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The dynamic characteristics of an aluminum honeycomb sandwich panel are experimentally determined under free boundary conditions and the computational model is updated according to the experimental results. The study confirms that the adhesives used to bond the core and face sheets affect the dynamic response of the sandwich panel through the adhesive fillets formed between the face sheets and the core during the bonding process. The viscous damping of the structure is also determined by experimental modal analysis. It is observed that the results of the experimental and computational results agree well when the effects of adhesive fillets and viscous damping are considered. Furthermore, a dynamic response analysis under random vibration is conducted to reveal the differences between the results of the initial and the updated models. [ABSTRACT FROM AUTHOR]

The dynamic performances of a sandwich beam with a shear thickening fluid (STF) core subjected to a random excitation are investigated. First, the STF is prepared and a new constitutive model is proposed based on the oscillatory rheological measurements. Next, a flexural vibration model of the sandwich beam with an STF core under random load is developed, and a parametric study is carried out. It is found that the response frequencies and damping ratios for the first three modes of the beam increase with the standard deviation of the external random excitation. The sandwich beam with STF provides better damping for larger broadband excitation. Additionally, the beam with an STF core will produce a response both inside and outside the load frequency domain. Furthermore, an optimal thickness ratio for the structure that maximizes the damping ratio of the structure is identified. It is important to note that this optimal thickness ratio of the structure varies with the order of vibration modes. This research provides valuable insights into the design of structures using STF and also contributes to the development of dynamic constitutive models for STF. [ABSTRACT FROM AUTHOR]

In recent years, there has been extensive research on detecting damage or identifying changes in stiffness in structures by analyzing their dynamic properties or responses. The fundamental idea is that damage or loss of integrity in a structural system can affect its response to dynamic forces, leading to changes in properties like eigenfrequencies, modal damping ratios, mode shape, and transfer functions. In Vietnam and some other countries in the Southeast Asia region, the prevailing climate conditions, slow economic development, and geographical location have resulted in the construction of predominantly short-span bridges with a limited number of spans. This is primarily because these bridges connect small channels and waterways. This characteristic provides a basis for developing and applying research findings specifically for this group of bridges, as they are seldom encountered and researched in other countries worldwide. This paper presents a damage identification technique for short-span bridges based on changes in the representative power spectral density (RPSD) and the static moment of area (SSM). The proposed method is applied to experimental data obtained from various bridge models, including prestressed concrete, reinforced concrete, and composite steel bridges. It is important to note that changes in RPSD and SSM are independent of traffic conditions on the bridge but instead rely on the structural and material properties of the bridge spans. By utilizing RPSD and SSM, new advancements can be made in assessing the structural condition of bridges using vibration signals. [ABSTRACT FROM AUTHOR]

The dynamic response of a thermoplastic composite sandwich structure is optimized under random vibration. First, the experimental modal analysis data of a set of test samples are processed by a sequential set of statistical analysis such as descriptive statistics, factor analysis, and paired sample t-test. Then, the sample with the highest ability to represent the group is taken as the reference data. Three different computational models, which are defined according to whether the solid to be meshed is considered an area or a volume, are constructed. Modal analysis results of the computational models are compared to the reference experimental data to evaluate the performance of the models. To predict the dynamic response of the sandwich beam, it is excited through a random signal in the transverse direction. The nodal acceleration responses are computed in 17 evenly spaced points located on the upper finishing layer of the sandwich beam. Finally, a geometry optimization study is conducted to predict the optimum thicknesses of the 7 layers bonded together to form the sandwich beam. The optimum layer thicknesses that minimize the nodal accelerations at 17 evenly spaced points on the sandwich beam are computed. The current study shows that the shell model has the closest values to the experimental data compared to other models. As far as the dynamic response of a TPC sandwich structure is concerned, it is concluded that the shell model better represents the structure during the modeling phase and leads to concurrently reduced weight and nodal acceleration, when optimized. [ABSTRACT FROM AUTHOR]

This paper proposes an equivalent spectrum method to predict the fatigue crack propagation (FCP) life of metallic materials subjected to random loading. To adequately account for the coupling effects between crack propagation and the random response of structures, a coupling analysis model is introduced. The stress intensity factor (SIF) can be estimated based on the power spectral density (PSD) of an equivalent displacement. Random vibration fatigue tests were conducted to evaluate the proposed model on aluminum alloy specimens. Results indicate significant variations in natural frequency with crack length. The predicted results are compared with the experimental values, demonstrating satisfactory prediction accuracy of the proposed coupling analysis model. This model enables the assessment of coupling effects between crack length and random response, facilitating more precise predictions of FCP life in metallic materials and guiding the expanded application of damage tolerance criteria in structural engineering. [ABSTRACT FROM AUTHOR]

The high-speed maglev train is a potential innovative and convenient transportation. Its stability and vibration performances while moving on bridges are still the fundamental considerations to be determined. The stable control condition of the high-speed maglev train moving on an irregulated track is analyzed theoretically employing a simplified moving electromagnet model at first. The Routh–Hurwitz stability criterion is introduced to determine the limiting values of the electromagnetic control parameters. It is interesting that the obtained stable critical values of the control parameters are not sensitive to the moving speed and the bridge parameters. The stable critical value of the electromagnetic control parameters is dominated by the negative stiffness and negative damping mechanism. The coupled vibration system of the high-speed maglev train–bridge considering the track irregularity is then established. The explicit time-domain integration method based on spectral decomposition is applied to solve the random vibration of the system, while the classical Newmark-β method is used to solve the deterministic responses. The numerical results are compared and validated with the Monte Carlo simulation and the measurement data. The statistical response characteristics of the high-speed maglev train and the bridge under random track irregularity are then analyzed. The vibration of the train fluctuates obviously during the suspension process with a great standard derivation. Like the comment wheel rail train on bridge, responses increase obviously with the increase of train speed and the deterioration of the track irregularity. [ABSTRACT FROM AUTHOR]

