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Based on the first-order shear deformation theory, the vibration balance equation of composite sandwich plates with embedded viscoelastic layers (CSPEVL) is obtained by using Hamilton principle. The Navier closed-loop solution is used to solve the damping plate structure with four simply supported constraints. The correctness of the derived vibration balance equation is proved by comparing with the simulation results and reference. The verified equations are employed to analyze the dynamic characteristics of the CSPEVL. The results show that as the relative thickness of damping layer decreases, the first four order vibration frequencies of the whole structure all show a declining trend. However, the first four order loss factors are all distributed in an upward convex parabola. In addition, the damping performance of composite damping plate can be significantly enhanced by increasing the width/thickness ratio and aspect ratio of composite plate. More importantly, when the total thickness of the damping layer is constant, the symmetrical distribution of multilayer damping film greatly improves the dynamic performance of the composite structure. The work provides theoretical guidance for the dynamic optimization and structural design of damping sandwich composite structures. [ABSTRACT FROM AUTHOR]

To improve wind turbines' reliability and lifespan, taking the two-stage fixed shaft gearbox of wind turbines as study object. The oil stiffness and meshing stiffness of the transmission system are calculated, and the composite stiffness is obtained with the consideration of lubricating film. Then analyzed the dynamic characteristics of wind turbines' transmission system before and after consider the oil stiffness in different operating conditions. The findings indicate that after considering the gear lubrication effect, the composite stiffness gradually decreases as rotational speed increase; within a certain rotational speed range, the tooth-surface load can be reduced, making the system run more smoothly. Therefore, the presence of oil film and its impact on its stiffness cannot be ignored. This study has certain guiding significance in improving the transmission efficiency and reducing noise of wind turbines. [ABSTRACT FROM AUTHOR]

The friction pair gap affects not only the temperature increase of the multi-disc wet clutch, but also the efficiency of the helicopter transmission system. Consequently, a rotational–axial engagement and disengagement-coupled kinetic model of a wet multi-disc clutch considering asperity contact, hydrodynamic lubrication, spline resistance, and a separating spring model are developed in this paper. The effects of operating conditions on the dynamic characteristics of the wet clutch are investigated. Further, the gap deviation coefficient is proposed to characterize the dynamic behavior of the friction pair gap. As the control oil pressure increases from 1.3 MPa to 1.7 MPa, the gap deviation coefficient increases by 8.6%. Moreover, as the rotation speed increases from 888 rpm to 2488 rpm and the lubricant oil temperature increases from 25 °C to 85 °C, the gap deviation coefficient decreases by 1.1% and 4.44%, respectively. Therefore, an appropriate increase in lubricant oil temperature and rotation speed can facilitate the friction pair gap to be more uniform. These results are useful for the development of optimal control strategies for aviation wet clutch systems. [ABSTRACT FROM AUTHOR]

As the proportion of renewable energy infiltrating the power grid increases, suppressing its randomness and volatility, reducing its impact on the safe operation of the power grid, and improving the level of new energy consumption are increasingly important. For these purposes, energy storage stations (ESS) are receiving increasing attention. This article discusses the structure, working principle, and control methods of grid-following and grid-forming energy-storage converters, which are currently commonly used. A simulation analysis was conducted to investigate their dynamic response characteristics. The advantages and disadvantages of two types of energy storage power stations are discussed, and a configuration strategy for hybrid ESS is proposed. This paper presents research on and a simulation analysis of grid- forming and grid-following hybrid energy storage systems considering two types of energy storage according to different capacity scenarios. Finally, a comparative analysis between the systems is presented. A simulation model was established using PSD-BPA (Power System Department-Bonneville Power Administration) to analyze the impact of the capacity ratio of grid-following and grid-forming ESS on their dynamic response characteristics in a hybrid ESS. In addition, a development direction for future ESSs is indicated.

To improve the application depth and breadth of intelligent unit devices made from piezoelectric structures, their kinetic properties shall be urgently studied. Herein, based on the basic equations and boundary conditions of piezoelectric materials, an interpolation coverage function of node displacement was introduced into the displacement shape function and potential shape function of coupling electromechanical finite element method (FEM), forming an electromechanical coupling enriched FEM generalized shape function. Together with the variation principle, an electromechanical coupling enriched FEM was put forward, and its motion equations were deduced. Next, the free vibration and transient response of the piezoelectric structure were analyzed, and the accuracy and validity of the new method were validated with numerical cases. Results show this method has high application prospects for analyzing the dynamic properties of piezoelectric material structures. [ABSTRACT FROM AUTHOR]

