The thin-walled metallic tube-core sandwich structures with convenient preparation, low cost and the ability to form significant plastic deformation have broad application prospects in the field of impact protection. In this paper, the novel metallic tube-core sandwich panels with geometrically asymmetric face-sheets and transverse density gradient distribution of tubes are designed. The dynamic response and energy absorption mechanism of the sandwich panels are studied numerically. The dynamic response process and characteristics of metallic tube-core sandwich panels are obtained, and the effects of detonation height, explosive mass, mass distribution of the panel and transverse density gradient distribution of the tubes on the deformation and energy absorption are discussed. The results show that the dynamic response process of the metallic tube-core sandwich panels can be divided into three stages: core compression, overall deformation, and elastic deformation recovery. With the increase of explosive mass and the detonation height, the central displacement of the back face-sheet of the sandwich panel increases and the energy absorption ratio of the tube-core layer decreases. When keeping the total thickness of the face-sheet unchanged, the sandwich panel with thick front face-sheet and thin back face-sheet has strong ability to absorb energy and resist deformation. The sandwich panel with positive density gradient distribution of cores has strong ability to resist deformation, and the sandwich panel with the negative density gradient distribution of cores has strong ability to absorb energy. The application of the metallic tube-core sandwich panel with an appropriate increase in the thickness ratio of the front and back face-sheets and a positive density gradient distribution of the tubes can better disperse the blast shock wave, enhance the energy absorption efficiency of core layer, and obtain better anti-blast effect.

A type of metal corrosion probes was proposed using piezoelectric tube stack and electro mechanical impedance (EMI) technique. The probe consists of a piezoelectric tube stack and a metal bar. The transfer matrix model of the multilayer structured probe in longitudinal vibration mode was established, and the electrical impedance was derived to solve the first resonance and anti-resonance frequencies. The theoretical results were validated by comparing them with those of the special cases in the published literature. In addition, the probe performance was studied systematically through theoretical analysis, artificial uniform corrosion experiments, temperature-sensitive experiments, accelerated corrosion tests, and wireless impedance measurement experiments. The results show that the first resonance and anti-resonance frequencies of the probe are increased with the decrease of the bar length, the increase of the corrosion days, and decreased with the increase of temperature. The measured impedance spectra of the wireless impedance measurement system are very consistent with the test results of the traditional impedance analyzer. The present study provides an important reference for developing the novel metal corrosion probes of wireless quantitative measurement.

In practical engineering, fault diagnosis of rotating machinery often faces various complex situations such as noise interference, limited fault samples and variable working conditions, which pose new challenges to the application of data-driven deep learning methods that lack prior knowledge. Traditional fault diagnosis methods based on wavelet analysis can extract rich prior knowledge of faults, but a fixed (structured) or single wavelet basis is difficult to directly adapt to complex fault scenarios. To address these issues, a multiscale wavelet packet-inspired convolutional network (MWPICNet) was proposed for fault diagnosis of rotating machinery in this paper, inspired by traditional multiscale wavelet packet analysis. The proposed MWPICNet internally coupled the time-frequency domain conversion with filtering denoising, feature extraction and classification. First, the multiscale wavelet packet-inspired convolutional (MWPIC) layer and soft-thresholding activation (ST) layer were alternately used for signal decomposition and nonlinear transformation, extracting multiscale time-frequency fault features and filtering out the noise layer by layer. Each MWPIC layer could be approximately seen as a single-layer wavelet packet transform of the signal under multiple learnable wavelet bases, and learnable thresholds in the ST layer were used to sparse the wavelet coefficients. Then, the frequency band weighting (FBW) layer was designed to dynamically adjust the weights of each frequency band channel. Finally, a global power pooling layer (GPP) was introduced to extract discriminative frequency band energy features that were helpful for fault identification. The efficacy of the proposed MWPICNet is verified through case studies designed for different complex scenarios on three fault diagnosis datasets.

To investigate the difference of wind-induced swing characteristics between long span conductors and jumper lines, a refined finite element model coupling the jumper lines, long span conductors and insulator strings is constructed. The research elucidates the different dynamic characteristics, included mode and aerodynamic damping ratio, between the conductors and jumper lines. Combining with the frequency-domain method, multiple cases are calculated to analyze the effect of wind field and line parameters on the dynamic response of conductors and jumper lines. Results show that: The fundamental frequency of jumper lines is approximately 1.5~2.0 times that of conductors. The effect of aerodynamic damping on jumper lines is much smaller than that of conductors. The dynamic response of conductors is dominated by the background response, while the resonance response is not significant. However, the resonance response increases the wind -induced swing response by more than 30%, which should be considered in the wind-resistance design of jumper lines. The resonance response characteristics of jumper lines are determined by their own dynamic characteristics, and are relatively less affected by the upstream wind. The fundamental mode plays a decisive role in the resonance response of jumper lines. Based on the quasi-static and inertia force method, this paper derives the resonance part of peak fluctuating wind force for jumper lines, introduces the resonance factor, and amend the gust response coefficient. The amended gust response coefficient increases by about 9%~12% compared to the code.

