The impact vibration test is widely used in modal analysis, because of its convenience, low cost, and efficiency in identifying multiple modes with a single impact.To achieve efficient and accurate estimation and uncertainty quantification of modal parameters in the impact test, a fast Bayesian fast Fourier transform method was proposed.The likelihood function was first developed based on the equation of motion and the complex normal assumption of measurement error, and the Laplace approximation was then adopted to obtain the posterior distribution of modal parameters, i.e., fitting the posterior distribution with a Gaussian distribution, whose mean was computed by minimizing the negative log likelihood function (NLLF) while the covariance matrix was obtained by taking the inverse of the Hessian matrix of NLLF at the posterior mean.A coordinate descent algorithm was proposed to minimize the NLLF taking advantage of the analytical gradient of NLLF.The Hessian matrix was obtained via the calculus of complex matrix, allowing an efficient implementation.Finally, the performance of the proposed method was validated through synthetic and laboratory data.A comparison with the methods based on free and ambient vibration tests was also provided, respectively.

In mine operations and natural gas transportation operations, the shock wave and flame wave caused by methane explosion bring great harm.In order to reduce the damage caused by explosion to the life and property safety, the fillability of Fe-nickel foam and powder combination was utilized in a self-built pipe network system.The optimal combination of foamed iron-nickel and powder was obtained through the explosion suppression experiment in the pipe network.The mechanism of NH4H2PO4 microsuppression of methane explosion was analyzed by using the pyrolytic characteristics of powder and by Materials Studio analysis.The experimental results show that the combination of 30-ppi foamy Fe-Ni and 70 gNH4H2PO4 powder can effectively inhibit the methane explosion in the pipe network, and the peak methane explosion pressure can decrease by up to 82.5%.The flame propagation speed of each branch is reduced to 10.01 m/s, 10.99 m/s, 11.78 m/s and 9.78 m/s respectively.The peak temperature of each branch can be reduced to 359 K, 341 K, 324 K, and 337 K respectively.The mechanism of this combination to inhibit methane explosion is mainly reflected in the endothermic reaction of the two, and the chemical inhibition is reflected in the decomposition of a large number of active groups such as NH3•, NH2• and NH• when heated to capture the key free radicals in the methane explosion, reducing the concentration of free radicals required for the methane explosion process.

As a novel type of pulsed water jet, the pressurized pulsed water jet has the advantages of large amplitude pressurization, controllable jet parameters, and high energy utilization rate, which shows broad application prospects in the field of hard rock fragmentation. To improve the rock fragmentation performance of the jet, a pressurized pulsed water jet generation system developed by ourselves was used to conduct the granite fragmentation experiments. Based on three-dimensional morphological scanning technology, a precise macroscopic performance expression method of rock fragmentation was proposed to explore the effects laws of different process parameters on rock fragmentation performance, and the mechanism of fine-grained fracture and damage distribution was revealed. The results show that there is a clear step-like increase in the rock fragmentation performance parameters when the jet pressure is 60 MPa, the rock fragmentation performance parameters drop sharply when the target distance is greater than 100 mm, and the rock fragmentation performance parameters reach the maximum when the nozzle diameter is 0.5 mm. The granite forms a crack network composed of "primary cracks, radial cracks, and derived cracks" under the impact of the jet. The crater is in the shape of a spoon, with a large entrance area and a shallow depth, and the failure mode is sheet-like detachment caused by the expansion of internal fractures. Meanwhile, the jet's damage and destruction to the rock has a local effect, as the depth increases, the overall damage area distribution range remains basically unchanged, and the dense damage region and damage degree decrease rapidly. The research results provide theoretical support for the engineering application of pressurized pulsed water jet for hard rock fragmentation.

To investigate the mechanical properties and damage evolution mechanisms of limestone under cyclic loading, a series of laboratory experiments, theoretical analyses, and numerical simulations were conducted. Initially, single and constant-amplitude cyclic impact tests on limestone were performed using the Split Hopkinson Pressure Bar (SHPB) apparatus. Based on the Weibull damage theory, a dynamic load-induced damage evolution model was developed. Additionally, numerical simulations of cyclic blasting on limestone were carried out using ANSYS/LSDYNA. The results indicate that, under a single impact, an increase in impact pressure leads to an elevation in peak stress and yield strain of the limestone. Under cyclic impacts, as the impact pressure rises from 0.15 MPa to 0.30 MPa, the number of impacts required to fracture the specimens decreases gradually, from 13 to 3. With an increasing number of impacts, the yield strain of the specimens increases, while the elastic modulus and peak stress decrease, ultimately leading to failure when the cumulative damage approaches unity. As the number of blasting events increases, the crushing zone around the blast holes in the model expands, the main cracks continue to propagate, and damage accumulates. The damage variable defined in this study achieves a comprehensive and unified description of the entire process of cumulative damage evolution under cyclic impact loading. The rock damage expression established under blasting loads effectively reveals the distribution characteristics of rock damage during a single blasting event, aligning with the theoretical framework of engineering blasting and providing valuable insights for engineering blasting operations.

