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2024 Vol. 43, No. 9 Published: 2024-05-15 1 Elastic-plastic seismic response characteristics of railway hollow high pier ZHANG Yongliang, SUN Peng, HUANG Yanbo, LIU Pei The rectangular hollow section pier of a railway high-pier long-span simply-supported beam bridge is taken as the research object,calculation model for four kinds of pier heights were constructed, and factors such as the position of truncation and the number of reinforcement bars were considered. IDA analysis is carried out by using Opensees software to build a single pier calculation model, and the elastic-plastic seismic response characteristics of railway high piers are summarized and suggestions on seismic design is put forward. The results show that when the ratio of longitudinal reinforcement is between 0.63 and 0.89%, the pier height is less than 42 meters and the longitudinal reinforcement length is arranged over the pier, the section of hollow pier bottom is weak.When the height of the pier is greater than 67 meters and the longitudinal reinforcement is divided into sections, the section at the bottom of the hollow pier, the section at the truncation of the longitudinal reinforcement and a section in the pier may be the weak part, but the section at the bottom of the hollow pier is the area where the plastic hinge appears first.The plastic hinge in pier shaft can be produced only when it is stimulated by strong ground motion. The influence of ground motion peak acceleration should be considered in the selection of longitudinal reinforcement.Increasing the number of reinforcement bars at pier bottom is beneficial to reducing the plasticity of pier bottom section in general, but it may not improve the seismic performance of the whole pier under strong earthquakes. For high piers, when there are two or more plastic hinge areas in pier shaft, it is suggested to use the coefficient of curvature ductility as the evaluation index. 2024 Vol. 43 (9): 1-7 [Abstract] ( 174 ) HTML (1 KB)  PDF (6275 KB)  ( 140 ) 8 Performance tests of rotating-amplification type friction self-centering brace and its restoring force model verification WANG Debin1, ZHANG Xinyue1, FU Xing2, WANG Wenming3, LIU Lu4 A friction self-centering brace with displacement amplification function (SC-DAFB) is proposed to address the insufficient energy dissipation capacity of traditional self-centering braces and the self-centering capacity of displacement amplification dampers. SC-DAFB is based on the working mechanism of bridge amplification and has a basic structure and working mechanism that are explained in detail. The formula for calculating the restoring force of the brace at each loading stage is derived, and the low-cycle reciprocating loading test of 6 groups of SC-DAFB under different working conditions is carried out. The key mechanical properties of SC-DAFB, such as load bearing capacity, hysteresis curve, energy dissipation and residual displacement, are obtained and compared. The results show that reducing the initial amplification Angle can effectively improve the bearing capacity and energy dissipation performance of the brace. When the self-centering ratio is 1.3, the yield load and maximum load of the brace at the initial amplification angle of 30° increase by 47.6% and 29.4%, respectively, compared with the brace without displacement amplification. The theoretical calculation and the experimental results show good agreement, verifying the accuracy of the theoretical restoring force model. 2024 Vol. 43 (9): 8-17 [Abstract] ( 88 ) HTML (1 KB)  PDF (2966 KB)  ( 99 ) 18 Effects of particle-size distribution on buffering mechanism of waste concrete aggregate cushion layer under impact load SU Yuchen1, LI Pengfei1, ZHONG Heng1, WU Lin1, WANG Yuan2, LYaru1 Granular cushioning layer installed at top of concrete shed can effectively reduce boulder impact force and transmitted load. To study the effects of particle-size distribution on cushioning performance of waste concrete aggregate cushion, boulder impact tests and three-dimensional discrete-element-numerical simulations were carried out. The results show that for cushioning layer with same particle size, when normalized particle size (d50/R) increases from 0.15 to 0.75. Due to reduction of potential points of failure in shorter force chains, the force chains stability increases. It further limits the particle rearrangement mechanism (average particle movements and rotation angles are reduced by 41.3 % and 33.7 %, respectively) during boulder impact. The peak values of the boulder impact force and transmitted load increased by 36.3% and 282.2%, respectively. For composite particles group, when non-uniformity coefficient (Cu) increases from 1.1 to 8.0, the porosity around coarse particles were filled with finer particles, the coordination number increases and force chain stability was enhanced (average translation distance and rotation angle were reduced by 22.4% and 45.3%), The peak values of boulder impact force and transmitted load increased by 26.0% and 174.6%, respectively, the cushioning performance of cushion decreased. Based on the experimental and numerical simulation results, a cushion reduction coefficient α related to the median of uniform particle size (d50/R) and non-uniformity coefficient (Cu), and the semi-empirical formula of drop hammer impact force considering protective effect of cushion was established. It may further provide technical and theoretical guidance for mountain shed tunnel engineering design. 2024 Vol. 43 (9): 18-26 [Abstract] ( 82 ) HTML (1 KB)  PDF (3060 KB)  ( 37 ) 27 Natural vibration characteristics of coupled cable strand system and global identification algorithm for cable force ZHANG Zhuojie1,2, WANG Xicheng1, WU Zhaoshuai1, ZHEN Xiaoxia3, LI Danfeng4 Cable is an essential force transmission component of the cable supported structures, and its cable force directly affects the service condition and lifespan of the structures. In general, for cable supported structures with locally rigid coupling, the cable strand vibration is independent and coupled. the vibration characteristics of the parallel strand cables are different from those of the single cable strand or the cables with good integrity. In order to effectively identify the tensions in the parallel strand cables with rigid couplings, Firstly, the model of multi-strand coupled system was established and the vibration equations of the system was derived, According to the vibration equations of the system, the parametric analysis of vibration characteristics was performed on the coupled system; Then, combined the filled function method and optimization theory, the identification algorithm for cable force of multi rigid couplings cable strands was constructed, the global identification of cable force was realized; Finally, the correctness and reliability of the algorithms were demonstrated by the experiment and finite element simulation. The results show that the rigid coupling ensures that each cable strand vibrates synchronously, the natural vibration frequencies of the parallel strand cables appear fractional frequency doubling, and there are local differences in the overall vibration modes; The cable force identification algorithm based on global optimization theory proposed in this paper exhibits low requirements for initial values, high calculation accuracy, and convergence efficiency, and can be extended to other parameter identification problems. 