The floating offshore wind turbine (FOWT) has strong background response due to overall sway, which presented in the frequency domain as the peak response being dominated by the excitation frequency and varying with the changing of load frequency.The frequency imbalance occurs when using traditional tuned mass damper (TMD) for vibration control, and resulting in poor performance.A magnetorheological elastomer-pounding tuned mass damper (MRE-PTMD) was designed and proposed for semi-active control of FOWT.In this device, the stiffness adjustable characteristic of MRE was utilized to achieve real-time adjustment of damper frequency through semi-active control technology, maintaining optimal control of the FOWT.At the same time, the viscoelastic limiting device was introduced to protect the MRE material and realize the collision energy dissipation.Taking the barge type FOWT as an example, a 17 degrees of freedom dynamic equation including the control device was established to study its vibration reduction performance and parameter influence under the combined action of wind and waves, and compared with traditional TMD.The results show that the proposed control device can adjust the control parameters of the damper in adaptive manner through real-time tracking of the structural response, and has better vibration reduction performance and adaptability compared to traditional TMD.Increasing the mass ratio of dampers is an effective way to improve the performance of MRE-PTMD.By designing the damper mass ratio and collision parameters reasonably, MRE protection and device miniaturization can be achieved without significantly affecting the vibration reduction effect.

A mathematical model of the graded metamaterial beam was established by using the spectral element method for calculating the vibration transmission characteristics of the beam.The effects of the graded mass parameters and graded position parameters of the local resonators on the vibration suppression performance of the metamaterial beam were studied theoretically.Based on the spectral element model of the metamaterial beam, a non-dominated sorting genetic algorithm II for the multi-objective optimization was introduced to optimize the graded parameters of the local resonators for achieving relatively superior vibration suppression performance of the beam.With the varied graded values of the local resonators, a Pareto solution set was obtained.The advantage performance of the optimal multi-parameter configuration was explored by comparisons with the conventional configuration and the optimal single-parameter graded configuration.The results indicate that with an appropriate selected Pareto optimal solution, the metama-terial beam can obtain wider attenuation bandwidth and higher average attenuation intensity as compared with the conventional configuration and the optimal single parameter configuration.When the mass variable Δm=-0.002 6 kg and the position variable Δa=0.077 m for the graded local resonators, the attenuation bandwidth of the graded metamaterial beam is 524 Hz and the average attenuation intensity is -26.1 dB.Compared with the corresponding values of the conventional metama-terial beam, the corresponding performance is improved by 59.0% and 39.6%, respectively.The research can provide theoretical guidance for the design of the graded metamaterial beam with local resonators.

To further understand the impact of corner rounding treatment on the flow characteristics of two tandem square cylinders with small gaping ratios, the numerical simulation based on unsteady Reynolds-averaged Navier-Stokes approach at Re=22 000 was carried out, where the corner rounding treatments of 0, 5%, 10%, 15%, 16%, 17%, and 20% was applied to the upstream square cylinder, and the effect of rounded corner ratio on the aerodynamic characteristics and flow field was also comprehensively analyzed.The results indicate that as the rounded-corner ratio of the upstream square cylinder increases, the drag coefficient of the upstream square cylinder gradually decreases, while the drag coefficient of the downstream square cylinder remains relatively unchanged.The lift coefficients of both the upstream and downstream square cylinders exhibit an initial decrease followed by an increase, with optimal aerodynamic performance occurring around a rounded-corner ratio of 16%.The increase in the rounded-corner ratio of the upstream square cylinder will lead to a decrease in the mean wind pressure coefficients of the upstream and downstream square cylinders, and the fluctuating wind pressure coefficient of the upstream and downstream square cylinders shows a trend of first decreasing and then increasing.Compared to the square cylinder without corner rounding, the corner rounding treatment of the upstream square cylinder decreases the shear flow diffusion angle, bringing the separation vortex closer to the square cylinder wall, which results in an earlier flow reattachment on the downstream square cylinder and accelerates the vortex shedding rate.

Addressing the challenge that the traditional energy harvesting devices struggle to efficiently harvest low-frequency vibration energy, this paper utilizes the interaction between magnets to design a magnet-induced negative stiffness mechanism and extends it to the triboelectric nanogenerator (TENG), proposing a pendulum-type tristable triboelectric nanogenerator (PT-TENG) for harvesting low-frequency vibration energy. Firstly, the model design and working principle of the PT-TENG are introduced. Secondly, the electromechanical coupling model of the PT-TENG is established. Subsequently, the numerical methods are used to study the mechanical characteristics and electrical performance of the PT-TENG. Furthermore, the effects of key system parameters on the performance of the PT-TENG are analyzed. Finally, a prototype of the PT-TENG is fabricated, and the validation and application demonstration experiments are conducted. The results show that the PT-TENG can efficiently convert low-frequency vibration energy into electrical energy, with a maximum output power of 0.27 mW, capable of driving the LED array. Moreover, the low-frequency energy harvesting bandwidth of the PT-TENG can be effectively broadened by selecting appropriate system parameters. Therefore, this paper has guiding significance for low-frequency vibration energy harvesting and the design of self-powered devices.