Benefited from its high process feasibility and controllable costs, binary-metal layered structured LiNi0.8Mn0.2O2 (NM) can effectively alleviate the cobalt supply crisis under the surge of global electric vehicles (EVs) sales, which is considered as the most promising next-generation cathode material for lithium-ion batteries (LIBs). However, the lack of deep understanding on the failure mechanism of NM has seriously hindered its application, especially under the harsh condition of high-voltage without sacrifices of reversible capacity. Herein, single-crystal LiNi0.8Mn0.2O2 is selected and compared with traditional LiNi0.8Co0.1Mn0.1O2 (NCM), mainly focusing on the failure mechanism of Co-free cathode and illuminating the significant effect of Co element on the Li/Ni antisite defect and dynamic characteristic. Specifically, the presence of high Li/Ni antisite defect in NM cathode easily results in the extremely dramatic H2/H3 phase transition, which exacerbates the distortion of the lattice, mechanical strain changes and exhibits poor electrochemical performance, especially under the high cutoff voltage. Furthermore, the reaction kinetic of NM is impaired due to the absence of Co element, especially at the single-crystal architecture. Whereas, the negative influence of Li/Ni antisite defect is controllable at low current densities, owing to the attenuated polarization. Notably, Co-free NM can exhibit better safety performance than that of NCM cathode. These findings are beneficial for understanding the fundamental reaction mechanism of single-crystal Ni-rich Co-free cathode materials, providing new insights and great encouragements to design and develop the next generation of LIBs with low-cost and high-safety performances.

This study aims to comprehensively investigate the dynamic characteristics of the tower of a scaled wind turbine model through wind tunnel tests. A model was scaled from the NREL 5 MW prototype wind turbine with a geometric scale ratio of 1/75, based on the similarity rules in thrust coefficient and dynamic characteristics. A series of wind tunnel tests were carried out on the scaled wind turbine model under different operating conditions and parked conditions with different yaw angles, and the modal parameters of the scaled model were identified by the stochastic subspace identification method and rotor stop tests. It was found that the vibration response of the tower in the fore–aft direction achieved its maximum value when the yaw angle was 90° with feathered blades, while the tower vibration response in the side–side direction was relatively severe with the yaw angle ranging from 10° to 50°. These observations are found to be well aligned with the aerodynamic characteristics of the airfoil. Moreover, the experimental results indicate that the scaled wind turbine model can reflect the vibration responses of its full-scale counterpart in the fore–aft direction. The natural frequencies and mode shapes of the scaled model can be accurately identified by different methods, but the identified damping ratios are relatively scattered. [ABSTRACT FROM AUTHOR]

The main functions of the space information system, such as providing the backbone transmission, broadband access, and global connectivity, are realized based on the network topology. Thus, it is necessary to recognize the temporal dynamics of the network topology. A temporal continuity expression method is proposed to describe the topological dynamic characteristics of the network in space information systems. Based on orbit dynamics, a time-dependent adjacency matrix of the space information system can be established by introducing the geometric linkable factor, the link distance intensity factor, and the relative angular velocity factor of the node. The adjacency matrix describes the dynamic characteristics from two layers: one is the physical layer using a time-dependent function, which represents the feasibility of inter-satellite link construction in the system cycle; the other one is the transport layer, described by a piecewise continuous function that varies with time, which characterizes the link quality during the connection period between two satellites. The results show that compared with the existing network topology description methods, the proposed method describes the network topology more accurately, which can distinguish the network topology characteristics at any time, and is more conducive to the understanding and application of the network topology of the space information system. [ABSTRACT FROM AUTHOR]

As the harshness of the underwater operating environment and complexity of underwater tasks gradually increase, underwater hydraulic manipulators with high reliability and precision attract more research attention. To improve the reliability and dynamic performance of the traditional electro-hydraulic proportional valve (EHPV) used in the underwater hydraulic manipulator, an improved electro-hydraulic proportional valve with a discrete pilot stage (DEHPV) is proposed. In the pilot stage, two 2-position 3-way normally open high speed switching valves (HSVs) are used, and the initial oil spring stiffness in the control chamber is large enough to maintain the dynamic performance of the DEHPV. First, the working principle and configuration of the DEHPV are both given, and the coupled electric-magnetic-mechanical-fluid model of the DEHPV is presented. Moreover, a dual-valve hybrid pulse width modulation (DVHPWM) control strategy is proposed to improve the position tracking accuracy of the DEHPV. Furthermore, a co-simulation model of the DEHPV considering the multi-field coupling law is established to study the dynamic characteristics. Extensive experiments are carried out to verify the effectiveness of the proposed structure as well as its good dynamic performance and control accuracy. [ABSTRACT FROM AUTHOR]

