ABSTRACT. There has been a continued effort for development of optimization strategies to solve scientific and engineering problems. Early developments include traditional gradient-based search techniques, which are relatively simple and achieve solutions of reasonable quality for simple problems. In case of complex applications involving extensive computations, on the other hand, the quality of solution is degraded extensively using these approaches. This is mainly due to the search algorithm getting trapped at local optima in the search space. Later approaches include random search techniques, which have the potential of reaching the global solution by jumping out of local optima points. These approaches are better suited to solving complex engineering and scientific problems. Moreover, problems with multiple requirements, which are commonly encountered in practice, can be tackled with such approaches, where traditional approaches fail to solve. A class of such approaches comprises metaheuristic optimization techniques inspired by individual/collective behavior of living species and natural phenomena.

This presentation outlines and discusses the requirements and attributes of the optimization approaches in the context of bio-inspiration and nature inspiration, and these are exemplified by the behavior of selected living species and natural phenomena. A set of algorithms developed based on such behaviors is described, application examples including dynamic system modelling, control system design, and model-free control techniques are presented and discussed using these algorithms.

ABSTRACT. One of the most promising candidates for a real-time SHM system for thin aircraft structures is the Lamb wave-based inspection method. The Lamb wave-based SHM systems have a great potential as an integrated structural monitoring system thanks to the ongoing machine learning revolution. Despite the fact that the current ML algorithms have demonstrated robust classification capabilities, it is undeniable that the success of such models depends heavily on the input data. The fundamental reason for this is because these ML models are often created to perform standalone tasks, which makes them highly data-dependent. In order to address these problems, the current study suggests a transfer learning strategy. The transfer learning model imports pre-trained layers from earlier ML models to help it learn new data. The proposed unified TL model utilizes pre-trained layers of a Resnet-autoencoder to assist a 1D-CNN classifier in learning from new data. The model is constructed in two phases, where in first phase, the autoencoder is trained on noisy baseline differential signals from "Open Guided Waves" publically available benchmark datasets. In later stage, the trained layers from the autoencoder is then merged with a 1D-CNN classifier to diagnose new data. The proposed model identified both damaged and undamaged cases from the set of 144 unseen samples with an impressive 82% accuracy. The study will assess strategy's generalization ability in both composite and metallic plate-like structures.

ABSTRACT. This work presents the results of an experimental method for non-destructively testing round cylindrical elements, both solid (filled) and hollow (shells). The method is based on vibrations and is used for tracking a certain range of vibrational modes, namely the radial ones with a prior specific emphasis on the so-called ovalling mode. This mode may be extracted from the response of the cylinder as a result of its excitation by a mechanical stress applied in the radial direction. The present method uses a single concentrated source of excitation and two vibration sensors diametrically positioned and fastened onto the surface of the cylinder. The ovalling mode may then be extracted from the frequency response through adding the signals recorded by the two sensors and which are in phase in the case of a test object with a circular cross-section. This method has been applied to solid cylinders as well as to hollow ones and has given promising results. Practical applications of the technique aim at conducting in-situ inspection of round construction columns made of concrete for the identification of corrosion severity or other strength-weakening defects. It may also be implemented to steel pillars supporting bridges or harbor piers as well as to pipes in oil and gas industry. Other applications in wood industry concern the identification of rot infection in the trunks of trees on stand and logs for a quality-sorting prior to saw processing them.

ABSTRACT. There is a strong push for the development of on-demand structural health monitoring (SHM) systems for aerospace structures. With an abundance of monitoring data, the data driven-SHM approach has the potential to give real-time diagnostics. The challenge, however, lies in identifying damage in the intricate composite structures of real-world aircraft when they are still in their early stages. The goal of the study is to assess how well the Convolutional Neural Network (CNN) architecture can diagnose damage to CFRP plates. The study makes use of guided wave diagnostic data from a publicly accessible "open guided-waves" database for training and testing. The guided wave-based measurements in the database were generated by testing a 2 mm-thick CFRP composite plate with dimensions of 500 mm X 500 mm. The training database consists of a total of 528 samples, containing an equal number of distinct damaged and undamaged situations. The CNN model is then tested with 144 previously unseen samples to determine its generalization ability. Additionally, the paper develops principles for building CNN-based deep learning architectures that can handle discrete time-series data and assess the status of the structure.

