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.

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. 

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.

In actual industrial production, different operating conditions lead to variations in data distribution, posing a challenge for bearing fault diagnosis under different working conditions. To address this issue, a fault diagnosis method based on multi-adversarial and balanced distribution adaptation was proposed. Firstly, an improved residual network was used to directly extract domain-invariant features from the original vibration signals, enhancing feature extraction efficiency while preserving rich fault feature information. Secondly, a domain adaptation method combining correlation alignment and multi-adversarial domain adaptation was proposed, which can simultaneously align marginal distribution and conditional distribution of source domain and target domain to minimize data distribution differences between domains.Thirdly, the balanced distribution adaptation method was improved with designing a balance factor to allocate weights to the marginal distribution and conditional distribution in the adaptation process, so as to enhance cross-domain fault diagnosis effect. Finally, the effectiveness of the proposed method was validated using publicly available bearing fault datasets. Experimental results show that compared to popular domain adaptation methods, the proposed method achieves higher fault diagnosis accuracy, showing practical application value in bearing fault diagnosis tasks under different working conditions.

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.

Aiming at the problem of a single vibration signal containing fault information being easily hidden and the weak diagnostic ability of a single deep learning model leading to low accuracy in bearing fault diagnosis, a deep learning fault diagnosis method based on multi-domain information fusion is proposed in this paper. Variational Mode Decomposition (VMD) method is adopted to decompose the original vibration signal into multiple IMF components, while fast Fourier transformation FFT transforming each IMF component into frequency domain samples. After that, multiple IMF components and their corresponding frequency domain samples are inputted into multiple deep metric learning (DML) models and deep belief network DBN models for preliminary diagnostic analysis, respectively. And then a simple soft voting method is used to fuse these preliminary diagnostic results to obtain the final diagnostic result. Finally, through the analysis of bearing fault diagnosis experiments, the results show that the proposed method not only has good diagnostic performance, but also outperforms information fusion diagnosis methods based on time domain and frequency domain, respectively.

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

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

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.

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.

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.

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.

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.

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 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. 

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.

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.

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.

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.

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.

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. 

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.

In real industrial environments, various compound faults may coexist in rolling bearings, making it challenging to acquire ample data for training. To address this issue, a zero-shot compound fault diagnosis approach is proposed based on envelope spectrum semantic construction. During the training phase, a semantic space and a feature space are established using single fault data. Subsequently, during the recognition phase, compound fault recognition in zero-shot scenarios is realized through the combination of the semantic and feature spaces. Furthermore, recognizing the envelope spectrum's capability in effectively characterizing rolling bearing fault features, the fault signals are preprocessed using envelope spectrum to enhance the bearing fault characteristics. The physical significance of the signal envelope spectrum is leveraged to construct the semantics for both single and compound bearing faults. Experimental results reveal that the proposed model achieves an accuracy of 87.83% in compound fault recognition, outperforming the compared models.

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.

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.

Earthquake is one of the most damaging natural hazards, extremely sudden and devastating. Seismic waves belong to the typical low-frequency wave with the range of 0~20 Hz. However, it is extremely challenging to isolate the low-frequency wave by the traditional isolation structure. Recently, a novel isolation idea has been formed to isolate the low-frequency seismic wave by proposing the local resonance seismic metamaterials, Nevertheless, there are still challenges in isolating ultra-low frequency seismic waves. Therefore, in response to the traditional local resonance seismic metamaterials not considering their own energy absorption characteristics, combined with the good energy absorption characteristics of negative Poisson's ratio materials, an innovative negative Poisson's ratio local resonance seismic metamaterial isolation barrier is proposed. This new seismic metamaterial is expected to isolate the ultra-low seismic waves. Based on the periodicity theory, COMSOL Multiphysics is used to explore the mechanism of band gap formation and its vibration reduction characteristics. The cell structure of the novel seismic is established, and the periodic boundary condition is applied. The eigenfrequency analysis is carried out to obtain the frequency bandgap of the new seismic metamaterial, and a desired ultra-low and ultra-wide frequency bandgap with the range of 0.612 Hz~13.35 Hz is obtained using a small size of the isolation barrier. and the Poisson's ratio, density, and elastic modulus of the negative Poisson's ratio material have a certain impact on the frequency bandgap. In practical engineering, negative Poisson's ratio materials with smaller negative Poisson's ratio, density, and elastic modulus should be selected. A study on the isolation effect of actual seismic waves with different main frequency ranges has found that it has a significant isolation effect on seismic waves with main frequencies greater than 0.612Hz.

