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Setup and Solution

Figure 24.19: The Design Tool Dialog Box Objectives Tab

g.In the Manage Sensitivity Data dialog box, click Export... and save the sensitivity data as forcedrag.s.

24.4.5. Step 5: Compute Lift Sensitivity

1.Select force-lift from the Observable Names selection list and select Maximize from the Sensitivity Orientation list in the Adjoint Observables dialog box.

Design → Adjoint-Based → Observable...

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2.Initialize and Calculate the adjoint solution using the Run Adjoint Calculation dialog box to obtain the sensitivities for the force-lift observable.

Design → Adjoint-Based → Calculate...

You can export the sensitivity data for the lift observable as you did for the drag, but it is not strictly necessary if you plan to perform the multi-objective optimization in the current Fluent session.

24.4.6. Step 6: Modify the Shape

In this section, you will load the previously saved force-drag sensitivity data and perform the multiobjective design change.

1.Open the Design Tool dialog box if it is not already open.

Design → Adjoint-Based → Design Tool...

force-lift is now displayed in the Design Change tab because it is the currently selected observable. The Design Change tab functions as a dashboard for the design modification, where you can select which boundaries are subject to modification, enable or disable conditions that you have defined, specify relative weighting if you have multiple freeform objectives, and view predicted results. You will return to it to perform the design change after you have configured the objectives and the morphing region.

2.Retain the default selection of Polynomials from the Morphing Method list.

This morphing method is appropriate when you prefer mesh quality over adherence to the design conditions; otherwise the Direct Interpolation is recommended.

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Setup and Solution

3.Load the previously saved force-drag sensitivity data.

a.Open the Objectives tab.

The force-lift observable is already listed because Include current data is enabled.

b.Click Manage Data... to open the Manage Sensitivity Data dialog box.

c.Click Import Sensitivities... and select the force-drag.s file you created earlier. Click OK.

d.Close the Manage Sensitivity Data dialog box.

4.Define the objective for each observable.

For this example, you will seek a design change that increases the lift and results in a 10% reduction in drag.

a.In the Objectives tab, select the force-lift observable. The current value of the lift is displayed along with options to specify the objective for the lift.

b.Select Increase Value from the Objective list.

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This indicates that you want to increase the lift, but are not prescribing a specific target change.

c.Enter 100 for Target/Reference Change.

This setting is used to normalize the scale of the change in value of the observable, which can be important in cases where multiple observables are considered that may be of different scales.

d.Click Apply.

e.Select force_drag.s in the list of observables.

f.Select Target Change In Value from the Objective list.

This indicates that you are prescribing a specific change in the value of the observable, rather than a freeform increase or decrease.

g.Enter -10 for Target/Reference Change and enable the As Percentage option.

10% is a generally a reasonable maximum target change for a design change. Using a target change that is too large may result in very large deformations and/or overshooting the local optimum.

h.Click Apply.

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Setup and Solution

5.Configure the morphing region.

You already specified the dimensions of the region earlier when exporting the force-drag sensitivity. Now you will also configure the control-point density.

a.Click the Region Conditions tab in the Design Tool dialog box.

b.Enter 30 for Points in the X Motion and Y Motion group boxes.

c.Click Apply.

You can use the Mesh Display dialog box to display the mesh, in order to see the increase in control points.

Many other settings are available in the Region Conditions tab, including constraints on controlpoint motion, symmetry conditions, and continuity conditions. For additional information, see the section on defining region conditions in the Fluent User's Guide manual.

6.Compute the design change and modify the mesh.

a.Return to the Design Change tab.

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b.Select wall in the Zones To Be Modified selection list.

Only zones that are selected in the Zones To Be Modified list (or that have prescribed motions applied) will be modified as part of the design change.

c.If multiple freeform objectives were defined (that is, multiple objectives with Increase Value or Decrease Value selected in the Objectives tab), you would need to specify the Weight for each. In this case only one objective (force-lift) is freeform, so no input is required for Weight.

d.Retain the default settings of Control-Point Spacing for Freeform Scaling Scheme, and 0.1 for Freeform Scale Factor.

These settings allow you to adjust the magnitude of the attempted design change (Freeform Scale Factor) and the basis for the scaling (Freeform Scaling Scheme).

e.Click Calculate Design Change.

The Results list is updated to reflect the Expected change for each observable.

Note that the drag is predicted to decrease by 10% as you requested, and the lift is predicted to increase.

f.Click the Preview... button in the Mesh group box to preview the design change in the graphics window.

g.Select wall on the Preview Morphing dialog box and click Display.

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Setup and Solution

Figure 24.20: Morphing Preview of Cylinder

h.Click the Modify Mesh button to apply the calculated mesh deformation that will reposition the boundary and interior nodes of the mesh. Information regarding the mesh modification is printed in the console:

Updating mesh (steady, mesh iteration = 00001,			pseudo time step 1.0000e+00)...
Dynamic Mesh Statistics:
Minimum Volume	= 3.46267e-04
Maximum Volume	= 6.36270e-01
Maximum Cell Skew = 3.69248e-01		(cell zone 11)
Minimum Orthogonal Quality = 6.30752e-01 (cell			zone 11)

i.Display the new mesh geometry.

Results → Graphics → Mesh → Edit...

The effect on the mesh is shown in Figure 24.21: Mesh After Deformation (p. 820):

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