Product: Abaqus/Explicit
User subroutine VDISP:
can be used to prescribe translational and rotational boundary conditions;
is called for all degrees of freedom listed in the associated boundary condition;
allows user to specify values for either the degree of freedom or its time derivatives such as velocity and acceleration;
releases the boundary condition by default if the user does not specify a value for the boundary condition;
can be used to apply a concentrated load, instead, by adjusting the default motion of the node;
can be called for blocks of nodes for which the boundary conditions are defined in the subroutine.
At the beginning of each step user subroutine VDISP is called once to establish the initial velocity; and then, it is called once on each configuration, including the initial configuration, to establish the nodal acceleration.
The first call to user subroutine VDISP is made to establish the initial velocity, which is indicated by the passing of a step time value of 
into the subroutine, where 
is the current time increment. If displacement is prescribed, the returned variable, rval, corresponds to 
, where 
and 
are the initial displacement and velocity respectively. If velocity is prescribed, the returned variable corresponds to the initial velocity . If acceleration is prescribed, the returned variable corresponds to 
where is the initial velocity.
The default value of rval is consistent with the velocity at the end of previous step or that specified as an initial condition in case of the first step. You only need to reset the rval if a different initial velocity is desired. The arrays u and v stand for the default initial displacement and velocity, respectively. The array a contains a zero value.
During time incrementation user subroutine VDISP is called once for each configuration, including the initial configuration, to establish the nodal acceleration.
If displacement is prescribed, the returned variable should be set equal to the displacement at stepTime+dtNext, where stepTime is the step time and dtNext is the next time increment. If velocity is prescribed, the returned variable should be set equal to the mean velocity at stepTime+dtNext/2. If acceleration is prescribed, the returned variable should be set equal to the acceleration at stepTime. Note that stepTime is zero for the initial configuration.
The variable rval has a default value that is computed as if the boundary condition is released. You only need to reset the rval if the boundary condition is active. The variable u contains values at stepTime. Whereas, the variable v contains initial velocity when stepTime is zero and, otherwise, velocity at stepTime—dt/2. The variable a contains values at stepTime computed as if the bondary condition is released.
Tip: If you wish to apply a concentrated load, instead of the boundary condition, you can compute the change in acceleration due to this load and modify the rval value to account for that change. Note that the nodal mass and the rotary inertia are available in VDISP for computing the change in acceleration. Also, note that the default value of rval already reflects all other forces acting at the node.
subroutine vdisp(
c Read only variables -
1 nblock, nDof, nCoord, kstep, kinc,
2 stepTime, totalTime, dtNext, dt,
3 cbname, jBCType, jDof, jNodeUid, amp,
4 coordNp, u, v, a, rf, rmass, rotaryI,
c Write only variable -
5 rval )
c
include 'vaba_param.inc'
c
character*80 cbname
dimension jDof(nDof), jNodeUid(nblock),
1 amp(nblock), coordNp(nCoord,nblock),
2 u(nDof,nblock), v(nDof,nblock), a(nDof,nblock),
3 rf(nDof,nblock), rmass(nblock), rotaryI(3,3,nblock),
4 rval(nDof,nblock)
c
do 100 k = 1, nblock
do 100 j = 1, nDof
if( jDof(j) .gt. 0 ) then
user coding to define rval(j, k)
end if
100 continue
c
return
endrval(nDof, nblock)
Values of the prescribed variable for degrees of freedom 1–6 (translation and rotation) at the nodes. The variable can be displacement, velocity, or acceleration, depending on the type specified in the associated boundary condition. The variable type is indicated by jBCType. The variable rval has a default value that is computed as if the boundary condition is released. You only need to reset the rval if the boundary condition is active.
nblock
Number of nodal points to be processed in this call to VDISP.
nDof
Number of degrees of freedom (equals 6).
nCoord
Number of coordinate components (equals 3).
kstep
Step number.
kinc
Increment number.
stepTime
Value of time since the step began.
totalTime
Value of total time. The time at the beginning of the step is given by totalTime-stepTime.
dtNext
Next time increment size.
dt
Current time increment size.
cbname
User-specified name corresponding to the associated boundary condition.
jBCType
Indicator for type of prescribed variable: 0 for displacement, 1 for velocity, and 2 for acceleration.
