2.8. Performing a Steady-State Thermal Analysis (GUI Method)

This section describes how to use the menus on the Mechanical APDL GUI to perform the same steady-state thermal analysis described in Example of a Steady-State Thermal Analysis (Command or Batch Method). In this version of the sample analysis, instead of issuing commands, you select options from the GUI menus.

Step 1: Give the Analysis a Title

After you have started Mechanical APDL and entered the GUI, you need to begin the analysis by assigning a title to it. To do so, perform these tasks:

  1. Choose Utility Menu> File> Change Title. The Change Title dialog box appears.

  2. Enter the text Steady-state thermal analysis of pipe junction.

  3. Click OK.

Step 2: Set Measurement Units

You need to specify units of measurement for the analysis. For this pipe junction example, measurements use the U. S. Customary system of units (based on inches). To specify this, type the command /UNITS,BIN in the Input window and press ENTER.

Step 3: Define the Element Type

The example analysis uses a thermal solid element. To define it, do the following:

  1. Choose Main Menu> Preprocessor> Element Type> Add/Edit/Delete. The Element Types dialog box appears.

  2. Click Add. The Library of Element Types dialog box appears.

  3. In the list on the left, scroll down and pick (highlight) "Thermal Solid." In the list on the right, pick "Brick20node 90."

  4. Click OK.

  5. Click Close to close the Element Types dialog box.

Step 4: Define Material Properties

To define material properties for the analysis, perform these steps:

  1. Choose Main Menu> Preprocessor> Material Props> Material Models. The Define Material Model Behavior dialog box appears.

  2. In the Material Models Available window, double-click the following options: Thermal, Density. A dialog box appears.

  3. Enter .285 for DENS (Density), and click OK. Material Model Number 1 appears in the Material Models Defined window on the left.

  4. In the Material Models Available window, double-click the following options: Conductivity, Isotropic. A dialog box appears.

  5. Click the Add Temperature button four times. Four columns are added.

  6. In the T1 through T5 fields, enter the following temperature values: 70, 200, 300, 400, and 500. Select the row of temperatures by dragging the cursor across the text fields. Then copy the temperatures by pressing Ctrl+C.

  7. In the KXX (Thermal Conductivity) fields, enter the following values, in order, for each of the temperatures, then click OK. Note that to keep the units consistent, each of the given values of KXX must be divided by 12. You can just input the fractions and have the program perform the calculations.

    8.35/12
8.90/12
9.35/12
9.80/12
10.23/12

  8. In the Material Models Available window, double-click Specific Heat. A dialog box appears.

  9. Click the Add Temperature button four times. Four columns are added.

  10. With the cursor positioned in the T1 field, paste the five temperatures by pressing Ctrl+V.

  11. In the C (Specific Heat) fields, enter the following values, in order, for each of the temperatures, then click OK.

    .113
.117
.119
.122
.125

  12. Choose menu path Material> New Model, then enter 2 for the new Material ID. Click OK. Material Model Number 2 appears in the Material Models Defined window on the left.

  13. In the Material Models Available window, double-click Convection or Film Coef. A dialog box appears.

  14. Click the Add Temperature button four times. Four columns are added.

  15. With the cursor positioned in the T1 field, paste the five temperatures by pressing Ctrl+V.

  16. In the HF (Film Coefficient) fields, enter the following values, in order, for each of the temperatures. To keep the units consistent, each value of HF must be divided by 144. As in step 7, you can input the data as fractions and let the program perform the calculations.

    426/144
405/144
352/144
275/144
221/144

  17. Click the Graph button to view a graph of Film Coefficients vs. temperature, then click OK.

  18. Choose menu path Material> Exit to remove the Define Material Model Behavior dialog box.

  19. Click SAVE_DB on the Mechanical APDL Toolbar.

Step 5: Define Parameters for Modeling

  1. Choose Utility Menu> Parameters> Scalar Parameters. The Scalar Parameters window appears.

  2. In the window's Selection field, enter the values shown below. (Do not enter the text in parentheses.) Press ENTER after typing in each value. If you make a mistake, simply retype the line containing the error.

    RI1=1.3   (Inside radius of the cylindrical tank)
RO1=1.5   (Outside radius of the tank)
Z1=2      (Length of the tank)
RI2=.4    (Inside radius of the pipe)
RO2=.5    (Outside radius of the pipe)
Z2=2      (Length of the pipe)

  3. Click Close to close the window.

Step 6: Create the Tank and Pipe Geometry

  1. Choose Main Menu> Preprocessor> Modeling> Create> Volumes> Cylinder> By Dimensions. The Create Cylinder by Dimensions dialog box appears.

