitude (a_w); Reynolds number (Re_Г); and the ratio of the sphere diameter to the ring diameter (d_sphere / d_ring) from 1 to 4, on the resulting vortex formations. The collision with a smooth sphere (n_w = 0) is observed to produce secondary and tertiary vortex rings, considered a two-dimensional phenomenon. As the n_w increases, the hill experiences early separation compared to the valley due to the faster expansion of the boundary layer. When the wavenumber increases from n_w = 2 to n_w = 4, the quantity of tertiary vortices in the valley interconnect to create a series of vortex loops. Furthermore, increased Reynolds numbers result in greater deformation and a heightened rate of energy dissipation. Additionally, increasing the ratio of sphere diameter to ring diameter enhances the interaction between the vortex ring and the oscillating sphere, leading to the formation of more intricate vortex structures, characterized by an increase in the number of vortex filaments.

ABSTRACT. This paper presents a modeling approach to study the motion of an ogive-nosed projectile moving from air to water. Using Rayleigh's pressure formula, the hydrodynamic forces and moments acting on a truncated cone-shaped body are calculated. This method is then extended to evaluate the hydrodynamic effects on submerged portions of the body with arbitrary convex profiles (by dividing the object into segments parallel to its axis of symmetry, each approximated as a truncated cone). Depending on initial conditions (such as impact velocity and angle), computational results show that the projectile may either ricochet off the water surface or penetrate it and continue move into the water. The motion characteristics, including velocity and rotation angle, are significantly influenced by these initial conditions.

ABSTRACT. In this paper, Rayleigh surface waves in a Type II thermoelastic half-space are investigated. The Stroh formalism is applied to compute the eigenvalues and eigenvectors of harmonic plane waves in the medium. These eigensystems are then used to derive an expression for the horizontal-to-vertical (H/V) displacement ratio of Rayleigh waves in the half-space. Numerical simulations examine the influence of the thermo-mechanical coupling coefficient on the H/V curve, and the results are presented graphically.

ABSTRACT. Architected materials based on Triply Periodic Minimal Surfaces (TPMS) offer superior mechanical properties; however, investigations into their 2D counterparts remain limited. This paper presents a systematic numerical investigation into the elastic and failure properties of 2D Primitive TPMS lattice structures by varying their geometric parameters (C1 and C2). A phase-field damage model is employed to simulate the entire mechanical process, from elastic deformation to crack initiation and propagation until complete failure. The results indicate that the mechanical performance depends not only on the relative density but also strongly on the shape parameters themselves. Notably, two structures with nearly identical densities exhibited a five-fold difference in strength. Furthermore, this study demonstrates that 2D Primitive structures can exhibit auxetic properties, with a negative Poisson's ratio as low as -0.12 recorded for the case of C1=1.2 and C2=0.8. The failure mechanisms were identified to originate from the specimen's center, where stress concentration is highest. These findings provide a crucial dataset and deep insights into the geometry-performance relationship, paving the way for the design and optimization of 2D TPMS materials for demanding engineering applications.

ABSTRACT. Pervious concrete (PC) is a key material in sustainable urban development, but its design is complicated by the inverse relationship between permeability and compressive strength. To optimize its use, various predictive models—analytical, numerical, and data-driven—have been developed. However, a comparative validation of these diverse approaches on a consistent experimental dataset is lacking. This study aims to validate and compare the performance of three fundamental predictive frameworks: an analytical model based on micromechanics, a numerical simulation using the phase-field method, and an Artificial Intelligence (AI) approach, specifically a "white-box" symbolic regression model. An experimental case study involving the fabrication and testing of PC specimens was conducted to provide a new, independent dataset for validation. The results show that the symbolic regression, finite element method, and micromechanical models demonstrate strong agreement with the experimental data, achieving a high coefficient of determination. While black-box AI models often offer high accuracy, this study highlights that simpler, interpretable models provide a compelling balance of precision and practical applicability for engineering design.

ABSTRACT. Concrete is a man-made construction material composed of a mixture of cement, aggregates, water, and admixtures, characterized by high compressive strength, durability, and widespread use in most construction projects. This paper primarily focuses on numerical simulations of the compressive strength of concrete, taking into account key material characteristics such as aggregate content and the interfacial transition zone between aggregates and the cement paste matrix. The numerical results are compared with experimental data to evaluate the accuracy and reliability of the computational model. The findings indicate that the numerical model effectively captures the experimental trends, demonstrating its capability to predict the compressive strength of concrete with high precision. Furthermore, this study provides valuable insights into the mechanical behavior of concrete, which can support the optimization of design and the improvement of structural performance. Based on these results, the proposed formula can be applied to practical engineering applications, contributing to the development of durable and high-performance concrete materials.

ABSTRACT. In this work, we establish a criterion for well-posedness of Eringen’s non local elasticity theory for problems of harmonic plane waves in domains with non-empty boundaries, and introduce a novel method for solving well-posed problems. The criterion for well-posedness says that for problems of harmonic plane waves, Eringen’s non-local elasticity theory is well-posed when the constitutive boundary conditions contain all equilibrium boundary conditions, otherwise it is ill-posed in the sense of no solutions. With this well-posedness criterion, it is easy to check whether a non-local harmonic plane wave problem is well-posed or not. If it is a well-posed problem, its solution will be found by employing the novel method. It has been shown that Eringen’s method, which has been used widely to solve problems of non local harmonic plane waves, does not give their correct solutions. Therefore, it must be replaced by the novel method. As an application of the criterion for well-posedness and the novel method, two well-posed problems of harmonic plane waves are considered including Rayleigh waves and SH waves propagating in traction-free non-local isotropic elastic half-spaces. Exact solutions of these problems have been obtained including explicit expressions of displacements, local and non-local stresses and dispersion equations.

ABSTRACT. For conventional composite, the effective elastic modulus is independent of particle size. However, this is no longer true for composite containing imperfectly bonded inclusions. In other words, the macroscopic property depends on the size of inclusion. Size effects became an essential question due to the progressive reduction in size of electronic devices or semiconductors. The aim of this work is to construct a scaling law for the macroscopic elastic modulus of composite with interfacial traction discontinuities

ABSTRACT. This study introduces a multiscale modeling approach that combines Molecular Dynamics (MD) and the Finite Element Method (FEM) to evaluate the mechanical behavior of polymer composites reinforced with nanoparticles, using functionally graded interphase modeling. At the atomic scale, MD simulations explore interfacial adhesion, characterization of perturbed zone (called “interphase”) between the matrix and the nanoparticle, and mechanical behaviors of each phase in the heterogeneous material. As deduced from the MD simulations when computing mean squared displacement, the interphase can be modeled as a functionally graded zone. These findings are then integrated into FEM to assess the local mechanical fields as well as macroscopic properties of nanocomposite, through different boundary conditions. Different types of functionally graded interphase are simulated including linear, exponential and power law. The effects of reinforcement fraction and functionally graded interphase are investigated accordingly. Overall, the proposed methodology offers a physicsinformed and computational strategy for investigating the mechanical behavior of nanoparticle-reinforced composites.

ABSTRACT. The dynamic response of viscoelastic functionally graded (FG) beams subjected to an axial compressive force and a convoy of moving harmonic loads is presented. Material properties of the beam vary throughout thickness according to the power distribution. The Mori–Tanaka homogenization technique is applied to determine the effective material properties. Besides, the Kelvin–Voigt viscoelastic model is also applied to determine the effect of damping on dynamic responses of the FG beams. Equations of motion for the FG beams subjected to an axial compressive force and a convoy of moving loads are established based on the Finite Element Method (FEM). The effects of the different material distribution, the velocity of the convoy of moving harmonic loads, the axial compressive force, distances between loads and damping, the excitation frequency on the dynamic responses of the beam are discussed. Numerical results show that the afore-mentioned effects play a very important role in the dynamic deflections of the beam.

