Helix

To create a helix (coil) with a circular cross section, on the toolbar click (

). You can also right-click the node to add this node from the context menu. Then enter the properties of the helix using the sections in the window.


	To create a helix with a noncircular cross section, define the cross section using a work plane. Define the helix centerpoint as a 3D curve using a Helix node with a minor radius = 0 or a Parametric Curve node, and then use a Sweep node to sweep the cross section from the work plane along the curve to create the helix.

Object Type

From the list, select (the default) to create a solid helix, or select to create a hollow helix that consists of surfaces only.

Size and Shape

This section contains a number of properties that determine the size and shape of the helix.

The field contains a positive number. The default value is 3 turns.

There are two radii:

•

The (SI unit: m) field is the radius from the center of the helix (the default is 1 m).

•

The field (SI unit: m) is the radius of the cross section (the default is 0.1 m). The can be zero, in which case a curve object is created. You can use this together with the feature to create helices with noncircular cross sections.

There are two pitches:

•

The field (SI unit: m) determines the axial distance between similar positions on two consecutive turns of the helix (the default is 0.3 m).

•

The field (SI unit: m) determines the radial distance between similar positions on two consecutive turns of the helix (the default is 0, which means that each turn has the same radius).

Select or from the list. The chirality or handedness of the helix can be either right handed (the default) or left handed. For a right handed helix, a clockwise screwing motion moves the helix away from the observer; for a left handed helix, a clockwise screwing motion moves it toward the observer.

From the list, select an option to create the end caps of the helix:

•

Select (the default) to create end caps that are parallel to the helix axis.

•

Select to create end caps that are perpendicular to the helix axis.

•

Select to create end caps that are parallel to the spine of the helix.

The and options modify the helix in the vicinity of the end caps. They only give a valid geometry if the axial pitch is relatively small or large, respectively.

Position

This is the center position for the starting turn of the helix. Enter the coordinates in the , , and fields. The default position is the origin.

Axis

Select the : , , , , or .

•

Select , , or (the default) to define the axis direction parallel to one of the coordinate axes.

•

Select to define the axis direction using Cartesian coordinates in the , , and fields. The default axis is in the z-direction (0, 0, 1).

•

Select to define the axis direction using spherical coordinates θ and

(angles of inclination and azimuth, respectively) in the and fields. The default angles are 0.

Rotation Angle

Rotate the helix around its axis by entering an angle in the field. The default value is 0 degrees.

Coordinate System

The coordinate system in which the position, axis, and rotation angles above are interpreted. From the list, select (the default, for a standard global Cartesian coordinate system) or select any work plane defined above this node in the geometry sequence. If you choose a work plane, the work plane and its coordinate system appear in the Graphics window, using an extra coordinate triad with the directions , , and (which are the used to specify the position of the helix).

Advanced Settings

By default, the check box is selected, which prevents the twisting that would otherwise occur due to nonzero torsion for curves that do not belong to a fixed plane. Twist compensation rotates the base circle during the sweep along the helix curve by an amount equal to the integral of the curve torsion.


	Twist compensation affects the position of the vertices on the top side of the helix. Clear the Twist compensation check box to turn it off. See Figure 2-6 below.

Figure 7-3: The helix on the left has twist compensation (the default). For the helix on the right, twist compensation has been turned off.

From the list, select (the default) to represent the helix using splines, or , to represent the helix using Bézier curves. The difference is that using Bézier curves, the intersections between the surfaces that form the helix are visible edges, whereas they are hidden when using splines.

The value in the field is a relative tolerance that controls the accuracy of the geometric representation of the helix. The geometric representation is an approximation, which is necessary because it is not possible to exactly represent a helix using NURBS (nonuniform rational basis splines). The default value is 10−4 (or 0.01%).

Selections of Resulting Entities

If you want to make the resulting entities contribute to a cumulative selection, select a cumulative selection from the list (the default, , gives no contribution), or click the button to create a new cumulative selection (see Cumulative Selections).

Select the check box to create predefined selections (for all levels — objects, domains, boundaries, edges, and points — that are applicable) in subsequent nodes in the geometry sequence. To also make all or one of the types of resulting entities (domains, boundaries, edges, and points) that the helix consists of available as selections in all applicable selection lists (in physics and materials settings, for example), choose an option from the ( if in a geometry part) list: , , , , or . The default is , which is suitable for use with materials and physics defined in domains. For use with a boundary condition, for example, choose . These selections do not appear as separate selection nodes in the model tree. Select to not make any selection available outside of the geometry sequence.