In order to explore the effect of reticular polymer material on gasoline-air mixture explosion suppression of horizontal storage tank, a horizontal storage tank experiment system (L/D≈3.1, V=1000L) was designed and built. The law of the effect of filling rate of explosion suppression material on gasoline-air mixture explosion characteristic parameters was analyzed, and the mechanism of explosion suppression material on gasoline-air mixture explosion was explored. The results show that the explosive power of the horizontal tank is significantly weakened, the flame propagation is retarded, and the flame propagation speed decreases after the filling of the mesh polymer material. With the increase of filling rate, the maximum explosion overpressure, the average pressure boost rate and the explosion power index gradually decrease, and the arrival time of the maximum overpressure gradually prolongates. In the process of flame propagation in the explosion suppression material, Due to the influence of "cold wall effect", "wall effect" and material thermal decomposition, the development process of oil and gas explosion is inhibited.

This article integrates theories of fluid mechanics, thermodynamics, and rotor dynamics to establish a mathematical model for the pressure field, temperature field, and characteristic parameters of hybrid bearings under shock loads. The finite difference method and Euler method are used to calculate and analyze the impact of shock loads on the thermal fluid performance of bearings. The results show that the axis trajectory of the hybrid bearings after being subjected to shock is a closed curve, and the parameters such as bearing capacity show a sinusoidal variation trend. Shock loads with opposite directions and equal amplitudes make the bearing capacity and axis trajectory of the hybrid bearing show a symmetrical variation trend. For every 120N increase in shock amplitude, the peak value of horizontal bearing capacity change increases by about 33%-47%, and the peak value of vertical bearing capacity change increases by about 1.9%-2.3%; When the shock parameters or structural parameters of the bearing change, the minimum oil film thickness of the bearing changes significantly. For example, for every 120N increase in shock amplitude, the minimum oil film thickness changes by about 0.3 μ m; The maximum oil film pressure, which takes into account the thermal effect, is reduced by about 2% compared to the results of the isothermal model, the minimum oil film thickness is reduced by about 7%. The initial position of the axis trajectory changes significantly, but the trend of parameter changes remains basically unchanged.

In order to solve the shortcomings of low optimization efficiency and limited search range of traditional aerodynamic measures optimization methods for bridge sections, a wind tunnel test-driven aerodynamic shape optimization method for main girder sections is proposed, which combines Kriging surrogate model and multi-point search strategy. The aerodynamic shape of the new box girder section of the 2000 m suspension bridge is optimized in the multi-parameter design space composed of the horizontal plate width L of the inverted L-shaped deflector, the height H of the lower central stabilizer and the track position J of the maintenance vehicle. Firstly, the improved Latin hypercube experimental design method is used to obtain the initial sample points in the design space, and the flutter critical wind speed of the initial sample is obtained by wind tunnel test. Then, the initial Kriging surrogate model of design parameters and flutter critical wind speed is established. Then, the update point update proxy model is added using the newly proposed parallel add-point criterion. Finally, the design parameters of the best section matching of flutter performance are obtained by optimization, and the correctness of the optimization results is verified by wind tunnel test. The results show that the Kriging surrogate model combined with the multi-point search strategy optimizes the aerodynamic shape of the bridge section, which significantly improves the optimization efficiency. The flutter critical wind speed of the optimal section is 51 % higher than that of the original section, and 13 % higher than that of the inverted L-shaped baffle alone. The horizontal plate width L of the inverted L-shaped deflector has the most significant influence on the flutter performance.

As a typical system for electromagnetic levitation, the maglev ball requires an accurate theoretical model for precise control. Therefore, a system identification method based on a revised electromagnetic force formula and an IMC-PID controller is proposed, which effectively improves the accuracy of the theoretical model and the efficiency of parameter tuning. Firstly, the derivation process of the electromagnetic force formula is analyzed, and an electromagnetic simulation model is established. The formula for the electromagnetic force-levitation gap and bias current is revised. Secondly, by collecting the response of the actual current to the sinusoidal target signal, the relationship between the bias current and the levitation gap under the same electromagnetic force is obtained. The above steps are performed using steel balls of different masses, thus the relationship between the levitation gap and the bias current under different electromagnetic forces is obtained. The revised formula is used for fitting, resulting in the specific values of the parameters for the physical system of the maglev ball. Combining the dynamic equations, the levitation gap and bias current at the equilibrium point are defined as displacement and control current, respectively. The displacement stiffness, current stiffness, and precise transfer function of the maglev ball system are derived. Finally, based on the internal model control theory, an IMC-PID controller is designed. All PID parameters are calculated through a single parameter, and control simulation and experimental verification are carried out. The experimental results show that the theoretical model obtained from system identification matches the response of the physical system highly, verifying the accuracy of the system identification results. The IMC-PID controller also significantly improves the efficiency of parameter tuning.

