11.4. Step 1: Create a New Project
1. Copy ICEPAK_ROOT/tutorials/optimization/optimization.tzr to your working directory.
Replace ICEPAK_ROOT by the full path name of the directory where ANSYS Icepak is installed on your computer system.
2. Start ANSYS Icepak, as described in Starting ANSYS Icepak in the Icepak User's Guide.
When ANSYS Icepak starts, the Welcome to Icepak panel opens automatically.
3. Click Unpack in the Welcome to Icepak panel.
The File selection panel appears.
4. In the File selection panel, select the packed project file optimization.tzr and click Open.
The Location for the unpacked project file selection dialog appears.
5. In the Location for the unpacked project file selection dialog, select a directory where you would like to place the packed project file, enter a project name in the New project text field, then click Unpack.
11.5. Step 2: Build the Model
This tutorial uses an existing model. ANSYS Icepak will display the model in the graphics window. To
Note
You can rotate the cabinet around a central point using the left mouse button, or you can translate it to any point on the screen using the middle mouse button. You can zoom into and out from the cabinet using the right mouse button. To restore the cabinet to its default orientation, select Home position from the Orient menu.
Save the problem to a new project file (this enables you to expand on the problem without affecting the original file).
File
→
Save project as1. In the Project name text box, enter the name optimization-new.
2. Click Save.
11.6. Step 3: Define Design Variables
The large heat sink needs to be optimized in terms of the number of fins and fin thickness. Therefore, you will define the following design variables for the large heat sink: fin count (in the range from 2 to 18) and fin thickness (in the range from 0.254 mm to 2.032 mm).
1. Define the finCount and finThick design variables for the heatsink_big and specify their initial values.
a. Expand the hs_assembly_2 node in the Model manager window.
b. Select the heatsink_big in the Model manager window and click the Edit object button ( ) to open the Heat sinks panel.
c. Click the Properties tab.
d. Under the Fin setup tab, type $finCount next to Count, and press Enter on the keyboard to open the Param value panel.
Important
All function names are case-sensitive.
e. In the Param value panel, enter 12 for the Initial value of finCount, and click Done to close the panel.
f. In the Heat sinks panel, under the Fin setup tab, type $finThick next to Thickness, and press Enter on the keyboard to open the Param value panel.
g. In the Param value panel, enter 0.762 for the Initial value of finThick, and click Done to close the panel.
h. Click Done in the Heat sinks panel to close the panel.
2. Specify the constraint values for the design variables.
Solve
→
Run optimizationExtra
Alternatively, you can click the button.
a. Turn on the Optimization option in the Setup tab. Then click on the Design variables tab.
The design variables that you had defined will be listed in the panel, and their initial values will be shown in the Base value text box.
b. Select finCount from the list, then enter 2 for the Min value constraint,18 for the Max value constraint.
c. Select Allow only multiples, keep the default value of 1, and click Apply.
d. Select finThick from the list, then enter 0.254 for the Min value constraint,2.032 for the Max value constraint, and click Apply.
e. Make sure Allow only multiples is only activated for finCount, not finThick.
f. Click Done to close the Parameters and optimization panel.
11.7. Step 4: Generate a Mesh
For this model, you will not generate a mesh in advance. Meshing will be automatically performed for each design trial during parametric trials.
Model
→
Generate Mesh.1. Make sure that the Mesh type is Mesher-HD and the Mesh assemblies separately option is turned on.
2. Make sure the Allow minimum gap changes is enabled in the Misc tab.
3. Click Close in the Mesh control panel to close the panel.
11.8. Step 5: Physical and Numerical Settings
Problem setup
→
Basic parameters1. Keep all the defaults in the Basic parameters panel.
2. Click Accept in the Basic parameters panel to accept the settings and close the panel.
Solution settings
→
Basic Settings 1. Make sure Number of iterations is 125.2. Make sure the convergence criteria for Flow is 0.001, and for Energy is 1e-7.