Flexible multibody system (FMBS) refers to a mechanical system, which consists of flexible components and kinematic pairs, and undergoes both overall motions and deformations. FMBS serves as a useful dynamic model for many advanced industrial products, such as flexible robots, helicopter rotors and deployable space antennas. Traditionally, the design of flexible components in an FMBS mainly relies on the trial-and-error method, which is time-consuming and cannot guarantee the best design. In addition, the optimization design of the flexible components in an FMBS usually uses a component-based approach without accounting for the interaction between a component to be optimized and the FMBS of concern. Yet, when a component gets more and more flexible, the interaction between the component and the FMBS plays a nonnegligible role in optimization and requires the FMBS-based optimization. This feature article presents the basic ideas and methods for the dynamic topology optimization of an FMBS mainly based on the studies of the authors over the past decade. The article focuses on four emerging topology optimization problems of an FMBS as follows, (i) topology optimization of dynamic responses and dynamic characteristics, (ii) fully coupled and weakly coupled optimizations, (iii) topology optimization of time-varying systems, and (iv) optimization designs and prototype tests of flexible robots. Together with concluding remarks, the article addresses some open problems of the dynamic topology optimization of an FMBS for future researches. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of different airflows on micro-scales have been explored from many perspectives since the late 1970s. On the one hand, most analytical tools and research subjects in previous contributions vary significantly: some only focus on fluctuant velocity features, while others pay attention to directional features. On the other hand, despite the wide variety of existing analytical methods, they are not systematically classified and organized. This paper aims to establish a system including state-of-the-art tools for airflow analysis and to further design a holistic toolkit named Airflow Analytical Toolkit (AAT). The AAT contains two tools, responsible for analyzing the velocity and direction characteristics of airflows, each of which is integrated with multiple analytical modules. To assess the performance of the developed toolkit, we further take typical natural and mechanical winds as cases to show its excellent analytical capability. With the help of this toolkit, the great differences in velocity and directional characteristics among different airflows are identified. The comparative results reveal that not only is the velocity of natural wind more fluctuating than that of mechanical wind, but its incoming flow direction is also more varying. The AAT, serving as a powerful and user-friendly instrument, will hopefully offer great convenience in data analysis and guidance for a deeper understanding of the dynamic characteristics of airflows, and further remedy the gap in airflow analytical tools. [ABSTRACT FROM AUTHOR]

Using coal gangue as a subgrade filler will produce good benefits, and its application prospects are very broad. It is of great engineering and scientific value to study the improvement method and dynamic characteristics of coal gangue subgrade filler under traffic load. Combining the properties of coal gangue material, fly ash and lime and soil were added to improve the bearing behavior of coal gangue subgrade filler. Then, a compaction test was carried out using the principle of orthogonal experimental design. By analyzing the compaction test results, the optimal proportion of each additive was obtained. A large-scale dynamic triaxial test was carried out with the proportion of each admixture in the maximum dry density group in the compaction test. Based on the dynamic triaxial test results, the effect of confining pressure on the permanent strain was analyzed, the analysis model of permanent deformation and cycle number of traffic loading was proposed, and the correctness of the model was verified. In addition, a modified Hardin–Drnevich model was established, which can describe the dynamic stress–dynamic strain curve of coal gangue subgrade filler under traffic load, and then, the dynamic modulus and damping ratio were analyzed. [ABSTRACT FROM AUTHOR]

The prominent problem of articulated steering structure of engineering vehicle is that there is pressure oscillation in the hydraulic system during steering, which seriously affects the performance of steering system. To solve this problem, the maximum stroke difference of left and right cylinders and the minimum maximum cylinder pressure are the optimization objectives, and the position of cylinder hinge point is the design variable. The multi-objective optimization design of articulated steering system is carried out by using the particle swarm optimization algorithm. After optimization, the maximum pressure of the steering system is reduced by 13.5%, and the oscillation amplitude is reduced by 16%, so the optimization effect is obvious. The dynamic characteristics of the hydraulic steering system under different loads, such as pressure and flow rate, are obtained through field steering tests of wheel loaders. The results show that the load has an important effect on the pressure response of the system, and the causes and influencing factors of pressure and flow fluctuation are determined. The relationship between mileage and hydrogen consumption is obtained, which provides data support for vehicle control strategy. The high-pressure overflow power consumption accounts for 60% of the total work, and the work lost on the steering gear reaches 36 kJ. The test results verify the rationality and correctness of the optimization method of steering mechanism and provide data support for the improvement in steering hydraulic system. [ABSTRACT FROM AUTHOR]

Aiming at the prominent problem of unbalanced coupled vibration of the cantilever coaxial dual-rotor system, the coupled mechanism of the cantilever dual-rotor system was theoretically derived, simulated, and experimentally studied by taking the dual-rotor system of an open rotor engine as the research object. Firstly, the equivalent dynamic model and coupled dynamic equation of the dual-rotor system were established by finite element method(FEM), and the coupled vibration mechanism of the cantilever coaxial dual-rotor system was analyzed. Then, the mode analysis, critical speed analysis, and unbalanced response analysis of the dual-rotors system were conducted by finite element software. The concept of the self-sensitivity coefficient was established to quantitatively evaluate the sensitivity of the system to unbalanced vibration and coupled state. Finally, according to the actual structure, a cantilever coaxial dual-rotor test platform was designed to perform the unbalanced vibration suppression experiment under different speed ratios, and the simulation results were verified by the experimental results. The research results show that the self-sensitivity coefficient proposed by the simulation can be used as the theoretical basis for the actual vibration measuring point arrangement and unbalanced vibration suppression strategy of the dual-rotor system. The unbalanced vibration reduction of the dual-rotor system can be reduced by more than 80% by applying the multi-step vibration suppression strategy of balancing the inner rotor first and then the outer rotor. This study has certain guiding significance for the layout of sensor measurement points and the coupled vibration suppression of the system in the dual-rotor system. [ABSTRACT FROM AUTHOR]

