The crashworthiness of an aircraft is not only affected by its own structural design, but also closely related to the crash speed, the landing attitude, and the runway environment.The full-scale structure of a typical civil aircraft was taken as the study object, and a full-scale aircraft crash dynamics model, was established, which was then validated by the experimental data from the literature.Numerical simulations of crashes under different impact speeds, pitch angles, roll angles, and runway environment factors were further conducted to explore the influences of different factors on the aircraft crash response.The results show that as the impact speed increases, the initial peak of the crash load on the lower part of the fuselage and the platform load gradually increase, and the area of deformation of the fuselage gradually increases.With the increase of the pitch angle, the waveform of the crash load changes significantly, the load peak decreases significantly, the peak acceleration of the floor gradually decreases, the acceleration of the mid-fuselage structure is more sensitive to the change of the pitch angle, and the impact speed of the local fuselage structure of the aircraft is significantly affected by the aircraft pitch angle.Under the condition that the overall vertical impact speed of the aircraft remains unchanged, the greater the pitch angle, the greater the impact speed of the front fuselage section, and the overall non-linear increase trend from the nose to the rear fuselage is presented.The roll angle has little effect on the aircraft’s crash load and the acceleration peak of the wing, but has a significant effect on the acceleration peak of the fuselage floor.The deformation on the side of the fuselage bottom at the near roll direction increases, and a new plastic hinge is produced.Compared with the rigid runway, when crashing on the clay runway, the vertical impact load peak of the aircraft decreases, and the heading impact load peak increases significantly.The aircraft crashes on the clay runway and produces a gully-like deformation.The shape of the gully and the deformation expansion process under different pitch angles are significantly different.The deformation of the fuselage and the peak acceleration of the floor are smaller when crashing on the clay runway, and the risk to the safety of the passengers is smaller than that on the rigid runway.

Based on the background of the development of the South China Sea of China, the calcareous sand foundation has been attracted wild attention.The calcareous sand foundation will bear repeated impact loads during pile driving process, and the behavior of calcareous sand under repeated impact considerably differs from that of common silica sand on land.The improved split Hopkinson pressure bar (SHPB) system was selected for one-dimensional impact tests of silica and calcareous sand with uniformly particle size.The test results reveal that the dynamic apparent stiffness of silica sand is approximately 6.00-8.00 times that of calcareous sand.The dynamic apparent modulus values of the two sands increase with the increase of the number of impacts, N.The dynamic apparent modulus of calcareous sand decreases with the increase of the mean diameter, d50.For calcareous sand, with increasing particle size, the compression index Cc increases, and the yield pressure is approximately 40% of that of silica sand under the same conditions.Compared to silica sand, calcareous sand reaches a better energy absorption capacity at a lower stress.Under the same axial stress, the energy absorption efficiency increases with increasing particle size and decreases with the increase of the number of impacts.Finally, the evolution law of particle breakage of uniformly graded calcareous sand samples during repeated impact processes was explored.It is found that there is an exponential relationship between the normalized particle size and the breakage probability under repeated impacts.

To effectively ensure the safety of personnel and equipment within highway construction zones, a novel movable assembled guardrail structure has been proposed. The key parameters of this guardrail structure were investigated based on the Long Short-Term Memory (LSTM) network model and the Non-Dominated Sorting Genetic Algorithm II (NSGA-II). The crashworthiness of the guardrail structure was analyzed using finite element numerical simulations and full-scale vehicle crash tests. The research results indicate: (1) The optimized guardrail base has a friction coefficient of 0.583, and the guardrail height is set at 1014.27 mm. (2) Compared to traditional concrete guardrails and W-beam guardrails, the movable assembled guardrail offers superior cushioning effects, as evidenced by lower post-collision acceleration values and reduced vehicle rollover values. (3) The effectiveness of the finite element simulation was validated through the results of full-scale vehicle crash tests. The crashworthiness of the guardrail meets the requirements for Grade A, providing valuable insights for the design of safety facilities in highway construction zones.

A new type of local resonance sandwich metastructure beam is proposed in this paper. The energy dissipation, absorption and deformation resistance capability of the metastructure beam under low-velocity impact was analyzed with the finite element method, and the influence of bending wave bandgap and different impact positions on the structural energy dissipation was studied. The impact experimental platform was established, and the displacement of the center point of the panel under the impact of steel balls at different heights was measured and compared with the numerical results. The results show that, local resonance sandwich metastructure beam has stronger energy dissipation characteristics than the ordinary sandwich beam, which can effectively suppress the deformation of the structure. The resonance element composed of the lead and silica gel plays a dominant role in the process of absorbing energy, and the total energy absorption of the lead and silica gel accounts for 81.55%. The bending wave bandgap of a superstructure beam has a significant impact on the impact resistance characteristics of the structure. When the impact energy is concentrated within the bandgap range, the structure exhibits strong energy dissipation characteristics. The low-speed impact characteristics of the local resonance sandwich metastructure beam studied in this paper provides certain guidance and ideas for the design of new generation of impact resistant structures.

