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A concept of technology for non-destructive testing of modernized freight cars based on analysis of their vibration
Get PDFPaper presents a part of research concerning freight cars modernization. The main causes of damage of freight cars plating are chemical interactions of the carried material and the car body as well as mechanical damages. The introduced structural change consists in the use of composite panels to protect the steel plating of a car body. Therefore, it is necessary to carry out a series of studies. In this paper results of virtual simulations of the freight car vibration during its motion as well as verification of a possibility to create a method to verify technical condition of the freight car during its exploitation based on excited vibrations are presented
Finite element simulation of the airbag deployment in frontal impacts
Get PDFVirtual modeling and simulation are increasingly used to help develop restraint systems, and airbag simulation is the necessary steps during airbag research and design progress. In this work, the squeezed airbag has been simulated by a uniform pressure method in which the pressure of the airbag is considered as constant. The main aim of this study is evaluate the performance of deploying of passenger side airbag using finite element methods (FEM) to handle different collision scenarios
An improved homotopy analysis method with accelerated convergence for nonlinear problems
Get PDFIn this paper we propose an accelerated convergence method, which is combined with the homotopy analysis method (HAM), to solve nonlinear problems. The HAM is applied to obtain approximate expressions. According to the numbers of terms in the approximations, some ratio-control parameters are introduced in the solution expressions. By solving simultaneous algebraic equations, all artificial parameters can be optimally identified, including the so-called convergence-control parameter ℏ. Twoexamples are given to illustrate the validity of the new method. Comparison with L-P perturbation method and Runge-Kutta method reveals that the improved HAM is better than the standard HAM and applies especially to the problems with complicated nonlinear terms
Bifurcation and chaos characteristic analysis of spur micro-segment gear pair
Get PDFCustomers call for better performance, such as miniaturization, low noise, and higher load capacity of gear system. The micro-segment gear is a new tooth form whose tooth profile curve is composed of many micro segments. This paper investigates the bifurcation and chaos characteristics of spur micro-segment gear pair. To improve the authenticity of the solution, the time-varying mesh stiffness is expressed in term of piecewise function, and the normal profile deviation is expressed in the form of Fourier series. The influence of damping coefficient, excitation frequency, internal and external excitation on bifurcation and chaos properties of the system are analyzed. The numerical results show that the dynamic system is very sensitive to damping coefficient. With the increasing of damping coefficient, the number of bifurcation and impressive jump tends to decrease; and the intervals of dimensionless frequency leading to unstable or chaotic motion have a trend to concentration. The influence of external and internal excitation on bifurcation characteristics are also investigated. Comparison results show that, internal excitation has a greater effect than external excitation based on corresponding amplitude-frequency diagrams and bifurcation diagrams
Modal and dynamic responses of the human head-neck complex for impact applications
Get PDFThe human head-neck is the most complex structure in the human body and its behavior under vibration remain poorly understood. Therefore, a comprehensive theoretical or experimental analysis is needed. This study is mainly based on an available finite element human head-neck complex and concentrates on its modal and dynamic responses. Resonance frequencies and responses of the human head-neck complex’s finite element model in impact simulations have been analyzed. These dynamic responses show a very good agreement with the previous studies. The fundamental frequency of modal analysis of finite element model is 35.25 Hz which is reasonably close to existing literatures. However, our modal dynamic analysis of an elaborated human head-neck complex introduces supplementary dynamic responses like nasal sideward cartilages’ “flipping” modes and the mandible’s “mastication” modes. Modal validation is performed which indicates a requirement for elaborated modeling to make out all the extra resonance frequencies. Moreover, the influence of damping factor on biomechanical response or natural frequencies is also investigated. It can be found that damping factor has got an inverse proportionality between damping factor effect on natural frequency and that on biomechanical responses. This demonstrates the significance of identification of the suitable damping factor evaluating biomechanical response in modal dynamic analysis and validation
Research on static and dynamic characteristics of a compound bearing with tilting pads and rolling bearing
