Middle Surface

BETA CAE Systems S.A.

Tutorial

FROM SOLID TO SHELL

AUTOMATIC CREATION OF MIDDLE SURFACE

Table of Contents

Automatic creation of MIDDLE surface.............................................................................................1 1. Introduction ...................................................................................................................................2

1.1. Prerequisites ............................................................................................................................. 2 1.2. Problem description .................................................................................................................. 2 1.3. Data files ................................................................................................................................... 2

2. Reading the CAD file.....................................................................................................................3 3. Extracting the middle Skin with the Middle-Multi functionality .......................................................4 4. Conclusion ....................................................................................................................................8

FROM SOLID TO SHELL – Automatic Creation Of Middle Surface

BETA CAE Systems S.A. 2 ANSA v13.x Tutorials

1. Introduction This tutorial presents the Middle-Multi functionality that can be used in order to extract a middle skin description from a solid part. In this tutorial it will be presented how can this functionality be used in order to overcome some problematic regions. The steps described in this tutorial include: • Read the ANSA file and check topology. • Examine the main features of the geometry and plan a working approach. • Extract the middle skin description using the Middle>[Multi] functionality.

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.

1.2. Problem description

The geometry of the solid part is shown below.

1.3. Data files

The files of this tutorial are located in the directory tutorial_files/middle_multi. One ANSA file named middle_multi.ansa contains the geometry. The resulting ANSA database can be found for reference in the file middle_multi_result.ansa .

Inner ribs

Inner big ribs

Main body



2. Reading the CAD file Start ANSA. Set middle Tolerance

settings in Windows > Options > Settings> Tolerances. In RESOLUTION, set 1mm and 4mm for Curves and CONS resolution respectively.

Now read in the file middle_multi.ansa.

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.

Activte 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. Notice: orientation will be automatically applied when using the Middle>Multi functionality.

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.

First we will extract the middle skin surface from the inner ribs of the model and then we will extract the middle skin surface from the outer entities.

OPEN

FILE

ORIENT



3. Extracting the middle Skin with the Middle-Multi functionality

From the TOPO>FACEs group activate the MIDDLE>Multi function In the Middle-Multi window that appears give a Thickness value so that the algorithm can start searching for entities that have a thickness equal or less from this value. It is recommended to start from a small value and increase it after each step. The first value that we use is 3mm. Pressing the 'Auto' button we will get the first region with thickness less or equal to 3mm.

In the field 'Thick. step' we can define the thickness range after that a new property will be applied on our extracted faces. In our case we will apply a new PID every 0.25mm. The 'Mean thick.' indicates the mean thickness found in the highlighted region. The 'PID thick.' indicates the thickness that will be applied in the new Property for the extracted middle face.

In the lowest part of the 'Middle' window we have the options to check the result and confirm if we want to accept it. This can be achieved by activating the 'Preview' flag. If this flag is not activated the middle surface will be created without confirmation from the user. Furthermore we have the option to put the new created entities in a new Part. We can also keep the new entities not visible, by activating the option 'Hide middle faces'. When the option 'Focus current pair' is active then it will “zoom in” the next region that will be found.



The first region is identified. (case 1) The algorithm marks the two opposite sites with red and green and the thickness with blue. In order to get better results we should extract the middle face first from the ribs and then from the other entities.

Notice: In order to extract the middle face from a region the opposite sites should be alike and the blue should be the thickness. The next region is selected (case 2). The selection has no problems so we press the OK button in the 'MIDDLE' window. The middle surface is extracted.

After the middle face of this region is extracted the region of case 3 is highlighted. Press 'OK' to extract the middle face of it.



As next rib is highlighted (case 4). Press 'OK' to extract the middle face of it.

When this rib is highlighted (case 5) press OK to extract the middle skin surface.

Now that we fixed the ribs that are surrounding the cylinder, we can move on and extract the middle skin from the cylinder. The cylinder is identified as the next pair. Extract the middle skin surface by pressing the OK button. Notice: In order to have a better control if the red, green and blue faces are defined correctly, we can activate the CROSSHATCHES.



After finishing the extraction of the middle surface from the cylinder the last pair is identified. Press the OK button to extract the middle surface.

After this only the basis of our model is left. Because of the fact that this can not be identified automatically it is easier and faster to define the pair manually. We switch to the Manual mode by pressing the 'Manual' button. Select the red, the green and the blue faces by activating the corresponding flag from the 'Group Selection' section. By using the 'feature angle selection tool' we can easier make these selections. Define the blue path (thickness) and press OK.



After this step the middle surface is extracted. Then we can apply a shell-mesh on the model.

The tutorial is complete. Save the file and quit. 4. Conclusion In this tutorial you have followed all the basic steps to extract the middle surface description of a solid part by using the MIDDLE>Multi functionality. Not all capabilities were demonstrated. Refer also to ANSA v13.x User’s Guide and to the On-Line Help for the functionality of ANSA and detailed description of functions and procedures.

Documents

Middle Surface