The multi-cell thin-walled tube can provide higher crushing load and specific energy absorption during the axial crushing process due to the introduction of more angular elements and longer plastic hinges through the cross-section topology design, but its crushing deformation mode and energy absorption efficiency are still affected by the structural size effect. A modified multi-cell tube (MMT) was constructed by introducing a vertical spiral groove on the outer surface of the outer cylindrical shell of the first-order multi-cell tube (MT). The deformation mode of the small aspect ratio multi-cell tube was induced by the prefabricated groove defect to reduce the peak crush force and reduce the load fluctuation. The grooved multi-cell tube was processed by machining, and the quasi-static and low-velocity impact compression experiments were carried out on the unfilled grooved multi-cell tube and the aluminum foam filled multi-cell tube (FMT). The effects of the depth and position of the spiral groove on the deformation characteristics and energy absorption performance of the structure are further discussed by numerical simulation. The results show that: The introduction of spiral groove and the filling of aluminum foam can significantly improve the crushing load efficiency of the multi-cell tube and effectively reduce the load fluctuation during the compression process. The grooves on the MMT outer tube can induce the folding deformation mode of the cylindrical shell structure, effectively reduce the peak crush force during the loading process, and obtain a more stable MCF curve.

Based on the research background of twin rotor actuator, a single drive twin rotor actuator active control device is proposed in this paper, which is mainly composed of mass block, space transmission gear group, motor and controller. The centrifugal force generated when the rotor is driven by the gear is used as the active control force to reduce the structural vibration. Compared with the traditional active mass damper, this design not only does not need to consider the linear travel limit of the guide rail, but also solves the problem that the motor in the dual drive twin rotor actuator is difficult to synchronize through structural optimization, and realizes more efficient and stable vibration control. In order to study the vibration damping performance of the single drive twin rotor actuator, firstly, the mechanical model of the single drive twin rotor actuator system, the single degree of freedom structure and the state equation of the single driven twin rotor actuator are established based on the mechanical analysis of Lagrange equation. Secondly, a controller combining pole assignment method and Super-Twisting Sliding mode control algorithm is designed for vibration reduction of single drive twin rotor actuator system, and the control parameters contained in the controller are optimized based on the improved Dung beetle optimization algorithm. Compared with other control algorithms, the proposed method not only enables easier acquisition of controller parameters but also eliminates tedious trial-and-error tuning, thereby streamlining practical engineering im-plementation. Finally, the stability of the system is proved by the Lyapunov function, and the feasibility and effec-tiveness of the Super-Twisting sliding mode control algorithm based on the single drive twin rotor actuator system are verified by the simulation experiments.

In the road simulation tests, the electro-hydraulic actuator is subjected to the constant gravitational eccentric load of the tested vehicle, resulting in the distortion of the acceleration waveform in the closed-loop control system of the electro-hydraulic actuator and thereby affecting the accuracy of road spectrum reproduction. In the developed road simulator, an electro-hydraulic pressure-controlled static load balancing device is employed to counteract the gravitational effect of the tested vehicle, thus resolving the issue of acceleration waveform distortion caused by the gravitational eccentric load. The composition principles of the road simulation platform and the electro-hydraulic pressure-controlled static load balancing device are presented. The transfer function mathematical model and block diagram of the road simulator system are established, and the stabilities of the position closed-loop and the pressure closed-loop are analyzed. The output characteristics of the hydraulic power mechanism of the road simulator and the inertial load characteristics of the tested vehicle are deduced. On this basis, the distortion mechanism of the acceleration waveform in the closed-loop control of the electro-hydraulic actuator is analyzed. Subsequently, the AMEsim simulation models of the electro-hydraulic pressure-controlled static load balancing device and the closed-loop control of the electro-hydraulic actuator are established to conduct simulation and experimental verification on the phenomenon of acceleration waveform distortion. The results are in line with those of the theoretical analysis. The AMEsim dynamic simulation model of the road simulator, taking into account the characteristics of the body, shock absorption, and tires of the tested bus, is established. With the collected road spectrum data of the cobblestone road as the reproduction target, the simulation and experiment of road spectrum reproduction are carried out respectively. The simulation results are basically consistent with the experimental results, verifying the suppression effect of the electro-hydraulic pressure-controlled static load balancing device on the acceleration waveform distortion and also validating the effectiveness of the established AMEsim simulation model. The research findings possess significant reference value for the development of high-precision road simulator.

