5 middle skin

BETA CAE Systems S.A.

Tutorial 5

FROM SOLID TO SHELL

EXTRACTING THE MIDDLE

SKIN GEOMETRY

Table of Contents

5.1. Introduction .................................................................................................................................2

5.1.1. Prerequisites .......................................................................................................................2

5.1.2. Problem description.............................................................................................................2

5.1.3. Data files .............................................................................................................................2

5.2. Reading the CAD file...................................................................................................................3

5.4. Planning the approach ................................................................................................................6

5.5. Separating the Parts ...................................................................................................................7

5.6. Assigning PIDs with corresponding thickness ............................................................................9

5.7. Creating the middle skin of the smaller Parts ...........................................................................15

5.8. Creating the middle skin of the main shell ................................................................................42

5.9. Connecting the small Parts to the main shell ............................................................................49

5.10. Shell meshing..........................................................................................................................68

5.11. Conclusion ..............................................................................................................................72

FROM SOLID TO SHELL – Extracting the Middle Skin Geometry

BETA CAE Systems S.A. Tutorial 5 - 2 ANSA v.12.0.1 Tutorials

5.1. Introduction

This tutorial presents the techniques that can be used in order to extract a middle skin description from a solid part. Although there is not a single function or approach for all such problems, the user will find representative situations and the recommended function and method to deal with them. The steps described in this tutorial include:

• Read the STEP file and check topology.

• Examine the main features of the geometry and plan a working approach.

• Remove small features.

• Separate the solid in Parts (main body, ribs etc.) using the Part Manager.

• Extract the middle skin description for each Part using different CAD functions.

• Extend and connect all ribs to the main body.

• Create a draft surface mesh and examine it.

5.1.1. Prerequisites

It is highly recommenced to have performed Tutorials 1 and 2, or to already have a basic ANSA background. Not all steps are described to the last detail.

5.1.2. Problem description

The geometry of the solid part is shown below.

5.1.3. Data files

The files of this tutorial are located in the directory tutorial_files/05-middle_skin. One

STEP file named skin.step contains the geometry. The resulting ANSA database can be found

for reference in the file skin.ansa .



5.2. Reading the CAD file

Start ANSA.

Set middle Tolerance settings in SETTINGS>

TOLERANCES.

In RESOLUTION, set 1mm and 4mm

for Curves and CONS resolution respectively.

Now read in the STEP file skin.step.

Select the CAD file in the File Manager and press OK.

The CAD file is read and topology is applied. The geometry should be clean with no gaps.

De-activate DOUBLE CONS visibility flag

temporarily to check that no free red CONS are visible.

Activate back DOUBLE CONS visibility and SHADOW display mode.

Press FACEs>ORIENT to assign a uniform

orientation to all the visible Faces.

Press FACEs>INVERT if required to flip the orientation.

Save the ANSA database locally from FILE>SAVE AS.

The fact that only yellow double CONS are visible everywhere means that this is a closed volume description of a solid part. In the following steps you will extract the middle skin surface in order to mesh it with shell elements of equivalent thickness.

Apart from ensuring that the topology is clean you will also perform some detail removal of features that are not to be retained.

RESOLUTION

SETTINGS

TOLERANCES

OPEN

FILE

ORIENT

DOUBLE

DOUBLE

SHADOW



5.3. Removing unwanted details

Rotate the part to view the emboss letters at the bottom of the part.

Such detail will not be included and so can be removed.

Activate the OR function of the Focus Group.

Perform a box selection, with the left mouse button, of the area as shown.

Having isolated the area, activate the LOCK flag button in the

Focus group.

You will delete all the Faces that form the letters.

Activate the NOT function of the Focus group and remove the

large Face from visible.

Activate the DELETE function from the Geometry group and

select all the visible Faces.

Confirm with middle mouse button.

Press OK in the Warning window that appears next to confirm the deletion of the Faces.

(Note that DELETED Faces still reside in the database and can be retrieved by the UNDEL function).

Press the ALL function of the Focus group to bring all the

locked entities to visible. Openings are left at the location of the letters. As there is underlying Surface description to cover the openings (you can check this using the SURFs>INFO function on this Face) you will close them using the CONS>FILL HOL function.

OR

NOT

ALL

LOCK

DELETE



Activate the CONS>FILL HOL function. In the Fill Hole

Parameters window that appears type in a value of 100 and press the Select button.

All the openings of the letters are identified.

Press OK to fill them.

De-activate the LOCK flag button.

Press the ALL function of the Focus group.

Activate the function FILE>COMPRESS [ALL]. This will completely erase the deleted Faces. You should use this function only when you are certain you will not need any deleted entities back and you want to reduce the size of the database.

Save the file from FILE>SAVE.

FILL HOL

LOCK

ALL

COMPRESS

FILE



5.4. Planning the approach

In this step you should examine the part in order to plan your working approach. That is you must identify which is the main shell body, what groups of ribs exist, and if there are any regions that should be modeled with solid elements due to their bulk shape. In the image below such areas are shown schematically in different colors (no solid regions are present in this example).

