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ULiege - Aerospace & Mechanical Engineering

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doc:user:conditions:rotations

# Prescribed Rotations

Displacements and rotations imposed with respect to an axis are extensions of imposed displacements (translations) and are used to rotate/move a set of nodes around an axis, which can be in motion too. As for displacements, this is done with LoadingSet. The motion of the axis is also defined in the LoadingSet.

## Translation of the axis

If the axis is defined by points p1 and p2, its motion can be defined by commands similar to the following ones:

loadingset.define(p1, Field1D(TX,RE), dx1, fctX1)
loadingset.define(p2, Field1D(TZ,RE), dz2, fctZ2)
 p1 reference Point at the origin of the axis dx1, dy1, dz1 amplitudes of the x,y,z displacements of point p1 fctX1, fctY1, fctZ1 x,y,z displacement Functions y=f(t) of p1 p2 reference Point at the end of the axis dx2, dy2, dz2 amplitudes of the x,y,z displacements of point p2 fctX2, fctY2, fctZ2 x,y,z displacement Functions y=f(t) of p2

## Case #1: Radial displacement imposed with respect to the axis

loadingset.defineRad(gObject, Field1D(TX,RE), p1, p2, ampl, fct)
 gObject Geometric entity field name of the variable which is concerned by the motion ampl amplitude fct Functions y=f(t) (time dependence) p1 reference Point at the origin of the axis p2 reference Point at the end of the axis

## Case #2: Rotation imposed around the axis

loadingset.defineRot(gObject, field, p1, p2, option, ampl, fct)
 gObject Geometric entity field name of the variable which is concerned by the motion (only Field3D(TXTYTZ,RE) is allowed) ampl amplitude fct Functions y=f(t) (can depend on time and position) p1 reference Point at the origin of the axis p2 reference Point at the end of the axis option = False : the boundary condition is a given angle, in degrees = True : the boundary condition is a given angular speed, in degrees/second

## Case #3: 2 successive Rotations imposed around 2 axes

loadingset.defineRot2(gObject, field, axe1, ampl1, fct1,
axe2, ampl2, fct2, option)
 gObject Geometric entity field name of the variable which is concerned by the motion (only Field3D(TXTYTZ,RE) is allowed) axe1 first axis of rotation (Axe object). ampl1 amplitude of the first rotation fct1 Functions y=f(t) of the first rotation (can only depend on time) axe2 second axis of rotation (Axe object). The motion of this axis drives the global translation of the object ampl2 amplitude of the second rotation fct2 Functions y=f(t) of the second rotation (can only depend on time) option = False : the boundary condition is a given angle, in degrees = True : the boundary condition is a given angular speed, in degrees/second

The geometry is transformed in the following way:

• the rotation around the FIRST axis is applied to the object,
• then, the object is translated according to the SECOND axis motion,
• finally, the geometry is rotated around the SECOND axis.

In other words, it means that the second axis of defineRot2 behaves as the single axis of defineRot.