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*Direct -method of nonlinear dynamic (seismic )analysis

*Direct -method of nonlinear dynamic (seismic )analysis

*Direct -method of nonlinear dynamic (seismic )analysis

(OP)
Hi all,
I believe some expert(s) on ABAQUS around here could answer this one:

I have a pipe modeled with shell elements(S8R).
The simultaneous loads are (1) internal pressure(2)ground acceleration time history.
The pipe is like a cantilever.ie.
One end of pipe is clamped(fixed,all dof zero)to the ground where the ground acceleration is input ,and the other end is free.

Since the material is workhardening(combined) I need to use Direct method of time integratin to solve this nonlinear problem.

(1)I can not fix all dof at one end at the same time apply acceleration at the same fixed end(conflicting boundary conditions)in the same step.Can I fix one end  and apply internal pressure in STEP-1 and
specify ground acceleration (at the same fixed end) in STEP-2,thus avoiding conflicting BCs?

(2) Alternatively can I do the same analysis without fixing any end,just by specifyng internal pressure, and ground motion at one end.?I tried this one out but there were warning saying moment was zero everywhere.

(3) or
Can apply fixed BC at one end in the model definition,and apply acceleration input at the fixed end and internal pressure  in STEP-1.When I do this way,the solution is going for some time and then there were warning and error messages(negative eigen values) and the program aborts.

The pipe is about 85mm mean dia and internal pressur is 10Mpa and acceleration is sine sweep with amplitude 4.5m/s^2 at 5HZ frewuency.

Any suggestions?

--brc--






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