Journal of Vibroengineering
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Induction motor pre-excitation starting based on vector control with flux linkage deviation decoupling
Full text linkThe traditional starting methods for induction motors are easy to cause excessive starting current, which causes serious damage to AC speed regulating system. With analysis on the essence of magnetic field control, A method on asynchronous motor pre-excitation starting based on flux linkage compensation deviation decoupling is proposed in this paper. Based on vector control, a DC flux linkage with stable amplitude and direction is established by using DC pre-excitation starting method. According to the fluctuation of flux linkage in dynamic process and the coupling of the system, flux compensation algorithm and deviation decoupling control are used to decouple the flux compensation and the system to realize the smooth starting of the motor. The experimental results show that the proposed method can effectively reduce the starting peak current and improve the starting performance
Friction pendulum test and parameter optimization for the vibration reduction of a 100 kv isolating switch
Full text linkAn earthquake is a natural disaster with a high destructive force. According to previous history, a great many power grid facilities are damaged during the earthquake, and the damage to electrical equipment in substations are often very serious. This article takes the isolating switch in the substation as an experimental object. Firstly, the friction pendulum for vibration isolation is designed and manufactured according to the numerical simulation, and then the seismic test and vibration isolation test of the high voltage isolating switch are designed. The input waveforms and input acceleration intensities of the seismic test were designed experimentally. The test data of the isolating switch under the seismic condition and the vibration isolation condition with the friction pendulum vibration isolation system installed are mainly investigated. The measured acceleration of the top of the isolating switch bracket is used to compare and analyze the vibration isolation performance of the friction pendulum. Then, it can be seen that the friction pendulum system has the vibration isolation effects on the isolating switch. Especially, the isolation effects of friction pendulum are better when the acceleration intensity become higher. In order to obtain a better curvature radius and friction coefficient of the friction pendulum, based on the results of this test, the systematically numerical simulation tests for optimization on the friction pendulum vibration isolation system are conducted. The simulated top displacement of the isolating switch and the stress change of the root of the porcelain bottle were obtained. By comparing the vibration isolating performance of the friction pendulum under different parameters, numerical simulations show that the vibration isolation performance of the friction pendulum is better when the radius of curvature is 1200 mm and the friction coefficient is 0.04. The numerical results demonstrate that reasonable design of friction pendulum parameters can play a significant role in isolating vibration for power equipment
Consideration of longitudinal vibration of automobiles in planar model with taking road deformation and loss of contact into account
Full text linkThis article considers longitudinal planar vibration of a two-axle automobile moving linearly with a constant velocity and subjected to pre-deterministic kinematic excitation caused by the rough road surface. The automobile is modeled as a vibration system which has three masses and four degrees of freedom. The deformed road is modeled as an elastic beam which is simply supported at the two ends and lying on Kelvin’s visco-elastic ground. The change in dimensions of the contact areas is considered. The loss of contact between the wheels and the road surface is taken into account by producing the contact state parameters in the differential equations of motion of the vibration system. The partial differential equation which describes the motion of deformed road is then transformed into a set of all ordinary differential equations by applying the Bubnov-Galerkin’s method. Some typical results coming from numerical consideration are also presented in the article
Comparison of the seismic and wind analyses of two tower cranes
Full text linkTower cranes act as essential support equipment for the development of the city’s construction projects, not only for new projects but also in the rehabilitation of old structures. In the present study, we analyze and compare two different tower cranes, where the differences are essentially based on the geometry, weight, and consequently the reach and load capacity of each structure. In general, these types of structures correspond to slender steel structures designed to carry high loads. Despite the great importance given to these structures, many disasters have occurred causing damage to people or to urban equipment in the vicinity due to total or partial collapse. We developed a 3-D mathematical linear model of the structures in SAP2000 and compared the analytical frequencies with in situ measurements. The maximum error for the first two translationally identified modes in the x and y directions was 4.9 %. These structures are very flexible, with frequencies below 0.5 Hz. We then applied and evaluated the impact of two types of exceptional action, seismic (maximum reference acceleration of 1.5 m/s2 and 1.7 m/s2) and wind load characteristics of an urban area (surrounded by buildings), for the two structures not carrying any load. The effects resulted in no serious consequences, with wind being the most severe action in certain cross-sections and seismic action in others. One very important and innovative aspect of this study was the in situ characterization of the frequencies and the verification that the mathematical model reproduced the behavior of the real structure very well. We complemented this study by measuring four more structures and proposing a law to estimate the frequency as a function of the length of the tower plus jib. However, we also found from a literature review of recently published work that, contrary to the six structures that we analyzed, it is difficult to extrapolate this law for other types of tower cranes
