Importing a non-axisymmetric mandrel from STEP using LS PrePost

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Introduction

In this example a non-axisymmetric shape is to be imported into Cadfil. In this case, this is a non-round pressure vessel as a STEP file. For this example LS-PrePost, a free software package, will be used for processing this.

Creating a shell in LS-PrePost

The step file may be mad up of mane surfaces, the first task is to stitch these into a single shell. In LS-PrePost this is done by selecting all surfaces required for the mandrel within the 'stich faces' tool. This will create a single shell that will be used as the mandrel.

Setting the reference coordinate system

Once the shell has been created, it is important to ensure that the coordinate reference is correct. For Cadfil, the origin should be in the centre of the mandrel, with the x axis along the rotational axis of the mandrel.

From the picture above, the current origin is in the wrong place, and the x direction is incorrect. Therefore the first task will be to set up a second reference geometry in the required location.

The main part of the mandrel has been hidden in the picture above, but it is possible to see that the second coordinate system has been set up in the correct place, in the centre of the mandrel with x as the axis of rotation. All the remains is to move the mandrel geometry from this new coordinate system to the original coordinate system

This is done by using the Transform function in the geometry tools. The created shell is the source entity to be moved from the created coordinate system, to the origin coordinate system

Creating the mesh

Now that we have a shell in the correct position, we can look at creating the mesh.

In LS Pre-Post, this is done in the 'FEM> Elements and Mesh> Auto Mesher' function, creating a triangular mesh from the correctly transformed shell.

Once the mesh has been created, it can be saved as a keyword file (using the file extension .k). This mesh can then be imported into Cadfil as a mandrel.