The Potala Palace is a famous world cultural heritage in our country. And its area is located with active faults and frequent major earthquakes. Reliable seismic risk assessment can provide a basis for seismic protection of Zang-style ancient buildings in the study area, including the Potala Palace. Compared with the shortcomings of traditional seismic hazard analysis methods, this paper proposes a systematic process of seismic hazard assessment by using the seismic physical prediction method based on the multi-locking segment rupture theory. According to the relationship between seismic intensity and the attenuation of ground motion parameters, considering the conditions of the site itself, the seismic risk assessment of the area where the Potala Palace is located was carried out. The results show that the study area is located in the Linzhi selsmic zone, and the seismic risk of the study area in the next 100 years is mainly the next M8.5 main shock or M7.8 landmark earthquake in the Linzhi selsmic zone. The seismic fault is located in the southeast bank fault of Namco near the middle section of the Yadong-Gulu fault, and the epicenter is near 30.3°N and 90.1°E. The Potala Palace complex is located in bedrock, regardless of the magnification of the mountain site, and the seismic action at the ground end of the structure is equivalent to that of bedrock. The research conclusion provides a theoretical basis for the seismic study of the structure of the Potala Palace complex.

The steel bridge tower is one kind of tall and slender structure which is highly sensitive to wind loads and prone to vortex-induced vibrations (VIVs). To investigate the VIV characteristics of a 217-meter-high steel bridge tower, 1:100 scale free-standing aeroelastic model wind tunnel tests were conducted. The experimental results show that in-phase VIVs occur in the low wind speed ranges, and out-of-phase VIVs occur in the high wind speed ranges at the wind directions range of 0° - 30°. The most unfavorable wind directions of in-phase and out-of-phase VIVs are 0° and 10°, respectively. In-phase along-wind displacement and out-of-phase torsion angle are 609.5 mm and 4.3°, respectively. Furthermore, the VIV triggering mechanisms were studied by computational fluid dynamics (CFD). The numerical simulation results show that the frequency of alternating vortex shedding near the two tower columns is close to the fundamental natural frequency, and the periodic pressure difference generated by this phenomenon leads to in-phase and out-of-phase VIVs. The findings and conclusions of this study provide some reference for the wind-resistant design of similar steel bridge towers.

Due to the harsh environment of the heliostat, the strong wind not only affects the concentrating efficiency of the heliostat, but also causes damage to the heliostat. To this end, the project team designed a dynamic vibration absorber for heliostats. This paper will optimize the design from three aspects : magnetic field strength, mass ratio and structural dimensions, so as to improve its frequency shift range and vibration absorption effect. Firstly, the mathematical model of the absorber-heliostat system is established, and the optimal parameters of the absorber are determined for structural design. Then, the magnetic circuit, thermodynamics and dynamics simulation of the absorber model are carried out to analyze the rationality of the absorber structure. Finally, the effectiveness of the device is verified by experiments. The simulation results show that the magnetic field strength and temperature of the optimized vibration absorber meet the actual use requirements. The expected frequency shift range of the system is 3.97 Hz, and the vibration absorption effect is 29.38%. The experimental results show that the structure optimization is effective, and the experimental results are basically consistent with the simulation results. When the excitation current increases to 6A, the system frequency shift range is 3.813Hz, which is 240.45% higher than that before optimization. Under the excitation of 8.67Hz, as the current increases, the amplitude of the heliostat gradually decreases. In the range of 1.8A~2.4A, the vibration absorption effect can reach 15.90%, which is 32.50% higher than that before optimization. The research results in this paper can provide reference for the design of heliostat wind-induced vibration absorber.

The transfer function model of acoustic structural unit is established through the time-domain simulation method of three-dimensional finite element analysis, and is accurately expressed as the function of structural parameters. The transfer function representation can simplify the design process of acoustic structure. First, two acoustic structural units are established, and their amplitude-frequency characteristics are simulated. And meanwhile, the simulated amplitude-frequency characteristics are verified by experimental measurements. Next, based on the amplitude-frequency characteristics, transfer functions of the two structural units are fit by adopting different zero-pole matching schemes. The results show that the fitting accuracy is the highest when matching 7 poles and no zero to fit the transfer function of the expansion chamber unit, and matching 2 poles and 2 zeros to fit the transfer function of the Helmholtz resonator unit. Then, the influence of the structural parameters of the acoustic unit on the amplitude-frequency characteristics is analyzed. Subsequently, based on the high accuracy form of the fitting function, the transfer function model of the acoustic structural unit is established by numerical simulation and fitting calculation. Finally, a composite acoustic structure composed of an expansion chamber and a Helmholtz resonator is constructed, and its transfer function is calculated based on the transfer function models of the units. The results of COMSOL and transfer function model are compared to verify the established unit transfer function models.

In order to reveal the influence of the confining pressure on the formation and expansion mechanism of rock fissures under particle impact, particle impact rock-breaking experiments and micro-nano industrial CT scanning experiments were carried out, which clarified the influence of the confining pressure on the characteristics of the rock fissure expansion under the action of particle impact; and numerical simulations were carried out on the particle impact under the conditions of different confining pressures, to analyze the evolution process of the rock's stress and fissure fields, and to reveal the intrinsic mechanism of the confining pressure influencing the expansion of fissures. The results show that after the particles impact the rock, a fracture zone and intergranular main crack propagation zone are thus formed in the rock. The shear stress and tensile stress caused by compressive stress are the main reasons for the formation of the fracture zone, while the formation of the intergranular main crack propagation zone is mainly due to tangential derived tensile stress. The confining pressure induces prestress between rock particles such that the derived tensile stress needs to overcome the initial compressive stress between the particles to form tensile fractures. And the increase in the confining pressure leads to increases in the proportion of shear cracks and friction effects between rock particles, resulting in an increase in energy consumption for the same number of cracks，which inhibits the formation of the fracture zone and intergranular main crack propagation zone.