Although related to the local thickness of the part, these areas do not necessarily correspond to different PIDs that should be assigned. This is a grouping of the model which you will follow to separate it into different Parts in the ANSA Part Manager. Having the Parts separated will help you in performing the middle skin extraction using different techniques. The function MEASURE is very useful in order to make measurements of the various ribs.

outer fittings

main shell

clip

inner ribs

outer ribs

plate hole



5.5. Separating the Parts

You will separate the regions shown in the previous section in different Parts in the Part Manager. To facilitate selection of Faces you will isolate the areas using the functions of the Focus group.

Activate the NOT function and remove from visible all Faces

apart from those that belong to the inner ribs (you will need to perform more selections than those shown here).

You should leave only these Faces visible. You will now place these Faces in a new Part.

Activate the Part Manager from the PARTS function.

By default there is one Part with all the Faces.

Use the NEW>PART function to create a new empty Part.

The Part Edit window opens

Type in the name inner_ribs and press OK

The new Part appears as EMPTY in the Part Manager.

Activate the SET function to select the Faces to be placed in the Part.

NOT

PARTS



Select with box selection all the Faces.


Left click on the icon of the Part you want to place the entities to.

The icon is redrawn, displaying now all the Faces.

Press ALL from the Focus group to bring all the Faces back to

visible. Proceed in a similar manner to create 4 more new Parts:

outer_ribs plate_hole outer_fittings clip

that contain the Faces as shown in section 5.4.

In the end you should view the Parts as shown in the Part Manager. Left click on the name of the skin.step Part in

order to place the cursor in it and rename it to main_shell.


ALL



5.6. Assigning PIDs with corresponding thickness

Having separated the working areas into different Parts you can now assign PIDs to Faces with the proper thickness values. You will use the Part Manager for the visibility control of the Parts. As a first step isolate the inner_ribs Part.

Activate the Parts function.

Press the ALL function of the Part Manager.

All icons become red and all the Parts are visible on the screen. Press the NONE function of the Part Manager.

All the icons change back to black and all Parts become not visible on the screen. Now left click once on the Part inner_ribs to

make it visible on the screen. Its icon changes to red again (visible). You can switch between visible and not visible every time you click on a Part icon.

PARTS



Only the Faces of inner_ribs Part are now

visible. You will now use the MEASURE function to measure the various thickness values in this Part. Depending on the level of detail you want to work with, you can take several measurements in different areas and you can apply all these values to different Faces, or you can assign an average value.

Moving to the first inner rib.

Activate the MEASURE function and select the two Hot Points

shown. Confirming with middle mouse button, the reported distance is 3mm. Ignoring the round fillets this rib can be replaced by a uniform shell mesh with PID thickness 3mm.

The second rib consists of two distinct areas. A thick base of thickness 3mm …..

…and a thin of 1mm. You should assign two different PIDs in this case.

1

2



Switch to PID color mode.

You now view the Faces in their PID color. (Note that the assigned color when you open a CAD file is random. In your case you may see different PID colors. You can always change the PID color from the ColorEdit button in every Property card). You will now assign selected Faces to PIDs of the corresponding thickness.

Activate the FACEs>SET PID function.

Select with left mouse button the Faces shown (use careful left mouse for selection and right mouse for de-selection). Confirm with middle mouse button.

The Properties window opens listing all the available PIDs of the database. Currently there is only one Default PSHELL Property in

the database and all the Faces share it. Press the NEW button to create a new PID.

A new Shell Property card opens.

Type in the name thickness=3.0mm and the

value 3 in the two corresponding fields.

Here you can also define the color of the Property from ColorEdit.

Press OK to accept and close the card.

SET PID

PID ..



Back in the Properties window, the newly created PID is marked in black.

Double click on it to select it.

The Faces have changed PID.

The color is now different.

Next select the rest Faces of the ribs. Select the remaining Faces of the ribs and confirm with middle mouse button.

Again the Properties window opens. Press NEW to create a new PID.

Type in the name thickness=1.0mm and the

value 1 in the corresponding fields.

Press OK to confirm and close.

Back in the Properties window double click on the highlighted in black PID to select it.



Again the Faces change color as they are assigned to a different PID. You can proceed with the remaining Parts in a similar manner. Use the Part Manager to isolate them and the MEASURE function to identify the corresponding thickness values.

Use also the MEASURE function in “Entities” mode, in order to measure the closest distance between two CONS. The outer_ribs Part contains ribs whose

thickness varies between 1.8 and 2.2 mm. You can create a new PID with thickness 2.0mm for both of them for simplicity.

Similarly the clip Part has a thickness of

1.0mm.

The outer_fittings Part has different

thickness values (1.0mm, 2.0mm and 2.4mm) at three different locations.



The plate_hole Part has two values, 1.2mm

and 2.0mm.

Finally the main_shell has a uniform

thickness of 1.2mm.

In the end you should have the results shown below.

The Properties window should contain six PIDs. PID 1 is now unused and so can be removed. Select it to become highlighted and press the DELETE button. The Confirm Delete window appears.

Press OK to confirm the deletion of the unused PID.



5.7. Creating the middle skin of the smaller Parts

Here you will use various functions to create the middle skin of all the small Parts that are connected to the main shell_body Part.

Again the Part Manager can be very valuable in isolating the working area.

Activate the Part Manager and with right-click on the icon of the

Part inner_ribs, select the option LOCK.