This paper proposed a theoretical model for analyzing the vibration responses of multilayer functionally graded graphene platelet-reinforced composite (FG-GPLRC) cylindrical shell under moving random loads. Four GPLs distributed patterns and two ways of moving random load are taken into account. The proposed model is established by employing differential quadrature finite element method (DQFEM) combined with pseudo excitation method (PEM) and is solved by utilizing Newmark-β method in the framework of first-order shear deformation shell theory (FSDST). The general boundary conditions of FG-GPLRC cylindrical shell structure are simulated by adopting the penalty function method. The effective material properties of multilayer FG-GPLRC cylindrical shell are derived based on the modified Halpin–Tsai model and mixture rule. Then, the convergence, accuracy, universality and robustness of the established model are verified by comparing the presented results with the corresponding results coming from finite element simulation software (ABAQUS and COMSOL) and the open literature. Finally, the influences of material parameters including the distribution pattern and weight fraction of GPLRC, structure parameters and the velocity and way of moving random load on the vibration response of multilayer FG-GPLRC cylindrical shell structure subjected to moving random loads are investigated systematically. This research can provide the theoretical basis for evaluating the vibration response of multilayer FG-GPLRC cylindrical shell structure subjected to moving random loads. [ABSTRACT FROM AUTHOR]

AbstractIn this study, the boundaries of the chaotic region in the response of a shape memory alloy (SMA) microelectromechanical beam with a magnetostrictive layer under non-Gaussian parametric noise were determined using an analytical approach. By introducing several dimensionless parameters, the nonlinear governing equations for the random vibration of the system were derived. Subsequently, an enhanced version of Melnikov’s function was derived for the stochastic equations, leading to the calculation of analytical expressions to define the boundaries of the chaotic region. The resulting boundaries of the chaotic zone were plotted to illustrate the behavior of the cantilever exposed to noises with varying bandwidths and magnetic field intensities (MFIs). The primary objective of this research is to establish a comprehensive analytical framework for the assessment of dynamic instability in advanced microelectromechanical systems (MEMS). This framework will take into account the complexities associated with nonlinearity, inherent smart functionalities, and stochastic behaviors of the external loads. The results provide valuable insights into how different parameters influence system instability, serving as a foundation for the design of such systems. To validate the methodology and satisfy the necessary conditions for the Melnikov’s function, Poincaré mapping was employed to confirm the analytical results. A good correlation between these results was observed as presented in the results. [ABSTRACT FROM AUTHOR]

This paper investigates the control performance of a novel grounded inerter-based dynamic vibration absorber (GI-DVA) for random vibration reduction. First, the dynamics equations of the coupled system are written and the transfer function is obtained based on the Laplace transform. Then, assuming that the primary structure is under random white noise excitation, the displacement variance of the primary structure is calculated based on the exact definition of the H 2 norm, by solving the Lyapunov equation. By imposing that the partial derivatives of the response variance of the primary structure with respect to the system parameters are simultaneously equal to zero, the optimum design values of the H 2 optimized GI-DVA were derived numerically for given different mass ratio. It can be found that the optimal design parameters as the inerter-to-mass ratio, the stiffness ratio and the damping ratio increase, while the frequency ratio decreases with the increase in the mass ratio. Under the optimal conditions, the response analysis showed that the primary structure response controlled by the H 2 optimized GI-DVA can decrease with the increase in the mass ratio, but is less sensitive to large mass ratios, and can be robust to the mistuning on the optimum design parameters. Then, the control performance evaluation is first performed in the frequency domain, which reveal that the dynamic response reduction capacity of the H 2 optimized GI-DVA are significantly 62% and 48% superior to the H 2 optimized classic DVA (CDVA) and high-performance passive nontraditional inerter-based DVA (NIDVA-C4), respectively. Furthermore, for the root mean square response evaluation (H 2 performance), the H 2 optimized GI-DVA can provide significantly H 2 performance 58% and 50% than the H 2 optimized CDVA and NIDVA-C4, respectively. To obtain more realistic results, the time domain simulation is performed, which showed that the GI-DVA can provide significantly performance for random vibration reduction. [ABSTRACT FROM AUTHOR]

A novel lever-type stiffness-based grounded damping dynamic vibration absorber with grounded stiffness is presented in this paper, and the analytical design parameters are derived in detail. At the first, the equations of motion are established and the analytical solution of the primary structure displacement is obtained. It is found that with the introduction of grounded stiffness, the coupled system could be unstable and the stability condition is established. Then, the optimum stiffness ratio, the optimum damping ratio and the optimum grounded stiffness ratio are expressed as the function of mass ratio and lever ratio by minimizing the mean squared displacement response of the primary structure previously established. From the results analysis, the system stability is verified, and it is found that with the change in the lever ratio when the mass ratio is selected, there are three cases for the optimum grounded stiffness ratio, i.e., negative, zero and positive. Thus, for the vibration reduction of primary structure, the proposed dynamic vibration absorber (DVA) with positive grounded stiffness has the best control performance among the three cases. Compared with some typical designed DVAs under harmonic and random excitation, the results show that with the proposed optimum DVA the resonance amplitude and the frequency band of vibration reduction can greatly reduce and broadened, respectively, and the random vibration mitigation can be greatly increased. According to the existing literature, the proposed lever-type stiffness mechanism is justified, which means that the proposed DVA is practical and can be used in many engineering applications. [ABSTRACT FROM AUTHOR]

This paper proposes a novel framework for the random vibration fatigue assessment of thin‐walled plate with multiple holes based on the fatigue damage response spectrum method. Compared with other frequency‐domain evaluation methods, this framework fully exploits the dynamic characteristics of complex structures, decoupling the external excitation characteristics from the spatial characteristics of the structural response. This approach significantly enhances evaluation efficiency by avoiding the complex calculations associated with stress response spectral moments. The proposed method is employed to evaluate the contribution of each mode to the overall damage, additionally, the stress mode shapes are used to identify and refine the mesh around fatigue hotspots. Modal damage contribution factors are proposed to identify the key modes. By leveraging both structural dimension reduction and modal reduction techniques, the proposed framework can swiftly and accurately locate fatigue hotspots within complex structures and conduct precise fatigue assessments using the Absolute Sum ‐ Square Root of the Sum of Squares hybrid method. Finite element simulation analysis is conducted on a single‐lap structure containing numerous circular openings, validating the accuracy and efficiency of the proposed stochastic vibration fatigue assessment. Highlights: A framework for assessing random vibration fatigue of thin‐walled plate with localized featuresEmploy stress modes to pinpoint the locations of critical fatigue holesUtilize modal damage contribution factors to identify key modesImplement damage combination considering the identified key modes [ABSTRACT FROM AUTHOR]