ABSTRACT. Millimeter-wave radar is a new type of equipment that has been applied in bridge deflection health monitoring in recent years，with the advantages of all-weather, low power consumption, non-contact and high precision. In this paper, based on the background of Suzhou Wujiang East Taihu Bridge, based on theoretical analysis and optimization function construction, an error reduction method of millimeter-wave radar applied to bridges across rivers and lakes is proposed. At the same time, the experimental verification is carried out according to the bridge load experiment and health monitoring, and the comparative analysis shows that this method can effectively improve the measurement accuracy, which provides theoretical support and reference for the application of millimeter-wave radar in the health monitoring of bridges across rivers and lakes.

ABSTRACT. Time Integration methods are the most powerful tool for solving structural dynamic systems. The well-known trapezoidal rule is unconditionally stable, while it fails for some simple nonlinear models, motivating unceasingly emerging of time integration methods with better stability in the past decades, such as the dissipative methods and energy-conserving methods. The dissipative methods can put off the moment at which integration methods begin to diverge, but their accuracy is lower than that of non-dissipative ones. The energy-conserving methods can provide stable solutions for stiffness nonlinear systems, but they need extra time to modify energy functions, so their efficiency and feasibility method need to be improved. In this context, this paper develops a family of multi-sub-step time integration methods with BN-stability for nonlinear structural dynamic systems, named the Multi-Sub-Step-BN-stable-n (MSSBNn, n stands for the number of sub-steps). In the proposed methods, each time step is divided into n sub-steps, and then the state vectors at the end of the time step are calculated by the sub-step information. The algorithmic parameters are designed with the BN-stability, local truncation error, amplification factor, and so on, ensuring that for any nonlinear structural dynamics, the proposed methods are unconditionally stable, second-order accurate, and controllably dissipative, and they do not introduce additional computational burdens. The spectral characteristics, overshoot characteristics, and convergence rates of the proposed methods are also deliberately investigated in this work. It has been found that the proposed methods are unconditionally stable, second-order accurate, controllably dissipative, and zero-order overshoots. Also, increasing the number of sub-steps can enhance their accuracy effectively. Besides, some numerical experiments are realized, showing the superiority of the proposed methods in stability, accuracy, and energy conservation.

ABSTRACT. Abstract. Recently, in the civil engineering area, structural control technology took real consideration, especially in the recent works and researches. However, the active mass damper is an active device used in several cases to suppress undesired structural vibrations caused by winds or earthquakes. The active device offers the possibility of adjustment of the structural responses in real-time. In this paper, an active mass damper is proposed to mitigate the vibration caused by ground acceleration. The tested structure is a three-scaled structure excited using the 2003 Boumerdès earthquake excitation. Whereas, to calculate the desired force of control a proportional integral derivative algorithm is proposed in a closed-loop. The active control is evaluated via numerical simulation results of compared displacement responses of the uncontrolled structure to those of the active-controlled structure. The carried-out results proved the effectiveness of the active control strategy to suppress the vibration of the excited structures.

ABSTRACT. This paper presents pole placement of a nonlinear system consisting of an electromagnetic cantilever beam. A pair of identical magnets and coils are mathematically modelled to create the nonlinear stiffness in the electromagnetic system. The nonlinear stiffness can be obtained for various input electrical current to the coils. First, the control algorithm is developed using the Receptance method. The method requires a suitable curve fitting to the frequency response functions using rational fraction polynomial and the concept of the describing function. In the next step, the transfer function of the open-loop nonlinear system is extracted at low level of excitations, in which the system is weakly nonlinear. The evaluation of the mass, spring, and damper matrices, which are generally required in conventional methods, is avoided here since the frequency response functions are used in the design of the controller. In further steps, the excitation level is increased in order to generate a strongly nonlinear system and the open-loop receptances are obtained at various excitation levels. The poles of the nonlinear system are assigned using the linear feedback control and the Sherman-Morrison formula at various levels of excitation. The system's response is dependent on the amplitude of response, thus an iterative approach is required to obtain the feedback gains. At various excitation levels, the performance of the nonlinear control has been considered. When the excitation level varies, feedback control can adapt to the changes in the amplitude, and the performance of the active control system is well maintained. A parametric study has also been carried out to investigate the effect of the distance between the magnets and coils on the performance of the active control system.

