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.

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 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.

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.

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.

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.

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 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.

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.

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 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. 

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.

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.

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.

In the field of earthquake engineering, building seismic resilience assessment is a research focus, which holds great significance in guiding designers to enhance the level of structural seismic design and helping managers raise awareness of structural disaster prevention. This study focuses on an existing frame structure located in the 8-degree seismic region (0.30 g). Three perspectives (repair cost, repair time, and personnel loss) were considered while evaluating the seismic resilience of the structure before and after reinforcement based on GB/T 38591-2020 "Standard for seismic resilience assessment of buildings". Furthermore, the economic benefits of the seismic strengthening program by considering the yield rate on reinforcement. The results demonstrate that the employment of viscous dampers and BRB effectively controls the dynamic response of the structure. Notably, there is a maximum drop of 76.9% and 29.8% in the story drift ratio and mean acceleration, respectively. Repair time and personnel loss are two important perspectives that affect the level of seismic resilience under rare earthquakes. The implemented seismic strengthening program greatly increases the structure's seismic resilience, even if the level of seismic resilience is still one star both before and after strengthening. These research findings serve as a valuable reference for the evaluation and improvement of seismic resilience in existing buildings.

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. 

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.

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.

In the actual transportation of large power transformer equipment, different degrees of damage often occur under the external action such as wind and wave, so it is necessary to study the dynamic response of the equipment under the most unfavorable environment and discuss the safety of the transportation equipment.Therefore, taking an offshore DC converter valve tower as the research object, the dynamic response of the valve in sea transportation is studied based on its own vibration characteristics. In view of the complex and varied marine transportation environment, many research conditions, and long calculation period of time-frequency analysis, a pseudo-static analysis method is proposed on the basis of power spectrum analysis. The results show that when the ratio of wave frequency to fundamental frequency is less than 0.15, the structural stress response can be obtained directly by pseudo-static method, and the displacement response needs to be amplified by 1.3 times. When the frequency ratio is close to 1, the amplification correction factor of the structural response is linearly correlated with the frequency ratio. The above research provides a basis for the safety assessment and reinforcement of the equipment in marine transportation.

After the cased charge explodes, damage elements such as shock waves and fragments will be generated. Improving the calculation accuracy of damage element power parameters is of great significance for research on weapon destructive effects and engineering protection. In order to improve the calculation accuracy of power parameters of fragments and shock waves, a more accurate calculation formula for the initial velocity of fragment was proposed based on the modified energy conservation equation by analyzing the distribution law of cased charge explosion energy. The equivalent charge mass conversion method was used to calculate the equivalent charge mass of the shock waves generated by the cased charge explosion, by analyzing the formation process of the initial shock wave of the cased charge, a theoretical calculation model of the shock wave power parameters was established, and the scientificity and reliability of the calculation model were verified through experimental data. Through the established theoretical model, the calculation formula for the distance from the detonation source when the two damage elements overlap is derived, and the influencing factors are quantitatively analyzed. Research shows that the accuracy of the calculation method in this paper is better than the traditional calculation method of damage element power parameters, the errors in initial velocity of fragment, the overpressure peak value of shock waves, the arrival time of wave front and the experiment are 3%, 4.9% and 1.1%, respectively. The movement distance when the fragment barrage overlaps with the shock wave front is directly proportional to the explosive energy (detonation heat) and inversely proportional to the casing thickness (charge mass ratio).

Harmonic drive is a transmission mechanism that relies on controllable deformation produced by flexible components, which are subjected to continuous alternating stress. As a result, the risk of failure is significantly higher than that of conventional transmission mechanisms. Changes on the fault location, kinematic relationship, and bearing area may cause interval distribution and periodic transformation of fault characteristic frequency. The running of harmonic drive based on the close coordination of several rotational components in narrow space, the transmission of single fault may cause the appearance of fault characteristics of multiple faults, the fault location is difficult. Therefore, an equivalent method is proposed to clarify the time-varying patterns of flexible bearing fault frequency by equating the kinematic relationship of continuous transient with that of conventional bearing. The calculation procedure of fault characteristic frequency for circular spline, flex-spline, flexible bearing, and cross roller bearing is presented. A fault simulation experiment is conducted to validate the theoretical analysis, fault characteristics for multiple faults are provided. The results show that the experiment results are consistent with the theoretical analysis, and the fault characteristic frequency can be obtained based on the proposed method.