• The analytical solution of multipoint ground motion in multilayer submarine field is derived for the first time. • The transfer function and coherence function of multipoint ground motion at this site are derived for the first time. • The influence of soil stiffness and sea water height on ground motion is analyzed. In ocean engineering anti-seismic filed, the marine environment is usually regarded as the coupling field of seawater-layered porous seabed-elastic bedrock. This paper presents a theoretical method to study the spatially variable seismic underground motions in stratified seabed system. Based on the potential flow theory, Biot's porous model and random vibration theory, the transfer function and coherence function model of the underground seismic motions in the marine coupling field are derived. On the basis of the above theoretical derivation, the program of the spatial variability seismic underground motions of the coupling field is simulated and developed, and its accuracy and effectiveness are verified. Moreover, the effects of soil stiffness and overlying seawater level on the seismic response are also analyzed. Numerical results show that spatially variable seismic underground motions are significantly different from those on the ocean bottom. The simulation of spatially variable seismic underground motions for layered seabed field is significant for both theoretical study and ocean engineering application. [ABSTRACT FROM AUTHOR]

This paper introduces the Monte Carlo simulation (MCS) procedure in combination with an effective finite element method (FEM) based on the refined first-order shear deformation theory (r-FSDT) to examine the random vibration of functionally graded sandwich (FGS) plates with different skin layers subjected to double explosive load (DEL). In the stochastic design methodology, the formulation of the state function for design conditions commonly involves integrating random input parameters, assumed distribution functions, and the stochastic responses derived from problem models. The motion equation of the FGS plate is derived by using Hamilton’s principle. Then, the Newmark-beta method is applied to solve linear second-order ordinary differential equations. Finally, the random vibration of the FGS plate is studied by considering the normal distribution parameters. In general, this research tries to shed light on the effects of geometric parameters and material properties and guide the design of FGS plates subjected to double explosive load with uncertain input parameters. [ABSTRACT FROM AUTHOR]

Fatigue failure remains a major concern in the design and performance evaluation of machine components and structures as it accounts for a significant proportion of mechanical failures. This article presents a fatigue evaluation methodology based on SN (stress-cycles to failure) curves to understand and predict the fatigue behaviour of complex components under various loading conditions with widely varying device geometry and dynamics. In order to accurately interpret and utilize the SN curves, the paper outlines key factors influencing material fatigue, including stress amplitude, mean stress, stress concentration, environmental effects, and surface finish. The integration of these factors into the SN curve-based assessment is discussed to tailor fatigue evaluations to specific machine components and structures. To demonstrate the practical application of SN curves in fatigue assessment, two case studies of machine components and structures are presented. The paper ends with a summary and conclusions, the most important of which is that the greatest impact on design fatigue life consists of accurately estimated stresses resulting from the load conditions and the dynamics of the structure. [ABSTRACT FROM AUTHOR]

Previous research on seismic response analysis of dams primarily treated earthquakes as deterministic events; only a few studies on arch dams have explored earthquakes as random processes. This study introduces a three-dimensional seismic analysis of the Morrow Point arch dam, considering fully correlated random ground motion. The random ground excitation is characterized by the power spectral density function (PSDF) of the Kern County earthquake, for which the response time history is available. The spectral analysis technique describes the PSDF of the dam's response using the desired transfer function derived from Abaqus software. The analysis method is similar to that employed in finding the PSDF of the response of offshore structures from a given wave spectrum (PSDF). The method is validated by confirming the results of the proposed method with those of modal spectral analysis for empty dams and those of the time history analysis of the full reservoir dam. The results from the numerical study show that (1) the PSDF of responses obtained by modal spectral analysis using the first ten modes of the dam matches with those obtained by the direct analysis using transfer functions for the empty dam; and (2) mean peak arch stresses increases along the height of the dam from base to top, whereas mean peak cantilever stresses decreases; further, the mean peak arch stresses are less than the mean peak cantilever stresses at the base. [ABSTRACT FROM AUTHOR]

Vibrations during transportation often cause mechanical damage to fresh produce. Addressing or mitigating this damage requires efficient packaging solutions that maintain fresh produce integrity during transit, thereby preserving produce quality and market value. This study investigates the effects of various transportation profiles and packaging designs on apple bruising using simulated truck vibrations. Two apple varieties, Fuji and Jonagold, were packaged in corrugated paperboard boxes with paper pulp trays, plastic crates with paper pulp trays, corrugated paperboard boxes with volume packing and plastic crates with volume packing, all commercial apple packaging. The packaged apples were exposed to two random vibration profiles: leaf spring and air ride suspensions, both set at four different intensities ranging from 0.2 to 0.7 Grms for 1, 3 and 5 h. The findings revealed that both packaging type and vibration parameters significantly influenced apple bruising. Especially, plastic crates with paper pulp trays led to the most severe bruising, whereas corrugated paperboard boxes with volume packing afforded the most protection. Regardless of the packaging design, leaf spring suspension resulted in more apple bruising compared to air ride suspension. The findings of this study provide practical insights for packaging engineers to mitigate the apple bruising during transportation. [ABSTRACT FROM AUTHOR]

Bearing degradation is the primary cause of electrical machine failures, making reliable condition monitoring essential to prevent breakdowns. This paper presents a novel hybrid model for the detection of multiple faults in bearings, combining Long Short-Term Memory (LSTM) networks with random forest (RF) classifiers, further enhanced by the Grey Wolf Optimization (GWO) algorithm. The proposed approach is structured in three stages: first, time and frequency domain features are manually extracted from vibration signals; second, these features are processed by a dual-layer LSTM network, which is specifically designed to capture complex temporal relationships within the data; finally, the GWO algorithm is employed to optimize feature selection from the LSTM outputs, feeding the most relevant features into the RF classifier for fault classification. The model was rigorously evaluated using a dataset comprising six distinct bearing health conditions: healthy, outer race fault, ball fault, inner race fault, compounded fault, and generalized degradation. The hybrid LSTM-RF-GWO model achieved a remarkable classification accuracy of 98.97%, significantly outperforming standalone models such as LSTM (93.56%) and RF (98.44%). Furthermore, the inclusion of GWO led to an additional accuracy improvement of 0.39% compared to the hybrid LSTM-RF model without optimization. Other performance metrics, including precision, kappa coefficient, false negative rate (FNR), and false positive rate (FPR), were also improved, with precision reaching 99.28% and the kappa coefficient achieving 99.13%. The FNR and FPR were reduced to 0.0071 and 0.0015, respectively, underscoring the model's effectiveness in minimizing misclassifications. The experimental results demonstrate that the proposed hybrid LSTM-RF-GWO framework not only enhances fault detection accuracy but also provides a robust solution for distinguishing between closely related fault conditions, making it a valuable tool for predictive maintenance in industrial applications. [ABSTRACT FROM AUTHOR]

