专业外语

The Application ofFEM in ProjectBased on ANSYS

Liu Li LiMingwan Jia Liangmian (Schoo of Graduate, Shijiazhuang Railway Institute, Shijiazhuang Hebei 050043)

Abstract:Through combining the project example with FEM (finite element method), the points for attention and op-timized tropism are illustrated in the process of building mode,l meshing, element choice, solution etc by ANSYS,and the whole course with FEM is elaborated in details. At the same time, the commanding circuit for the project ex-ample and the application fields of FEM based on ANSYS are introduced synthetically, which provide reference for the application of ANSYS in other fields.

Key words:finite element method; ANSYS; project analysis

0 Introduction

With the rapid development of science and technology, the speed of products is upgrading quickly. Engineering staff who only need high level of training in engineering practice, theoretical accomplishment and ability to calculate, can design the products more suitable for market demand in the shortest possible time . At present, using finite element method (fem) has become a mainstream product. At the same time in the finite element theory perfect emerged a large number of professional general finite element software, such as ANSYS, ADNA, ASKA, COSMOS, SUSTUS,MARC and so on, in which the commercial software ANSYS is the most common. This paper focuses on the static analysis [1] in gas transmission pipeline as an example, based on the ANSYS finite element analysis of the application in engineering .

1.Introduction to the basic idea of finite element method and ANSYS software

1. 1.Basic idea of finite element method

Finite element method (fem) is an important branch of computational mechanics and the continuum discretization in numerical methods for solving all kinds of mechanical problems [2]. Its basic ideas can be summed up in two aspects: one is discrete; The second is piece-wise interpolation [3]. Solution of the discretization is a continuous domain artificially divided into a certain number of units, and unit interactions can only through the node transmission, through discrete, a continuum is divided by the combination of limited number of units. Piece-wise interpolation is choose trial function for each unit, and numerical integration within the unit [3], finally based on the analysis of each unit to complete the overall.

1.2.Introduction of ANSYS software

ANSYS is an effective and general finite element analysis software, which melt structure, fluid, electromagnetic field, acoustic field and thermal field analysis into an organic whole, used in various industries, and has strong modeling capabilities, solving ability, ability to nonlinear analysis and post-processing ability, more field coupling ability and secondary development ability,.It also can carry on the static characteristics analysis, buckling analysis, modal analysis, harmonic response analysis, spectrum analysis, the explicit function analysis and so on ,which can be efficiently applied in engineering analysis. Based on ANSYS finite element analysis of the basic

process is shown in figure 1 .

Figure 1 Finite element analysis flow chart

2.Examples of application

Below for a static analysis of a natural gas pipeline as an example to illustrat the basic process based on ANSYS finite element analysis. As shown in figure 2 for the natural gas pipeline section in which the role of the surface of the gas is under pressure, and stress field distribution of tube wall. The parameters: the outer diameter of the pipe 0. 8 m, diameter 0. 6 m, material elastic modulus of 200 gpa, poisson's ratio 0. 26, load to 1 mpa [1] .

First before entering the processor, the command is / Prep7.

Figure 2

2.1. Geometric model design

Modeling is divided into a bottom-up modeling and top-down modeling, and in the actual application is not strictly limited, according to the analysis of characteristics of the object, both can also be used in combination.ANSYS, either directly finite element model, but also to create a geometric model, and then by dividing the grid into a finite element model.For practical engineering parts directly finite element model to enter large amounts of data, the process is tedious, error-prone, which is more convenient to use.ANSYS program provides a complete Boolean operations, such as addition, subtraction, intersection, segmentation, bonding, overlap, drag, extend, rotate, move, copy and other functions, users can take advantage of these features to establish arbitrarily complex entitiesmodel.

In the present embodiment, since the adopted PLANE82 unit, so just create a pipeline interface plane model will be able to meet the precision and analytical requirements. Solid model shown in Figure 3.

Figure 3 Entity model diagram 2.2. Geometric model into a finite element model

For finite element model in ANSYS, the solution must use the geometric model by defining various properties and meshing into a finite element model to calculate the analysis. In this case the following specific steps.

