Search

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

After increasing the train speed, the wheel-rail coupling effect is intensified, as is the coupling effect between the train and the surrounding air, which causes the severe vibration of the train. Considering this problem and taking the high-speed train as the object of this study, a method for the coupling of aerodynamics and vehicle dynamics is proposed. Its validity is then demonstrated by the results of field tests and moving model experiments. On this basis, the fluid–structure coupling characteristics of a high-speed train passing through a tunnel are studied, as well as the effects of different coupling methods and track irregularities. The obtained results demonstrate that the interaction between the tail car and the surrounding air is significant. In the tunnel and at its exit, the lift and the car body acceleration significantly change, especially when the coupling of aerodynamics and vehicle dynamics, as well as the vertical and lateral track irregularities, are simultaneously imposed. When the head car travels out of the tunnel, the lift of the middle and tail cars both dramatically will change. It is deduced that the fluid–structure interaction has a significant effect on the swing phenomenon of the tail car. This phenomenon is the result of the combined effects of aerodynamics and track irregularities. The different frequencies of the lateral displacement for each car body, except the frequencies of the car bodies themselves, are mainly determined by vertical track irregularities. [ABSTRACT FROM AUTHOR]

In this paper, through finite difference and finite element coupling algorithms with structured grid, the fluid–structure coupling problems of the pressure of the fluid as well as stress and strain of the heterogeneous porous medium under the initial pressure of MPa magnitude are calculated, respectively. The porous medium is a cavity cylinder with fractal characteristics. The parameters of porosity, elastic modulus and Poisson's ratio of porous media with different fractal dimensions (D = 2. 3 , 2.4 and 2.5) are obtained by theoretical calculation. Through theoretical derivation, the amplitude of WM function is expressed by the fractal parameter porosity, which can predict the uneven characteristics caused by the nonuniformity of pore size distribution after explosion. The results show that with the increase of fractal dimensions, the porosity increases, and both the elastic modulus and the Poisson's ratio decrease. The Poisson's ratio has a linear relationship with porosity, which is well consistent with the modified formula in the literature. Under the same initial pressure, the stress and strain values of the material without fractal characteristics are much larger than those of the material with fractal feature which has an obvious fluctuation by extracting the average values. It indicates that the fractal porous media with rough surface can effectively reduce the pressure wave peak at the wall surface, and reduce the size of the stress and strain concentrations to prevent the vibration of the cylinder. As expected, if the initial pressure increases with an equal fractal dimension, the stress and strain values of the fluid–structure coupling will increase too. When the initial pressure is equal, the peak value of pressure in wall decreases gradually with the increase of fractal dimension, and the stress and strain values also decrease. [ABSTRACT FROM AUTHOR]

For the analysis of dynamic characteristics of fluid-conveying pipes with piecewise linear support, a fluid-structure coupling dynamic model based on the finite element method is proposed. A user-defined pipe element based on Euler-Bernoulli beam is developed for modeling the pipes, considering the dynamic flow conditions. A nonlinear spring element is utilized to model the clamp between the pipe and the base. The dynamic responses of the system are obtained through the direct time integration. The stiffness of the clamp support is investigated by the analytical method and the experimental method, in which it is found that the clamp stiffness is piecewise linear. For different pipe geometries the user-defined element model, analytical model and measurement data are compared. The results show high quality of the element developed in this paper. Finally, the dynamic characteristics of the pipe system with piecewise linear support subjected to base harmonic excitation are calculated and the effects of the system parameters on pipe behaviors have also been studied. As a consequence, the model proposed in this paper can represent the piecewise linear nonlinearity of the clamp support and be used conveniently to investigate the effects of the fluid-structure coupling on the system behaviors. [ABSTRACT FROM AUTHOR]

Complex structures often include hollow parts. These hollow parts constitute the skeleton of the structure and are largely responsible for its global behavior, hence the importance of analyzing them precisely. The method we propose in this paper is a modal method based on the modal analysis of elements of hollow parts. This method does not require nodal degrees of freedom on the boundaries between the elements: "modal" elements are created, and these elements can be assembled through modal mass and stiffness matrices in the same way as the finite element method. Thus, it is possible to choose the precision of the analysis by choosing the quantity of modes used in the modal analysis of the elements. We will study not only structural systems but also coupled fluid-structure systems, and our results will be compared with experimental tests. [ABSTRACT FROM AUTHOR]