Aiming at a single-point mooring Floating Production Storage and Offloading (FPSO) unit in the South China Sea, this study establishes a time-domain coupling analysis model using the hydrodynamic analysis software ANSYS AQWA, based on three-dimensional potential flow theory. The motion response of the FPSO and the tension in the mooring lines were calculated under both operational and extreme sea conditions. The study systematically analyzed the stiffness of the mooring system, hull motion response, and mooring line tension under different single-line and double-line failure scenarios, and quantitatively assessed the safety performance of the mooring system. The results show that double-line failures have a more significant impact on reducing the longitudinal and lateral stiffness of the mooring system. Specifically, the failure of double cables within the same group at the ship's stern results in the lowest longitudinal stiffness, while the failure of double cables within the same group on the side of the hull leads to the lowest lateral stiffness. These conditions cause more severe hull motions, with maximum longitudinal and lateral displacements reaching 25m and 40m, respectively, under operational conditions. For ten-year return period wave conditions, single-line failures allow the remaining mooring lines to meet safety requirements; however, same-group double-line failures bring the remaining line tension close to breaking strength, significantly increasing failure risks. Under hundred-year return period wave conditions, the safety standard of transient breakage is met when a single cable is broken, while double-line failures cause consecutive breakages in the remaining lines, ultimately leading to complete loss of FPSO control. This study provides important references for optimizing FPSO mooring system design and evaluating safety under extreme sea conditions.

Pointing the issue of inaccurately predicting the vibration behavior of multiply bellows, an analytical model is proposed to predict the axial natural frequency of bellows by treating it as a homogeneous beam, three boundaries are considered in the model. Subsequently, finite element simulations are conducted to perform modal analysis on bellows with different numbers of layers. The results from the model are compared in detail from various perspectives with those obtained from simulations, which validate the accuracy of the analytical model. Finally, a sensitivity analysis of the frequencies to several important parameters is carried out. The study demonstrates that the analytical model yields results that closely match those from finite element simulations. Furthermore, the error increases with the number of layers, attributed to the accumulation of interfaces between layers and increase in structural volume, leading to high simulation results. The inherent frequency increases with the number of bellows layers, and the increase in the convolutions and the single-layer thickness results in a nonlinear law decrease in the natural frequency. However, as the plate height increases, the frequency curve appears a bulge. The results provide valuable insights for the dynamic characteristic prediction of multiply bellows. 

Hydraulic slotting technology is an effective method for enhancing the permeability of coal seams. The spatial arrangement and angle of the slotting process significantly influence its effectiveness under in-situ stress conditions. However, conventional slotters have structural limitations, preventing the adjustment of the slot angle during field operations, which makes it difficult to achieve optimal slotting geometry. This paper presents the development of a new type of directional hydraulic slotter for coal seams. The device's directional functionality is enabled by an angle regulator and a movable nozzle mechanism. The rotary motion of the drill pipe periodically adjusts the nozzle angle, allowing for directional slotting and modification of the slot angle. This paper also presents a motion analysis of the angle adjustment mechanism, showing that when the radius r is 18 mm, the adjustable angle reaches 17.7°. Comparative flow field and rock-breaking experiments were conducted to evaluate the performance of jet diffusion angle, impact force, and rock-breaking efficiency. The results indicate that the directional slotter can control jet diffusion to some extent, maintaining a relatively focused jet pattern under high pressure. The jet diffusion angle is significantly influenced by the hose configuration, being smallest when the hose is in its natural extension state. Under similar conditions, the impact force of the directional slotter exceeds that of the conventional slotter, which correlates closely with its flow field characteristics. The directional slotter is capable of adjusting the slot angle without compromising its slotting efficiency. Furthermore, the cutting depth is increased by 30.87%, and the rock-breaking characteristics are consistent with the flow field and impact force behaviors. The development of this coal seam directional hydraulic slotter offers an effective solution to the limitations of conventional slotters, ultimately enhancing coal seam gas extraction efficiency and improving mine safety.

The mechanical properties and applications of cylindrical spiral springs along their axial direction have been extensively studied, but the horizontal mechanical properties under axial compression are still very rare. Taking modular cylindrical spiral springs as research object, the stiffness, ultimate compression shear, frequency dependence, loading frequency dependence, fatigue and other horizontal and vertical mechanical behaviors of the modular springs were explored based on performance testing in this study. The horizontal and vertical mechanical calculation models of the modular springs were proposed and validated. And the S-N curve of the modular springs was established based on the S-N curve of 40SiMnVBE material by introducing comprehensive correction factors. The results indicate that the horizontal stiffness of the modular spring increases with the increase of axial preloading value, and the horizontal stiffness has directionality, with the 0-degree direction being higher than the 90 degree direction. The correlation between horizontal loading frequency, loading cycles, and loading displacement is relatively small under different preloading values. The horizontal ultimate displacement also increases with the increase of the preloading value, with an increase of 30%. After repeated horizontal ultimate loading, the performance of modular springs is stable and has superior self-recovery ability. The proposed horizontal and vertical mechanical calculation models can well reflect the mechanical behavior of the modular springs, with theoretical and experimental errors of 3.54% and 1.32% in axial and horizontal stiffness values, respectively. After experiencing 107 cycles of axial fatigue, the mechanical properties of the modular spring remain stable and the appearance is undamaged. The S-N curve of the spring established based on the comprehensive correction factor can reflect its fatigue performance.