Vortex-induced vibration (VIV) is a crucial contributor to the fatigue damage of slender marine structures such as offshore risers and wellhead and must be accounted for during design. Currently, engineering methods that predict VIV for such structures commonly rely on VIV databases for cylinders but fail to account for surface defects resulting from factors such as corrosion. Therefore, resulting predictions may overlook the magnification effect of vibration caused by surface defects, leading to an underestimation of structural vibration amplitude and fatigue damage. To address this issue, a model experiment was conducted to analyze the flow-induced vibration response characteristics of defective cylinders with varying defect depths and incoming flow angles. The results showed that the modal properties of the defective cylinder were complex, exhibiting several modes such as galloping, VIV, and resonance modes. Surface defects can induce galloping vibration mode and significantly increase the cylinder's vibration amplitude, up to a maximum of 7.5 times. Furthermore, at an attack angle of 0°, the defective cylinder demonstrated the highest amplitude and largest resonance range, while at an attack angle approaching α=90°, the amplitude of the defective cylinder sharply decreased and was lower than that of the intact cylinder. Surface defects can also suppress vortex vibration modes, thereby suppressing galloping. The cylinder had the maximum galloping amplitude at a defect depth of 7.5%. In addition, surface defects can also lead to an increase in the range of resonance flow velocity.

Piezoelectric smart aggregates are intelligent devices with excellent force-electric coupling performance and have been widely applied in structural health monitoring within the civil engineering field. However, current research primarily focuses on the driving and sensing characteristics of these devices, while their energy harvesting capabilities have not been extensively studied. Additionally, when these devices are embedded in concrete structures or soil, they may be subjected to sulfate attack, which could impact their performance. Despite this, research on the resistance of these devices to sulfate attack is still limited. Therefore, this study focuses on the stacked piezoelectric smart aggregate. Initially, the energy harvesting characteristics of the device under harmonic load and rail-sleeper force were tested. Subsequently, a 121-day experiment was conducted in a sodium sulfate solution to simulate sulfate attack, and the energy harvesting characteristics and load-bearing capacity of the device were assessed after the sulfate attack. The results indicate that stacked piezoelectric smart aggregates exhibit excellent energy harvesting performance, though they are significantly affected by sulfate attack. Even after the sulfate attack, the devices maintain favorable conductance characteristics and demonstrate strong load-bearing capacity, with all load capacities exceeding 75kN.

To investigate the impact of chord length distribution patterns on the performance of high-specific-speed axial-flow pumps, this study selected three common chord length distribution methods. Taking a high-specific-speed axial-flow pump with a specific speed of approximately 1200 as the benchmark, the study maintained consistent specific speed and disk ratio. Based on an automatic optimization design platform, the study conducted optimization research on the impeller of axial-flow pumps with different chord length distribution patterns and compared their external characteristics and cavitation performance. The research results indicate that, compared with the original design, the impellers optimized with linear chord length distribution and linear cascade density distribution exhibit minor differences in external characteristics. The distribution pattern with reduced chord length at the blade tip can effectively enhance impeller efficiency under design flow rate and high flow rate conditions. In this distribution, the maximum chord length is located near 0.7 times the impeller diameter. However, this distribution also results in a decrease in impeller efficiency under low flow rate conditions, primarily due to increased leakage flow intensity in the blade tip clearance under low flow rates. Furthermore, under low flow rate and design flow rate conditions, the pump designed with the reduced chord length at the blade tip has a larger critical cavitation margin, whereas the opposite is true under high flow rate conditions. Nevertheless, during severe cavitation, the blade surface of the impeller with reduced chord length at the blade tip exhibits a smaller vapor bubble area, which improves pump performance under severe cavitation conditions to some extent. This study reveals the influence of different chord length distribution patterns on the performance of axial-flow pump impellers, and the results can provide reference for the optimization design of similar rotating machinery.

The health monitoring of bridge structures is crucial in ensuring traffic safety, extending service life, and improving operational and maintenance efficiency. However, the existing bridge monitoring methods still require improvements in measurement performance, cost, and efficiency. To address this, research is conducted on the application of a novel non-contact microwave full-field vibration measurement method for lightweight bridge monitoring. The hardware architecture of the microwave full-field vibration measurement system is outlined, along with the sensing principles of full-field multi-target recognition and vibration displacement extraction. Leveraging the advantages of microwave full-field vibration measurement, a lightweight bridge monitoring method is established from three aspects: equipment, sensing, and data. A microwave-based measurement technique for multi-span deflection and multi-cable tension in the full field of the bridge is proposed. A linear slide vibration measurement experiment was conducted under different conditions to verify the effectiveness of microwave full-field vibration measurement in suppressing multi-target coupling interference compared to traditional microwave vibration measurement technology. An outdoor dynamic response test was carried out on a tied-arch bridge, where multi-point deflection changes and cable force distribution of the bridge were measured and analyzed. The results demonstrate that the proposed method can efficiently and accurately measure bridge deflections and cable forces, providing a new technical approach and perspective for lightweight bridge health monitoring. A comparative experiment was conducted between the microwave vibrometer and traditional accelerometer for measuring cable fundamental frequencies, further validating the accuracy of the proposed method.

