Journal of Engineering and Thermal Sciences
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Sliding mode control based on improved virtual reference model for damping adjustable hydro-pneumatic suspension systems
Get PDFThis paper proposed an improved virtual reference model for semi-active suspension to coordinate the ride comfort and handling stability of a vehicle. The reference model combines the virtues of sky-hook and ground-hook control logic, and the hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the handling stability especially in high speed condition. The full scale vehicle model considering the heave-pitch-roll motion is presented, and the theory of hydro-pneumatic suspension with continuous adjustable damper is also illustrated. A sliding mode controller is designed to track the states of the reference model. The stability of the sliding mode control strategy is analyzed by means of Lyapunov function approach taking into account of the nonlinear damper characteristics and sprung mass variation of the vehicle. Finally, the performances of the controller are validated under three typical working conditions: the random road, speed bump road and sharp acceleration and braking. The simulation results indicated that, compared with the traditional passive suspension, the proposed control algorithm can offer a good coordination between ride comfort and handling stability of a vehicle. The designed controller could be commercially implemented in semi-active suspension systems
Research on dynamic performance and motion control of robot manipulator
Get PDFAmongst the robotics and autonomous systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. In this paper, the purpose is to research on dynamic performance and motion control of robot manipulator for the more precise, crucial and critical tasks in industry. Firstly, the forward and inverse kinematics was accurately described by obtaining the link transformation matrices from each joint in robot manipulator. To find admissible solutions along the path, the workspace of the manipulator was determined by joint limit condition and validated by actual measurement. And then, the dynamic performance of robot manipulator is researched by using the forming flexible multi-body system. Furthermore, the frequency response curves are obtained by exciting vibration simulation based on vibration model, which the predicted method was validated by comparing simulation and experimental results. Finally, the control system architecture was given and the grasping process was conducted by gripper based on motion trajectory control in the workspace
Optimization of passive constrained layer damping (PCLD) treatments for vibration reduction
Get PDFAn efficient method to reduce the frequency averaged transverse vibration level of a plate by optimizing the position of attached passive constrained layer damping PCLD is presented. This method uses a multilayer anisotropic plate model which is an equivalent single layer plate model (ESL) where transverse shear stresses and displacements are continuous at each layer’s interfaces. Hence, for a laminate composed of an arbitrary number of layers, all the quantities are related to those of the first layer. The optimization process is based on the use of the ESL plate model combined with the genetic algorithm (GA) and Latin Hypercube Sampling (LHS) algorithm implemented in a Rayleigh-Ritz resolution program. The convergence acceleration of the method is achieved thanks to the combination of genetic algorithm and the use of the ESL plate model instead of a three-dimensional mesh that requires more computing resource
Modal analysis for a complex military trucks structure
Get PDFThe artillery weapon system muzzle disturbance is influenced largely by the carrier vibration through firing. In case of military trucks carrying cannons, the longitudinal bending vibration is the most important factor affects the muzzle disturbance. The corner stone of this article is the modal and sensitivity analysis of a chosen military truck carrying cannon in order to investigate how much the longitudinal bending natural frequencies of this truck deviated from the nominal value as a result of truck components layout or position variation and some system design parameters variations. This deviation is examined to clarify the most sensitive parameters that affect the longitudinal bending natural frequency. The dynamic characteristics of the truck, such as the natural frequencies and the mode shapes, are determined by using finite element method in order to create the truck flexible system. Via intermediate file, the flexible truck model is imported into commercial FE code “ABAQUS” software for modal analysis whose solutions agree well with an experimental data. This study shows a complete and deep investigation of the dynamic response calculations for a complex flexible military truck. In addition, the sensitivity analysis compels the designer to identify the critical variables which affect the longitudinal bending vibration beside obtain additional information about weapon system dynamics
Application of alpha-stable distribution approach for local damage detection in rotating machines
