ABSTRACT. Novel class of higher order signal processing technique, the nonlinear frequency response functions based on the higher order spectra, are proposed, developed and investigated for vibro-acoustical monitoring of structure/materials non-linearity and signal non-Gaussianity due to damage for cases of the phase coupled interferences of an excitation. The proposed techniques developed for stationary and non-stationary conditions of structure/material testing. The significance of the proposed techniques is that they provide a measure of the structure/material output HOS in response to the structure/material input HOS and eliminate the influence of the phase coupled interferences of structure/material excitation on non-linearity and non-Gaussianity detection/diagnosis.

The proposed techniques are novel generalizations of the classical frequency response functions for the higher order spectral analysis.

Validation of these novel techniques by simulation and experiments in laboratory and in field conditions will also be presented for testing turbomachinery blades and deep foundation concrete plies in stationary and non-stationary conditions. It is shown that the proposed techniques provide an essential effectiveness gain for the detection of non-linearity due to fatigue damage in comparison with the classical HOS for the case of the phase coupled interferences of a structure excitation.

ABSTRACT. The human middle ear is composed of three bones, i.e. the malleus, the incus and the stapes. Since the middle ear is the smallest and one of the most complicated biomechanical structures in the human body, its analysis is especially demanding and difficult. In case of hearing loss, the middle ear structure has to be modified to improve the hearing process. A use of implantable middle ear hearing devices is the most innovative methods of hearing loss treatment. The main objective of this paper is to find conditions when periodic vibrations appear as a consequence of stimulation by the implant. To achieve this aim, electromechanical model of the implanted middle ear is built and solved analytically.The results are compared to numerical simulations and experimental tests performed on temporal bones.

ABSTRACT. In this work, an acoustic waveguide is modeled in the presence of energy leakage through the elastic surface limiting the waveguide. The harmonic mode of oscillations in the waveguide is induced by generating oscillations by a piezoceramic transducer, the electrodes of which are supplied with a potential difference of a harmonic type. Waves from the acoustic part of the waveguide are recorded by a piezoceramic receiver. The source and receiver operate on thickness vibration modes. The equations for parts of the acoustic system are the equations of electro elasticity and the acoustic medium. To simplify the problem, the emitter and receiver were modeled by one-dimensional equations of the theory of electro elasticity. In an acoustic waveguide, impedance attenuation on the lateral surface was taken into account, and an axisymmetric problem for an acoustic fluid was considered. The conjugation conditions at the interfaces of continuum are satisfied in the integral sense. The impedance boundary conditions generate a spectral problem with complex roots. The boundary conditions for the receiver are supplemented by the equation of current flow through an external circuit with complex conductivity. Numerical experiments are carried out, and comparison with the solution of the problem in the absence of attenuation is carried out. The results of the work can be used for medical purposes to study blood flow in vessels with elastic walls. Acknowledgements. This work was supported by the Russian Science Foundation (project No. 21-19-00423).

ABSTRACT. The present research consists of analyzing the free vibration of composite plates using a new four-variable high-order refined shear function compared to five variables in other high-order theories. Among the advantages of this new theory: It takes into account the shear effect in the calculation of strains without the use of shear correction factors and which gives rise to such a parabolic variation of shear stresses in thickness by satisfying the conditions of nullity of shear stresses at the surfaces (upper and lower). The numerical results obtained by the present high-order shear theory predict natural frequencies with such accuracy while comparing with the elasticity solution and other solutions of the high-order theories available in the literature. In the light of the results obtained we can say that the present high-order shear theory is accurate, simple and effective for studying the dynamic behavior of composite plates.

ABSTRACT. The dynamic behavior of a nonlinear elastic plate on a viscoelastic foundation under the action of a moving oscillating load is studied in the case of the internal resonance accompanied by the external resonance. The damping properties of the viscoelastic foundation are described by the generalized Fuss-Winkler model with the damping term given via the standard linear solid model with the Riemann-Liouville fractional derivatives. The external load is presented by a linear viscoelastic oscillator governed by the constitutive equation based on the fractional derivative Kelvin-Voigt model. The process of vibrations of such a system is described by a set of nonlinear ordinary differential equations of the second order in time with respect to generalized displacements. The method of multiple time scales is used for solving the obtained set of equations in combination with the method of expansion of the fractional derivative in a Taylor series. The assumption of viscosity of oscillator to be finite value leads to the solution of characteristic equation for defining the behavior of complex conjugate roots. Resolving equations for determining of the nonlinear amplitudes and phases of force driven vibrations of the plate are obtained. Comparative analysis of the numerical studies is carried out for oscillators with fractional derivative in damping description for the cases of small and finite viscosity. The influence of the fractional parameters of the environment and the foundation on the amplitudes of nonlinear vibrations is also shown.