In order to accelerate the improving speed of vertical bearing capacity of the surface conductor after it is sprayed to the target layer, and shorten its setting time, a vibrating solid pipe process was proposed, and the influence of vibration parameters on the vertical bearing capacity of the pipe in this process was studied. Firstly, based on the analysis of the mechanical process in the process of vibrating solid conduit, the similarity relationship of the simulation test of the vibrating solid conduit system was deduced by using the dimensional analysis method. Secondly, a simulation test platform for the vertical bearing capacity of the conduit was designed and built. The influence law and significance of different vibration frequency and vibration time on the vertical bearing capacity of the pipe were obtained by using the control variable method and the variance analysis method. Finally, a finite element model of the prototype conduit-clay was established, and based on this model, the influence of vibration on the vertical bearing capacity enhancement of the prototype conduit was analyzed. The results of indoor simulation test and finite element numerical simulation both indicate that vibration will accelerate the improvement of the vertical bearing capacity of the conduit. However, there are some deviations between the vibration parameters required for the prototype conduit obtained from simulation experiments and those in practical applications. This is due to the fact that indoor simulation experiments were conducted under a 1g gravity field, which resulted in differences in parameters between the model soil and the prototype deep-water soil. Therefore, this study provides a new idea for accelerating the improvement of the vertical bearing capacity of conduits and has certain engineering value. This study provides new ideas for accelerating the vertical bearing capacity of conduits and has certain engineering value. 

Compared with the chip type ultrasonic motor, the sandwich type ultrasonic motor has the advantages of good vibration characteristics, compact structure, strong environmental adaptability and high fatigue life, so it has been paid more and more attention in the design of ultrasonic motor. In order to make full use of the vibration characteristics of sandwich structure, an embedded annular ultrasonic motor based on in-plane vibration is proposed in this paper. By using the traveling wave generated on the ring stator, the inner and outer driving teeth of the stator can drive the designed flexible rotor on both sides. The flexible rotor can realize the pre-pressure compensation between the stator and the rotor and better fit the stator, so that the contact mode between the stator and the rotor can be changed into cylindrical contact. Changing the phase of the input two-phase voltage signal can realize the motor steering, and the ultrasonic motor can realize two different output modes by changing the fixed mode. In this paper, the overall structure, working principle and structure size design of the ultrasonic motor are introduced. After analyzing the influence of the stator structural parameters on the characteristic frequency, the interference mode separation is realized in the stator operating frequency band, and the simulation analysis of the ring stator is carried out, including the mode analysis, harmonic response analysis and vibration characteristic analysis. Finally, the feasibility and working principle of the proposed ultrasonic motor ring stator are verified by experiments.

During the cutting process with an end mill, energy flow drives material flow. The variation of energy flow dictates the transformation and transfer of material flow, thereby influencing the surface formation during milling. Based on the instantaneous cutting behavior of the milling cutter under vibration, energy composition and transfer conversion relationship was revealed during the cutting process. Instantaneous state parameters of nodes to quantitatively characterize the energy of milling cutters at each node was used. Flow rates, flow potentials, and resistances were employed to describe the flow state of the energy structure. Exergy efficiency was used to analyze the distribution characteristics of useful energy output during the cutting process. Experimental validation was performed using the instantaneous cutting energy efficiency and specific cutting energy of the milling cutter. The results showed that calculated and experimental results of instantaneous cutting energy efficiency, calculated and experimental results of specific cutting energy of the milling cutter exhibited a grey relative correlation coefficient exceeding 0.81, and a relative error of less than 19.9%. The aforementioned models and methods enable the revelation of the dynamic variations in energy flow during the milling process.

In response to the limited vibration reduction performance of single-layer rubber isolation systems for ship power equipment, a particle damping rubber isolation system is proposed by combining particle damping technology and rubber isolators. A coupled simulation method based on multibody dynamics discrete element (MBD-DEM) was proposed to establish a simulation model of a cantilever beam particle damping vibration reduction system, and experimental verification was carried out. The average error between the simulation and experimental results of the equivalent damping ratio was 7.0%. On this basis, a single-layer particle damping isolation system for ship power equipment was established, and the influence of particle filling rate, size, and material parameters on the isolation performance of the isolation system and its energy dissipation characteristics were studied. The research results indicate that a filling rate of 90% has the best vibration isolation effect; The isolation effect improves with the increase of particle size; When the filling particles are tungsten carbide particles, the vibration isolation effect is the best, and the vibration acceleration level at the resonance frequency is reduced by 7.7dB.

Sensitivity analysis of structural vibration modes (eigenvalues and eigenvectors) is widely used in structural vibration control, optimal design and damage identification. At present, the main modal sensitivity algorithms are modal superposition method, Nelson’s method and their improved algorithms. When these algorithms are applied to modal sensitivity analysis of large-scale engineering structures, there is generally a defect of low computational efficiency. In order to save the calculation cost, this paper proposes an improved subspace iteration method of modal sensitivity based on approximate flexibility. Firstly, the calculation problem of modal sensitivity is transformed into the calculation problem of modal eigen-pairs after minor modification of the structure by difference operation. Then, an approximate flexibility calculation formula is proposed to quickly estimate the inverse of the modified stiffness matrix of the structure, which is applied to the subspace iteration process to quickly obtain the modal eigen-pairs after minor modification, and accordingly the corresponding modal sensitivity can be quickly calculated. Two structural models are taken as examples to verify the proposed method. The results show that the calculation accuracy of the proposed method is basically consistent with the existing modal sensitivity algorithm, but the calculation time is greatly reduced. The proposed method is more suitable for vibration modal sensitivity analysis of large-scale engineering structures than the existing methods.