Get PDFIn this paper a novel method for informative frequency band selection for local damage detection is presented. Local damage in bearings/gearbox provides specific vibration signature, i.e. train of impulses with cycle related to fault frequency. The proposed approach is based on the α-stable distribution, which is an extension of the Gaussian one. The choice of this distribution is motivated by its superiority towards other distributions when modeling impulsive data. We introduce here the new selector (to select informative frequency band) which is based on the stability parameter α. Moreover we propose also the new time-frequency maps based on the measures of dependence adequate for α-stable distribution, namely autocodifference and autocovariation maps. The introduced methodology is illustrated by analysis of simulated and real vibration signals from heavy-duty rotating machinery. The results prove that proposed approach allows detection of multiple damages in signal and location of informative frequency band related to these damages. Moreover the analyzed examples indicate the α-stable distribution approach for some cases can give better results in contrast to the classical methodology based on the spectral kurtosis
Adaptive algorithm with variable step size for numerical analysis on nonlinear fatigue damage accumulation of steel bridge
Get PDFAn adaptive algorithm with variable step size was firstly established in the paper in order to predict fatigue life of steel bridge welded components accurately and efficiently. The coupled damage constitutive model is developed within ABAQUS through user defined material subroutines to introduce damage revolving formulation into the fatigue damage analysis and the fatigue damage evolution process of the steel bridge components was finally studied. It is demonstrated that the adaptive variable step size algorithm for predicting fatigue life of steel bridge components is scientific and effective. Secondary development based on commercial software is more convenient and suitable to explore the mechanism of local damage accumulation process of various structures. The efficiency of the adaptive algorithm is not so high when the material damage is described by the linear Miller criterion, while it can effectively improve the calculation speed when the nonlinear Lemaitre damage evolution criterion is applied
Vibration characteristics analysis of a centrifugal impeller
Get PDFCrack fault of a centrifugal impeller occurred while working. The finite element model of the impeller was established and vibrational characteristics were analyzed for to find the reason of the crack fault in this paper. The resonance frequencies of the impeller were identified with the help of Campbell diagrams. The modal experiments were carried out with hammering method, the modal parameters were obtained and the correct of the simulations was verified under the same constraints with the FEM model. Computation effort was saved while accuracy was retained making use of the cyclic symmetry technique in ANSYS. The results showed that simulating results agreed well with that of the experiments
Mobile manipulators collision-free trajectory planning with regard to end-effector vibrations elimination
Get PDFA sub-optimal point-to-point trajectory planning method for mobile manipulators operating in the workspace including obstacles taking into account the damping of the end-effector vibrations is presented. The proposed solution is based on extended Jacobian approach and redundancy resolution at the acceleration level. Fulfilment of the condition stopping the mobile manipulator at the destination point is guaranteed, which leads to elimination of the end-effector vibrations and significantly increases positioning accuracy. The effectiveness of the presented method is shown and compared to the classical Jacobian pseudo inverse approach. A computer example involving a mobile manipulator consisting of a nonholonomic platform (2, 0) class and SCARA-type holonomic manipulator operating in two-dimensional task space including obstacle is also presented
Simplified computational method for mooring forces of mooring systems
Get PDFThe most common marine mooring systems of floating structures are taken as the numerical models. The effects of wave parameters and structural parameters on the wave forces are studied. A simplified formula of wave forces is established and the valuing ranges of key parameters are determined. Results obtained by the simplified computational method show great agreement with those obtained by numerical simulations and physical modelling experiments. The mooring forces can be obtained easily and efficiently by the proposed method
Convenient displacement monitoring technique using smartphone
Get PDFIn this paper, a displacement monitoring APP called D-Viewer is proposed and developed. By means of common laser device and projection plate, structural displacement can be monitored dynamically, using the APP. Firstly, the laser spot centroid recognition method was studied. Second, the displacement monitoring APP was developed. Finally, in order to verify the feasibility of the method, a series of static and dynamic experiments using smartphone were conducted. Results show that this method can be used as a convenient, fast, low-cost structural displacement monitoring method