ansys 有限元自学手册

李兵.人邮2013.4

实体模型 –> 修正后划分 有限元网格

offset WP 偏移工作平面

 

 

 

模型的建立

将cT轮廓曲线 提取出来输入三维造型软件进行建模的方法，这种方法由于要对轮廓曲线进行很大调整因此会产生比较大的误差，并且会耗费大量的时间。

在Mimics软件中提取头颈骨骼对应的灰度阈值并形成轮廓曲线．通过自动造型构成了具有大量三角形 利用逆向工程软件Geomagic和软件Mimics接口将曲面导入Geomagic中对曲面进行自动修正和优化。形成了具有NURBS曲面的模型

有限元计算机模型的建立

将IGES格式的几何模型导入有限元分析前处理软件建立模型的外表面后，可以先对轮廓和线进行处理，根据需要的网格疏密规定面和线上的单元大小。随后选取适合的单元类型，通过自动网格生成技术映射到三维实体上，变成体单元。这样划分的单元密度随自己定义的情况而变化．有针对性。当然也可以直接对几何模型进行三维有限元网格的自动划分，这样的单元密度分布就比较均匀。自动化分单元后，为保证模拟计算时结构的收敛和节省CPU运算时间，可以手动调整个别结构有问题、质量不高的单元，还能根据几何外形进行单元平滑，提高几何相似性。
根据以上的方法将cl划分具有15998个四面体单元(SouD45)和4033个节点的有限元网格模型。按照同样的方法将颈椎的C2划分成有限元网格模型。然后通过装配将cl和c2装配如图3所示的有限元网格模型。对于肌肉和韧带．本文利用弹簧单元来进行模拟。最后所得的头颈有限元计算模型如图4所示，模型具有四面体单元127749个，弹簧单元354个，节点32816个。

有限元分析

对已建立的头颈有限元计算模型赋予材料属性．施加约束并设定初始条件，参考文献(4)的头部所受的冲击载荷曲线，如图5所示，并将其施加在头部，经过9小时有限元动力响应计算，得到了模型各节点位移响应历程和应力响应历程，图6为头部某节点的位移响应历程曲线，与文献(4)中的试验结果相比较。本次计算的结果是与试验结果大致相符的，这也证明了所建的头颈有限元计算模型是有效的。进一步对计算结果进行后处理，我们可以得到如图7和图8所示的头部和颈部在任意时间的变形和应力分布，这对在探讨头颈部在受到冲击载荷时所受损伤的视理有着重要意义的。

微计算机信息 

 

1. 导入mimics

2. 几何模型 阀值选取,区域增长,分离蒙罩.建立3D表面模型.体积 面积  阀值范围

3. 面风格划分 网格重划器magics, 参数默认 , 保存为.lis的ansys element 文件.

 

 

 

 

1. 截取图像，在画笔（Window操作系统自带软件）中打开，修改，使得图片光滑自然，得到脑血管的边界轮廓图像，以.bmp的单色图片格式保存。

2. 运行Matlab7.0软件，导入生成的.bmp图片文件。在自写程序datamat（功能是显示单色图片像素点的坐标）中指定脑血管单色图片.bmp的路径，得到脑血管轮廓各点的二维坐标

3.复制坐标点数值，在EXCEL（Window操作系统自带软件）中保存为.cvs格式（因为坐标需要分号分开，所以要先保存为分隔符格式的文件）的文件，然后将文件改成.dat格式文件。

4. 运行Ansys软件，导入生成的点坐标文本文件(.dat格式)，重现脑血管轮廓各点，然后对它进行镜像和旋转，使它的形状和原来的一样，接着用样条线连接各轮廓像素点坐标，重新生成脑血管的边界轮廓

5.定义脑血管的属性为弹性结构，按照课题前期结果[9]，分别输入脑血管动脉的压力-应变关系相应数值。按照脑血管动脉压力6个不同时刻的压力值，输入压力，可以得到不同压力下的脑血管内血液分布情况。

同样一步步操作，在Ansys软件中得到脑血管的平面图，然后分别对他们进行二维网格划分，首先将血管顶端设为入口，底端设为出口，接着定义元素类型，然后定义材料属性，最后设定划分尺寸为0.5，以.msh格式导出。

6.