Aiming at the problem of non-uniqueness of solution and singular integral in acoustic boundary element method, based on the idea of CHIEF method, the conventional boundary element equation and the equivalent source equation are combined, and the coupling equivalent relation between the coefficient matrix of the two equations is used to indirectly replace the singular coefficient matrix in the conventional boundary element method, and then a coupled CHIEF method with unique solution in full frequency domain, high computational accuracy and high stability is proposed. In this method, the equivalent source equation is used as the supplementary equation, which not only solves the failure of the interior point supplementary equation of the traditional CHIEF method, but also avoids the direct calculation of singular integrals by the indirect substitution of matrix, which significantly improves the computational efficiency and accuracy. Through typical examples of acoustic radiation and scattering, the results of the proposed method, conventional boundary element method, conventional Burton-Miller method and equivalent source method are compared. The results show that not only the unique solution can be obtained in the full wavenumber domain, but also the calculation accuracy and efficiency of the proposed method are better than those of the conventional boundary element method and the conventional Burton-Miller method, and the condition number of the coefficient matrix is much lower than that of the equivalent source method.

To study the extreme wind pressure distribution in semi-closed stations, the wind pressures induced by high-speed trains passing through railway stations are simulated. The accuracy of the numerical model is also verified against the field-measured data. Based on this validated numerical model, the extreme wind pressure distribution at the train head and tail is analyzed for the two typical station regions (near platform Region I and far from platform Region II) under the traveling train speed of 250km/h, 300km/h and 350km/h, respectively. The corresponding empirical equations are established. The results show that there is a nonlinear relationship between extreme wind pressures and train speeds. At the same train speed, the extreme wind pressures in Region I and Region II decrease exponentially with the horizontal distance, whereas the decrease rate is inversely proportional to the vertical distance. When the horizontal distance is less than 15m, the positive extreme wind pressures due to train head in Region I are always larger than those in Region II at the same vertical distance, while the absolute values of the negative extreme wind pressures due to train head in Region I are always smaller than those in Region II. When the horizontal distance exceeds 15m, the extreme wind pressures gradually tend to be steady, and the corresponding steady values in Region I are larger than those in Region II. The empirical equations developed in this paper can accurately describe the extreme wind pressure distribution in the semi-closed station. The research results can provide reference for the structural design of semi-closed stations.

The rectangular hollow section pier of a railway high-pier long-span simply-supported beam bridge is taken as the research object,calculation model for four kinds of pier heights were constructed, and factors such as the position of truncation and the number of reinforcement bars were considered. IDA analysis is carried out by using Opensees software to build a single pier calculation model, and the elastic-plastic seismic response characteristics of railway high piers are summarized and suggestions on seismic design is put forward. The results show that when the ratio of longitudinal reinforcement is between 0.63 and 0.89%, the pier height is less than 42 meters and the longitudinal reinforcement length is arranged over the pier, the section of hollow pier bottom is weak.When the height of the pier is greater than 67 meters and the longitudinal reinforcement is divided into sections, the section at the bottom of the hollow pier, the section at the truncation of the longitudinal reinforcement and a section in the pier may be the weak part, but the section at the bottom of the hollow pier is the area where the plastic hinge appears first.The plastic hinge in pier shaft can be produced only when it is stimulated by strong ground motion. The influence of ground motion peak acceleration should be considered in the selection of longitudinal reinforcement.Increasing the number of reinforcement bars at pier bottom is beneficial to reducing the plasticity of pier bottom section in general, but it may not improve the seismic performance of the whole pier under strong earthquakes. For high piers, when there are two or more plastic hinge areas in pier shaft, it is suggested to use the coefficient of curvature ductility as the evaluation index.

Aiming at the problem that it is difficult to recognize the caving coal gangue in the process of fully mechanized caving mining under the background of strong noise, a coal and gangue recognition method fusing low-level auditory feature Mel spectrum and high-level auditory feature auditory neurotransmitter firing rate is proposed. Firstly, according to the frequency spectrum characteristics of the sound signal of the tail beam of collapsed coal and gangue impact hydraulic support, an auditory model suitable for the coal gangue recognition task is established based on the auditory neural filter bank model. Then, the auditory model is used to analyze the sound signal of collapsed coal and gangue to obtain auditory neurotransmitter firing rate. Afterwards, the auditory neurotransmitter firing rate is fused with the peak feature extracted by Mel spectrum to obtain the auditory perception diagram of coal and gangue sound. Finally, coal and gangue were recognized with the ConvNeXt model based on the fusion auditory features constructed. The experimental results showed that the proposed coal and gangue recognition method with fusion auditory features had high recognition accuracy under different signal-to-noise ratios, and its superiority was particularly evident under the condition of large background noise (signal-to-noise ratio of -5dB), with accuracy reaching 91.52%, which was significantly superior to the method using low-level auditory features and spectrum as recognition features and using time-frequency domain features combined with machine learning, verifying the robustness of the proposed method to noise.

Typically used in drum washing machines, the friction damper has an insufficient damping effect at low load and high-frequency dewatering, which causes the washing machine shell to vibrate severely. In order to address this problem, a novel type of non-Newtonian fluid variable damping damper is proposed in this paper. Based on the non-Newtonian fluid shear thinning properties and the one-dimensional viscous flow equations in the damper holes, the vibration suppression effect and the physical mechanism of the washing machine during its operation were investigated. The non-Newtonian fluid has apparent shear thinning characteristics when compared to the conventional solid-state friction damper, which significantly reduces the output damping force of the non-Newtonian fluid variable-damping damper and fixes the drawback of the conventional damper that the apparent elastic coefficient rises at high frequencies. A systematic investigation of the vibration damping effect of dampers with various structural parameters on the low load eccentric operation of a washing machine shows that a smaller gap height is more advantageous for the dissipation of vibration energy and that appropriately increasing the viscosity of the non-Newtonian fluid or the number of piston heads can enhance the vibration suppression effect while also being beneficial for noise reduction. The results demonstrate that the variable damping damper can produce a good vibration damping effect for the entire washing process of the washing machine, especially for the high-frequency drying process, and the acceleration attenuation ratio can reach up to 83.49%, the energy attenuation is up to 98.44%, and the noise reduction is up to 10.38dB. This can be achieved through reasonable damping structure design and non-Newtonian fluid proportioning.