  2. Set the "Outer radius" field to RO1, the "Optional inner radius" field to RI1, the "Z coordinates" fields to 0 and Z1 respectively, and the "Ending angle" field to 90.

  3. Click OK.

  4. Choose Utility Menu> WorkPlane> Offset WP by Increments. The Offset WP dialog box appears.

  5. Set the "XY, YZ, ZX Angles" field to 0,-90.

  6. Click OK.

  7. Choose Main Menu> Preprocessor> Modeling> Create> Volumes> Cylinder> By Dimensions. The Create Cylinder by Dimensions dialog box appears.

  8. Set the "Outer radius" field to RO2, the "Optional inner radius" field to RI2, the "Z coordinates" fields to 0 and Z2 respectively. Set the "Starting angle" field to -90 and the "Ending Angle" to 0.

  9. Click OK.

  10. Choose Utility Menu> WorkPlane> Align WP with> Global Cartesian.

Step 7: Overlap the Cylinders

  1. Choose Main Menu> Preprocessor> Modeling> Operate> Booleans> Overlap> Volumes. The Overlap Volumes picking menu appears.

  2. Click Pick All.

Step 8: Review the Resulting Model

Before you continue with the analysis, quickly review your model. To do so, follow these steps:

  1. Choose Utility Menu> PlotCtrls> Numbering. The Plot Numbering Controls dialog box appears.

  2. Click the Volume numbers radio button to On, then click OK.

  3. Choose Utility Menu> PlotCtrls> View Settings> Viewing Direction. A dialog box appears.

  4. Set the "Coords of view point" fields to (-3,-1,1), then click OK.

  5. Review the resulting model.

  6. Click SAVE_DB on the Mechanical APDL Toolbar.

Step 9: Trim Off Excess Volumes

In this step, delete the overlapping edges of the tank and the lower portion of the pipe.

  1. Choose Main Menu> Preprocessor> Modeling> Delete> Volume and Below. The Delete Volume and Below picking menu appears.

  2. In the picking menu, type 3,4 and press the ENTER key. Then click OK in the Delete Volume and Below picking menu.

Step 10: Create Component AREMOTE

In this step, you select the areas at the remote Y and Z edges of the tank and save them as a component called AREMOTE. To do so, perform these tasks:

  1. Choose Utility Menu> Select> Entities. The Select Entities dialog box appears.

  2. In the top drop-down menu, select Areas. In the second drop-down menu, select By Location. Click the Z Coordinates radio button.

  3. Set the "Min,Max" field to Z1.

  4. Click Apply.

  5. Click the Y Coordinates and Also Sele radio buttons.

  6. Set the "Min,Max" field to 0.

  7. Click OK.

  8. Choose Utility Menu> Select> Comp/Assembly> Create Component. The Create Component dialog box appears.

  9. Set the "Component name" field to AREMOTE. In the "Component is made of" menu, select Areas.

  10. Click OK.

Step 11: Overlay Lines on Top of Areas

Do the following:

  1. Choose Utility Menu> PlotCtrls> Numbering. The Plot Numbering Controls dialog box appears.

  2. Click the Area and Line number radio boxes to On and click OK.

  3. Choose Utility Menu> Plot> Areas.

  4. Choose Utility Menu> PlotCtrls> Erase Options.

  5. Set "Erase between Plots" radio button to Off.

  6. Choose Utility Menu> Plot> Lines.

  7. Choose Utility Menu> PlotCtrls> Erase Options.

  8. Set "Erase between Plots" radio button to On.

Step 12: Concatenate Areas and Lines

In this step, you concatenate areas and lines at the remote edges of the tank for mapped meshing. To do so, follow these steps:

  1. Choose Main Menu> Preprocessor> Meshing> Mesh> Volumes> Mapped> Concatenate> Areas. The Concatenate Areas picking menu appears.

