SMS:2D Mesh Module Tools

The following tools are contained in the Dynamic Tools portion of the tool palette when the Mesh Module is active. Tools specific to a model interface are described with the corresponding model. Only one tool is active at any given time. The action that takes place when clicking in the Graphics Window depends on the current tool. The following sections describe the tools in the 2D Grid tool palette.

Create Mesh Nodes

The Create Mesh Nodes tool is used to manually create a node using the mouse. A node will be created at the location where the mouse button is clicked inside the Graphics Window. If the node is created inside the triangulated area of a current mesh, and the Insert nodes into triangulated mesh option is turned on, then the new node will be added as part of the mesh. If the new node is not added as part of the current mesh, then the z-value assigned depends on the nodal z-value option.

Select Mesh Nodes

The Select Mesh Nodes tool is used to select nodes. A single node is selected by clicking on it. A second node can be added to the selection list by holding the SHIFT key while selecting it. Multiple nodes can be selected at once by dragging a box around them. A selected node can be deselected by holding the SHIFT key as it is clicked.

If the nodes are not locked (see the menu command Nodes | Locked), then a single node can be clicked and dragged to a new location. As the node is being dragged, its new location is shown in the Edit Window. If a single node selected, the X, Y, and Z Coordinate fields in the Edit Window become available to set the node location exactly. If multiple nodes are selected, the Z Coordinate field in the Edit Window becomes available. The value shown is the average elevation value of all selected nodes. If this value is changed, the new value will be assigned to all selected nodes.

With one node selected, the Edit Window shows the node id number and the number of elements to which it is attached. With two nodes selected, the Edit Window shows both node id numbers and the distance between the nodes. With multiple nodes selected, the Edit Window shows the number of selected nodes.

Right-Click Menu

See the 2D Mesh Nodes Menu and 2D Mesh Elements Menu articles.

Create Nodestrings

The Create Nodestrings File:SMS Create Nodestring tool.png tool is used to create node string. Nodestrings are used for operations such as assigning boundary conditions, forcing breaklines into the mesh, and renumbering the mesh. To create a nodestring:

1. Click on a node. The node will be highlighted in red and a prompt will be shown in the Help Window.
2. Click on any node to add it to the nodestring. The selected node is also highlighted in red and a solid red line is drawn between the two nodes. Continue adding nodes to the nodestring in this manner.
   1. Note: For most operations, nodes in the nodestring should be adjacent, but this is not required. A breakline, for example, will usually be made of nodes which are not adjacent.
   2. Press the BACKSPACE key to backup one node. Press the ESC key to abort the nodestring creation.
   3. Double-click a node or press the ENTER key to end the nodestring creation.
3. The SHIFT and CTRL keys assist in creating large nodestrings which are made up of adjacent nodes. These can be used after at least one node has been selected and function as follows:
   1. SHIFT. Holding down the SHIFT key and selecting another node will add to the nodestring all nodes between the two. The path chosen is the shortest distance between the two nodes. This is useful for creating continuity strings which run along a cross section of the mesh.
   2. CTRL. Holding down the CTRL key and selecting another node will add to the nodestring all nodes on the mesh boundary between the two, going counter clockwise from the first node to the second node. Both nodes must be on the boundary of the mesh or SMS will beep.
   3. CTRL + SHIFT. Holding down both the CTRL and SHIFT keys and selecting another node will add to the nodestring all nodes on the mesh boundary between the two, going clockwise from the first node to the second node. Both nodes must be on the boundary of the mesh or SMS will beep.

Select Nodestrings

The Select Nodestrings File:SMS Select Nodestring tool.png tool is used to select nodestrings. When this tool is chosen, a small icon appears near the center of each nodestring. A nodestring is selected by clicking inside this icon. A second nodestring can be added to the selection list by holding the SHIFT key while selecting it. Multiple nodestrings can be selected by dragging a box around their icons. A selected nodestring can be deselected by holding the SHIFT key as its icon is clicked.

When nodestrings are selected, the Z Coordinate field in the Edit Window becomes available. The value shown is the average elevation value of all nodes in the selected nodestrings. If this value is changed, the new value will be assigned to all nodes in the selected nodestrings.

