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In an ANSYS/LS-Dyna analysis it is often desirable to apply a displacement load without generating a shock load, especially during quasi-static analyses. This is done by minimizing the force, and thus the acceleration applied to the part. If a displacement load is ramped on as a linear curve, it applies a non-zero velocity at the beginning of the transient, which effectively applies a very large acceleration load.
CAE Associates has written a macro that will convert a displacement load into a smooth, sinusoidal velocity curve which minimizes the acceleration load. The macro, called 'dynload.mac', is called with the following input arguments:
ARG1 = timea (starting time for the load)
ARG2 = timeb (ending time for the load)
ARG3 = disp1 (starting displacement at timea)
ARG4 = disp2 (ending displacement at timeb)
ARG5 = final time point in the analysis (tfinal)
ARG6 = 1 or 0 (0 = apply displacement and hold)
(1 = apply displacement and reverse)
ARG7 = name of the time vector
ARG8 = name of the velocity vector
For example:
dynload, 0, 0.001, 0, 5., 0.0011, 1, 'DT', 'VEL'
• Creates a vector DT with time points from 0 to 0.0011 and vector VEL with
velocities that will result in a maximum displacement of 5. The velocity vector
will reverse (go negative) to produce a final displacement of 0.
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