  2. Click Pick All.

  3. Choose Main Menu> Preprocessor> Meshing> Mesh> Volumes> Mapped> Concatenate> Lines. A picking menu appears.

  4. Pick lines 12 and 7 (or enter in the picker).

  5. Click Apply.

  6. Pick lines 10 and 5 (or enter in picker).

  7. Click OK.

Step 13: Set Meshing Density Along Lines

  1. Choose Main Menu> Preprocessor> Meshing> Size Cntrls> ManualSize>Lines> Picked Lines. The Element Size on Picked Lines picking menu appears.

  2. Pick lines 6 and 20 (or enter in the picker) .

  3. Click OK. The Element Sizes on Picked Lines dialog box appears.

  4. Set the "No. of element divisions" field to 4.

  5. Click OK.

  6. Choose Main Menu> Preprocessor> Meshing> Size Cntrls> ManualSize> Lines> Picked Lines. A picking menu appears.

  7. Pick line 40 (or enter in the picker).

  8. Click OK. The Element Sizes on Picked Lines dialog box appears.

  9. Set the "No. of element divisions" field to 6.

  10. Click OK.

Step 14: Mesh the Model

In this sequence of steps, you set the global element size, set mapped meshing, then mesh the volumes.

  1. Choose Utility Menu> Select> Everything.

  2. Choose Main Menu> Preprocessor> Meshing> Size Cntrls> ManualSize> Global> Size. The Global Element Sizes dialog box appears.

  3. Set the "Element edge length" field to 0.4 and click OK.

  4. Choose Main Menu> Preprocessor> Meshing> Mesher Opts. The Mesher Options dialog box appears.

  5. Set the Mesher Type radio button to Mapped and click OK. The Set Element Shape dialog box appears.

  6. In the 2D shape key drop-down menu, select Quad and click OK.

  7. Click the SAVE_DB button on the Toolbar.

  8. Choose Main Menu> Preprocessor> Meshing> Mesh> Volumes> Mapped> 4 to 6 sided. The Mesh Volumes picking menu appears. Click Pick All. Mechanical APDL builds the meshed model and displays it in the Graphics window. If a shape testing warning message appears, review it and click Close.

Step 15: Turn Off Numbering and Display Elements

  1. Choose Utility Menu> PlotCtrls> Numbering. The Plot Numbering Controls dialog box appears.

  2. Set the Line, Area, and Volume numbering radio buttons to Off.

  3. Click OK.

Step 16: Define the Solution Type and Options

To specify a steady-state solution that uses a program-chosen Newton-Raphson option, do the following:

  1. Choose Main Menu> Solution> Analysis Type> New Analysis. The New Analysis dialog box appears.

  2. Click OK to choose the default analysis type (Steady-state).

  3. Choose Main Menu> Solution> Analysis Type> Analysis Options. The Static or Steady-State dialog box appears.

  4. Click OK to accept the default ("Program-chosen") for "Newton-Raphson option."

Step 17: Set Uniform Starting Temperature

In a thermal analysis, set a starting temperature.

  1. Choose Main Menu> Solution> Define Loads> Apply> Thermal> Temperature> Uniform Temp. A dialog box appears.

  2. Enter 450 for "Uniform temperature." Click OK.

Step 18: Apply Convection Loads

This step applies convection loads to the nodes on the inner surface of the tank.

  1. Choose Utility Menu> WorkPlane> Change Active CS to> Global Cylindrical.

  2. Choose Utility Menu> Select> Entities. The Select Entities dialog box appears.

  3. Select Nodes and By Location, and click the X Coordinates and From Full radio buttons.

  4. Set the "Min,Max" field to RI1 and click OK.

  5. Choose Main Menu> Solution> Define Loads> Apply> Thermal> Convection> On Nodes. The Apply CONV on Nodes picking menu appears.

  6. Click Pick All. The Apply CONV on Nodes dialog box appears.

  7. Set the "Film coefficient" field to 250/144.

  8. Set the "Bulk temperature" field to 450.

  9. Click OK.

Step 19: Apply Temperature Constraints to AREMOTE Component

  1. Choose Utility Menu> Select> Comp/Assembly> Select Comp/Assembly. A dialog box appears.

  2. Click OK to select component AREMOTE.

  3. Choose Utility Menu> Select> Entities. The Select Entities dialog box appears.

  4. Select Nodes and Attached To, and click the Areas,All radio button. Click OK.

  5. Choose Main Menu> Solution> Define Loads> Apply> Thermal> Temperature> On Nodes. The Apply TEMP on Nodes picking menu appears.