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.

Due to the low stiffness of serial industrial robots, the robotic milling process is prone to chatter due to the improper selection of processing parameters or robot pose, which will reduce the surface quality of the workpiece and damage the robot equipment.In order to predict the chatter stability of robotic milling, the variation of robot end stiffness along with the spatial pose was studied by constructing the stiffness model of the robot.The dynamic model of the spindle system was constructed, then the influence of the speed effect on the dynamic characteristics of the tool tip was studied, and the mapping function between the spindle speed and the natural frequency of the tool tip was constructed by data fitting method.A robotic milling dynamic model considering the coupling effects between the robot and spindle system was proposed.The damping ratio and modal mass at the tool tip of the robotic milling system were obtained by hammer experiments, and the stability lobe diagram of the robotic milling system considering different factors was obtained.The variation law of milling chatter stability under the coupling effects of the robot-spindle system was revealed and verified by experiments.The results show that the stability lobe diagram obtained when considering the robot-spindle system coupling effects is more consistent with the actual milling state, which can effectively improve the prediction accuracy of robotic milling chatter stability.

During the high-efficiency milling, under the action of high-frequency and intermittent cutting loads, the contact angle and posture between the milling cutter and the workpiece change frequently, making the relative friction and stress waves generated at the tool-workpiece interface dynamically change, leading to difficulty in accurately identifying and predicting friction damage and wear life during high-efficiency milling. A dynamic contact relationship model between the milling cutter and the workpiece under the influence of cutter error and milling vibration was constructed. The frictional force on the flank face of the milling cutter tooth was solved. Based on the one-dimensional string theory, a solution method for calculating the propagation distance, change rate and attenuation rate of frictional stress wave on the flank face of the cutter tooth was proposed. The results show that the stress wave peak value and change rate are greater near the cutting edge. The attenuation process of frictional stress waves in high-efficiency milling cutters shows biased exponential attenuation. The correlation verification results of the stress wave calculation method show that the energy of the feature points on the flank face of the cutter teeth has a correlation of more than 0.8 with the experimental accumulated wear depth, verifying the accuracy of the model.

A novel fault diagnosis method is proposed, which combines a multi-scale convolutional neural network (MSCNN) with a bi-directional long short-term memory network (BiLSTM) using an attention mechanism. This approach addresses the issue of feature extraction in traditional fault diagnosis methods, which often result in limited representation of fault information and the inability to deeply explore fault characteristics under complex working conditions. Firstly, the method employs pooling layers and convolutional kernels of different sizes to capture multi-scale features from vibration signals. Then, a multi-head self-attention mechanism (MHSA) is introduced to automatically assign different weights to different parts of the feature sequence, further enhancing the ability to represent features. Additionally, the BiLSTM structure is used to extract the internal relationships between features before and after, enabling the progressive transmission of information. Finally, the maximum-kernel mean discrepancy (MK-MMD) is utilized to reduce the distribution differences between the source and target domains at various layers of the pre-trained model, and a small amount of labeled target domain data is used to further train the model. The experimental results show that the proposed method has an average accuracy of 98.43% and 97.66% on the JNU and PU open bearing datasets, respectively, and the method also shows a very high accuracy and fast convergence speed on the bearing fault dataset (CME) made by Chongqing Changjiang Bearing Co. and provides a practical basis for the effective diagnosis of vibration rotating component faults. 

The wheel polygon and rail corrugation as typical wheel-rail periodic wear of high-speed railway, aggravate wheel-rail vibration and affect driving safety. In order to explore the interaction under extreme conditions when wheel polygon and rail corrugation coexist, firstly, considering wheel-rail periodic wear of high-speed railway, the finite element model of wheel-rail system is established, and the frequency-dependent wheel-rail periodic wear competition mechanism is explored. Then, from the perspective of frequency-dependent wheel-rail periodic wears, the wheel-rail friction coupling vibration characteristics of wheel-rail periodic wears in the same/different phase contact are compared. Finally, from the perspective of frequency-independent wheel-rail periodic wears, the wheel-rail friction coupling vibration characteristics of the interaction of wheel-rail periodic wear are studied. Results show that under the extreme conditions of the coexistence of frequency-dependent wheel polygon and rail corrugation, the wheel-rail system is the most unstable. The instability of the wheel-rail system will be aggravated when the frequency-dependent wheel-rail periodic wear are in the same phase, and with the increase of wave depth, the difference in wheel-rail friction coupling vibration between the same phase and different phase will be increased. the closer the frequency-independent periodic wear frequency of wheel-rail is, the more obvious the influence on the stability of wheel-rail system is.