The icon of the Part is highlighted in yellow indicating the Lock status of this Part. Exit the Part Manager with ESC.

Press the ALL function of the Focus group.

Only the entities that belong to the Locked Part remain visible.

You can furthermore use the OR function of the Focus group to

isolate the first rib.

PARTS

ALL

OR

LOCK



You will split the rib along its thickness.

Activate the FACEs> DACH [DIVIDE FACE] function.

Select with the left mouse button one CONS across the thickness.

ANSA identifies the whole string of Faces and provides a preview of the splitting.

Press OK in the Divide Parameters window that appears.

The Faces are cut in the middle. Turn over to the other side near the base of the rib.

Here as there are no Faces to cut you will use 3D Curves.

Activate the visibility flag button CURVEs, to be able to view the

3D Curves to be created.

Activate the CURVEs>MIDDLE function (by default located in the

buffer window which is accessed by right-mouse button on the Group Name).

Select consecutively the CONS on one side and confirm with middle mouse button.

DIVIDE FACE

DACH

CURVEs

MIDDLE



Next select consecutively the CONS on the opposite side.


ANSA creates 3D Curves in the middle of the two selected paths.

(SHADOW mode has been de-activated here for clarity).

Activate the CURVEs>NEW function to close the 3D Curves

path at the ends. Select the two Hot Points as shown and confirm with the middle mouse button.

Similarly on the other side.

NEW



Now you will create a new Face for the rib.

Activate the FACEs>NEW function.

Activate the “AUTO” flag in the New Face Options window that appears, to create a planar Face.

Select sequentially the CONS and 3D Curves

that form the boundaries of the rib to be created.


A new Face is created. Note the cyan CONS indicating triple connectivity. The new Face belongs to the same Part and PID as the Faces whose CONS were used for its creation.

Therefore it has the proper PID and thickness of 3.0mm.

De-activate the visibility of CURVEs.

Activate the NOT function of the Focus group and select the new

Face in order to make it not visible.

Activate the FACEs>DELETE function to delete these Faces.

Select with left mouse button box selection.

Press OK in the Warning window that appears next.

NEW

NOT

DELETE



Press ALL to bring all the Faces of the Locked Part back to visible.

Isolate the second rib using the OR function.

There may be cases when you cannot split a rib using the DACH [DIVIDE FACE] function, because of improper shape or Surface.

In this case you can insert Hot Points manually on the CONS that run across the thickness of the rib.

Activate the HOT PNTs>PARAM function.

Select with the left mouse button a CONS from one end. The Input window appears.

Type 0.5 and press Enter.

A Hot Point is inserted at a parametric distance of 0.5 along the CONS.

While still in the function select other CONS with the right mouse button to insert more Hot Points at the same parametric distance.

ALL

OR

PARAM



Again a Hot point is inserted half way.

Activate the FACEs>CUT function.

Cut the Face along the two Hot Points shown.

The Face is cut.

Proceed in a similar manner all along the thickness of the rib.

CUT



Rotate to the other side. Here instead of using the CURVEs>MIDDLE function to create 3D-Curves along the base centerline, you will create 3D-Curves that “cut” the thickness at certain locations.

Activate the CURVEs>NEW function, select two Hot Points

with the left mouse button and confirm with middle.

Create more 3D-Curves in this way.

Activate the HOTPNTs>PARAM function to insert Hot Points in the

middle of the 3D-Curves. Specify a value of 0.5 and press Enter.

Using right-mouse button pick the remaining 3D-Curves to insert a Hot Point on them also.

NEW

PARAM



Activate the CURVEs>NEW function and create straight

Curves that connect the Hot Points in the middle. For non-straight Curves..

Activate the CURVEs>TRANSF function and select one of the two

curved CONS. Confirm with middle mouse button.

An arrow appears indicating the start of the segment. Select with the left mouse button two Hot Points as new start and end point positions for the new 3D-Curve to be created.

A new 3D-Curve is created by a transformation of the selected segment to adjust to the new start and end positions.

Activate the FACEs>NEW [AUTO] function and create a

planar Face selecting with the left mouse button all the 3D-Curves and CONS that form its boundaries. Confirm with middle mouse button

NEW

1

2

TRANSF

NEW



As you have selected CONS that belong to Faces of different PIDs, the Properties window appears in order to select a single PID for the new Face. Double click on PID thickness=3.0mm.

Still as this rib consists of more than one thickness you must separate and assign a different PID.

Activate the CONS> PROJECT [NORMAL] function and select the CONS shown.


Next select the interior middle Face to project the CONS onto.


NORMAL

PROJECT



Having formed the interior of the rib, remove it from visibility in order to delete the outer Faces easily.

Use the NOT function. Make sure you remove both Faces that form

the rib.

Activate the FACEs> DELETE function and select with box

selection all the remaining visible Faces. Press OK to confirm.

Press ALL to bring all Faces back to visble.

Switch to PID color view mode.

All Faces appear in the color of PID with thickness 3.0mm.

Activate the FACEs>SET PID function and select with the left

mouse button Face shown.

Confirming with middle mouse button opens the Properties window.

Select the PID thickness=1.0mm.