Temperature changes the force and motion state of each component during the rolling bearing operation, and affects the slipping characteristics of the rolling bearing. To solve this problem, the oil injected lubricated axle box bearings are taken as the research object, and a finite element model is established to simulate the temperature field distribution based on the heat generation and heat transfer mechanism of the bearings to obtain the temperatures of each element. On this basis, the rolling bearing dynamic model is established by considering the effects of temperature on thermal deformation, lubricant parameters, equivalent stiffness and friction coefficient. The effects of the internal temperature of the axle box and the temperature of the lubricating oil on the kinematic, frictional and slipping characteristics of the bearings were investigated. The results show that: increasing the internal temperature of the axle box will reduce the speed fluctuation of rolling element and cage, reduce the friction, and inhibit the slipping phenomenon; while increasing the temperature of the lubricating oil will increase the speed fluctuation and friction, and aggravate the slipping. The results of this paper can provide theoretical basis for bearing performance analysis and life prediction.

It is difficult for the existing three-point powertrain mounting system (PMS) to effectively reduce the unsteady vibration and shock of the vehicle, a study on the unsteady vibration control of the a four-point PMS based on the semi-active hydraulic damping strut ((HDS) in this paper is carried out considering that increasing the longitudinal damping of the mounting system can improve the unsteady vibration and shock of the vehicle. Firstly, the dynamic characteristics of the semi-active HDS are analyzed, and its stiffness and damping characteristics meet the requirements of vibration control under unsteady state. Secondly, the subjective and objective dynamic response evaluation indexes of vehicle vibration under unsteady condition are proposed, and the design method for determining the structural parameters of the semi-active HDS under unsteady condition is established. Finally, an objective evaluation method is used to carry out the experimental research of the new four-point PMS under the unsteady state of the vehicle, and the vibration and shock attenuation effect of adding semi-active HDS on the engine start-stop, engine at idle speed, P-D-P gear shift, P-R-P gear shift and R-D-R gear shift are analyzed. The research results show that adding semi-active HDS to the original three-point PMS can effectively reduce the vibration and shock of the vehicle under unsteady state, which verifies the effectiveness of the new four-point PMS with semi-active HDS established in this paper.

To improve the energy harvesting efficiency of the counter-rotating horizontal-axis tidal turbine (CRHATT) and investigate the influence of various design parameters on its power output, this study first establishes a hydrodynamic analysis model for the CRHATT by integrating the improved delayed detached eddy simulation (IDDES) model with sliding mesh technology. Subsequently, a parameterized optimization scheme for the turbine design is proposed using the Taguchi method. Finally, the effects of five key parameters, including the distance between the front and rear turbines (L), the tip speed ratio of the front turbine (λF), the tip speed ratio of the rear turbine (λR), the diameter ratio (DR/DF), and the initial position phase difference (θ), on the hydrodynamic performance of the CRHATT are systematically analyzed. The results reveal that the design factors significantly influence the turbine's performance. The optimized CRHATT achieves a 28.3% increase in energy harvesting efficiency compared to the baseline design. The relative influence of the design parameters on the energy harvesting efficiency is ranked as follows: λR＞λF＞L＞DR/DF＞θ. Further analysis of the turbine wake under different parameter combinations indicates that the optimized design not only enhances wake development behind the front turbine but also enables the rear turbine to more effectively utilize the wake, thereby improving the overall energy harvesting efficiency. These findings provide valuable engineering insights and guidance for optimizing the performance of CRHATTs.

In order to achieve the anti-roll effect of ship at zero speed, this paper proposes a fin stabilizer control strategy based on the Proximal Policy Optimization algorithm, and conducts zero-speed anti-rolling tests on a ship model in a towing tank. Firstly, this paper constructs an S175 ship model device and anti-rolling test system, formulates an experimental scheme for controlling the roll motion based on forced roll motion device and wave tank. Secondly, the ship's anti-roll motion is learned and trained using the PPO algorithm, and generating the optimal fin flapping angle scheme for anti-rolling in real time according to the decision reward value obtained from training. Finally, based on the established software and hardware test system for the ship roll motion control, the anti-rolling test of ship model under regular and irregular waves were carried out in the tank. The results indicate that the established anti-rolling system achieves a better anti-rolling effect for the ship in various sea conditions. 

In the process of real-time hybrid simulation test, no compensation method can completely eliminate the influence of the actuator dynamic characteristics, so the instantaneous control parameters, such as instantaneous time delay and instantaneous amplitude error, play an important role in evaluating the accuracy of real-time hybrid simulation test. The current real-time hybrid simulation instantaneous control parameters calculation method is based on the Hilbert transform to initially realize the calculation of instantaneous amplitude and instantaneous time delay, but when the method calculates the instantaneous frequency, the physical significance of the negative frequency obtained from the calculation is not clear, which affects the promotion and application of the method. In this paper, a calculation method based on the direct orthogonal method is proposed, in which the empirical modal decomposition is used to construct the eigenmode function firstly, and then the orthogonal function is constructed by using the empirical AM-FM decomposition for the eigenmode function to calculate the instantaneous frequency and the instantaneous control parameter, so as to avoid the problem of the negative frequency caused by the Hilbert transform. The method is applied to calculate the instantaneous control parameters in the real-time displacement tracking test, and the comparison results show that the validity of the instantaneous frequency and time lag can be significantly improved compared with the traditional method, which provides a basis for the evaluation and compensation of real-time hybrid simulation tests.

