以ACIS与HOOPS为平台的冷冲压压边条建模技术研究

探讨机械制造业冷冲压工艺中的压边条三维建模方法。应用ACIS平台和HOOPS平台,以汽车压边条生成与分析系统为实例,讨论了ACIS与HOOPS的工作模式、网格数据的生成、曲面造型,三维图形渲染与曲面光顺技术。介绍压边条建模系统的实现过程。

Dynamic responses of a multilayer piezoelectric hollow cylinder under electric potential excitation

The dynamic responses of a multilayer piezoelectric infinite hollow cylinder under electric potential excitation were obtained. The method of superposition was used to divide the solution into two parts, the part satisfying the mechanical boundary conditions and continuity conditions was first obtained by solving a system of linear equations; the other part was obtained by the separation of variables method. The present method is suitable for a multilayer piezoelectric infinite hollow cylinder consisting of arbitrary layers and subjected to arbitrary axisymmetric electric excitation. Dynamic responses of stress and electric potential are finally presented and analyzed.

Science Letters:Analytical solution for fixed-end beam subjected to uniform load

A bi-harmonic stress function is constructed in this work. Ariy stress function methodology is used to obtain a set of analytical solutions for both ends fixed beams subjected to uniform load. The treatment for fixed-end boundary conditions is the same as that presented by Timoshenko and Goodier (1970). The solutions for propped cantilever beams and cantilever beams are also presented. All of the analytical plane-stress solutions can be obtained for a uniformly loaded isotropic beam with rectangular cross section under different types of classical boundary conditions.

Parameters That Influence Buckling Forces of a Fully Embedded Pile Based on the Finite Difference Method

This paper work aims to present the effect of the soil stiffness （k）, boundary conditions of piles and embedded length of piles （L） on a buckling force of a fully embedded pile and subject to an axial compression force only, based on the finite difference method. Based on this method, MATLAB sottware is used to calculate the buckling forces of piles. Effect of the soil stiffness （k）, boundary conditions of piles and embedded length of piles （L） on a buckling force have been studied for reinforced concrete pile, whereas the modulus of horizontal subgrade reaction is adopted constantly with depth, increasing linearly with depth with zero value at the surface and increasing linearly with depth with nonzero value at the surface.

A state space solution for the bending problem of thick laminated piezoelectric open cylindrical shells

Based on the theories of three-dimensional elasticity and piezoelectricity, and by assuming appropriate boundary functions, we established a state equation of piezoelectric cylindrical shells. By using the transfer matrix method, we presented an analytical solution that satisfies all the arbitrary boundary conditions at boundary edges, as well as on upper and bottom surfaces. Our solution takes into account all the independent elastic and piezoelectric constants for a piezoelectric orthotropy, and satisfies continuity conditions between plies of the laminates. The principle of the present method and corresponding results can be widely used in many engineering fields and be applied to assess the effectiveness of various approximate and numerical models.

Improvement and application of wall function boundary condition for high-speed compressible flows

In order to develop a wall function boundary condition for high-speed flows so as to reduce the grid-dependence of the simula- tion for the skin friction and heat flux, a research was performed to improve the compressible wall function boundary condition proposed by Nichols. Values of parameters in the velocity law-of-the-wall were revised according to numerical experiments and the expression of temperature law-of-the-wall was modified based on theoretical analysis and numerical simulation. Be- sides, the formula of the heat conduction term in near-wall region was derived so that the coupling between the wall function boundary condition and CFD code was realized more accurately. Whereafter, the application study of the modified wall func- tion was carried out. The numerical case of supersonic turbulent boundary layer on a flat plate illustrated that the modified wall function produces reasonable results of skin friction and heat flux, and profiles of velocity, temperature and turbulent eddy viscosity for coarse grids with the initial wall spacing of y＋〈400, and that the modifications to the original wall function can obviously improve the simulation precision. As for the application of separation flows, it was found from the numerical cases of supersonic cavity flow and hypersonic axisymmetric compression comer that the compressible velocity law-of-the-wall originally established based on the fully-developed attached turbulent boundary layer approximately holds in the near-wall re- gion inside the separation flows, which ensures that reliable skin friction and heat flux can be given by the wall function inside the separation flows, while for the region near separation and reattachment points, the wall function gives results with a rela- tively large error, because the velocity law-of-the-wall used in the wall function takes on obvious deviation from the real ve- locity profiles near the separation and reattachment points.

Pressure Boundary Conditions for Blood Flows

Simulations of blood flows in arteries require numerical solutions of fluidstructure interactions involving Navier-Stokes equations coupled with large displacement visco-elasticity for the vessels.Among the various simplifications which have been proposed, the surface pressure model leads to a hierarchy of simpler models including one that involves only the pressure. The model exhibits fundamental frequencies which can be computed and compared with the pulse. Yet unconditionally stable time discretizations can be constructed by combining implicit time schemes with Galerkin-characteristic discretization of the convection terms in the Navier-Stokes equations. Such problems with prescribed pressure on the walls will be shown to be efficient and accurate as an approximation of the full fluid structure interaction problem.

A Study on the Transport Process in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells

Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.

Existence of Solutions for Three Dimensional Stationary Incompressible Euler Equations with Nonvanishing Vorticity

In this paper,solutions with nonvanishing vorticity are established for the three dimensional stationary incompressible Euler equations on simply connected bounded three dimensional domains with smooth boundary.A class of additional boundary conditions for the vorticities are identified so that the solution is unique and stable.