Analysis of dynamic response law and time-frequency characteristics of high cut slope under the action of earthquake
Full text linkThis study aimed to reveal the dynamic response law and time-frequency characteristics of the slope under the action of earthquake. Based on an actual project in earthquake area, the stability of the slope under natural and seismic conditions was calculated and the meso parameters of rock and soil were obtained by indoor rock and soil specimen parameter test firstly. Meanwhile, a three-dimensional particle flow model of the high-cut slope was established by the three-dimensional particle flow software PFC3D. Then, the law of dynamic response of the slope acceleration was obtained by inputting the horizontal wave of 2008 Wenchuan earthquake. Furthermore, MATLAB programming was used to analyze the time-history signal of acceleration of the slope, and finally the time-frequency characteristics of the high cut slope under the action of earthquake were studied. The results show that the dynamic response characteristics of soil particles in horizontal and vertical directions show surface-tending effect and elevation amplification effect respectively under the action of earthquake. The analysis of time-frequency characteristics showed that the Fourier dominant frequency of soil particles is distributed between 0-5 Hz under the action of earthquake, the low frequency band (0-15.625 Hz) accounts for as high as 88.07 %, and the high frequency band (125-250 Hz) accounts for as low as 0.34 %
A method to diagnose compound fault of rolling bearing with ITD-AF
Full text linkIn an engineering practice, the faults of rolling bearing are mostly represented as being compound and hard to diagnose. For that, intrinsic time-scale decomposition (ITD) algorithm was combined with Auto-correlation Function (AF) to extract the characteristics of compound faults of rolling bearing in aviation engine. Firstly, ITD algorithm was used to decompose acceleration signal into multiple rotational and residual trend component; secondly, rotational components were reconstructed to figure out their AF; finally, characteristic frequency of rolling bearing under compound faults mode was extracted by Hilbert spectrum envelope. To validate the effectiveness of the method, a comparative study on sensor installation positions and vibration acceleration signal of different compound faults has been carried out. The result of study shows that the proposed ITD-AF method is capable to extract compound fault characteristics of rolling bearing in an effective and precise manner and the installation positions of sensors, rotation speed and fault type shows insensitivity to extraction
Kinematics analysis of a FLHL robot parallel-executed cylinder mechanical integration system with force/position hybrid control servo actuator
Full text linkIn this research subtopic, an electro-hydraulic servo four-legged heavy load (FLHL) robot has been designed and developed. This paper proposes an integration layout cylinder design scheme for a non-lightweight hydraulic servo four-legged robot with high loads and torques of hip joint, and derives the mathematical element analysis model for a parallel hydraulic servo cylinder system. The multiple inherent characteristics of the parallel-executed cylinder integration system model are further explored. Based on the controllable functional requirements of interconnected joints and weakening the influence of internal force coupling, a design idea of force/position hybrid control scheme for the parallel-executed cylinder is determined, and then the force/position signal module design unit is used to reversely solve the force/position hybrid control. Considering the inherent requirements of the servo-executed cylinder force control unit module, the implementation process of magnetic flux compensation and speed compensation is discussed in detail. The minimum amplitude controller is applied to the servo-executed cylinder force unit module, and the proportional integrated controller has been determined in the servo-executed cylinder position control unit module. A compound control strategy proposed in this paper is verified on a parallel hydraulic servo platform. The experimental verification results reveal that the values of position/force attenuation amplitude and lag phase are not greater than 9 % and 18°, respectively. In addition, the feasibility of the interconnected implementation of the hybrid control scheme proposed in this paper is further deepened. The effective conclusion of this research will be accepted in the application field of FLHL robot control system
Numerical simulation analysis of a PGR exterior body structure considering vibroacoustic characteristics