Compared to traditional real-time hybrid simulation (RTHS), multi-axis real-time hybrid simulation (maRTHS) offers a more realistic simulation of complex structures under multi-dimensional dynamic loads. However, addressing time delay compensation in multi-axis servo loading systems requires a multi-input multi-output control strategy, which is significantly more complex and challenging than the time delay compensation problems in conventional real-time hybrid simulation. This paper proposes a decentralized unscented Kalman filter-based two-stage adaptive time-delay compensation (D-UKF-TAC) method. This method allocates control tasks to individual actuators for independent compensation, reducing the computational complexity of time delay compensation while maintaining high accuracy and ease of implementation. Using the benchmark problem of maRTHS as a basis, simulations were conducted to validate the effectiveness of the D-UKF-TAC method. The results demonstrate that under the nominal model, the D-UKF-TAC method can reduce time delay compensation to 0 ms, eliminating delay effects and significantly improving compensation accuracy. In uncertain models, compared to the benchmark LQG control method, the D-UKF-TAC method reduces the maximum standard deviation of evaluation metrics by 94.07%. Furthermore, under varying levels of measurement noise, the D-UKF-TAC method consistently exhibits high precision and robustness.

In view of the difference between the airflow state in the tensile section and the compression section of the throttling pipe air damping spring, the dynamic mechanical model of the air damping spring with stretch and compression separation flow is constructed, and the mathematical expressions of its equivalent stiffness and equivalent damping coefficient under the stretch and compression separation flow are given. Based on the MTS test bench, its static and dynamic characteristics were tested. The results indicate that the maximum relative errors of the static hysteresis loop, its area, equivalent stiffness, and equivalent damping coefficient are less than 2.4%, 7.2%, 9.67%, and 9.03%, respectively, which verified the effectiveness of the model, and analyzed the perturbation law of the key design parameters of the throttling pipe on its static and dynamic characteristics. The research results provide a new idea for the innovative design of double-throttling pipe air damping springs.

In order to solve the analytic Jacobian matrix of the non-smoothing nonlinear system and realize the amplitude-frequency response analysis of the system, an alternate state space method based on the time-domain shooting method was proposed. Firstly, the state transition conditions of the non-smoothing nonlinear force are derived, state transition points are solved using the dichotomy method, and the non-smoothing nonlinear system is divided into several smoothing nonlinear systems. Then, the response sensitivity equations of the smoothing nonlinear system are derived, and the response sensitivity mapping equation of the non-smoothing nonlinear system before and after the state transition points are established to characterize the response sensitivity jump relationship, and then an alternate state space method is developed to solve the response sensitivity mapping equation to obtain the Jacobian matrix of the system. Finally, the periodic response boundary value problem is established based on the shooting method, and the periodic response analysis is realized through the Jacobian matrix and Newton iteration, and the frequency domain response analysis is realized by combining the continuation method. Numerical results show that the proposed method can effectively solve the amplitude-frequency response and stability of impact oscillator and time-varying stiffness dry friction system, and has a good engineering application prospect.

This paper focuses on the axial-flow water-jet propulsion pump as the research object. Based on biomimetic principles, a biomimetic noise-reduction design is applied to the impeller blades of the water-jet propulsion pump. The hydrodynamic performance and flow-induced noise of the pump before and after the biomimetic design are numerically calculated using a CFD/CAA hybrid method. By comparing and analyzing the results, it is found that although the efficiency of the biomimetic pump with the biomimetic design of the impeller trailing edge is lower than that of the prototype pump, it demonstrates better noise reduction performance. The overall sound pressure level of the pump’s flow noise is reduced by up to 4.96 dB in the frequency range of 25–4000 Hz. Finally, experimental measurements of the hydrodynamic performance and flow noise of both the original and the biomimetic water-jet propulsion pumps are conducted. The experimental results show that the overall sound pressure level of the flow noise in the frequency range of 10–4000 Hz for the biomimetic pump is 3.84 dB lower than that of the prototype pump, verifying the actual noise reduction effect of the biomimetic design on the water-jet propulsion pump.

This paper proposed a new type of graded stiffness module in optical fiber hydrophone towed array. In the vibration isolation module, a single high-stiffness thick rope is replaced by a number of low-stiffness thin ropes, and the length allowance of each thin elastic rope is designed. When working, each elastic rope is stressed in turn to realize the adaptive change of stiffness under different towed speeds, so as to achieve the best vibration isolation effect. The simulation analysis show that the vibration reduction amount of the new vibration isolation module is about 5.2dB@0.66Hz higher than that of the ordinary vibration isolation module at low towed speed. The towed comparison test in the lake shows that the new vibration isolation module has about 2~3dB@100Hz lower towed noise at the speed of 2m/s, about 1~2dB@100Hz lower towed noise at the speed of 3m/s, and about 1.5dB@100Hz lower towed noise at the speed of 6m/s.