MHD EYRING-PRANDTL FLUID FLOW WITH CONVECTIVE BOUNDARY CONDITIONS IN SMALL INTESTINES

In this paper, we have discussed the food movement in stomach with thermal bound- ary conditions. Eyring-Prandtl fluid model is considered. Formulation of the considered phenomena have been developed for both fixed and moving frame of references. Regular perturbation is used to find the solution of stream function, temperature profile and pressure gradient. Analysis has been carried out for velocity, ＂stream function, temper- ature, pressure gradient and heat transfer＂. Appearance of pressure gradient is quite complicated so to get the expression for pressure rise we have used numerical integra- tion. It is perceived that the velocity close to the channel walls is not same in outlook of the Eyrin^Prandtl fluid parameter taken as fl and Hartman number M. The velocity decreases by increasing β and M.

Measurement and Numerical Simulation of a Small Centrifugal Compressor Characteristics at Small or Negative Flow Rate

For centrifugal compressors used in automotive turbochargers, the extension of the surge margin is demanded because of lower engine speed. In order to estimate the surge line exactly, it is required to acquire the compressor characteristics at small or negative flow rate. In this paper, measurement and numerical simulation of the characteristics at small or negative flow rate are carried out. In the measurement, an experimental facility with a valve immediately downstream of the compressor is used to suppress the surge. In the numerical work, a new boundary condition that specifies mass flow rate at the outlet boundary is used to simulate the characteristics around the zero flow rate region. Furthermore, flow field analyses at small or negative flow rate are performed with the numerical results. The separated and re-circulated flow fields are investigated by visualization to identify the origin of losses.

Examples of Boundary Layers Associated with the Incompressible Navier-Stokes Equations

The author surveys a few examples of boundary layers for which the Prandtl boundary layer theory can be rigorously validated.All of them are associated with the incompressible Navier-Stokes equations for Newtonian fluids equipped with various Dirichlet boundary conditions(specified velocity).These examples include a family of(nonlinear 3D) plane parallel flows,a family of(nonlinear) parallel pipe flows,as well as flows with uniform injection and suction at the boundary.We also identify a key ingredient in establishing the validity of the Prandtl type theory,i.e.,a spectral constraint on the approximate solution to the Navier-Stokes system constructed by combining the inviscid solution and the solution to the Prandtl type system.This is an additional difficulty besides the wellknown issue related to the well-posedness of the Prandtl type system.It seems that the main obstruction to the verification of the spectral constraint condition is the possible separation of boundary layers.A common theme of these examples is the inhibition of separation of boundary layers either via suppressing the velocity normal to the boundary or by injection and suction at the boundary so that the spectral constraint can be verified.A meta theorem is then presented which covers all the cases considered here.

Influence of volute distortion on the performance of turbocharger centrifugal compressor with vane diffuser

As the geometry of the volute of turbocharger compressor is non-axisymmetric,it causes a distortion at the outlet of the diffuser and influences the upstream components.A distortion model in which a pressure distortion was applied as outlet boundary condition was established to simulate the distortion induced by the volute.It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the outlet of the diffuser to replace the volute.Based on the distortion model which was verified,the influence of the amplitude of the distortion on the performance of centrifugal compressor was studied in detail.The results show that the distortion severely harms aerodynamic stability of the investigated compressor.The larger the amplitude of the distortion,the worse the performance of the compressor.The distortion induced by asymmetric volute propagates to upstream components and causes local flow separation at part of diffuser and impeller,and then causes the compressor surge.When the amplitude of the volute distortion is 10%,the stable flow range of the centrifugal compressor decreases to near zero.To authors’knowledge,the relationship between the compressor performance and distortion amplitude is first obtained quantitatively,which provides evidence to improve the performance of turbocharger compressor by decreasing the distortion induced by asymmetric volute.

Variational Formulation of 1-D Unsteady Compressible Flow in a Deforming Tube

The variational principles for 1-D unsteady compressible flow in a deforming tube derived in a previous paper are improved essentially by reconstructing the initial/final-integral terms according to a new method suggested in a recent paper. As a result, the inherent shortcoming of variational principles of being unable to admit physically rational initial/final-value conditions in initial/boundary-value problems is successfully eliminated. Thus, a new theoretical basis for the time-space finite-element analysis is provided.

Mathematical Modelling and Experimental Investigation of Gas Flow in Minichannels and Microchannels

The first part of this study is focused on the numerical modelling and experimental investigation of transonic flow through a 2D model of the male rotor-housing gap in a dry screw compressor.Numerical simulations of the clearance flow are performed with the help of the in-house compressible Navier-Stokes solver.Experimental measurements based on the Schlieren method in Toepler configuration are carried out.The objective of the second part of the study is to derive the analytical solution of gas microflow development in a gap between two parallel plates.The microflow is assumed to be laminar,incompressible and the velocity slip boundary conditions are considered at the walls.The constant velocity profile is prescribed at the inlet.For the mathematical description of the problem,the Oseen equation is used.The analytical results are compared with the numerical ones obtained using the developed incompressible Navier-Stokes solver including the slip flow boundary conditions.

Incompressible limit and stability of all-time solutions to 3-D full Navier-Stokes equations for perfect gases

This paper studies the incompressible limit and stability of global strong solutions to the threedimensional full compressible Navier-Stokes equations, where the initial data satisfy the "well-prepared" conditions and the velocity field and temperature enjoy the slip boundary condition and convective boundary condition, respectively. The uniform estimates with respect to both the Mach number ∈(0, ∈] and time t ∈ [0, ∞) are established by deriving a differential inequality with decay property, where ∈∈(0, 1] is a constant.As the Mach number vanishes, the global solution to full compressible Navier-Stokes equations converges to the one of isentropic incompressible Navier-Stokes equations in t ∈ [0, +∞). Moreover, we prove the exponentially asymptotic stability for the global solutions of both the compressible system and its limiting incompressible system.