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BETA CAE Systems S.A.

Tutorial 6

MORPHING

EXTERNAL AERO

Table of Contents

6.1. Introduction .................................................................................................................................2

6.1.2. Prerequisites .......................................................................................................................2

6.1.3. Problem description.............................................................................................................2

6.1.4. Data files .............................................................................................................................2

6.2. Read the ANSA database ...........................................................................................................3

6.3. Create the Morphing box.............................................................................................................6

6.4. Morphing the model ..................................................................................................................24

6.5. Improve the quality of the surface mesh ...................................................................................28

6.6. Conclusion ................................................................................................................................31

MORPHING – External Aero

BETA CAE Systems S.A. Tutorial 6 - 2 ANSA v.12.0.1 Tutorials

6.1. Introduction

This tutorial presents the use of several functions of the MORPH menu that can be used in order to reshape a CFD mesh (surface and volume) and create variations of the initial model very fast and easily. The steps described in this tutorial are:

• Read the ANSA database containing the CFD mesh.

• Create the Morphing Boxes.

• Morph the model using the completed Boxes.

• Check and improve the quality of the surface mesh after Morphing.

6.1.2. Prerequisites

Reading the 4 pages of section Intro.2.1. Getting Started of this Guide is recommended in order to obtain a familiarization with the ANSA interface and terminology.

6.1.3. Problem description

The images below show part of the Morphing actions performed in this tutorial:

6.1.4. Data files

The file required for this tutorial is tutorial_files/06-morph_aero/morph_aero.ansa . The

results can be found in the file morph_aero_result.ansa in the same directory for reference.



6.2. Read the ANSA database

Start ANSA and activate FILE>OPEN to read the ANSA file. The File Manager window appears. Navigate and select the file morph_aero.ansa.

Switch to MESH menu and activate SHADOW.

This CFD mesh is in FE-model form (no Geometry data).

Switch to PID display mode.

This example contains the surface mesh of a half vehicle and (for demonstration purposes) part of the shells that belong to the road and symmetry surfaces.

In addition, there are a few volume elements that belong to the fluid mesh.

You can imagine this as part of your complete model.

Since this is FE-model mesh, its visibility is controlled by the FE-Mod. flag button. For this type of mesh you can also control the visibility of different type of elements.

Press the F12 key to activate the Deck Parameters window (it is assumed that by default the

NASTRAN Deck is active and this window has the format shown).

De-activate the SOLID flag at the top of the window and press Apply.

Press ESC to exit.

F12



Now the solid elements are not visible.

De-activate the WIRE flag button. This allows the clearer observation of the shape of the model (it is also de-activated here for clarity of the images).

Activate the PARTS function to open the Part Manager.

Notice that there are four Parts. The volume mesh, a section of the wind tunnel box, the vehicle and one Part contains a 3D Curve that is supposedly a target for one of the variations that will be produced.

In order to perform controllable and accurate Morphing you must create some 3D Curves from the base model. These will be used to fit the Morphing Boxes, but they will also serve as reference lines in order to retrieve the original shape.

To be able to view the 3D Curves that you will create (and the existing ones as well) you must first activate the CURVEs flag.

Activate the PERIMETERs> FL2CURV function (this function

is by default located in the buffer window, accessed by right-click on the PERIMETERs group Name).

Activate the flag in the Corner Angle window, in order to easily select a string of element edges.

Select with the left mouse button one edge (you can de-select with right mouse button) in order to select the whole feature line at the top of the rear windshield.

Confirm with middle mouse button.

The Part Manager opens so that you place the new 3D Curve in a Part.

Press the NEW [PART] function.

The Part Edit window opens.

Type in the name initial_curve and press

OK.

PARTS

CURVEs

FL2CURV



Back in the main Part Manager window a new EMPTY Part appears.

Clink on it to place the new 3D Curve there.

Still in the PERIMETERs>FL2CURV function, select the bottom edge of the rear windshield.


As the Part Manager opens again click on the initial_curve Part.



6.3. Create the Morphing box

Switch to MORPH menu.

Press F3 to view the model from the side.

Activate the BOXES>ORTHO function to create an orthogonal

Morphing Box.

Select with left mouse button box selection the area shown.


ANSA prompts you in the Text Window to pick a coordinate system.

Press again middle mouse button, so that ANSA creates the Morphing Box aligned with the global coordinate system.

The Part Manager opens.

Press NEW [PART]

In the Part Edit window that opens, type the name morphing_box and press OK.

Left click on the new Part to place the Morphing Box there.

The Morphing Box appears in green. The box is straight and has eight Control Points at its corners. The fact that the Control Points are green as well implies that there are no elements that intersect with the faces of the box.

ORTHO



Activate the BOXES>INFO function.

Select the Box with left mouse button. ANSA highlights the box and all the elements that are contained in it. Press ESC to exit the function.