Full text linkPrevious studies have attempted to identify weak links in the dynamic characteristics of the planetary gear reducer (PGR) exterior body structure (EBS). Through numerical simulation, these studies analyzed the modals and natural frequencies and the vibration types of each order of the EBS. However, these scholars have never focused on the main factors affecting the dynamic characteristics of the EBS of this subject. This study in the topic has analyzed the vibroacoustic characteristics of an EBS and optimized its design using numerical simulation. Herein, the contribution of the vibration transfer path from the excitation points on the exterior body to the machine foot is emphatically revealed, and the influences of the main structural parameters on the transfer characteristics are discussed. An optimal EBS for a PGR with lower acoustic vibrations is designed in detail, and a composite EBS with damping vibration attenuation and acoustic absorption is proposed. The radiation acoustic characteristics without acoustic protection and damping materials are analyzed. These research results are implemented in order to realize the dynamic characteristics, transmission, and radiation acoustic characteristics as objects of optimization, and the structural design parameters of the PGR exterior body are deeply optimized using dynamic modification and sensitivity analysis. This topic focuses on the vibroacoustic coupling of EBS in stationary fluid and average flow field, based on the analysis method of theoretical modeling and numerical calculation, the EBS dynamic response and vibroacoustic characteristics under the action of frontal excitation external acoustic flow field are studied, which will be beneficial to explore the comprehensive optimization design of GPR dynamic and vibroacoustic properties
Flutter performance optimization of a long-span truss girder bridge in mountainous canyon
Full text linkSteel truss stiffening girders are widely used when designing long-span bridges in mountainous areas owing to their distinct characteristics compared to the streamlined box girder. However, natural wind in mountainous areas is very complex with high turbulence and large attack angles which adversely affect the flutter performance of long-span bridges with truss girders. Aerodynamic countermeasures are widely adopted to improve flutter performance. This paper studies the flutter performance and the effects of various aerodynamic countermeasures on the flutter improvement of a 1060 m truss-stiffened girder suspension bridge spanning mountainous canyon by wind tunnel tests of the sectional model and full-bridge model. First, sectional model tests with the original girder section were carried out under various wind attack angles. Subsequently, to improve the flutter stability of the bridge under the most unfavorable wind attack angle, several aerodynamic countermeasures including central upper stabilizer, horizontal stabilizer, combined central upper and horizontal stabilizers, and sealed central traffic barrier were proposed and sectional model tests with optimized girders were conducted. The results show that the aerodynamic mitigation effect of the central upper stabilizer, horizontal stabilizer, as well as combined measure, is closely related to the geometric dimension of the stabilizing plate. It is found that large geometric dimensions effectively increase the flutter critical wind speed of the truss girder. Considering sealed central traffic barrier measure, the smaller ventilation rates result in larger flutter critical wind speed of the girder. The sealed central traffic barrier measure with a 50 % ventilation rate is deemed as the most optimal aerodynamic countermeasure in consideration of aesthetics, economy, and safety. Finally, the effectiveness of optimal countermeasure is validated through an aeroelastic full-bridge model test. The research is conducted to provide references on flutter performance optimization of similar bridges in the future
Research on vibration mechanism and control technology of building structure under earthquake action
Full text linkThe large engineering building structures are costly and thus complex to maintain due to their chances of failure under various hazardous conditions. These buildings are needed to be protected against the damage due to the hazards like earthquake, wind, seismic waves, etc. This article focuses on the investigation of vibration mechanism and control strategies for protection of buildings from the hazardous situations. The article presents a robust solution of utilization of magnetorheological dampers for vibration control applications in complex structures. It aims at developing a reliable decentralized model to track and monitor the building structures and control them before the earthquake actions are encountered. This article develops a novel dynamically optimized and decentralized mechanism using the PID controller for the self-regulation of conventional PID controller-based method. The major goal of decentralization is to ensure that each of the subsystem is compatible with one another and can also work independently with a higher efficiency at the time of fault. The combination of decentralization and self-regulation is tested for a tall building structural model with 10 floors. The proposed approach is compared with the conventional PID based mechanism under the faulty condition in order to illustrate its dynamism and usefulness for practical implementation. The proposed simulated model provides 95.54 % earthquake tracking precision and can be used for developing the earthquake protective schemes for the adequate survivability of tall building structures as well as to safeguard the human occupant in it