Importing Geometry

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Summary

This example covers:

  1. Accepted file formats
  2. Setting up the CAD geometry
  3. Importing 2D and 3D geometry to the model
  4. Mesh refinement for more complex geometry

The files used in this tutorial are located at the bottom of the page!

Importing Geometry

This example covers the appropriate setup and format for CAD files, and how these can be imported to a Flex project within Designer.

CAD File Formats:

CAD files can be imported to a project in STEP formats. During the import process, the geometry will be meshed and converted to a Nastran bulk data file using the Gmsh pre-processor.

An existing meshed geometry from another pre-processor, exported in a BDF format, can also be imported as the model geometry.

Note: OnScale does not use this mesh to run the model, but instead bases a structured grid from it.

Geometry Setup:

For this example, we will work from a 3D solid model of a transducer. This is shown below in a half-section view.

Note: All geometry must be included within one CAD file. It is not possible to make changes from within Designer.

tempsnip.png

As the transducer will be submerged in water for the model, a fluid body was added to the geometry before it was exported as a STEP file.

It is important that the fluid body has clearly defined straight edges. If a circular body was created around the transducer, for instance, then the structured mesh would fill in the gaps between this body and a rectangular bounding box. This may cause a problem with the background material definition, with the extra region defined as void by default.

tempsnip.png 

Tip: This example does not cover the creation of the CAD model, or the use of a specific CAD package. However, a simple process to create the fluid body would be to subtract the transducer solid bodies from a new solid body created for the fluid. Subsequent assembly of the two parts will result in a model as shown above.

2D:

This example does not cover the creation of the CAD model, or the use of a specific CAD package. However, a simple process to create the fluid body would be to subtract the transducer solid bodies from a new solid body created for the fluid. Subsequent assembly of the two parts will result in a model as shown above.

Note: It is essential that all 2D surfaces in the CAD file are on the x-y plane. If this is not the case, the geometry will not be imported correctly.

To import this into Designer, start a new model through the ribbon menu (Home > File > New) which will bring up a blank model window if one is not already present. The STEP file can then be imported to the project using the Import Geometry dialog: Home > Import Geometry

Select the CAD file: Select File > … > ‘CAD_transducer_fluid_body_2D.STEP’

Under conversion options, adjust the resolution factor to generate a finer mesh: Conversion Options > Feature Resolution Factor > 0.1

The rest of the options can be left as default; in most cases the rest of the options do not need to be changed.

Click Import to add the geometry to the model. For larger or more complex geometries, the import process may take some time.

The 2D geometry will now be visible in the workspace, with each part assigned a distinct colour and listed under Model Tree > Setup > Geometry. At this point you should check that the geometry has been imported correctly, with no errors which could cause an issue with the model (missing parts or poor feature definition, for example). If there are any issues, it may be necessary to refine the imported geometry as discussed later in the Complex Geometry and Mesh Refinement section of this example.

Tip: An associated BDF will be created in the working directory after a CAD file is imported and meshed. This file can be imported again or used in future projects without the need for further pre-processing.

Note: Always double check that the geometry has been imported with the correct units. These can be viewed in the Geometry section of the model tree or checked visually using the model dimensions tool to turn on axes rulers.

3D:

The process to import 3D geometry is identical to importing 2D geometry.

Use the Import Geometry dialogue again to import 'CAD_half_transducer_fluid_body.STEP', with a feature resolution factor of 0.1

In this case, it is easy to see the difference that the feature resolution factor has on the model, as shown below for values of 0.1 and 0.5 respectively:

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Tip: Some of the detail is lost, particularly around curved edges/surfaces, but all of the main parts are still represented. This may not be the case if working with more complex geometry or very thin features. It is always a case of considering what details are important to capture in the imported geometry and ensuring that the model is accurate enough.

 

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