ansys 有限元自學手冊

李兵.人郵2013.4

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實體模型 –> 修正後劃分 有限元網格

offset WP 偏移工做平面

 

 

 

模型的創建

將cT輪廓曲線 提取出來輸入三維造型軟件進行建模的方法，這種方法因爲要對輪廓曲線進行很大調整所以會產生比較大的偏差，而且會耗費大量的時間。

在Mimics軟件中提取頭頸骨骼對應的灰度閾值並造成輪廓曲線．經過自動造型構成了具備大量三角形 利用逆向工程軟件Geomagic和軟件Mimics接口將曲面導入Geomagic中對曲面進行自動修正和優化。造成了具備NURBS曲面的模型

有限元計算機模型的創建

將IGES格式的幾何模型導入有限元分析前處理軟件創建模型的外表面後，能夠先對輪廓和線進行處理，根據須要的網格疏密規定面和線上的單元大小。隨後選取適合的單元類型，經過自動網格生成技術映射到三維實體上，變成體單元。這樣劃分的單元密度隨本身定義的狀況而變化．有針對性。固然也能夠直接對幾何模型進行三維有限元網格的自動劃分，這樣的單元密度分佈就比較均勻。自動化分單元后，爲保證模擬計算時結構的收斂和節省CPU運算時間，能夠手動調整個別結構有問題、質量不高的單元，還能根據幾何外形進行單元平滑，提升幾何類似性。
根據以上的方法將cl劃分具備15998個四面體單元(SouD45)和4033個節點的有限元網格模型。按照一樣的方法將頸椎的C2劃分紅有限元網格模型。而後經過裝配將cl和c2裝配如圖3所示的有限元網格模型。對於肌肉和韌帶．本文利用彈簧單元來進行模擬。最後所得的頭頸有限元計算模型如圖4所示，模型具備四面體單元127749個，彈簧單元354個，節點32816個。

有限元分析

對已創建的頭頸有限元計算模型賦予材料屬性．施加約束並設定初始條件，參考文獻(4)的頭部所受的衝擊載荷曲線，如圖5所示，並將其施加在頭部，通過9小時有限元動力響應計算，獲得了模型各節點位移響應歷程和應力響應歷程，圖6爲頭部某節點的位移響應歷程曲線，與文獻(4)中的試驗結果相比較。本次計算的結果是與試驗結果大體相符的，這也證實了所建的頭頸有限元計算模型是有效的。進一步對計算結果進行後處理，咱們能夠獲得如圖7和圖8所示的頭部和頸部在任意時間的變形和應力分佈，這對在探討頭頸部在受到衝擊載荷時所受損傷的視理有着重要意義的。

微計算機信息 

 

1. 導入mimics

2. 幾何模型 閥值選取,區域增加,分離蒙罩.創建3D表面模型.體積 面積  閥值範圍

3. 面風格劃分 網格重劃器magics, 參數默認 , 保存爲.lis的ansys element 文件.

 

 

 

 

1. 截取圖像，在畫筆（Window操做系統自帶軟件）中打開，修改，使得圖片光滑天然，獲得腦血管的邊界輪廓圖像，以.bmp的單色圖片格式保存。

2. 運行Matlab7.0軟件，導入生成的.bmp圖片文件。在自寫程序datamat（功能是顯示單色圖片像素點的座標）中指定腦血管單色圖片.bmp的路徑，獲得腦血管輪廓各點的二維座標

3.複製座標點數值，在EXCEL（Window操做系統自帶軟件）中保存爲.cvs格式（由於座標須要分號分開，因此要先保存爲分隔符格式的文件）的文件，而後將文件改爲.dat格式文件。

4. 運行Ansys軟件，導入生成的點座標文本文件(.dat格式)，重現腦血管輪廓各點，而後對它進行鏡像和旋轉，使它的形狀和原來的同樣，接着用樣條線鏈接各輪廓像素點座標，從新生成腦血管的邊界輪廓

5.定義腦血管的屬性爲彈性結構，按照課題前期結果^[9]，分別輸入腦血管動脈的壓力-應變關係相應數值。按照腦血管動脈壓力6個不一樣時刻的壓力值，輸入壓力，能夠獲得不一樣壓力下的腦血管內血液分佈狀況。

一樣一步步操做，在Ansys軟件中獲得腦血管的平面圖，而後分別對他們進行二維網格劃分，首先將血管頂端設爲入口，底端設爲出口，接着定義元素類型，而後定義材料屬性，最後設定劃分尺寸爲0.5，以.msh格式導出。

6.

運行Fluent軟件，導入獲得的腦血管.msh二維網格文件，驗證網格的正確性及網格的平滑和掃描，定義單位。定常的方法分5或6個步驟進行分析：一、定義求解器，這裏選擇pressure-based求解器；二、定義湍流，這裏選擇k-epsilon湍流模型；三、定義流體，這裏定義流體類型爲血液，其密度爲1050kg/m³，粘性爲0.004kg/m^-s；四、定義邊界類型，這裏設定入口速度爲0.4m/s；入口壓力設爲70mmhg；五、初始化速度和壓力；六、迭代300次，分別觀察壓力分佈和速度分佈，這裏選擇腦血管感興趣的觀察區域內的觀察點，經過Fluent軟件計算系統計算相應的數值，保存數值及各時刻不一樣參數的圖片，製做相應的動畫。

7.

由於腦血管分叉口爲本實驗重點研究對象，分叉口內血液流動速度及壓力對研究腦血管疾病有密切聯繫，所以這裏把腦血管分叉口做爲感興趣的觀察區域以便研究腦血管分叉口的的動力學特性，根據不一樣分析步驟，將腦血管分爲五個不一樣的區域，見圖3.6，A爲入口，B爲出口，C爲分叉口頸部，D爲分叉口體部，E爲分叉口頂部。在Fluent軟件計算系統下於每一個區域內各採集流速、壓力各五個不一樣數據，計算後取平均值；於相應的壁面取五個切應力的數值，計算後取平均值，記錄並保存數據。

 

 

 

 

 

 

 

 

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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.

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

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  • 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

 

 

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Thought Catalog

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

 

 

 

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      約束方程的定義 . p59:

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