Based on the lubrication analysis model and dynamic characteristics mathematical model of foil dynamic pressure gas bearing,the dynamic equation of foil dynamic pressure gas bearing-rotor system was established combining Newton's mechanical equation,and the calculation method of the stiffness and damping coefficient was studied.The vibration and speed of the foil dynamic pressure gas bearing-rotor system was tested,and the stiffness and damping coefficient was calculated.The linear and nonlinear instability phenomena of the foil dynamic pressure gas bearing-rotor system during the acceleration process was analyzed combining the mapping method,and the influence of speed on the stiffness and damping coefficient was studied. The results show that the main stiffness coefficient of the foil dynamic pressure gas bearing rotor-system increases with the increase of speed, while the cross stiffness decreases with the increase of speed and the trend of change is relatively gentle. The damping coefficient decreases with the increase of speed. The damping of the system suppresses disturbances and the accumulation of low-frequency energy, avoiding foil vibration and effectively improving the stability of the system operation.The proposed dynamic characteristic coefficient calculation method, combined with gas lubrication theory and dynamic model, and combined with experimental testing, can effectively obtain the dynamic characteristics of the bearing-rotor system. [ABSTRACT FROM AUTHOR]

The cutting force suffered by the machine tool in the cutting process can be assumed to be the combined force of the steady state force and the dynamic disturbing force.In order to investigate the dynamic characteristics of electric spindle system supported by gas bearings,sine wave was used as dynamic disturbance loading form,and the dynamic characteristics of a simplified model of a gas bearing rotor system were studied by combining the harmonic excitation method with the bidirectional fluid-structure coupling numerical simulation. The dynamic stiffness and damping coefficients were identified. Through modal analysis,the system vibration modes and natural frequencies of the rotor under different steady-state forces were obtained. The results show that with the increase of steady-state force,the growth rate of Kyy of the lower radial bearing is greater than that of Kxx,while the cross stiffness and cross damping are almost unchanged.The main stiffness of the lower radial bearing is greater than the cross stiffness,and the main damping is greater than the cross damping. When the steady-state force ranges from 50 N to 200 N,the y-shift at the lower end of the rotor first increases and then decreases with the increase of dynamic disturbance frequency. The resonance frequency of the system increases with the increase of the steady-state force. [ABSTRACT FROM AUTHOR]

CGN Delingha 50MW parabolic trough solar power plant is China's first commercial trough solar power station. There are 190 heat collecting loops in the solar field of the power plant. Due to the mutual coupling of heat collecting loops layout location, environmental conditions, medium flow, working medium physical property changes and other factors, the hydrodynamic characteristics of the solar field are complex. In practical operation, balancing the flow of the heat absorbing medium in each loop of the large-scale trough solar thermal power plant and stabilizing the outlet medium temperature are difficult problems. Taking CGN Delingha 50MW parabolic trough solar power plant as the research object, this paper adopts the idea of modular modeling to establish the mathematical model of the main equipment in different systems of the power plant, to build the dynamic model of its solar field, steam generation system, heat storage system and steam turbine system. Based on the parallel computing function of the real-time dynamic simulation platform STAR-90, the real-time coupling calculation between different systems is realized. The error of the built model in steady-state is less than 2%, and the dynamic results of the model are in good agreement with the actual operation data. The modeling method in this paper is universal and can be a reference for dynamic modeling of other large-scale trough solar thermal power plants.

Abstract\nHIGHLIGHTSFor the sake of improving climbing ability of railway vehicle, gear-rack system is added to traditional vehicle to form rack vehicle. Aiming at the influence of the different gear-rack systems on the rack vehicle dynamic behavior, this article considers the gear-rack meshing impact based on the analysis of the generation mechanism of the gear-rack meshing excitation. The gear-rack meshing model and four kinds of rack vehicle coupled dynamics models are established, and the model is verified by experiments. Based on the model, the gear-rack nonlinear meshing behavior and rack vehicle dynamics characteristic of two kinds of Strub system, double row teeth Abt system and Locher system under different slopes is explored. and the dynamic characters of the rack vehicle system is analyzed. Finally, the optimal gear-rack system is obtained by comparing the dynamic behavior of different vehicles. The results show that: The dynamic behavior of rack vehicles with different gear-rack systems is significantly different, and Locher system has the optimal dynamic behavior. The gear-rack nonlinear meshing behavior and the vehicle safety of the coaxial Strub system and the double row teeth Abt system are poor, which are obviously affected by the track irregularity. The impact of the gear-rack nonlinear contact force of the coaxial Strub system reaches 29.8 kN. The maximum wheel/rail vertical force of the double row teeth Abt system reaches 51.4 kN. The vehicle stability of the different shaft Strub system is the worst, and the maximum stability index is 1.368. The conclusion of this paper provides theoretical support for the design and safe operation and maintenance of the world’s mountainous rack railway.Considering the disturbance effect of gear-rack meshing impact and wheel/rail dynamic contact behavior, a complete dynamic model of rack vehicle is established based on multi-body dynamics.The influence of the different kinds of gear-rack system on the dynamic characteristics of rack vehicle and nonlinear meshing behavior of driven gear-rack system are explored. [ABSTRACT FROM AUTHOR]