For demonstrative purposes, in this draft form you can morph the model.

Activate the MORPHING> MV.FREE function.

In the Move window that appears de-activate the Y-axis flag.

Select the two corner Control Points and confirm with middle mouse button.

As the middle mouse button is pressed the cursor is snapped to the closest selected Control Point. Moving the mouse reshapes the model. (It is always advisable to perform MV.FREE morphing just to check visually the results while creating the Morphing Boxes).

Press ESC to exit the function without morphing the model.

Activate the PARTS function.

In the Part Manager right click on the Parts shown and select the option LOCK. The icons become yellow and from now on when you press ALL from the Focus group only the entities that belong in the locked Parts will appear.

PARTS

Esc

MV.FREE



Now you will begin reshaping the Morphing Box In order to fit it to the vehicle. First of all it is always suggested that the outer limits of the Boxes are not too close to the model. This provides more space for morphing actions, and also enables the Boxes to retain a more orthogonal shape when Control Points are moved for Morphing. You will now extend the size of the Box 200mm upwards.

Activate the TRANSL [MOVE] function from the Geometry group of functions (at the bottom of the GUI).

In the Selection Mode window switch to Nodes mode. Select with the left mouse button the four top Control Points. (To avoid selecting nodes by mistake, you can de-activate the FE-Mod. visibility flag button). Confirm with middle mouse button.

In the Translate window that opens type the vector 0,0,1 and the distance 200 and press OK.

The box is enlarged upwards.

Next activate the CONTROL POINTS>PROJECT [NORMAL] function.

Select a node of the model that lies on the symmetry line. Next select the edge of the Morphing Box shown.

NORMAL

PROJECT

1

2

MOVE

TRANSL.



ANSA creates a Control Point on that edge.

Activate the BOXES>SPLIT function. Select with the right-

mouse button (right button implies the selection of an existing Point and not the creation of a new one).

ANSA splits the Morphing Box in two. Zooming in close you can see the thick lines implying tangency condition in this direction.

Activate the BOXES>DELETE function.

Select the excess Box and confirm with middle mouse button.

The remaining Control Points on the symmetry plane may remain green or turn red. This is because the elements are marginally identified as intersecting the face of the Box. Red Control Points imply that no Morphing is allowed on them so as not to distort the continuity of the model. Either way this does not affect you at the moment.

DELETE

SPLIT



Activate again the CONTROL POINTS>PROJECT [NORMAL] function.

Select the node shown (top symmetry node of the rear windshield). Next select the top Morphing Box edge. ANSA creates a new Control Point.

Activate the BOXES>SPLIT function.

Select with right-mouse button the new Control Point.

ANSA splits the Box. Note again the thick tangency lines.


Select the node shown (top left node of the rear windshield). Next select the top Morphing Box edge. ANSA creates a new Control Point.

1

2

1

2 NORMAL

PROJECT

NORMAL

PROJECT

SPLIT





ANSA splits the Box.


Select the node shown (top left node of the rear windshield). Next select the vertical Morphing Box edge. ANSA creates a new Control Point.



SPLIT

NORMAL

PROJECT

1

2

SPLIT



The Boxes have now been properly split so that one of their edges can be fitted exactly along the top of the rear windshield. All their edges are at the moment straight lines. Before reshaping the edges you can perform a box selection with CONTROL POINTS> DELETE function (This is just in case you have multiply-defined Control Points at some locations.).

Activate the EDGES> EDGE.FIT [ADD PNTS].

Select the Morphing Box edge. Confirm with middle mouse button.

Next select the 3D Curve (the one you created earlier). Confirm with middle mouse button.

ANSA adds Control Points and fits the Morphing Box edge to the 3D Curve. The edge now has curvature.

ADD PNTS

EDGE.FIT



De-activate the visibility flag of FE-Mod. This should only leave visible the Morphing Boxes and the initial 3D Curves. You will now create symmetry copies of the above. This will ensure that during Morphing the Symmetry conditions are respected.

Activate the SYMMETRY [COPY] function from the Geometry group of functions at the bottom of the GUI.

In the Selection Mode window switch to Entities mode. Select with left mouse button the Morphing Boxes and the 3D Curves. Confirm with middle mouse button.

Press OK in the Warning window that appears. Press OK in the Input window that appears next.

Symmetric copies of the selected entities are created.

COPY

SYMMETRY



Activate the HATCH visibility flag button to view the hatches on the Faces of the Morphing Boxes. Their color indicates their connectivity type. Green implies unconnected, while yellow connected. You can observe that along the symmetry plane the Boxes are not connected.

Activate the BOXES>TOPO function. Select the Boxes to be connected topologically (you can select all the Boxes). Confirm with middle mouse button.

ANSA performs topology and the Boxes are now properly connected.