This study introduces an Asymmetric Nonlinear Energy Sink (ANES) to enhance robust Targeted Energy Transfer (TET) in vibration control. Traditional cubic Nonlinear Energy Sinks (NES) often struggle with varying excitation levels in random vibrations. The ANES integrates a cubic NES, extra inertia, and asymmetric stiffness components like a tension-only rope, two linear springs, and a viscous damper. The rope adds asymmetric stiffness by only applying tension force. This setup effectively absorbs vibrational energy across different levels of excitation, facilitating energy transfer from low-damped to high-damped modes. Numerical simulations demonstrate the ANES’s superior performance compared to traditional NES, supported by modal energy redistribution, Nonlinear Normal Modes (NNM) analysis, and Frequency-Energy Plots (FEP). These findings suggest that this type of ANES is a promising advancement for practical NES applications in vibration control. [ABSTRACT FROM AUTHOR]

We report the development of a space-compatible packaging system for an integrated monolithic ultra-stable optical reference toward China's next-generation geodesy mission with low orbit satellite-to-satellite tracking. Building on our previous work, we optimized the mounting structure and thermal insulation mechanism using the finite element method. The comprehensive simulation results demonstrated the robustness of the entire packaging system with enough margins to withstand severe launch loads and maintain an ultra-high geometric cavity length stability. A long-term prediction of the vacuum maintenance around the cavity during in-orbit operation was conducted. An engineering prototype, within which an integrated monolithic optical reference has been mounted, was built based on our optimized design, and it has successfully passed typical aerospace environmental tests, including sinusoidal vibration (∼10 g, 10–100 Hz), random vibration (∼0.045 g2/Hz, 10–2000 Hz), and thermal cycling (0–45, 3 °C/min, lasting for 90 h). The experimental thermal time constant of the prototype exceeded 9.5 × 104 s, enabling a temperature stability of 1.1 × 10−6 K/Hz1/2 at 10 mHz on the optical cavity, with external active temperature control. The design is also suitable and useful for laboratory and terrestrial applications. [ABSTRACT FROM AUTHOR]

To provide reference and theoretical guidance for establishing human body dynamics models and studying biomechanical vibration behavior, this study aimed to develop and verify a computational model of a three-dimensional seated human body with detailed anatomical structure under complex biomechanical characteristics to investigate dynamic characteristics and internal vibration behaviors of the human body. Fifty modes of a seated human body were extracted by modal method. The intervertebral disc and head motions under uniaxial white noise excitation (between 0 and 20 Hz at 1.0, 0.5 and 0.5 m/s2 r.m.s. for vertical, fore-aft and lateral direction, respectively) were computed by random response analysis method. It was found that there were many modes of the seated human body in the low-frequency range, and the modes that had a great impact on seated human vibration were mainly distributed below 13 Hz. The responses of different positions of the spine varied greatly under the fore-aft and lateral excitation, but the maximum stress was distributed in the lumbar under different excitations, which could explain why drivers were prone to lower back pain after prolonged driving. Moreover, there was a large vibration coupling between the vertical and fore-aft direction of an upright seated human body, while the vibration couplings between the lateral and other directions were very small. Overall, the study could provide new insights into not only the overall dynamic characteristics of the human body, but also the internal local motion and biomechanical characteristics under different excitations. [ABSTRACT FROM AUTHOR]

The random vibrations of jacket offshore platforms caused by wave loadings can reduce the service life and fatigue failure of the offshore platforms. The nonlinear energy sink (NES) has great application potential because of its lightweight, high robustness and wide frequency band of vibration attenuation. The NES is introduced to mitigate the vibrations of the jacket offshore platform as a passive control device under wave loadings. The dynamic model of jacket platforms is developed with the NES system. The optimal parameters of the NES system are obtained by exhaustive search method. The results show that the NES system can effectively mitigate the responses of the deck level of jacket platforms under different wave states. The NES system could reduce the response under various deck's mass and stiffness of jacket platforms. The present study proves the feasibility of the NES system in the application of vibration control for marine structures. [ABSTRACT FROM AUTHOR]

Aviation aircraft will be subjected to a large number of complex random vibration loads during service， and its structure is prone to vibration fatigue，which leads to damage or even failure，which can cause serious losses. The stress intensity factor（SIF）solution method for cracked beams under random vibration loading is investigated，and a time-domain method based on Hudson's theory is proposed to estimate the vibration fatigue crack growth life by combining with the Paris formula. The theoretical analysis and vibration fatigue test are conducted on a typical cantilever beam as an object. The results show that the life prediction results of the proposed time-domain method based on the Hudson's theory is better than that of the experimental estimation results，which can verify that the method can effectively describe the random vibration crack growth behavior.

Non-stationary non-Gaussian random vibration problems of structures are challenging and drawing increasing attention. In the present study, firstly, an explicit time-domain method (ETDM) is proposed to determine the higher-order response statistics of linear systems subjected to non-stationary non-Gaussian random excitations, in which the first four orders of cumulants of dynamic responses are directly formulated through the cumulant operation rule based on the explicit expressions of responses. Secondly, an equivalent linearization – explicit time-domain method (EL-ETDM) is further developed to solve the non-stationary non-Gaussian random vibration problems of Duffing systems, in which the equivalent linear system is derived discarding the assumption of Gaussian response, and the corresponding higher-order cumulant analyses of the linearized system are accomplished by the efficient ETDM. The present approach can account for non-Gaussian random excitations with arbitrary forms, and two specific applications to the Poisson white noise and the square form of Gaussian random process are investigated. Four numerical examples are presented to demonstrate the effectiveness of the proposed methods.