Product development is a complex process involving intricate components, dynamics and constantly evolving internal and external environments, as well as numerous influencing factors. In order to accurately simulate and predict the effectiveness of the development process, this paper proposes a system dynamics simulation method based on information maturity. Different types of development processes are simulated, and the discussion includes the impact of activity information correlation, information evolution coefficient, start time, and other parameters on the dynamic behavior of the process. This study examines a specific mold development process as a case study to validate the method's feasibility, accurately predicting the duration and cost of the process. It also investigates dynamic fluctuations resulting from uncertain events such as changes in customer demand and resource shortages. The method provides support for process optimization and resource scheduling. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A hydraulic support is one of the most important pieces of equipment in fully mechanized coal mining, and its stability and reliability will have a direct impact on fully mechanized coal mining. In order to deeply elucidate the dynamic working characteristics of a hydraulic support during lifting, lowering, and moving, and to provide theoretical support for further optimizing the stability and reliability of a hydraulic support, the dynamic characteristics of a hydraulic support are studied in this paper. Firstly, in order to study the dynamic working characteristics of hydraulic support lifting, a rigid–flexible coupling dynamic simulation model of a hydraulic support is established; in order to study the dynamic working characteristics of hydraulic support moving, a microcontact dynamic model of a hydraulic support and the caving face roof and floor based on G-W contact theory is proposed, and the first rigid–flexible–mechanical–hydraulic coupling dynamic simulation system of a hydraulic support and the roof and floor of a caving face is established in the industry. Then, based on this foundation, simulation experiments are conducted for hydraulic support lifting, moving without pressure, and moving with pressure, respectively. The working characteristic parameters of the hydraulic support are collected and analyzed. The results show that working speed, working height, surface contact conditions, residual working resistance, and impact load have different effects on the stability and reliability of the hydraulic support. This study can provide in-depth technical support and theoretical guidance for understanding and improving the dynamic working characteristics of the hydraulic support. [ABSTRACT FROM AUTHOR]

Finite element models are widely used in dynamic analysis of misalignment rotor, but present finite element rotor models cannot simulate the axis characteristics of angle misalignment rotor, which consistent with the one with no misalignment. For achieving the precisely modeling of angle misalignment rotor, a novel modeling method called cross-coordinate substructure modeling method is introduced to establish the model of misalignment rotor, in which different parts of rotor rotate around different axis. Based on this modeling method, the 3D solid models of angle misalignment rotor are established with the help of ANSYS, and the modal characteristics and critical speeds of the misalignment rotor are achieved through modal analysis and harmonic response analysis. The numerical simulation based on Newmark method and experiment tests is carried out to obtain the response characteristics of the rotor model under the combined action of unbalanced force and misalignment load. The results show that the modal "rotation of rotor" appears, and the more amounts of response peaks can be aroused in harmonic response analysis when the rotor occurs angle misalignment. The typical fault characteristics of angle misalignment rotor in the spectrums and orbit diagrams are generally consistent both in the numerical simulation and experiment test. The research results can provide a theoretical basis for simulation and identification of the misalignment fault in rotating machinery system. [ABSTRACT FROM AUTHOR]

The ejector-driven hydrogen recirculation system plays an important role in enhancing efficiency of the PEM fuel cell. It's necessary to have deep knowledge of dynamic characteristic of the ejector for optimizing system state, but until now related research is not adequate. In this paper, dynamic characteristic of the ejector for the hydrogen recirculation system of the PEM fuel cell is studied using active periodic pressure excitation. Test plant is set up and active periodic pressure excitation with small amplitude is superimposed on steady pressure at the ejector primary flow inlet. Experiment result shows that in frequency domain, amplitude ratio of dynamic pressure at primary flow inlet to the dynamic delta-pressure, equal to pressure at mixing outlet minus that at backflow inlet, is independent of excitation frequency for each steady operating point. In the complex coordinate, vector of dynamic pressure at primary flow inlet is in parallel with that of dynamic delta-pressure, for all frequencies and for all stable operating points. Furthermore, amplitude ratio of dynamic pressure at primary flow inlet to dynamic delta-pressure exhibits linearity with entrainment ratio of the ejector for all stable operating points. Experiment on the 120 kW fuel cell system validates the same dynamic characteristic. • Dynamic characteristic of ejector studied using active periodic pressure excitation. • Ratio of dynamic primary-flow pressure to delta pressure independent of frequency. • Vector of primary-flow pressure in parallel with that of the dynamic delta-pressure. • Ratio of primary-flow pressure to delta pressure in linearity with entrainment ratio. [ABSTRACT FROM AUTHOR]

The micro-electro-mechanical system is widely used for energy harvesting and thermal wind sensor, its efficiency and reliability depend upon the pull-in instability. This paper studies a micro-electro-mechanical system using He-Liu [34] formulation for finding its frequency-amplitude relationship. The system periodic motion, pull-in instability and pseudo-periodic motion are discussed. This paper offers a new window for security monitoring of the system reliable operation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Test & Measurement Technology is the property of Publishing Center of North University of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An integrated and bionic passive vibration isolation system is proposed based on the double-diamond bionic structure and inerter to solve the problems of poor low-frequency vibration isolation performance, narrow vibration isolation frequency band, and big additional mass of current passive vibration isolation system. To analyze the low-frequency vibration isolation performance and the valuable frequency band, the nonlinear dynamic model of the system is established, then the system transmission characteristics and stability are studied. It is found that the system can reduce the amplitudes of resonant peaks, broaden the valuable frequency band, and the system stability is excellent. Seen from the performance analysis, the introduction of the inerter with smaller additional mass makes the system have better vibration isolation performance and wider effective vibration isolation frequency band. The proposed system provides a new solution for vibration control in practical engineering. [ABSTRACT FROM AUTHOR]

