Details of the uniformExcitation pattern

[mlw]

Hi everyone,

I have been using the uniformExcitation pattern to simulate dynamic loading and notice that it allows for acceleration amplification/attenuation through the the soil/structure.
Where can I find more details as to how the uniformExcitation pattern is implemented in OpenSees?

Thanks

mlw

[vesna]

Here you will find header and cpp files of the UniformExcitation class:
http://opensees.berkeley.edu/WebSVN/lis ... fdacf15f65

[mlw]

Vesna,

Thank you for your reply.
Could you please clarify my understanding of the computer code presented on the link which you provided:

1) At time step=0 the velocity of all nodes is set to zero
2) The velocity at time step=1 is calculated from the uniformExcitation pattern acceleration at time step=1, and applied to all the nodes which are free in the dof of the uniformExcitation pattern.
3) The node velocities are iteratively adjusted considering the stiffness of the model until convergence is achieved.
4) The node velocity array is updated to the new velocity of each node at the end of time step=1
5) The velocity at time step=2 is calculated from the uniformExcitation pattern acceleration at time step=2, and applied to all the nodes + the node velocity array from the previous time step.
6) The node velocities are iteratively adjusted considering the stiffness of the model until convergence is achieved.
7) The node velocity array is updated to the new velocity of each node at the end of time step=2
etc

Is this understanding correct?

Much thanks
mlw

[fmk]

nope:

assuming you are using Newmark, a newton iteration strategy & uniform exciatation
1. at time step 0 nodal disp, vel & accel are set to 0.
2. at each time step dT:
a. loads are applied (-MAg contribution from Uniform exciatation) & unbalanced force, dR, is determined (resisting force - applied forces)
b. tangent, A, is formed based on current state, Newmark factors, dT & rayleigh factors if any
c. incremental disp is determined, = inv(A)*dR
d. incremental vel & accel is determined from Newmark based on incremental disp
e. nodes are incremented with the disp, vel & accel increments & element state updated
f. unbalanced force is again determined
g. go to b) if convergence not achieved.

[mlw]

Thank you, the description has made the process clear.

mlw