  6. Click Pick All. A dialog box appears.

  7. Set the "Load TEMP value" field to 450.

  8. Click OK.

  9. Click SAVE_DB on the Mechanical APDL Toolbar.

Step 20: Apply Temperature-Dependent Convection

In this step, apply a temperature-dependent convection load on the inner surface of the pipe.

  1. Choose Utility Menu> WorkPlane> Offset WP by Increments. A dialog box appears.

  2. Set the "XY,YZ,ZX Angles" field to 0,-90, then click OK.

  3. Choose Utility Menu> WorkPlane> Local Coordinate Systems> Create Local CS> At WP Origin. The Create Local CS at WP Origin dialog box appears.

  4. On the "Type of coordinate system" menu, select "Cylindrical 1" and click OK.

  5. Choose Utility Menu> Select> Entities. The Select Entities dialog box appears.

  6. Select Nodes, and By Location, and click the X Coordinates radio button.

  7. Set the "Min,Max" field to RI2.

  8. Click OK.

  9. Choose Main Menu> Solution> Define Loads> Apply> Thermal> Convection> On Nodes. The Apply CONV on Nodes picking menu appears.

  10. Click Pick All. A dialog box appears.

  11. Set the "Film coefficient" field to -2.

  12. Set the "Bulk temperature" field to 100.

  13. Click OK.

  14. Choose Utility Menu> Select> Everything.

  15. Choose Utility Menu> PlotCtrls> Symbols. The Symbols dialog box appears.

  16. On the "Show pres and convect as" menu, select Arrows, then click OK.

  17. Choose Utility Menu> Plot> Nodes. The display in the Graphics Window changes to show you a plot of nodes.

Step 21: Reset the Working Plane and Coordinates

  1. To reset the working plane and default Cartesian coordinate system, choose Utility Menu> WorkPlane> Change Active CS to> Global Cartesian.

  2. Choose Utility Menu> WorkPlane> Align WP With> Global Cartesian.

Step 22: Set Load Step Options

For this example analysis, you need to specify 50 substeps with automatic time stepping.

  1. Choose Main Menu> Solution> Load Step Options> Time/Frequenc> Time and Substps. The Time and Substep Options dialog box appears.

  2. Set the "Number of substeps" field to 50.

  3. Set "Automatic time stepping" radio button to On.

  4. Click OK.

Step 23: Solve the Model

  1. Choose Main Menu> Solution> Solve> Current LS. The program displays a summary of the solution options in a /STAT command window.

  2. Review the summary.

  3. Choose Close to close the /STAT command window.

  4. Click OK in the Solve Current Load Step dialog box.

  5. Click Yes in the Verify message window.

  6. The solution runs. When the Solution is done! window appears, click Close.

Step 24: Review the Nodal Temperature Results

  1. Choose Utility Menu> PlotCtrls> Style> Edge Options. The Edge Options dialog box appears.

  2. Set the "Element outlines" field to "Edge only" for contour plots and click OK.

  3. Choose Main Menu> General Postproc> Plot Results> Contour Plot> Nodal Solu. The Contour Nodal Solution Data dialog box appears.

  4. For "Item to be contoured," pick "DOF solution" from the list on the left, then pick "Temperature TEMP" from the list on the right.

  5. Click OK. The Graphics window displays a contour plot of the temperature results.

Step 25: Plot Thermal Flux Vectors

In this step, you plot the thermal flux vectors at the intersection of the pipe and tank.

  1. Choose Utility Menu> WorkPlane> Change Active CS to> Specified Coord Sys. A dialog box appears.

  2. Set the "Coordinate system number" field to 11.

  3. Click OK.

  4. Choose Utility Menu> Select> Entities. The Select Entities dialog box appears.

  5. Select Nodes and By Location, and click the X Coordinates radio button.

  6. Set the "Min,Max" field to RO2.

  7. Click Apply.

  8. Select Elements and Attached To, and click the Nodes radio button.

  9. Click Apply.

  10. Select Nodes and Attached To, then click OK.

  11. Choose Main Menu> General Postproc> Plot Results> Vector Plot> Predefined. A dialog box appears.

  12. For "Vector item to be plotted," choose "Flux & gradient" from the list on the left and choose "Thermal flux TF" from the list on the right.

  13. Click OK. The Graphics Window displays a plot of thermal flux vectors.

Step 26: Exit from Mechanical APDL

To leave the program, click the QUIT button in the Toolbar. Choose an exit option and click OK.