Curves

This section provides an overview of the Curve entity in MotionView.

Theory/Background

A Curve consists of two or more column vectors that can be either used to create XY data (referred as 2D spline) or a line geometry in 3D modeling space (3D curve). The 2D spline can be used as reference input for other MotionView entities such as a force or motion. The 3D curve can be used for certain types of constraints such as a Point-to-Curve constraint.

curves_entity_2d_example_mv

2D Curve in MotionView

Curves have many varied applications, some of which are listed below:

Forces	Forces are used to define nonlinear characteristics for the forces. The curve may represent a spring force versus deformation characteristic or a damping force versus deformation velocity characteristic. This data is frequently measured experimentally.
Motions	Motions are used to define nonlinear displacements versus time, velocity versus time, and/or acceleration versus time.
Vectors, Differential equations	Curves may be used to define relationships that are difficult to describe analytically.

Note - A 3D Curve can also be used for certain types of constraints, such as a Point-to-Curve constraint.

The figure below shows the various types of Curves that are available for modeling in MotionView:

curves_entity_types_diagram_mv

There are two types of curves that can be defined in MotionView:

•

2D Curves

•

3D Curves

Each of the above types can further be defined as a:

A Cartesian curve simply consists of two or more vectors, that could be defined independent to each other, yet they should consist of same number of data points.

A Parametric curve is defined in terms of one free parameter, u. Referring to the image below, assume a curve C is defined with respect to a coordinate system OXYZ. The coordinates of any arbitrary point on the curve P, as measured in OXYZ, can be represented uniquely in terms of the free parameter u with three functions, f(u), g(u), and h(u), that define the x-, y- and z-coordinates of P. The extent of the curve is governed by the start and end values of u. This is a parametric representation for a curve.

curves_entity_parametric_curve_example_mv

A Parametric Curve represented by a free parameter u

A 2D Parametric curve has three vectors - that is, one free parameter vector U, and two dependent vectors X and Y.

A 3D Parametric curve has four vectors - that is, one free parameter vector U, and three dependent vectors X, Y, and Z.

Creating and Editing Curves

To learn how to add an "Entity" to a model, please see the Entity Manual topic.

1.	A Curve entity can be added to the model using two different methods:

-	From the MotionView Reference Entity toolbar, right-click the Curves icon .

-	From the Project Browser, right-click on the Model label (or on any System/Analysis of your choice) and select Add > Reference Entity > Curve from the context menu.

The Add Curve dialog is displayed.

add_curve_dialog_mv

2.	In the Add Curve dialog, double click the System collector button and select the desired system from the Select a System or Assembly or Analysis dialog.

Note - The selection of System collector for the entity can also be done after the entity has been added.

3.	Specify a Label for the curve (if you want to use a different label then the default).

The label can be a descriptive name.

4.	Specify a Variable name for the curve (if you want to use a different variable name than the default).

The variable name can be descriptive, however it should not contain any special characters (other than ‘underscore’).

5.	Optionally, you can also specify a Comment for the curve.

6.	When you are finished specifying the properties, click OK, Apply, or Cancel.

-	Clicking OK will add/create the curve entity and close the dialog.

-	Clicking Cancel will cancel the curve creation operation and close the dialog.

-	Clicking Apply will add/create the curve; however the dialog will remain open so that additional curves can be added in the same way.

7.	Once an Curve entity has been added to the model, the panel for the curve will automatically be displayed in the panel area. See the panel example below:

curves_panel

Curve Panel - Properties Tab

The Properties tab displays various options that allow you to select and define the curve.

Click on the individual links below to learn more about each specific type of curve:

2D Curves

3D Curves