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COMSOL使用方法的例子（Heat equation）.pdf

发布时间：2022-06-08 发布人：admin 分类：说明书 资料大小：1.39M 资料格式：pdf 举报 版权申诉
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    COMSOL 4.2 Tutorial COMSOL Multiphysics (formerly FEMLAB) is a finite element analysis, solver and Simulation software / FEA Software package for various physics and engineering applications, especially coupled phenomena, or multiphysics. COMSOL Multiphysics also offers an extensive interface to MATLAB and its toolboxes for a large variety of programming, preprocessing and postprocessing possibilities. The packages are cross-platform (Windows, Mac, Linux,Unix.) In addition to conventional physics-based user-interfaces, COMSOL Multiphysics also allows for entering coupled systems of partial differential equations (PDEs). How to create a new model in COMSOL 1. Start COMSOL Multiphysics 2. Work through the COMSOL Model Wizard which will require you to select the coordinate system for the model, the relevant physics to the problem, and the type of study you wish to perform (Time dependant or stationary). 3. Define the parameters, equations and variables pertinent to the model (sub directory (Global Definitions). 4. Define the geometry of the model (Geometry). 5. Select the materials you wish to use in your model (Materials).
    6. Select the boundary, bulk and initial conditions for your system for each physics you are using (This will be entered separately for each different physics you are using e.g. you will need to enter these for Laminar Flow and again for Heat Transfer if you are using both ). 7. Choose the element size to be used (Mesh). 8. Adjust solver parameters and compute (Study). 10. Display the desired results in the most meaningful way (Results). Not all of these steps are always necessary when building a model. The order is also variable depending on the complexity of the model. Example 1. (Heat transfer) Consider a cylindrical heating rod which is sheathed by a concentric tube of thickness 0.05 m and which starts 0.05 m away from the center. The entire assembly is immersed in a fluid and the system is at steady-state, as shown below. We wish to determine the temperature distribution within the sheath. After thinking about the problem, assume that we arrived at the following approximations (make sure you understand how we arrived at following approximations for your future quiz and test): The temperature of the heater is constant at 400K. The temperature at R1 is the same as the temperature of the
    heater, 400K. The fluid temperature is constant at 300K and this is the temperature of the surrounding sheath at R2. Given that heat diffusion should be the same at any given θ it is reasonable to define this problem in 2D as follows. Solution using COMSOL:
    Startup 1. Start COMSOL by clicking the COMSOL Multiphysics 4.2 icon. 2. When COMSOL starts, the Model Wizard will be open automatically. This wizard asks you to define the spatial dimension you’ll be using for the model as well as the applicable physics and the type of study you wish to perform (either time dependant or stationary). For this problem start by selecting 2D, continue by clicking the blue, right pointing arrow at the top right of the Model Wizard screen. 3. Next select the applicable physics for the model. In this case heat transfer in solids will be selected. This can be found under the Heat Transfer module. Click the triangle to the left of
    the Heat Transfer module to see the drop down menu which contains Heat Transfer in Solids, left click this so that it is highlighted then click the blue, right pointing arrow at the top right of the Model Wizard menu screen. Multiple physics can be added to a single model by left clicking the physics to add and then left clicking the blue + sign at the bottom left of the Model Wizard menu screen. 4. The final step in the Model Wizard is to select the type of study you would like to perform on our model. In our case stationary will be sufficient to find the steady state solution to this problem. As with the physics add the stationary study by left clicking on “Stationary” below the preset studies icon. Click the finish flag at the top right of the Model Wizard to finish startup. Model Builder and Saving
    Now that we are finished with the Model Wizard we will turn our attention to the Model Builder portion of the program. This is just to the left of where the Model Wizard had been. Before we continue with the Model Builder let us take a second to save our model. This is done by clicking “File” at the top left of the screen and then selecting “Save As” as is the case with most programs. This file will be named “Heat Transfer Example”. By default COMSOL will save all COMSOL files in a folder it creates called COMSOL42 however this folder name will change with the version of COMSOL being used. After giving our file a name and clicking the save button seen in the above image notice that the first icon within the model builder now has the name of our file. From this point on we can essentially just work our way down the Model Builder’s list of options filling in values and conditions where we need them.
    Geometry Now we are ready to add the geometry of the model. This is very simple because our assumptions have placed the problem into only 2 dimensions. Our geometry consists of only of a rectangle. 1. To create this rectangle first find the geometry icon in the model builder menus and right click it, this will bring up the menu shown at right. 2. Find the “Rectangle” button in this new menu and left click this. 3. At this point the rectangle has been added, however the dimensions of this rectangle need to be changed to fit the dimensions in the problem. We do this by left clicking the white rectangle just to the left of the geometry icon. This will expand the geometry tab to show all the sub tabs contained within geometry. If you added the rectangle correctly you will see the tab called Rectangle 1. This contains all the information regarding this object and to adjust the dimensions and position of this rectangle this is where we do so. Left click the tab labeled Rectangle 1.
    4. If you have completed the above steps successfully your screen should resemble the one above. Notice that by default the corner of the rectangle has been placed at the origin (position x= 0, y =0) and given width and height of 1m. For this problem the height needs to be 5 cm (0.05 m) and the width needs to be 30 cm (0.3 m). Enter these values into the designated fields and press the blue building icon at the top right of the rectangle menus. This is the “Build All” button and will add your rectangle to the model.
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