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The damage mechanism of 2D woven fiberglass panels under random vibration loadings was investigated by means of an experimental analysis and compared with the damage mechanism under constant-amplitude loadings. Based on experimental observations, it was found that the failure mode under vibration loadings was delamination, and predicting the vibration fatigue life using the traditional S – N curve would result in significant errors. Therefore, a prediction method was proposed to accurately estimate the vibration fatigue life of a 2D woven fiberglass panel by modifying the conventional S – N curve. An experimental verification showed that this method has a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

This paper gives its contributions in four stages. First, we propose the analytical expressions of power spectrum density (PSD) responses and cross-PSD responses to seven classes of fractional vibrators driven by fractional Gaussian noise (fGn). Second, we put forward the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators excited by fractional Brownian motion (fBm). Third, we present the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators driven by the fractional Ornstein–Uhlenbeck (OU) process. Fourth, we bring forward the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators excited by the von Kármán process. We show that the statistical dependences of the responses to seven classes of fractional vibrators follow those of the excitation of fGn, fBm, the OU process, or the von Kármán process. We also demonstrate the obvious effects of fractional orders on the responses to seven classes of fractional vibrations. In addition, we newly introduce class VII fractional vibrators, their frequency transfer function, and their impulse response in this research. [ABSTRACT FROM AUTHOR]

The paper presents theoretical analyses of renovating a historical bridge in order to decrease stresses. The installation of additional equipment, including a vibration absorber, is relatively easy to perform if such a need is indicated by the current bridge diagnostics or the monitoring of the structure’s vibrations. Moreover, absorbers could be mounted in such a way as not to alter the appearance of the historic structure. The authors focused on the problem of optimising the cooperation between a dynamic vibration absorber (DVA) and a structure under dynamic load moving with constant velocity. A simple degree of freedom (SDOF) system – as a model of the absorber and a multi-degree of freedom (MDOF) system – as the primary structure, were adopted in the calculations. Every force is regarded as a random variable, as well as interarrivals of moving forces. Two different situations and solutions were presented. The first case is when the stream of moving forces with a constant velocity is modelled as the filtered Poisson process. The second one when one of the forces is located in the point of the beam in which the response of the beam has the maximum value.

Physics research is constantly pursuing more efficient silicon detectors, often trying to develop complex and optimized geometries, thus leading to non-trivial engineering challenges. Although critical for this optimization, there are few silicon tile mechanical data available in the literature. In an attempt to partially fill this gap, the present work details various mechanical-related aspects of spaceborne silicon detectors. Specifically, this study concerns three experimental campaigns with different objectives: a mechanical characterization of the material constituting the detector (in terms of density, elastic, and failure properties), an analysis of the adhesive effect on the loads, and a wirebond vibrational endurance campaign performed on three different unpotted samples. By collecting and discussing the experimental results, this work aims to fulfill its purpose of providing insight into the mechanical problems associated with this specific application and procuring input data of paramount importance. For the study to be complete, the perspective taken is broader than mere silicon analysis and embraces all related aspects; i.e., the detector–structure adhesive interface and the structural integrity of wirebonds. In summary, this paper presents experimental data on the material properties of silicon detectors, the impact of the adhesive on the gluing stiffness, and unpotted wirebond vibrational endurance. At the same time, the discussion of the results furnishes an all-encompassing view of the design-associated criticalities in experiments where silicon detectors are employed. [ABSTRACT FROM AUTHOR]

This paper gives its contributions in four stages. First, we propose the analytical expressions of power spectrum density (PSD) responses and cross-PSD responses to seven classes of fractional vibrators driven by fractional Gaussian noise (fGn). Second, we put forward the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators excited by fractional Brownian motion (fBm). Third, we present the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators driven by the fractional Ornstein–Uhlenbeck (OU) process. Fourth, we bring forward the analytical expressions of PSD and cross-PSD responses to seven classes of fractional vibrators excited by the von Kármán process. We show that the statistical dependences of the responses to seven classes of fractional vibrators follow those of the excitation of fGn, fBm, the OU process, or the von Kármán process. We also demonstrate the obvious effects of fractional orders on the responses to seven classes of fractional vibrations. In addition, we newly introduce class VII fractional vibrators, their frequency transfer function, and their impulse response in this research.