2024 Vol. 43 (9): 27-35 [Abstract] ( 80 ) HTML (1 KB)  PDF (2686 KB)  ( 30 ) 36 Non-stationary state vibration fatigue strength of high-speed train equipment compartment apron board under aerodynamic load CHENG Yajun1,2, YANG Mingzhi1, LIU Letian3, YU Chunyang2, LI Fansong3 The skirt board of the high-speed train equipment cabin plays an important role in improving the aerodynamic performance of the train. In addition to being subjected to vibration loads, the skirt board also bears a large aerodynamic load. As the operating speed continues to increase, the aerodynamic load borne by the skirt board becomes stronger and stronger. To ensure the normal operation of high-speed trains, fatigue assessment of the skirt board is particularly important. This article focuses on the non-steady-state vibration characteristics of the skirt board under the action of aerodynamic loads, using measured aerodynamic loads as input to obtain impulse response function (IRF) using finite element simulation, and using time-domain convolution integral method to calculate the acceleration at the acceleration measurement point. The model is verified by comparing with experimental data, and the comparison results show that the overall error is less than 10%. Then this method is used to calculate the dynamic stress of the concerned unit, and it is evaluated through the vibration fatigue strength analysis method. The evaluation results show that the fatigue strength of the skirt can meet the requirements of trains with speed of 400 km/h. 2024 Vol. 43 (9): 36-42 [Abstract] ( 69 ) HTML (1 KB)  PDF (2644 KB)  ( 62 ) 43 2D aerodynamic admittance of train on steel truss girder based on pressure-measuring wind tunnel tests DUAN Qingsong1, MA Cunming2 Identification method of two-dimensional aerodynamic admittance for the train is established, based on the pressure measurement method of sectional model. In turbulent flow field, the cross-correlation characteristics of buffeting forces on train on truss girder section at wind attack angle 0° is obtained. The three-dimensional aerodynamic admittance of the train vehicle on steel truss girder are also identified. Meanwhile, the three-dimensional aerodynamic admittance and two-dimensional aerodynamic admittance are comparatively investigated. It could be seen that, with the increasing of nondimensional reduction frequency and cross-spacing, the cross-correlation characteristics of buffeting forces on the train is gradually decreased. The cross-coherence function of buffeting force could be well-fitted by the Jakobsen model. When the reduction frequency k1B/2 is less than 0.3, the aerodynamic admittance value is 1. The three-dimensional aerodynamic admittance would significantly underestimate the aerodynamic admittance value. When the reduction frequency kB/2 is larger than 0.3, the three-dimensional aerodynamic admittance function value is larger than the two-dimensional aerodynamic admittance, and the value is decreased with the increasing of reduction frequency. The mathematical expression of two-dimensional aerodynamic admittance function and coherence function of the train is given. The results could provide parameters for the analysis of the coupling vibration for the wind-train -bridge system. 2024 Vol. 43 (9): 43-49 [Abstract] ( 61 ) HTML (1 KB)  PDF (1729 KB)  ( 43 ) 50 Feature extraction of underwater target acoustic signals based on deep manifold learning ZHOU Yu, WANG Jin, TENG Fei, PAN Bisheng, WANG Yourui, LEI Yingke With the increasing complexity of the marine environment, the data obtained from observing underwater target acoustic signals exhibits several challenging characteristics, including high dimensionality, nonlinearity, and lack of structure. These characteristics undoubtedly pose significant difficulties in extracting features from underwater target acoustic signals. In this study, a novel method for extracting features from underwater target acoustic signals is proposed, utilizing manifold autoencoders. Initially, the original data is globally optimized by leveraging the autoencoder reconstruction error to identify potential low-dimensional representations. Subsequently, the concept of preserving neighboring reconstruction weights through manifold learning is employed to enforce local constraints on the latent representation, thereby preserving its inherent topological structure. Finally, a generative adversarial network architecture is introduced for regularization, ensuring that the latent representation adheres to a specific distribution. This approach achieves a synergistic preservation of both local and global low-dimensional embedding. The proposed method was applied to extract essential features from four types of deep-water ships in the DeepShip open dataset. The quality of these features was evaluated by employing the classic classifier SVM for classification recognition. A comparison was conducted with existing methods for feature extraction in deep learning and manifold learning. The results showed an average improvement of 14.96% in recognition accuracy. 2024 Vol. 43 (9): 50-59 [Abstract] ( 76 ) HTML (1 KB)  PDF (2614 KB)  ( 19 ) 60 Vibration suppression design of quadcopter drone with parameter tracking robust observer WANG Zhihao1, WEN Xinyu1, CAO Songyin2, ZHOU Liangliang3 The parameter tracking robust observer design method is proposed for a class of quadrotor UAV subject to vibration. Firstly, the auxiliary filter is constructed to excite the vibration properties. Meanwhile, filter parameters are adjusted to reject the adverse effect of noise acting on the auxiliary state variables. The active vibration suppression can be simplified to the constant parameter estimation problem, which avoids the coupling of the estimated values and the operation of redundant parameters. Then a cascade structure of frequency parameter observer and tracker is designed to accurately estimate the vibration information. According to the above analysis, the compensation signal is reconstructed by auxiliary variables and frequency parameters. As a result, satisfactory vibration suppression performance can be achieved in combination with the controller. The designed observer has strong robustness without the phase lag caused by the time varying signal, which is often occurred in the conventional tracker. Finally, the performance of the system is demonstrated using the Lyapunov theorem, and the simulations are used to illustrate the effectiveness of the proposed method. 2024 Vol. 43 (9): 60-68 [Abstract] ( 64 ) HTML (1 KB)  PDF (2077 KB)  ( 52 ) 69 Dynamic modeling and vibration suppression of flexible macro-micro manipulator system WENG Yinxiang1, YANG Yiling1, WU Gaohua1, CUI Yuguo1, WEI Yanding2 Regarding the problem of micro-nano vibration of the flexible micromanipulator during high-speed and large-range macro motion, a system dynamics model is established, and an improved discrete sliding mode control strategy is designed to suppress micro-elastic vibration. Firstly, a comprehensive mechatronic dynamics model is established by combining the assumed modal method, Lagrange equation, and asymmetric hysteresis model for the macro-micro manipulation system composed of an air-floating macro-motion platform and a piezoelectric fiber micromanipulator. After that, a discrete sliding mode control strategy with nonlinear adaptive characteristics is implemented by regulating the switching gain with a variable-speed convergence law based on the proposed model. Finally, a measurement and control platform for the macro-micro manipulation system is built, and the trajectory tracking and vibration suppression experiments are conducted. In trajectory tracking, the designed control strategy can accurately track the given signal with minor errors for different frequencies of sinusoidal reference trajectories. During vibration suppression, the residual vibration stabilization time of the micromanipulator was reduced by 26.1% and 50.0% compared to the pre-improvement period when the macro-actuated platform was moving along the trapezoidal versus the S-trajectory and 53.6% and 53.3% compared to the no-control period, respectively. The effectiveness of the dynamics model and discrete sliding mode control is verified, and the control accuracy and efficiency of the system are improved. 