2.2.1. define the element attributes

(1) Unit Types: ANSYS provide a total of 16 categories of unit mode, for different analytical entities, as well as want to get the analysis result, Combination of ANSYS software, the choice of matching unit.In this case selection of PLANE82 unit, because of the force of the gas pipeline belonging to the plane strain problem, and PLANE82 2-D 8-node structural solid elements, with high accuracy of the results, can be used either as a flat-screen unit can also be used as an axisymmetric elementso the selection of this unit is more appropriate.

(2) Real constants: in ANSYS, corresponding to each unit type has element real constant term and a specific input sequence, So, in entering the real constant must pay attention to search the infoumation in the unit manual for this content, otherwise it will affect the analysis process.A unit can have multiple sets real constant, but some units do not require real constants, PLANE82 in the analysis of the plane strain problem do not need to enter a real constant.

(3)Material properties: As for linear material generally used, its properties include the elastic modulus, coefficient of linear expansion, the main Poisson's ratio, Poisson's ratio, shear modulus, damping ratio, homogeneous material damping coefficient, friction coefficient, mass density and so on. In specific analysis, according to the specific content of the analysis to select certain of the above options.In this case need to define the elastic modulus of 200 GPa, Poisson's ratio 0 26.

2.2.2. Set mesh control options

The meshing control option is not required, as to use the default meshing controls are appropriate for most models, if you do not set the meshing controls, ANSYS will use the default settings on the grid divided.

(1）Cell shape control: According to the divided entity can be used triangular or quadrangular (2D) and tetrahedral or six-sided (3D)Unit. This example uses quadrilateral element.

(2) Grid type: free mesh and mapping grid in two forms to choose from. The cases were mapped meshing.

2.2.

3. Meshing Controls

The meshing control mainly refers to the control of cell size.The cell size determines the generated node, the number of units and the finite element model near the extent of the entity, and thus determine the accuracy of the analysis results. The same entity, in accordance with the purpose of the analysis, the different parts of different sizes and the type of density grid can be used. We are more concerned about the parts of the mesh fine, and the irrelevant places are classified as coarse.Taking into account the limited resources of the computer, in the actual operation of the process, often subject to multiple debugging to achieve the desired Result.The present embodiment radial unilateral divided into four portions circumferentially divided into 80 parts. 2.3. Meshing

Meshing command mainly is Xmesh,,,the example follows complete meshing with amesh finite element model

shown in Figure 4.

Figure 4 Finite element model of Fig.

The pre-processing command stream as: mp, ex, 1, 2e11$mp, prxy, 1, 0. 26$et, 1, 82 keyopt, 1, 3, 2$cyl4,,, 0. 6, 0, 0. 8,90 /replot

aplot$arsym, x, 1$arsym, y, 1, 2$nummrg, all $numcmp, all

/title, geometric model$aplot

/pnum, line, 1 $lplot$csys, 1 $lsel, s, loc, x, 0. 7 $lesize, all,,, 4 $allsel$lsel, u, loc, x, 0. 7 $lesize, all,,, 20$amesh, all$allsel

/title, elements in model$eplot$finish

Next, enter the solving process with the command / solu

2.4. Solving

2.4.1. Define the type of analysis

ANSYS, can be a variety of analyzes, such as static analysis, modal analysis, buckling analysis, transient analysis.In this case the gas pipeline conducts a static analysis.

2.4.2. The boundary constraints

In ANSYS, the boundary constraints imposed by the linear displacement of the structural mechanics, rotational displacement; thermal temperature; pressure, velocity fluid mechanics; magnetic potential energy in the magnetic vector magnetic potential energy; electrical voltage. In this embodiment, the X-direction displacement of the pipe vertical line and horizontal Y direction should be restrainted. 2.4.3.Load

The need to increase the load on the object of analysis includes concentrated loads, surface loads, body loads, inertia loads, coupling field loads.The load can be applied on the geometric model can also be applied to the finite element model, or a mixture of the two to use.However, the load on the geometric model is independent of the finite element mesh, it is not necessary to modify the grid to reload, but the finite element model and you want to modify the grid, you must first remove the load, and then modify the grid and then reload.But regardless of the applied model in which solving the load must all be converted to the finite element model.