With one nodestring selected, the Edit Window shows the number of nodes in the nodestring, its type, and its length. With multiple nodestrings selected, the Edit Window shows the number of selected nodestrings and their total length.

Right-Click Menu

See the 2D Mesh Nodestrings Menu article.

Create Elements

Most elements in SMS will be created using automatic mesh generation techniques. At times, however, it is necessary to manually create a single element or a small group of elements.

Although SMS supports various types of elements, only those element types supported by the current numerical model will be available in the tool palette. Some of these element types are linear while others are quadratic. A linear element has only corner nodes, while a quadratic element has midside nodes between the corner nodes.

The following linear elements are supported:

• 2-node lines File:Line2.png
• 3-node triangles File:Tri3.png
• 4-node quadrilaterals File:Quad4.png

The following quadratic elements are supported:

• 3-node lines File:Line3.png
• 6-node triangles File:Tri6.png
• 8-node quadrilaterals File:Quad8.png
• 9-node quadrilaterals File:Quad9.png

Linear and quadratic elements cannot coexist in a single mesh. If linear elements exist in a mesh, then the quadratic element creation tools are dimmed out. Similarly, if quadratic elements exist in a mesh, then the linear element creation tools are dimmed out. To create a single linear or quadratic element:

1. Select the tool which corresponds with the type of element to be created.
2. Click on the corner nodes which will make the element, one-by-one. Do not click midside nodes. As each node is clicked, it becomes highlighted in red.
3. Alternatively, a box can be dragged around the corner nodes which will make the element. A beep will sound if the box does not surround the exact number of corner nodes required by the selected tool.

The mid-side nodes in quadratic elements are created automatically, as is the center node of a nine-node quadrilateral. Before a new element is created, SMS performs the following quality checks:

• The new element cannot overlap other elements.
• A quadrilateral element cannot twist or overlap itself.
• A quadrilateral element cannot be concave.

If any of the these fails, the new element is not created.

Select Elements

The Select Elements File:SelectMeshElement.png tool is used to select elements. A single element is selected by clicking inside it. A second element can be added to the selection list by holding the SHIFT key while selecting it. Multiple elements can be selected at once by dragging a box around them. Holding the CTRL key and dragging the mouse selects any elements through which the line is drawn. A selected element can be deselected by holding the SHIFT key as it is clicked.

When elements are selected, the Z Coordinate field in the Edit Window becomes available. The value shown is the average elevation value of all nodes in the selected elements. If this value is changed, the new value will be assigned to all nodes attached to the selected elements. Caution must be used when changing node elevations in this manner. Do not create large flat areas where surrounding elements may become dry because this can cause ponds to form when the finite element analysis is performed.

With one element selected, the Edit Window shows the element id number, its type, and its area. With multiple elements selected, the Edit Window shows the number of selected elements and their combined area.

Right-Click Menu

See the 2D Mesh Elements Menu article.

Swap Edges

The Swap Edges tool is used to manually swap the edges of two adjacent triangles. This is useful in such cases as preserving a geometrical feature in the mesh or avoiding an artificial dam in a channel.

Two adjacent triangles form a quadrilateral with an element edge down one diagonal. When the diagonal is clicked, it gets swapped to the other diagonal, as long as the quadrilateral is not concave.

Merge/Split Elements

The Merge/Split Elements tool is used to either merge two triangles into a quadrilateral or split a quadrilateral into two triangles. This is a useful tool to use when trying to avoid certain mesh drying problems.

To split a quadrilateral element, click inside it. An element edge appears on the diagonal which will make the triangles uphold the Delaney criteria. To merge two adjacent triangles into a quadrilateral, click the common edge. A quadrilateral will form as long as it is not concave.

Label Contours

The Label Contours tool is used to manually create a contour label using the mouse. To add a label, click on the point where the label should be created. The label will remain on the screen until either it is manually removed or the automatic contour label options are changed. To manually remove a contour label, hold the SHIFT key and clicking on it. There are also available automatic contour label options.

Related Topics

• Editing 2D Meshes
• Mesh Module