The selected Face now has the correct PID. You can now move on to the next Part.

NOT

DELETE

SET PID

PID..

ALL




Right-click on the icon of the inner_ribs Part

and select the UNLOCK option.

Next right-click on the icon of the outer_ribs

Part and select LOCK. Exit the Part Manager

Press ALL from the Focus group to keep visible on the entities of

the Locked Part.

PARTS

LOCK

UNLOCK

ALL



Activate the FACEs>DELETE function and select the three

Faces that lie along the thickness (one Face on one rib and two on the other).

Press DELETE to confirm.

Activate the FACEs>MIDDLE function.

Select with left mouse button one Face.

Next select the opposite Face. As soon as the second Face is selected a preview of the new Surface is given, and the Accept Surface window appears. Press Yes to confirm.

A new Face is created in the middle of the two selected ones. The initial Faces were not deleted; instead they were made not visible so that you can examine the new Face more clearly.

1

2

DELETE

MIDDLE



Proceed to the creation of middle Faces on the other rib.

Note that the middle Faces are not connected topologically.

Activate the FACEs>TOPO function and select with box

selection the CONS as shown. Confirm with middle mouse button.

Press the INVERT function of the Focus group to invert the status of

visible and not-visible entities. Now only the initial Faces are visible.

Activate the FACEs>DELETE function and select all the Faces.

Press OK to confirm their deletion.

TOPO

DELETE

INVERT



Press ALL to bring all Faces to visible.

You can proceed to the next Part.


Unlock the outer_ribs Part and lock the

plate_hole one.

Press ALL to bring its Faces to visible.

PARTS

ALL

LOCK

ALL



Activate the DELETE function from the Geometry group of

functions and carefully select the Faces that run along the thickness plus the interior Faces of the cylindrical opening.


Press OK in the Warning window that appears next.

Activate the FACEs>MIDDLE function

Select the two square shaped Faces.

Press OK in the Accept Surface window. The middle Face is created.

Press INVERT to bring the original Faces to visible.

Activate the FACEs>DELETE function and delete them.

Press ALL from the Focus group.

DELETE

MIDDLE

1

2

INVERT

DELETE

ALL



Activate the FACEs>OFFSET [FACES] function and select the four Faces that form the cylindrical opening.


An arrow appears indicating the positive offset direction (Note that this coincides with the gray side of the Faces in SHADOW mode). The Offset Value window opens

Type in the value 0.6 (half of the local thickness) and activate the Keep PID & Part flag.

Press OK to proceed.

New Faces are created by offset of the original ones. Press Yes in the Confirm window to delete the original Faces.

You now have the middle surface description of this Part. You only need to connect the Faces.

FACES

OFFSET



Activate the FACEs>EXTEND function. The function is located

by default in the buffer window, which is accessed by right click on the Group Name.

Activate the flag in the Extend Face Options window that appears.

Select a red CONS from the cylinder and confirm with middle mouse button.

Next select the bottom Face.

The cylindrical Face is extended and connected topologically with the bottom Face. Proceed in a similar manner with the three remaining Faces for extension.

At some point you may notice that the Shadow of the bottom Face is disabled. This is because as you extend and connect Faces the large Face is cut in a shape of a not-closed internal perimeter, causing problems in the shadow operation.

However extending and connecting all four Faces closes this inner perimeter and shadow is again possible. Notice that because the Faces were extended one by one there are some small open gaps identified by the red CONS.

EXTEND

2 1



Activate the FACEs>TOPO function, select the Faces shown,

and confirm with middle mouse button.

Topology is applied. Finally some left over Hot Points can be removed.

Activate the function HOT PNTs> DELETE and select with box

selection as shown.

The unnecessary Hot Points are removed.

Finally, delete the inner circular Face to open the hole, using the DELETE function. You can proceed with the next Part.

TOPO

DELETE



In the Part Manager set the outer_fittings Part in Lock

status.

Press ALL to bring the Faces of this Part to visible.

Focus on the first fitting.


carefully select - the inner Faces, - the Faces that lie along the thickness - and the outer fillet Faces. Only the outer cylindrical Faces are not selected here (Only the Faces shown below should remain).

Press OK to confirm deletion.

Activate the FACEs>OFFSET [FACES] function.

Select the two remaining Faces and confirm with middle mouse button.

ALL

PARTS

DELETE

FACES

OFFSET



The arrow appears indicating the positive offset direction. Type in the value 0.5 and keep the flag active.

Press OK. Confirm the deletion of the original Faces

You have the middle surface of this area. Move on to the second fitting.


carefully select - all the Faces along the thickness - and the outer Faces of the cylinder (please refer to next image to clarify which Faces should remain). Press middle mouse button to confirm. Press OK in the Warning window that appears.

Now you will create - middle Faces for the triangular shaped ribs - and offset Faces for the cylinder.

DELETE



Activate the FACEs>MIDDLE and select the two Faces of a rib.

Press OK in the Accept Surface window.

Proceed similarly for the second….

…and third rib.

Next, activate the FACEs>OFFSET [FACES] function and select the Faces of the cylinder.


The arrow indicates the positive offset direction.

In the Offset Value window that appears type the value 1.2 (half of the local thickness) and press OK.