jDof(nDof)
Indicator for prescribed degrees of freedom. The values given by rval(j,k) are prescribed only if jDof(j) equals 1.
jNodeUid(nblock)
Node numbers.
amp(nblock)
Amplitude values corresponding to the associated amplitude functions. These values are passed in for information only and will not contribute to the values of the prescribed variable automatically.
coordNp(nCoord, nblock)
Nodal point coordinates.
u(nDof, nblock)
Initial displacements when stepTime is negative, and, otherwise, displacement at stepTime. All translations are included if one or more translational degrees of freedom are prescribed. All rotations are included if one or more rotational degrees of freedom are prescribed.
v(nDof, nblock)
Initial nodal velocities when stepTime is non-positive and, otherwise, mean velocities at stepTime-dt/2 during time incrementation. All translational velocities are included if one or more translational degrees of freedom are prescribed. All angular velocities are included if one or more rotational degrees of freedom are prescribed.
a(nDof, nblock)
Contains a zero value when stepTime is negative and, otherwise, the accelerations, computed without accounting for the boundary condition, at stepTime. All translational accelerations are included if one or more translational degrees of freedom are prescribed. All angular accelerations are included if one or more rotational degrees of freedom are prescribed.
rf(nDof, nblock)
Nodal point reaction at stepTime-dt. All reaction forces are included if one or more translational degrees of freedom are prescribed. All reaction moments are included if one or more rotational degrees of freedom are prescribed.
rmass(nblock)
Nodal point masses.
rotaryI(3, 3, nblock)
Nodal point rotary inertia.
In this example a sinusoidal acceleration is imposed on the reference node of a rigid body. Nonzero initial velocity is also specified for the rigid body. User subroutine VDISP given below illustrates how the return value array is to be computed for different phases of the solution. The analysis results show that both the initial velocity and acceleration are correctly specified.
Input file
*HEADING Test VDISP with S4R element *NODE, NSET=NALL 1, 2, 2., 0. 3, 0., 2. 4, 2., 2. 9, 1., 1., 0. *ELEMENT, TYPE=S4R, ELSET=SHELL 10, 1,2,4,3 *SHELL SECTION, ELSET=SHELL, MATERIAL=ELSHELL 2.0000000e-02, 3 *MATERIAL, NAME=ELSHELL *DENSITY 7850.0, *ELASTIC 2.5000000e+11, 3.0000000e-01 *RIGID BODY, REF NODE=9, ELSET=SHELL *INITIAL CONDITIONS, Type=VELOCITY 9, 1, 0.4 *STEP *DYNAMIC, EXPLICIT, DIRECT USER CONTROL 0.01, 0.8 *BOUNDARY, USER, TYPE=ACCELERATION 9, 1 *OUTPUT, HISTORY, TIME INTERVAL=0.01, OP=NEW *NODE OUTPUT, NSET=NALL U, V, A *END STEP
User subroutine
subroutine vdisp(
c Read only variables -
* nblock, nDof, nCoord, kstep, kinc,
* stepTime, totalTime, dtNext, dt,
* cbname, jBCType, jDof, jNodeUid, amp,
* coordNp, u, v, a, rf, rmass, rotaryI,
c Write only variable -
* rval )
c
include 'vaba_param.inc'
parameter( zero = 0.d0, half = 0.5d0, one = 1.d0 )
c
character*80 cbname
dimension jDof(nDof), jNodeUid(nblock),
* amp(nblock), coordNp(nCoord,nblock),
* u(nDof,nblock), v(nDof,nblock), a(nDof,nblock),
* rf(nDof,nblock), rmass(nblock),
* rotaryI(3,3,nblock), rval(nDof,nblock)
c
c Impose acceleration
c
if( jBCType .eq. 2 ) then
c
if( stepTime .lt. zero ) then
c
c Initialization 1
c
do 310 k=1, nblock
do 310 j=1, nDof
if ( jDof(j) .gt. 0 ) then
v0 = v(j,k)
rval(j,k) = v0/dt
end if
310 continue
c
else
c
c Time incrementation
c
amplitude = 2.0
period = 0.8
twopi = 6.2831853d0
c
do 350 k=1, nblock
do 350 j=1, nDof
if ( jDof(j) .gt. 0 ) then
rval(j,k) = amplitude*
* sin( twopi*stepTime / period )
end if
350 continue
end if
end if
c
return
end