Cable hoisting system in the lifting process due to the hook suddenly jump tongue or breakage will lead to the weight off the hook fall, which will make the load-bearing cable jump vibration, for this kind of multi-span continuous suspension structure of the jump vibration problem, is still to be explored. To this end, the paper firstly based on the principle that the vibration law of single-span cable with time change is the same as that of multi-span continuous cable, the load-bearing cable is cut into several single-span cable structures at the supporting place, so as to establish the vibration differential equations of each single-span cable structure, and then the characteristic equations of the load-bearing cable containing the intrinsic frequency and the shape function are derived according to the principle of dynamic equilibrium and deformation coordination of the single-span cable structure, and then the initial velocity is constructed by taking the position of decoupling as the initial velocity condition, and the sudden decoupling of the weight is then calculated. Then the sliding-jumping model after sudden decoupling is constructed, and the main vibration and free vibration modes of the load-bearing cables are established, and finally analyzed by combining with the cable hoisting system used in the construction of Meixi River Bridge. The results show that: after the weight decoupling, the frequency and amplitude of the load-bearing cable in the first 3 cycles gradually decrease with the increase of time, thus generating the jumping vibration, and the frequency of the load-bearing cable starts to stabilize later, and the 1st-order vibration waveform plays a dominant role, and all points are simple harmonic vibration with the same attitude; the change of the lifting weight doesn't change the form of the load-bearing cable's nonlinear motion, but it will obviously affect the nonlinear vibration frequency and amplitude. Through the analysis of the main vibration characteristics of the change rule, found that the most unfavorable decoupling position of the cable hoist system is located in the tenth point, the second point and the fourth point.

To clarify the complex nonlinear characteristics of multi particle dampers, different equivalent single particle mechanical models have been proposed based on the analysis of multi particle motion states. However, the differences in assumptions of different mechanical models have a certain impact on the correct understanding of the vibration reduction mechanism of particle dampers. On the basis of fully analyzing the motion state of a single particle, a full state equivalent single particle mechanics model is proposed, as well as the corresponding simulation analysis methods. On this basis, the vibration reduction performance corresponding to different equivalent mechanical models is discussed. The parameter influence analysis was conducted based on the full state equivalent single particle mechanics model subsequently. The research results under free vibration indicate that the additional damping ratio of the structure exhibits nonlinear attenuation with the displacement of the structure. The assumption of different motion states has a certain impact on this nonlinear characteristic. The comparative analysis results under harmonic excitation show that the excitation amplitude has a significant impact on the vibration reduction effect, which variation pattern also influenced by the assumptions of different mechanical model. The analysis of vibration reduction effect under earthquake motion shows that the assumption of motion state has a certain impact on the vibration reduction performance. The variation law of vibration reduction performance with peak acceleration corresponding to different mechanical models has certain similarities with that under harmonic excitation. The parameter influence analysis of the damping performance based on the full state equivalent model shows that different parameters have a certain impact on the damping effect. Among them, the influence of rolling friction is not significant. The influence analysis of different mechanical model assumptions on vibration reduction performance mentioned above has good research significance for further understanding the complex nonlinear characteristics of particle dampers, as well as the parameter influence analysis in the end.

An oscillator chain composed of three oscillators with the same mass is designed and tested to clarify the influence of stiffness characteristics on the non-reciprocity of vibration energy transfer. The differences of vibration energy transfer in both positive and negative directions of the oscillator chain with different stiffness characteristics (oscillators are only connected by linear springs, oscillators are only connected by purely nonlinear springs, oscillators are connected by linear springs and purely nonlinear springs) are studied experimentally. Sweep frequency and fixed frequency excitations are applied to the oscillator chain in positive and negative directions, respectively. The acceleration and displacement responses are compared in the two experiment cases. The results show that the non-reciprocity is weak when only the linear springs are used, and the non-reciprocity is significantly enhanced when the purely nonlinear springs are added to the chain. The oscillator chain exhibits the strongest non-reciprocity when only the purely nonlinear springs are installed. The experiments demonstrate that the larger the proportion of nonlinear part in the restoring force, the stronger the non-reciprocity of vibration energy transfer.

The symmetrization of coefficient matrices in wave equations is an effective approach to unifying diverse types of wave equations and mitigating the challenges associated with wave propagation modeling, having achieved remarkable successes in the domains of acoustic wave equations and elastic wave equations in both isotropic and anisotropic media. This paper aims to derive the symmetric format of coefficient matrices for the wave equation in two-phase media. Subsequently, we incorporate a multi-axis perfectly matched layer (PML) and adopt the upwind summation by parts―simultaneous approximation terms(SBP-SAT) finite difference method to discretize the wave equation. Furthermore, an energy-based approach is utilized to assess the stability of the proposed method. Numerical simulations demonstrate that the presented discretization framework exhibits high integration capability, robust stability, and strong scalability. Additionally, our approach enables stable simulation of wave propagation in curved domains while reducing implementation costs, thereby underscoring the broad application prospects of coefficient matrix symmetrization methods and their discretization frameworks in the field of wave propagation modeling.