ABSTRACT. This paper analyses free vibrations of multiple cracked multi span continuous nanobeams made of Functionally Graded Material (FGM) based on the Nonlocal Elastic Theory (NET) and the Dynamic Stiffness Method (DSM). FGM characteristics vary nonlinearly throughout the height of the beam element. The NET considers the nonlocal parameter that perfectly captured the size effect of nanostructures. First, the dynamic stiffness matrix and the nodal load vector of the multiple cracked FGM nanobeam element using Timoshenko beam theory and massless double spring model of crack are established. Then, effect of crack parameters on free vibration of the multiple cracked FGM multi span continuous nanobeams is examined. The theoretical developments are validated by numerical examples. The influences of the nonlocal, material, geometry parameters and elastic foundation on the free vibration are then analyzed. It is shown that the study can be applied to other FGMs as well as more complicated framed structures.

ABSTRACT. This paper examines the dynamic behavior of a three-layer infinite panel subjected to stationary vibrations induced by the surrounding acoustic environment. The study employs the method of transient functions and the Fourier transform, enabling an accurate description of the influence of external loads and boundary conditions on the structure. Particular attention is given to the construction of influence functions for normal and tangential displacements, as well as tangential stresses in the panel’s core. The core has a regular structure, and the model accounts for transverse shear deformations, allowing for a more precise evaluation of the structure’s damping properties. The paper addresses a coupled problem of three-layer panel vibrations in an acoustic environment, incorporating boundary conditions defined by the compensating load method. The obtained analytical solutions and numerical simulations facilitate an in-depth investigation of the material’s damping properties and further assessments of the dynamic behavior of structures, considering the characteristics of the materials used and the effects of harmonic waves of various configurations acting on the panel. The findings of this study can be valuable for the design of vibration isolation elements and acoustic shielding screens, as well as for structural components of aircraft and marine vessels. Additionally, the results have engineering applications in the analysis of stability and vibration characteristics of multilayer panel structures.

ABSTRACT. The increasing demands of modern society have led to reduced attention to health, contributing to the rising incidence of cancer, particularly breast cancer. Early and accurate diagnosis is crucial for effective treatment, yet invasive procedures can cause significant psychological distress. This study proposes a non-invasive, multi-method approach to enhance tumor identification and optimize treatment planning. First, MATLAB-based pixel analysis of ultrasound elastography images identifies suspicious regions based on tissue stiffness variations. Next, ANSYS simulations assess the biomechanical properties of these regions, analyzing stress-strain distribution to determine tumor location and stiffness accurately. Finally, GEANT4 simulations optimize radiation dosing to maximize tumor cell destruction while minimizing damage to healthy tissue. This research advances precision medicine by integrating computational modeling with medical imaging and radiotherapy optimization, offering a personalized, non-invasive approach to improve diagnostic accuracy and treatment efficacy.

ABSTRACT. This paper studies the bending of functionally graded triply periodic minimal surface (FG-TPMS) plates with two boundary conditions using the third-order shear deformation (TSDT) theory. The characteristic equations are derived from Hamilton’s principle and the approximation of field variables under the Ritz-Chebyshev series. Numerical examples regarding static analysis of FG-TPMS plates are illustrated to confirm the reliability and accuracy of the proposed approach. The influences of three TPMS architectures, including Primitive (P), Gyroid (G), and wrapped package-graph (IWP) and thickness-to-length ratios on the plate response are investigated.

ABSTRACT. In this report, the concept of electro-mechanical receptance is developed for cracked functionally graded beams bonded with a piezoelectric layer. The double spring model of transverse edged crack is adopted for vibration in functionally graded Timoshenko beams subjected to concentrated harmonic excitation. Therefore, the electrical response of the piezoelectric layer is established in an analytical form, allowing the concept of electro-mechanical receptance for (EMR) the piezoelectric functionally graded beams to be defined. The obtained electro-mechanical receptance is analyzed along material and crack (position and depth) parameters, and its potential applications for crack detection for the beams are discussed.

ABSTRACT. Shear deformation theories (SDTs) are crucial for modeling thick beams and plates since transverse shear deformation substantially influences structural behavior. Conventional models, like classical plate theory (CPT) and first-order shear deformation theory (FSDT), exhibit constraints in precisely representing shear effects. Higher-order shear deformation theories (HSDTs) have been formulated to resolve these challenges, using a shear strain distribution function f(z) to enhance shear stress predictions. This article briefly reviews innovative shear deformation theories that integrate an f(z) function, including their mathematical formulations, benefits, applications, and prospective research avenues.

ABSTRACT. Granular flows are common phenomena observed in natural disasters such as landslides and rock avalanches. These geophysical mass flows commonly represent inherently complex behavior due to the interplay of multiple impact factors, especially the particle shape effect and the underlying erodible bed. In this work, we systematically study the effects of particle shape on granular column collapse on an erodible bed using the superquadric discrete element simulations. The non-spherical particle shapes are accurately defined utilizing the aspect ratio A and blockiness B, resulting in a change from elongated to platy and cubic shapes. The granular column is composed of different superquadric grains; meanwhile, the erodible bed is kept constant in a weak binary-size mixture of spherical grains for simply describing and quantifying the erosion behavior of erodible grains. The results show that the degrees of erosion slightly increase with decreasing the elongation of superquadric grains. The runout distance of the granular columns changes complicatedly with the increase of the particle aspect ratio, while it declines significantly with increasing blockiness. The blockiness of superquadric grains also reveals significant impacts on the erosion behavior of granular materials. These findings may improve the understanding of more general scenarios of granular mass flows on complex surfaces such as an erodible bed.

ABSTRACT. Debris flows are catastrophic natural disasters that potentially damage the downstream facilities and may affect human lives. These natural hazards are commonly mixtures of a muddy fluid phase and a solid phase composed of different particle sizes, shapes, roughness, and distributions. To mitigate their impacts, different structural countermeasures such as closed-type check dams [1], slit dams [2], and baffle systems [3] are proposed. In which, slit dams represent the ability to dissipate flow energy, trapping boulders, and allowing muddy fluid and fine solid material to pass through; however, the roles of large-grain content on the structure-debris flow interaction and slit-dam ability remain elusive. In this work, we explore this missing understanding by simulating the debris flow composed of muddy fluid phase and solid phase with different binary-size mixtures utilizing a coupled CFD-DEM approach. The results show that the increase of the large-grain content not only improves the run-up behavior but also enhances the magnitude of impact forces on slit dam. Furthermore, the increase of the large-grain content tends to change the bounce-back behavior of both muddy fluid phase and solid phase as a consequence of increasing the pore space. These findings may provide a useful reference for structural engineers in designing debris-flow mitigating impact structures.

ABSTRACT. This study introduces a meshfree framework for topology optimization of plates made of bi- directional functionally graded materials (2D-FGMs). The plates are modeled based on the third-order shear deformation theory (TSDT) to accurately capture the effects of transverse shear without requiring shear correction factors. To avoid the limitations of mesh dependency, the radial point interpolation method (RPIM) is employed as the underlying numerical technique. The material properties are assumed to vary continuously along both in- plane directions following a power-law distribution. The optimization process is driven by the proportional topology optimization (PTO) method, a gradient-free heuristic that enables efficient redistribution of material based on structural performance. Numerical examples are presented to demonstrate the effectiveness of the current approach in obtaining optimal topologies with enhanced stiffness and smooth material distribution. The results show the capability of the RPIM-PTO framework in handling the 2D-FGM plate with TSDT models, providing valuable insights for the lightweight design of advanced functional structures.

