Lines

The geometry of the model objects is defined by lines. They form the basis for surfaces, members, and solids. When entering members or surfaces graphically, the lines are created automatically.

Each line is defined by a start node and an end node. For the description of complex line types, intermediate nodes are required.

Dialog Box "New Line"

The line number is assigned automatically, but can be changed. The order plays no role for the numbering. It does not have to be continuous either; gaps in the numbering are allowed.

Basis

The Base tab manages the most important line parameters.

Line Type

Various line types are available for selection in the list.

Line Types

Single Line / Polyline

Setting Line Graphically

The 'New Line' dialog, which appears when called up via the pull-down menu, is shown in the image New Line. The image above shows the input dialog for graphical input, which is started using the button .

A single line is defined by a start node and an end node. It represents the direct connection between the two nodes.

A polyline is a polygonal chain of several straight segments. Therefore, in the dialog (see image New Line), the numbers of the intermediate nodes are specified in addition to those of the start and end nodes. For simplicity, single lines are also managed as polylines.

For graphical input, you can select existing nodes, grid points, or snap objects as definition nodes. However, you can also place the nodes freely in the work plane.

Arc

Arc Parameters

An arc is defined by three nodes. In the 'Arc' tab, you can enter, select graphically, or create the start node P₁, the end node P₂, and the control point P₃. The graphic illustrates the order of the nodes.

From the three nodes, RFEM determines the 'arc parameters': stroke h, radius r, opening angle α, and the arc center. If you change a parameter, the node coordinates are adjusted accordingly. When changing the opening angle, you can use the list to specify which of the three definition nodes should be moved.

If you define the arc graphically using the button , you can select or newly place the nodes directly in the work window.

Creating Arch Graphically

Circle

Parameters of Circle

A circle is defined by its center and the radius. In the 'Circle' tab, you can enter or graphically define the coordinates of the circle center, and specify the circle radius. The normal vector controls in which plane the circle is generated. Using the buttons, you can select this vector to define an inclined plane, or specify one of the global axes. The rotation of the circle about the normal determines the control point on the circle line. Its coordinates are specified in the last three fields.

If you define the circle graphically using the button , you can set the center and radius in the work window by clicking the corresponding points.

Defining Circle Graphically

Elliptical Arc

This line type allows you to create a conic section curve. To do this, define the three control points of the ellipse and the arc angle in the 'Elliptical Arc' dialog tab (cf. image Parameters of an Arc).

Ellipse

Three nodes are required to define an ellipse. In the 'Ellipse' tab, you can enter, select graphically, or newly define the two nodes P₁ and P₂ to determine the principal axis of the ellipse. The control point P₃ describes the length of the minor axis.

Parabola

Defining Parabola

This line type allows you to create a conic section curve. To do this, define the two end nodes of the parabola and the control point in the 'Parabola' dialog tab. From these specifications, RFEM determines the parabola parameters and the focus.

Spline

Splines allow you to model arbitrary curves. To do this, select the definition nodes of the curved line one after the other using the button in the 'Node No.' section.

If you define the spline graphically using the button , you can set or newly define the nodes in the work window by clicking.

Defining Spline Graphically

NURBS

NURBS (non-uniform rational B-Splines) are required for modeling freeform surfaces. These are splines whose control points do not lie on the curve itself. You can define NURBS graphically by setting the control points one after the other by mouse click.

Defining NURBS Graphically

Rotation

The Rotation tab offers various options for rotating the line. For the 'Angle' option, the angle β must be specified by which the local line axis x is to be rotated. A positive value causes a clockwise rotation along the positive x-axis.

The line axis system can also be aligned to an 'auxiliary node'. You can select this node graphically or create it anew. Then specify the reference plane x-y or x-z.

Line Rotation via Help Node with Illustration of Line Axes

The 'Interior' option is suitable for aligning curved or multi-part lines to the center.

The rotation of a line can facilitate the input of line loads that act in the local line direction y or z. The line rotation does not affect surfaces or members, as these use their own coordinate system.

Member

A member property can be assigned to each line (see chapter Members).

Nodes on Line

With this node type, nodes can be placed on the line without dividing the line (see image Defining Nodes on Line ).

Support

A line support can be assigned to each line (see chapter Line Supports).

Mesh Refinement

The line can be discretized in a suitable way by a mesh refinement (see chapter Line Mesh Refinements).

Welded Joints

If several surfaces are rigidly connected to the line by welds, the type of connection can be described in more detail (see chapter Line Welded Joints).

Intersecting Line Settings

The check box is accessible when membrane surfaces are created for the "Cutting Pattern" add-on (in preparation). It allows you to define the specifications for intersecting lines of membrane cutting patterns.