2024 Vol. 43 (9): 69-76 [Abstract] ( 53 ) HTML (1 KB)  PDF (2544 KB)  ( 40 ) 77 Free vibration characteristics analysis for rotating shaft based on CUF theory HE Congshuai1, ZHU Junchao1,2, HUA Hongxing2, XIN Dakuan1 This work presented a dynamic analysis model for the rotational shaft under classical boundary conditions, based on Carrera unified formulation (CUF). Utilizing the CUF framework, the complete 3D dynamic model was simplified to a 2D dynamic model while maintaining 3D solution accuracy. The displacement field of the rotational shaft was constructed using two-dimensional Taylor polynomials and improved Fourier series. The boundary conditions were handled through the penalty function method, and the vibration characteristics were solved using energy functionals and Hamilton principle. The effectiveness and correctness of this method were verified by comparing it with finite element results. Furthermore, the study investigated the impact of the boundary penalty function factor, geometric parameters, and rotational speed on the vibration characteristics of the rotational shaft. The proposed method exhibits high efficiency and precision, offering an effective approach to analyze the vibration characteristics of rotational shaft. 2024 Vol. 43 (9): 77-83 [Abstract] ( 41 ) HTML (1 KB)  PDF (2042 KB)  ( 46 ) 84 Wind induced vulnerability analysis for a whole light steel building WU Fengbo1, YAO Xingui1, ZHOU Haojie2, HUANG Guoqing2, NIE Shidong2, JI Xiaowen3, GONG Ting4 Light steel houses are widely used in low-rise buildings such as residential houses and factories. The structures are light in weight and thus sensitive to wind loads. It has been severely damaged in typhoons, which has caused a lot of economic losses, thus the wind disaster risk assessment of light steel structures is of great significance. Based on this, the wind-induced fragility and vulnerability of light steel buildings will be studied. Firstly, an analysis framework for the wind-induced vulnerability of the overall structure of light steel houses is proposed based on stochastic simulation technology, which involves the wind load randomization method, the wind-induced fragility analysis method of the main structure and the envelope structure, and the wind-induced vulnerability analysis procedure of the overall structure. Then, the proposed framework has been used to analyze the wind-induced vulnerability of a specific light steel structure, and the numerical analysis results demonstrate that the proposed method takes into account the combined effect of windborne debris and wind pressure, and the change of internal pressure. In addition, the method can integrate the wind-induced loss of the main structure and the envelope structure to obtain the overall vulnerability curve of the structure. 2024 Vol. 43 (9): 84-93 [Abstract] ( 53 ) HTML (1 KB)  PDF (2759 KB)  ( 13 ) 94 Dynamic response analysis of long-span arch bridge under near-fault pulse seismic motion XU Lueqin1,2, YUAN Maojun1, ZUO Ying1, SHEN Zhengxuan1, XU Lihan1 To reveal the effects of the characteristics of velocity pulses and pulse parameters on the seismic response of large-span arch bridge under near-fault pulse-type ground motions, the record-decomposition incorporation (RDI) method was first introduced to synthesize artificial near-fault pulse-type ground motions. By comparing the accuracy of different equivalent pulse models, the synthesis method was optimized and validated. Taking a large-span arch bridge as the engineering background, artificial near-fault ground motions with different parameter characteristics were synthesized using the optimized method, and the influence mechanism of pulse components and residual components on the seismic response of the arch bridge was discussed. Finally, the influence of different pulse parameters on the seismic response of the arch bridge was studied. The research results show that the optimized RDI method can effectively simulate the original near-fault pulse-type ground motions and obtain artificial ground motions with different pulse parameters. The high-frequency components of near-fault ground motion records are found to have a significant adverse effect on the seismic response of the arch bridge. As the amplitude of the pulse increases, the effects of forward-directionality and fling-step pulses on the seismic response of the arch bridge are both obviously increased; and when the pulse period increases, both types of pulse effects have significant adverse effects on the seismic response of the arch bridge. With respect to the influence of the pulse number, the near-fault ground motions with bidirectional pulses cause a greater in-plane response of the arch bridge when compared to those with multi-directional pulses. 2024 Vol. 43 (9): 94-104 [Abstract] ( 69 ) HTML (1 KB)  PDF (6130 KB)  ( 38 ) 105 Acoustic emission recognition method for valve internal leakage based on convolutional attention mechanism HUANG Xin, QU Wenzhong, XIAO Li Because of long-term exposure to high temperature and high-pressure environment, the gate or disc of the valve structure, one of the key equipment components of nuclear power plant, is prone to thermal deformation or wear, resulting in poor sealing, which lead to internal leakage accidents. Real-time on-line identification of internal leakage state of valve is of great significance for improving thermal efficiency and valve reliability of nuclear power units. It’s easy for the acoustic emission signal of valve leakage to be covered by the base noise of the actual industrial site, which result in the misjudgment of valve leakage state. In order to realize quick and accurate identification of valve internal leakage state, in present paper, the valve internal leakage detection test bench is built, the valve internal leakage monitoring and analysis system based on acoustic emission method is developed, and the convolutional block attention module is introduced into the convolutional neural network to realize efficient and rapid identification of valve internal leakage state. The results show that: Based on the acoustic emission signal frequency domain data of the valve leakage, the convolutional block attention module can effectively and accurately identify the valve leakage state. When the internal leakage rate is 26L/h, the recognition accuracy is up to 98%, with good reliability and robustness. 