ABSTRACT. Plastic product has been used for many practical applications such as automotive, aerospace, construction, and electronics devices. Product quality is really important for plastic products that produced via using injection molding process. Reducing defects that is an effective method to improve the product quality such as minimizing warpage during injection molding process for enhancing the quality of plastic product. These defects normally are appeared during injection molding process such as warpage, shrinkage, shot-shot, and weld-lines that can be predicted via using computer simulation technique. The warpage can be disposed by controlling the injecting parameters such as melt temperature, filling time, injection pressure, and mold temperature. The response surface modeling (RSM) is the effective method that used to deal with engineering problems such as predicting goal and optimizing the manufacturing process. This paper demonstrates a RSM method of reducing the warpage of polymer product produced by injection molding process. The warpage results are archived through a computer aided engineering (CAE) tool. The results show that RSM and simulation techniques have been effectively used for minimizing the warpage of 0.574 mm with optimal parameters set of melt temperature of 220oC, filling time of 2s, injection pressure of 105.3 MPa, and mold temperature of 40oC, respectively. The results are valuable references for the real production in the near future.

ABSTRACT. This paper presents a novel two-scale topology optimization approach for coated structures infilled with cellular materials. Here, two optimization problems are defined, one for the macro-structure (which is the coated structure), and one for the micro-structure (which is the representative unit cell of the cellular material. For the coated structure, it is assumed that the coating layer is solid, while the substrate is infilled by a cellular material. The strain energy method is applied to the micro-scale domain to evaluate the effective elastic tensor of the cellular material. This effective elastic tensor is passed into the macro-domain as the material properties. The two optimization problems are solved concurrently via an iterative scheme based on the Method of Moving Asymptotes. For identification of coating and substrate layers during optimization, a scheme being inspired from the dilation and erosion operators is proposed. Each operator includes a density-filter being followed by a Heaviside- projection. The two operators differ from each other by the filter radius and the threshold value. Applying the two operators, coating layer and substrate layer can be identified from only one set of macro-scale design variables. The optimization results in the numerical examples demonstrate that the proposed approach is effective in design of coated structures infilled with cellular materials.

ABSTRACT. This paper investigates the propagation of electromagnetoacoustic shear horizontal waves (briefly called EMA-SH waves) propagating along the interface of two piezoelectric half-spaces, without using the quasi-static approximation. By employing the complex variable function method, the necessary and sufficient conditions for the existence of EMA-SH waves are established, and explicit formulas for the slowness are derived. From these results, we directly obtain those for EMA-SH waves under the quasi-static approximation, known as Maerfeld-Tournois waves. These results are useful tools to evaluate the effects of piezoelectricity on acousto-optic interactions and have broader implications for various practical applications.

ABSTRACT. Machining time is the key factor to improve the productivity of a computer numerical control (CNC). The CNC program is rapidly created via using an integrated system of computer-aided design/computer-aided manufacturing (CAD/CAM). The machining time is dependent on many cutting conditions such as the spindle speed, the feed rate, the depth of cut, and the step over. Therefore, it is really difficult to get a minimization time of machining process via controlling these cutting parameter during milling process. This paper demonstrates a method of minimizing the machining time of milling process via using CAD/CAM simulation and Taguchi methodology. The milling type is the DMU 50, a type of DMG MORI SEIKI. The cutting tool is the end mill type of solid carbide end-mill with the diameter of 20 mm. The results show that the machining time can be minimized to improve productivity of the milling process on the CNC machine tool. The factors that impact on the machining time can be found. The paper hopes that the results will be applied in the manufacturing process in the near future.

ABSTRACT. The research firstly about study about the theoretical superiority and drawbacks of the Contra-Rotating Propeller (CRP) system in comparison with the single-rotating propeller and its scope in application in the real world for various fields. The main purpose of this study is applying the CFD simulation to investigate the aerodynamics performance of the CRP system with various configuration with the difference in number of blades, distance between two stages of rotors and varying the rotational speed to evaluate how the CRP would perform under those modification. The process starts with choosing a specific type of aircraft and its currently equipped engine, nextly, applying QBlade for designing the propeller blade by determine the chord and twist distribution, Solidworks application for generating the geometry of the propeller, then, the simulation process conducted by Ansys Fluent to determine the thrust generation by each modified configuration. The results contribute to a deeper understanding of how variation in changing technical parameters would affect the aerodynamics performance of the CRP by using the CFD simulation which provides a proper initial prediction in thrust performance through all the variation. This research works as the initial step in the complete design process of a CRP system tailored for a specific aircraft model, as further research such as durability simulations, deformation analysis, or acoustic measurements should be conducted to address the noise-related drawbacks of this propulsion system compared to single-propeller systems.

ABSTRACT. The growing demand for clean energy in urban areas has intensified interest in rooftop wind energy systems. This study examines the impact of wind velocity profiles on the performance of horizontal-axis wind turbines (HAWTs) mounted on inclined rooftops in dense urban settings. Using Computational Fluid Dynamics (CFD), two configurations are analyzed: (1) two buildings with rooftop turbines separated by 5 meters, and (2) adjacent buildings with turbines. An actuator disk model incorporating the Betz limit is applied to estimate theoretical maximum power output, with boundary conditions defined from literature-based and Global Wind Atlas wind profiles. Results show that turbines on windward edges consistently outperform those downstream, which suffer from wake effects and reduced wind speeds. Performance losses are most severe when buildings are closely spaced. The findings highlight the critical influence of installation positioning on urban wind turbine efficiency and provide quantitative insights into aerodynamic interactions around rooftop systems. This work advances CFD-based assessment of urban wind resources and supports the integration of renewable energy technologies into sustainable building design.

ABSTRACT. This article presents the design and analysis for compliant toggle mechanism. The operational principle relies on the displacement amplification produced by the compliant toggle mechanism (CTM), which converts minor angular movements of the crank into greater linear displacements at the output stage. The displacement amplification ratio of the proposed stage is determined by kinematic analysis. The analytical results are further validated by finite element analysis. The findings demonstrate that the CTM offers significant displacement amplification and structural integrity. It can be a potential mechanism for use in precision engineering applications with micrometer motion, compactness, and reliability.

ABSTRACT. This study presents a comparative analysis of Novikov double line of action (DLA) gears and conventional involute gears, aligned with standards MN 4229–63, GOST 15023–76, and GOST 30224–96, as well as classical calculation sequences by Reshetov, Chernilevsky, Ivanov, and Ryakhovsky. Using a unified input dataset, geometry, and force transmission, both contact and bending stresses were evaluated across the different approaches. A worked example demonstrates that a DLA gear pair with a center distance of 80 mm can replace an involute pair at 160 mm while maintaining allowable contact stresses (σH ≈ 271.8–433.3 MPa compared to 348.9 MPa) and without increasing bending stress and the volume and mass of a Novikov gear pair can be reduced to about one-seventh of those of a comparable involute pair. The sensitivity analysis identifies the helix angle, axial overlap ratio, module, and tooth numbers as dominant factors influencing load sharing and capacity. Practical requirements for realizing the advantages of DLA gearing include precise control of center distance, micro geometry modifications, and sufficient system stiffness. The results provide a concise reference for selecting DLA Novikov gears in high power–density and space–constrained drive applications.