FACES

OFFSET

MIDDLE



Accept the deletion of the original Faces. The middle geometry is defined. You should now connect the ribs to the cylinder.

Activate the FACEs>EXTEND function.

Activate the flag in the Extend Face Option window Select the red CONS and confirm with middle mouse button. Next select the target Face for the extension, from its cross hatch.

The Face of the rib is extended and connected topologically to the cylinder. Note that Shadowing for this Face now fails. This is because of the open cut that had been made on it.

Activate the FACEs>PRJ-CUT function.

Select the Hot Point with the left mouse button.

EXTEND

PRJ-CUT

1



Next select the CONS. The Hot Point is projected and a cut is made. Note that the projected position remains highlighted. Press middle mouse button to be able to select a new Hot Point.

Select the Hot Point on the other side and then the CONS. A similar cut is made and the shadowing is again enabled.

Perform the same actions (EXTEND and PRJ-CUT) on the other rib.

Note that for the third rib you should not use the EXTEND function, because this Face is near coplanar with the yellow CONS below.

2



Activate the HOT PNTs>MULTPR function and select with the left

mouse button the Hot Points shown. Confirm with middle mouse button.

Next select the yellow CONS below. The Hot Points are projected.

Next activate the SURFs> COONS function.

Select the two CONS. Confirm with middle mouse button. Upon confirmation of the Surface the Properties window opens to select a PID. This happens because you have selected CONS that belong to Faces of different PIDs.

You can select from the list, or left click on the screen on a Face (in this case the triangular one) whose PID you want to use for the new Face. (In case that the resulting COONS Face is distorted (warped) because the Face of the rib is not perfectly aligned with the CONS to be connected, you may have to create a new rib Face using 3D Curves that will connect the projected Hot Points with the corner Hot Points of the rib).

MULTPR

COONS



The middle geometry of these fittings has been extracted.

Press the INVERT button from the Focus group.

Activate the FACEs>DELETE function and select with box

selection the Faces for deletion. You can proceed with the Part clip.

Open the Part Manager and Lock the clip Part.

INVERT

DELETE

PARTS




Activate the !NOT function from the Focus group.

Left click on the three Faces on the outer side.

As you select the Faces, they become not visible. Press middle mouse button to confirm.

Only the selected Faces remain visible.

Activate the FACEs>OFFSET [FACES] function and select the Faces.


Type 0.5 and press OK. Confirm the deletion of the original Faces.

ALL

!NOT

FACES

OFFSET



The offset middle Faces remain visible.

Press INVERT from the Focus group.

Delete the remaining Faces.

INVERT

DELETE



5.8. Creating the middle skin of the main shell

Depending on the complexity of the part and the requirements that you have for your modeling, you can either keep one side (the outer or the inner) of the solid description and use it for meshing as it is, or you may also want to offset it to the middle position. In ANSA you can offset Faces either by an absolute distance and create new geometrical description (as you have already performed with some small features), or you can use the OFFSET [LINK] option, which is faster as it does not create new Faces. Instead, it virtually offsets the existing ones either by an absolute distance or by a percentage of the Property thickness of the Faces. This functionality is also embedded in the FACEs>SKIN function which, in addition, detects and separates automatically one side from a solid description of a part. The limitations of the SKIN function are that the solid description must be cleaned up and must form a closed volume, and that the resulting geometry cannot have cyan triple connectivity (no t-junctions etc.). Therefore, this function should only be used on solid description of a pressed formed part. This is the reason for which you have treated the ribs separately in advance.

In this tutorial you will use the SKIN function to perform the task as described above.

Activate the Part manager and Lock the main_shell Part.


This Part is not currently a closed volume definition.

Deactivating SHADOW and DOUBLE CONS visibility temporarily shows all the openings.

In order to use the SKIN function you should close the openings first.

The CONS>FILL HOL function can be used for this. However bear in mind that in order for the FILL HOL function to work there must be proper underlying Surface description.

PARTS

ALL



Activate the SURFs>INFO function and select the Faces

from their cross hatch. Examine that there is Surface covering the openings. If some openings have no Surface, you should close them using functions that create new Surfaces (like FACEs>NEW [MANUAL Auto and Auto Fit] or SURFs>COONS).

In this Part all openings happen to have underlying Surface. However there is also an additional point that should be considered. The CONS>FILL HOL function can close opening that belong to no more than two different underlying Surfaces. To help the function you can create some Faces manually first.

This opening has three Surfaces that cover it, and hence the FILL HOL function will not close it.

Activate the FACEs>NEW function. Select the MANUAL

mode. Select the two red CONS and confirm with middle mouse button. Next select the fillet Face whose Surface you will use. Select from the crosshatch.

A new Face is created based on the existing fillet Surface. Now the two openings require only one underlying Surface, so the FILL HOL function will close them.

NEW

INFO

1 2

4

3



Create similar Faces in other openings.

Now activate the CONS>FILL HOL function.

The Fill Hole Parameters window opens.

Type in the value 200 and press Select.

ANSA identifies and highlights openings. Press OK to proceed.

Several opening were automatically closed.

De-activate again SHADOW and DOUBLE flags to view any remaining openings. Such remaining openings should be located at the base of the outer_ribs Part. Again these

were left, as they require more than two Surfaces in order to be closed.