The stiffness of the joint surface is an important factor that affects the dynamic characteristics and machining accuracy of a machine tool. To accurately determine the dynamic parameters of the machine tool, a prediction model is used to obtain the contact stiffness of the bed joint surface, and an equivalent dynamic model is established. Firstly, the contact stiffness prediction model is developed. Secondly, the prediction model is used to identify the contact stiffness of the joint surface between two materials (cast iron and mineral composite). Thirdly, using the contact characteristic parameters of the joint surface, a finite element model based on spring element constraint is created. Finally, comparing the finite element modal frequency with the experimental modal frequency reveals that the finite element modal frequency, based on the spring element constraint, aligns well with the experimental modal frequency. This indicates that the model is effective for both cast iron and mineral composites. The results demonstrate that incorporating the contact stiffness of the joint surface in the finite element model of the machine tool bed leads to a more reasonable representation. This provides a theoretical foundation for analyzing the dynamic characteristics of the machine tool and optimizing its structure.

To enhance transverse stiffness of a long-span railway suspension bridge, a composite-spatial cable structure consisting of main and secondary diagonal cables is proposed. Then, the parameters of diameter of composite-spatial cables, anchorages of main diagonal cables with stiffening beams and the surface, and the number of secondary diagonal cables on transverse deflection-span ratio of the bridge are optimized by the effective utilization of the materials and static analysis method. Finally, the analysis method for coupling vibrations of wind-vehicle-bridge system is used to obtain the limit of transverse deflection-span ratio of the bridge based on the driving performance, and the influence of the main and secondary diagonal cables on the enhancement rate of the limit of transverse deflection-span ratio is analyzed. The results show that on the basis of considering the effective utilization rate of composite-spatial cables, anchorages of main diagonal cables and stiffened beams should be located near 1/4 of the main span, and it is optimal when the vertical distance between anchorages of main diagonal cables with stiffening beams and the surface and the tower is equal, and it is enough to set a secondary diagonal cable for each group of composite-spatial cables; in the optimal layout of composite-spatial cables, transverse deflection-span ratio of the bridge can be reduced by 14.18%, the limit of transverse deflection-span ratio can be increased by 16.79%.

Aiming at the rotor-runner system with rubbing problem of hydro-generator set, the Magneto-Rheological Fluid Damper ( MRD ) is adopted to control the shaft vibration, in order to investigate the influence of MRD on vibration pattern of unit shaft system and corresponding effect on suppression of system rubbing faults. Firstly, the unit axial position function is introduced into MRD nonlinear dynamics model, and the dynamic model of MRD-rotor-runner system with axial distribution parameter under rubbing fault is established. Secondly, based on numerical simulation method, the nonlinear dynamic behavior of rotor-runner system with or without considering MRD is comparatively analyzed using unit speed as control parameter. Finally, the effects of different MRD axial arrangement parameters on the dynamic behavior of rubbing rotor-runner system are investigated. The results show that the addition of MRD has a good restraining effect on unsteady motion of rotor and runner, which can significantly reduce vibration amplitude of rotor and runner, and effectively avoid the occurrence of rubbing faults in unit shaft system. The vibration dampening effect of MRD on the system is the best when damping parameters s1 and s2 are taken to be 0.25 and 0.95, respectively. By reasonably arranging MRD in unit shaft system, the system vibration can be effectively improved, thus providing useful guidance for vibration control of hydro-generator set.

Shanghai Strong Earthquake Network obtained several strong earthquake records such as the 6.0 magnitude earthquake in Kyushu, Japan, on May 3, 2020. By analyzing and processing the seismic records, the H/V spectral ratio curves of each strong earthquake station are calculated respectively, and the fundamental resonance frequency and sediment thickness of each station are obtained by combining with the distribution map of the buried depth of bedrock of Shanghai Institute of Geological Survey. The results show that: (1) there is an obvious correlation between the peak value of H/V spectral ratio curve and the thickness of the sedimentary layer, and the empirical formula of the thickness of the sedimentary layer and the resonance frequency of the fundamental order in Shanghai is established through data fitting, and the basic period distribution map of the Shanghai market is drawn, which can provide a certain reference for the seismic fortification of Shanghai. (2) There will be multiple peaks in the spectral ratio curve of seismic records on the thick sedimentary layer site, and the second peak represents the higher-order resonance frequency of the sedimentary layer. (3) The empirical formula of shear wave velocity and sediment thickness in Shanghai area is obtained through data fitting.

In the process of deepwater drilling, the riser and blowout preventer system are an essential part of the entire operation process. Due to many risks involved in the operation process, therefore, establishing an accurate mechanical analysis model of the coupling system between riser and BOPs, accurately analyzing its mechanical behavior and performance, is of great significance for guiding the safety of drilling operations. At present, most people only focus on independent modeling of the riser and ignore the potential impact of the blowout preventer group, which will lead to differences between the established model and the actual situation, and making it difficult to accurately analyze the mechanical properties of the riser system. This paper puts forward the rigid-flexible coupling concept of riser and BOPs, derives the kinetic energy and potential energy of the coupling system, establishes the theoretical model by Lagrange method, and uses Newmark- β Perform numerical calculations on the dynamic model using the direct integration method. A simulation modeling was established using ADAMS software to conduct comparative analysis of dynamic response under different operating conditions. The results indicate that the lateral displacement envelope and bending moment envelope of the riser obtained from the theoretical model in this paper, as well as the lateral displacement time history curve and bottom bending moment time history curve of the middle node of the riser, are in good agreement with the ADAMS simulation results, indicating the importance of the theoretical model in this paper, which can provide reference and support for the design and analysis of risers in China.