ABSTRACT. Propagating flexural waves in structure can be manipulated through the so-called Acoustic Black Holes (ABH) effects. Upon a proper tailoring of the structural thickness, the phase velocity of the bending wave gradually reduces alongside thickness thinning, thus entailing high energy concentration and effective energy dissipation using a small amount of damping materials. The phenomenon arouses increasing interests from the scientific community and inspires innovative design solutions for light-weight and highly damped structures. The topic has been widely explored, mainly for thick-walled structures. Whether sensible ABH effects can still be produced in thin-walled structures through proper design remains unknown. In this paper, we report thorough numerical and experimental investigations to demonstrate that ABH effects can be readily achieved in a compound ABH structure of thin thickness with viscoelastic material filling. The compound structural design makes effective use of both ABH effects and the shear effects of the damping material, mainly along the mid-plane of the structure, to collectively generate a significant enhancement of the structural damping. While the shear-induced damping dominates the lower frequency region, ABH-induced damping becomes dominant once the ABH effect is cut-on. A good compromise between the two effects requires the stiffness of the damping materials and other ABH parameters to be properly chosen in order to ensure broadband benefit in terms of vibration reduction through damping enhancement.

ABSTRACT. The subject of the paper will be a description of essential research work based on two requirements, which are the reduction of energy demand for the drive of machine mechanisms with a non-constant transmission and the provision of constant input revolutions speed. A solution will be presented, which is characterized by the construction and production of two dynamic stands. A number of tests and measurements were carried out on the stands. The most important results will be demonstrated in this contribution, including theoretical procedures leading to the solution of the presented issues. The goal is to reduce the energy consumed for the drive and to minimize the residual oscillation of the working links of the mechanisms.

ABSTRACT. High-rise buildings have become normalized for urban cities as it minimizes the available land used to house many tenants. The stability of the buildings is often subjected to extraneous loading from the wind and ground. When the excitation frequency matches one of the modes of the building, resonance occurs which causes large deformations. As a result, catastrophic damages and failures can occur when buildings are allowed to be excited for long periods of time. Damping mechanisms are widely adopted in industrial applications for their ability to minimize unwanted vibrations, increase a system’s stability, and shift the natural frequency. A two-story building model was developed and its natural frequencies were studies using finite element analysis techniques. Afterwards, a vibration absorber was created to minimize the structural failure with a tuned mass damper. The effectiveness of the absorber was compared both analytically and computationally. A multi-modal vibration absorber can be employed for high-rise buildings in order to minimize the damage from natural effects such as earthquakes and strong winds.

ABSTRACT. Magnetorheological elastomers (MREs) are materials that exhibit a change in their mechanical properties, such as stiffness and damping, in response to an applied magnetic field. This property, known as the magnetorheological (MR) effect, is a result of the alignment of ferromagnetic particles in response to the field. The alignment of these particles can be used to control the mechanical properties of the material, allowing it to be used in semi-active vibration isolation. Despite the inherent viscoelastic-property change of MREs, their MR effect is adversely affected by the slow response time and suspension of the particles that are dispersed within the material. In this work, a hybrid MRE is developed by encapsulating MR fluid inside the material to account for the shortcomings and enhance the performance of MRE in longitudinal vibration isolation. A semi-active base isolator is fabricated using the hybrid MRE as the elastomeric element. A hysteresis model using a combination of Bouc-Wen and LuGre friction models is modelled to portray the dynamic behaviour of the hybrid MRE. The results show that the developed hysteresis model can effectively predict the dynamic response of the hybrid MRE. The experimental testing data highlight the enhancement in the performance of the hybrid MRE by the inclusion of the MR fluid. The hybrid MRE exhibited a better change in stiffness and damping in response to the applied magnetic field. Overall, the findings point to the promising application of the hybrid MRE material in semi-active vibration isolation.

ABSTRACT. The adequacy of the fuzzy inference system is investigated in reducing building vibrations by controlling the damping forces of a magnetorheological damper. A three-story building model is adopted from the literature to assess the controller performance under a time history seismic excitation. Three sets of rules are investigated, and for each rule, two different shapes of membership functions are considered. Story displacements, accelerations, and inter-story drifts are employed to measure the controllers’ effectiveness. The third set of rules provides the best displacement, accelerations, and drift reduction for the first two stories. In comparison, the second set of rules provides the best reduction of the third story drift and accelerations. As such, further investigation is warranted, which would include different variations of rules and input parameters to enhance controllers’ performance.

