SMS:2D Mesh Elements Menu

The Elements Menu includes the following commands:

Options

General command – set up the default element options.

Triangulate

Generation command – triangulates the selected nodes to form triangle elements.

Optimize Triangulation

Generation command – swaps edges of triangular elements to meet the Dulanay criterion.

Select Thin Triangles

General command – selects all thin triangular element that meet the definition specified in the options command.

During the process of triangulation, a mesh of triangular elements is created around existing nodes. This usually creates triangular elements outside the desired mesh boundary. Many of these exterior triangles are very skinny, and some are virtually invisible. The Select Thin Triangles command from the Elements menu finds and selects skinny triangular elements which are on the mesh boundary.

Thin triangles interior to the mesh will not be selected when this command is performed, since deletion of interior triangles would result in gaps in the mesh. After the thin triangles have been selected, they can be removed by selecting the Delete macro.

Find

General command – finds the element with a specified ID or location.

The Find Element command from the Elements Menu is used to locate an element either with a specific ID, or surrounding a specific location. When this command is executed the Find Element dialog opens.

When the Find by ID option is selected, then the element with the specified ID is highlighted in red. If there is no element with the specified ID, then an error message is given. Conversely, when the Find by nearest (x,y) coordinate option is selected, the element which surrounds to the specified (x, y) location is highlighted in red. With either of these methods, if the current tool is the Select Elements tool, then the found element becomes selected in addition to being highlighted.

Assign Material Type

General command – requires a selected element. Sets the material type of the selected elements based on the option defined in the options command.

Each element in the mesh is assigned a material type. The default material ID can be set in the Element Options dialog. A selected element is assigned a new material type by choosing the Assign Material Type command from the Elements menu. If the Assign default material option is selected in the Element Options dialog, then the default material is automatically assigned to the selected element. If the Prompt for material when assigning option is selected in the Element Options dialog, then the Materials Data dialog opens from which a material type can be chosen.

Merge Triangles

Conversion command – merges triangle pairs that meet the standard for rectangles defined in the options command. Can operate on selected elements.

Split Quadrilaterals

Conversion command – splits quadrilateral elements into two triangular elements. Can operate on selected elements.

QUAD8 ↔ QUAD9

Conversion command – converts all QUAD8 to QUAD9 elements and vice versa. Only applies to the FESWMS model. Can operate on selected elements.

Linear ↔ Quadratic

Conversion command – converts all elements from linear to quad or vice versa. Only applies to TABS and FESWMS models.

Refine

Generation command – splits all selected elements into four elements.

At times, there is not enough definition in a finite element mesh. The Refine command from the Elements menu splits each of the selected elements into smaller elements. After the selected elements have been refined, SMS automatically creates transitions, from the refined area of higher density to the unrefined area of lower density, using triangular elements. Refine options are set in the Element Options dialog.

Relax

Generation command – moves all the nodes on the interior of the selected elements to the centroid of their contributing area. Iterates based on option set in the options command.

The process of creating and editing a finite element mesh can result in poor quality elements. These elements may have poor interior angles or may violate the area change guideline for adjacent elements. The Relax command from the Elements menu can improve adjacent element areas and interior angles by moving nodes. This command moves nodes to improve the elements shape. Several options are available. Relaxation is an iterative process. The number of iterations performed and other options are specified in the Element Options dialog. If no elements are selected, then the relaxation is performed on all elements in the mesh.

Fix Bad Area Transitions

Generation command – removes nodes that cause bad area transitions as defined in the element quality control.

The process of creating and editing a finite element mesh can result in poor quality elements. These elements may violate the area change guideline for adjacent elements, specifically, the area of the smaller of the adjacent elements divided by the area of the large element may be less than a recommended ratio. This ratio is set in the Mesh Quality entry of the 2D Mesh Display Options.

The Fix Bad Area Transitions command from the Elements menu can improve adjacent element areas by removing nodes. The adjacent elements of each node in the mesh are examined for guideline violations. If more that one are found, a calculation is made to determine if the removal of the node and the retriangulation this would cause would maintain compliance for the newly formed elements and their neighbors. If this is the case the node is removed.

Obsolete Commands

The following commands have been removed from the current version of SMS.

Rectangular Patch

Patch command – creates elements from four selected node strings. See the article Patches for more information. See also Element Patch Workflow.

Triangular Patch

Patch command – creates elements from three selected node strings. See the article Patches for more information. See also Element Patch Workflow.

Related Topics

• Mesh Module
• Element Options Dialog