A large number of scientific instruments and equipment in the space station need to be locked by unloosening bolts. Aiming at the problem of frequency drift induced by unloosening bolt locking during the development of active vibration isolator for space station, the dynamic mechanism modeling and experimental verification of nonlinear connection of active vibration isolator for space station in locking state are explored.The mechanical analysis of the locking release device of the isolator based on the unloosening bolt is carried out, and the equivalent dynamic model of the system based on the Iwan model is established according to the nonlinear distribution of the stress on the contact surface of the unloosening bolt, and the nonlinear characteristics of the dynamic response are analyzed.The prototype of the active vibration isolator of the space station is developed for sinusoidal vibration test to verify the accuracy and effectiveness of the established dynamic model, which provides a reference for the environmental adaptability design of the space station precision scientific equipment.

A four-point synchronous fluctuating wind speed measurement system with horizontal pair intervals of 10m, 20m and 30m was established in a plain landform terrain site of Nagqu town, Xizang, at an altitude of 4500m. Continuous records of wind speeds for 1.5 years at this high altitude site were obtained. The maximum average wind speed in 10 minutes and the fluctuating wind speed reached 33.6m/s and 45m/s, respectively. The measured mean values of longitudinal and transverse turbulence intensity are 0.134 and 0.123, respectively, which are between the turbulence intensity of the Exposure Category A and the Exposure Category B specified in DL/T 5551-2018. Based on the synchronous fluctuating wind speed of any two measuring points, the spatial correlation coefficient and turbulent integral scale of the downwind fluctuating wind speed component along the conductor direction were calculated. The generalized extreme value model can better reflect the probability distribution of turbulent integral scale based on high wind speed samples. The higher the field observation sample wind speed, the larger the average turbulence integral scale. When the wind speed sample limit is set as 8m/s and 20m/s, the difference between the average turbulence integral scale is 22.5%. The average turbulence integral scale with high wind speed samples above 20m/s is 106.96m, which is 2.1 times of the 50m specified by DL/T 5551-2018, and the wind load acting on the wires increases by about 6.1%. The wind load on the wires in the high-altitude plain landform may be underestimated.

The large-span photovoltaic support structure is light and flexible, and is vulnerable to wind-induced aeroelastic effects. In order to study the aerodynamic damping characteristics of this structure, an aeroelastic model wind tunnel test was carried out to a typical large-span flexible photovoltaic support structure with module inclination of 0° and 10° under different wind speeds and pretensions. Based on the aeroelastic test results, empirical wavelet transform (EWT) and variational modal decomposition (VMD) combined with the improved random reduction method (RDT) were used to identify the aerodynamic damping ratio of photovoltaic structure under different wind speeds and directions, module inclinations, and cable pretensions. The study results show that the aerodynamic damping ratio is sensitive to the change of wind direction angle. When the module has an inclination of 10°, the aerodynamic damping of a large-span photovoltaic structure shows a negative value under the windward wind azimuth of 180°. Increase of pretension may lead to decrease of aerodynamic damping ratio of a horizontally installed module under a high wind speed. The aerodynamic damping ratio generally decreases with the increase of wind speed, it basically shows positive values under low wind speeds but may become negative under high wind speeds. Although the aerodynamic damping ratios identified by different methods were not the same, both of them show consistent variation pattern of aerodynamic damping.

Aiming at the problems of pressure pulsation and vibration impact in large flow tandem pumps, a vibration reduction and noise reduction approach with variable phase angle for tandem external gear pumps is proposed. The mathematical equations for the instantaneous flow rate and pulsation non-uniformity coefficient of tandem external gear pumps are derived. The instantaneous flow pulsation of tandem external gear pumps with different phase angles is theoretically analyzed, and the variation law of pulsation non-uniformity coefficient when changing phase angle is analyzed. The relationship between flow pulsation and pressure pulsation is derived. For tandem pumps with actual phase differences of 0 ° and 20 °, the double throttle valve is installed at the outlet of the tandem pump to obtain pressure pulsation under different operating conditions. The derived pressure pulsation is consistent with the experimental values. The pressure pulsation is composed of a series of i-th harmonics, with the same frequency as the flow pulsation, but different amplitudes and phases. And the experimental results showed that the pressure pulsation rate of the 20 ° phase angle tandem pump decreased by 34.05% compared to 0 °. The 20 ° phase angle tandem pump can reduce the vibration amplitude at most frequencies at 0 ° phase angle. Changing the phase angle of a tandem pump can reduce the vibration amplitude caused by fluid pulsation, and the variable phase angle does not have an impact on the outlet flow rate of the tandem pump.

The study of meso-damage evolution in steel fiber concrete is important for the health inspection of in-service steel fiber concrete structures. A multi-channel acoustic emission system was used to collect acoustic emission signals from concrete and steel-fiber concrete specimens (steel fiber content of 15 and 45 kg/m3, respectively.) during splitting tests. Then, the damage characteristics of concrete and steel fiber concrete are analyzed by combining principal component analysis and k-means clustering algorithm. Research showed that steel fiber inhibits the propagation of cracks in concrete and effectively improve the post-peak toughness of concrete. The acoustic emission characteristics parameter of counts and energy changes reflect the meso-damage evolution process of macroscopic deformation and failure in steel fiber concrete. Finally, two damage mechanisms are identified for mortar matrix cracking and steel fiber pullout in steel fiber concrete. Compared with mortar matrix cracking, the acoustic emission signals generated by steel fiber pull-out behaviors have the characteristics of high count, high amplitude, strong energy, and long duration.