2024 Vol. 43 (9): 105-114 [Abstract] ( 56 ) HTML (1 KB)  PDF (3075 KB)  ( 55 ) 115 Dynamic compression tests and damage analysis for ultrahigh performance concrete LIU Jixuan1, CHEN Xudong1, SHI Dandan1, WANG Luyao2, NING Yingjie2, GAN Yuannan3 In order to explore the damage characteristics of ultra-high performance concrete (UHPC) under dynamic compression, the dynamic compressive mechanical properties of UHPC under different strain rates (52 /s ~ 368 /s) were studied by split Hopkinson pressure bar (SHPB) device, and the failure process of the specimen was analyzed based on DIC technology. The failure process of the specimen was analyzed based on high-speed camera and DIC technology. The results show that Under the impact load, the UHPC specimen can still remain intact after failure. The dynamic compressive strength and toughness of UHPC show obvious strain rate sensitivity. With the increase of strain rate, steel fiber can better absorb impact energy and restrain the increase of critical strain. Under different strain rates, the early development rate of cracks is basically the same, and the final width of cracks increases with the increase of strain rate. The crack development is greatly affected by the strain rate, and the final width of the crack increases with the increase of the strain rate. The final width of the crack at low strain rate is not its maximum width. This study provides a theoretical support for the service performance and damage assessment of UHPC. 2024 Vol. 43 (9): 115-120 [Abstract] ( 56 ) HTML (1 KB)  PDF (2077 KB)  ( 61 ) 121 Road roughness recognition based on GA-LSTM adaptive Kalman filtering LI Shaohua1, LI Jianwei1,2, FENG Guizhen2 Accurately and rapidly identifying the current road excitation information of the vehicle is the key to realize the intelligent chassis control and ensure the ride comfort of the vehicle. Aiming at the problems of low accuracy and poor adaptability of traditional road roughness recognition algorithms, a road roughness recognition algorithm based on genetic algorithm(GA)optimized long short-term memory neural network(LSTM)adaptive Kalman filtering was proposed. Based on the two-degree-of-freedom vehicle suspension model, the feature input variables of the LSTM neural network were selected by the grey correlation method, and the model parameters of the LSTM neural network were optimized by GA to accurately identify the road grade. Based on this, the noise matrix in the Kalman filtering algorithm is updated in real time, and the adaptive recognition of road roughness under complex road conditions is realized. Simulation and experimental results show that the proposed adaptive Kalman filtering algorithm with GA-LSTM can quickly and accurately identify road roughness and road grade. Compared with the traditional Kalman filtering algorithm, The correlation coefficient, root mean square error and maximum absolute error are increased by 3.11 %, 37.5 % and 51.2 %, respectively, indicating that the proposed algorithm has good adaptability to complex working conditions. 2024 Vol. 43 (9): 121-130 [Abstract] ( 44 ) HTML (1 KB)  PDF (4433 KB)  ( 18 ) 131 Robot grinding chatter monitoring based on improved EMD and GA-BPNN LIU Wei, LIU Wang, CAO Dahu, GE Jimin, WAN Linlin, CHEN Jia Industrial robots are widely used in robotic weld seam grinding tasks due to their flexibility. However, due to the weak rigidity of the robot, the system is prone to chattering in the process of weld grinding, so the monitoring of chattering in the machining process is the basis for ensuring the machining quality. Aiming at the phenomenon of modal aliasing in the processing of vibration signals, an improved empirical modal decomposition method based on the arrangement entropy algorithm was proposed, and the abnormal signals in the vibration signals were detected and eliminated by the arrangement entropy algorithm. The energy entropy of the intrinsic mode function with the largest correlation was extracted as the eigenvalue by the correlation coefficient method, and the four time-domain features of variance, peak-to-peak, root-mean-square, and crag were extracted at the same time. Using genetic algorithm to optimize the BP neural network to establish the chatter recognition model, and finally the five extracted feature parameters were substituted into the recognition model as feature vectors to monitor the machining state. The experimental results show that the proposed improved empirical modal decomposition algorithm combined with the BP neural network model optimized by genetic algorithm can effectively monitor the chatter in robotic weld grinding. 2024 Vol. 43 (9): 131-138 [Abstract] ( 54 ) HTML (1 KB)  PDF (3130 KB)  ( 10 ) 139 Dynamic response characteristics and damage constitutive model of coal samples under impact load YANG Ke1,2,3, XU Rijie1,2,3, LIU Shuai1,2,4, LIU Wenjie1,2,3, ZHANG Jie1,2,3 In order to study the dynamic response law of deep coal body, the uniaxial impact compression tests with different strain rates were carried out on the coal samples of Xinhu Mine by using the Split Hopkinson Pressure Bar (SHPB) test system. The results show that the dynamic compressive strength of coal samples under impact load has obvious strain rate effect, and the strain hardening phenomenon becomes more obvious with the increase of strain rate. The reflection energy, transmission energy, absorption energy and energy consumption density of coal samples have a linear function relationship with strain rate, and the proportion of energy consumption has an exponential function relationship with strain rate, and all of them maintain a positive correlation. Based on the classical Zhu-Wang-Tang (ZWT) model, Weibull distribution and Drucker-Prager (D-P) criterion, a dynamic statistical damage constitutive model considering the damage and viscosity characteristics of coal samples was established, and the accuracy and universality of the constitutive model were verified. The model can better describe the dynamic mechanical behavior of coal samples, and provide a basic research for the safe mining of deep coal under the influence of dynamic load. 2024 Vol. 43 (9): 139-148 [Abstract] ( 45 ) HTML (1 KB)  PDF (2565 KB)  ( 28 ) 149 Vibration characteristics of shale gas horizontal well vibration cementing casing string QI Linshan1, YIN Yiyong1, QU Congfeng2, LIU Binhui2, WANG Liyan1, BAI Hanqin3, WANG Tong1 This paper represented an approach to solving the casing string’s vibration characteristics and dynamic responses in vibration cementing of horizontal well for shale gas extraction. Considering the specific distributed supports of the centralizer, the dynamic model of the casing string was established by matrix transformation method, which was verified by experiments. Based upon the obtained dynamic model, the influences that the parameters of the centralizer’s supports and the casing string bring to the casing string’s vibration characteristics were studied, and the laws of dynamic responses and amplitude attenuation of the casing string in vibration cementing were investigated. It is shown that the natural frequencies of the casing string increase with the increment of the centralizer stiffness, the number of the centralizer supports, and the casing’s outer diameter. In the meantime, the increment of the centralizer stiffness accelerates the amplitude attenuation of the casing string. Furthermore, the effective propagation distance of the casing string vibration is improved by increasing the excitation force while using the low-frequency resonance. These achievements lay foundations for design of the equipment applied in vibration cementing of horizontal well for shale gas development. 