The vibration analysis of piping systems involves multiple devices, components, and connection relationships, making it a typical system - level dynamic analysis problem. External excitation forces are the primary cause of piping vibration. Rapidly predicting the vibration response of multi - branch piping systems under external excitation forces helps to understand the vibration performance of piping systems. In this paper, based on the transfer matrix method, the piping system is equivalent to a tree - shaped structure. An automatic recursive algorithm for the total transfer matrix is proposed to achieve rapid calculation of the vibration response of piping systems with an arbitrary number of branches under external excitation forces. The method presented in this paper has the same accuracy as the finite element method, and it has advantages in terms of calculation speed and memory usage. When the piping components can be modeled using the transfer matrix, this method can serve as an efficient alternative to the finite element method.

High-speed and high-frequency motion in die bonding machines causes bonding head large vibration. And Existing control systems cannot detect or suppress bonding head vibration, leading to difficulty in maintaining long-term bonding precision. This study proposes an optimized input shaping method for vibration suppression. The method utilizes Particle Swarm Optimization (PSO) to automate the adjustment of Input Shaper (IS) parameters. These parameters include pulse type, number, amplitude, and time delay, which are optimized based on a second-order simulation model of the bonding head dynamics. This approach significantly reduces design complexity compared to traditional manual tuning. Experimental results from a single-axis system demonstrate a 71.3% reduction in residual vibration amplitude and a 34% decrease in stabilization time.

The six-dimensional components of ground vibration should be considered to accurately obtain the seismic response of transmission towers. In addition, the seismic response of the tower-line system with the assumption of rigid joints is not consistent with the actual situation because the bolt joints of angle steel towers will slip. Therefore, to study the seismic response of the tower-line system more accurately, the translational-rotational seismic response of the tower-line system considering the bolt slippage effect is investigated. First, the rotational component is extracted from the translational seismic data recorded by SMART-1 array by Surface Fitting Method, and then the skeleton curve describing the mechanical properties of the tower joints is determined based on the hysteresis curve of the nodes under cyclic loading. The spring elements are used to simulate the bolt joint slippage, and the real constants of the spring elements are determined according to the nodal skeleton curve. Finally, a finite element model of the tower-line system with the bolt slippage effect is established. The multidimensional seismic response of the tower-line system considering the bolt slippage effect is investigated, and the effects of changes in soil parameters and seismic incidence angle are analyzed. The results show that the seismic response of the tower-line system changes drastically after considering the bolt slippage effect and six-dimensional ground motion, and the location of the maximum stress elements also changes. In order to obtain a more accurate seismic response of the tower-line system, the influence of the bolt slippage effect and rotational component should not be ignored. The influence of the bolt slippage effect on the translational-rotational seismic response of the tower-line system is larger in the case of better soil conditions, and it varies with the change of seismic incidence angle. In the practical simulation calculation, the soil conditions and seismic incidence angle of the structural location should be clarified.

Ground motion has multiple -dimensional spatial components. Most of the current velocity pulse identification methods do not consider the influence of the vertical component. Therefore, this paper proposes an energy - based method for pulse identification in space. This method rotates and synthesizes the three components of the ground motion record in various directions in space, calculates the pulse energy in each direction, determines the direction with the maximum energy, and then identifies the pulse in that direction. The identification results enrich and improve the existing pulse -like ground motion database. The relationships between the peak value of the pulse - like ground motion identified in this direction, the maximum peak ground velocity (PGV) in space, and its direction are studied. Regression models for the velocity peak of spatial pulses, magnitude, and fault distance, as well as for the period and magnitude, are established. The results show that the direction of maximum spatial pulse energy is highly consistent with the direction of maximum spatial PGV in terms of pulse significance. The velocity peak of spatial velocity pulses decreases with the increase of the fault distance and increases with higher magnitude. Compared to the existing spatial models, the pulse peak value of the model in this paper is higher. Compared with the models that only consider horizontal components, the pulse period of this paper's model is longer, but as the magnitude increases, the gap between them gradually narrows. The research results of this paper can provide a reference for the seismic input of engineering structures considering spatial pulse.

