Constraint Settings

You can select one of the following settings for each constraint option:

• Free—Allows freedom of movement in the specified direction.

• Fixed—Constrains the entity, preventing movement in the specified direction.

• Prescribed—Prescribes a specific displacement or rotation in the specified direction. Prescribed has an effect on the entity similar to a load.

When you select Prescribed, an input field appears to the right of the column. You can enter a value, mathematical expression, or parameter name in this field.

◦ For translation options, enter an enforced displacement value in length units. For non-Cartesian coordinate systems like cylindrical and spherical coordinate systems, the degrees of freedom related to angles are interpreted as angular translations (units of length) and not as angles. To specify a prescribed or enforced angular rotation along angular directions like theta or phi, specify the angular translation as Radius*theta (R in length units and theta in radian) with a unit of length. Select an appropriate length unit for the value that you specify.

For example—To assign a prescribed rotation of 1 degree in the theta direction of a cylindrical coordinate system (or the phi direction for a spherical coordinate system) measure the radius R of the hole or entity to which you want to apply the prescribed rotation from the origin of the reference coordinate system. The radius R is in length units. Now, calculate the angular translation (R*theta in length unit) in the theta direction as follows:

R*theta (theta in radian) = R*theta (theta in degree)*Pi/180~= 0.01744*R

This is the preferred method to assign enforced displacement or translation for a centred reference coordinate system.

Interpret Angular Translations in Radians—This check box is visible only in the native mode and if you select a cylindrical or spherical coordinate system. If you select this check box, the theta and phi values entered are interpreted as angles in radian and not as length. In this case, the Creo Simulate engine calculates the radius of the hole or entity on which you apply a constraint. It then automatically calculates the effective prescribed translation in length units as Radius*theta (theta in radian) in the given angular direction. For non-centred coordinate systems the radius could also be interpreted as the radial distance of the entity from the origin of the reference coordinate system. This is the preferred method to assign enforced displacement or translation in the angular direction.

For example—To assign an enforced displacement of 1 degree in theta or phi direction of a cylindrical or spherical coordinate system, make sure you select this check box and enter the equivalent radian value as follows:

1 degree*Pi/180~=0.01744 radians in the corresponding angular direction. With this check box selected, changing the units of length has no effect on the value.

◦ For rotation options, enter an enforced rotation in radians.

In defining prescribed displacement constraints, you should consider various guidelines and behaviors.

• Function of coordinates (FEM mode)—Enables you to define a constraint as a function of coordinates.

When you click the Function Of Coordinates button, the button and option menu appear to the right. Select a function from the option menu or click to use the Functions dialog box to define a new function or edit an existing one.

The software uses only the translational degrees of freedom for solid models because solids have only three degrees of freedom. The software disregards any setting you select for the rotational degrees of freedom. If you apply the constraint to shell or beam models, the software uses both translational and rotational settings because the shell formulation has all six degrees of freedom.