FILL HOL



Close these openings also. Again you can use functions like SURFs> COONS, or the FACEs>NEW [MANUAL]. Note that if you use the FACEs>NEW [MANUAL] function, you should close each opening by creating three Faces (one for each underlying Surface) carefully selecting the proper Face to use its Surface.

The advantage of using the NEW [MANUAL] is that you can then switch to MESH menu and use the MACROs>JOIN function to join the left-over boundaries of these openings.

..and because you have created Faces that lie on the same Surface as their neighbors there are no remaining CONS. This leaves a cleaner geometry that you can work more easily with.

You can delete a few remaining Hot Points with HOT

POINTs>DELETE and box selection.

Now you have a closed volume of the Part and you can therefore use the FACEs>SKIN function.

DELETE



Activate the FACEs>SKIN function.

Select with box-selection all the Part. Confirm with middle mouse button.

ANSA identifies and highlights in white the edges that run along the thickness of the Part.

The message “Edit edges” appears in the Text Window, and the user can add or remove some of the identified edges with left and right mouse button respectively.

Indeed there are some edges here that should not have been included in the “thickness” path.

Zoom in and de-select them with right mouse button.

Zoom in even further at this corner and using right and left mouse button selections leave only the edges shown in this region.

SKIN



Press F9 to zoom all. Examine the highlighted edges. They should all be correct now. Confirm with middle mouse button.

ANSA separates the inner and outer Faces and highlights them in green and red color. The message “Select side to keep” appears next in the Text Window. Select with the left mouse button a Face from the red side to keep the outer description.

Only the Faces of the selected side remain visible and the Middle Surface window opens.

The thickness and proper offset values are filled automatically in the window. Check the LINK option and round off the thickness value to exactly 1.2.

Press OFFSET to proceed with the Link offset of the Faces by 0.5 of their property thickness.



You can check the “virtual” link offset using the SURFs>INFO

function. The Faces have been virtually offset by half of the PID thickness, while the Surfaces remain at their original position.

Save the file from FILE>SAVE. Note:

When you offset Faces to the middle skin position (whether by OFFSET [FACES] or OFFSET [LINK]) you should check that there are not any Faces that are flipped inside out, due to their size and position, or the fact that their radius of curvature is smaller than the offset distance.

In this example a couple of Faces have this problem.

INFO

Original position

Offset position



5.9. Connecting the small Parts to the main shell

The remaining Faces now describe the middle surface of the solid Part.

Perform a box selection HOT POINTs>DELETE to remove any

unnecessary Hot Points.

Now you will proceed with the connection of the small Parts to the main_shell Part.

You will work per Part in the same order as that followed for the middle surface extraction. As the task is now simpler you may not need to isolate the working areas using the Part Manager.

Starting with the inner_ribs.

You will use the FACEs>EXTEND function, as before, to connect them to the main_shell.

However you should prepare the boundary CONS by segmenting them properly.

Activate the HOT POINTs> INTERS. function.

Select with the left mouse button the two CONS shown. ANSA inserts Hot Points on both of them at their nearest position.

Perform the same at the other side shown.

Now activate the FACEs>EXTEND function.

Ensure that the flag “Project & Topo” is active in the Extend Face Options window. Select the red CONS and confirm with middle mouse button.

INTERS.

EXTEND

DELETE



Next select the bottom Face. ANSA extends the Face and connects it topologically.

Performing the same action for the other side of the rib, leads to

the disabling of Shadow. Ignore this for now and proceed with the extension of the last round red CONS to the fillet.

Use the EXTEND function again here.

Zoom in to this area. Notice that as the extension was performed in steps, there are some gaps that remain.

Activate the FACEs>TOPO function.

Select with box selection and confirm with middle mouse button.

TOPO

EXTEND

EXTEND



Topology is appied. These small yellow CONS will be joined later in the MESH menu.

Finally, to correct the SHADOW problem activate the

FACEs>PRJ-CUT function and select the Hot Point and the top CONS. ANSA makes the projection and the cut, and Shadow is recovered.

Use again the functions: HOT POINTs>INTERS FACEs>EXTEND FACEs>TOPO to connect the second inner rib.

Perform another PRJ-CUT to recover Shadow.

1

2

PRJ-CUT

PRJ-CUT



Move on to the outer_ribs.

Use the HOT POINTs>INTERS. function to get Hot Points at the

intersection of the two CONS.

Now taking advantage of the fact that the rib is planar you will use the function FACEs> PLN.CUT [SINGLE] to cut the main_shell

Part.

Activate the function and select the three Hot Points of the rib Face, to define the cutting plane.

As the point positions are selected the cutting plane is displayed as a cyan net. Next select the Faces to be cut. Confirm with middle mouse button.

ANSA cuts the selected Faces.

1

2

INTERS.

3

1

2

SINGLE

PLN.CUT



Activate the HOT POINTs> PROJECT and select the Hot

Point shown and then the yellow CONS, in order to properly segment it. Now you must create Faces in order to close the gap and connect the rib.

Activate the SURFs>INFO function and select the Face from

its cross hatch.

Its Surface is revealed.

Notice that it is marginally not enough in order to cover the gap.