Electronic components, during assembly, transportation, and operation, are exposed to a diverse array of dynamic loads, encompassing high and low frequency vibrations, shock, impact, and most importantly, random vibrations. Such rigorous loading conditions necessitate the design of electronic components that can endure these harsh circumstances. Analytical methods, owing to their cost-effectiveness, are predominantly employed to investigate the longevity and resilience of these electronic structures, circumventing the need for protracted and costly experiments. In this study, an analytical discussion is presented concerning the random vibration loads applied to printed circuit boards (PCBs) fitted with surface-mounted components. The electronic package is modelled using the multi-layer plate theory, where the board, solder layer, and component are all conceptualized as elastic rectangular plates. The ensuing stress and potential failure of solder joint layers due to the random vibration loading are scrutinized, alongside an examination of how problem parameters, such as the width of the board and the imposed boundary conditions, impact the stress values within the solder joints. The results derived from the analytical solution reveal that solder stresses induced by random vibrations are diminished in shorter joints, enhancing their reliability. The findings of this research corroborate the results obtained from finite element modelling, thereby validating the analytical approach. [ABSTRACT FROM AUTHOR]

The aim of this paper is to determine the fatigue damage of structures subject to random vibrations generated by Qualmark chamber. In real life, structures are generally subjected to complex multiaxial random load. To determine their fatigue life, many criteria have been elaborated, mostly in time domain. To minimize the computing time, the fatigue damage analysis should be done in the frequency domain. Tests that lead to the failure of the structures are commonly used to determine their weakness. But these tests are sometimes costly. To this end, in this paper an original new numerical model of the Qualmark chamber that leads us to determine the generated excitation at each point of its table is proposed. This model is validated using experimental measurement where adjustment process is proposed. Then, we develop a numerical strategy that leads to determine the multiaxial fatigue damage of structure under random vibrations using Matsubara's criterion developed in the frequency domain of structures tested with Qualmark chamber. A numerical application of a PCB tested with Qualmark chamber is presented at the end of this paper where fatigue damage is determined at each point using the developed strategy. Boundaries condition of the PCB is then determined using the proposed Qualmark table model. [ABSTRACT FROM AUTHOR]

Physics research is constantly pursuing more efficient silicon detectors, often trying to develop complex and optimized geometries, thus leading to non-trivial engineering challenges. Although critical for this optimization, there are few silicon tile mechanical data available in the literature. In an attempt to partially fill this gap, the present work details various mechanical-related aspects of spaceborne silicon detectors. Specifically, this study concerns three experimental campaigns with different objectives: a mechanical characterization of the material constituting the detector (in terms of density, elastic, and failure properties), an analysis of the adhesive effect on the loads, and a wirebond vibrational endurance campaign performed on three different unpotted samples. By collecting and discussing the experimental results, this work aims to fulfill its purpose of providing insight into the mechanical problems associated with this specific application and procuring input data of paramount importance. For the study to be complete, the perspective taken is broader than mere silicon analysis and embraces all related aspects; i.e., the detector–structure adhesive interface and the structural integrity of wirebonds. In summary, this paper presents experimental data on the material properties of silicon detectors, the impact of the adhesive on the gluing stiffness, and unpotted wirebond vibrational endurance. At the same time, the discussion of the results furnishes an all-encompassing view of the design-associated criticalities in experiments where silicon detectors are employed.

Robot manipulators are now used in various domains and environments, where they can be subjected to random vibrations. Random vibrations mainly affect the torque control signal, and a torque controller is therefore required to be designed for stabilization purposes. However, for security or intellectual property protection reasons, most commercialized robots are manufactured with unknown and inaccessible torque controller interface such that the user can only design a position/velocity controller. This paper proposes an adaptive task-space velocity controller free from the inner controller’s structure and exhibiting stochastic and deterministic disturbances rejection to deal with these issues. To deal with the unknown inner controller, the paper exploits the fact that most torque controllers use a velocity feedback term, and it considers the other terms as an unknown functions vector. To cope with random disturbances, it is demonstrated that the random excitation matrix can be linearly parameterized, and therefore, a direct adaptive method is constructed. Using radial basis function neural network (RBF NN), an indirect adaptive method is developed to cope with deterministic uncertainties. Through Lyapunov theory, the paper proves that all the closed-loop signals are bounded in probability. The effectiveness of the proposed approach is further demonstrated through simulation comparisons.