2024 Vol. 43 (9): 149-157 [Abstract] ( 56 ) HTML (1 KB)  PDF (2511 KB)  ( 12 ) 158 Minimum variance unbiased adaptive load estimation based on sparse constraints LI Dongsheng1, WEI Da2 This paper presents an improved algorithm for load estimation based on sparse constraints, an improvement of the traditional minimum variance unbiased load estimation algorithm. The improvement is achieved by applying a sparse constraint on the force vector with the PM technique utilizing the space-sparse characteristic of the force to be estimated. This constraint transforms the unconstrained optimization of force estimation into a constrained optimization based on the l1-norm, effectively solving the force drift problem and improving the robustness of force estimation. Moreover, an adaptive estimation algorithm is introduced to realize the adaptive estimation of measurement noise covariance, as the conventional approach of manually setting the noise covariance is inconvenient in engineering applications. The performance of the proposed algorithm is evaluated through numerical simulations and experiments on a three-story shear building。 2024 Vol. 43 (9): 158-165 [Abstract] ( 43 ) HTML (1 KB)  PDF (2049 KB)  ( 54 ) 166 Modal frequency analysis of traveling waves in carbon nanotube rotating functionally gradient conical-cylindrical connected shell PANG Lei1, CHENG Long1, LIU Wenguang1, ZHANG Yuhang1, L Zhipeng2 This paper focuses on the impact of carbon nanotubes on the vibration characteristics of rotating FGMs joined conical-cylindrical shells, aiming to enhance their performance and stability. First, artificial springs are employed to simulate the connection conditions between boundary conditions and shell structures. The energy equations of the system are derived by considering different distribution patterns of carbon nanotubes and utilizing the microscopic mechanics model. Furthermore, the displacement function is constructed by using Chebyshev polynomials, and the modal frequency equations of the structures are solved by using Rayleigh-Ritz method. The effects of parameters, including the ceramic volume fraction exponent, the boundary conditions, and the carbon nanotube volume fraction, on the traveling wave modal frequency of structures are thoroughly examined using numerical examples. The major results in the paper include: the traveling wave frequency is notably influenced by the V-shaped distribution within the gradient exponent range of 0 to 5; with an increase in rotational speed, the impact of boundary constraints intensifies, resulting in enhanced stability of the structure; increasing the volume fraction of carbon nanotubes leads to higher traveling wave modal frequencies of the structures. 2024 Vol. 43 (9): 166-174 [Abstract] ( 71 ) HTML (1 KB)  PDF (2026 KB)  ( 3 ) 175 Sound source localization method based on improved Laplace wavelet time delay extraction NING Fangli, DUAN Shaodong, LI Jing, HUO Jiahui An acoustic source localization method based on refined Laplace (R-Laplace) wavelet time delay extraction is proposed to solve the localization problem of impact sound generated by penetrating projectiles hitting multi-layer hard targets. This method constructs Laplace wavelet through prior information processing, calculates the correlation coefficient with the acoustic signal to obtain the time delay information, and combines the search matching algorithm to obtain the sound source position of multiple impacts. The sound source acquisition and positioning system was built, and several hard target impact sound tests were carried out. The outdoor experimental results show that compared with the traditional location algorithm based on time difference of arrival (TDOA), this method can accurately locate 4 sound sources on different impacted layers. The average positioning error is 0.3 m, which proves that the algorithm has a large potential for application in sound source localization problems based on time difference of arrival and is important for practical applications of sound source localization problems. 2024 Vol. 43 (9): 175-185 [Abstract] ( 34 ) HTML (1 KB)  PDF (3463 KB)  ( 6 ) 186 Dynamic modeling and analysis of shipborne stable platforms in non-inertial system QIU Weihan, NIU Anqi, WANG Shenghai, QIU Jianchao, FAN Kunlong, CHEN Haiquan In order to solve the large magnitude and multi-dimensional irregular rocking motions generated by ships in bad sea conditions, a 6-DOF parallel platform is proposed to isolate the ship's motion, and the dynamics characteristics of the scheme are thoroughly investigated. Firstly, the velocity, Jacobi matrix, and energy equations of the platform member in inertial coordinates are derived based on vector relations, and its explicit dynamical equations in a non-inertial system are obtained from the Lagrange equation and the principle of virtual work. Secondly, Adams is used to build a virtual scaling model of the platform, and P-M wave spectrum and RAO are used to simulate the rocking motion of the ship under a complex sea state, and the co-simulation of MATLAB and Adams is realized based on Simulink. Finally, the motion examples under 5 levels of sea state are calculated and analyzed, and the driving force error between the theoretical results and the simulation results is within 0.11%, which verifies the correctness of the dynamics model in this paper, and the computational results show that the platform can compensate the ship's roll, pitch, and yaw rocking motions by 95.7%, 97.7%, and 87.9%, respectively, which verifies the validity of the proposed scheme. The research results are of guidance for the dynamics control of the Ship-borne stabilized platform in the non-inertial system. 2024 Vol. 43 (9): 186-194 [Abstract] ( 44 ) HTML (1 KB)  PDF (2624 KB)  ( 10 ) 195 Failure determination of polyurea coated oil and gas pipelines with local defects under blast load CUI Ying1,2, LI Zhangjian2,3, FANG Jun2,3, ZHAO Junhai4, QU Zhan1,2, ZHAO Ben2,3 With buried blast experiment, the anti-explosion performance of polyurea elastic reinforcement buried petroleum pipeline with localized defects was researched thoroughly. Furthermore, with the experimental data and numerical simulation, the damage assessment criterion of polyurea elastic reinforcement buried petroleum pipeline with localized defects subjected to shallow buried blast loading was established. The results show that under the condition of scale distance of 0.23m/kg1/3 and shallow buried blast loading exerted on, there were obvious dent deformations on the surface facing the blasting of the normal buried pipeline with localized defects and the polyurea buried petroleum pipeline with localized defects both, and the dent deformation values of the polyurea pipeline with localized defects was 28.87% lower than that of the normal buried pipeline. It was venerable to have damage on the buried pipeline surface facing explosive and joint ends of buried pipeline. According to the comparison of the overpressure, the values of the normal buried pipeline with localized defects was higher than that of the polyurea enhanced one, and the beginning time of deformation of the normal buried pipeline with localized defects was earlier than that of the polyurea enhanced one, which indicated that the polyurea could decrease the value of overpressure and delay the response time effectively. Finally, considering the calculation of cross-section ellipticity of pipeline cross-section deformation for failure determination, the damage assessment formula based on a new critical ellipticity of pipeline cross-section had been established according to pressure and impulse (P-I) damage assessment theory. 