The mechanical performance of lead-core rubber bearings exhibits significant sensitivity to temperature variations. However, the current seismic design standard for bridges neglects this influence, potentially leading to lower reliability of seismic designs than expected. Based on the temperature data measured from 2014 to 2023 of Shanghai, a representative city in a warm region, and Harbin, a representative city in a cold region, two Gaussian Mixture Models are established for the probability distribution of the temperature variations in the two cities and 1,000 Monte Carlo samples are generated, incorporating stochastic variations in bearing installation temperatures and seismic event temperatures. The mechanical parameters of the bearings are adjusted based on seismic event temperatures. The combined effects of seismic actions and the temperature variation on the responses of the bearings and the base bending moments of the piers, as well as their probability distributions, are investigated. Based on the 90th-percentile response, a comparative evaluation between domestic and the European standards is conducted. The results indicate that the temperature sensitivity of lead-core rubber bearings cannot be ignored. In cities where winter temperatures significantly fall below 0℃, this sensitivity notably increases shear forces on the bearings and bending moments at the pier base. Conversely, for cities where the minimum temperature remains at or above 0℃, the impact of temperature sensitivity is relatively minor, and correction may not be required. 

The intelligent evaluation of bridge structure conditions is a crucial prerequisite for bridge maintenance and enhancing structural disaster resistance, with structural damage detection (SDD) being the core research focus. However, existing methods easily suffer from insufficient sensitivity to damage feature indicators, as well as weak global attention and cross-channel coupling capabilities. To address these issues, this paper proposes a novel bridge SDD methodology based on an adaptive embedding and cross-channel attention mechanisms assisted Transformer neural network (AECCA-former). This approach is based on the Transformer neural network as the core framework. In the feature extraction layer, it employs an adaptive embedding mechanism that integrates overlap patch embedding and dilated overlapping patch embedding to achieve adaptive feature vector embedding. This enhances the flexibility of block-wise encoding, addressing the SDD needs under different operating conditions. Additionally, a cross-channel attention mechanism is applied in the Transformer encoder for feature extraction, which strengthens the method's ability to extract features from multi-channel measurement responses. Numerical simulations on an elastic supported bridge indicate that the AECCA-former outperforms convolutional neural networks in feature extraction and provides more reliable, accurate, and robust SDD results under different SDD cases. Practical SDD results from the Z24 Bridge further indicate that AECCA-former can effectively identify structural damage even with a limited number of sensors.

To study the fatigue performance and failure mechanism of single seven-wire steel strand under axial combined action of axial tension and bending, a corresponding tension-bending fatigue test device was designed, followed by experimental studies with 24 test conditions consisting of three bending lengths of 2.0m, 2.5m, and 3.0m, three vertical displacements of 40mm, 50mm, and 60mm, and three initial axial tensile forces of 56kN, 77kN, and 98kN. The experimental results showed that, the steel strand always breaks near the central clamping area, where the maximum bending stress amplitude exist. According to the different fracture mechanisms and fracture characteristics, the fracture forms in this study are usually divided into four main types: flat, inclined, cup-cone, and split. The upper wires with the largest bending deflection angle always broke first, followed by  middle wires, while lower wires finally broke. Keeping the initial average axial tensile stress remaining constant, the life of the last broken wire is about 1.2~4.3 times that of the first broken wire, whose fatigue life was within 12~159 thousand cycles. The fatigue life of the steel strand under tension-bending fatigue was mainly affected by the bending stress amplitude. Micro-sliding wear between the wire and the clamp, and the loading frequency were also an important influencing factor.

In order to analyze the dynamic response of semi-submersible platforms in the complex deep-sea environment, this study had undertaken the establishment of a three-dimensional numerical wave tank. This tank was designed to incorporate and analyze the complex coupling effects of various marine environmental loads, including wind, waves, and currents. Taking a semi-submersible platform in the South China Sea with a working water depth of 1100m as the research object, the study delved into investigating the platform's dynamic response under varying sea conditions. First, a numerical water tank was constructed based on the N-S (Navier-Stokes) equation and VOF (Volume of Fluid) multiphase flow model, and dynamic mesh technology was used to reflect the real-time update of the flow field and the ocean platform mesh. Subsequently, the mooring force time history was meticulously calculated, factoring in the stiffness of the mooring cables. The mooring system was then implemented by applying the calculated mooring force at the corresponding position on the platform. Finally, the dynamic response of the offshore platform obtained from the analysis was compared with the results of a numerical model created using ANSYS-based AWQA software. The research results indicate that the platform surge and heave responses obtained from the numerical wave tank analysis are close to those obtained from the AWQA software analysis. Moreover, the numerical wave tank analysis highlights the influence stemming from the turbulent characteristics of the flow field, resulting in the sway response of the platform. The maximum displacement amplitudes for the platform's surge, heave, and sway responses are 26.0000m, 3.5553m, and 0.3897m, respectively, under the sea conditions of a-hundred-year recurrence period. The use of numerical wave tank methods for offshore platforms allows for more accurate simulations of the marine environment, resulting in improved precision in dynamic responses. Ultimately, this approach provides a reliable foundation for the structural design of semi-submersible offshore platforms. 