Blades are typical thin-walled curved components that operate in harsh environments. Under the action of alternating stress, fatigue fracture occurs after a certain number of cycles, which seriously affects the reliability and durability of the engine. In order to study the fatigue performance of blades under vibration, blades were processed with different process parameters, and their surface roughness, residual stress, and microhardness were tested. Vibration fatigue tests and fatigue fracture analysis of the blades were also performed. The results show that the dangerous position of the TC17 titanium alloy blade is on the back of the blade, 48.1mm from the blade tip and 26.9mm from the air inlet edge; the surface roughness of the blade is 0.373μm, the surface stress concentration coefficient is 1.014, the surface residual stress is -319.38MPa, and the surface microhardness is 412.53HV. The highest fatigue life of 8.91×105 cycles was obtained when the surface residual stress was considered. The residual stress has the most significant effect on the fatigue life of the blade, followed by the surface stress concentration coefficient, and finally the microhardness. The fatigue failure mode of the milled blade is a surface single-source start, and the fatigue source area has obvious radiation characteristics, the crack extension area has fatigue stripes and secondary cracks, and the instantaneous fracture area has toughness characteristics, which belongs to toughness fracture.

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 current sound insulation evaluation standard refers to the traffic noise data measured in northern Europe in the 1980s as the basis for the spectrum correction for traffic noise. For the purpose of exploring whether Ctr correction is still appropriate in evaluating current urban road traffic noise and more precisely evaluating the sound insulation performance of building components that are affected by traffic noise. A variety of urban traffic road noise is monitored in this paper, a new set of traffic noise spectrum correction curves CA is proposed in accordance with the measurements, weighted sound insulation is computed for 11 common exterior window structures at different frequency frequencies, and differences in sound pressure level spectrums with various spectrum corrections are analyzed and compared. Results of the study indicate that road traffic noise spectrums in different cities possess similar characteristics such as high low-frequency sound pressure levels, stable medium frequency sounds, and low high-frequency sounds. In today's urban environment, the low-frequency energy of road traffic noise is much lower than the frequency spectrum referenced by Ctr, and its energy spectrum distribution is closer to C100-3150. After comparing and analyzing the spectrum correction of traffic noise in 11 groups of external windows with the current standard, CA falls within the range between C and Ctr reference spectra. Considering that the correlation coefficient between CA and the C and Ctr reference spectra is greater than 0.9 and higher than the correlation coefficient R2 between C and Ctr, CA has a greater potential for application and representativeness for analyzing the urban traffic noise spectrum. Consequently, the research results can provide data references for residential sound insulation and noise reduction projects affected by urban traffic noise.

The relevant regulations for the amplification effect of ground motion on irregular terrain were all based on isolated terrain. However, mountainous topography often existed in the form of mountains, and adjacent topography would affect the earthquake wave propagation and change the law of ground motion. Therefore, it was of great significance to study the ground motion amplification factor of non-isolated terrain for the seismic design of mountain buildings and improving the accuracy of post-earthquake disaster assessment. In this paper, the typical topographic amplification effect occurred in the unfavorable section of Moxi platform during the Luding MS6.8 earthquake was described. Then, the influence of complex topography (ridge and canyon) on the amplification factor of ground motion of the platform was deeply explored by simulation. The spatial distribution of amplification factor, Fourier spectrum of acceleration and amplitude ratio were quantitatively studied, and the motion rules of complex topographic on platform surface were obtained through a large number of analyses. The results showed that the regulations in “Seismic Code” underestimated the topographic effect of the platform in some cases, and the suggestive value of the amplification factor was difficult to ensure the safety of the structure. Thus, it needed to be adjusted and refined. In addition, the adjacent ridges and canyons had obvious effects on the platform surface and should not be ignored. Therefore, it was suggested that the relevant specifications should increase the adjustment coefficient to consider the interaction between adjacent landforms.