Still, you can modify the Surface.

Activate the function SURFs>EXTEND.

Select the Face from its cross hatch. As the Surface is previewed, select with the left mouse button one edge of the Surface. Slide the mouse to extend the Surface. Left click to lock the Surface to its new boundary.

Next select the other edge of the Surface and extend it in the other direction. Press middle mouse button to confirm the modification.

PROJECT2

1

INFO

EXTEND

3

1

2



Check again the Surface with SURFs>INFO to ensure it is large

enough.

Activate the FACEs>NEW function.

Select the MANUAL option and select the CONS in a sequential manner (ignore the small gaps). Confirm with middle mouse button. Next select the rib Face so that its Surface is used for the new Face.

The rib is now properly connected. The narrow Face will be joined later in the MESH menu so that a good quality mesh is achieved.

Move on to the other outer rib. Here the rib is not planar all the way. You will therefore use a combination of functions.

INFO

NEW




Select the two CONS with the left mouse button. Hot Points are created at their intersection.

Now Activate the FACEs> PLN.CUT [SINGLE] function. Select with the left mouse button the three Hot Points.

Confirm with middle mouse button. The cutting plane is displayed.

Next select the Faces to be cut.


Now activate the CONS>PROJECT [NORMAL] function.

Select the two CONS and confirm with middle mouse button.

INTERS.

NORMAL

PROJECT

SINGLE

PLN.CUT



Next select the two Faces to project the CONS onto. Confirm with middle mouse button.

Now the cut is complete. If shadow is disabled, use the FACEs>PRJ-CUT function and “close” the cut on this Face.

Activate the SURFs>COONS function.

Select sequentially the red CONS (skipping the open gaps). Confirm with middle mouse button.

The Accept Surface window appears and the generated Surface is previewed.

Press OK to proceed.

COONS

1 9

8 76 5

43 2



Note that as you have selected CONS from Faces that belong to different PIDs and Parts, ANSA opens the Properties window to select the desired PID for the new Face.

Instead of picking from the list you can left click on the screen on a Faces of the rib in order to use its PID.

Then the Part Manager opens to place the new Face to a Part. Again you can left click on a Face from the screen to use its Part also.

Having specified PID and Part, ANSA completes the creation of the Face by applying topology. (You can switch to PID display mode to check the correct PIDs).

Move on to the plate_hole Part.

Here you will use again the FACEs>EXTEND function. Prior to the use of the EXTEND function you should segment the CONS accordingly.


Select the two CONS. Perform the same for the other pair.

INTERS.



Activate the FACEs>EXTEND function (located in the buffer

window). Select one red CONS and confirm with middle mouse button. Next select the Face you want to extend to.

Perform the same operation for the other two CONS. If shadow is disabled, use the FACEs>PRJ-CUT function to “close” the cut on this Face.

Apply topology with the FACEs>TOPO function to close

the small gaps.

Moving to the outer_fittings Part.

Because here the Faces are inclined, the EXTEND function may not give the desired result.

EXTEND

TOPO

1 3 2



Activate the CONS>PROJECT [USER] function, The USER option allows you to specify the

direction vector for the projection. Select the two CONS and confirm with middle mouse button.

Next select the Face to project the CONS onto. Confirm with middle mouse button.

The Vector Definition window opens. Here you can pick from the screen two Hot Points in order to specify this vector.

Press OK.

ANSA projects and cuts the Face in the specified direction. You now need to create Faces to make the connection.

USER

PROJECT

1

2



Check the underlying Surfaces with SURFs>INFO.

They are large enough to cover the gap. Hence the FACEs>NEW [MANUAL] function can be used.

Activate the function FACEs> NEW and select the MANUAL

mode. Select the two CONS and confirm with middle mouse button. Next select the Face to use its Surface.

Move on to the other side. Again activate the function and select now the four red CONS sequentially and confirm with middle mouse button (selecting all four CONS will ensure proper connectivity of the new Face, otherwise you will need to use the TOPO function). Next select the Face to use its Surface.

The connection is made.

INFO

NEW

1 3

2

4



Move on to the other outer fitting. Here the fitting intersects with the main_shell Part.

Because the large Face is planar you can easily find the intersection (there is no need to use the CURVEs>SURF.INT function.

Activate the FACEs> PLN.CUT [SINGLE] and select three Hot Points from the large Face to define the

cutting plane. Next select the Faces to be cut and confirm with middle mouse button.

ANSA cuts the excess part.

Activate the DELETE function from the Geometry group of

functions. Select the excess Faces and confirm with middle mouse button. Press OK in the Warning window that opens.

SINGLE

PLN.CUT

DELETE



Rotate to the other side. The cylindrical Faces are not connected to the planar bottom Face.

Activate the CONS> PROJECT [NORMAL] function and select the red CONS shown (Shadow is de-

activated here for clarity). Confirm with middle mouse button.

Next select the planar Face. Confirm with middle mouse button. ANSA makes the cut.

Activate the FACEs>TOPO function to connect topologically

the cylindrical Faces to the planar Face. Select the CONS and confirm with middle mouse button.

NORMAL

PROJECT

TOPO



The cyan CONS are a confirmation of the connection.