In view of limitations of the bending vibration model of crushing-toothed roller and the torsional vibration model of crusher system, in order to explore the influence of impact-crushing composite load excitation on vibration characteristics of toothed roller and crusher system, bending-torsional coupling dynamic equation of crusher system under composite load excitation of toothed roller is derived by using the impact dynamics method and the energy method through the Lagrange equation. Based on Runge-Kutta method, numerical simulation is carried out to analyze bending vibration response of toothed roller and torsional vibration response of crusher system under five types of load excitations. The simulation results showed that, compared with constant load excitation, disturbance impact load can increase the bending amplitude of toothed roller along load direction by 87.79%.Disturbance crushing load can increase the bending amplitude of the toothed roller by 29.36% and 29.61% in x direction and y direction respectively, and torsional vibration angle also can increase by 0.0037rad. The bending amplitude and torsional amplitude of toothed roller generated by composite load excitation are 0.006 m and 0.023 rad respectively to accelerate the fatigue damage of toothed roller and transmission equipment and affect the efficient and reliable operation of crusher system. The study results can provide a certain reference for revealing structural dynamic characteristics and damage mechanism of toothed roller and transmission equipment under composite load excitation that include high energy frequent impact and so forth.

In order to investigate effects of the extended tooth contact (ETC) on nonlinear dynamic characteristics of the gear transmission system, time-varying mesh stiffness considering the ETC effect is introduced into dynamic model of the system. Global dynamic responses of the gear transmission system are obtained using the incremental harmonic balance (IHB) method, and effectiveness of the dynamic model of the system with the ETC effect is verified as compared experimental results with theoretical results that are characterized by dynamic responses. Stability and bifurcation characteristics of dynamic responses of the system are determined employing the improved Floquet theory. Jump phenomena and nonlinear softening-spring characteristics of the system are revealed based on dynamic responses, influences of the ETC effect on dynamic characteristics of the system are analyzed, and effects of loads on stability and bifurcation characteristics of dynamic responses are investigated. Results show that there are jump phenomena at saddle-node bifurcation points, nonlinear softening-spring characteristics caused by separations of engaged teeth; saddle-node bifurcation points in frequency response curves of the system move upward in the vertical direction with increasing loads, which result in unstable regions of frequency response curves gradually become small; the largest amplitude of frequency response curve of the system considering the ETC effect is reduced by 9.79% as compared with that of frequency response curve of the system neglecting the ETC effect.

Under the influence of complex noise, the problems of low diagnostic accuracy and weak generalization ability appear in the fault diagnosis of aviation engine bearings.It is based on minimum average composite entropy and parallel convolution.This method first takes the minimum average composite entropy composed of Raney entropy and sample entropy as a fitness function, and uses the improved Mantis algorithm as the optimization algorithm to optimize the key parameters of VMD for signal fault feature extraction.The extracted signal features were subsequently transformed into angular and field and angular difference fields. Finally, the convolutional neural network is used for fault diagnosis.The experimental data and bench experiments show that the classification accuracy of the proposed model is as high as 99.3%. Compared with the contrast model, the noise resistance under complex noise conditions is improved by more than 15%, and the generalization ability is improved by 3.68%.

To solve the problem of the signal spectrum divided boundaries are overly dense and the number of modal components need to be preseted and lack of adaptability in the Empirical Fourier Decomposition (EFD) method, an improved Empirical Fourier Decomposition based on energy spectral line (ESL-IEFD) method is proposed and applied in the diagnosis of weak faults in rolling bearings. Firstly, the sliced integrated energy values of the fast spectral correlation diagram of the bearing vibration signal are calculated, and the S-G (Savitzky Golay) algorithm with good filtering and smoothing performance is used for processing to obtain the energy spectral lines. Secondly, using the local minimum position of the energy spectral line and the two endpoints of the spectrum as segmentation boundaries, the spectrum is reasonably divided and the number of modal components is adaptively determined. Then, the zero phase filter and inverse Fourier transform constructed are applied to filter and reconstruct each component for each frequency band, respectively. Finally, analyze the components with obvious fault characteristics in the envelope spectrum of each component to diagnose bearing faults. The simulated and experimental signal analysis results show that compared with EFD and optimised EFD, ESL-IEFD method is more reasonable and less dense in frequency band division, and can adaptively determine the number of modal components. In terms of fault diagnosis effect, it can effectively extract single weak fault features of inner and outer rings, as well as separate and extract composite fault features of inner and outer rings, and accurately diagnose bearing fault types.

Fault diagnosis models optimized through deep transfer learning have proven effective in addressing civil aircraft fault diagnosis tasks under variable working conditions, ensuring component reliability in in complex operational environments. However, the scarcity of high-confidence fault samples, particularly under varying conditions, due to the stringent safety requirements in civil aviation hinders the model's inference capabilities and increases the risk of overfitting. To overcome these challenges, we propose a Condition Diffusion-based Fault Diagnosis (CDFD) algorithm. The algorithm integrates a denoising diffusion model to conditionally generate high-confidence fault samples, thereby alleviating overfitting caused by sample scarcity. Unlike traditional diffusion methods that focus solely on sample distribution inference, the CDFD algorithm couples fault sample generation with decision-making optimization,  ensuring the quality of generated samples and significantly enhancing the diagnostic model’s generalization. Experimental validation on both simulated and real-world fault data demonstrates the efficiency of the proposed algorithm in handling real civil aircraft fault diagnosis tasks.