To disclose the possible dynamic behaviours of vehicle-track systems subject to an entire railway network, random vibration analysis is of great concern in railway engineering due to the system geometric and parametric uncertainties. In this work, an emphasis is therefore put on the highly efficient simulation and numerical analysis of track geometry excitation and its induced system uncertain behaviours. Considering the spatial variability, frequency coherence and constant evolution of track irregularities, the random analysis of track irregularities belongs to a big data analysis scope. By introducing practical tools of power spectral density (PSD), frequency coherence analysis and correlated variable random simulation method, a strategy for obtaining representative and realistic track irregularity PSD samples is proposed. Besides, the modelling method of vehicle-track interactions, where versatile programming tactics to couple the track slab and subgrade elements with incompatible elemental sizes, is introduced. By combining the simulation methods of track irregularities and vehicle-track dynamic interaction, the dynamic performance of vehicle-track systems can be evaluated efficiently, and the full view of system dynamics is revealed with probabilistic characteristics. [ABSTRACT FROM AUTHOR]

Due to the absence of power demands and yet effective performances, the semi-active tuned mass dampers (STMDs) have been broadly investigated. However, there is still a gap between the theoretical simulations and practical implementation of controlled tuned mass dampers. Moreover, using displacement and velocity sensors make such control systems less cost-effective, less reliable, and more complex. In this paper, the acceleration-based ground-hook semi-active control (ABGH) was proposed for an electromagnetic regenerative tuned mass damper (ERTMD). In this manner, a prototype of a compact back iron-based ERTMD was manufactured. The concept of a controllable system with switched transistor was utilized for the proposed ERTMD. Comparative simulations between the controlled and passive ERTMD was conducted and then validated by experimental results of the ERTMD prototype implemented in a protected mass test-bench similar to a typical vehicle unsprung mass. This paper concluded that the proposed control policy can be utilized for the ERTMD to increase the regenerative ability of the fabricated ERTMD under random excitations.

High cost and significant power absorption do not allow exploiting modern active control strategies for improving vehicle suspension performance. Meanwhile, the semi-active control policies are not able to overcome a weighted unsprung adverse effect, which represents a cornerstone of the implementation in-wheel motors for a new type of electric vehicle. This paper discusses and analyses the implementation of a proposed energy-harvesting based tuned mass damper (TMD) to be implemented in electric vehicles. In this manner, a full vehicle suspension model embedded with four TMDs was created to simultaneously enhance the car comfort and road-holding responses with a corresponding large-scale energy harvesting. In the proposed 11-DOFs (degrees-of-freedom) vehicle model, the full-vehicle body was suspended using suspension systems, including the compacted back-iron based design of an electromagnetic TMD. The performed simulations indicated the considerable advantage and potentialities of using the TMDs based suspension. In terms of the RMS (root-mean-square), the car body acceleration was reduced by 21.7%, while the road-holding was enhanced by 5.7%. Moreover, the proposed regenerative electromagnetic tuned mass damper (ETMD) allows for harvesting vibration energy up to 58 W for a vehicle driven on a road class D and a speed of 30 m/s.

Summary: Tensegrity domes are reticulated prestressed structures composed of bars in compression and cables in tension. These structures are flexible lightweight systems with low structural damping, and thus, they are sensitive to vibrations induced by strong wind and earthquakes. The present work deals with the robust multimodal control of a large‐scale tensegrity dome of Geiger's type. Assuming random excitations and linear behavior of the structure around an equilibrium prestressed configuration, the control is achieved in the low‐frequency range using multiple tuned mass dampers (MTMDs). The optimal MTMD parameters, ensuring optimal performances, are obtained using a root mean square displacement (RMSD)‐based approach. The optimization strategy is firstly applied, in a deterministic context where the structural parameters uncertainties are not included, to control the fundamental resonant frequency of the dome structure and then extended to perform multimodal control using multiobjective optimization. In addition, in real‐life situations, it's very hard to describe actual engineering structures in precise model yielding to unavoidable internal and external uncertainties. To deal with these uncertainties, it has been shown that the proposed multimodal control is also able to carry out robust control in presence of structural uncertainties. The proposed optimization strategy applied to the dome structure is compared to other optimization strategies, from the open literature. The obtained results showed the efficiency of the proposed methodology of the passive control in both contexts, that is, the deterministic and the non‐deterministic where uncertainties are considered. [ABSTRACT FROM AUTHOR]

A detailed analytical design for hybrid (metal-composite) bolted joints in static and dynamic (random vibrations) analysis is presented in this paper. Due to the fact that a space structure must be lighter and stiffened, the joints design represents an important aspect in the overall mass-stiffness optimization process of the structure. The hybrid joint studied represents the attachment between a real space thruster bracket structure made from aluminum alloy and a composite spacecraft platform subjected to quasi-static and dynamic loads. These computing techniques, originally designed for metal joints, were translated to hybrid metal-composite joints using the finite element method (FEM). As a result, using the FEM technique, the design methods proposed have validated the ability to incorporate and describe in detail the effects of important phenomena such as clamping, friction, clearance and secondary bending of the joint, which are complex three-dimensional phenomena of major importance in the design process of a hybrid joint.