The elastic wave transmission properties in periodic metamaterials are characterized by their band structures, and the star-shaped negative Poisson's ratio mechanical metamaterials have excellent prospects for vibration mitigation and noise reduction applications due to their wide bandgap. To further improve their low-frequency vibration mitigation behavior, a load-bearing star-shaped elastic wave metamaterial micro-structure is designed based on a locally resonant arrow-shaped vibrator. The microscopic load-bearing and bandgap properties of the unit cell are calculated with and without the additional vibrator by using the structural finite element method combined with two categories of periodic boundary conditions, respectively. The vibration reduction characteristics of its order-constructed meta-structure are analyzed via structural finite element method. The titanium alloy specimens of the meta-structure are fabricated by 3D printing technique and the dynamic tests are carried out on vibration mitigation performance. The results show that the additional vibrator breaks the diagonal rotational symmetry of the intrinsic modes of the star-shaped metamaterial in the 45° wave vector direction, which opens a low-frequency locally resonant bandgap. This study strengthens the low-frequency vibration mitigation characteristics of star-shaped metamaterials while ensuring their microscopic load-bearing performance, which is also of reference value for the design and regulation of elastic band structures of other elastic-wave metamaterials.

Pattern recognition is a critical step in the modeling and application of mechanical systems, as well as a cornerstone of industrial processes. However, the high sparsity and noise inherent in mechanical systems introduce new challenges to pattern recognition, making many implicit patterns difficult to uncover using traditional physical methods. In this context, machine learning methods offer a powerful alternative by leveraging algorithmic induction and reasoning to identify hidden patterns, thus uncovering the specific expressions and laws governing mechanical systems. Nevertheless, in practical applications, training samples inevitably contain numerous undetected patterns, referred to as false-negative samples. To address this issue, multi-instance learning, a weakly supervised learning algorithm, demonstrates significant advantages. This study introduces multi-instance learning into the domain of pattern recognition for mechanical systems, constructing a hybrid deep learning model to infer patterns. The findings validate that the multi-instance learning approach effectively addresses the weak-label problem, simultaneously reducing the precision requirements of datasets and significantly enhancing model stability.

The issue of low diagnostic accuracy is caused by the significant differences in fault data distributions between the source and target domains under different operating conditions, as well as the difficulty in effectively characterizing the nonlinearity and non-stationarity of the fault signals. A fault diagnosis method for harmonic gear reducers is proposed, which combines centralized information fusion with deep transfer learning networks. Firstly, modal components of the complex signals are extracted using variational mode decomposition (VMD) based on the dragonfly algorithm (DA), and a uniaxial time-frequency image is obtained through the combination with Hilbert time-frequency mapping. Secondly, the three-axial time-frequency images are fused by wavelet transform to construct the fused image samples. Thirdly, on the basis of the residual network (ResNet), the convolutional block attention module (CBAM) is integrated, and the joint maximum mean discrepancy (JMMD) method is introduced to measure the joint distribution difference between different domains, and the domain migration deep network is constructed to realize the migration fault diagnosis of harmonic reducer under variable working conditions. Finally, the experimental verification is carried out by the experimental platform of the harmonic reducer. In the variable working condition diagnosis task, the highest recognition rate of the proposed method can reach 98.75%, and the average diagnosis result is 95%, which can realize the fault diagnosis of the variable working condition harmonic reducer.

In order to study the influence of pipeline-equipment coupling effect on the seismic response of vertical mixed frame structure of petrochemical equipment, a scale specimen of shaking table test of vertical mixed frame structure of petrochemical equipment was designed with geometric similarity ratio of 1:10. The finite element software ABAQUS is used to establish three kinds of working conditions, including not considering equipment coupling effect, considering equipment coupling effect and considering pipeline-equipment coupling effect, with a total of four specimen models. Through time-history analysis, the influence of pipeline-equipment coupling effect on the dynamic characteristics, failure forms and damage of vertical hybrid frame structures under frequent and rare earthquakes is compared and analyzed. The results show that ABAQUS model is consistent with the first three modes of PKPM calculation structure, and the period error is less than 2%. ABAQUS calculation results can well reflect the dynamic response characteristics of the structure. Considering the coupling effect of equipment (pipeline-equipment), the basic natural vibration period of the structure increases significantly, and the inter-story displacement angle increases by 1.48 times to 2.79 times. Under frequent earthquakes, the inter-story displacement angle of the bottom story exceeds the requirements of the code, and the horizontal acceleration amplification coefficient of each floor shows an increasing trend. The acceleration amplification coefficient of the main equipment is stronger than that of the floor where it is located, and the damage of the lower floor of the structure is obviously aggravated, which makes it impossible to keep the main structure in a "small earthquake elasticity" state. After considering the coupling effect of multi-support cross-layer pipeline, the structural dynamic response is more significant than only considering the equipment specimen because the deformation of multi-support cross-layer pipeline is inconsistent with the floor. Considering the influence of pipeline coupling effect between equipment, the dynamic response of the structure is slightly reduced. Combined with the above conclusions, we can refer to ASCE code in structural design at this stage. When the equipment mass accounts for more than 25% of the total system mass, the coupling effect should be considered, and it is suggested to increase the elastic-plastic time history analysis of the equipment model.  