When a structure is randomly excited by its installation base, significant vibration stress may be caused within it, thus causing damage to the structure. The authors find in the vibration fatigue test that when the notched slender beam specimen is excited by stationary Gaussian random base movement, the measured acceleration response and strain response of the specimen have obvious nonstationary characteristics. The vibration responses of the specimen under Gaussian and non‐Gaussian random base excitations are calculated by the finite element method and corresponding vibration fatigue tests were completed. The nonstationary characteristics of the responses from calculations and experiments are analyzed. Finally, a method for calculating the fatigue life of the specimen under nonstationary response is given, and the calculated results are compared with the measured data. The results indicate that the method proposed in this article performed excellent calculation fatigue life with measured strain data. [ABSTRACT FROM AUTHOR]

The assessment of runway smoothness or roughness is intimately tied to the vibrational response of aircraft during taxiing. In this study, employing the pseudo excitation method (PEM) based on random vibration analysis, we unearthed the relationship between the random vibrations of five distinct aircraft types and runway irregularities. Initially, we established two three-dimensional (3D) models of aircraft taxiing vibration and derived the response output under roughness excitation. Subsequently, we employed MATLAB to analyze the power spectral characteristics of the vibrational response in different parts of the aircraft. Lastly, we examined the effects of taxiing speed, aircraft type, runway roughness, and lift on the aircraft's vibration. Our findings indicate that the distribution of vibration power spectral density (PSD) exhibits multiple peaks, correlating with the degrees of freedom of the aircraft. We further note that the frequency that aligns most closely with the response peak should be the focus of investigation. High-frequency excitation impacts the pilot and nose landing gear more significantly than the passenger and main landing gear. Absent the consideration of lift, increased taxiing speed amplifies the impact of roughness excitation on aircraft taxiing safety. Larger aircrafts are more sensitive to long-wave roughness. With lift in consideration, all aircraft types exhibit a speed sensitivity to vibration, which should be the primary concern in runway roughness evaluations.

This paper presents the process of conducting the structural analysis of AlAinSat-1 CubeSat through a numerical solution using Siemens NX. AlAinSat-1 is a 3U remote-sensing CubeSat carrying two earth observation payloads. The CubeSat is scheduled for launch on SpaceX Falcon 9 rocket. To ensure the success of the mission and its ability to withstand the launch environment, several scenarios should be analyzed. For AlAinSat-1 model the finite element analysis (FEA) method is used, and four types of structural analyses are considered: modal, quasi-static, buckling, and random vibration analyses. The workflow cycle includes idealizing, meshing, assembling, applying connections and boundary conditions, and eventually running the simulation utilizing the Siemens Nastran solver. The simulation results of all analysis types indicate that the model can safely withstand the loads exerted during launch. Also, the numerical results of the Command and Data Handling Subsystem (CDHS) module of AlAinSat-1 are experimentally validated through a vibration test conducted using an LV8 shaker system. The module successfully passed the test based on the test success criteria provided by the launcher.

The U-shaped beam, a novel beam type, is extensively used in urban rail transit due to its ability to block radiation noise from wheel–rail interactions, providing effective noise control at the source. This study aims to investigate the dynamic response and structure-borne noise of a 25m concrete simply supported U-shaped girder at a vehicle speed of 80km/h, and to assess the effectiveness of novel track vibration damping devices. Grounded in stochastic vibration theory, this study employs pseudo excitation methods (PEM) to obtain the frequency domain response of a finite element model of the U-shaped girder. The structure-borne noise is then analyzed using the acoustic indirect boundary element method (BEM), with frequency-domain responses from PEM as input conditions. The eastern extension section of Nanjing Metro Line 2’s simply supported U-shaped beam is used as a case study for practical and theoretical analyses of dynamic characteristics and structural radiation noise. This study reveals that the sound pressure level of the mid-span section’s bottom plate is higher directly below and above it, while it is lower on either side of the web. Considering the ground reflection effects, sound pressure levels are highly closer to ground reflections. The damping device significantly attenuates vibration noise in the frequency range of 50–200Hz, with the bottom plate exhibiting superior vibration reduction effects compared to the web. The predictive method aligns closely with field test results, validating the feasibility of the approach. This study demonstrates that the U-shaped beam effectively controls rail transit noise, and the novel track vibration damping devices significantly reduce vibration noise, particularly in the bottom plate. This research provides valuable insights for noise control in urban rail transit systems. [ABSTRACT FROM AUTHOR]

A bi-Gamma distribution model is proposed to determine the probability density function (PDF) of broadband non-Gaussian random stress rainflow ranges during vibration fatigue. A series of stress Power Spectral Densities (PSD) are provided, and the corresponding Gaussian random stress time histories are generated using the inverse Fourier transform and time-domain randomization methods. These Gaussian random stress time histories are then transformed into non-Gaussian random stress time histories. The probability density values of the stress ranges are obtained using the rainflow counting method, and then the bi-Gamma distribution PDF model is fitted to these values to determine the model's parameters. The PSD parameters and the kurtosis, along with their corresponding model parameters, constitute the neural network input–output dataset. The neural network model established after training can directly provide the parameter values of the bi-Gamma model based on the input PSD parameters and kurtosis, thereby obtaining the PDF of the stress rainflow ranges. The predictive capability of the neural network model is verified and the effects of non-Gaussian random stress with different kurtosis on the structural fatigue life are compared for the same stress PSD. And all life predicted results were within the second scatter band. [ABSTRACT FROM AUTHOR]

To resolve the issue of predicting the leak rate in proton exchange membrane fuel cells (PEMFCs) under long-term random vibration conditions. Considering the mechanism of bolt vibration loosening and rubber vibration relaxation, a leakage mechanism model of the PEMFC sealing structure under vibration conditions is proposed, and the validity of the model is verified by experimental comparison. The model clearly reveals the quantitative effects of structural parameters and material parameters on the leakage rate of PEMFC under vibration conditions. The research results show that under long-term random vibration conditions, the change of PEMFC leakage rate with time is mainly divided into three stages: response stage, stable stage, and leakage stage. Compared to bolt vibration loosening, the rubber vibration relaxation has a more significant impact on PEMFC leakage, the leakage rate of the fuel cell stack is 433ppm after 10,000 hrs of vibration. In addition, increasing the bolt preload, changing the bolt distribution, reducing surface roughness, and reducing gasket thickness can effectively suppress PEMFC leakage under random vibration conditions, the minimum leakage rate of the fuel cell stack can be reduced to around 170ppm per 10,000 hours. The proposed mechanism model provides an effective method for predicting the leakage rate of PEMFC sealing structures. [ABSTRACT FROM AUTHOR]

To accurately predict the vibration response of large-span floor under crowd walking, the random crowd load model was established according to the relationship among variable step size, variable step frequency and variable step speed during pedestrian walking. Based on the thin plate vibration theory, the crowd-large-span floor coupling dynamic equation considering human-structure interaction was deduced, and the variation rule of dynamic characteristic parameters and acceleration response of large- span floor under random crowd action was calculated and analyzed. The results show that under the random crowd walking, the instantaneous frequency of the large-span floor is decreased with latter increasing, and the instantaneous damping ratio is increased with latter decreasing. With the increasing of the number of people walking, the minimum instantaneous frequency of the structure is decreased significantly, and the maximum instantaneous damping ratio is increased significantly, while the instantaneous acceleration and root mean square acceleration of the large-span floor show the trend of increasing with latter decreasing. Under the different number of people walking, the acceleration response of the structure with and without pedestrian randomness is significantly different. The maximum difference rate of instantaneous acceleration can reach 53.90%, and the maximum difference rate of root mean square acceleration can reach 61.57%. [ABSTRACT FROM AUTHOR]