Get PDFAccording to the high stiffness requirement of bearings on spindle systems of precision machine tools, a kind of compound bearing composed of tilting pads and rolling bearing is proposed in this paper. In the start and stop process, the weight of rotor parts is borne by the rolling bearing, and the tilting pads avoid wear. When the spindle is reaching a certain speed, the rolling elements is disengaged from the outer ring of the rolling bearing, and the load is carried by the tilting pad bearing alone. The pivot position of the tilting pads can be defined by two characteristic parameters: Radial Pivot Position Coefficient (RPPC) and Circumferential Pivot Position Coefficient (CPPC). The influence laws of the pivot position parameters on the performance of compound bearing are synthetically analyzed. The results show that the stiffness of compound bearing can be effectively improved by proper design of the two pivot position parameters. The theoretical researches on this new compound bearing in this paper provide reference for bearing design of high stiffness spindle system
Identification of viscoelastic material properties based on Big Bang-Big Crunch optimization method
Get PDFAn efficient identification method of the dynamic properties of viscoelastic damping materials using an optimization technique is proposed. A Zener fractional derivative model is used to describe the frequency-dependent dynamic characteristics of materials. In this study, the viscoelastic material is used in a Passive Constrained Layer Damping (PCLD) configuration in order to increase the shear deformation in the material. Mean Square Velocities (MSVs) of a clamped-free beam covered with a PCLD patch are measured in an environmental chamber at different frequencies and used as reference MSVs. The excitation force is performed thinks to a low mass magnet fixed on the beam and placed inside a coil subjected to an electrical current. Numerical MSVs are calculated using an equivalent single layer plate model with warping functions chosen to ensure continuity of transverse shear stresses and displacements layer's interfaces
The polynomial dimensional decomposition method in a class of dynamical system with uncertainty
Get PDFIn this paper, polynomial dimensional decomposition (PDD) method is applied to study the dynamical model for the first time. PDD method can reserve the amplitude-frequency characteristics of the exact solution which is obtained by the Monte Carlo simulation (MCS) method except the frequency close to the resonance, the perturbations appear around the resonance frequency. All these results are shown on the two degrees of freedom (DOF) spring system with uncertainties; the dynamical characteristics of stiffness and hybrid uncertainty uncertainty are studied in seven cases respectively. The higher PDD order approximates better to the MCS results
Relative ride vibration of off-road vehicles with front-, rear- and both axles torsio-elastic suspension
Get PDFWheeled off-road vehicles are known to transmit higher magnitudes of low frequency whole-body vibration (WBV), which have been associated with an array of health disorders among human drivers apart from fatigue and reduced work rate. In this study, the ride performance potentials of a torsio-elastic suspension employed in the front-, rear-, and both axles of an off-road vehicle are investigated. A three-dimensional ride dynamic model of the vehicle is formulated and analyzed under excitations arising from correlated random elevations of two terrain tracks. The model validity is demonstrated on the basis of reported field measured data of a rear-suspended frame-steered articulated forestry vehicle. The ride responses are evaluated in terms of unweighted and weighted root mean square (rms) accelerations along the translational and rotational axes near the driver seat. The results show that fully-suspended vehicle can yield substantial reductions in vibration along all the axes, and suspension in the axle in the proximity of driver cabin is relatively more effective in limited the WBV exposure. It is further shown that the linkage suspension helps preserve roll stability while providing adequate ride performance
Research on vehicle handling inverse dynamics based on optimal control while encountering emergency collision avoidance
Get PDFVehicle driving safety is the urgent key problem to be solved of vehicle independent development while encountering emergency collision avoidance with high speed. And it is also the premise and one of the necessary conditions of vehicle active safety. A new technique for vehicle handling inverse dynamics which can evaluate the emergency collision avoidance performance is proposed. Firstly, the steering angle input of 3-DOF vehicle mode is established. The steering angle input imposed by driver is the control variable, and accurately tracking the expected path was the control object. The optimal control problem can be converted into a nonlinear programming problem while using the state variables conversion, which was solved by the sequential quadratic programming (SQP) algorithm. The results show that vehicle can well track the expected path in high speed