ABSTRACT. Cutting tools vibrate with small motion over frequencies ranging from a few 100 Hz to a few kHz. Estimating small motion over these wide range of frequencies using newer vision-based modal analysis methods requires video to be recorded at high frame rates and resolutions. High frame rates are necessary for proper temporal resolution and high resolution is necessary for properly spatially resolving small motion. However, since most cameras trade resolution for speed, registering high-frequency small motion with video becomes nontrivial. To recover cutting tool modal parameters from high resolution but potentially temporally aliased video, this paper discusses the use of the compressed sensing technique. Compressed sensing enables non-uniform random sampling at sub-Nyquist rates and leverages sparse structures of signals to allow for exact recovery of signals that are not aliased. Though compressed sensing has significant potential, it requires video to be randomly sampled at the time of acquisition. Since existing camera hardware does not allow for this yet, this paper instead demonstrates modal parameter recovery from motion registered from video that is randomly down-sampled at non-uniform rates from video that was originally properly and uniformly sampled. Recovered parameters from aliased video agree with those from video sampled properly.

ABSTRACT. Rotating machinery encompass the gamut from tiny dentist drills to the mighty steam turbines and pervade our lives. In general however, their vibrational behavior is only roughly understood. Most commercial analysis techniques focus on their linearized response which is woefully inadequate to explain reality. The most likely reason that the industry accepts this discrepancy and a clear shortcoming on the part of modeling is that nonlinear analysis is indeed very complicated and hence, insufficient attention has been paid to it. In addition, the relative depth of knowledge required of the rotor dynamic analyst in diverse areas such as advanced dynamics, structural mechanics, fluid mechanics, and contact mechanics, in addition to nonlinear analysis is just too overwhelming. The talk will discuss the importance of nonlinear dynamical principles for the important tasks of design, diagnostics and control. The overall approach is to consider nonlinear rotor dynamics from the point of view of a scientist who wants to understand and exploit the complex behavior of real systems. It will also gather and analyze the most common nonlinearities one observes in rotating machinery and summarize the state of the art. The talk will aim to point out the gaps in knowledge to stimulate a discussion of those problems which deserve research focus.

ABSTRACT. Submerged floating tunnel (SFT) is an innovative traffic structure for crossing long straits and deep lakes. Compared with traditional bridges and tunnels, SFT has advantages of small influence on the ecological environment around it, all-weather operation, relatively lower construction costs, and arranging different lines along SFT. At the same time, the influence of typhoon, fog, etc. natural environment in the sea or river on the operations of the SFT is little , especially suitable for the long straits and deep lakes with depth of 50-200 meters and more than 3000 m long. It is these advantages that the SFT is considered as the most competitive sea-crossing structure for long waterways in the 21st century. SFT will be subjected to various actions from structure itself and marine environment, such as the weight of the structure itself, the buoyancy, operating vehicle load, waves, currents, the drag force of ships, accidental fire, collision, earthquake, climate and temperature and other actions of marine life. Mechanical behavior of SFT is extremely complex, the design requirement for security is very high. Taking the channel to be built in Dongwuyang fiord as the engineering background, The conceptual design for Dongwuyang channel project is the combination of submerged floating tunnel (SFT) with 1000m long and im-mersed tube tunnel with 570m long. For the preliminary design of submerged floating tunnel, the length of every tube segment is 100m. There are 10 tube segments in total and the section of tube is hexagon-alike. The tube segments are connected by the special joints, and each tube segment is tensioned by two groups of anchor cables. The distance between anchor cables is 50m. Each group of anchor cables has 4 cables with a designed inclination angle of 45°. The vibration response and internal force deformation of the SFT in Dongwuyang fiord are analyzed under the action of the dead load plus buoyancy, ambient wave, current load and vehicle load. The calculation results show that the displacement and bending moment of the SFT tube body and the cable force of the anchor cables are the largest under the action of dead load and buoyancy, and the maximum vertical displacement value is 7.02cm. The structural response under vehicle load is smaller than under dead load plus buoyancy, and the maximum vertical displacement value is only about 0.92cm. Under the action of wave force with wave height H=4.39m, period T=6.2m, wavelength L=59.8m in 100-year, the maximum horizontal and vertical displacement amplitude of the SFT tube body are 1.05cm and 0.90cm, respectively. Under the action of the maximum flow velocity of 1.33m/s, the maximum mid-span vibration displacement of the SFT tube body is 2.1mm. It shows that the SFT has sufficient dynamic stiffness under the combined action of live load (vehicle, wave and current), and the flexural to span ratio of SFT is within l/2000-2500.