The load to be added in the present embodiment of the gas pressure on the wall, which may be applied in the composition of the inner walls of the four https://www.360docs.net/doc/2e18737302.html,mand solving process flow:

/solu

antyoe, static$lplot$lsel, s,,, 3, 6, 3 lsel, a,,, 10, 12, 2 $nsll, s, 1 $sf, all, pres, 1e6$lsel, s,,, 2, 9, 7$nsll, s, 1$d, all, ux lsel, s,,, 4, 7, 3$nsll, s, 1$d, all, uy$allsel solve$finish

Solving into the post-processing stage.ANSYS has two post-processor post1 First, generic post-processor is used to

view the entire model Result at each time point; second,the processor time history POST26 for viewing the entire model a point on the curve Result over time. In this example into the post1. 2.5. View Results

Graphical display of Result and lists display can present the results in the general postprocessor.Available graphical display includs deformation maps, node Figure unit Figure vector display Result chart, cracks or crushed map and so on. The list shows the order more, it does not list these commands can be a simple process, and then the Result data list shows the end result.In this case will graphically display the results of the analysis: the displacement field contour shown in Figure 5; X-direction stress Contour maps shown in Figure 6; Y-direction stress contours shown in Figure 7; equivalent stress contour shown in Figure 8; equivalent strain contour map shown in Figure 9.

The pipeline maximum radial displacement can be seen from Figure 5 to 9. 59Lm, or very small, in its allowed within the safe range.By Figures 6 and 7, the X direction of the maximum stress value is 37. 5nPa, the inner surface in the vertical direction; the Y direction of the maximum stress value 37.5nPa, the inner surface in the horizontal direction; maximum stress occurs in the pipelinean inner surface for 400nPa; equivalent strain of the maximum value occurs in the inner surface of the pipeline, the value 200Lm allowed

values are smaller than the pipe

Figure 5 Contour map of the displacement field

Post-processing commands flow: / postl

/title, contour of sum displacements

plnsol, u, sum

/title, stress contour in x direction plnsol, s, x

/title, stress contour in y direction plnsol, s, y

/title, contour of equivalent stress plnsol, s eqv

/title, contour of equivalent strain plnsol, epto, eqv$finish

Figure 6 X-direction stress contour map

Figure 7 Y-direction stress contour map

Figure 8 Equivalent stress contour map

Figure 9 Equivalent strain contour map

(3) High Availability: SAN eliminates the single point of failure, storage devices and servers can be extended in the case of non-stop, so as to ensure Paul high availability In a SAN environment, one-to-one relationship between the original application server and fault redundant servers transform into a multi pair.A relationship that multiple application servers can share a single fault redundant servers, reducing the required equipment, and thus significant cost savings.

(4) High efficiency: SAN integration and improve the utilization of the tape or disk devices (up to 80%), significantly improve storage ROI.Storage resources centralized management and shared between the host, in order to achieve the Investment and Inclusion within the enterprise.

(5) Open connection: SAN can regards multiple operating systems and multi-vendor storage devices as a unified storage pool management, customers can continue to use their existing equipment to avoid replacement of existing storage devices.

(6) Cost savings: use a SAN, can reduce the equipment investment by sharing tape drives, the same enterprise, the need for high-speed access to large amounts of data from multiple servers the SAN also help save cost

(7) Manageability: Systems management software can easily SAN storage capacity assigned to the server, all from a single management console storage capacity and SAN infrastructure platform, and optimize the performance of Fibre Channel network.

3.Conclusion

In this case, the gas pipeline static analysis is a fundamental step in ANSYS finite element analysis and basic content.The ANSYS function is very powerful, can provide us with more areas of a full range of analysis, its secondary development,and Parametric Technology can reduce design time and optimal design Result, improve design quality, so that based on ANSYS finite element analysis in engineeringwill can be of great use of space and development potential in the field of design.

References

[1] Zhang Zhaohui ANSYS8 0, structural analysis and examples of analysis [M] Beijing: Mechanical Industry Press, 2005

[2] Long Yu-ball Lung Chi-fly, Cen a new finite element theory [M] Beijing: Tsinghua University Press, 2004

[3] Duping An, Gan Ah Zhong, Yating finite element method) theory, modeling and application [M] Beijing: National Defense Industry Press, 2004