Lines

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

Every line is defined by a start and an end node. To define complex types of lines, intermediate nodes are required.

Dialog Box "New Line"

The line number is assigned automatically, but it can be changed. The order is irrelevant for the numbering. It does not have to be continuous, either; gaps in the numbering are allowed.

Main

The Main 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

Selecting the line entry on the drop-down menu opens the "New Line" dialog box shown in the image New Line. The image above shows the input dialog box for graphical input, which you start by clicking the button.

A Single Line is defined by a start node and an end node. It represents a direct connection between both nodes.

A Polyline is a polygonal chain consisting of several straight line segments. Therefore, the dialog box (see the image New Line) shows the numbers of the intermediate nodes in addition to those of the start and end nodes. For the sake of simplicity, single lines are managed as polylines, too.

When entering polylines graphically, existing nodes, grid points, or snap objects can be selected as definition nodes. However, you can also set nodes freely into the work plane.

Arc

Arc Parameters

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

Based on these three nodes, RFEM determines the "Arc parameters": the rise h, the radius r, the opening angle α, and the arc center. If you change a parameter, the node coordinates will be adjusted accordingly. When changing the opening angle, you can use the list to define which of the three definition nodes should be moved.

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 point of the normal to the circle plane controls in which plane the circle is generated. Use the buttons to select this point, or define one of the global axes.

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

Defining Circle Graphically

Elliptical Arc

This line type can be used to create a conic section. Define three control points for the ellipse and the arc angle in the "Elliptical Arc" tab (see the image Arc Parameters).

Ellipse

To define an ellipse, three nodes are required. To define the principal axis of the ellipse, you can enter the two nodes P₁ and P₂, select them graphically, or define new nodes in the "Ellipse" tab. The control point P₃ describes the length of the minor axis.

Parabola

Defining Parabola

This line type can be used to create a conic section. Define the two end nodes of the parabola and the control point in the "Parabola" tab. Based on this information, RFEM determines the parameters of the parabola as well as the focus.

Spline

Splines can be used to model any kind of curve. Click the button in the "Nodes Nos." section to select the determining nodes of the curved line one after the other.

If you define the spline graphically using the button, you can define the nodes by clicking into the work window, or you can define new ones.

Defining Spline Graphically

NURBS

NURBS (non-uniform rational basis splines) are required for modeling freeform surfaces. NURBS are splines whose control points do not lie on the curve itself. You can define NURBS graphically by defining the control points one by one with a mouse click.

Defining NURBS Graphically

Rotation

The Rotation tab offers various options for rotating the line. If the "Angle" option is set, specify the angle β by which the local line axis x should be rotated. A positive value causes a clockwise rotation along the positive x-axis.

The line axis system can also be aligned to a "Help node". You can select this node graphically or create a new one. Then, enter the reference plane x-y or x-z.

Line Rotation via Help Node with Illustration of Line Axes

The "Inside" option is useful for aligning curved or segmented lines to the center.

Rotating a line can facilitate the input of line loads acting in the local line direction y or z. The line rotation does not affect surfaces or members, because they have their own coordinate system.

Member

Member properties can be assigned to any line (see the chapter Members).

Nodes on Line

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

Support

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

Mesh Refinement

The line can be appropriately discretized by mesh refinements (see the chapter Line Mesh Refinements).

Welded Joints

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

Cut Line Settings

The check box becomes available when membrane surfaces for the Cutting Pattern add-on are created. This way, specifications for cutting lines of membrane cuts can be made.