ABSTRACT. Slender boring bars are used to bore deep holes. These bars are susceptible to cutting process-induced vibrations that can result in large amplitude chatter vibrations. Chatter can damage the workpiece and the tool if not suppressed. This paper proposes a solution to damp boring bar vibrations by integrating an impact damper within the boring bar. Impact dampers are commonly used in civil and space structures due to their simple design and construction. They contain a mass that collides with the system to be damped and absorbs its vibrational energy through momentum exchanges. Though there are some reports of uses of impact dampers with cutting tools, there are none that systematically characterize the influence of the role of the gap between the impacting mass and the main system, or the role of the coefficient of restitution, or the role of impacting interface characteristics, or the role of the ratios of mass, stiffness, and damping between the two systems. Such analysis is only possible using analytical and/or numerical models. Presenting such an analytical model that allows for systematic parametric analysis to characterize which parameters govern vibration suppression of the boring bar integrated with an impact damper is the main aim and new technical contribution of this paper. To characterize the performance of the impact damped boring bar, the bar is modeled as a Euler-Bernoulli beam with a ball-like mass assumed placed inside a hollow cavity of the boring bar. The ball travels to-and-fro and strikes the boring bar when it vibrates. Impacting interfaces are modelled using a stiffness and viscous damper system. Governing equations for the beam with an integrated damper are obtained by applying the extended Hamilton’s principle. A parametric analysis is performed and a root mean square (RMS) of vibration amplitude is evaluated to understand damper’s effectiveness by contrasting the response to that of a solid boring bar without a damper. Our analysis suggests that the RMS amplitude reduced when the interface damping is larger than that of the boring bar’s whereas when the interface stiffness is larger than that of the boring bar’s modal stiffness, there is a slight increase in RMS values. For large interface damping, the gap is found to play a significant role, and no role when the interface damping is low. There also appears to be threshold for the gap beyond which the performance of the system degrades. Peak RMS amplitudes is suppressed by up to 66% for certain combinations of gaps and the ratios of mass, stiffness, and damping between the two systems. Our analysis suggests that there is a need for an optimization to tune all system parameters. Since our model is generalized, it can be used to perform such an optimization that can in turn guide prototyping for experimental validation.

ABSTRACT. This paper describes and analyse a novel vibration absorber/harvester system that uses electromagnetic transducer in order to recover energy. The energy transducer is mounted in a pendulum, which plays a dynamic absorber role. This pendulum absorber with harvester system is suspended on the semi-active suspension consists of the MR damper and SMA spring. Since the vibration energy is effectively localized to a pendulum damper, energy can be recovered from the vibration absorber instead of the primary structure. An energy harvesting vibration absorber will give the added benefit of energy harvesting. Theoretical investigations are followed by a series of experimental tests that validate the theoretical predictions.

Acknowledgements This research was financed in the framework of the project: ”Theoretical–experimental analysis possibility of electromechanical coupling shaping in energy harvesting systems” no. DEC-2019/35/B/ST8/01068, funded by the National Science Centre, Poland.

ABSTRACT. Process pipework in the oil and gas industry is subjected to various sources of dynamic excitations. These may include structural vibration, flow-induced excitations, gas pulsations, vibration due to imbalance in machinery, etc. Sometimes, vibration could even be due to a combination of the aforementioned sources. Such vibration can lead to metal fatigue in process pipework which eventually leads to loss of containment of hydrocarbons. In this talk, two case studies are presented to demonstrate how data measured from an operational plant can be used first to understand the vibration problem at hand and then to find a solution/mitigation to the problem. The first case study examines the vibration of a 48” discharge pipe of a venturi separator in a refinery plant which had suffered from repeated vibration induced fatigue cracks. The second case study concerns a 2” double block and bleed valve attached to the discharge dampener of a reciprocating compressor which had its bleed flange repeatedly cracked due to vibration. In both case studies, various measurement techniques were deployed to diagnose the problem and propose mitigation measures.

ABSTRACT. Circular cylindrical shells are important components in diverse engineering fields such as civil, mechanical, aerospace and offshore engineering. In all types of failures in engineering, the buckling of thin-walled circular cylindrical shell under axial load is of significant importance and has been of interest to engineers and scientists for over a century. There have been extensive researches on the buckling of open circular cylindrical shells, but still few researches on analytical solutions for non-Levy boundary conditions, as it is difficult to solve eighth-order governing partial differential equations. In view of the above-mentioned gap in the field, this work aims at developing an extended separation-of-variable (eSOV) method to obtain closed-form solutions for the eigenbuckling of open circular cylindrical shells with arbitrary homogeneous boundary conditions. In this eSOV method, the mode functions are expressed in the product form of eigenfunctions in two coordinate directions, and the critical buckling loads corresponding to two-direction eigenfunctions are assumed to be independent of each other in mathematical sense. By employing Rayleigh principle, two-direction eighth-order ordinary characteristic differential equations are derived. Then the two-direction eigenfunctions are expressed in terms of the eigenroots of the characteristic differential equations. Finally, closed-form mode functions and explicit equations for critical buckling load are achieved. It is worth mentioning that the general solution methods presented in this work for open circular cylindrical shells can be simplified to those of closed circular cylindrical shells and rectangular and annular cross-sectional beams. For closed circular cylindrical shells and Levy type open circular cylindrical shells, the solutions of this work are the same as the exact solutions. For non-Levy type open circular cylindrical shells, the present method are validated by comparing with other numerical methods. This work can provide a reference for the construction of new numerical and analytical solutions and guidance for parametric designs.