The smart aggregate based on piezoelectric stacks is a new type of transducer, which usually use piezoelectric stacks as the core element. Compared with traditional smart aggregates, it has superior electromechanical coupling performance, which can effectively improve the accuracy and reliability of structural damage diagnosis and has important application prospects in the field of structural health monitoring. However, the current study mainly focused on the device design and theoretical modeling, the device performance based on electromechanical admittance needs to be further evaluated. A temperature-sensitive experiment was designed to analyze the variation of the resonant frequencies of the device under temperature gradient; a 28-day water immersion experiment was carried out to plot the variation of the resonant frequencies of the device with the number of water immersion days; three soil specimens with dimensions of 200 mm 200 mm 200 mm were prepared, and the devices were embedded into the soil specimens to conduct water content monitoring experiment. The water contents of the soil specimens were monitored by the quantitative indicators under different water contents. The results show that the resonance frequencies of the smart aggregates based on piezoelectric stacks decrease linearly with the increase of temperature; the maximum shift of the resonance frequencies do not exceed 10% during 28 days of water immersion, indicating good stability; the quantitative indicators calculated based on admittance signals all increase with the increasing moisture content of the soil specimens, which can effectively monitor the changes in soil moisture content.

Traditional force correction iterative hybrid test method uses a fixed model for restoring force correction, it has the problem of insufficient model accuracy causing increase in iteration rounds. Here, aiming at this problem, a force correction iterative hybrid test method based on adaptive model was proposed. This method could use restoring force correction values of all iteration rounds and true restoring force of physical substructure in each iteration round to build an adaptive model for iterating restoring force correction, and improve iteration’s convergence speed and accuracy. Taking a single-layer frame viscous damper seismic reduction structure as an example, effects of different weight distribution coefficients and initial model parameters on iteration convergence speed and accuracy were analyzed. Effects of structural natural vibration periods on this method were analyzed through separately verifying structures with different natural vibration periods. The results showed that different weight distribution coefficients and model parameters more largely affect iteration convergence speed and accuracy; when the weight distribution coefficient is 0.025 and the initial model parameter is 0.80, the proposed method’s iteration convergence speed and accuracy are much higher than those of traditional force correction iterative hybrid test method; the force correction iterative hybrid test method based on adaptive model has much better convergence speed and accuracy than traditional force correction iterative hybrid test method in different single-layer frame structures; for structures with a natural vibration period less than 1.0 s, the proposed method has more obvious advantages.

With the increasing complexity of the marine environment, the data obtained from observing underwater target acoustic signals exhibits several challenging characteristics, including high dimensionality, nonlinearity, and lack of structure. These characteristics undoubtedly pose significant difficulties in extracting features from underwater target acoustic signals. In this study, a novel method for extracting features from underwater target acoustic signals is proposed, utilizing manifold autoencoders. Initially, the original data is globally optimized by leveraging the autoencoder reconstruction error to identify potential low-dimensional representations. Subsequently, the concept of preserving neighboring reconstruction weights through manifold learning is employed to enforce local constraints on the latent representation, thereby preserving its inherent topological structure. Finally, a generative adversarial network architecture is introduced for regularization, ensuring that the latent representation adheres to a specific distribution. This approach achieves a synergistic preservation of both local and global low-dimensional embedding. The proposed method was applied to extract essential features from four types of deep-water ships in the DeepShip open dataset. The quality of these features was evaluated by employing the classic classifier SVM for classification recognition. A comparison was conducted with existing methods for feature extraction in deep learning and manifold learning. The results showed an average improvement of 14.96% in recognition accuracy.

Unsupervised domain adaptation methods have become an important approach for bearing fault diagnosis under multiple operating conditions. However, existing multi-source unsupervised domain adaptation methods often ignore the contribution of signals from different perspectives to cross-domain fault diagnosis, thus failing to comprehensively represent the fault characteristics of bearings. Additionally, these methods often encounter discrepancies of the prediction results from different source domains for the same target domain task. To address these issues, a time-frequency features fused multi-source unsupervised domain adaptation (TFFMUDA) method is proposed for bearing fault diagnosis. TFFMUDA takes both time-domain and frequency-domain signals as inputs, which interact through a feature coupling mechanism. Meanwhile, the diagnostic consistency of different source domains for the same target domain is guaranteed through classifier alignment strategy. Experimental results on a real bearing fault case demonstrate that the proposed method achieves clearer decision boundaries for fault classes and exhibits improved accuracy for bearing fault diagnosis compared to existing domain adaptation methods.

The behaviors of nonlinear aeroelasitc system show limit cycle oscillations under smooth airflow and irregular, nonlinear, randomly varying oscillations under the turbulence. A fractional-order direct adaptive controller (FDAC) based on output feedback is proposed to suppress the vibration of nonlinear aeroelastic system under wind disturbance. First, the FDAC is designed based on fractional calcus and direct adaptive control theory. Then, the appropriate range of fractional order parameters are deduced. The advantage of FDAC on aeroelastic control and disturbance rejection is theoretically analyzed, compared with integral order direct adaptive controller (DAC). The stability of proposed controller is proved by Kalman-Yacubovich lemma. Simulation results reveal that the proposed FDAC can significantly improve the performance of vibration control and disturbance rejection, under large and random wind disturbance for nonlinear aeroelastic system. The simulation results also verify the theoretical inclusions. 