In this paper, the primary resonance of a fractional-order Rayleigh-Duffing system under harmonic excitation is studied by multi-scale method. Firstly, the approximate analytical solution is obtained based on the multi-scale method. The numerical simulation shows that the analytical solution agrees well with the numerical solution, and the accuracy of the approximate analytical solution is verified. Then, the amplitude-frequency and phase-frequency equations for the steady-state solution are established, and its stability conditions are obtained based on the Lyapunov stability theory. Finally, through numerical simulation combined with amplitude-frequency curves, it is found that the parameters such as nonlinear stiffness coefficient, linear damping coefficient, and fractional order have important effects on the system dynamics characteristics, which is of great significance for the optimization and control of such systems.

Concrete-filled steel tube (CFST) structures have been widely applied to the construction of high-rise buildings and large-span bridges due to their excellent mechanical and seismic performance. However, with the increase of service time, the debonding defects between steel tube and core concrete will adversely affect the building safety. In this paper, the ultrasonic phased array method and the acoustic impact method are proposed to detect the debonding defects in concrete-filled steel tubes, and two special-designed inspection instruments are developed. For the ultrasonic phased array method, total focusing method is applied for image reconstruction, and the reflection coefficient at the steel-concrete interface is extracted for debonding evaluation. For the acoustic impact method, the energy distribution of flexural vibration mode and thickness mode in the echo data is analyzed by wavelet transform. The two proposed methods are successfully applied to the health evaluation of Shenzhen SEG Building after the abnormal shaking incident. The debonding defects of the concrete-filled steel tube columns of the SEG Building are detected and the comprehensive debonding ratio are calculated. Results of the field tests show that the comprehensive debonding rate of the SEG building is about 50%, showing a serious debonding degree. Comparative analysis of the detection results of these two methods shows that both the ultrasonic phased array method and the impact acoustics method can be used for semi-quantitative detection of debonding defects in concrete-filled steel tube columns. The impact acoustics method has a higher detection efficiency, while the ultrasonic phased array method has a higher detection resolution and detection accuracy.

Complexity Pursuit (CP) is a classical method for blind source separation of vibration signals. Two main approaches for estimating the de-mixing matrix using Complexity Pursuit are Complexity Pursuit-Gradient Descent (CP-GD), based on the complexity calculation of source signals, and Temporal Predictability-Generalized Eigenvalue Decomposition (TP-GED), based on the temporal predictability. The equivalence and computational performance of these two algorithms were studied based on vibration simulation. Firstly, the specific theories and algorithm procedures of CP-GD and TP-GED algorithms were presented. Secondly, the variations of source signal complexity and predictability corresponding to the de-mixed vectors were intuitively demonstrated and compared using two- and three-degree-of-freedom vibration systems. Finally, the accuracy and computation cost of the two algorithms were compared through modal parameter identification examples with multiple operating conditions and multiple degrees of freedom. The research results show that under low damping ratio and high signal-to-noise ratio conditions, the de-mixing matrices obtained with both methods are the same. Considering the computational cost of calculating signal complexity and performing gradient descent, the CP-GD algorithm has a higher computational cost than the TP-GED algorithm.

