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*TORQUE-TWIST

Purpose

To define torque-twist curves for non-linear materials.

Theory

Refer to Non-Linear Elastic materials for further information on this feature.

Note also that the old *STRESS/STRAIN keyword has effectively been superseded by the new non-linear material definition keywords which explicitly distinguish between bending, axial and torsional stiffness. Refer to related keywords *MOMENT-CURVATURE and *FORCE-STRAIN.

Keyword Format

A block of lines that defines a torque-twist curve, repeated as often as necessary. The block begins with a line defining the curve name. It is followed by as many lines as necessary to define each point on the curve.

Line defining the curve name:

CURVE=Curve Name

Line defining a point on a curve:

Torque, Twist

Each curve must have at least two points defined. This type of torque-twist curve may not be associated with non-linear beam elements which are defined using the rigid riser format for geometric properties specification.

Table Input

Notes

(a)This keyword is used to define generalised torque-twist curves that define GJ for a particular set of elements. Torque-twist curves may be assigned to element sets using the *GEOMETRIC SETS keyword.

(b)Use as many lines as you need to completely define a particular torque-twist curve. Simply leave Column 1 blank for second and subsequent lines. For subsequent torque-twist curves, put the curve name in Column 1 and specify the torque-twist data in the same way.

(c)The points defining the non-linear torque-twist curve may be specified in any order. Flexcom subsequently sorts the data pairs into ascending order of twist.

(d)If the twist in an element lies between the torque-twist data points you specify, Flexcom uses linear interpolation to determine the relevant stiffness for the element.

(e)If the twist in the element lies outside the specified range of the torque-twist curve, then Flexcom simply extrapolates from the first or last section of the curve as appropriate.

(f)If none of the specified twist terms have a negative value, the curve is assumed to be symmetrical about the origin (i.e. the behaviour of the element is the same for both positive and negative twists).