Utility tunnel is infrastructure system that concentrate multiple municipal pipelines in underground passages. As linear structure, it inevitably cross non-homogeneous soil. To accurately assess the seismic damage of shallow-buried utility tunnel in non-homogeneous soil, this paper derives an equivalent nodal force formula suitable for horizontal non-homogeneous field based on viscous-spring artificial boundary. A 3D model of the utility tunnel-soil is constructed using finite element software, and a plugin is developed to simulate the 3D oblique incidence of SV waves in horizontal non-homogeneous field. The maximum interlayer displacement angle of the utility tunnel is taken as the damage indicator, the peak ground acceleration (PGA) serves as the seismic intensity indicator, and the IDA (Incremental Dynamic Analysis) method is used for structural vulnerability analysis. The effects of SV wave incidence angles, seismic wave types, and non-homogeneous field on the seismic performance of the utility tunnel are considered. The results show that the failure probability of utility tunnel increases with both the incidence angle and the PGA. Under the action of pulse waves, the failure probability is higher than under non-pulse waves. When the incidence angle is 30° and the PGA exceeds 0.6 g, the probabilities of life safety (LS) and collapse (CP) increase. The failure probability in non-homogeneous regions is higher than in sand and clay. The maximum interlayer displacement angle increases with the incidence angle and is accompanied by increased PGA dispersion. The vulnerability curves provided in this paper can serve as a reference for seismic design of underground structures.

As an effectively simplified method in the field of structural response analysis, Endurance Time Analysis method limits its application to pulse-like ground motions because the endurance time acceleration function synthesized based on the frequency-domain ground motion spectra do not accurately reflect the pulse characteristics in the domain. In order to apply the ETA method to the dynamic response analysis of cable-stayed bridge under near-fault pulse-like ground motion, the contributions of these components toward the dynamic responses under different intensity measures were investigated based on Incremental Dynamic Analysis, and the response prediction model for cable-stayed bridge considering the effects of pulse and strength characteristics was established. Coupled with the response results under residual motion obtained via the ETA method, the estimated response under pulse-like motion was predicted using the proposed prediction method. The results show that, the established prediction model can accurately express the quantitative relationship between the response under high-frequency component and the original ground motion. Based on a comparison of the average results of the IDA and the ETA analytical model under pulse-like motion at 0.6g, the maximum average error was found to be approximately 10%, with good prediction accuracy. The results of the study provide technical support for the efficient and reasonable calculation of the dynamic response of cable-stayed bridge under near-fault pulse-like ground motion.

The duration of ground motion significantly affects the seismic response of structures, making it essential to incorporate duration effects in the seismic design of engineering structures and regional seismic hazard analyses. This study presents a ground motion significant duration prediction model based on the Light gradient boosting machine（Light-GBM） algorithm. Utilizing the NGA-West2 database, 15,541 ground motion records were selected, and their significant durations were calculated. Feature importance analysis was employed to select input parameters, and Bayesian optimization was used to fine-tune the model's hyperparameters. The resulting predictive model was then compared with traditional models and deep learning approaches to validate its accuracy and robustness. The results indicate that the proposed model exhibits excellent predictive performance, high computational efficiency, and strong generalizability. These findings provide valuable insights for ground motion duration prediction and seismic hazard analysis.

Due to the diverse types and shapes of artifacts, a general-purpose seismic isolation device for museum showcases is proposed to enhance the applicability of seismic measures to different artifacts. The versatility of the isolation device was validated through shaking table tests and finite element simulations. The results show that the designed seismic isolation device has excellent isolation performance and can be applied to various artifacts weighing less than 8 kg and a height-to-width ratio of less than 3. None of the six different types of artifacts with significant mass differences were damaged under a unidirectional seismic action with a PGA of 0.62g, and the maximum displacement of the isolation device remained within the design range. The isolation device starts to activate under a seismic action with a PGA of 0.2g, maintaining an isolation rate of about 80%, which does not vary with changes in the input earthquake PGA or the type of artifact. As the input earthquake PGA increases, the residual displacement of the isolation device also increases. Reducing the friction coefficient of the sliding rails or increasing the stiffness of the springs can further reduce residual displacement and enhance the self-resetting capability of the isolation device.