ABSTRACT. All major urban areas throughout the world have underground metro systems for their mass rapid transit systems. To safeguard human life and enhance service efficiency, it is crucial to understand how underground tunnels are affected by earthquakes. For their seismic analysis, choosing an earthquake ground motion that is maximum and realistic which are crucial. In this essay, the case history of the subterranean Surat metro tunnels is examined, along with how they responded to the 2001 Bhuj earthquake in Gujarat. The time-based history of the earthquake used for analysis is done matches the projected earthquake at that specific site, so that a realistic reaction of the tunnels is produced. Therefore, the Surat zone's response spectra companionable time history was produced initially. The finite element program MIDAS GTS nx has been used to simulate the tunnel-soil system. Analysis reveals forces in RC liners and subsidence in soil-tunnel systems are larger in deep tunnels as compared to shallow tunnels. Even the analysis expresses the actual earthquakes for another site may overvalue or undervalue the response at the target site. The free-field ground motions are affected by the earthquake's maximum response at the ground surface, which has been studied.

ABSTRACT. The construction of sea-crossing channels has become an important part of the transportation infrastructure construction, and is developing in the direction of larger span, deeper foundation and more complex system. Com-pared with traditional bridges, the sea-crossing bridges are facing the challenges of structural durability, wind resistance, complex environment and construction difficulties. In order to deal with the various challenges encountered in the design, construction and operation of the sea crossing channels, this paper puts forward the scheme combining immersed tunnel with submerged floating tunnel for crossing the Dongwuyang water area in Fujian Province, China after considering the topographic, geological and hydrological conditions. The cross section of SFT tube, arrangement of cables and the type of foundation were preliminary designed. The tube deformation, stress and cable force of the submerged floating tunnel under different load combinations were also analyzed by Midas/Civil. The global dynamic response analysis of SFT structure under the wave and current load was carried out by ABAQUS. The static stress distribution of the SFT concrete tube was analyzed by the 3D finite element model. The results show that under the action of environment and service loads, the design indexes such as internal force, deformation and acceleration of the SFT tube meet the requirements of the design code, which indicates the SFT scheme is feasible, and it has good advantage for the deep-water construction environ-ment.

ABSTRACT. Ground-borne vibrations resulting from construction activity or road traffic may set vibrations in buildings. The effects of these induced vibrations on buildings may range from no-effect to minor cosmetic damage to serious damage, depending on factors such as the amplitude and time-dependence of the vibration, the structure of the building and the type soil it rests on and the duration of exposure. Various codes and standards from various countries set recommendations regarding the exposure of buildings to soil–induced vibrations with emphasis on the characteristics of the vibration signals for limiting their effects on the building structure and for not reducing the comfort of their tenants. These facts are shortly reviewed in this presentation in conjunction with the effects of vibrations on the human body.

ABSTRACT. In this contribution, a new form of semianalytical results related to inertial objects that are traversing longitudinally homogeneous infinite structures, introduced in the author's previous works, is used to analyse plane models of a railway track composed of a guiding structure in the form of a beam and a supporting structure composed of discrete masses, springs, and dampers. The aim of these analyses is determination of critical velocities of the moving force and of the onset of instability of moving masses or oscillators. Further emphasis is placed on the connection between the lowest critical velocity and the onset of instability and on the dynamic interaction between proximate moving inertial objects.

The three-layer railway track model is widely used to determine the dynamic response due to its computational efficiency. It consists of a beam representing the rail, spring/damper elements serving as the rail pads and concentrating masses of half sleepers. Below that, the spring/damper elements model the ballast vertical and shear stiffness and damping and the foundation that includes all layers below the ballast. Concentrated masses stand for dynamically activated ballast mass. Realistic values can be determined either by experiments or analytically by exploiting the ballast stress cone theory.

All presented results are obtained semianalytically for dimensionless parameters exploiting integral transforms and contour integration. Regarding the critical velocity of a moving force, it is shown that there can be at most three critical velocities. Other terms such as pseudocritical and false critical velocities are introduced. It turns out that these values are strongly associated with the onset of instability of a single moving mass. Nevertheless, the so-called instability lines can have quite irregular behaviour, especially at low damping levels. Several examples are given and obtained results are justified. General conclusions useful for track design are drawn.