The traditional rectangular floating breakwater has simple structure and convenient installation, but its effect on long wave attenuation is limited; In order to effectively improve the wave attenuation performance of this kind of floating breakwater, a new type of floating breakwater structure with triangular wing plate is proposed in this paper. Firstly, based on the viscous incompressible fluid dynamics theory, the fluid-structure interaction numerical model of floating breakwater was established, and its applicability and feasibility were verified by comparing with the published results; Then, the wave attenuation performance of the new breakwater was numerically analyzed under different wave conditions. The calculation results showed that the wave attenuation performance reached the optimal value when the wing angle is 22.5 °; On this basis, the influence of different box draught on the wave attenuation effect was further analyzed. The analysis results of the vorticity field and velocity field showed that the wave attenuation performance of the floating breakwater with triangular wing plates is significantly better than that of the traditional rectangular floating breakwater because it not only reduces the transmitted waves through the reflection of the wing plates, but also effectively dissipates the incident wave energy through the formation of eddy. The new breakwater structure proposed in this paper can provide some reference for the application of wave attenuation in practical engineering.

Due to the complex downhole environment, the cementing casing system’s response under vibration conditions is very complicated. To reveal the dynamic behavior of the cementing casing system, considering factors such as fluid and centralizer, a dynamic model of the cementing casing system was established firstly. And the vibration characteristics and vibration displacement response of the system were solved by using the separation variable and modal superposition method. On this basis, the correctness of the model was verified by modal tests and vibration response tests. Finally, the influence mechanism of casing string parameters, fluid parameters, and centralizer stiffness on the vibration characteristics and vibration displacement response of the system was studied, and the propagation law of vibration on the casing string was analyzed. The results indicate that the fluid density and casing material parameters have a significant impact on the vibration characteristics. The size parameters of the casing string, damping ratio, and stiffness of the stabilizer have a significant impact on the vibration characteristics and displacement response of the system. On the premise of meeting the requirements of cementing technology, selecting small-diameter thin-walled casing, cement slurry with low viscosity coefficient, and low stiffness stabilizer will be beneficial for improving the amplitude of vibration displacement response. During the cementing operation, the selection of excitation frequency should comprehensively consider the amplitude and distribution of vibration response. The study provides theoretical basis for accurately solving the vibration characteristics of the cementing casing system and the design of vibration cementing equipment parameters.

The bellows vibration absorber has important application value in vibration and noise reduction of oil and gas pipelines. The aperiodic bellows with variable parameters can improve the fatigue life of the vibration absorber to a certain extent while ensuring the vibration reduction performance through structural optimization, but there is still a lack of effective theoretical calculation methods for the mechanical properties of the variable parameter bellows. Aiming at the bellows vibration absorber structure with variable circular radius, the plate-shell model is established, and the stiffness and stress of the bellows is given through the governing equations and connection conditions of the circular plate and circular shell. Then, the accuracy of the plate -shell model is verified through the comparison with both of the finite element and literature results. Finally, for the aperiodic bellows structure with variable parameters, the influence of the circular radius of bellows on the stress is analyzed. The research results show that the larger the radius of the circular shell, the smaller the total normal stress caused by the membrane internal force and bending moment in the meridian plane, which is beneficial to improve the fatigue life of the vibration absorber. The relevant research results of this research can provide effective theoretical supporting for the structural design and optimization of the bellows vibration absorber with variable parameters.

Runway roughness is a critical excitation factor during aircraft taxiing, significantly impacting runway service life and the safety of ground operations. To elucidate the mechanism by which roughness excitation influences the dynamic response of the aircraft-runway system, a three-dimensional whole aircraft model considering spatial vibrations and a dual-layer runway structure model incorporating a semi-rigid base were established in this study.  both three-dimensional and two-dimensional runway roughness using measured and simulated data were reconstructed. A novel explicit integration method was introduced to solve and analyze the time-domain responses of the aircraft-runway coupled system, characterized by multiple parameters and high degrees of freedom. The results indicate that under the excitation of measured three-dimensional roughness, the vibration response at the aircraft's forward section is significantly greater than that near its center of gravity. The transverse effect of roughness excitation causes a disparity in the dynamic loads on the left and right main landing gears. Besides vertical vibrations, pitch and roll motions also substantially affect the aircraft's dynamic response. Compared to two-dimensional roughness, the dynamic load coefficient under three-dimensional roughness excitation is 1.20 to 1.52 times that under two-dimensional conditions, and the longitudinal dynamic strain at the bottom layer under three-dimensional roughness excitation is 1.20 to 1.49 times that under two-dimensional conditions. Therefore, the analysis and evaluation of actual runway roughness should shift from two-dimensional to three-dimensional assessments. When runway roughness deteriorates to a poor level according to current standards, the aircraft's vibration response increases exponentially. It is recommended that runway roughness levels be maintained at a medium or higher standard. The degree of runway roughness significantly affects both longitudinal strain and vertical displacement of the pavement, which should be considered in the analysis and design of pavement structures.