ABSTRACT. The study focused on simulating the operating modes of a permanent magnet synchronous motor of the electric vehicle’s power system. The simulation was conducted on Matlab software (version 2022) with different operating modes. The simulation results showed that the value of the output parameters such as motor speed, motor torque, voltage and current amplitude changed continuously and were consistent with the actual operating modes of electric vehicles. This confirmed the operating efficiency of the electric motor controller and the reliability of the field-oriented control (FOC) method in the electric motor control system. At start mode, the increase of supply current and voltage was controlled to create a large motor torque of 100 N.m for starting and accelerating from 0 to 5 m/s. At steady speed mode after starting, the controller maintained the motor speed at 5 m/s with almost constant amplitude and frequency of supply current and voltage for a constant torque and speed of motor. At acceleration mode, the current increased and maintained at a large value of about 160A and voltage amplitude gradually increased to a value of 300V to create a large motor output torque of 165N.m for a high speed requirements in a short time. At deceleration mode, the supply current was controlled to decrease sharply to the value of -180A for creating the braking torque and the regenerative braking mode occurred as the motor acted as a generator.

ABSTRACT. Marine diesel engines require efficient cooling systems to provide operating dependability, efficiency, and longevity under challenging circumstances. Shell-and-tube heat exchangers have been used for a long time, but plate heat exchangers (PHEs) are now more popular since they are easier to maintain, don't become dirty as easily, and can be made in any size. This study presents an overview of PHEs in maritime cooling applications, emphasizing their operational principles, benefits, and drawbacks in comparison to traditional systems. Critical determinants influencing PHE performance—namely, plate geometry, material selection, flow characteristics, and fouling—are examined, along with trends in advanced designs, including welded and brazed configurations. This paper highlights ongoing research advancements and identifies areas of deficiency, particularly in terms of the need for systematic assessment in marine-specific environments. Proposed future approaches include enhanced materials, computational fluid dynamics, and data-driven techniques for performance prediction and optimization. This study compiles essential information and research perspectives to aid in the effective incorporation of PHEs in contemporary cooling systems for marine diesel engines; nevertheless, it is not intended as a comprehensive evaluation.

ABSTRACT. This study proposes a meshless interpolation method based on Interpolating Modified Moving Least Squares (IMMLS) to accurately simulate the large deformation behavior of hyperelastic materials. In numerical analysis, IMMLS is an advanced meshless interpolation technique based on the Element-Free Galerkin (EFG) method. Hyperelastic materials exhibit complex nonlinear constitutive relationships, making them a distinct class of elastic solids. These materials are typically analyzed within the framework of finite deformation theory due to their ability to undergo large strains. Therefore, a thorough understanding of their nonlinear behavior is essential for developing accurate and efficient numerical models. While traditional mesh-based approaches often struggle with large deformation problems, meshless techniques have demonstrated superior flexibility and the ability to overcome these limitations. To evaluate the effectiveness of the proposed method, the Neo-Hookean model was applied to assess the performance of the algorithm in large deformation problems. Material properties used in this study were obtained from existing literature to ensure accuracy. The simulation results were compared against those obtained using the Finite Element Method (FEM) as well as reference data from previous studies. Furthermore, the numerical algorithm and computational program were validated by benchmarking the results against reference solutions generated in MATLAB. Finally, the discussion is extended to explore potential applications of IMMLS, highlighting its relevance in broader engineering contexts. The findings of this study serve as a benchmark for future in-depth research in this domain.

ABSTRACT. Bio-inspired helicoidal composite materials have extensive applications across various engineering disciplines. Additionally, thin-walled structures have attracted considerable interest from the scientific community. Nonetheless, research focused on the behavior of bio-inspired helicoidal composite (BIHC) thin-walled beams is still comparatively scarce. This study aims to perform buckling analysis of BIHC thin-walled beams utilizing a First-Order Shear Deformation Theory. The governing equations are formulated based on Lagrange’s equation. Furthermore, the Ritz method is employed to ascertain the critical buckling load of the beams. A comprehensive investigation is conducted into the impacts of different helicoidal configurations, boundary conditions, and slenderness ratios on the buckling response of the beams. This study introduces several innovative findings as a benchmark for subsequent research endeavors.

ABSTRACT. This paper presents a model of a quintuple-layer composite beam composed of functionally graded materials (FGMs) and shear connectors. A finite element model is developed based on the first-order shear deformation theory (FSDT) of Timoshenko, using a two-node beam element with eleven degrees of freedom per node. The interlayer sliding interaction is taken into account in the formulation. Based on the proposed theory, a computational program is implemented in the MATLAB environment and validated against various benchmark models. The results obtained from this study provide a foundation for further developments, including free vibration analysis and dynamic response investigations of complex beam structures.

ABSTRACT. Triply Periodic Minimal Surface (TPMS)-based material models exhibit a unique combination of lightweight characteristics and high mechanical performance, making them highly suitable for applications in aerospace, biomedical engineering, and energy absorption. This paper presents an efficient numerical model based on an iogeometric analysis (IGA) framework for analyzing the free vibrational characteristics of TPMS-based plate structures. The model leverages higher-order plate theory, which requires only three independent fundamental variables while naturally satisfying shear stress boundary conditions. Numerical examples regarding the free vibration behavior of TPMS plates are presented first to verify the accuracy and reliability of the present approach through comparisons with existing solutions. In this work, several TPMS architectures, such as Gyroid, Primitive, I-graph and wrapped package-graph (IWP) are considered to assess the effects of geometry, thickness ratio, and material distribution on natural vibration frequencies. Furthermore, to comprehensively evaluate the influence of material distribution on the vibrational response, this work considers three distinct types of porosity distribution along the plate thickness: symmetric porosity, asymmetric porosity, and uniform porosity. The obtained results reveal the sensitivity of free vibrational characteristics to geometric as well as material parameters, particularly when comparing different distribution functions. This study highlights the potential of applying TPMS architectures in the design of high-performance and lightweight engineering structures.

ABSTRACT. Thermoelastic vibration of sandwich beams with a porous core is studied in this paper using a finite element procedure. The sandwich beams with material properties depending on temperature consist of homogeneous faces and a porous core. The porosities in the core are graded in the thickness direction by a trigonometric function. Equation of motion in term of finite element analysis is derived in the framework of Timoshenko beam theory. The effects of the porosity coefficient, temperature change, and aspect ratio of the sandwich beam on the vibration of the sandwich beams are studied in detail and highlighted.

ABSTRACT. The reliability of deep-sea hydraulic systems is critically dependent on the effectiveness of their O-ring seals in preventing water ingress. Operating at extreme ocean depths, these systems face immense hydrostatic pressures, posing a significant challenge to maintaining seal integrity over extended periods. This study utilizes 2D axisymmetric Finite Element Analysis (FEA) with ANSYS software to thoroughly evaluate the sealing performance of O-rings under these severe conditions and various operational parameters. The FEA model incorporates the complex material behavior of the O-ring elastomer, which is essential for accurate simulation. This includes both hyperelasticity, accounting for the material's ability to withstand large, reversible deformations under initial compression and pressure, and viscoelasticity. The viscoelastic property, specifically stress relaxation is modeled using the Prony series. This time-dependent behavior is a primary concern for the long-term reliability of static seals in deep-sea applications. The research centers on analyzing the "Safety Margin" indicating the seal's capacity to maintain sufficient contact pressure against the mating surfaces to prevent leakage. The simulations explore how this Safety Margin is affected by different factors, particularly the housing height and the ambient pressure corresponding to various operational depths. The findings clearly demonstrate that increased ambient pressure at greater depths exacerbates stress relaxation, potentially leading to a significant reduction in the effective sealing area - the "lethal percentage" where seal integrity is compromised.