2024 Vol. 43 (9): 195-203 [Abstract] ( 35 ) HTML (1 KB)  PDF (3629 KB)  ( 13 ) 204 Multiple attempts of differential evolution Bayesian finite element model revision based on Kriging model QIN Shiqiang, LI Ning, SONG Renxian The standard Differential Evolution Adaptive Metropolis (DREAM) algorithm requires parallel computing with multiple Markov chains, which suffers from low convergence efficiency and high computational costs. To address these challenges, this study proposes a novel framework called MT-DREAM(ZS), based on the Kriging model, for multiple-try differential evolution Bayesian finite element model updating. This framework extends the DREAM algorithm by introducing historical vector differential sampling, Snooker update, and multiple-try Metropolis sampling. Furthermore, it utilizes the Kriging model as a surrogate for the finite element model to enable efficient random sampling, allowing for rapid exploration of high-dimensional posterior distributions of correction parameters using a minimal number of parallel chains. To validate the effectiveness of the proposed MT-DREAM(ZS) method, this study conducts the experiment on a consolidated steel plate beam model and compare the updating performance with the standard DREAM algorithm. The results demonstrate that MT-DREAM(ZS) achieves fast convergence of the Markov chains, improving the convergence efficiency by a significant factor of 3.42 compared to DREAM. Moreover, the updating accuracy and stability are enhanced. Additionally, the utilization of the Kriging model substantially reduces computational costs. The proposed framework provides a new approach to address the challenges of low convergence efficiency and high computational costs in the updating of multi-parameter uncertain models. 2024 Vol. 43 (9): 204-213 [Abstract] ( 56 ) HTML (1 KB)  PDF (2980 KB)  ( 73 ) 214 Meso-microstructure evolution mechanism and residual strength tests of high-strength concrete after high temperature ZHAO Dongfu1,2,3,4,5, LI Hao1, HAO Tengfei1, LIU Mei1 In order to analyze the meso-microstructure evolution mechanism and establish the relationship model between high temperature history and meso-microstructural evolution and the relationship model between high temperature history and residual strength, an experimental study was conducted on C60 high strength concrete specimens experiencing different heating temperature and constant temperature times. The internal temperature field of the specimens was measured by thermocouples and analyzed by finite element simulation analysis of ABAQUS. The result showed that the variation of temperature field in the two tests was basically consistent. The meso-microstructure changes after different high temperature history were analyzed qualitatively and quantitatively by scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness test, mercury intrusion porosimetry (MIP) and ultrasonic, and the results of different means were related to each other. Then the relationship model between high temperature history and microstructural evolution was established. The residual compressive strength after high temperature history was obtained by strength test. Then the relationship model between high temperature history and residual strength was established. The research showed that as the heating temperature and time rose, the water of crystallization is lost, the hydrides and gels have different degrees of decomposition, the calcium hydroxide, dolomite and ettringite decreased, the acoustic time increased, the amplitude and frequency decreased, the microhardness decreased and the porosity increased. Finally, the relationship among high temperature history, meso-microstructure and residual strength of the high-strength concrete was obtained. 2024 Vol. 43 (9): 214-225 [Abstract] ( 39 ) HTML (1 KB)  PDF (4951 KB)  ( 12 ) 226 Human induced vibration comfort based on random walk model WU Gangjie1, CHEN Deyi1, HUANG Shiping2, LI Zhihai1 To study the effects of random loads on the vibration of pedestrian bridge structures, Firstly, a bi-directional random walking model was established and an analytical solution for the structural vibration response under random load was derived. Secondly, the influence of crowd density on the structural vibration response was compared and analyzed. Finally, by studying the correlation between the pedestrian's subjective sensation time and the total time, the comfort amplification factor was defined. Taking a pedestrian overpass in Jingzhou City as an example, the vibration comfort evaluation was conducted to verify the applicability of the bi-directional random walking model and the comfort amplification factor. The results show that the acceleration response of pedestrian bridge structure increases first and then decreases with the increase of crowd density. There is a significant correlation between the perceived time and the total time of pedestrians, and a corresponding relationship can be established according to the comfort amplification factor. The comfort amplification factor decreases with the increase of vibration response peak value, while it increases with the increase of crowd density. These results have reference significance for the quantitative calculation of pedestrian bridge vibration comfort. 2024 Vol. 43 (9): 226-233 [Abstract] ( 51 ) HTML (1 KB)  PDF (3059 KB)  ( 41 ) 234 Comb filtering effect of reflected ultrasound on coating interface and interface bonding quality imaging detection ZHOU Guozheng1,2, JIANG Yu3, LIANG Jun1,2, JIANG Dachao1,2, YUAN Maodan3 The bonding quality of the coatings can be effectively characterized by ultrasonic nondestructive testing. This paper investigated the ultrasonic wave propagation at the coating interfaces and found that the reflected signals show clear comb filtering effect. Moreover, theory studies proved that the amplitude and phase of the reflected ultrasonic waves will change with the interfacial stiffness. Therefore, a spectral index based on the comb filtering effect was proposed to evaluate the bonding quality. Experiments of different coating samples were carried out by high-frequency ultrasonic scanning system, along with the destructive cross-cut test. The results show that the reflection coefficient and the spectral index can distinguish between samples of level 0 and level 2 from cross-cut test. In addition, the spectral index based on comb filter effect can significantly improve the contrast of the imaging results. This work will provide theoretical basis and technology support for online and full-coverage nondestructive testing of coatings. 