High-temperature superconducting pinning maglev technology has great potential for high-speed transportation due to its passive stability and friction-free characteristics. However, at high speeds, the weak damping characteristics of the system make it challenging to attenuate system vibrations caused by external excitation effectively. An electromagnetic shunt damper can be added to the high-temperature superconducting vehicle system to address this challenge. However, due to the complexity of the high-temperature superconducting vehicle system and external excitation, it is challenging to determine the optimal electromagnetic shunt damper parameters through analytical calculation. This study proposes a method for optimizing electromagnetic shunt damper parameters based on the NSGA-II multi-objective optimization algorithm. The high-temperature superconducting vehicle dynamic simulation model with electromagnetic shunt damper is established, and the dynamic simulation is carried out according to the actual operation conditions. Taking the dynamic indexes as the objectives, the optimal electromagnetic shunt damper parameters are then selected within a reasonable range based on dynamic indexes used as objectives in the NSGA-II algorithm. The effectiveness of the optimization method is verified through simulations and experiments on a levitation model vehicle with electromagnetic shunt damper under random vibration conditions. Finally, the optimized electromagnetic shunt damper parameters are applied to an engineering high-speed high-temperature superconducting pinning maglev vehicle through simulation. The calculation results demonstrate that various performance indexes are improved after optimization. This optimization design provides a reference for applying electromagnetic shunt damper in high-temperature superconducting pinning maglev vehicles. [ABSTRACT FROM AUTHOR]

The multi-output response spectral replication correction algorithms for the multi-shaker random vibration test are investigated. In the existing matrix power correction algorithm, the control of auto and cross spectral densities is coupled which may bring some unexpected errors. The ideal spectral correction mode is that the control of auto and cross spectral densities should be independent of each other. For this purpose, a novel spectral decoupled correction algorithm is proposed with a spectral decoupling decomposition method in this work. Two lower triangular matrices are introduced to modify the auto and cross spectral densities separately during equalization procedure. Due to the positive definite constraint for the power spectral matrix, the coherence coefficient and phase difference in the cross spectral densities cannot be controlled independently when the number of the control channels is more than two. A simulation example is provided and the control results with the matrix power correction algorithm and proposed spectral decoupled correction algorithm are compared. Finally, a tri-axial shaker random vibration test is carried out and the results prove the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This paper conducts a tutorial review of the analytic theory of seven classes of fractional vibrations based on elementary functions. We discuss the classification of seven classes of fractional vibrations and introduce the problem statements. Then, the analytic theory of class VI fractional vibrators is given. The analytic theories of fractional vibrators from class I to class V and class VII are, respectively, represented. Furthermore, seven analytic expressions of frequency bandwidth of seven classes of fractional vibrators are newly introduced in this paper. Four analytic expressions of sinusoidal responses to fractional vibrators from class IV to VII by using elementary functions are also newly reported in this paper. The analytical expressions of responses (free, impulse, step, and sinusoidal) are first reported in this research. We dissert three applications of the analytic theory of fractional vibrations: (1) analytical expression of the forced response to a damped multi-fractional Euler–Bernoulli beam; (2) analytical expressions of power spectrum density (PSD) and cross-PSD responses to seven classes of fractional vibrators under the excitation with the Pierson and Moskowitz spectrum, which are newly introduced in this paper; and (3) a mathematical explanation of the Rayleigh damping assumption. [ABSTRACT FROM AUTHOR]

This article introduces a novel regenerative suspension system designed for active seat suspension, to reduce vibrations while recovering energy. The system employs a four-quadrant electric actuator operation model and utilizes a brushless DC motor as an actuator and an energy harvester. This motor, a permanent magnet synchronous type, transforms DC into three-phase AC power, serving dual purposes of vibration energy recovery and active power generation. The system's advanced vibration control is achieved through the switching of MOSFET transistors, ensuring the suspension system meets operational criteria that contrast with traditional vibro-isolation systems, thereby reducing the negative effects of mechanical vibrations on the human body, while also lowering energy consumption. Comparative studies of the regenerative system dynamics against passive and active systems under random vibrations demonstrated its effectiveness. This research assessed the system's performance through power spectral density and transmissibility functions, highlighting its potential to enhance energy efficiency and the psychophysical well-being of individuals subjected to mechanical vibrations. The effectiveness of the energy regeneration process under the chosen early excitation vibrations was investigated. Measurements of the motor torque in the active mode and during regenerative braking mode, and the corresponding phase currents of the motor, are presented. [ABSTRACT FROM AUTHOR]

A generalized framework for the electromechanical model of piezoelectric energy harvesters is presented with high-order electric field assumption. This assumption enables the accurate description the non-uniform distribution of the electric field across the thickness of piezoelectric layers. The Euler–Bernoulli, Timoshenko and Reddy's assumptions for displacements are included in the general form and handled in a uniform manner. In consideration of the axial displacement variable and the electromechanical coupling, the governing equations and boundary conditions are derived through the application of Hamilton's principle. These equations are solved by the differential quadrature method. The outcomes demonstrate that the proposed theory is capable of accurately predicting the outcomes of the finite element analysis. Subsequently, the limitations of different beam models are also discussed. The necessity of the non-uniform electric field assumption becomes more pronounced when the harvester is excited by random vibrations. Compared to the results obtained with the uniform electric field assumption, the use of a non-uniform electric field is capable of correcting 15% of the voltage amplitude. [ABSTRACT FROM AUTHOR]

• Proposed a method for multi-axis random vibration topology optimization. • Enhancing vibration resistance and extending life during the topology phase. • Prompting the structure to add load-bearing paths to resist random vibration loads. • Guiding the topology towards forming a vibration-resistant structure. • Expanding HCA into the field of random vibration performance topology optimization. Considering the lack of effective solutions for multi-axis random vibration topology optimization problems, and recognizing that multi-axis random vibration excitation is the most common loading conditions experienced by structures during their operational life, this paper proposes a multi-objective topology optimization method for multi-axis random vibration. By combining Hybrid Cellular Automata (HCA) and Analytic Hierarchy Process (AHP), this method aims to enhance the vibration resistance of structures and extend their fatigue life during the topology optimization phase. To validate the effectiveness and engineering practicality of this method, two engineering cases were designed: a cantilever beam case and an automotive steering knuckle case. Multi-objective topology optimization were conducted with objectives including mass, stiffness, and vibration intensity metric (root-mean-square stress). The two cases demonstrate that the control group's topology model exhibits weaker resistance to random vibrations and shorter fatigue life. In contrast, the validation group's topology model introduces an additional load path near the excitation point, effectively dissipating the impact of vibration excitation. This enhances the structure's vibration resistance and significantly extends its fatigue life. [ABSTRACT FROM AUTHOR]