• A novel linear carbon dioxide compressor is introduced. • Resonance springs can be replaced with gas springs and magnetic springs. • The dynamic characteristics of the proposed compressor are studied. • The designed compressor achieves over 20 % reduction in leakage. In this study, an innovative two-stage linear CO 2 compressor with dual piston is proposed and its simulation model is developed. The dynamic characteristics of the two-stage dual-piston compressor are comprehensively analyzed. The simulation results indicate that the dual-piston configuration leads to gas forces oscillating around the zero axis, resulting in a reduction in the mean gas force, allowing for the replacement of the resonance spring with gas springs and magnetic springs. The dynamic performance of the two-stage linear compressor is compared with that of a single-stage linear compressor. The moving center offset of the dual-piston two-stage compressor is reduced by approximately 90 %. The gas equivalent stiffness and the equivalent damping at the TDC (Top Dead Center) get lower than the single-stage one by 25.7 % and 11.6 % as the pressure ratio is set at 2.5. The leakage during the compression process gets lower by more than 20%. The dual-piston compressor demonstrates excellent capacity and modulation capabilities, with a theoretical increase in cooling capacity of over 300 W when the stroke is increased from 6 mm to 8 mm. [ABSTRACT FROM AUTHOR]

A seawater hydraulic variable ballast system (SHVBS) is used to dynamically adjust the weight of the submersible. The balance valve is a crucial component of SHVBS which has two working conditions called charging and discharging process. In this paper, an experiment simulating the ocean is built to obtain the dynamic characteristics of the balance valve, including the starting pressure and the pressure difference. Then there are analyzed by a kinematic model. The results show that as the depth increases, the pressure difference increases during charging process, while it remains unchanged during discharging process. Charging process is much worse than discharging process for balance valve. When the depth is 600 metres, the pressure difference during charging process is 45 times higher than during discharging process. Furthermore, friction force is the main factor that affects the starting pressure, while the hydraulic force mainly affects the pressure difference. [ABSTRACT FROM AUTHOR]

Traditional two-dimensional dynamic fault detection methods describe nonlinear dynamics by constructing a two-dimensional sliding window in the batch and time directions. However, determining the shape of a two-dimensional sliding window for different phases can be challenging. Samples in the two-dimensional sliding windows are assigned equal importance before being utilized for feature engineering and statistical control. This will inevitably lead to redundancy in the input, complicating fault detection. This paper proposes a novel method named attention-based two-dimensional dynamic-scale graph autoencoder (2D-ADSGAE). Firstly, a new approach is introduced to construct a graph based on a predefined sliding window, taking into account the differences in importance and redundancy. Secondly, to address the training difficulties and adapt to the inherent heterogeneity typically present in the dynamics of a batch across both its time and batch directions, we devise a method to determine the shape of the sliding window using the Pearson correlation coefficient and a high-density gridding policy. The method is advantageous in determining the shape of the sliding windows at different phases, extracting nonlinear dynamics from batch process data, and reducing redundant information in the sliding windows. Two case studies demonstrate the superiority of 2D-ADSGAE. [ABSTRACT FROM AUTHOR]

The coincidence degree is an important parameter to reflect the number of meshing teeth of gear pairs at the same time. The appropriate coincidence degree of reasonable selection can improve transmission bearing capacity and ensure transmission stability, thereby improving the performance and reliability of the gear transmission system. The analysis of the influence of system parameters on system vibration characteristics under different coincidence degrees is of great significance for optimizing the transmission system performance, improving work efficiency and reducing fault risk. Combining meshing performance and dynamic characteristics of gear teeth, firstly, stiffness excitation and meshing impact excitation of the herringbone gear system are determined, and the lumped parameter method is used to establish the nonlinear dynamic model of the bending-torsion-shaft coupling of herringbone gear pairs under complex excitation source. Then, the nonlinear dynamic equations are subject to elimination of rigid body displacement and dimensionless treatment. Finally, the influence of system parameters on system dynamic characteristics under different coincidence degrees is studied. The research shows that when the coincidence degree changes from 2.72 to 3.08, the root mean square (RMS) value of comprehensive relative vibration acceleration of the gear pair is reduced by about 40%, which shows that increasing the coincidence degree can improve the stability of the gear system. In addition, with the change of system parameters, increasing coincidence degree can eliminate the jump phenomenon in the system and reduce the amplitude of jump and resonance peak.

This paper proposes a dynamic characteristics improvement of battery charger for personal mobility devices (PMDs) using a model predictive control (MPC). The battery charger is used to charge a battery of PMDs such as electric scooters, electric bicycles, and electric skateboards and an output voltage of the battery charger is generally controlled by a proportional-integral (PI) controller. The PI controller requires a gain tuning to improve a dynamic characteristic, however, an overshoot of the output voltage can be occurred in transient state when the gain is increased. Therefore, to improve the dynamic characteristic of the battery charger for PMDs, this paper presents the MPC method to control the output voltage of the battery charger for PMDs. The effectiveness of the proposed MPC method is proved by the simulation and experimental results.

