# Area Object Dividing and Meshing

CSiBridge allows area objects to be divided into smaller objects in the object-based model, and meshed into elements in the analysis model. Dividing the object is accomplished using the Advanced > Edit > Areas > Divide Areas command. Meshing an area object is accomplished using the Advanced > Assign > Areas > Automatic Area Mesh command.

The options for dividing and meshing a selected area object add points that lie on the edges of the object, use straight lines that cross the edges of the object, or specify points that must lie within the selected area object. These basic types of area object dividing/meshing are described in this topic, as follows:

• Dividing/meshing by adding points on the edges of an area objects

• Cookie cutter dividing/meshing using lines that cross an area object

• General dividing/meshing

## Dividing/Meshing By Adding Points On the Edges of An Area Object

Note:  Dividing/meshing by adding points on edges of area objects is applicable to triangles and quadrilaterals only.

Consider the following figure that shows an area object defined by points 1 through 4 and edges A through D. Points 5 and 6 lie on edge A, point 7 is on edge B, and point 8 is on edge C. Edge D has no points. Dividing/meshing based on points on the edges of an area objects adds an equal numbers of points on opposite edges of the area object. Thus, in the above example, the program adds point 9 to edge C and point 10 to edge D, as shown in the following figure. Edges A and C have two points each and edges B and D have one point each. Point 9 has been added to edge C at a relative distance from point 4 that is similar to the distance along edge A of point 5 from point 1. Point 10 has been added to edge D at a relative distance from point 1 that is similar to the distance along edge B of point 7 from point 2.

With an equal number of points defined on opposite edges of the area object, the program divides/meshes the object by drawing lines between the points on the opposite edges, as shown in the following figure. In this example, the dividing/meshing breaks the original area object into six area objects. Adding points to the edges of area objects can be accomplished by specifying the number of objects/elements to be created, the size of the objects/elements to be created, or direct determination of intersections of specified lines and edges. The specific options are described in the Advanced > Edit > Areas > Divide Areas and Advanced > Assign > Areas > Automatic Area Mesh topics. The options can be generally described as follows:

• Divide/mesh into a specified number of objects/elements along two adjacent edges of the original area object: For this option, specify the number of objects/elements to be created along two adjacent edges of the object. The program then adds points to each edge so that dividing/meshing lines can be drawn  between the opposing points on the edges to create the specified number of objects/elements. The points along the edges are taken to be equally spaced.

• Divide/mesh into objects/elements that do not exceed a specified size along two adjacent edges of the area object: For this option, specify the maximum length of the resulting objects/elements along two adjacent edges. The program then determines the number of points to be added along each edge to achieve the desired divided objects/meshed elements based on the specified lengths. The points along the edges are taken to be equally spaced.

• Divide/mesh into objects/elements based on specified points on the edges of the area object and points determined from the intersection of specified lines and the edges of the area object: For this option, select the area object and the straight line or point to be used in the dividing/meshing. The specified line and point must lie in the plane of the area object. The program will not extend the specified line to make it intersect an edge; it must be drawn or defined such that it intersects an edge. The program adds points along the edges at the intersection of the selected line or projected trajectory of the line and the selected object's edge.

## Cookie Cutter Dividing/Meshing Based on Lines Crossing the Area Object

Consider the following figure that shows an area object defined by points 1 through 4 and edges A through D. Also shown are Line 1, Line 2 and Line 3, which lie in the plane of the area object. Cookie cutter meshing uses the specified lines that cross the edge(s) of the selected area object, as shown in the following figure. As needed, the program adds points along the edge opposite the line/edge intersection point to generate the divided objects/meshed elements. The following figure shows how in this example the program uses the lines and projected points to cookie cut divide/mesh the original area object into six objects/elements. Cookie cut dividing/meshing based on lines crossing the selected area object can be accomplished using a straight line object or a selected point. The specific options are described in the Advanced > Edit > Areas > Divide Areas and Advanced > Assign > Areas > Automatic Area Mesh  topics. The options can be generally described as follows:

• Cookie cut divide/mesh based on straight line objects: In this method the dividing/meshing lines are directly specified.

• Cookie cut divide/mesh based on point objects: The dividing/meshing lines are determined from specified points, a specified rotation angle and the original area object local axes. Two dividing/meshing lines are defined through each specified point. The directions of the dividing/meshing lines are rotated the specified angle from the original area object local 1 and 2 axes. Positive rotations appear counterclockwise when the local 3 axis is pointing toward you.

## General Divide/Mesh

The general divide/mesh option divides/meshes the area objects into quadrilateral elements based on three parameters:

• A specified maximum object/element dimension.

• Specified points that lie in the plane of and inside the area object. The points can not lie on the edge of the area object; they must be inside it.

• Specified lines that lie in the plane of and inside the area object. The end points of the lines can not lie on the edge of the area object; they must be inside it.

The maximum object/element dimension is always specified.  The specification of points and lines inside of the area object is optional. Consider the area object shown in the following figure that has the point labeled A inside it. The figure below shows the result of general dividing/meshing of the area object considering point A and specifying a maximum object/element dimension that is approximately one quarter of the length of the sides of the area object. The specific options are described in the Advanced > Edit > Areas > Divide Areas and Advanced > Assign > Areas > Automatic Area Mesh topics.