ABSTRACT. Medical endoscopy capsules play a crucial role in diagnosing gastrointestinal disorders, including gastric polyps, internal bleeding, and Crohn's disease. Despite significant advancements, commercially available capsules remain passive, typically measuring 11 × 26 mm, and lack active actuator systems. The emergence of onboard actuator systems presents a promising alternative to passive capsules. Among these, vibro-impact-driven capsules have demonstrated effectiveness, utilizing internal vibration and impact forces to achieve bidirectional rectilinear motion under external resistance. This innovative approach uniquely accommodates all components within the capsule, eliminating dependence on external accessories. However, the integration of power sources and actuators into pill-sized capsules continues to pose a formidable challenge. Efforts to minimize capsule dimensions have yielded designs exceeding the standard 11 × 26 mm size, with dimensions such as 12 mm in diameter and 36 mm in length. This study introduces the design, analysis, and experimental validation of a compact vibro-impact actuator that meets the specified dimensional requirements. The design process adheres to the principles of multi-body dynamics and nonsmooth systems, while analysis leverages bifurcation techniques and numerical simulations. For the first time, a vibro-impact actuator measuring 10 mm in diameter and 13 mm in length has been successfully developed, analyzed, and experimentally validated. These findings pave the way for broad applications of active capsules in practical settings

ABSTRACT. This paper presents the design and performance evaluation of a novel compliant microgripper that integrates a double-bridge type displacement amplification mechanism with a parallelogram guiding structure to achieve high-precision micro-object manipulation. The amplification process is implemented in two sequential stages, enabling large output displacements from small displacement inputs, while maintaining structural stability and low parasitic motion. Analytical modeling and finite element analysis (FEA) were conducted to assess the mechanical behavior, amplification ratio, stress distribution, and resonance frequencies. The results show that with an input of 70 µm, the gripper achieves a maximum jaw displacement of 450.78 µm and a peak stress of 296.20 MPa, remaining within the safety limits. While the theoretical amplification ratio reaches 11.88, FEA results reveal a reduced ratio of 6.44 due to geometric nonlinearity. A correction function based on regression analysis was introduced to improve theoretical accuracy. Additionally, sensitivity studies confirm that material properties and flexure hinge thickness significantly affect displacement performance. These findings demonstrate the effectiveness and robustness of the proposed gripper for precision applications, while also highlighting directions for future optimization and experimental validation.

ABSTRACT. This paper provides a comprehensive review of Steer-by-Wire (SBW) systems, representing the next generation of automotive steering technology. Evolving from traditional mechanical, hydraulic, and electric power steering, SBW fundamentally eliminates the physical mechanical link between the steering wheel and road wheels, relying instead on electronic signals, sensors, and actuators. This innovative architecture offers significant advantages such as increased vehicle design flexibility, weight reduction, and the seamless integration of advanced driver assistance systems and autonomous driving functionalities. However, implementing SBW systems faces critical challenges, including ensuring robust control system reliability and accurately reproducing realistic haptic feedback for the driver. Among the latest and most promising solutions to address these challenges, Magneto-rheological Fluid (MRF) technology is emerging, particularly for enhancing force feedback. MRF-based SBW systems leverage the fluid's ability to rapidly change viscosity under a magnetic field, enabling dynamic, customizable steering feel and quick response to varying driving conditions. This allows for adaptive steering characteristics, significantly improving driver experience and control by simulating authentic road sensations. Future research continues to focus on refining control algorithms, ensuring long-term durability, and deepening integration with autonomous driving, further solidifying SBW's pivotal role in the future of vehicle dynamics.

ABSTRACT. The investigation of vehicle dynamic behaviors using nonlinear dynamic models is quite complex, causing great difficulty integrating them with control models. This paper presents the design of a supervised self-learning algorithm based on artificial neural networks to solve the above problem. A radial basis function is designed in this work to train the data, which is obtained from the previous simulation process. The input parameters of the controller include the time simulation, the vehicle's moving velocity, and the steering angle. The expected outputs include the roll angle, yaw angle, yaw rate, and vehicle trajectory changes over time. The simulation results indicate that the training error is insignificant compared to the original data. This is valid within the trained range. On the other hand, the resulting error will increase as the input values exceed the initial training range. The paper's achievements will be the basis for developing applications to predict vehicle dynamic behaviors in the future.

ABSTRACT. Steer-by-Wire (SbW) systems eliminate the traditional mechanical connection between the steering wheel and the road wheels, offering greater design flexibility and enhanced vehicle dynamics. Despite these advantages, delivering realistic and adjustable haptic feedback remains a significant challenge. This paper explores the integration of magnetorheological (MR) fluid-based haptic feedback mechanisms into steer-by-wire (SbW) systems, with the goal of enhancing driver experience and safety in modern vehicles. An MRF-based actuator-either in the form of a rotary brake is integrated into the steering column to generate controllable resistive torque, simulating the road feel. A non-linear model of the MRF actuator is developed to describe the relationship between the coil current, the steering shaft rotational velocity, the MRF fluid properties (physical constants, viscosity with and without magnetic field) and the output torque. Optimal control techniques, including Linear Quadratic Regulator (LQR), are applied to regulate the actuator response, ensuring stable and natural steering feedback under varying driving conditions. These results underscore the potential of MR fluid-based SbW systems as a compelling pathway for future steer-by-wire technologies, offering an optimal blend of performance and safety.

ABSTRACT. Productivity is really important for any production systems to get advantages than their competitors in the market in over the world. Productivity can reach high goal via controlling the working process of each equipment in the production line. Traditional methods are difficult to get high yield by using normal tools that need more time to process. The efficiency of a production system can be improved by using a digital tool to simulate and analyze before put it into the real production. This paper demonstrates a method of optimizing the production operation of the production system via using Tecnomatix Plant Simulation software to improve the production efficiency. By introducing the digital tool, the machines can be arranged and managed to increase the production efficiency of the manufacturing system such as flexible manufacturing system and computer integrated manufacturing. The paper hopes that the results will be applied in production to enhance the product quality in the near future.

ABSTRACT. In the recent years, various meshfree methods have been developed to enhance accuracy and flexibility in solving solid mechanics and structural analysis problems. Among them, the Tchebychev Point Interpolation Method (TPIM) and Tchebychev–Radial Point Interpolation Method (TRPIM) are notable extensions of the Point Interpolation Method (PIM). This paper presents a weak-form based meshfree TRPIM approach for solving 2D elasticity problems. Unlike the conventional RPIM, which employs polynomial basis functions such as [1, x, y, ...], TRPIM utilizes Tchebychev (Chebyshev) polynomials to enrich the approximation space. This approach mitigates the Runge phenomenon, achieving spectral-like accuracy and improving numerical stability. Numerical examples in 2D elasticity analysis confirm the effectiveness of TRPIM in computing displacement distributions, stresses, and deformation characteristics of structure. The method produces highly accurate results, exhibiting minimal errors when compared to analytical solutions, while also demonstrating improvements over conventional RPIM approach.

ABSTRACT. Robotic exoskeletons have emerged as a promising technology for lower-limb rehabilitation, offering precise, repeatable, and adaptive assistance to patients with mobility impairments. This paper presents an intelligent control strategy for a robotic exoskeleton designed for knee rehabilitation, leveraging electromyography (EMG) signals and convolutional neural networks (CNNs) to enable personalized assistance. The proposed approach utilizes CNNs to extract relevant features from EMG signals in real time, allowing for accurate prediction of user intent and adaptive control of the exoskeleton. A closed-loop control system is implemented to ensure smooth and responsive movement assistance, enhancing the rehabilitation process. The effectiveness of the proposed system is validated through experiments with human subjects, demonstrating improved tracking accuracy, reduced muscle fatigue, and enhanced user comfort compared to traditional control methods. The results highlight the potential of EMG-driven CNN-based control in improving patient-specific rehabilitation strategies, paving the way for more intelligent, adaptive, and efficient exoskeleton-assisted therapy.