To accurately identify bridge roughness during vehicle travel, this paper proposes an IPSO-BPNN (Improved Particle Swarm Optimization, Backpropagation Neural Networks) adaptive unknown input discrete Kalman filter algorithm. Using a vehicle-bridge coupling model, the vertical displacement at the tire-bridge contact point is treated as the unknown input, while wheel displacement, acceleration, and vehicle body acceleration are used as the observation vector to design the unknown input Kalman filter. An improved particle swarm optimization algorithm is applied to obtain the optimal measurement noise covariance matrix for different bridge roughness levels. A BP neural network classifies bridge roughness levels in real time, and both methods work together to adaptively update the Kalman filter’s measurement noise matrix. Simulations under various driving speeds, bridge roughness levels, and vehicle-bridge mass ratios were conducted, and a shaking table experiment was designed to validate the approach. To match the quarter suspension model of the vibration table, the parameters of the two-degree-of-freedom vehicle model and the bridge model are scaled proportionally to ensure the similarity of the deflection curve and vertical displacement of the bridge after scaling. Results show that the proposed method improves root mean square error, maximum absolute error, and correlation coefficient by 11.29%, 33.52%, and 2.84%, respectively, demonstrating high accuracy and robustness.

In order to study the propagation law of traffic vibration in the ancient pagoda, based on the measured traffic load data, the global model and local refined model of the Bayun Pagoda were established by using the finite element analysis software. The time-history analysis was carried out to study the influence of different vibration source distances on the dynamic response and fatigue damage of the pagoda. The results show that the horizontal vibration frequency of the Pagoda is 5-15 Hz, the vertical vibration frequency is 3-10 Hz, and the vibration is mainly concentrated in the low frequency band. With the increase of floors, the horizontal and vertical vibration velocities of the tower are on the rise, especially the horizontal vibration velocity shows obvious whipping effect, while the increase of vertical vibration decreases gradually. When the vibration source distance increases, the horizontal vibration velocity decreases as a whole, but there is local vibration amplification. When the distance of the vibration source is close to 2.5 meters, the horizontal vibration velocity at the maximum load-bearing point of the tower body is close to the allowable vibration limit, which has potential safety hazards. Through local refined modeling, the stress distribution of the tower body and the fatigue life of key parts can be further analyzed. The research results can provide reference for the preventive protection of similar cultural relics.

The structural system of the novel main-cable-looped suspension bridge is relatively flexible, making it prone to wind-induced buffeting, leading to structural vertical deformation. Therefore, it is crucial to study the wind-induced buffeting deformation response for the novel suspension bridge structural system. According to the first novel main-cable-looped suspension bridge in China, a three-dimensional finite element model of the Yellow River Three Gorges Bridge was established using ANSYS software. The steel truss girder segment model was manufactured, and wind tunnel testing was conducted at different wind attack angles to determine the aerodynamics coefficients for the steel truss girder. Based on the wind field characteristics of the bridge site, the harmonic synthesis method was used to establish the three-dimensional fluctuating wind of the steel truss girder, and the simulated fluctuating wind was verified. Time domain analysis was conducted on the nonlinear buffeting response of the Yellow River Three Gorges Bridge, and the effect of fluctuating wind parameters on the vertical deformation response of the novel suspension bridge structural system was studied. The results show that the ground-anchored hanger can significantly control the upward structural deformation for the novel main-cable-looped suspension bridge under wind-induced buffeting. The upward structural deformation of the girder and the main cable at the middle span can be reduced by about 7% and 14%, respectively. Under the action of wind-induced buffeting, the maximum vertical deformation of the novel main-cable-looped suspension bridge increases nonlinearly with the increase of the average wind speed, and the growth rate of the maximum vertical deformation of steel truss girder and U-shaped main cable at the middle span is significantly changed when the average wind speed is 19.5 m/s. Within 10 range, with the increase of wind attack angle, the maximum vertical deformation of the novel main-cable-looped suspension bridge increases firstly and then decreases. The maximum upward deformation of steel truss girder and U-shaped main cable span reaches the peak at the wind attack angle of -4 and the maximum downward deformation reaches the peak at the wind attack angle of 0

Bridge surface roughness is an important factor affecting the vehicle-bridge dynamic interaction, meanwhile, accurate identification of bridge surface roughness is crucial for bridge dynamic parameter identification and structural safety assessment based on the vehicle response. Consequently, a novel algorithm for estimating bridge surface roughness from a single-axle test vehicle was proposed. Compared with previous methods, the proposed method only requires one acceleration sensor to be installed on the vehicle. The proposed method includes the following procedures. First, establishing a state-space model of the VBI system with unknown excitation (such as bridge surface roughness); Then, the VBI system response can be obtained from the numerical simulations or field tests, and the improved state space model of VBI system can be reconstructed by combining and expanding the vehicle response; Finally, the Kalman filter algorithm is applied to identify the VBI system state and bridge surface roughness. Based on theoretical, numerical, and field results, it is shown that this method has good noise resistance and high accuracy in identifying the road surface roughness and bridge surface roughness with different conditions. Moreover, it is suggested to consider a lower vehicle speed to ensure sufficient and consistent measurement data.

