冲击载荷下液压缸内压的流固耦合仿真与振动分析

该文为了研究液压缸受到冲击荷载时冲击瞬间内部流场的变化情况,用有限元分析软件Ansys Workbench对受冲击时液压缸内部流场压力进行了流固耦合分析,同时用动力学波动方程对相同模型的内部压力进行了分析、求解,并把两种方法计算出的轴向中心线压力分布进行了对比.对比结果表明两种方法对最大压力数值的预估误差为3.67％,...     

Lower-bound shakedown analysis of axisymmetric structures subjected to variable mechanical and thermal loads

This paper is concerned with axisymmetric structures subjected to various combinations of steady and (irregularly) pulsating mechanical and thermal loads. The numerical method is based on the static shakedown theorem, which deals with elastic-perfectly-plastic bodies. Linear temperature dependence of the yield condition in a 4D stress space is considered. The pseudo-residual stress field is simulated by the Temperature Parameter Method and the yield surface is linearized, so that the shakedown analysis is transformed into a linear programming problem and hence the computational difficulties otherwise encountered are overcome. The shakedown analysis of cylinders and spherical shells with and without defects is presented in this paper. Results presented show that the method is beneficial for the shakedown analysis of complicated structures subjected to various combinations of loads.     

Lower-bound shakedown analysis of a simply supported plate carrying a uniformly distributed load and subjected to cyclic thermal loading

A lower-bound analysis is used to obtain the shakedown boundary for a simply supported circular plate carrying a uniformly distributed load subjected to cyclic thermal loading. Situations where the yield stress is constant and a function of position in the plate are examined. For low levels of thermal loading the results are in agreement with the upper-bound calculations of Ponter.     

The influence of elastic shear deformation on the transverse shear failure of a fully clamped beam subjected to idealized blast loading

The influence of elastic shear deformation on the transverse shear response of a fully clamped beam is investigated in the present paper. The beam is made from a rigid, perfectly plastic material and subjected to a uniformly distributed pressure pulse loading. The elastic shear deformation is idealized by an elastic, perfectly plastic spring with a constant spring coefficient. Analytical solutions are obtained for the transverse shear response, which are then used to predict the occurrence of a transverse shear failure. The method presented in the paper may be extended to study the blast-induced shear failure of other structural elements when the elastic shear deformation needs to be considered.     

Classical buckling of a thin-walled tube subjected to bending moment and internal pressure

The classical buckling of a thin-walled circular cylindrical shell which is subjected simultaneously to uniform bending moment and internal pressure is investigated in an approximate fashion by assuming an appropriate eigenmode and obtaining a “best-fit” solution of the resulting equations. In this way, explicit formulae are derived for critical loading combinations and for the characteristics of the modal form. These formulae agree reasonably well with a wide range of numerical data previously obtained by Seide and Weingarten. A feature of the scheme is that it is feasible to interpret the results in physical terms, and to envisage the roles of bending, twisting and stretching in the critical solution.     

Dynamic analysis of a rotating beam subjected to repeating axial and transverse forces for simulating a lathing process

The dynamics of the workpiece of a lathe is simulated in the presented paper. A rotating Rayleigh beam is chosen as a simple model of the workpiece. The beam or the workpiece is subjected to forces from the cutting tool of the lathe. The external forces, in transverse and axial directions, are traveling in a repeating or periodic motion. The force in the axial direction is a large cutting force resulting in coupled bending deformation while forces in the transverse directions are the contacting forces.In this paper, the governing equations of the rotating Rayleigh beam are derived by Hamilton's principle. The external, periodic forces resulted from the tool are expressed in Fourier series. Galerkin's method is then chosen for disceretizing the partial differential equations. The instability regions of the responses are determined by using the method of multiple scales and the Floquet theory. Fast Fourier transform gives the frequency domain responses for examining the dynamic characteristics. The numerical results are discussed. Parametric studies are also performed.     

Development of a real time monitor and multivariate method for long term diagnostics of atmospheric pressure dielectric barrier discharges: application to He, He/N2, and He/O2 discharges

In this paper we present the development and application of a real time atmospheric pressure discharge monitoring diagnostic. The software based diagnostic is designed to extract latent electrical and optical information associated with the operation of an atmospheric pressure dielectric barrier discharge (APDBD) over long time scales. Given that little is known about long term temporal effects in such discharges, the diagnostic methodology is applied to the monitoring of an APDBD in helium and helium with both 0.1% nitrogen and 0.1% oxygen gas admixtures over periods of tens of minutes. Given the large datasets associated with the experiments, it is shown that this process is much expedited through the novel application of multivariate correlations between the electrical and optical parameters of the corresponding chemistries which, in turn, facilitates comparisons between each individual chemistry also. The results of these studies show that the electrical and optical parameters of the discharge in helium and upon the addition of gas admixtures evolve over time scales far longer than the gas residence time and have been compared to current modelling works. It is envisaged that the diagnostic together with the application of multivariate correlations will be applied to rapid system identification and prototyping in both experimental and industrial APDBD systems in the future.     

Creep crack growth analysis using <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">t</Emphasis></Subscript>-parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in C _t and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the C _t values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.