运行Fluent软件，导入得到的脑血管.msh二维网格文件，验证网格的正确性及网格的平滑和扫描，定义单位。定常的方法分5或6个步骤进行分析：1、定义求解器，这里选择pressure-based求解器；2、定义湍流，这里选择k-epsilon湍流模型；3、定义流体，这里定义流体类型为血液，其密度为1050kg/m3，粘性为0.004kg/m-s；4、定义边界类型，这里设定入口速度为0.4m/s；入口压力设为70mmhg；5、初始化速度和压力；6、迭代300次，分别观察压力分布和速度分布，这里选择脑血管感兴趣的观察区域内的观察点，通过Fluent软件计算系统计算相应的数值，保存数值及各时刻不同参数的图片，制作相应的动画。

7.

因为脑血管分叉口为本实验重点研究对象，分叉口内血液流动速度及压力对研究脑血管疾病有密切联系，因此这里把脑血管分叉口作为感兴趣的观察区域以便研究脑血管分叉口的的动力学特性，根据不同分析步骤，将脑血管分为五个不同的区域，见图3.6，A为入口，B为出口，C为分叉口颈部，D为分叉口体部，E为分叉口顶部。在Fluent软件计算系统下于每个区域内各采集流速、压力各五个不同数据，计算后取平均值；于相应的壁面取五个切应力的数值，计算后取平均值，记录并保存数据。

 

 

 

 

 

 

 

 

icef CFD  A TOTURIAL

If you want ANSYS ICEM CFD to behave exactly as this tutorial describes, you should go to the Settings Menu, click Selection, and disable Auto Pick Mode in the DEZ. Most experienced ICEM CFD users prefer to enable Auto Pick Mode as it improves efficiency.

 

Initially, all surfaces, curves, and points of the geometry are in the generic part GEOM. The different geometries must be assigned to appropriate parts for further processing.

Create fluid and solid Material Points for the interiors of the cylinder and blade, respectively.

The material point that will be created will help us to keep the FLUID region separate from the SOLID region. This is not strictly necessary since blocks can simply be created in the FLUID part rather than creating a material point.

Initial Blocking and Associations

The blocking strategy for this model involves an internal O-Grid longitudinally in the pipe, surrounding separate blocking for the blade. Within the ANSYS ICEM CFD, projection-based, mesh generation environment, the block faces between different materials (at the Fluid-Solid interface) are projected to the closest geometry surface. Block faces within the same material may be associated to specific CAD surfaces only if necessary for the definition of internal walls.

 

Here, you create the initial blocking, and then fit the blocking more closely to the geometry by associating the vertices and edges to the geometry.

(is this made me very embarrassed before ?

In the Display tree, enable the display of Vertices, and enable vertex Numbers.

 

Associate the vertices to points on the geometry.   (very interesting

Associate the block edges to curves on the geometry.

 

 

AORTA,  Foloow SEE:

Tetra/Prism Mesh Generation for an Aorta

 

 

  1. Import STL data into ANSYS ICEM CFD.

  2. Set up global and part parameters for meshing.

  3. Generate the mesh using the Octree approach.

  4. Generate the mesh using the Delaunay approach.

  5. Examine the mesh using cut-planes.

  6. Smooth the mesh to improve the mesh quality.

 

 

 

 

Solid Full Display

Step 1: Creating Parts

Split the geometry.   segment surface by Angle 35 ?

Create the INLET part.Create the OUTLET part.

Extract the feature curve from the inlet and outlet surfaces. Geometry > Create/Modify Curve   > Extract Curves from Surfaces

Step 2: Creating the Material Point

Selection of Points for Creating Material Point

Step 3: Generating the Octree Mesh

Measure the smallest diameter on the aorta geometry.use this value to set the minimum size for the mesh.