2024 Vol. 43 (9): 234-240 [Abstract] ( 21 ) HTML (1 KB)  PDF (2043 KB)  ( 13 ) 241 Dynamic analysis of an equivalent time-varying stiffness system for local faults of rolling bearing GUO Baoliang1, ZHAO Yuxiu2, SHI Lichen1, LI Ling1, DUAN Zhishan1 In response to the dynamic modeling problem of local faults in rolling bearings, by analyzing the changes of each rolling element when entering, exiting the load zone and falling into the fault position, based on Hertz contact theory, the contact deformation retention factor is defined, the equivalent time-varying stiffness function of rolling bearings is proposed, and a single degree of freedom with time-varying stiffness dynamic model of local fault rolling bearings is established. Theoretical analysis and experimental research are conducted. The research results indicate that when the rolling element enters or exits the load zone, the number of load-carrying rolling elements in the load zone increases or decreases, causing a small increase or decrease in the equivalent time-varying stiffness of the system; when the rolling element falls into the fault position, the effective contact stiffness decreases to different degrees due to different contact deformation retention factors, which leads to a decrease in the equivalent time-varying stiffness of the system. The change of the equivalent time-varying stiffness of the system causes the contact deformation and contact force of other rolling elements in the load zone to change in different magnitudes, thus balancing the external radial load. The impact on the rolling elements near the center of the load zone is more obvious, but it does not affect the effective contact stiffness of each rolling element. An abrupt change in the equivalent time-varying stiffness of the system occurs, leading to system vibration. When the outer ring fails, the equivalent time-varying stiffness varies equally. When the inner ring malfunctions, the change in equivalent time-varying stiffness is modulated by the rotation of the inner ring and the amplitude is different. The proposed single degree of freedom time-varying stiffness dynamic model is more in line with reality. 2024 Vol. 43 (9): 241-248 [Abstract] ( 44 ) HTML (1 KB)  PDF (3265 KB)  ( 16 ) 249 Structural parametric optimization of hybrid viscous damper based onGA-BPNN surrogate model LIN Yongjun, CHEN Hao, GUO Song The present investigation aims to explore optimizing design parameters for a hybrid viscous damper employing advanced techniques and methodologies—computational fluid dynamics (CFD) simulation and optimization based on surrogate models. Firstly, the effects of damper parameters on mechanical performance are analyzed. Key parameters, including gap width, cylinder inner diameter, piston thickness, and damping hole diameter, are selected based on orthogonal experiment theory. Initial sample points are obtained through CFD simulation and optimized Latin hypercube design (OPLHS). Secondly, to establish a surrogate model that precisely reflects the intricate correlation between design parameters and energy consumption performance, a genetic algorithm (GA) and a back-propagation neural network (BPNN) approach are employed. Furthermore, the GA-BPNN surrogate model is cyclically updated and combined with the non-dominated sorting genetic algorithm (NSGA-II), aiming at the optimal energy dissipation capacity. The optimization was realized in the whole design space, and the optimal construction parameters of the hybrid viscous damper with a double outlet bar are determined under the viscosity of the typical damping medium. Finally, the influence mechanism of structural parameters on the flow performance of viscous dampers is discussed. The optimal design parameters for the entire viscosity case, including the damper hole diameter, piston thickness, cylinder inner diameter, and gap width, are 1.31mm, 120.78mm, 199.87mm, and 0.5mm, respectively. Compared to the baseline design, the maximum damping force and energy consumption ratio increased by 33.8% and 64.8%, respectively. This method provides a reference for optimizing design parameters and related research for viscous dampers. 2024 Vol. 43 (9): 249-260 [Abstract] ( 32 ) HTML (1 KB)  PDF (6785 KB)  ( 8 ) 261 Fault feature extraction of RV reducer cycloidal gear based on adaptive narrowband demodulation of IAS signals ZHANG Jiayuan, GUO Yu The RV reducer is widely used in industrial robots, and it has great significance to research the fault detection method of its key components. Due to the complex structure of the RV reducer, low rotating speed of the cycloidal gear, and weak fault impact etc, it is difficult to extract the fault features of the cycloidal gear using conventional vibration analysis methods. To solve above problems, a method based on encoder signals for extracting the fault features of the cycloidal gear in RV reducer is proposed. Firstly, the encoder angle signals are collected, and then the instantaneous angular velocity signals are obtained using the forward difference method. Based on this, the angular domain synchronous averaging is used to extract the cycloidal gear period-related synchronous components, eliminate asynchronous interference, and select the gear harmonics frequency bands with rich fault information by constructing a sideband signal-to-noise ratio index for bandpass filtering. Finally, the filtered signal is narrowband demodulated to achieve fault feature extraction of the cycloidal gear in the RV reducer. Experimental results show that this method can effectively extract the fault features of the cycloidal gear in the RV reducer, and achieve adaptive optimization of bandwidth selection. 2024 Vol. 43 (9): 261-266 [Abstract] ( 51 ) HTML (1 KB)  PDF (2046 KB)  ( 27 ) 267 Vulnerability of building laminated glass against wind-induced projectiles impact ZHANG Yong, LI Shouke, GUO Fan, LEI Jiayan, PENG Xiong, SUN Hongxin, LIU Min The finite element simulation method is used to study the impact vulnerability of building laminated glasses for windborne debris. The finite element model of laminated glass impacted by windborne debris is established with LS-DYNA, and the reliability of the finite element model is verified by comparative experiments and numerical simulation results. The crack development and stress propagation of laminated glass impacting by spherical windborne debris are analyzed. By changing the impact position and the aspect ratio of the laminated glass panel, as well as with different radius and material of windborne debris, the impact effects on the laminated glass are studied. The impact failure probability of the laminated glass is calculated by using the two-parameter Weibull distribution. It is shown that, compared impact location with the middle and edge of laminated glass, the impact resistance with corner impact is the worst; at the same impact velocity, the failure probability of laminated glass increases with the increasement of windborne debris radius; compared with stone debris and wood debris, the critical impact damage velocity is the lowest when steel debris impact laminated glass; as the panel area is constant, the failure probability decreases firstly and then increases with increasement of aspect ratio. 2024 Vol. 43 (9): 267-275 [Abstract] ( 54 ) HTML (1 KB)  PDF (5203 KB)  ( 14 ) 276 Design of seat nonlinear suspension with integrated adjustment functions YAN Zhenhua1, GUO Xiaozhe1, LI Zhongyi1, LI Xiaoguang1, SONG Sixin2 In order to improve the low-frequency vibration isolation capability of engineering vehicle seats and adapt to the differences in driver height and weight parameters, a nonlinear seat suspension with integrated height and weight adjustment functions was designed. A mathematical model was established between the core design parameters and their force displacement characteristics, and the main design parameters were determined. Based on ADAMS software simulation, the force displacement characteristics and adjustment function of the seat suspension were verified, and a physical prototype was manufactured for experimental verification. The results show that the designed suspension has good nonlinear characteristics, with adjustable height and weight parameters, and the adjustment of parameters does not affect the low-frequency vibration isolation ability of the suspension. 