Blade tip timing (BTT) is an effective technique for non-contact vibration measurement of rotor blades of aeroengine, but its sampling pattern leads to the highly undersampled property of the sampled signals. Anti-aliasing spectrum analysis is required to extract the key indicator of the rotor blade, which is natural frequency. The improved multiple signal classification (MUSIC) method using the forward smoothing strategy can achieve anti-aliasing but cannot fully utilize the advantages of the smoothing method. Therefore, this paper proposes a forward-backward smoothing MUSIC method for BTT signal processing. By establishing the symmetrical placement conditions of the sensor, the forward-backward smoothing is used to replace the forward smoothing to obtain a more accurate autocorrelation matrix estimate, thereby improving the blade natural frequency estimation performance. Through simulation and experiments, it is verified that the aliasing and noise suppression capabilities of the forward-backward smoothing MUSIC method are improved under the same sample number, algorithm parameters, etc. 

With the great improvement of the performance of modern aircraft , the aviation airborne integrated equipment rack has to withstand a very harsh mechanical environment under the condition of strict weight restriction, aiming at the fatigue failure of a rigid connection equipment rack in the durable vibration test. combined with the actual anti-vibration urgent needs to carry out vibration isolation design research, how to reasonably select the vibration isolator is the most core key technology. This paper systematically expounds the complete process and process of vibration isolation design based on theoretical calculation, simulation analysis and experimental verification, which is different from the previous empirical design, and establishes a forward vibration isolation design method based on the active requirements of the product itself for the performance parameters of the vibration isolator. the target frequency of the vibration isolation system and the key parameters of the vibration isolator are theoretically analyzed and calculated, and the selection of the vibration isolator is determined. Further simulation analysis and experimental verification are carried out. The results show that according to this vibration isolation design method, the vibration isolation effect of vibration isolator selection is obvious, the overall vibration isolation efficiency is more than 55%, the theoretical calculation and simulation analysis are accurate, and the test passes smoothly. It verifies the rationality and effectiveness of the forward vibration isolation design flow in a strong vibration environment, and has important practical significance and broad application prospects.

Carbon fiber-reinforced polymer (CFRP) rebars can promote the life-cycle performance of concrete structures due to their high strength and corrosion resistance. However, the application of CFRP rebars into concrete structures is limited because their linear-elastic behavior deviates from the traditional ductile seismic design. To investigate the seismic performance of CFRP-reinforced concrete (CFRP-RC) columns, four CFRP-RC columns, one RC column, and one CFRP/steel hybrid RC column were tested under quasi-static loads, with parameters including longitudinal reinforcement ratio, stirrup spacing, and axial compression ratio. Crack patterns, bearing capacity, residual deformation, and energy dissipation were investigated. Results indicated that the RC column was controlled by rebar buckling and core concrete crushing, while the CFRP-RC columns were controlled by the brittle fracture of the CFRP rebars, which were easily sheared due to the lateral resistance of stirrups against the compressive CFRP rebars. CFRP-RC columns exhibited high strength with a drift larger than 5%, small residual drift, and weak energy dissipation, exhibiting distinct advantages and disadvantages: “strong bearing capacity and low damage” but “low ductility and brittle failure”. The test formed a key dataset to provide a basis for seismic design and application of CFRP-RC structures.

Both ground motion and structure have multidimensional characteristics, and the structure will not only generate translational motion but also torsion under seismic action, and the traditional tuned mass dampers generally can only control the translational motion of the structure, but not the torsional response of the structure effectively. Therefore, a new type of multidimensional eddy current tuned mass dampers (MEC-TMD) is proposed in this paper, which can simultaneously control the translational and torsional responses of the structure. On the basis of analyzing the intrinsic structural form of the dampers and deriving the formula for calculating the damping force, a typical eccentric structure is taken as the research object, and the damping control efficiency of the MEC-TMD is compared with that of the traditional TMD by using finite element numerical simulation method considering the effects of ground vibration at different sites, so as to preliminarily validate the effectiveness of the MEC-TMD proposed in this paper. The results show that the proposed MEC-TMD has good control effect on both translational and torsional response of the structure under seismic action, and the development of this damper has positive significance and application value for the effective control of torsional response of the structure. 

In order to accurately and reliably identify short-wave irregularities on high-speed railway tracks, an improved Hilbert-Huang algorithm is proposed to solve the problem of modal aliasing and endpoint effects in the Hilbert-Huang transform method. The modified Akima method is used to optimize the piecewise cubic Hermite interpolation method, and re-weight the interval of the constructed AM and FM signal, which effectively avoids the overshoot and undershoot problems of the envelope curve and maintains smoothness; based on the local characteristic scale extension method of the boundary, the constructed composite signal is processed to suppress divergence in endpoint effects. The improved Hilbert-Huang algorithm is compared with EEMD algorithm. The results show that the improved Hilbert-Huang algorithm has better signal separation effect. Based on the improved Hilbert-Huang algorithm, the measured signal of short-wave irregularities on high-speed railway tracks is decomposed, and the marginal spectrum and Hilbert spectrum are used to analyze the IMF component. The obtained wavelength and position information are in good agreement with the actual measurement results. 