Assign the mesh sizes.2 for Max element. Select Enabled for Curvature/Proximity Based Refinement and enter 0.5 for Min size limit.   Set Refinement to 18.

Specify the parts for prism creation.

Modify the global prism settings.

0.25 for Ortho weight.

Number of volume smoothing steps to 0.

 

Compute the mesh.

Mesh Method is set to Robust (Octree). Enable Create Prism Layers.

 

Examine the mesh

Disable the display of surfaces.

Select Solid & Wire.

 

how you can replace the Octree volume mesh with a Delaunay volume mesh for smoother volume transition.

 

7. Use cut planes to examine the mesh.

Select Wire Frame.Select Manage Cut Plane.Set the following parameters:

Set Fraction Value to 0.95.

Enable the display of volumes in the display control tree.

Select Solid & Wire.

Examine the mesh using a cut plane in the X direction.

Select Middle X Plane in the Method drop-down list.

Disable Show Cut Plane in the Manage Cut Plane DEZ.

REALLY INTERESTING

 

 

8. Smooth the mesh.

The smoothing approach involves initial smoothing of the interior elements without adjusting the prisms. After initial smoothing, you will smooth the prisms as well.

20 for Smoothing iterations and 0.2 for Up to value.

Freeze for PENTA_6  

9.Check the mesh for any errors that may cause problems during the analysis.

Make sure no errors/problems are reported during the check.

Set Fraction Value to 0.62.

 

 

 

Step 4: Generating the Delaunay Mesh

In this step, you will replace the Octree mesh with the Delaunay mesh because it has a smoother volume transition.

 

Select Quick (Delaunay) from the Mesh Method drop-down list

Compute the mesh.

The Create Prism Layers option can be disabled as the prisms were already generated during the Octree mesh generation.

Existing Mesh is selected in the Select drop-down list.

Ensure that Load mesh after completion is enabled.

 

Examine the mesh using cut planes.

Smooth the mesh.

As the prisms were smoothed in the previous step, you will smooth the other elements without adjusting the prisms.

20 for Smoothing iterations and 0.2 for Up to value.

Select Freeze for PENTA_6.

 

Check the mesh for any errors that may cause problems during the analysis.

 

 

Step 5: Saving the Project

Select the solver.

Set the appropriate boundary conditions.

Click Create new under AORTA_WALL ,Select wall from the list of Boundary Conditions in the Selection dialog box

Similarly, set the boundary conditions for INLET to velocity-inlet and OUTLET to pressure-outlet, exhaust-fan, outlet-vent.

Set the boundary conditions for FLUID to fluid.

 

Write the input file for ANSYS FLUENT.

 

The mesh was created in units of millimeters (mm), and hence needs to be scaled to meters.

 

6. Further Setup

You can solve this example for transient, laminar flow using ANSYS FLUENT. A basic setup could include the following:

  • Material properties

    • Density: 1060 kg/m3

    • Viscosity: 0.0035 kg/m-s

  • Solver setup: transient, laminar flow

  • Boundary conditions

    • The transient velocity profile (one cycle) is available with the tutorial example file (AorticInflowWaveform.prof). The profile assumes a cardiac output of 6.8 l/min and 75 beats per minute.

      Note:  Run at least 1.5 cycles to remove the effects of the initial condition.

    • Assume zero pressure at the outlets.

  • Post-processing

    • The periodic solution can be visualized by plotting the inlet pressure for 3 cycles.

    • Other results of interest include wall shear, static pressure on the wall, and velocities along the length.

A more advanced setup could include two-way FSI, which can be done using ANSYS.

 

 

 

 

encountered a serious problem

 

 

Thought Catalog

i.e., entertaining, journalistic, and literary.

 

 

 

足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球足球

ansys continue…

 

 

 

 

Use the Swept command to create a solid body or a sheet by sweeping one or more sections along one, two, or three guide strings.

 

 

X有限元分析 ansys13.0      约束方程的定义 . p59:

Xfluent 流体计算应用教程 ２版．温正．

posted @ 2013-09-02 21:58  好哥TOP  阅读(1732)  评论(0)  编辑  收藏  举报