2024 Vol. 43 (9): 276-280 [Abstract] ( 62 ) HTML (1 KB)  PDF (1292 KB)  ( 21 ) 281 Moment-rotating angle restoring force performance of SCRF damper SHI Qingxuan1,2,3, WANG Puzhen1, RONG Chong2,3, WANG Peng1,2,3, WANG Bin1,2,3 To meet the requirements of energy dissipation structures for the resilience performance, a self-centering rotary friction (SCRF) damper based on shape memory alloy is proposed to address the problem that traditional friction dampers do not have self-centering capability and have a large residual deformation after the earthquake. SCRF is a combination of a friction energy dissipation device and shape memory alloy (SMA) self-centering device. The construction form and working mechanism of the SCRF damper are introduced, the moment-rotation hysteretic model of the SCRF damper is established through theoretical derivation, the moment-rotation hysteretic model is verified by the numerical simulation of ABAQUS. The hysteresis performance of SCRF under low cycle hysteresis load is analyzed, and the parameters are analyzed. The results indicate that the theoretical hysteresis model was consistent with the numerical simulations. Increasing the friction coefficient and slope height between the contact surfaces can improve the maximum bearing capacity, energy dissipation capacity and effective stiffness of damper, however, the height of the slant surface that exceeds a certain limit will reduce the self-centering ability of damper. The preload of SMA bolts can increase the friction initiation moment of the damper, which has little effect on the energy dissipation capacity and the maximum load capacity of the damper. 2024 Vol. 43 (9): 281-290 [Abstract] ( 38 ) HTML (1 KB)  PDF (2953 KB)  ( 61 ) 291 Effects of changes in passenger car front styling on pedestrian lower limb injuries WANG Bingyu1,2,3, LIU Tianquan1, HAN Yong1,2,3, OTTE Dietmar4, QIN Liyan1,2,3, LI Hong5 The change in vehicle front-end shape after the publication of the EU Pedestrian Protection Directive and the effect of that change on pedestrian lower extremity injuries were investigated. For this purpose, 283 accident cases with pedestrian lower limb injuries were selected from the German In-depth Accident Study Database (GIDAS), and the accident cases were divided into two groups according to the production year of the accident sedan. Descriptive statistics were employed to get the front structure values of each accident vehicle in the two groups, and then the Wilcoxon signed-rank test was used to identify the front structure parameters with significant differences between the two groups. Finally, the risk curves of severe lower extremity injury and fibula/tibia fractures were established by binary logistic regression for the two groups to analyze the change of vehicle front shape and the effect on pedestrian lower extremity injury after the issuance of the Pedestrian Protection Directive. The results demonstrated that the new models had a wider front bumper with shallower bumper projection, a higher hood leading edge, and a lower height of the lower edge of the sub-bumper. At crash speeds of 0-40 km/h, for pedestrians up to 60 years of age, the protection performance of vehicles produced after the release of the EU Pedestrian Protection Directive for severe overall lower limb injuries and fibula/tibia of pedestrians has been improved compared to previous vehicles. 2024 Vol. 43 (9): 291-297 [Abstract] ( 39 ) HTML (1 KB)  PDF (2019 KB)  ( 53 ) 298 Non-stationary random seismic response of asphalt concrete core wall WANG Zongkai, SONG Zhiqiang, LIU Yunhe Because of its good environmental adaptability, the asphalt concrete core dam is the finest dam type for the deep overburden site in southwest China's strong seismic zone. Unfortunately, research on the seismic safety evaluation of asphalt concrete core dams under non-stationary random earthquake action is relatively limited. The modified Clough-Penzien power spectrum combined with a random function is utilized in this research to construct a series of non-stationary random ground motion sets that fit the response spectrum while taking into account the non-stationary properties of ground motion frequency and intensity. The mean value and variation range of the horizontal acceleration and vertical permanent deformation of the dam crest are statistically evaluated and tested using an asphalt concrete core dam on a deep overburden layer as an example. The mean value and variability of the response of the overburden and the dam body along elevation are revealed, and the probability density evolution method is used to expose the evolution process of the probability density of the horizontal acceleration of the dam crest over time. At the same time, 55 non-stationary random ground motions generated are magnified and the non-stationary random seismic vulnerability curve of asphalt concrete core dam on deep overburden is developed by combining MSA vulnerability analysis method. The vulnerability curve of dam body with collapse rate as control index of damage level is given. It provides a new method and idea for seismic safety evaluation of asphalt concrete core dam on deep overburden. 2024 Vol. 43 (9): 298-308 [Abstract] ( 44 ) HTML (1 KB)  PDF (4138 KB)  ( 60 ) 309 Test and numerical study on impact failure of drilling coal samples under high strain rate ZHANG Yin1,YIN Lidong1, DAI Lianpeng2, ZHANG Jiping1, LI Jiajun1, YANG Chenchen1 Coal seam drilling is a simple, economical and effective means of impact damage reduction and mitigation. In view of the high strain rate loading after the occurrence of impact pressure, revealing the physical process of impact damage of drilled coal rock and its mitigation mechanism is of great significance for quantitatively designing the parameters of coal seam drilling. In order to study the influence of boreholes under high strain rates on the mechanical properties of coal samples, impact tests were carried out on prefabricated borehole coal samples through indoor SHPB tests and numerical simulation of particle flow. The experimental results show that borehole under high strain rate loading has a significant weakening effect on the dynamic compressive strength of coal samples, with the increase of the number of boreholes, the dynamic compressive strength of coal rock decreases by 11.9%, 20.4%, and 23.2%, respectively; and with the increase of the spacing of drilling holes, the dynamic compressive strength decreases by 20.4%, 14.9%, 8.5%, and 16.4%, respectively. The stress-strain curves of coal samples containing drill holes have a stress drop phenomenon and plastic energy consumption platform period, and the stress drop range and plastic platform range show an upward trend with the increase of the number of holes. The destruction of coal samples by borehole under high strain rate loading has obvious deformation localization guiding effect; when the coal rock is destroyed, the initial primary cracks are generated in the tensile stress area of the hole edge in the parallel loading direction, the secondary cracks are perpendicular to the direction of the primary cracks, and the inter-hole cracks are generated in the inter-hole bridges. The stress concentration zone redistributes with the breakup of the hole bridges, and the hole-side bearing zone is far away from the borehole. The peaks of AE event numbers of coal samples after drilling showed different degrees of backward shift, and the distribution of AE events was characterized by bimodal peaks when L≤2.5d, and single peaks when L>2.5d. 2024 Vol. 43 (9): 309-320 [Abstract] ( 76 ) HTML (1 KB)  PDF (6545 KB)  ( 30 )

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