In order to ensure the safety of wind resistance braking of next-generation high-speed trains equipped with wind resistance braking devices in harsh wind environments, according to the existing research results on the design of wind resistance braking machine, working attitude and system layout, a certain type of standard locomotive set as a reference was equipped with 8 sets of "butterfly" wind resistance braking devices, and the aerodynamic model of the train and the dynamic model of vehicle track system under the effect of crosswind were established respectively. The dynamic behavior of the high-speed train assembled with wind-resistant braking device was simulated and calculated under wind load, and the safe speed threshold of wind-resistant braking was determined through the evaluation of the safety indexes of train operation. The results show that under the action of crosswind, the stability and safety of high-speed train operation with wind resistance braking device is mainly controlled by the head car, when running at 200~400 km/h, the aerodynamic coefficient is in quadratic nonlinear relationship with 0~30 m/s crosswind, with the increase of crosswind strength, the growth rate of drag coefficient decreases gradually, and the growth rate of lateral force coefficient and lift coefficient increase gradually; the rate of wheel weight load reduction is the controlling indicators of 200~400 km/h wind resistance braking safety assessment, in the wind speed of 10~30 m/s range, There is an approximately linear correlation between wheel load shedding rate and the operating speed; Referring to national technical standards and relevant test data, the wind resistance braking safety speed zone calculated by simulation effectively falls within the train operating safety zone, When operating in 20 m/s cross-wind environment, the safe speed of wind resistance braking does not exceed 186.1 km/h; in 15 m/s crosswind environment, the safe speed of wind resistance braking does not exceed 324.6 km/h; in 10 m/s crosswind environment, the safe speed of wind resistance braking does not exceed 370.1 km/h. The crosswind wind speed and the safe speed area of wind resistance braking derived from this paper can provide technical reference for the optimized design and the operation and safety control of the wind resistance braking device. 

Blade tip timing (BTT) technology is currently the trend in condition monitoring and fault diagnosis of rotating blades in major equipment. Nonetheless, the BTT technique, with characteristics of non-uniformity and under-sampling, presents challenges in identifying the blade vibration parameters. To address the issue of asynchronous vibration parameter identification in rotating blades, this paper initially utilizes the fast Fourier transform (FFT) algorithm to extract the non-integer engine order and the amplitude of blade asynchronous vibration frequency. Subsequently, an improved multiple signal classification (MUSIC) algorithm is employed to propose an integer engine order search strategy for blade asynchronous vibration frequency based on MUSIC algorithm (EOS-MUSIC). Finally, this study proposes an asynchronous vibration parameter identification algorithm of rotating blades based on the EOS-MUSIC algorithm and the FFT algorithm. The MATLAB software was utilized for simulating the signals of blade asynchronous vibration, and the feasibility and reliability of the proposed algorithm were validated by comparison with the existing MUSIC algorithm. Experiments on impeller blade vibration were conducted on a large-scale centrifugal compressor test rig. The absolute error of the frequency identification was 3.36Hz, and the relative error was only 0.53% compared with the results of the strain gauge method. Based on the preprocessing of FFT algorithm, this paper extracts the blade asynchronous vibration parameters by engine order search, which overcomes the problems of long calculation period and severe identification errors of the existing MUSIC algorithm. This study provides theoretical support for the asynchronous vibration parameters identification of rotating blades. 

To address the issue of insufficient historical data for newly installed wind turbines and the significant data distribution differences between various turbines, this paper proposes an abnormal status detection method for wind turbines that integrates a self-attention mechanism with domain adaptation networks. Firstly, an encoder-decoder structure is employed to perform feature reconstruction from both source and target domain turbines in order to capture latent wind power patterns and domain-specific information. Then, a self-attention module is designed to extract cross-domain shared features through adversarial learning with a domain discriminator, and domain-specific information is automatically weighted based on the matching degree of cross-domain shared features, enabling dynamic feature reconstruction and thereby improving the model's adaptability to changes in the data distribution across different units. Finally, the reconstruction error is calculated as the abnormal score for anomaly detection. Results from actual wind turbine operation data demonstrate that this method can efficiently identify abnormal data with limited historical data and significantly improve detection accuracy compared to other deep learning and deep transfer learning methods.

To address the challenges of fault type coupling and data acquisition for rolling bearings in complex environments, researchers proposed a bearing compound fault diagnosis model based on semantic fusion zero sample learning. During training, a Semantic Autoencoder (SAE) establishes a link between visual space and semantic space, mitigating the domain migration issue. In testing, the model identifies unknown faults through similarity calculations. This approach introduces a semantic fusion encoding strategy, transforming the vibration amplitude and frequency characteristics of bearing faults into distinct semantic representations. This strategy retains extensive physical information and enhances semantic differences among fault types by fusing this data, thus significantly boosting the accuracy of composite fault classification. Moreover, the integration of a Convolutional Neural Network (CNN) with Adaptive Margin Center Loss (AMCL) optimizes fault feature extraction, capturing compound fault characteristics of bearings more accurately. Experimental results indicate an accuracy of 87.96%, surpassing that of the comparison model.