ABSTRACT. A stiffened structure is integral to complex structures such as ships and aeroplanes. An advantage of the stiffened plate is that it has a greater load-carrying capacity. Therefore, structural health monitoring of stiffened structures is essential in a ship structure. The stiffened structure is modelled as a coupled system with a plate and stiffener forming the subsystems coupled with welded joints. The complex coupled system is modelled using finite element analysis. The coupling springs between a plate and beam could replicate the modal characteristics of welded joints in a stiffened structure. Since the welding characteristics could change depending on the operating conditions, the coupling spring was varied to account for the uncertainty in the weld strength. A hyperspace of coupling springs, one longitudinal and two rotation springs, was spanned using the Latin hypercube sampling technique following a uniform distribution. The eigenvalue problem for the stiffened structure was solved, and the modal characteristics of the system were determined. Dynamic features of the system such as natural frequency, mode shape and frequency response function (FRF) were extracted. A metamodel for the system was developed using a Gaussian process emulator (GPE). The dataset was generated for a driving point response since the response magnitude was high at this location. A validation study carried out on the metamodel indicated a good prediction of the weld strength. Future work would include a study to span more sensing locations and damping.

ABSTRACT. In this paper hyperbolic shear deformation plate theory is presented for free vibration of functionally graded plates with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. Four different porosity types are used for functionally graded plates. Equations of motion are derived from Hamilton’s principle. In the solution of the governing equations, the Navier procedure is implemented. In the numerical examples, the effects of the porosity parameters, porosity types and geometry parameters on the free vibration of the functionally graded plates are investigated. It was found that the distribution form of porosity significantly influence the mechanical behavior of FG plates, in terms of frequency.

ABSTRACT. The aim of this paper is to investigate the stress distribution and static deflections of functionally graded sandwich plates with porosity effects. In order to get more realistic of stress distribution of the functionally graded sandwich plate with porosity effects, a higher-order shear deformation plate theory is used in the kinematic relations. The governing equations of the problem are derived by using the principle of virtual work. In the solution of the governing equations, the Navier procedure is used for the simply supported plate. In the porosity effect, four different porosity types are used for functionally graded sandwich plates. In the numerical results, the effects of the porosity parameters, porosity types and aspect ratio of plates on the normal stress, shear stress and static deflections of the functionally graded sandwich plates are presented and discussed. Also, some comparison studies are performed in order to validate the present formulations

ABSTRACT. The present work involves the prediction of flutter using different aerodynamic models. The results of four aerodynamic models viz., steady, quasi-steady, simplified quasi-unsteady and simplified unsteady, are compared using linear aeroelastic models for a wide range of non-dimensional flutter parameters. The result of the flutter analysis performed using {p} and {p-k} methods are verified with experimental results available in the literature. Aerodynamic models considered in the study pose different aerodynamic damping, which affects the accuracy of {p-k} method in predicting flutter boundary. The present work aims to bring a quantitative comparison between the results of the {p-k} method as well as the {p} method in combination with different aerodynamic theories for a broad range of parameters.

ABSTRACT. Structural fuse mechanisms such as the strong column-weak beam concept, fasteners, and base isolation are typically integrated into structural elements to dissipate seismic energy exerted during earthquakes. Under-designed footing, also known as rocking footing, has been identified as one of the most effective design alternatives for isolating the superstructure from the supporting soil medium. Limited studies are available to assess displacement requirements, taking into account both structural and foundation and soil reactions of rocking shallow foundations, based on the studies performed by previous researchers. This study concentrates on the assessment of dynamic responses of reinforced concrete framed structure on rocking shallow foundations. To predict the behavior, important parameters affecting the dynamic properties of the framed structures on the rocking shallow foundation must be identified. To evaluate the impact on shallow rocking footing, independent parameters such as soil type, soil stiffness, footing width, and structure height are considered in conjunction with seismic characteristics. A realistic structure, as per Indian standards, has been modelled and designed for this purpose, along with the foundation. In order to predict the behavior, the soil and foundation system were modelled as Beam on Nonlinear Winkler Foundation (BNWF). Several response parameters, including natural time period of the structure, settlement of the supporting medium, footing rotation, and lateral roof displacement corresponding to input independent parameters, will be observed from a series of nonlinear time history analyses to obtain the critical parameters and their effects on shallow rocking footing.