ABSTRACT. As structural design problems become increasingly complex in practice, optimization algorithms need to provide solutions within acceptable computational time, especially given the large number of design variables involved. This analysis proposes a Parallel Differential Evolution with Cooperative Multi-Search strategies (PDECMS), implemented using Compute Unified Device Architecture (CUDA) to accelerate execution by utilizing the computational power of Graphics Processing Units (GPUs). The algorithm employs three sub-populations with distinct mutation schemes to form an island model, initiating searches from diverse starting points. Throughout the evolutionary process, knowledge exchange between islands is facilitated through the synchronous migration of elite individuals. The proposed PDECMS is applied to five discrete sizing optimization problems of truss structures to assess its solution quality, convergence speed, and scalability. Results indicate that, for large population sizes, the PDECMS achieves at least a twofold speedup compared to its serial counterpart, while maintaining a solution quality comparable to existing methods. The improved performance is attributed to the cooperative multi-search strategy and GPU-based parallelization, which enable the algorithm to converge to optimal solutions in fewer iterations and reduced computational time. These findings demonstrate that PDECMS is a viable and efficient approach for solving large-scale, multi-variable structural optimization problems.

ABSTRACT. This study develops a comprehensive finite element modeling (FEM) framework for analyzing the dynamic response and implementing active control for piezoelectric composite plates under thermo-mechanical loads. A 3D 8-node isoparametric brick element is formulated based on Hamilton's principle, incorporating full thermo-electro-mechanical (TEM) coupling. The model is first rigorously validated against a published benchmark, showing excellent agreement for a static electro-mechanical case. The analysis of the uncontrolled dynamic response is then conducted, revealing that a uniform temperature increase significantly affects the plate's behavior, leading to a reduction in peak displacement but also a decrease in natural frequency. This highlights the complex interplay between thermal stress stiffening and material property degradation. Subsequently, a Proportional-Integral-Derivative (PID) active control system is implemented. Simulation results demonstrate the controller's high effectiveness, achieving a significant reduction in displacement for various actuator configurations and composite layups under thermo-mechanical loading. The study provides a validated and robust numerical tool for the design and analysis of smart composite structures under realistic operating conditions.

ABSTRACT. The turbulent energy cascade and the transformation of vortex topology during the collision and reconnection of a vortex ring with a vortex tube are numerically investigated using a vortex particle method. The first reconnection produces a distorted tube, which subsequently reconnects again, forming a new vortex ring and tube pair. The turbulence triggered by this second reconnection exhibits an energy cascade slope consistent with k−5/3, unlike the first reconnection. The observed changes in topology are primarily caused by the stretching and twisting of large vortices, while small-scale vortices play little role in initiating reconnection. Instead, these smaller structures mainly appear in regions of high kinetic energy, where they interact with and are influenced by the twisting of large-scale vortex structures. These findings not only enrich the fundamental understanding of vortex dynamics in fluid mechanics but also provide a theoretical basis for improving turbulence modeling in computational fluid dynamics (CFD). From a practical standpoint, insights gained from this research can contribute to optimizing aerodynamic performance, enhancing mixing efficiency in engineering systems, and advancing control strategies in aerospace and energy-related applications.

ABSTRACT. This study presents a novel method for optimizing the geometric dimensions of concrete-filled double-skin steel tubular (CFDST) columns under compression, considering their nonlinear inelastic behavior. The proposed approach combines the use of the XGB machine learning algorithm and the Whale Optimization Algorithm (WOA) (referred to as the combined XGB-WOA) to find the optimal geometric dimensions of the column given its capacity. Firstly, a Python script for a finite element model of the CFDST column is created and analyzed using Abaqus software. Subsequently, the WOA algorithm is incorporated in the developed Python script to find the optimal geometric dimensions by minimizing the weight of the columns while maintaining their ultimate load. To accelerate the computation time, the XGB model, trained on a database of 167 experimental CFDST columns, is used to predict suitable initial starting points for the WOA algorithm's iterations during the optimization process. The efficiency and accuracy of the proposed approach are demonstrated by applying it to find the optimum geometric dimensions of a test specimen of the CFDST column with a given capacity. The analysis results indicate that both the default WOA model and the combined XGB-WOA model can yield globally optimal solutions. The capacity of the column with optimum geometric dimensions closely aligns with that of the test specimen. Furthermore, the weight of the optimum column is 37% lower than that of the test specimen with the same capacity. Notably, the number of analyses required by the combined XGB-WOA model is reduced by half compared to the default WOA model, emphasizing the effectiveness of the proposed approach.

ABSTRACT. The article presents a finite element analysis (FEA) on the behavior of steel–lightweight aggregate concrete–fiber reinforced concrete composite slabs. The slabs were simulated using LS-DYNA software, in which the concrete was modeled by solid elements (SOLID), shear connectors were modeled by beam elements (BEAM), and corrugated steel sheets were simulated with shell elements (SHELL). The investigated parameters included the screw diameters (6.3 mm and 10 mm) and their spacings distributed on the steel sheets (100 mm, 200 mm, and 300 mm). Comparisons with experimental data from an author’s previous study confirmed the accuracy of the FEA model in predicting the moment capacity, deflection, end slip, and failure modes of those composite slabs. Additionally, extended parametric analysis demonstrated that employing larger diameter screws with denser arrangements enhances load-bearing capacity and reduces end slip.

ABSTRACT. This study analytically investigates the nonlinear stability of imperfect three-phase composite plates on elastic foundations in mechanical loads. Governing equations were formulated by us using higher-order shear deformation plate theory. By applying the Galerkin method, we determined explicit relations for load-deflection curves. Our results reveal the effects of fibers, particles, material properties, and geometrical properties on the buckling and post-buckling load capacity of these composite plates. This understanding enables the proactive design of composite materials and structures to meet specific technical requirements through component adjustments.

ABSTRACT. This research investigates the electroflexual properties of high-performance fiber-reinforced concrete (HPFRC) through an experimental program. The mortar matrix was embedded with smooth steel fibers at different volume fractions of 0%, 0.5%, 1.0%, and 1.5%. All flexural specimens had a rectangular prism shape with dimensions of 40 × 40 × 160 mm³ with a span length of 120 mm subjected to three-point bending load. The present study provides an in-depth evaluation of the electroflexural performance of HPFRC through the sensitivity factor (SFMOR). The results indicated that HPFRC series produced excellent self-sensing capabilities with sensitivity factors changed from 63.06 to 267.21. Furthermore, the SFMOR generally decreased with increasing fiber volume content. These findings highlight the significant potential of HPFRC for structural health monitoring (SHM) applications.

ABSTRACT. This paper presents a static analysis of functionally graded porous (FGP) thin-walled beams based on higher-order shear deformation beam theory. The material properties are assumed to vary through the thickness of the thin-wall. Three porosity distribution models, namely uniform porosity distribution (UPD) and symmetric porosity distribution with stiffer (SPD-1) and softer at the surface (SPD-2), are considered. Thin-walled I-beam profile with mono-symmetrical is analyzed under static loading conditions. The beam kinematics are formulated within the framework of higher-order thin-walled beam theory. The governing equations for the static problem are derived using Lagrange’s equations. Based on the Bézier approximation function, the Ritz method is employed to solve these equations. In addition, the numerical results explore the impacts of higher-order shear deformation, porosity coefficient, porosity distribution, and length-to-height ratio on the beams’ vertical displacement and twist angle. These outcomes are intended to assess the model’s accuracy and provide benchmarks for subsequent investigations.