In the process of lifting large span steel structures, node displacements and structural deformations are related to the safety and quality of the lifting construction. For the traditional contact monitoring methods, which are time-consuming, labour-intensive and expensive to maintain, a non-contact monitoring method is proposed with a drone as the carrier. Firstly, to address the problem of limited proximity of the UAV during the lifting of large-span steel structures, the Harris image stitching algorithm is used for panoramic stitching and combined with image weighting fusion to eliminate unfavourable cursors and stitching seams in the image stitching and achieve seamless stitching of overall, high-precision images of large-span structures. Secondly, the YOLOX vision algorithm incorporating the CBAM (Convolutional Block Attention Module) dual-channel attention mechanism is adopted to solve the problem of small target image recognition, coordinate extraction and displacement monitoring with different pixel areas under complex backgrounds. Finally, the four different testing models were compared and evaluated. The experimental results show that the average accuracy and confidence of the YOLOX detection model with CBAM attention mechanism are better than the other three network models, and the errors of the visually identified displacement information and the Leica total station are within sub-millimetre level, which meet the requirements of practical engineering accuracy and achieve small target displacement monitoring in complex backgrounds, with high economic benefits and wide application prospects.

Carbon Fiber Reinforced Plastic (CFRP) laminated structures are often subjected to the impact of foreign objects in high-impact service environments, which results in a number of unpredictable forms of damage and even uncontrollable damage patterns. In order to ensure the safety and reliability of these structures, the impact response and protection mechanism of carbon fiber composite laminated structures have been studied. Taking the carbon fiber composite laminated structure as the research object, a high-speed impact loading test device is constructed based on a first-stage light air gun, the linkage law between the energy absorption characteristics of the carbon fiber composite laminated structure and the impact energy is explored, the ballistic limit is determined by combining with the ballistic limit equations, and the damage modes under the effect of different impact velocities are clarified. At the same time, the cohesion unit is introduced to carry out numerical simulation research, which proves the damage mode of the cohesion unit between layers of the carbon fiber composite laminated structure, and reveals its damage mechanism under the high-speed impact loading environment. The results provide theoretical basis for the reverse design of composite laminated structures suitable for high-speed impact loading environment.

As one of the most common faults in gear transmission, tooth pitting will directly affect the time-varying meshing stiffness (TVMS) of the gear pair, and then leads to the change of dynamic characteristics of system. Thus, each pitting shape is considered as approximately a part of ellipse cylinder, and three damage levels are defined based on the position and number of pits: slight pitting, moderate pitting and severe pitting. The TVMS of perfect gear and that of gear with different pitting severity levels are calculated, and the effect of the position and size of pits on TVMS is discussed by use of the potential energy method. The fault dynamic response of one-stage spur gear transmission is studied and the results are qualitatively verified by the Drivetrain Dynamics Simulator (DDS). The results show that the model presented in this study can better match with the actual situation. With the increase of positional parameter, the pitted area moves gradually from the base circle to the top land. The longer the length of the major axis is, the more obvious the reduction of the TVMS in the pitted area is. While with the change of length of the minor axis, the reduction of the TVMS caused by different levels of pitting damages is basically identical in the same range of the angular displacement of the driving gear. The established model is capable of predicting the TVMS and vibration characteristics of a pitted gear system, and the corresponding vibration analysis results could provide theoretical reference for the detection and diagnosis of tooth pitting.

When tape springs are applied in the form of winding and stretching in spatially deployable structures, the problem of loosening often occurs.Here, a multi-tape spring winding and loosening model was proposed, in which a loosened winding segment was divided into an external Archimedean spiral expansion zone and an internal semi-circular arc transition zone, and a strain energy analytical model was established.According to the principle of minimum potential energy, stable loosening inner diameter and stable loosening form were solved, and critical center body radius, stable tip force and critical tip force were derived.A finite element model for multi-tape spring winding and loosening was established using the software ABAQUS, and the numerical analysis results of stable loosening inner diameter, stable loosening form, critical center body radius and critical tip force were compared with the theoretical model calculation results.Tests were conducted to verify stable loosening form and stable loosening inner diameter, and prove the correctness of the theoretical model.