The friction pair gap affects not only the temperature increase of the multi-disc wet clutch, but also the efficiency of the helicopter transmission system. Consequently, a rotational–axial engagement and disengagement-coupled kinetic model of a wet multi-disc clutch considering asperity contact, hydrodynamic lubrication, spline resistance, and a separating spring model are developed in this paper. The effects of operating conditions on the dynamic characteristics of the wet clutch are investigated. Further, the gap deviation coefficient is proposed to characterize the dynamic behavior of the friction pair gap. As the control oil pressure increases from 1.3 MPa to 1.7 MPa, the gap deviation coefficient increases by 8.6%. Moreover, as the rotation speed increases from 888 rpm to 2488 rpm and the lubricant oil temperature increases from 25 °C to 85 °C, the gap deviation coefficient decreases by 1.1% and 4.44%, respectively. Therefore, an appropriate increase in lubricant oil temperature and rotation speed can facilitate the friction pair gap to be more uniform. These results are useful for the development of optimal control strategies for aviation wet clutch systems.

In order to further improve the bearing stiffness, the porous aerostatic bearings can obtain bidirectional stiffness without additional preload guideway by combining vacuum preloaded (VPL) technology with the bearings. To explore the influence of working conditions and structural parameters on VPL porous aerostatic bearing performance, a numerical analysis of static and dynamic characteristics was performed based on the computational fluid dynamics (CFD) method. The influences of the air supply pressure, the vacuum degree, the permeability, the vacuum suction port diameter, the perturbation amplitude and the perturbation frequency were thoroughly investigated. The analysis shows that the stiffness of VPL porous aerostatic bearings increases by 22.34% compared with that of ordinary porous bearings, and working conditions and structural parameters have a significant influence on static and dynamic characteristics. It is expected that the results can guide performance research and optimization design for the high-stiffness aerostatic bearings. [ABSTRACT FROM AUTHOR]

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To design and optimize the thermal management of metal hydride (MH) tank, high-fidelity model (HFM) composed of numerous partial differential equations, is often adopted to capture the spatial evolution of key parameters accurately. However, computational difficulties raise in dealing with such nonlinear interconnections for system-level simulation. Therefore, the model reduction of MH system has drawn much attention aiming at the trade-off between accuracy and computational cost. In this paper, a hybrid modeling method which integrates advantages of the state-space model (SSM) and HFM, is proposed and applied for the model reduction of MH tank. In particular, four data-driven matrices are introduced to improve the model accuracy. The results show that the root mean square errors of the average temperature between hybrid reduced model (HRM) and HFM are 0.0399 K and 0.1989 K respectively for the cases without and with thermal management. In addition, the HRM is able to capture dynamic characteristic under perturbed input variables with a relative error of temperature within 0.4%, indicating great potential for system-level simulation. What's more, the analysis of predominant pole derived from the state matrices of different thermal managements, reveals that the expanded graphite has superior effect on the adjustment time extension compared with fins, while the fins have distinct advantages in heat transfer enhancement at the cost of volumetric hydrogen storage density. • A hybrid modeling method combining state-space model and data-driven correction is proposed. • The reduced model of MH tank shows great agreement with HFM under various operation parameters. • The accuracy of reduced model has also been verified for the MH tank with thermal management and perturbed variables. • The effect of thermal management on the dynamic characteristic of MH tank is summarized. [ABSTRACT FROM AUTHOR]

In order to improve the energy absorption performance of the aluminum foam, a multi-wall tube reinforced aluminum foam was proposed. The dynamic crushing characteristics of the aluminum foam, the multi-wall tube, and the multi-wall tube reinforced aluminum foam were studied by Hopkinson pressure rod tests & finite element analysis with software ABAQUS/Explicit. The deformation mode and energy absorption of the aluminum foam was compared with those of the multi-wall tube reinforced aluminum foam, with the strain rate effect on the coupling enhancement discussed. The results show that, the finite element analysis can simulate the test results well. The strain rate effect on the aluminum foam is not obvious, while that on the multi-walled tube and the multi-wall tube reinforced aluminum foam is considerably obvious, and the energy absorption improves with higher strain rates. Under the dynamic impact condition, the peak strength of the multi-walled tube reinforced aluminum foam has obvious coupling enhancement compared with that of the multi-walled tube or the aluminum foam, and the corresponding energy absorption of the former increases by 10.34% over the sum of those of the latter ones. The study on dynamic crushing characteristics of the multi-walled tube reinforced aluminum foam provides a reference for the application of energy-absorbing load-carrying components. [ABSTRACT FROM AUTHOR]