ABSTRACT. The Functionally graded materials (FGMs), owing to their superior mechanical properties, are increasingly employed in engineering applications such as beams, plates, and shells. A key requirement for these structures is optimization to improve performance and reduce production costs. This study develops an algorithm and computational program based on the finite element method and a refined plate theory to investigate the stability of rectangular FGM plates under in-plane harmonic loading. Stability regions are constructed with respect to varying loading and structural parameters, providing useful guidelines for selecting optimal plate designs and loading conditions

ABSTRACT. This study presents a novel computational methodology for the biomimetic reconstruction and mechanical analysis of trabecular bone structures utilizing Triply periodic minimal surfaces (TPMS) as functional infill materials. Beginning with high-resolution 3D scanning data, the comprehensive framework divides the structures into separated layers and conducts 2D Non-uniform rational B-splines (NURBS) surface fitting using the Balancing composite motion optimization (BCMO) algorithm. These layers are then connected through a 3D NURBS surface-to-solid transformation process, constructing a high-fidelity geometric bone model. This reconstruction process employs adaptive fitting algorithms with hierarchical NURBS basis functions, achieving outstanding accuracy (RMSE < 0.05 mm) while preserving topological features critical for mechanical performance. Distinct TPMS architectures such as Gyroid, IWP, and Primitive are parametrically embedded within the reconstructed bone volumes using level-set functions with spatially varying density parameters derived from the original bone mineral distribution. Isogeometric analysis (IGA) is utilized to reveal their mechanical behaviors under physiologically relevant loading conditions, reflecting the natural trabecular bone. Furthermore, a fabrication feasibility study is conducted, evaluating the potential for manufacturing through plastic 3D printing technologies. This integrated computational workflow provides significant advancements for patient-specific bone scaffold design, enabling precise control over both geometric accuracy and mechanical performance. The methodology demonstrates potential applications in personalized implant development and tissue engineering, where site-specific mechanical properties can be tailored to match natural bone behavior under complex loading scenarios using bio-inspired TPMS materials.

ABSTRACT. The Huet-Sayegh (HS) model is a well-known rheological model in pavement engineering for its excellence in predicting the linear viscoelastic (LVE) behavior of asphaltic materials. With traditional approach, the model’s parameters are identified by minimizing the error between predicted and experimental complex modulus data obtained in the frequency domain. However, with the advancement of testing techniques, it is beneficial to characterize the LVE behavior directly in the time domain. Consequently, there is a growing demand for determining the LVE model parameters based on time-domain data. A major challenge in applying the HS model in the time domain is the lack of an exact theoretical expression for its creep compliance function, making the parameter identification much cumbersome with conventional trial-and-error approaches. This paper proposes an efficient algorithm to address this challenge. The obtained results showed that the parameters of the HS model can be determined with high accuracy and within reasonable computational times.

ABSTRACT. Reliability is a critical factor for one-shot products such as automotive airbags, military equipment, and medical devices. Operational failures of these items can lead to severe consequences. Thus, establishing a testing program to demonstrate compliance with reliability requirements and confidence limits is essential. However, determining the required sample size presents significant challenges due to the destructive nature and high cost of each test for single-use or "one-shot" products. This paper investigates key statistical methods applicable to sample size determination and compares the requirements of each approach. Through practical examples with varying reliability requirements and statistical confidence levels, the study identifies strategies to minimize sample size in test program design. Additionally, the paper develops a framework to guide method selection based on available infigureation, cost constraints, and practical requirements. The research outcomes support engineers and managers in designing optimized testing programs for single-use or "one-shot" products, ensuring cost efficiency while maintaining statistical rigor.

ABSTRACT. Two-stage gear reducers are extensively utilized in industrial power transmission systems due to their capability to reduce speed, increase torque, and maintain high mechanical efficiency. This study presents an optimization framework for two-stage gearboxes that simultaneously satisfies contact fatigue strength, ensures proper oil-bath lubrication conditions, and minimizes the overall gearbox volume. The main objective is to establish a practical lookup table for optimal transmission ratio ranges, derived on theoretical calculations integrated with the Sequential Quadratic Programming (SQP) algorithm. This approach enhances both computational accuracy and efficiency. While the proposed results provide a valuable preliminary design reference, it is emphasized that adjustments may be necessary during actual implementation to accommodate manufacturing constraints and specific operational conditions.

ABSTRACT. Among the most crucial systems in a vehicle, the suspension system directly influences the safety and comfort. Coil springs are elastic components used in the suspension systems to reduce unwanted vibrations. Besides the traditional steel, alternative materials for helical springs with lightweight, efficient, and corrosion-resistant characteristics are recently gaining attention in automotive industry. This study aims to optimize the design of a Carbon fiber/Epoxy with carbon nanotubes (CF/E-CNT) helical spring (HS) for a light vehicle. As a result, this study first developed a numerical simulation for a steel HS that is validated based on the results that were published. The modeling geometry was done by collecting the actual HS with 2 more blocks above and below that are considered rigid bodies. In boundary conditions, the load is applied on the top block with a range from 360 to 3600 N, and fixed support is set to the below block, which makes the force distribution evener and increases the calculation accuracy. The selected better quality mesh size is 3mm and includes 133,235 nodes and 39,134 elements, that combine tetrahedral and hexahedral elements. Compared to the results of the reference’s numerical simulation, this paper achieves better agreement with lower error. In addition, the set of design parameters was then identified for optimizing the CF/E-CNT helical spring. The optimization objectives consist of minimizing deformation, shear stress, and weight. The comparison between optimized CF/E-CNT helical spring and reference’s data indicate that there is a significantly reduce in the weight and shear stress.

ABSTRACT. This paper investigates the influence of surface form errors on the Modulation Transfer Function (MTF) in off-axis optical systems, with a focus on surfaces 1 and 3, which are processed simultaneously on the same side of the system. Four distinct types of surface form errors, characterized by varying Peak-to-Valley (PV) values and tilt angles, are introduced to evaluate their impact on optical performance. By analyzing these errors, we establish tolerance ranges required to maintain an MTF greater than 0.5 at a spatial frequency of 25Hz. The results demonstrate that certain errors, particularly those with tilt components, exhibit a compensatory effect on the MTF, effectively broadening the allowable tolerance ranges for machining errors. Additionally, the study underscores the significant role of verticality errors in off-axis machining, which amplify surface form errors due to angular deviations. These findings provide critical insights for optimizing the manufacturing process of off-axis optical systems, enabling the achievement of stringent MTF requirements while relaxing certain machining tolerances. This work contributes to advancing the design and fabrication of high-performance optical systems for applications requiring exceptional precision.