Due to ethical issues and simplification of traditional biomechanical models, experimental methods and traditional computer methods were difficult to quantify the effects of foot excitation and shin posture on vibration behavior of the entire spine inside a seated human body under vertical whole-body vibration. This study developed and verified different three-dimensional (3D) finite element (FE) models of seated human body with detailed anatomical structure under the biomechanical characteristics to predict vibration behavior of the entire spine inside a seated human body with different foot excitation (with and without vibration) and shin posture (vertical and tilt posture). Random response analysis was performed to study the transmissibility of the entire spine to seat under vertical white noise excitation between 0 and 20 Hz at 0.5 m/s2 r.m.s. The results showed that although the foot excitation could reduce the fore-aft transmissibility in the cervical spine (23% reduction), it could significantly increase that in the lumbar spine (52% increase), which resulted in complex alternating stresses at lumbar spine and made the lumbar spine more vulnerable to injury in long-term vibration environment. Moreover, the shin tilt posture made the maximum fore-aft transmissibility in the lumbar spine move to the upper lumbar spine. The study provided new insights into the influence of foot excitation and shin posture on the vibration behavior of the entire spine inside a seated human body. Foot excitation exposed the lumbar spine to complex alternating stresses and made it more vulnerable to injury in long-term whole body vibration. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents the process of conducting the structural analysis of AlAinSat-1 CubeSat through a numerical solution using Siemens NX. AlAinSat-1 is a 3U remote-sensing CubeSat carrying two earth observation payloads. The CubeSat is scheduled for launch on SpaceX Falcon 9 rocket. To ensure the success of the mission and its ability to withstand the launch environment, several scenarios should be analyzed. For AlAinSat-1 model the finite element analysis (FEA) method is used, and four types of structural analyses are considered: modal, quasi-static, buckling, and random vibration analyses. The workflow cycle includes idealizing, meshing, assembling, applying connections and boundary conditions, and eventually running the simulation utilizing the Siemens Nastran solver. The simulation results of all analysis types indicate that the model can safely withstand the loads exerted during launch. Also, the numerical results of the Command and Data Handling Subsystem (CDHS) module of AlAinSat-1 are experimentally validated through a vibration test conducted using an LV8 shaker system. The module successfully passed the test based on the test success criteria provided by the launcher. [ABSTRACT FROM AUTHOR]

Steel beams are widely used load-bearing components in bridge construction. They are prone to internal stress concentration under low-frequency vibrations caused by natural disasters and adverse loads, leading to microcracks and fractures, thereby accelerating the instability of steel components. Therefore, dynamic stress monitoring of steel beams under low-frequency vibrations is crucial to ensure structural safety. This study proposed an external stress sensor based on PMN-PT material. The sensor has the advantages of high sensitivity, comprehensive frequency response, and fast response speed. To verify the accuracy and feasibility of the sensor in actual engineering, the LETRY universal testing machine and drop hammer impact system were used to carry out stress monitoring tests and finite element simulations on scaled I-shaped steel beams with PMN-PT sensors attached. The results show that: (1) The PMN-PT sensor has exceptionally high sensitivity, maintained at 1.716~1.726 V/MPa in the frequency range of 0~1000 Hz. The sensor performance is much higher than that of PVDF sensors with the same adhesive layer thickness. (2) Under low-frequency random vibration, the sensor's time domain and frequency domain output voltages are always consistent with the waveform of the applied load, which can reflect the changes in the structural stress state in real time. (3) Under the impact of a drop hammer, the sensor signal response delay is only 0.001 s, and the sensitivity linear fitting degree is above 0.9. (4) The simulation and experimental results are highly consistent, confirming the superior performance of the PMN-PT sensor, which can be effectively used for stress monitoring of steel structures in low-frequency vibration environments. [ABSTRACT FROM AUTHOR]

This paper investigated the fluid–structure interaction vibration response of an aircraft liquid-filled pipeline under external random vibration and internal pulsating pressure. First, the fluid–structure interaction solution is theoretically analyzed, and the advantages and disadvantages of the direct coupling method and the separation coupling method are compared, with the latter chosen as the simulation analysis method in this study. Second, taking the U-shaped oil pipeline of an aircraft engine as an example, simulation modeling was performed to compare and analyze the fluid–structure interaction vibration response of aircraft liquid-filled pipelines under different working conditions, obtaining the vibration response characteristics of stress danger points under various conditions. Finally, a test bench for an aircraft liquid-filling pipeline was built to explore the influence of external random vibrations with different kurtoses, different pipe wall thicknesses and different working conditions on the vibration response danger points of aircraft liquid-filling pipelines, verifying the simulation conclusions and providing a basis for aircraft liquid-filling pipeline design. [ABSTRACT FROM AUTHOR]

Featured Application: This paper is applied in the industrial monitoring of the stamping process, where vibrations are common, necessitating the use of image registration and homography estimation methods to align template images with test images. By employing machine-vision and image-processing techniques, the process is monitored in real-time to detect any anomalies, ultimately aiming to protect the stamping molds. Homography estimation is a crucial task in aligning template images with target images in stamping monitoring systems. To enhance the robustness and accuracy of homography estimation against random vibrations and lighting variations in stamping environments, this paper proposes an improved unsupervised homography estimation model. The model takes as input the channel-stacked template and target images and outputs the estimated homography matrix. First, a specialized deformable convolution module and Group Normalization (GN) layer are introduced to expand the receptive field and enhance the model's ability to learn rotational invariance when processing large, high-resolution images. Next, a multi-scale, multi-stage unsupervised homography estimation network structure is constructed to improve the accuracy of homography estimation by refining the estimation through multiple stages, thereby enhancing the model's resistance to scale variations. Finally, stamping monitoring image data is incorporated into the training through data fusion, with data augmentation techniques applied to randomly introduce various levels of perturbation, brightness, contrast, and filtering to improve the model's robustness to complex changes in the stamping environment, making it more suitable for monitoring applications in this specific industrial context. Compared to traditional methods, this approach provides better homography matrix estimation when handling images with low texture, significant lighting variations, or large viewpoint changes. Compared to other deep-learning-based homography estimation methods, it reduces estimation errors and performs better on stamping monitoring images, while also offering broader applicability. [ABSTRACT FROM AUTHOR]