ABSTRACT. Dampers are widely adopted in industrial applications for their ability to minimize unwanted vibrations and increase a system’s stability. The hybrid damper is a well know type of vibration countermeasure that combines different types of damping techniques. Hybrid damping techniques aim to provide an adaptable damping effect to a wide range of dynamic responses which extend the damper’s applications. The primary purpose of this paper is to numerically investigate the damping behaviour of a novel Piezoelectric-Magnetorheological hybrid damper. Piezoelectric actuators can passively ‘shunt’ large deformations and have actively adjustable properties through a change in supplied potential difference. On the other hand, Magnetorheological elastomers (MREs) can provide great damping characteristics when varying their induced magnetic field. Therefore, integrating both Magnetorheological Elastomers -Piezoelectric (MREP) structures can sufficiently enhance the damping properties. In this paper, the developed Finite Element (FE) model consists of a circular piezoelectric placed inside and attached to a cylindrical mold of MRE. The Static Structural analysis tool provided by the ANSYS workbench was used in the pre-processing, solving, and post-processing phases of the numerical modelling. The MREP damper was able to increase the stiffness of the overall structure by up to 16%.

ABSTRACT. The monitoring of road roughness is one of the first and most critical steps in road maintenance. Road networks need constant maintenance to function properly and avoid any hazardous accidents or blockage of the traffic flow. The International Organization of Standardization (ISO) developed the International Roughness Index (IRI) to unify road monitoring systems and to categorize roads based on their roughness levels. The ISO 8608 standard divides road roughness levels into eight different classifications ranging from best (Class A) to worst (Class H) roads. The road roughness profile of a certain road section could be measured by traditional equipment such as a dipstick profilometer, profilograph, or an automated road meter. However, these traditional methods are time-consuming and costly. Thus, this research proposes the use of dynamic vehicle accelerations of a regular moving car and artificial neural networks to estimate the road profile. This research also compares the accuracy and efficiency of using a full-car (7 degrees of freedom) numerical model and a quarter-car (2 degrees of freedom) numerical model in training the neural network and estimating the road profile. These numerical models will be used to create a library of input data sets (vehicle accelerations) and output data sets (road roughness profiles) which will be used to train the artificial neural networks (ANNs).

ABSTRACT. The flapping motion of caudal fin found in fishes like Mackerel and tuna has been extensively studied for its excellent propulsion characteristics. Locomotion is generally achieved through the oscillatory motion of the peduncle and a passive fin at the end. In the current work, the two body parts are modeled as Euler-Bernoulli beams with appropriate stiffeners at their joint. The fluid domain surrounding the structure is modeled using potential flow assumptions. The fluid-structure interaction results in an added mass effect which has a significant impact on the thrust generated. The first beam is excited harmonically over a frequency range spanning the first two resonances and the structure's tip velocity is estimated for each excitation. The mean thrust is then obtained from the steady-state velocity response using Lighthill's elongated body theory. The results from the study indicates that by proper tuning of the coupling between the peduncle and passive fin thrust can be controlled.

ABSTRACT. In several industries increased vibrations often occur at pumps, compressors or turbines and at the connected piping systems. These vibrations can have different causes. Different measures can be used to decrease this vibration level. In many cases additional supports are used to tighten the piping. But in some cases, it is not possible or very expensive and inconvenient to install additional piping supports or damping devices. Another very effective measure is the use of vibration absorbers. Especially vibration absorbers with an implemented damping characteristic enable a significant optimization of the vibration characteristic in a broad frequency range. In this paper the vibration absorber Magic Tube is presented. The vibration absorber is adjustable on site in a wide frequency range with different mass configurations. The design is introduced, and a case study shows the vibration reduction effect in the field.

ABSTRACT. The drillstring vibration response is subject to uncertainty due to the operating speed, manufacturing tolerance and downhole conditions. A drillstring-borehole contact exhibits complicated dynamic behaviour due to its nonlinear nature. The complexity in the drillstring vibration is due to the drillstring-borehole interactions, which induce nonlinearities due to friction and impact. The objective of the study is to analyse the drillstring-borehole interaction experimentally. A conceptual model of a system of the drillstring is developed, consisting of a flexible rotating shaft with two discs supported on roller bearings. The drillstring borehole interaction is modelled using a localised contact element. A run-up analysis was carried out to determine critical speeds, wherein a high whirling response is produced. An experimental uncertainty study is carried out by varying critical system parameters, such as the eccentricity of the unbalanced mass attached on the disc and the coefficient of friction of the contact element. The response is captured using an accelerometer at the bearing location and a laser vibrometer at the contact location. The maximum response was analysed at the critical speed of the rotor, wherein a high response is expected, namely the synchronous whirl and dry whip speed. A probability density function was obtained for the maximum response at the bearing location and the maximum velocity at the contact location. The results from the experimental study indicate that the response is sensitive to the modal interaction of the interacting whirling modes. Future work will include the development of a theoretical model of the system using the stochastic finite element method covering a wider range of parameter space.