Activate the FACEs>EXTEND function.

Select the red CONS and confirm with middle mouse button. Next select the planar Face.

ANSA extends and performs topology. Shadow is disabled.

Activate the FACEs>PRJ-CUT function and make a cut as shown

to recover Shadow. Then proceed with the extension of the other two fins in a similar manner. Note that one fin consists of two Faces that should be extended one by one.

EXTEND

PRJ-CUT



As the Faces are extended and connected some gaps, identified by the red CONS, remain.

Activate again the FACEs>TOPO function, select the CONS and

confirm with middle mouse button.

Activate the HOT POINTs> DELETE function and select with

box selection to remove all unnecessary Hot Points.

Rotate to the other side. The holes are not open.

TOPO

DELETE



Activate the DELETE function of the Geometry group.

Select the two Faces from their cross hatch. Confirm with middle mouse button. Press OK in the Warning window that appears next.

The holes are now opened.

Activate the FACEs>PRJ-CUT function and make cuts as shown,

to avoid any shadow problems, and have better shaped Macros Areas for meshing later. (Remember that any Faces that fail Shadow will also fail meshing later).

Finally, activate the FACEs>CUT function and make a cut between

the two Hot Points shown.

DELETE

PRJ-CUT

CUT



Activate the FACEs>DELETE and delete the excess Face.

Finally, move to the clip Part.

Activate the FACEs>EXTEND function and select the red

CONS. Confirm with middle mouse button. Select the Face to extend to.

ANSA extends, cuts and connects. Shadow is disabled.

DELETE

EXTEND



Use FACEs>PRJ-CUT to make the two cuts shown and recover

Shadow.

The clean up is completed. As mentioned earlier all the Faces that you have deleted remain in the database.

Activate the FACEs>UNDEL. function. All deleted Faces are

previewed, and the user can select Faces to be retrieved if necessary.

Using the FILE>COMPRESS [ALL] function will erase this data and will reduce

significantly the size of the database. Use this function only when you are certain that clean up is complete, and you will not need to retrieve the original data.


PRJ-CUT

COMPRESS

FILE

UNDEL.



5.10. Shell meshing

Switch to MESH menu.

Activate the MACROs>LENGTH function and select all the Macros.

Specify an element length of 4 in the Input window that appears and press Enter.

Switch to TRIA in the SHELL MESH>MIXED.. switch button.

Activate the SHELL MESH>FREE [Visible] function to mesh all the visible Macros with the FREE

algorithm and TRIA elements.

The part is meshed. (If a message “x Macros remain umeshed” appears in the Text Window, press the UNMESHED [MACROs] function to isolate them and check for problems in their topology).

You will proceed with a basic quality check and improvement. Keep only the SKEW flag active in the quality criteria buttons at the bottom.

Activate the HIDDEN view mode.

The skewed elements are viewed in green. (The bad elements identified here are according to the ANSA default skewness check. Press F11 to access the Presentation Parameters window and select the desired quality settings).

Activate the SHELL MESH>RECONS [Visible] function.

ANSA reconstructs the current mesh. The reported number of the visible skewed elements is lowered in the text legend on the left.

LENGTH

Visible

FREE

TRIA..

HIDDEN

Visible

RECONS



Press the EXTREME function of the Focus group to isolate the

Macros that have skewed elements. Zoom in to the area shown.

These skewed elements are a result of the short CONS, and correspondingly here Perimeters, that the Extension of the Faces left over.

Activate the MACROs>JOIN function and select them with the

left mouse button.

Joining these Perimeters results in the deletion of the mesh locally.

Before remeshing activate the SHELL MESH>RECON flag, so

that Reconstruction takes place in the background to get the optimum mesh.

Activate the SHELL MESH>RE-MESH [Visible] function.

The erased Macros Area is remeshed with the same meshing algorithm, in this case the FREE, and reconstruction is applied automatically.

EXTREME

JOIN

Visible

RE-MESH

RECON



The other two inner ribs have a similar problem that should be corrected in the same way.

In addition these Hot Points should be deleted with HOT

POINTs>DELETE.

Note that in order to avoid having to use the SHELL MESH>

REMESH function after Perimeter modifications you can activate the SHELL MESH>AMESH flag button.

Moving to the outer_ribs Part there are some narrow Macro Areas with skewed elements.

Use the function MACROs>JOIN and delete the left over Hot

Points.

(Note that in SETTINGS>GENERAL SETTINGS there is an option to delete automatically any unused Hot Points after a JOIN operation).

DELETE

A.MESH

JOIN



Make any other necessary similar modifications.

Note that you can switch to EL.THICK display mode and view the shell elements colored by the PID thickness according to a color bar.

SHADOW mode facilitates viewing.

Finally, pressing F11 access the Presentation Parameters window where you can activate the flag “Shell as Solid”.

This allows the visualization of shell elements as solid according to their PID thickness.

The tutorial is complete. Save the file and quit.



5.11. Conclusion

In this tutorial you have followed all the basic steps to extract the middle surface description of a solid part and mesh it with shell elements. Not all capabilities were demonstrated. Refer also to ANSA v12.x User’s Guide and to the On-Line Help for the functionality of ANSA and detailed description of functions and procedures.

5 middle skin

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