3. Click Accept to close the Basic settings panel.
11.9. Step 6: Save the Model
ANSYS Icepak will save the model for you automatically before it starts the calculation, but it is a good idea to save the model (including the mesh) yourself as well. If you exit ANSYS Icepak before you start the calculation, you will be able to open the project you saved and continue your analysis in a future ANSYS Icepak session. (If you start the calculation in the current ANSYS Icepak session, ANSYS Icepak will simply overwrite your project file when it saves the model.)
11.10. Step 7: Define Primary, Compound, and Objective Functions
Note
The objective of this tutorial is to minimize the thermal resistance of the heat sink while keeping the maximum temperature for the entire system below 70°C and ensuring that the total mass of the heat sinks does not exceed 0.326 kg. Therefore, you will define the following primary functions: thermal resistance for the large heat sink (bighsrth), mass of the large heat sink (bighsms), mass of the small heat sink (smlhsms), and global maximum temper-ature of 70°C (mxtmp). You will also define a compound function, the total mass of the heat sinks of 0.326 kg (totalmass). For the objective function, you will minimize the thermal resistance of the large heat sink (bighsrth).
1. Go to Solve
→
Run optimization to open the Parameters and optimization panel.2. In the Functions tab, define four primary functions.
a. Define the thermal resistance function for the large heat sink (bighsrth).
i. Click the New button under Primary functions.
ii. In the Define primary function panel, enter bighsrth next to Function name.
iii. In the Function type drop-down list, keep the default selection of Global value.
iv. In the Value drop-down list, select Thermal resistance of heatsink.
v. In the Object drop-down list, select the heatsink_big object under hs_assembly_2, and click Accept.
vi. In the Define primary function panel, click Accept to save the changes and close the panel.
b. Define the mass function for the large heat sink (bighsms).
i. Repeat step (a) for the bighsms as the Function name, Global value as the Function type, Mass of objects as the Value, and heatsink_big as the Object.
c. Define the mass function for the small heat sink (smlhsms).
i. Repeat step (a) for the smlhsms as the Function name, Global value as the Function type, Mass of objects as the Value, and heatsink_small as the Object.
d. Define a constraint function as the global maximum temperature of 70°C (mxtmp).
i. Click the New button under Primary functions.
ii. In the Define primary function panel, enter mxtmp next to Function name.
iii. In the Function type drop-down list, keep the default selection of Global value.
iv. In the Value drop-down list, keep the default selection of Global maximum temperature.
v. Select Constraint and keep the default selection of Max value.
vi. Enter 70 in the text entry field and click Accept to save the changes and close the panel.
3. Define a compound function.
a. Under Compound functions, click the New button to open the Define compound function panel.
b. In the Define compound function panel, enter totalmass for the Function name.
c. Next to Definition enter $bighsms+$smlhsms.
d. Select Constraint and keep the default selection of Max value.
e. Enter 0.326 in the text entry field and click Accept to save the changes and close the panel.
4. Define an objective function.
a. In the Parameters and optimization panel, select bighsrth from the Objective function drop-down list.
b. Keep the default selection of Minimize value.
11.11. Step 8: Calculate a Solution
1. Open the Parameters and optimization panel, if it is not already opened.
Solve
→
Run optimizationNote
Alternatively, you can click the button in the Model and solve toolbar.
2. Set up the optimization process.
a. In the Parameters and optimization panel, click the Setup tab.
b. Verify that the Optimization option is turned on, and keep all the defaults for this option.
c. Deselect Allow fast trials (single .cas file).
Note
Due to the geometry change based on the fin thickness and fin count, the fast trials option is not possible in this problem.
d. Select Sequential solution of flow and energy equations.
3. Click Run in the Parameters and optimization panel to start the calculations.
11.12. Step 9: Examine the Results
As ANSYS Icepak starts calculating solutions for the model, the Optimization run window opens and ANSYS Icepak displays the function values, design variables, and the running times for each optimization iteration. In addition, the function values and design variables are plotted versus iteration number, as shown in Figure 11.2 (p. 182).