Given the issues of imbalanced attention mechanisms, conservative pooling strategies, and the loss function's inability to comprehensively consider information from all classes leads to the learned features being relatively scattered in the FasterVit network, a rolling bearing fault diagnosis method based on the CFasterVit-TFAM and COS-UMAP models is proposed. The model consists of the FasterVit-TFAM network, the COS-UMAP dimensionality reduction algorithm, and the activation function CMSD-Softmax. Firstly, a new attention mechanism TFAM is proposed and combined with the FasterVit network to improve the balance and representation ability of information attention in the FasterVit network. Secondly, the COS-UMAP dimensionality reduction algorithm is used to replace the last pooling operation before the fully connected layer of the FasterVit network, effectively filtering and retaining important features in multidimensional data. Finally, replacing the cross-entropy loss function in the Softmax activation function with the mean standard deviation loss function allows for a more comprehensive learning of features and improves the model's generalization. The XJTU rolling bearing mixed fault experiment results show that the diagnostic accuracy of the TFAM attention mechanism is increased by 8% compared to other attention mechanisms, and the diagnostic accuracy of the COS-UMAP is increased by 15.8% compared to other dimensionality reduction algorithms. The diagnostic accuracy of the CMSD is increased by 0.5% compared to the cross entropy loss function. The proposed model achieves a recognition accuracy of 99.6% for fault samples, which is 1.4% higher than that of FasterVit and 7.8% higher than that of other network models. The simulation results of the rolling bearing dataset from Southeast University show that the proposed model achieves a recognition rate of 98.6% for fault samples, which is 2.2% higher than that of FasterVit. The average training time per round is reduced by 16.92 seconds, which is a maximum improvement of 12.2% compared to other network models, effectively improving the accuracy and generalization performance of the rolling bearing fault diagnosis model.

Combined with the advantages of the reconstructed gear test bench to obtain the working tooth surface image of the gear online, the method of gear pitting identification based on machine vision is discussed, and the experimental research is carried out. In view of the scarcity of gear pitting data, the Deep Convolutional Generative Adversarial Network (DCGAN) model is used to realize the diversification and high-quality augmentation of the gear pitting samples. Based on the previous research of ourselves, the effective working tooth surface area of the gear is extracted, and the tooth surface tilt correction as well as distortion correction are realized. By introducing the efficient channel attention, the U2-Net model is improved, and the accurate segmentation of the interested region of the gear pitting image is realized. On this basis, by counting the historical pitting rate of gears, a gear pitting identification model based on image signals is constructed, and the gear pitting identification is realized. The results show that the gear pitting identification method based on machine vision technology is feasible, and the recognition accuracy based on DCGAN and U2-Net models can reach 93.56%. The research maybe provides a more direct and reliable method for gear pitting identification, and have certain reference value for the condition monitoring of mechanical equipment.

Degradation between components in multi-component systems may have different degrees of mutual influence, which makes multi-component systems often have multi-stage degradation characteristics. In view of the above problems, this paper considers the influence of the interaction between the components of the multi-component system on the degradation mode, and proposes a multi-stage system degradation modeling and remaining useful life prediction method based on Wiener process with continuous degradation bidirectional random correlation effect. Firstly, a multi-stage Wiener process degradation model considering the influence of bidirectional random correlation is established by using the mutation point detection to describe the influence of random interaction between components on the degradation process of multi-component system. Secondly, to reflect the degradation heterogeneity of each component, and consider that the degradation rate of the component is composed of two parts: its own inherent degradation rate and the degradation rate generated by its related components. The drift coefficient and diffusion coefficient of each stage of the system are defined as random parameters, and the expectation maximization algorithm is used to estimate the unknown parameters. Finally, the Bayesian algorithm is used to update the posterior parameter distribution, predict the location of the mutation point, and derive the expression of the remaining life of the multi-stage degradation system considering the random correlation of degradation among the components according to the first passage time. The effectiveness of the method is verified by numerical simulation and C-MAPSS dataset.

Precision optical instruments in aircraft and ships face increasingly stringent requirements for the vibration environment, and active control methods via the Stewart platform have attracted extensive attention. Firstly, the development of Stewart active vibration isolation platform at home and abroad was investigated, and the main performance indicators such as payload (Kg), active bandwidth (Hz) and maximum amplitude attenuation (dB) were summarized. Secondly, the key technologies on Stewart active vibration isolation platform, including Stewart platform configuration, isotropic and dynamic stability, coupling factors and decoupling methods, dynamic modeling methods, nonlinear and hysteresis phenomena of smart material actuators, and active control algorithms, were summarized in detail. The study discussed how the main performance indicators were enhanced by these key technologies and identified unresolved issues； then, the advantages of multi-channel coupled adaptive algorithm using Stewart isolation platform in complex and time-varying vibration environment were summarized. Finally, the further development of Stewart active vibration isolation platforms in precision optical instruments was prospected.