De-activate the HATCH visibility flag button, to clear the display.

Bring back the visibility of the FE-Mod. If you use the BOXES>INFO function on one of the Boxes you will observe that every box on the left side contains all the elements of the original big Box. The Boxes on the right are empty.



Activate the function BOXES>LOAD [WHOLE DB].

Select all the Boxes and confirm with middle mouse button. ANSA searches all the elements in the ANSA Database (even the ones which are not currently visible) and places each one inside the proper Box.

You can observe the appearance of some red Control Points. Fortunately these are located at the front and the bottom as expected. ANSA does not allow moving Control Points for Morphing if there are loaded elements that intersect the Faces on which they rest.

Activate the BOXES>INFO function and select one Box.

You can see that now each Box contains only the elements that it should. You should always perform a LOAD [VISIBLE] or [WHOLE DB] operation before Morphing. This guarantees that the correct elements, and only them, are placed to the proper Boxes. This accelerates dramatically the Morphing actions later.

Press F3.

Perform a NOT operation to remove the top Boxes from

visible. This will allow you to view the vehicle more clearly.

WHOLE DB

LOAD

NOT

INFO




In the Move window leave only the X-axis active.

Select the center Control Point and confirm with middle mouse button.

Move the mouse to morph the model. You can notice two things: - There is no tangency normally to the symmetry plane. - As the top windshield is moved the lower is also affected. Press ESC to exit without morphing.

Activate the EDGES>TANGENT function.

Select the two Edges shown and confirm with middle mouse button. Tangency condition is imposed as implied by the thick lines.

Press ALL to bring all Boxes back to visible.


Select all the Boxes and confirm with middle mouse button. (The application of Tangency should also be considered as a box modification, so it is prudent to perform the LOAD operation again).

MV.FREE

TANGENT

WHOLE DB

LOAD





Select the center Control Point and confirm with middle mouse button. Performing a test morphing shows that now the symmetry condition is properly imposed.

Still the lower windshield is moved. What if we wanted it to be fixed?

From this point there are two ways to proceed. The first is to perform the modifications (SPLIT and EDGE.FIT) of the boxes simultaneously on both sides of the symmetry plane. The second is to delete the symmetric boxes, perform the modifications and symmetry copy again.

For simplicity and clarity of images the second way is followed.

Activating the BOXES>DELETE and viewing the model from the

top select the symmetric Boxes for deletion. Confirm with middle mouse button.


Select the node shown (bottom symmetry node of the rear windshield). Next select the top Morphing Box edge. ANSA creates a new Control Point.



MV.FREE

NORMAL

PROJECT

1

2

SPLIT

DELETE



ANSA splits the Box. Notice that one of the edges that was created by the SPLIT operation contains Control Points. This is because it took the Points of its neighboring edge. You can delete them if required with CONTROL POINTS>DELETE. On the other hand, they can be used for the fit to the lower windshield.

Activate the EDGES>EDGE.FIT [CURRENT PNTS].

Select the Morphing Box edge. Confirm with middle mouse button.

Next select the 3D Curve along the lower windshield. Confirm with middle mouse button.

ANSA fits the Edge to the Curve using the existing Control Points (no more Points are added).

CURRENT PNTS

EDGE.FIT



Press F3 to view the model from the side. Notice some slightly inclined edges. It is always recommended whenever possible to have well shaped Boxes. Remove the top Boxes from visible using NOT.

Activate the CONTROL POINTS>SLIDE function.

Select the four Control Points shown and confirm with middle mouse button.

Next select the four Edges on which they lie. Confirm with middle mouse button.

Finally select the corner Control Point, as guide, And slide it downwards so that the Boxes are better shaped. Press left mouse button to lock to the new position.

SLIDE



Press ALL to view all the Boxes.

View the model from the side and see how better the boxes now are. De-activate FE-Mod. flag. De-activate CURVEs flag as well.


In the Selection Mode window switch to Entities mode. Select with left mouse button the Morphing Boxes. Confirm with middle mouse button.

New symmetry copies are created.

COPY

SYMMETRY

ALL



Activate again the BOXES>TOPO function.

Apply topology to connect the Boxes along the symmetry plane.

Activate back the visibility flag buttons for CURVEs and FE-Mod.


Select the two Edges at the top and press middle mouse button… (Note that for clarity reasons the top row of Boxes has been removed from visible).

..and similarly at the bottom in order to apply the tangency condition.

TOPO

TANGENT



View the model from the top and rotate slightly to view from the “inside” of the vehicle. Notice how there is no tangency along the ceiling and the rear windshield.


Select the two Edges and confirm with middle mouse button.

Tangency is applied. Note that the same function can be used to remove tangency conditions in the same manner, if so required.

Activate the WIRE flag button in order to be able to view the nodes of the mesh.

