Geometries

What you’ll learn

• Creating geometries: Create simple geometries using geometry elements.
• Importing files related to geometries: Use imports in STEP, GDSII or mesh formats to set up the project.
• Modifying geometries: Use simple and boolean operations to make modifications to your model.

Working with geometries

Geometry editing in Quanscient Allsolve is done in the Model section. At the top of the Navigation panel, you’ll find the Geometry elements list followed by the geometric Entity tree.

During geometry editing, a number tag is attached to each geometric entity. These tags are used to target geometric entities in material and physics definitions, for example. The entity tags are locked only after confirming the model changes. Therefore, it is recommended to confirm the model changes before moving on to the next section. Not doing so may result in selecting incorrect entity tags which leads to simulation errors.

Geometry elements

All shapes, imports and operations are referred to commonly as Geometry elements.

• Import
  • Import step, GDSII or mesh (gmsh or nastran mesh) files
• Shapes
  • Box
  • Sphere
  • Cylinder
  • Torus
  • Cone
  • Rectangle (2D)
  • Disk (2D)
• Simple operations
  • Remove - Remove volumes.
  • Translate - Move selected volumes or create new copies by translating the selected volumes.
  • Rotate - Rotate selected volumes or create new copies by rotating selected volumes on defined axis.
• Boolean operations
  • Intersection - Portion common to both volume sets is kept.
  • Union - Merge all selected volumes/surfaces.
  • Difference - Subtracts volume set 2 from volume set 1.
  • Fragments - Split overlapping volumes into new, non-overlapping volumes.
  • Fragment all - Run automatic fragment of all against all. There is always an implicit Fragment all forced as the last element to prevent any overlapping elements.

Building elements

The geometry elements list can be thought of as a stack where each new element is added on top of all the previous ones. When adding new geometric shapes this does not have to be taken into account, but for targetting operations, it’s important to understand that each operation is working with entity tags of the state just before the operation.

Geometry elements list

As an example let’s consider the case above, with a .step file import and two boxes. When adding the difference operation, it can not be edited before the previous element (box 2) is built, and geometric entity tags up until that point are known.

The requirement also goes in the other direction. If you want to edit box 2 after the difference operation is built, the operation must first be “unbuilt” so that the tag selection will be correct. This can be done by building the previous element again, or by clicking the Edit button in the difference operation settings.

When you are finished editing the model, build the final state of the model by clicking Confirm model changes.

Confirm model changes

It is important to confirm the model changes before moving on, so that entity tags are locked. This will ensure that target regions have the correct tags.

Shapes

In Quanscient Allsolve, you can add various shapes to your project by following these steps:

1. If you haven’t yet activated geometry edit mode, do that by clicking Edit model.
2. Click + next to Geometry elements to see the available list of shapes and operations.
3. Add your shape of choice.
4. Adjust the properties of the added shape as necessary.
5. Click Apply to confirm changes to the shape.
6. Click Confirm model changes to finalize the changes. Now the model is updated and entity tags are locked.

Geometric operations

In the Quanscient Allsolve geometry elements, there is a selection of simple geometric operations, such as remove, translate and rotate, as well as some common boolean operations.

All of the operations have a target selection and possibly some settings to set before the operation can be applied and built. An exception is the fragment all operation that does not require any target or settings.

Translate and rotate: copying

In the geometry operations translate and rotate, there is a special feature, copying. In the settings for the operations, the user can enable copying and set the number of copies they want to create. Each copy is then rotated or translated by the amount specified in relation to the original copy.

Original box	Transform with 5 copies	Rotate with 3 copies

File imports

These geometric exchange formats are currently available for model geometry imports:

• STEP
  • .step
  • .stp
• GDSII
  • .gds
  • .gds2

You can also import the following mesh file formats:

• Gmsh
  • .msh
• Nastran
  • .nas

Importing STEP files

To create a geometry by importing a STEP file:

1. Enable model editing.
2. Add a new element.
3. Select Import file.
4. Select a STEP file with extension .step or .stp.
5. Build the file import by clicking Not built.

You can change the offset of the imported model or enable clean-up of detached entities from the import settings.

Finalize model creation by clicking Confirm model changes.

Importing GDSII files

To create a geometry by importing a file in the GDSII stream format:

1. Enable model editing.
2. Add a new element.
3. Select Import file.
4. Select a GDSII file with extension .gds or .gds2.

At this point, the GDSII file content is parsed, but a 3D model is not yet created.

To create the 3D model, perform the layer stackup:

1. Select Units for layer thickness. Layer thickness units can be overridden for any layer by providing units after the thickness value, like 0.2e2 nm.
2. Add all layers you want to use in the model from the bottom up.
3. Enter thicknesses for each layer.
4. Apply settings and build the import.

Finalize model creation by clicking Confirm model changes.

Layer stackup: stacked layers

By default all layers are added as relative stacked layers, starting from level 0 on the Z-axis. Each new layer is stacked on top of the previous one. Stacked layers can be moved up and down in the layers list after they are added.

Layer stackup: absolute layers

If you need to define cut-out layers or layers that otherwise span across multiple levels, use absolute layers:

1. In layer settings, select Convert to absolute.
2. Enter thickness and start position on the Z-axis.

Importing mesh files

Quanscient Allsolve supports Gmsh (.msh) and NASTRAN (.nas) mesh formats as direct mesh imports.

Importing a mesh file works in the same way as other file imports but includes some limitations:

• There can be only one mesh for a project.
• You cannot add any other shapes or operations before or after a mesh import.
• The simulation mesh is automatically selected and cannot be modified in any way after import.

NASTRAN mesh imports

Quanscient Allsolve allows importing NASTRAN mesh files.

If the mesh file is exported from COMSOL, choose the following export settings:

File extension	Data to export	Field format	Units
.nas	☑️ Domain elements	Large	Meters [m]
	☑️ Boundary elements	☑️ Export as second-order elements
	☑️ Geometric entity information

Default units

COMSOL has an option for default units. If the default unit is something other than meters, exported mesh files are scaled based on that unit, and not meters.

For successful mesh imports to Allsolve, imported files must be in meters.

Comparable mesh files

If you want to run the same simulation with another mesh for the same geometry:

1. Copy the project including a mesh import.
2. Remove the existing mesh file from geometry elements.
3. Import the comparable mesh file.

Caution: Geometry tags in comparable mesh files

In mesh files, all geometric entities (volumes, surfaces, curves and points) have an identifying tag. Comparable mesh files should have identical geometry tags.

As long as the tags remain identical within a geometry, switching the mesh file works. if the tags change, all interactions, materials, etc. that have target selection through tags, will run the risk of being falsely assigned.