Combined with theoretical calculation, finite element simulation and experimental measurement, the optimization design method of acoustic maze structure based on acoustic black hole is studied, and a small-size and broadband sound absorption structure with 5.01 and 7.75octaves is given.First, based on the transfer matrix method, the mathematical model of acoustic black hole is established, the reflection coefficient of acoustic black hole is calculated, and the theoretical calculation results are compared with the finite element simulation results.Then, based on the admittance variation law of the acoustic black hole, the single and double side branch acoustic maze structures are designed. By optimizing the design, the matching of the maze structure and the admittance of the acoustic black hole is realized.Finally, based on the matching results of the admittance of the acoustic maze structure, the simulated annealing algorithm is used to construct the optimization model, and the small-sized acoustic maze structure with broadband sound absorption is obtained, and the 3D sample is printed for experimental verification.The results show that the double side branch pipe acoustic maze is used to replace the ring cavity in the acoustic black hole pipeline. After optimization, the admittance of the side branch pipe maze and the acoustic black hole can achieve perfect matching, and the small size design of the structure can be realized under the premise of maintaining the sound absorption performance. The effective sound absorption bandwidth of the optimized structure is 13.36 times that before optimization, and the octavesare3.94 times those before optimization.

In order to control the low-frequency noise in the cabin of high-speed flying train, a flexible acoustic metamaterial based on Helmholtz resonance effect is proposed. Theoretical analysis was conducted on the noise reduction mechanism of the Helmholtz cavity, and the noise reduction characteristics of the unit cavity structure and array cavity structure were compared and analyzed using COMSOL software. The acoustic performance of flexible metamaterial was analyzed through the acoustic structure coupling module. The variation of the resonant frequency of the flexible acoustic metamaterial is studied parametrically, and analyzed the noise reduction characteristics of flexible acoustic metamaterials under different degrees of deformation. The casting process of divided draft was proposed to prepare flexible acoustic metamaterial samples, and the transfer loss of samples was measured using the four sensor testing principle. The research results show that there is a transmission loss peak at 300Hz in the test and simulation results of flexible acoustic Metamaterial, which shows the Helmholtz resonance frequency lower than the theoretical model and good low-frequency noise control effect. At the same time, flexible materials can avoid the impact of inertia on the installation environment, which is suitable for curved surface environment, and has good application prospects in the engineering field.

As an important source of unmanned aerial vehicle noise, reducing the aerodynamic noise of rotor is of great significance to improve public's acceptance of unmanned aerial vehicle. In view of this, a rotor design scheme with wavy-shaped blade tip structure was proposed. This scheme only used a specific wave line type as the wire for lofting design at the blade tip of the rotor. At the same time, the three characteristics of wavy-shaped leading edge, wavy-shaped trailing edge and wavy surface structure were coupled. This scheme can reduce the noise and retain the aerodynamic performance to the greatest extent. Then, the influence of wavy blade tip structure on rotor aerodynamic performance and aerodynamic noise were analyzed with computational fluid dynamics simulation and experimental research. The noise reduction mechanism was revealed, and the parameter optimization design of wavy tip was carried out. The simulation and experimental results showed that the rotor with wavy tip structure still has good aerodynamic performance. In terms of acoustic performance, the wavy blade tip structure reduced the broadband noise in the middle and high frequency ranges of the rotor. The rotor with waveform parameter N=8 has the best noise reduction effect, and the noise reduction was significant near the downwash flow of the rotor. The total sound pressure level was 1.5~4 dB lower than that of the Base rotor.

Holo-Hilbert spectral analysis (HHSA) is a new signal processing technique that utilizes double-layer empirical mode decomposition (EMD) to reflect the cross scale coupling relationships in nonlinear and non-stationary vibration signals. However, there is a serious mode mixing problem in the signal decomposition process of EMD, which leads to inaccurate Instantaneous phase and frequency estimation and affects the analysis accuracy of HHSA. Based on this, an ensemble Holo-Hilbert spectral analysis (EHHSA) method is proposed. In the analysis process based on EHHSA, an amplitude modulation marginal spectrum analysis method that can reveal modulation characteristics was defined by integrating carrier variables. Finally, the analysis of simulation and measured data on rolling bearings shows that the proposed EHHSA method and amplitude modulation marginal spectrum have stronger feature extraction performance and noise robustness compared to traditional spectral analysis methods.