Activate the CONTROL POINTS>MV.FREE

Keep all the degrees of freedom active in the Move window. Select the top front Control Point shown and confirm with middle mouse button.

TANGENT

MV.FREE



As you move the Control Point freely, select with the right mouse button a nearby node on the ceiling in order to snap the Control Point on it.


Select all the Boxes and confirm with middle mouse button.



Select the center Control Point and confirm with middle mouse button. Performing a test morphing shows that now the lower windshield is not affected by the morphing.

Note the effect of the application of Tangency condition in the longitudinal direction. The windshield is curved at the top, while at the bottom where there is no Tangency a sharp corner is formed. Use Tangency only in locations and directions that it is required. You can still perform some fine-tuning adjustments, but for now lets proceed to the next step, Morphing. Save the file from FILE>SAVE.

WHOLE DB

LOAD

MV.FREE



6.4. Morphing the model

Activate the PARTS function.

Press UNLOCK in the Part Manager to unlock all the Parts.

Press ESC to exit the Part Manager.

Activate the Deck parameters window by the F12 key. Activate the SOLID flag. In reality with a full volume mesh you should not do so. Visibility of volume elements is only enabled here to demonstrate their Morphing.

In a real case scenario you would perform the Morphing only with the shells visible and only at the end you would enable its visibility to perform quality control.

Press ALL to bring all the entities of the database to visible.

PARTS

ALL



Remove from visible the top row of Morphing Boxes using the NOT function.

Notice that now the target curve is also visible.

However its symmetry image is not present.


In the Selection Mode window switch to Entities mode. Select with left mouse button the target 3D Curve. Confirm with middle mouse button.

Press OK in the Warning and Input windows that appear next.

The Curve is symmetry copied.

Activate the MORPHING>EDGE.FIT [CURRENT PNTS].

Select the two Edges along the top of the windshield.


COPY

SYMMETRY

CURRENT PNTS

EDGE.FIT



Next select the two 3D Curves.


ANSA Morphs the surface and the volume mesh.

Activate the MORPHING>TRANSL function.

Select the three Control Points shown (pay attention to select the exact vertex Points and not any other Points along the Edges which are very close to them).

The Translate window opens.

Type in 150 in the z-direction and press OK.

ANSA moves the selected Control Points and the model is morphed again.

TRANSL



Finally, activate the MORPHING>SLIDE function.

Select the same three Control Points.


Next select the three Edges on which the Control Points lie.


Select the center Control Point and slide it along the Edge.

Left click on the new position.

The result has been achieved.

(Note here WIRE flag is de-activated to view the new shape).

Save the file.

SLIDE



6.5. Improve the quality of the surface mesh

Switching to ENT and HIDDEN display mode, the highly skewed elements are colored in green (the current check is performed with the default ANSA quality settings).

You will use the Reconstruction algorithm in order to remesh the model locally and improve its quality.

Before using Reconstruction you should specify some parameters.

Activate the SHELL MESH> PARAM function to access the

Meshing Parameters window.

Specify as target element length 30mm.

Press OK to confirm.

Finally, switch to TRIA type mesh in SHELL MESH>TRIA.

Activate the RECONS [Select] function.

Select the elements to reconstruct (use careful left and right mouse button selections).


TRIA

PARAM

Select

RECONS



Before the reconstruction algorithm takes effect ANSA provides a preview of the feature lines (green color) and PID boundaries (magenta color) that will be respected.

The feature lines are identified based on the value specified in the Meshing Parameters window.

You can, however, remove or add more feature lines by de-selecting or selecting element edges, while the Selection Mode window is in Edges mode.

Activate also the Corner Angle flag so that you can make string selections of element edges, within the

specified Corner Angle limit.

De-select any that you do not want to retain, or select some more, like the two lines shown here.

Press middle mouse button to confirm.

ANSA reconstructs the mesh and provides a preview of the result.

Press the Run Again to perform a couple more reconstruction passes.

Press OK at the end.

Proceed in a similar manner to correct other problematic regions.



Press Run Again and OK at the end.

The result should be a morphed model with good quality mesh.

An important note here is the fact that reconstruction is currently limited to surface mesh. If a Volume mesh is connected to the surface mesh, you cannot reconstruct it.

This leaves two options:

- For small Morphing displacements where the quality is not significantly deteriorated, you can keep the same mesh topology using the SHELL MESH>SMOOTH [SHELLS] for smoothing of the surface mesh only.

- For large Morphing displacements, you should only keep the surface mesh, which you can reconstruct and then create a new volume mesh form the morphed surface mesh.

Save the FILE from FILE>SAVE.



6.6. Conclusion

In this tutorial you have followed all the basic steps to create properly shaped Morphing Boxes that are fitted to the model in order to perform a controlled modification of it. In the case of surface only mesh, reconstruction was performed to correct the skewed elements that were distorted by the Morphing actions.

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