To study the service status and fatigue life of stitch wire, research was conducted on the stitch wire breaking in high-speed railway contact networks, and fatigue research was conducted. Based on the design parameters of the Wuhan-Guangzhou high speed railway, a dynamic simulation model of the pantograph and catenary was constructed to analyze the vibration state of the stitch wire at speed of 300km/h. Due to the lifting effect of the pantograph on the contact suspension during operation, the stitch wire mainly vibrates in the vertical direction and continuously bears alternating bending loads at the clamp position. Stitch wire were established in UG and the solid model was imported into LS-DYNA, and the refined model was subjected to stress load calculation; the stress concentration position of the stitch wire is located at the connection with clamp. Import stress history data into ANSYS nCode DesignLife to analyze the fatigue life of stitch wire under bending loads; finally, based on the Miner cumulative damage principle, the fatigue life of the stitch wire of the Wuhan-Guangzhou high speed railway at speed of 300km/h was calculated to be 4.58×106; the operating speed increases to 350km/h, and the fatigue life is 1.17×106; speed increased to 400km/h, fatigue life is 4.80×105.

As one of the basic engineering units, elastic beam systems are widely used in various fields, including architecture, aerospace, ocean engineering, and others.It is of great engineering significance to control the vibration level of elastic beam systems.To reveal the potential application of double-coupling nonlinear oscillators(DCNO) in the vibration control of double-beam systems, a dynamic behavior prediction model of double-beam systems with DCNOs was established, where the Lagrange method was used to predict the dynamic behavior of the double-beam system.On the basis of ensuring the correctness of the numerical results, the typical operating mode of the DCNO was studied, and the influence of the DCNO parameters on the dynamic behavior of the double-beam system was discussed.The results show that the introduction of the DCNOs can effectively realize the synchronous vibration control of each substructure of the double-beam system.On the one hand, when the DCNO is in the multi-frequency linear/nonlinear vibration control mode, the vibration of each sub-beam in the main resonance region of the double-beam system is effectively suppressed.Additionally, the multi-frequency nonlinear vibration control mode excites the complicated vibration responses of the double-beam system, resulting in the unidirectional transmission of vibration energy in time domain between elastic beams and DCNOs.On the other hand, according to the vibration control requirements, the working mode and vibration control effect of DCNOs can be realized by adjusting its core control parameters.Setting appropriate core control parameters for DCNOs is conducive to enhancing the vibration control effect of the DCNOs on the main resonance region of the double-beam system.

Based on the peridynamics method, a three-dimensional numerical model for rigid ball impact on glass panel was proposed considering the effects of material damage. And the effectiveness of the presented model was verified according to the Kalthoff-Winkler experiment. Finally, the impact failure evolution and crack propagation mechanism of the glass panel were explored considering the effects of the rigid ball initial impact velocity, the rigid ball diameter, and the glass panel thickness. The results show that the cracks in the glass panel exhibit a radial shape when the initial impact velocity is law. As the impact velocity increases, the circumferential cracks appear and a complex crack network gradually form in the glass panel. Meanwhile, the total length and the proportion of cracks in the glass panel increase with the increase of initial impact velocity, and the relationship between them is approximately linear. With the increasing of the rigid ball diameter, the contact area between the ball and the glass panel expands, which results in the more severe damage and easier formation of complex crack networks in the glass panel. In addition, increasing the glass panel thickness can prolong the impact duration, which makes the glass panel withstand greater impact energy. When the glass panel thickness is relatively thin, it results in more severe local structural damage and the smaller damage area; When the panel thickness is thicker, the structural damage area expands, while local damage weakens.

Inertia dampers are a new type of mechanical element, which are often interconnected with spring and damping elements to form inertia dampers to synergize energy dissipation and vibration damping. In the vibration control of engineering structures, inertia dampers (e.g., TIDs and TVMDs) often have better vibration damping capabilities than conventional viscous dampers. In order to investigate the vibration damping mechanism and advantages of the two types of inertia dampers, TID and TVMD, this paper, based on a simplified SDOF structure, utilizes the kinetic theory to derive the expressions for the additional equivalent stiffness coefficients and damping coefficients provided by the two types of inertia dampers to the structure under dynamic conditions. The explicit conditions for the inertia dampers to provide additional positive and negative stiffness and to produce the damping enhancement principle are derived from the analytical study of these expressions. In addition, this paper shows the negative stiffness characteristics of the inerter element based on the hysteresis curve and illustrates the amplification of the response of both ends of the viscous damping element by the inertia element and the spring element inside the damper under the damping enhancement principle, which intuitively explains the vibration-damping advantages of the inertia dampers.

A fault diagnosis method based on Multivariate State Evaluation Technology (MSET) and Correlation Analysis (CA) is proposed to address the issue of abnormal vibration warning and cause diagnosis for turbogenerator rotor in running state. Firstly, the residual error is calculated between the predicted value and the operating value in the current evaluation window based on MSET and Sliding Window Principle. Secondly, the residual error of the correlation coefficient between in the state matrix and in the current evaluation window is calculated. Thirdly, thresholds are set for the relative deviation mean or residual error of each parameter and the residual error of each correlation coefficient to extract the abnormal features. Finally, vibration warning and abnormal diagnosis are based on Euclidean Distance and the anomalous features. The fault diagnosis method is validated by the operation data of turbogenerators. The results show that the proposed diagnosis method is feasible and can extract more abnormal or fault features compared with the single parameter self-change evaluation or parameter correlation analysis. It has the ability to diagnose multiple faults, which is beneficial for anormal warning and improving the accuracy of diagnosis. 