Due to the absence of power demands and yet effective performances, the semi-active tuned mass dampers (STMDs) have been broadly investigated. However, there is still a gap between the theoretical simulations and practical implementation of controlled tuned mass dampers. Moreover, using displacement and velocity sensors make such control systems less cost-effective, less reliable, and more complex. In this paper, the acceleration-based ground-hook semi-active control (ABGH) was proposed for an electromagnetic regenerative tuned mass damper (ERTMD). In this manner, a prototype of a compact back iron-based ERTMD was manufactured. The concept of a controllable system with switched transistor was utilized for the proposed ERTMD. Comparative simulations between the controlled and passive ERTMD was conducted and then validated by experimental results of the ERTMD prototype implemented in a protected mass test-bench similar to a typical vehicle unsprung mass. This paper concluded that the proposed control policy can be utilized for the ERTMD to increase the regenerative ability of the fabricated ERTMD under random excitations. [ABSTRACT FROM AUTHOR]

Implementation of tuned mass dampers is the commonly used approach to avoid excessive vibrations in civil engineering. However, due to the absence of the compact dimension, there are still no practical applications of the tuned mass dampers in automotive industry. Meanwhile, recent investigations showed the benefit of utilizing a tuned mass damper in a vehicle suspension in terms of driving comfort and road holding. Thus, the current investigation aimed to explore a novel compact dimension tuned mass damper, which can provide both sufficient vibration mitigation and energy harvesting. This paper presents a prototype of a back-iron-based design of an electromagnetic regenerative tuned mass damper. The mathematical model of the tuned mass damper system was developed and has been validated by the experimental results of the tuned mass damper prototype implemented in a protected mass test-bench. The indicated results concluded that the attenuation performance dramatically deteriorated under random excitations and a reduction in the root-mean-square acceleration of 18% is concluded compared to the case with undamped tuned mass damper. Under harmonic excitations, the designed tuned mass damper prototype is able to reduce the peak acceleration value of the protected structure by 79%. According to the experimental results, the designed tuned mass damper prototype revealed a peak regenerative power of 0.76 W under a harmonic excitation of 8.1 Hz frequency 125 × 10 - 6 m amplitude. Given the simulated random road profiles from C to E, the back-iron electromagnetic tuned mass damper indicated that root-mean-square harvested power from 0.6 to 6.4 W, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we apply the previously developed Method of Memory Diagrams (MMD) to the description of an axisymmetric mechanical contact with friction subject to random vibrations. The MMD belongs to a family of semi-analytical methods of contact mechanics originating from the classical Cattaneo–Mindlin solution; it allows one to efficiently compute mechanical and energetic responses to complex excitation signals such as random or acoustic ones. For an axisymmetric contact driven by random normal and tangential displacements having fractal statistical properties, we calculate the friction-induced mechanical energy loss averaged over a large number of realizations. In the considered problem, this energy depends on a very restrained number of parameters: on the rms of random displacements, on the fractal dimension, and on the upper cut-off frequency of the fractal spectrum. In addition, a radial distribution of the dissipated energy has been obtained that has a direct relation to wear in the contact system. For small displacement amplitudes, wear should be expected in an annulus inside of a mean contact circle whereas for large displacements it will start at the contact center. [ABSTRACT FROM AUTHOR]

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In stochastic dynamics, ensuring the structural reliability of buildings and structures is of paramount importance, especially when subjected to environmental loads such as wind or earthquakes. To adequately address these loads and the uncertainties associated with them, it is often necessary to utilise advanced load models, frequently expressed using a power spectral density (PSD) function. The construction of these load models becomes challenging when only limited data is available and meaningful statistics cannot be reliably derived. To address this issue, safety bounds are commonly used in load models to account for uncertainties. Many PSD functions, such as the Clough–Penzien model, are described by parameters with a physical background and can therefore reflect the real case. The aim of this work is to expand these physical parameters in order to account for uncertainties. For this purpose, bootstrapping is used to derive more reliable statistics. By introducing a scaling parameter that allows for flexibility, bounds of the data set can be derived. Consequently, suitable PSD models are fitted to the derived bounds. The PSD function is thus represented by intervals for its physical properties instead of relying on discrete values. When applying such a bounded load model to a structure, advanced interval propagation schemes can be utilised to bound the failure probability. • A data-driven and physics-based approach to model PSD intervals is presented. • Modelling of safety bounds in PSD functions address uncertainties in load models. • A scaling parameter allows for flexibility in the derivation of the bounds. • Physical parameters of PSD models are expanded to account for uncertainties. • Applicable to stationary and evolutionary PSD models and real data records. [ABSTRACT FROM AUTHOR]