The structural damage location method based on the Lamb wave phased array principle has attracted extensive attention due to its high sensitivity. In order to solve the problem of blind spot and false image in the current method of damage location of linear piezoelectric sensor array based on phased array principle, a method of damage scanning location of circular array phased array is proposed in this paper. By placing the sensor array in the central ring of the structure, the phase-controlled fusion positioning method of circular excitation scanning in turn is adopted to reduce the positioning blind area and avoid false imaging, and the positioning accuracy of the structure is improved by probabilistic imaging method. Finally, the effectiveness and practicability of the method are verified by experiments.

In the process of dealing with complex monitoring data, the traditional Kernel Principal Component Analysis (KPCA) method is limited by its reliance on the Gaussian distribution assumption and static model characteristics, resulting in poor damage identification effect under changing environments. To address these limitations, this paper proposes a Dynamic Kernel Entropy Component Analysis (DKECA)-based damage identification method. The proposed method first constructs a time-delay matrix incorporating historical and current data to extract dynamic features from monitoring data. Subsequently, Kernel Entropy Component Analysis (KECA) is employed to select kernel principal components that maximize Rényi entropy, projecting the data onto a nonlinear feature subspace. Since the selection of kernel principal components based on Rényi entropy does not depend on specific data distributions, the method demonstrates superior performance in handling non-Gaussian data. Finally, damage identification is achieved through a T²-statistic-based control chart, with thresholds determined using kernel density estimation. The DKECA method is applied to damage identification for a wooden truss bridge and the Z24 bridge under varying environmental conditions, and its performance is compared with Principal Component Analysis (PCA), KPCA, and KECA. Results indicate that DKECA outperforms the other methods in processing nonlinear, non-Gaussian dynamic data and demonstrates superior damage identification capabilities under complex environmental conditions.

In bearing fault diagnosis tasks, the Laplace wavelet dictionary is commonly used for dictionary construction due to its high similarity to transient impacts caused by faults. However, traditional Laplace dictionary construction methods employ fixed frequency and damping ratio parameters, which struggle to adapt to the time-varying characteristics of fault impact features (e.g., fluctuations caused by rotational speed variations or load fluctuations). This limitation leads to a degradation in algorithm performance. To address this issue, this paper proposes a vectorized parameter-based dictionary construction method, which dynamically adjusts dictionary atoms to adapt to the variations in fault impact features. First, the bearing fault signal is partitioned based on fault characteristic frequencies, and optimal parameter ranges are selected through correlation filtering. Subsequently, a time-varying dictionary is constructed based on the observed signal characteristics. Finally, an OMP algorithm with an adaptive iteration termination criterion is employed to determine the number of iterations and complete signal reconstruction. Simulation and experimental results demonstrate that the proposed method outperforms traditional methods in terms of feature extraction accuracy.

A wavenumber integration superposition method is developed to predict underwater noise trans-media propagation. In this method, an array of distributed equivalent sources interior to a structure are employed to represent this object based on wave superposition principle. The equivalent sources in wave superposition method that are defined with the free-space Green’s function are analytically expressed using the displacement potential Green’s function in wavenumber integration technique to satisfy the boundary conditions. The strengths of the sources are revised theoretically. The underwater sound and the seismic wave are conveniently calculated using the superposition of the fields from the equivalent sources. It is the key feature of the present method that truncating and discretizing the field space are not required for the prediction. The performance of the proposed method including accuracy, stability, and convergence is studied numerically. Simulations indicate that this method has excellent computational performance and can accurately predict the trans-media sound and seismic wave field. 

High-performance acoustic modulation has always been an important goal pursued. In recent years, near-zero-refractive-index materials have received extensive attention from researchers due to their excellent transmission properties. In this paper, with the help of fractal phenomenon in nature, first-order and second-order fractal structural units are designed based on the improvement of Piano curves and the concept of spatial curvature. The transmission and reflection coefficients of the fractal structure are calculated by numerical computation, and the equivalent acoustic parameters of the fractal structure are obtained by inversion of the equivalent parameter method. The results show that the first-order and second-order fractal structures exhibit better near-zero density characteristics at 1456 Hz、884 Hz and 1178 Hz, respectively, and possess the characteristics of small-scale modulation of large wavelengths. Further, different acoustic metamaterial plates were fabricated based on the designed fractal structure units to realize wavefront shaping, acoustic stealth, and acoustic unidirectional transmission phenomena. Finally, the corresponding fractal structural unit samples were fabricated using 3d printing technology, and the transmission coefficients of the samples were experimentally tested to evaluate the transmission characteristics of acoustic waves inside them. The measured results are in good agreement with the analyzed results of the numerical analysis, which verifies the accuracy of the numerical analysis results and the validity of the structural design.