ABSTRACT. In response to the growing demand for urban transportation development, many cities are constructing metro systems, which often feature two parallel tunnels to improve transportation efficiency. However, in urban construction environments, underground space for such tunnels is typically limited. Therefore, during the planning and design of underground metro construction projects, it is essential to select a layout for the parallel tunnels that aligns with the specific construction conditions of each project. The mechanical interaction between the retaining structures of tunnel linings varies depending on the arrangement of the two parallel tunnels. This article employs the finite element method to analyze how various parallel tunnel arrangements influence the internal force distribution, assisting in the selection of the most suitable layout for metro construction. The results of the study indicate the following: Parallel tunnels with the same horizontal axis “Side-by-side”: when the two tunnels are at the same construction depth, the values of normal forces and bending moment in the tunnel linings exhibit significant deviations. Parallel tunnels with a vertical axis “Stacked or piggy back”: In this configuration, the tunnel located above experiences the smallest normal forces and bending moment values in the lining, making it a favorable option. Parallel tunnels with different horizontal and vertical axes “Offset arrangement”: In this arrangement, the tunnel in the lower position experiences the largest normal forces and bending moment values in the tunnel lining. Keywords: underground construction twin tunnels tunnel lining finite element method

ABSTRACT. The Tuned Liquid Damper (TLD) is studied for its application in mitigating vibrations of the primary structure. The motion of the liquid mass within the sloshing generates damping forces. Moreover, this fluid motion can induce oscillations of a flexible baffle, which can be utilized for energy harvesting by integrating piezoelectric materials. This paper presents a study on the feasibility of employing TLD for structural vibration control and energy harvesting, based on numerical simulation methods.

ABSTRACT. As part of the global transition to sustainable energy, wind power has emerged as a promising alternative, widely adopted in Vietnam and beyond. In recent years, the Savonius wind turbine, a vertical-axis design, has offered advantages such as omnidirectional wind capture and simple structure but suffers from low aerodynamic efficiency, limiting its broader application. Inspired by the principles of aerodynamic efficiency observed in modern high-speed aircraft, such as the F-22, F-117 and TU-160, this study explores blade modifications incorporating fuselage geometry features to enhance performance. To evaluate the influence of these new blade designs on the turbine’s power coefficient (Cp), computational fluid dynamics (CFD) simulations were carried out. The results indicate that the proposed modifications can enhance Cp values by up to 13.3% compared to the conventional Savonius design, particularly at higher tip speed ratios (λ > 0.8). This improvement paves the way for the practical application of Savonius wind turbines in urban wind energy harvesting, where compact and efficient designs are essential.

ABSTRACT. The flow past an obstacle body generates vortices at a regular frequency over time. These vortices travel downstream with the flow and induce fluctuating pressure fields. By using this phenomenon, piezoelectric flexible plates can be positioned downstream of the obstacle body. The resulting aerodynamic forces cause the piezoelectric plates to oscillate, thereby generating electrical energy. This paper focuses on investigating the potential for electrical energy harvesting from vortex shedding using numerical simulation methods of fluid structure interaction.

ABSTRACT. This paper presents an analytical approach to the design calculation of an Archimedean-type horizontal-axis wind turbine (HAWT). With the growing demand for clean and sustainable energy, wind turbines play a vital role in global energy solutions. This study focuses on applying Archimedean spiral principles to the rotor blade design to enhance aerodynamic efficiency. The analytical method employed integrates blade element momentum theory to evaluate critical parameters such as tip speed ratio, blade number, chord distribution, and twist angle. The Archimedean geometry is adapted to optimize blade shape for improving performance under varying wind conditions. The results aim to establish a set of design guidelines for small- to medium-scale wind turbines with enhanced power coefficients. The findings of this research contribute to the development of efficient, low-cost wind turbines suitable for decentralized renewable energy systems.

ABSTRACT. In recent years, there have been strong changes in the application of 3D printing in traditional production, especially 3D printing of composite plastics, as Adidas is doing with 3D-printed thick soles or even whole shoes for their 4D shoe line [1]. However, the application of 3D printing with other materials, especially 3D printing of metal, is facing many challenges in mass production due to the complexity in the process of creating finished products with physical properties equivalent to finished products completed by traditional mechanical processing. This article explores the potential of metal 3D printing by presenting the mechanical properties of H13 tool steel components fabricated via the Bound Metal Deposition (BMD) process. A key focus is understanding the impact of annealing on these properties by comparing samples in their as-printed and post-annealed states. Analyzing how this heat treatment alters the internal structure and enhances mechanical performance is crucial for qualifying these parts for industrial use. Our findings aim to contribute to the broader adoption of metal 3D printing in mass production.

ABSTRACT. This study presents a high-performance magnetorheological brake (MRB) featuring a 3D-printed tooth-shaped rotor. To overcome the limited shear force of conventional designs, a novel rotor geometry was optimized for enhanced magnetorheological fluid (MRF) interaction. Using finite element analysis and the Teaching-Learning-Based Optimization (TLBO) algorithm, a design was developed to achieve a target torque of 5 Nm with minimal mass. The intricate tooth-shaped rotor was successfully fabricated using Selective Laser Melting (SLM). Experimental results confirm the design's effectiveness, yielding a maximum braking torque of 4.2 Nm at an applied current of 2.5 A. This research demonstrates that combining structural optimization with additive manufacturing provides an innovative solution for producing efficient, compact, and powerful MRBs, with strong potential for precision applications in robotics and aerospace.

ABSTRACT. The widespread use of petroleum-based polymers has raised significant global environmental challenges, highlighting the urgent need for sustainable food packaging materials. In response to these concerns, active and intelligent food packaging systems have emerged as promising strategies that not only enhance food preservation and safety but also contribute to reducing the environmental impact of conventional plastic packaging. Active packaging seeks to improve the protective functions of films, thereby extending the shelf life of stored products, while intelligent packaging incorporates sensing or monitoring features to provide real-time information on food quality. We have explored polymer nanocomposites and colorimetric membrane systems as integrated approaches to smart food packaging. To advance active food packaging, we have developed nanocomposites based on polyvinyl alcohol, a water-soluble and biodegradable polymer, as the structural matrix. Various functional additives have been incorporated to enhance mechanical properties, barrier properties, antimicrobial and antioxidant activities, and UV resistance. These advances highlight the potential of biodegradable films with multifunctional protective properties. In parallel, we have developed electrospun nanofibrous membranes incorporating natural pH-sensitive anthocyanins as efficient colorimetric indicators. These membranes undergo distinct color changes in response to food spoilage, providing a simple and visible means of freshness detection without the need for specialized equipment. Taken together, these studies illustrate a pathway toward multifunctional smart food packaging that can simultaneously mitigate the environmental burden of plastic film waste and reduce food waste resulting from spoilage.

ABSTRACT. Complex fluids, or non-Newtonian fluids, are predominant in both nature and industry. They appear in phenomena such as mud and lava flows, and in processes including food and pharmaceutical manufacturing, mineral and ceramic processing, and the handling of concrete, inks, paints, and polymers. These materials exhibit intricate rheological behaviors—such as viscoplasticity, viscoelasticity, and thixotropy—that distinguish them from Newtonian fluids. Viscoplastic fluids flow only when the applied shear stress exceeds a critical yield stress. Their apparent viscosity may remain constant (Bingham type), decrease (shear-thinning), or increase (shear-thickening) with strain rate. Thixotropy, in contrast, is a time-dependent behavior linked to the evolution of the material’s microstructure, which can be disrupted and recovered during flow. Structural breakdown leads to reduced viscosity and enhanced fluidity, while recovery increases rigidity and possibly the yield stress. These phenomena arise from the spatial rearrangement of constituent particles under shear. In this talk, we investigate the hydrodynamics of such complex fluids using both meshfree particle-based methods—specifically Smoothed Particle Hydrodynamics (SPH)—and traditional grid-based numerical approaches. Applications include the rheological characterization of fresh concrete (a Bingham-type material) with coarse aggregates, seabed erosion, lubrication processes, and other fluid–structure interaction problems. Finally, future research directions will be discussed, including turbulence modeling for complex fluids, viscoelastic flow simulation, and experimental validation of computational results.