Coarse-grained soils are widely used in subgrade engineering. However, the coarse particles are prone to breakage under external loads, which significantly affects their engineering properties. Therefore, studying the particle breakage and constitutive relationships of subgrade coarse-grained soil fillers is of great importance. Considering the significant factors affecting subgrade conditions, a series of large-scale triaxial tests of red sandstone subgrade coarse-grained fillers were conducted, and the nonlinear stress-strain relationships of the coarse-grained soil samples were researched, and the phenomena of strain softening and strain hardening with the variation of the coarse particle content was analyzed. A quadratic fractal dimension gradation equation was established to describe the particle breakage evolution of the samples. Then, a particle breakage index was derived to analyze the particle breakage of coarse-grained soil samples under different gradations and confining pressures. Based on the camel-shaped cubic curve constitutive model, the constitutive relationships of red sandstone subgrade coarse-grained soil samples were studied. The correlations between particle breakage rate and confining pressure, as well as between constitutive model parameters and breakage rate, were analyzed. Subsequently, a constitutive model for red sandstone subgrade coarse-grained soil fillers considering particle breakage was established and its validity was verified. The research findings provide valuable insights into the mechanical performance evolution of coarse-grained soil fillers and offer guidance for the construction of weathered red sandstone coarse-grained soil fillers.

The hunting of high-speed trains affects passenger comfort, impairs train components, and even endangers the safety of train operation. it is crucial to recognize the hunting state, especially the small-amplitude hunting state before the onset of hunting instability. To address the issue of inaccurate identification in existing hunting monitoring methods under variable conditions, a small-amplitude hunting identification method with frequency invariance based on transfer learning is proposed. Firstly, considering that the frequency features of hunting are more stable than the time domain features under the influence of external factors, such as track irregularities. Therefore, a frequency invariant fusion module is constructed by combining hunting frequency and time-domain information (intra-domain transfer). Then, the combination of the module and inter-domain transfer enables the model to extract more invariant features from unlabeled data, thus improving the accuracy of hunting recognition. Finally, the method is applied to the measured data of high-speed trains, the average recognition accuracy of several different transfer tasks averaged over 95%. The recognition results were significantly better than non-transfer learning methods and other transfer methods. 

In order to solve the guiding problem caused by the decoupling of the left and right wheels in a wheelset, the concept of toe angle is introduced into an independently rotating wheel (IRW) running gear. A guiding scheme based on toe angles is proposed to recover the self-alignment ability for the IRW running gear. The steering principle is firstly described for the IRW running gear with toe angles. The equations of motion of the lateral dynamic model of an IRW set are obtained according to Lagrange’s equation. The multi-body dynamics is used to analyze the stability, guiding and curve passing performance of the new running gear with toe angle. The results show that the critical speed of the independently rotating wheel running gear first decreases and then increases with the increment of toe angle, exhibiting a maximum critical speed. The new running gear cannot automatically return to the center position if the toe angle is less than 0.2°. When the toe angle is not less than 0.2 °, the independently rotating wheel running gear can automatically return to the initial lateral position after passing through the excitation section. The running gear with the toe angle is possessed of the self-alignment ability. Moreover, the angle of attack of the left front wheel is relatively small when the running gear with the toe angles exceeding 0.25°negotiates the curved track. It has good curve passing performance. Therefore, the utilization of toe angle can improve the guiding performance of the independently rotating wheel running gear on straight and curved tracks. 

Track irregularities significantly impair the safety and stability of vehicle operation. Identifying the sensitive wavelengths of medium- and long-wavelength track irregularities and establishing corresponding management limits for metro lines hold significant reference value for line maintenance. A rigid-flexible coupled dynamic model of a metro vehicle is established that takes into account the flexibility of the carbody. The model is then validated using measured carbody accelerations. Multi-cosine waves are used to model longitudinal-level, alignment, cross-level, and gauge irregularities. The influence of different wavelengths and amplitudes of these irregularities on vehicle dynamic performance is investigated and the range of sensitive wavelengths of track irregularities is determined. Finally, the simulation results are extrapolated to the management value of each dynamic performance index using curve fitting, and three levels of management limits for track irregularity amplitude are proposed. The results show that the sensitive wavelengths of metro track irregularities are mainly affected by vehicle suspension modes, car body flexibility modes, and bogie hunting motions. The four types of track irregularities that should be prioritized in the control of the wave band, together with their minimum amplitude limits, are as follows: longitudinal-level (1.5 ~ 4 m and 6 ~ 10 m, with minimum limits of 2.4 mm and 4.7 mm, respectively); alignment (10 ~ 30 m, with a minimum limit of 1.6 mm); cross-level (1.5 ~ 4 m and 6 ~ 22 m, with minimum limits of 0.8 mm and 5.2 mm, respectively); gauge (10 ~ 15 m, with a minimum limit of 5 mm).

To evaluate the influence of metro induced vibration on precision instruments in a laboratory of a university, a measured transfer function formulation is proposed to predict the vibration responses on the ground surface and in the building. First, the frequency-domain excitation forces acting on the tunnel structure are determined by using a coupled train-track model, then the transfer functions between excitation and receiver points in the station-soil-building system are measured by a field hammer experiment in the station, and finally the vibration responses are obtained by the transfer function formulation. Based on this formulation, the vibration responses for the general non-ballast track and steel spring floating slab track are predicted and compared with the field measured data under the metro operation. The results show that the transfer functions obtained through field measurements accurately reflect the vibration propagation characteristics of the tunnel/station-soil-building system, indicating that the proposed formulation has good prediction accuracy.