The wind damage loss of low-rise building envelopes in typhoon-prone areas of Chinese coastal areas is worthy of attention. Based on the typhoon process, the vulnerability of low-rise building envelopes to multiple factors such as wind-induced internal and external pressures, debris impact, and structural resistance was investigated. A debris impact probability model was established for typical low-rise building scenarios, which can effectively consider practical factors such as wind direction, wind speed, the height and spacing of buildings, as well as the take-off position of the debris. The results show that it is necessary to consider the typhoon process in the wind damage vulnerability analysis of low-rise building envelopes. Typhoons with similar extreme wind speeds may also cause large differences in extreme damage to buildings. The occurrence times of extreme damage generally lag behind the moments of extreme wind speed, and the duration of extreme damage is related to the duration of typhoon. Compared with the previous models, the debris impact probability model newly established is more applicable to the typical low-rise building scenarios in Chinese coastal areas. 

In order to optimize forcing cone structures and analyze the dynamic characteristics of the engraving process under different forcing cone structures of a small caliber gun, established an internal ballistic equation system considering changes in projectile resistance and introduced it into finite element solution via using the vuamp subroutine to achieve the coupling calculation model of internal ballistics calculation and finite element simulation in the engraving process. The feasibility of the model was verified through simulation analysis of the full barrel motion of the projectile. Simulated and analyzed the velocity, acceleration, and resistance curves and variation patterns of the projectile during the engraving process under different forcing cone taper, rifling depth, and concave line width. The result indicates that the influence of slope chamber taper on the projectile's dynamic parameters during the extrusion process is not monotonic, while the changes in rifling depth and concave line width monotonically affect the projectile's dynamic parameters. This method can provide reference and guidance for the design and optimization of gun barrel structures and bearing band.

Cable is an essential force transmission component of the cable supported structures, and its cable force directly affects the service condition and lifespan of the structures. In general, for cable supported structures with locally rigid coupling, the cable strand vibration is independent and coupled. the vibration characteristics of the parallel strand cables are different from those of the single cable strand or the cables with good integrity. In order to effectively identify the tensions in the parallel strand cables with rigid couplings, Firstly, the model of multi-strand coupled system was established and the vibration equations of the system was derived, According to the vibration equations of the system, the parametric analysis of vibration characteristics was performed on the coupled system; Then, combined the filled function method and optimization theory, the identification algorithm for cable force of multi rigid couplings cable strands was constructed, the global identification of cable force was realized; Finally, the correctness and reliability of the algorithms were demonstrated by the experiment and finite element simulation. The results show that the rigid coupling ensures that each cable strand vibrates synchronously, the natural vibration frequencies of the parallel strand cables appear fractional frequency doubling, and there are local differences in the overall vibration modes; The cable force identification algorithm based on global optimization theory proposed in this paper exhibits low requirements for initial values, high calculation accuracy, and convergence efficiency, and can be extended to other parameter identification problems.

In order to study the dynamic coupling relationship of the floating base multi-robot suspension system under the action of irregular waves, firstly, the dynamic model of the floating base robot is established by using the theorem of momentum and the theorem of moment of momentum. Secondly, the dynamic model of the suspension system is established by using the D 'Alembert principle, and the coupling relationship analysis steps of the system dynamics are proposed. Finally, combined with an example, the dynamic coupling response process of the floating-based multi-robot coordinated suspension system under different wave heights, different wavelength ratios and different lifting speeds is simulated and analyzed. The conclusions obtained complement and improve the theoretical research of the system, and also provide technical support for judging the safe lifting environment of the floating base multi-robot suspension system in the actual lifting process.

Launch vehicle sea launch is a complex and nonlinear system. With relative motion between the launch vehicle and frame-type launcher, nonlinear and discontinuous impact loads between the adapter and guide rail occur at different speeds. Evaluating the strain rate effects of the adapter model is crucial. In this paper, we developed an improved phenomenological macro model based on polyurethane foam experimental data to accurately capture the system dynamics. We established two dynamic models of the sea launch system, one with and one without considering the strain rate effect of the adapter, and studied the dynamic characteristics of the launch vehicle during sea launch under high sea conditions. The results indicate that the strain rate effects have a significant impact on the contact load between the adapter and guide rail and the rolling motion law of the sea launch. This directly affects the safety assessment and design of the rolling limiting device for sea launch. Overall, the research provides important insights into the engineering and theoretical aspects of launch vehicle sea launch, highlighting the requirement to consider the strain rate effects of the adapters in sea launch dynamics modeling and safety assessment.

Aiming at the problem of difficult coordination between body height and suspension damping under complex operating conditions of vehicle air suspension system, a multi-mode switching terminal sliding mode control strategy for composite air suspension was proposed. Considering the effects of suspension system nonlinearity and external disturbances, a nonlinear dynamics model of composite air suspension was established. A multi-mode switching controller was designed to determine the optimal damping control mode under different body heights. An unknown input observer was used to estimate the suspension system state quantity, and a non-singular fast terminal sliding mode controller based on radial basis neural network was designed to control the linear motor output under the corresponding mode of electromagnetic. Finally, the dynamic performance of the suspension under the multi-mode switching terminal sliding mode control strategy was simulated and tested on the bench. The simulation results show that the control strategy can effectively coordinate the body height and suspension damping, and improve the smoothness and stability of the vehicle under complex working conditions. The test results show that compared with the passive suspension, the acceleration of the reed mass of the system is reduced by 32.5% and 33.7% in the time domain and frequency domain respectively, which verifies the effectiveness of the control strategy.