Assignment of h-Discretization in StressCheck

h-Discretization enables the user to h-refine (i.e. split) individual elements in the mesh, thus reducing the size of elements in the mesh and allowing the user to strategically add more elements in regions of interest. Note: h-Discretization is applicable to manually generated (i.e. hand-meshed) elements only.

To assign h-Discretization to a StressCheck model, select the h-Discretization tab in the Input dialog, set the Object and Method combo-boxes of the C/A/O/M to the desired configuration, and specify a h-Discretization name in the Name: box. Then, ensuring that only parent elements are displayed in the Model View (via Display Mesh Layers > Parent in the Display Objects toolbar), select the object(s) to be h-refined, input the desired h-refinement settings and click on Accept to add the h-Discretization assignment record.

To assign a different h-Discretization record to a different region of the model, simply specify a different h-Discretization name in the Name: box before clicking Accept. Finally, click the Mesh button to perform the h-Discretization assignment(s).

The below animation shows simple graded refinement for a selected element face:

Note: only one element attribute (e.g. edge or face) may be selected/h-refined per h-Discretization assignment. To continue h-refining attributes of the same element, a new h-Discretization assignment record must be added to the original parent element(s). To toggle between parent/child elements, use the Display Mesh Layers toggle in the Display Objects toolbar:

Note: assignment of element properties (e.g. materials) and boundary conditions (e.g., loads, constraints) is applicable to parent elements only. Attempting to assign properties and/or boundary conditions to child elements will result in an error message indicating that the user should first display parent elements before making any assignments to mesh objects.

Element Refinement Rules

The refinement is performed by subdividing each element using a user-specified parameter, the number of “midsides”. For example, if the object is Any Element, and the method is Uniform Division, and if the number of midsides selected is 1 then each quadrilateral element will be subdivided into 4 elements by locating a node in the midpoint of each side and connecting the nodes on opposite sides.

Note: When performing edge or face refinement, you may choose whether to apply the refinement only to the parent element of the selected edge/face, or to all elements which share the selected edge/face. When the parent element has either curved edges or faces, the resulting child elements will inherit the curvature of the original parent element. Mesh refinement is not supported for tetrahedral elements. Use the DeLast or Undo button to delete the last set of refined elements created.

Refinement Methods

StressCheck currently supports uniform, simple graded, and boundary layer (transition) h-refinement.

• Uniform refinement will subdivide an element equally in each direction.
• Graded refinement will subdivide an element by a geometric progression starting from the selected node, edge, or face.

Uniform Refinement

To perform a uniform mesh refinement choose Select > Any Element > Uniform Div. > Name: Test, Layer: 1, Midsides:1 and click on the element you want to refine and then click on the Accept button. This will create the h-discretization record. To activate the h-discretization meshing operation, click on the Mesh button. If instead of Any Element you select All Elements, the refine operation will be performed on all elements of the mesh. Figure 2 illustrates the effect of a uniform refinement operation applied to a straight sided hexahedral element:

Graded Refinement

To perform a simple graded refinement with one layer of elements at a node, choose Select > Node > Simple Graded > Name: Test, Layer: 1, Midsides: 1 > Grading: 0.15 and pick the node(s) to refine and click Accept. Graded refinement may be applied to a node, curve, edge, surface or face (3D only), and may be performed as described above. Figure 3a, 3b and 3c illustrate the effect of applying a grading factor of 0.15 to a node, an edge, or a face of a hexahedral element:

Boundary Layer Refinement

To perform a boundary layer (transition) mesh refinement choose Select > Edge > Bndry. Layer > Name: Test, Layer: 1, Midsides: 1 > Grading: 0.15 and pick the edge to refine. Click the Accept button, this will create the h-discretization record. To activate the meshing operation, click the Mesh button. Boundary layer refinement may be applied to a node, edge, or face, and may be performed as described above. Figure 4 illustrates the effect of applying a grading factor of 0.15 to the edge of an hexahedral element:

Refinement Layers

A record must be created in the StressCheck database that describes the reference objects, method, and refinement attributes for each h-discretization operation. Each record must be given a unique name, a layer attribute, and some additional attributes that depend on the object and method of discretization.

The layer attribute may be a string of characters that will be used to determine the order that the h-discretization operations are performed. The order is based on the alphanumeric sorting of the strings. Operations with the same layer attribute must be independent from each other and will be performed simultaneously.

For an example of performing h-Discretization on a 3D manually meshed part, refer to StressCheck Tutorial: Performing h-Discretization to Refine Manually Generated Meshes

Selecting Objects for h-Discretization Assignment

After enabling the display of Parent elements in the Display Mesh Layers toggle, you may select an object (such as an edge, face, surface or element) or a group of objects during h-Discretization assignment. An object is selected from the Model View by pointing to it and clicking on the left mouse button.

• A group of objects can be marquee selected by left-clicking and dragging the cursor until the desired group is completely enclosed in a rectangular box.
• Holding the Shift key down while left-clicking will allow selection of multiple objects for assignment.
• If the group includes objects which were not to be selected then individual objects can be removed from the group by holding the Ctrl key down while clicking on them.
• If you wish to cancel the current selection of objects, simply right-click on the Model View.

Note: assigning to geometric objects, if associated with elements, will result in the associated elements inheriting the assignment. It is recommended to assign h-Discretization to geometry whenever applicable in case the mesh is updated.

Specifying a Set for h-Discretization Assignment

Alternatively, if a there is a set definition containing a list of objects for assignment, the name of this set may be specified in the Set: combo-box instead of selecting the objects from the Model View. Simply select the name of the set, and the objects in the set list will automatically be selected in the Model View.

Adding a h-Discretization Assignment

Once an object or group of objects are selected, and the refinement settings are input, to add the new h-Discretization assignment record simply click the Accept button. Note: if an existing h-Discretization assignment record has already been selected from the record listbox, you first must choose Set: “New set” or re-select the action, object, or method. Then, you are able to create the new h-Discretization assignment record as usual.

Replacing/Deleting a h-Discretization Assignment

If the user wishes to edit the data in an existing h-Discretization assignment record, or delete an existing h-Discretization assignment record, the user first selects the assignment record from the record listbox directly under the C/A/O/M combo-boxes. Once it is selected, the Status column will read “Selected”, signifying the record can be replaced (updated) or deleted.

Replacing a h-Discretization Assignment Record

Once a h-Discretization assignment record is selected, the user may update the data in the h-Discretization tab, and then click Replace to update the h-Discretization assignment record. After clicking Replace, the Accept button will become active and the Replace and Delete buttons will become inactive.

Deleting a h-Discretization Assignment Record

Once a h-Discretization assignment record is selected, the user may click Delete to delete the h-Discretization assignment record. After clicking Delete, the Accept button will become active and the Replace and Delete buttons will become inactive.

Removing All h-Discretization Assignment Records

To remove all h-Discretization assignment records, regardless of h-Discretization ID, click the Purge button. All h-refinements should automatically be removed as well.