Random vibrations occur during the launch at the fastening interface between thruster brackets and basic support of satellite. These are generated in the launcher by the motion of some mechanical parts, combustion phenomena or structural elements excited by the acoustic environment. The goal of this comparative study is to find a simplified and efficient validation method using FEM PATRAN-NASTRAN software for thruster brackets in the random vibrations environment for space applications. The random vibration analysis requests complex pre/ post processing efforts and large hardware resources for various geometrical shapes. The PATRAN-NASTRAN random vibration analysis consists of frequency response analysis (111 solver) and Acceleration Spectral Density (ASD) diagram, taking into account the natural frequencies of the bracket. The Miles method computes the root mean square acceleration (aRMS) using the natural frequencies and the ASD diagram as input. As a conservative hypothesis in the random analysis, the three sigma standard deviation criteria in normal Gaussian distribution is applied at these RMS acceleration values, which means to multiply the aRMS by a load factor of three. Simplified method consists of using linear static PATRAN-NASTRAN analysis (101 solver) where the aRMS are introduced as loads. For validation of the simplified method, a comparative study was made between the random vibration and the linear static analysis. The final results are presented in detail in this article.

Passage of the train wheels induces ground-borne vibrations at the railwheel interface, where the main contribution is due to the axle loads moving on irregular track and wheel interface. These vibrations can cause problems such as the compaction and settlement of the foundation soil of the structures nearby, liquefaction of the soil or discomfort of people, just to name a few. Therefore predicting and controlling such phenomena is critically important for the design and operation of the railways. These vibrations are modeled using many different methods existing in the literature. In this paper we analyze the effects of groundwater depth and ground inclination angle on those vibrations using a random vibration model, where the elastic rail-soil system is modeled as a Winkler foundation. We examine the effects of changing fully saturated groundwater levels and changing ground inclination angles on such vibrations. We relate the groundwater depth and ground inclination angle parameters with the stiffness of the Winkler model using Terzaghi's, Vesic's and Bowles's bearing capacity formulas. The common 5-axle and the 6-axle tram load configurations and different train speeds of 30 km/hr, 40 km/hr, 50 km/hr are used in our implemented model. It is shown that the decrease in groundwater depth and/or higher ground inclination angle can significantly change the peak and rms vibration velocity and acceleration levels, both for the 5-axle and 6-axle configurations and all three different train speeds. We present exponential and exponential-trigonometric fit curves to the results of the implemented random vibration model, which can be used to model the approximate changes in the ground-borne vibration velocity and acceleration levels due to different groundwater depth and different ground inclination angles. We also discuss our results and their applicability. [ABSTRACT FROM AUTHOR]

• Random vibration analysis is performed on a composite pipe. • The fiber angle resulted in minimum natural frequency is obtained using analytical formulation. • The results of random vibration analysis are compared with seismic analysis. • Vibration analysis is performed treating fiber volume fraction and direction as random variables. In this research, random vibrations and failure analysis of composite pipe are stochastically investigated. For this purpose, free vibrations of the pipe are studied using both analytical and numerical methods considering effects of various parameters such as boundary conditions (B.C's), pipe dimensions and layup configurations. In the next step, random vibrations of the pipe under excitation of white noise are studied using numerical method. The power spectral density function (PSDF) of the stress responses along with the root mean square (RMS) of on-axis stress components are extracted and then failure occurrence is evaluated. Then, time history dynamic analysis is carried out on the same pipe and the results are compared. A real earthquake excitation is analyzed using both random vibrations and time history dynamic analyses. Comparing the results, advantages and disadvantages of each method are discussed. Finally, stochastic modelling is performed treating manufacturing-induced uncertainties as random variables. Thus, stochastic analysis of the composite pipe response exposed to random excitation is done. Results show the importance of taking into consideration manufacturing-induced inconsistencies for failure analysis of the pipe exposed to random excitation. [ABSTRACT FROM AUTHOR]