Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.

Lateral dynamic features of a railway vehicle

Abstract: The lateral dynamic features of a railway vehicle are investigated using two similar wheel/rail contact models: the Vermeulen–Johnson and the Shen–Hedrick–Elkins models. The symmetric/asymmetric bifurcation behaviour and chaotic motions of the railway vehicle are investigated in great detail by varying the speed and using the ‘resultant bifurcation diagram’ method. It is found that multiple solution branches exist and they can lead to more steady states in the dynamic behaviour of the railway vehicle. The coexistence of multiple steady states can lead to jumps in the amplitude of oscillations, resulting in problems for safe operation of the vehicle. Therefore, it should be avoided in everyday operation. Furthermore, the creation of multiple solution branches suggests that the critical speed of a vehicle should be determined from a comprehensive analysis of the various kinds of possible excitations and numerous tests.

Simulation of a railway vehicle's running behaviour: how elastic wheelsets influence the simulation results

Abstract: The straight running behaviour of a passenger coach is investigated for the cases of the wheelsets considered as elastic and as rigid bodies. The model used for this investigation includes rotating elastic wheelsets modelled in an efficient way for the computation and a nonlinear wheel-rail contact. The behaviour below and beyond the critical speed is studied for the configuration of rigid and elastic wheelsets. The comparison of the simulation results show a distinct influence of the structural elasticity of the wheelsets, especially a drop of the critical speed.

Modeling of the effects of phase shift on cutting performance in elliptical vibration cutting

Abstract: In the elliptical vibration cutting process, the elliptical locus is considered to be a vital factor that affects cutting performance. Besides the cutting speed and vibration amplitudes, the phase shift (i.e., the phase difference between the two-directional output harmonic vibrations forming the elliptical locus) is an intrinsic parameter that determines the shape and inclination of the elliptical locus with respect to the cutting direction. In this paper, a numerical recursive search method is proposed to investigate the effect of phase shift in elliptical vibration cutting. It has been shown that the critical speed ratio for considerably improving the cutting performance has a sinusoidal correlation with the phase shift. For elliptical loci with arbitrary shapes, the developed model theoretically predicts the maximal influential thickness of cut, surface roughness, and the tool-workpiece contact ratio as a function of phase shifts. Experiments were conducted to validate the developed model through the evaluation of the machined surface profile, roughness, and dynamic cutting force. The obtained results offer a method to determine the proper machining variables in cutting hard and brittle materials during the elliptical vibration cutting process with an arbitrary locus.

Influence of vehicle parameters on critical hunting speed based on Ruzicka model

Abstract: While introducing foreign advanced technology and cooperating with Chinese famous research institutes, the high-speed vehicles are designed and take the major task of passenger transport in China. In high-speed vehicle, the characteristic of shock absorber is an important parameter which determines overall behavior of the vehicle. The most existing researches neglect the influence of the series stiffness of the shock absorber on the vehicle dynamic behavior and have one-sided views on the equivalent conicity of wheel tread. In this paper, a high speed passenger vehicle in China is modeled to investigate the effect of the parameters taking series hydraulic shock absorber stiffness into consideration on Ruzicka model. Using the vehicle dynamic model, the effect of main suspension parameters on critical speed is studied. In order to verify the reasonableness of shock absorber parameter settings, vibration isolation characteristics are calculated and the relationship between suspension parameters and the vehicle critical hunting speed is studied. To study the influence of equivalent conicity on vehicle dynamic behavior, a series of wheel treads with different conicities are set and the vehicle critical hunting speeds with different wheel treads are calculated. The discipline between the equivalent conicity of wheel tread and critical speed are obtained in vehicle nonlinear system. The research results show that the critical speed of vehicle much depends on wheelset positioning stiffness and anti-hunting motion damper, and the series stiffness produces notable effect on the vehicle dynamic behavior. The critical speed has a peak value with the equivalent conicity increasing, which is different from the traditional opinion in which the critical speed will decrease with the conicity increasing. The relationship between critical speed and conicity of wheel tread is effected by the suspension parameters of the vehicle. The study results obtained offer a method and useful data to designing the parameters of the high speed vehicle and simulation study.