ABSTRACT. Post-earthquake damage survey reports reveal that reinforced concrete (RC) beam-column connections undergo large inelastic deformations during an earth-quake and their failure can compromise the overall stability of the reinforced concrete building. This stirred the concern for in-depth understanding of nonlinear behaviour and failure mechanism of such connections. In this paper, nonlinear finite element analysis of RC beam-column connection using concurrent multi-scale framework is performed to investigate the governing failure mechanism in the joint region under monotonic and reverse cyclic loading. Sensitivity analysis is carried out to finalise various modelling parameters like optimal mesh size, dilation angle, viscosity and strain rate. The developed computational model is therefore compared with the available experimental results to examine its efficacy in predicting the structural response. The obtained results advocate the capability of developed computational model in realistic assessment of the performance of RC beam-column connection and capturing the governing failure mechanism.

ABSTRACT. Indian Himalayan region spans across 10 different administrative states in the country and constitutes a significant portion of the Indian subcontinent. An ever-increasing population and scarcity of flat lands for construction in the hilly region forces construction of buildings on sloping terrain with foundations constructed at different levels. These buildings are inherently vulnerable to earthquakes due to the horizontal and vertical irregularities that are extremely hard to avoid because of the nature of the construction. Compounding on that fact, a large population of buildings in the region have been constructed without following the design provisions of earthquake resistant design and ductile detailing in IS 1893 (2016) and IS 13920 (2016) respectively. Consequences of such design and construction practices have shown to have devastating consequences in recent earthquakes such as the 2011 Sikkim earthquake and 2015 Nepal earthquake. The paper aims to assess the combine effect of seismic design provisions of Indian Standards on the seismic response of a set of Un-Reinforced Masonry (URM) infilled RC Step-Back building on hill. 3D analytical model with interaction of frame and infill actions have been taken into account by diagonal strut elements alongside the frame elements. Nonlinear analyses have been performed for realistic assessment of key parameters influencing seismic performance of such buildings.

ABSTRACT. Nuclear Power Plants (NPPs) are one of the distinctive components of a country's vital infrastructure system that provide for its energy needs. In India, several nuclear power stations (NPPs) are being built on combined piled-raft foundations in soft soil conditions, notably atop alluvium in an active seismic zone (CPRF). No research has been published so far that takes the nonlinearity of the soil for NPP buildings built on CPRF into account while considering seismic loads. The current study aims to explore, using a nonlinear finite element model, the dynamic reactions of the raft, pile with a raft, and CPRF of NPP. Furthermore, for a realistic simulation, it's critical to consider the various aspects of ground motion during time history analysis. The current work is focused on examining the seismic response of a nuclear containment structure employing a distributed array of inelastic springs, dashpots, and gap components to mimic the soil-foundation interface using a nonlinear Winkler-based technique. Consequently, a thorough 3D finite element numerical model of the nuclear structure was built and compared to the findings of earlier studies for nonlinear seismic analysis. In this article, investigations were done to consider the numerical analysis and combined pile and raft foundations to diminish the risk of NPPs caused by earthquakes (CPRF). The findings demonstrate that the critical regulating factor that determines how seismically resistant the building is is SSI.

ABSTRACT. Effective stiffness of structural elements i.e., beams, columns, shear walls etc. plays a pivotal role in seismic evaluation of Reinforced Concrete (RC) shear wall buildings which are predominantly considered through use of stiffness modifiers in Indian design standard like various national design standards worldwide. The reduction in stiffness of the structural members is mainly due to crack formation in members due to shrinkage, creep, bond-slip of the reinforcement, etc. which further aggravates due to large inelastic deformation caused by seismic events. stiffness modifiers for various structural members i.e., beams and columns have been recommended in revised Indian seismic standards (BIS 2016a), however specific guidelines for the same is missing for RC shear walls. This paper presents a comprehensive review of the available effective stiffness recommendation by various national seismic design standards viz., ASCE (ASCE/SEI 2017), Eurocode (Eurocode 2005), New Zealand code (NZS 2006), Turkish standards (TS500 2000) and assess the influence of effective stiffness on seismic evaluation of high-rise RC shear wall buildings. It is observed that a significant difference in peak strength is observed with variation in stiffness modifiers of beam and column, whereas there is no significant variation with a variation of stiffness modifiers of the shear wall as the shear walls have higher stiffness compared to other structural elements.