The vertical load-bearing capacity of Magneto-Rheological Elastomer (MRE) isolation bearings is low. However, vertical load has significantly influences on the mechanical performance of the MRE bearings, which limits the engineering applications of MRE bearings. By adding vertical rods to bear vertical loads and a constant magnetic field with permanent magnets, an isolation bearing with a structure of MRE sheets and steel plates alternately stacked and bi-directional adjustable shear stiffness was designed and built. The finite element method was used to analyze the effects of MRE layer thickness, permanent magnet thickness, and magnet placement on the bearing's magnetic circuit. The bearing has a core diameter of 60 mm, consisting of 26 layers of MRE and 25 layers of steel plates. Mechanical performance tests of the bearing were conducted under sinusoidal waves of different frequencies and amplitudes under different currents and weights. Based on the test results, the Particle Swarm Optimization algorithm was used to identify the parameters of the Bouc-Wen model of the bearing. The results show that the MRE bearing has a high vertical load bearing capacity and stable mechanical performance. The Bouc-Wen model can accurately describe the hysteresis characteristics of the bearing, and the fitting data is in good agreement with the experimental results.

In order to improve the axial crashworthiness of multi cell thin-walled structures, this paper proposes a hybrid multi cell Thin-walled Structure (MMTS) based on dynamic topology optimization to obtain the optimal cross-sectional configuration of thin-walled junctions under axial impact. The finite element method was used to compare the crashworthiness of hybrid multi cell thin-walled structures with window shaped multi cell structures and biomimetic tree shaped split structures designed based on experience under axial impact. In order to further improve material utilization, multi-objective optimization is carried out using structural dimensions as design variables. On this basis, a variable wall thickness analysis of the structure's cross-section is conducted to obtain the trend of impact resistance performance with wall thickness. The research results indicate that the collision resistance of mixed multi cell thin-walled structures is significantly improved compared to equal mass window type multi cell structures and tree shaped split structures. Compared with the initial design of MMTS, the optimized MMTS has increased specific energy absorption by 45.78%, reduced mass by 7.14%, and a smoother energy absorption process.

The presence of time delays in various control systems can have a significant impact on the performance of controllers. Ignoring time delays may result in reduced control effectiveness and even instability. This study investigates the effects of time delays on reinforcement learning based vibration controller. Firstly, a dynamic model of a piezoelectric cantilever beam is established using the finite element method, and the parameters of the dynamic model are corrected using experimental identification methods. Subsequently, the impact of different time delay conditions on the Proximal Policy Optimization (PPO)-based reinforcement learning (RL) controller and the PD controller are simulated and analyzed. Then, multiple reinforcement learning time-delay controllers are trained under different time-delay conditions, and the control effect of the time-delay controller is simulated and experimentally verified. Finally, the robustness of the reinforcement learning time-delay controller to time delay deviations is evaluated. The results show that the reinforcement learning time-delay controller not only has good control performance under the corresponding time delay conditions but also has a certain tolerance range for actual time delay deviations, demonstrating good robustness.

In order to make full use of fluid-induced helical elastic copper tube (HECT) vibration to enhance heat transfer and obtain higher comprehensive heat transfer performance of HECT heat exchanger device, the HECT heat exchanger with forward spiral baffle (HECT-FSB) and the HECT heat exchanger with reverse spiral baffle (HECT-RSB) were proposed. The two way-fluid structure coupling calculation method was adopted to study the effects of inlet velocity (Uin) on vibration-enhanced heat transfer and comprehensive heat transfer performance of HECT under swirling condition. The results show that with the increase of Uin, the amplitude and heat transfer coefficient of the HECT, and the pressure drop of the HECT heat exchanger all increase, while the PEC value decreases. The amplitude and heat transfer coefficient of the HECT, and the pressure drop of the HECT-RSB heat exchanger are significantly higher than those of the HECT-FSB heat exchanger. The PEC value of the HECT-FSB heat exchanger is higher than that of the HECT-RSB heat exchanger, and the vibration-enhanced heat transfer performance is better. When the Uin is 0.3 m/s, the PEC value of the HECT-FSB heat exchanger is 9.00% higher than that of the HECT-RSB heat exchanger. The HECT-RSB heat exchanger has the largest JF factor and the best comprehensive heat transfer performance. Compared with the heat exchanger in the published literature, the JF factor in the calculation range of Uin is increased by 2.7% on average. This research can provide technical support for improving the comprehensive performance of HECT heat exchanger device.