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Purpose: Elastic Ring Squeeze Film Damper (ERSFD) is normally incorporated into high-speed ball bearings to attenuate the vibration amplitude of the rotor system in aero-engines. At high rotor speeds, the bearing introduces considerable nonlinear excitation to the journal, causing it to exhibit distinct dynamic properties. As well, the deformation of the elastic ring in the ERSFD model significantly influences the hydrodynamic reaction force on the journal. This paper develops a high-speed ball-bearing excited ERSFD model with the deformation of the elastic ring analytically formulated. The effects of rotor operating speed and squirrel cage stiffness on the transient and steady-state dynamics of the journal were examined. Methods: The journal is modeled under the excitation of ball-outer raceway interaction rather than rotor unbalance force, emphasizing heavy thrust-applied load. Ball-outer raceway interaction is calculated using a modified quasi-static model. Elastic ring deformation is derived analytically through a thin-walled ring and the oil film pressure is governed by the generalized Reynolds equation. Runge–Kutta approach was used to numerically integrate the differential equations of motion, and the journal center orbit and vibration acceleration were experimentally measured. Results: The results show that as the squirrel cage stiffness increases by 1.23 times from 0.6855, the eccentricity and transmissibility for the ERSFD with bearings are increased by a factor of 1.8 and 3, respectively. Correspondingly, the values for the ERSFD without bearings are increased by a factor of 1.7 and 2.7. As the rotor operating speed increases by 1.75 times from 8000 r min−1, the eccentricity and transmissibility for the ERSFD with bearings are decreased by 28.6% and 54.6%, respectively; for the ERSFD without bearings, the eccentricity remains unchanged and the transmissibility is decreased by 26.2%. Conclusion: It was concluded that when the journal works at a steady state an increase in squirrel cage stiffness disadvantages attenuation in bearing excitation; adequately high rotor operating speeds benefit journal dynamics when bearing excitation is considered in ERSFD. At transient state, lower squirrel cage stiffness and higher rotor operating speed allow the journal to behave in stable periodic motion for the ERSFD with bearing excitation; however, for the ERSFD without bearing excitation, lower squirrel cage stiffness fails to make the journal whirl periodically, and the rotor operating speed has little effect on the transient dynamics of the journal. [ABSTRACT FROM AUTHOR]

The chain drive system represents a critical subsystem within the scraper conveyor. This paper proposes a joint simulation model for the drive system of the scraper conveyor, driven by the permanent magnet synchronous motor, in order to conduct a comprehensive analysis of the dynamic characteristics of the chain drive system during the operational process. Firstly, the dynamic simulation model for the mining scraper conveyor's chain drive system was established in ADAMS, taking into account its structural characteristics. Then, the mathematical model of the permanent magnet synchronous motor was established using the coordinate transformation theory, and the speed controller based on vector control was designed by using the theory related to sliding mode control. The coupling relationship between the chain drive system of the scraper conveyor and the permanent magnet synchronous motor drive system was investigated. Finally, a joint simulation model of the mechanical system and motor control system was created using ADAMS (View 2019) and MATLAB/Simulink (2020a). The dynamic characteristics of the chain drive system were analyzed, and the three typical working conditions of no load, half load, and rated load were considered. The results show that the contact force between the flat ring and the sprocket undergoes an initial increase, followed by a decrease, and finally another increase. As the load increases from no load to full load, there is a marked increase in the contact force between the loaded side chainrings. Due to the polygon effect, both the speed curve of the permanent magnet drive motor and the contact force curve between the ring chains exhibit periodic fluctuations. The research in this paper provides an idea for the coupling analysis of the scraper conveyor electromechanical system. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To meet the needs of the wind tunnel test research on the aerodynamic characteristics and flow mechanism of highspeed coaxial rotor, the Ф1. 5 m diameter coaxial rigid rotor test stand was developed in the FL-52 acoustic wind tunnel of Aviation Industry Aerodynamics Research Institute of China (referred to as the coaxial rotor test stand). The coaxial rotor test stand was composed of test stand system,rotor measurement and control system. A high power density AC frequency conversion motor drove the upper and lower rotors to reverse synchronously, which can realize the synchronous and accurate control functions such as rotor spindle inclination, rotor speed, rotor total pitch and periodic pitch. Through the ground mode test and dynamic balance adjustment of the coaxial rotor test stand, the resonance correlation between the rotating frequency and the natural frequency of the test stand was excluded. The wind tunnel test results of 1. 5 m diameter rotors were carried out by using the coaxial rotor test stand. The results show that the trimming strategy is reasonable in hovering and forward flight states, the efficiency of the upper rotor is higher than that of the lower rotor in hovering state, and the proportion of the pulling force of the upper rotor in the total pulling force is not changed much in the torque trimming state. [ABSTRACT FROM AUTHOR]

To solve the problems of the nonlinear damping force in the traditional squeeze film damper (SFD), a novel structure of G-type integral squeeze film damper (GISFD) based on ISFD is proposed for the first time. The finite element model and test rig of the ball bearing-rotor system are established to explore the influence of GISFD and ISFD on the dynamic characteristics of the unbalanced rotor system. The results show that both GISFD and ISFD can change the critical speed of the rotor system, reduce the bending strain energy of the shaft, and reduce the bearing dynamic load of the rotor system. Through comparison, it is found that the effect of GISFD is more obvious. The experimental results show that, compared with the unbalanced rotor system without damper, the peak-peak value of amplitude in the rotor system with GISFD and ISFD at 3000 rpm is reduced by 25.53 and 15.81%. The amplitude in the disk at the first-order critical speed is effectively reduced, and the reduction range reach 52.01 and 35.44%, respectively. GISFD has a more significant effect of suppressing unbalanced vibration, and has superior vibration damping performance when compared with ISFD. [ABSTRACT FROM AUTHOR]