The flexible deformation of gear teeth induces the collision of gear pair, which affects its transmission quality and dynamic performance. This paper calculated the actual meshing contact ratio of gear pair by considering the gear teeth flexibility (GTF), and calculated the rigid-flexible coupling time-varying meshing stiffness and load distribution coefficient of gear pair. The meshing-impact dynamic model and impact-collision energy dissipation model of spur gear system considering rigid-flexible coupling were established. The influence of GTF on contact ratio, time-varying meshing stiffness and dynamic meshing force was analyzed. Based on the multi-initial value bifurcation diagram, the bifurcation and evolution of the coexistence motion of the system with the change of load and the influence relationship with the energy dissipation were studied, and the maximum energy dissipation characteristics of the system when the two parameters change were revealed. It is found that the GTF affects the meshing area of single- and double teeth and increases the contact ratio. The GTF reduces the dynamic meshing force and makes the time-varying meshing stiffness transit smoothly when the single- and double teeth are engaged alternately. The impact of drive-side and back-side aggravates the impact energy dissipation of the coexistence motion. The change of load has a great influence on the bifurcation evolution of the coexistence motion of the system, and the change of the coexistence motion affects the impact energy dissipation characteristics of the system. Reasonable matching of the parameters and the initial values can effectively avoid the large impact energy dissipation and improve the reliability of the transmission system.

To establish damage criteria for fuel tanks subjected to high-velocity fragment impacts, ballistic experiments were conducted using tungsten spherical fragments to strike diesel tanks. The damage characteristics of fuel tanks under various conditions were investigated, and theoretical models for perforation-induced fuel leakage and ignition probability were developed. The effects of fragment mass, impact velocity, perforation heights, and fuel fill ratio on fuel tank damage probability were analyzed. The findings are summarized as follows: (1) The damage mode of the fuel tank is determined by the fragment impact location: impacts on the liquid primarily result in perforation-induced fuel leakage, whereas impacts on the ullage may lead to ignition. (2) The ignition probability of a tungsten fragment impacting the gas layer of a diesel fuel tank exhibits an S-shaped growth trend with increasing specific kinetic energy. When the specific kinetic energy reaches 24×104 kJ/m2, the ignition probability reaches its maximum value of 1. (3) The perforation-induced leakage damage probability is significantly influenced by fragment mass, impact velocity, and perforation height. A greater fragment mass, higher impact velocity, and lower perforation positions closer to the tank bottom significantly enhance the leakage damage probability. (4) Perforation height is the primary factor influencing the probability of perforation-induced fuel leakage damage in fuel tanks. Within the impact velocity range of 500~2500 m/s, a 10% reduction in perforation height can increase the probability of perforation-induced fuel leakage damage by up to 17.35%. (5) When fragments impact the diesel tank at lower velocities (<1000 m/s) or higher velocities (>2000 m/s), the overall damage probability of the tank is primarily influenced by leakage damage. In contrast, at intermediate impact velocities, the overall damage probability is predominantly determined by ignition damage.

Aeroengine data exhibits complex characteristics such as multivariate, nonlinear, and dynamic variations, with significant spatiotemporal correlations. The majority of research, when analyzing data, often limits itself to a single multi-sensor scale or temporal scale, and frequently neglects the long-term dependencies among the data, thereby constraining its application in the task of predicting the remaining useful life (RUL) of aircraft engines.. To address this, a spatio-temporal fusion Transformer network model is proposed. This model retains the advantages of the multi-head attention mechanism and positional encoding in the Transformer architecture to accurately capture long-term dependency features. Firstly, an efficient fully connected network is adopted to replace the original decoding module, matching the attributes of the nonlinear regression problem in aeroengine RUL prediction while simplifying the model structure. Secondly, a spatial attention mechanism module is introduced to deeply explore the spatial features among different variables. Finally, the improved AIC criterion is applied to identify critical hyperparameters of the Transformer, addressing the challenge of selecting its hyperparameters. Multiple sets of experiments conducted on the C-MAPSS and PHM08 Prognostics Data Challenge have confirmed the effectiveness of the proposed model and its superior performance in prediction accuracy.

Taking aero-engine compressor blades as the engineering background, the rotating blades are simplified into carbon nanotube reinforced composite (CNTRC) cantilever thin plates with pre-installation and torsion angles. The geometrical and physical parameters of CNTRC rotating blades are calculated by differential geometry theory and the extended rule of mixture. Considering the influence of centrifugal force, based on Kirchhoff hypothesis and Novozhilov theory, the partial differential kinetic equations of CNTRC rotating blades are established by Hamilton's principle. The partial differential equations of motion are discretised into ordinary differential equations by the Galerkin method. The free vibration characteristics of the CNTRC rotating blades are investigated. The effects of pre-installation angle, torsion angle, carbon nanotube volume fractions, carbon nanotube distributions, rotational speed, and hub radius on the natural frequencies of CNTRC rotating blades are analysed in detail.