A secondary multidirectional vibration isolation system (MR-SMDIS) was designed by utilizing the multidirectional vibration isolation characteristics of metal rubber (MR) vibration isolators. According to the spatial distribution angles and contact form of the spatial distribution of metal wires in MR, the linear stiffness ratio between axial and radial directions, damping ratio, and the ratio of nonlinear stiffness to linear stiffness were analyzed. The nonlinear response of an MR-SMDIS under random vibrations was analyzed using the extended harmonic equilibrium method with alternating frequency–time domain (HB–AFT). Random signals were further created to analyze the isolation efficiency and peak amplification of the MR-SMDIS. The particle swarm optimization (PSO) was used to optimize the axial and radial linear stiffness, damping, and nonlinear stiffness of the MR isolator. And the optimal preparation parameters for MR were solved with a genetic algorithm. Furthermore, random vibration experiments of the MR-SMDIS were conducted. The results showed that the relative error in identifying the dynamic parameters of the prepared MR isolators using parameter identification algorithms was within ± 13% compared to the design parameters. The MR-SMDIS met the design requirements regarding modal frequencies and peak amplification factors. The relative error between the experimental and numerical simulation results was within 15%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposed a theoretical model for analyzing the stochastic vibration responses of functionally graded three-stage conical–cylindrical combined shell structure (FG-TSCCCSS) subjected to various stationary stochastic excitations. The theoretical model is established by employing the differential quadrature method in conjunction with pseudo excitation method (PEM) in the framework of FSDT. The material property parameters of FG-TSCCCSS along the thickness direction are ascertained based on four-parameter power–law distributions in terms of volume fractions of constituents of FGMs. The FG-TSCCCSS mainly consists of three conical shell segments with different tapers and one cylindrical shell segment. The coupling between adjacent shell segments is achieved by means of common nodes. The various boundary conditions of FG-TSCCCSS are simulated by applying the penalty function method. Based on the above model, the convergence analysis of the established model for determining the value of the penalty factor and the number of differential quadrature nodes first. Then, the precision and reliability of the proposed numerical model are verified by comparing the present solutions with the results of literature works and finite element software. Finally, the stochastic vibration response analysis of FG-TSCCCSS is carried out by investigating the influences of power–law distribution, power–law exponent, boundary condition, stochastic excitation type and taper angle on the natural frequency and PSD acceleration response of FG-TSCCCSS. The paper can provide the theoretical reference and numerical tool for the random vibration response evaluation of combined shell structures of various engineering application fields. [ABSTRACT FROM AUTHOR]

A full triangular chiral (Tri-Chi) honeycomb, combining a honeycomb structure with triangular chiral configuration, notably impacts the Poisson's ratio (PR) and stiffness. To assess the random vibration properties of a composite sandwich panel with a Tri-Chi honeycomb core (CSP-TCH), a two-dimensional equivalent Reissner–Mindlin model (2D-ERM) was created using the variational asymptotic method. The precision of the 2D-ERM in free and random vibration analysis was confirmed through numerical simulations employing 3D finite element analysis, encompassing PSD curves and RMS responses. Furthermore, the effects of selecting the model class were quantified through dynamic numerical examples. Modal analysis revealed that the relative error of the first eight natural frequencies predicted by the 2D-ERM consistently remained below 7%, with the modal cloud demonstrating high reliability. The PSD curves and their RMS values closely aligned with 3D finite element results under various boundary conditions, with a maximum error below 5%. Key factors influencing the vibration characteristics included the ligament–rib angle of the core layer and layup modes of the composite facesheets, while the rib-to-ligament thickness ratio and the aspect ratio exert minimal influence. The impact of the ligament–rib angle on the vibration properties primarily stems from the significant shift in the core layer's Poisson's ratio, transitioning from negative to positive. These findings offer a rapid and precise approach for optimizing the vibration design of CSP-TCH. [ABSTRACT FROM AUTHOR]

A meshless model is proposed to carry out the free and stationary stochastic vibration analysis of the functionally graded combined rectangular and cylindrical shells (FG-CRCS) structure under the aerodynamic and thermal environment. The FG-CRCS structure contains three combined structure types including rectangular–cylindrical shell (RC-type), cylindrical–rectangular–cylindrical shell (CRC-type), and closed rectangular–semicylindrical shell (CRS-type). The effects of aerodynamic and thermal loads on the dynamic behaviors of the FG-CRCS structure with temperature-dependency of material properties are investigated by introducing the supersonic piston theory and thermo-elastic theory. Furthermore, the pseudo-excitation method (PEM) is adopted to simulate the random loads applied to the FG-CRCS structure. The dynamic equations of the FG-CRCS structure are established in the theoretical frame of the first-order shear deformation theory (FSDT), whose general boundary conditions and coupling relationship are regulated by the artificial springs. Then, the reasonableness of this meshless model to predict free and random vibrations in aerodynamic and thermal environments is verified by comparing it with published literature and FEM results. On this basis, the contribution of essential parameters (including the aerodynamic load, thermal load, and boundary condition) on the free and random vibration behaviors of the FG-CRCS structure is presented, which may serve as guidance for the design of the plate–shell coupled structures in aerospace. [ABSTRACT FROM AUTHOR]

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a novel vibration-fatigue testing methodology to characterize the frequency dependence of polymer material fatigue parameters under constant temperature conditions. In this investigation, 3D-printed PLA samples with frequency-tunable geometry were experimentally tested on an electro-dynamical shaker with a random vibration profile. Using the validated numerical models, the estimation of vibration-fatigue life was obtained and compared to the experimental results. Performing the numerical minimization of estimated and actual fatigue lives, the frequency-dependent fatigue parameters were assessed. In particular, the results indicate that the tested samples exhibit varying fatigue parameters within the loading frequency range of 250–750 Hz. Specifically, as the loading frequency increases, the fatigue exponent increases and fatigue strength decreases. These findings confirm the frequency dependence of fatigue parameters for 3D-printed polymer structures, underscoring the necessity of experimental characterization to reliably estimate the vibration-fatigue life of 3D-printed polymer structures. The utilization of the introduced approach therefore enhances the vibration resilience of the 3D-printed polymer mechanical component. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)