Requesting absAccel/absVel/absDisp

[oleviuqserh]

Hi Frank. Some few days ago, arbarbosa was asking about finding a way to record the absolute nodal accelerations of a given set of nodal DOFs by only using one recorder. In the following link, you can find a motivation drawn by himself, as well as, a potential solution proposed by myself to fit his needs. I think the solution I am proposing there seems to be quite better than the current approach of using the problematic -timeseries option; approach which for the time being has only been implemented in the interpreter to get the absolute nodal accelerations of one DOF at once.

[url] http://opensees.berkeley.edu/community/ ... =2&t=28614 [\url]

Thank you.

[fmk]

your approach is impossible due to the fact that the nodes have no concept of absolute or relative accelerations .. what the accelerations are at the nodes
depends on the LoadPattern. The only option for obtaining the absolute for multiple dof's with uniform excitation is for me to see if i can add multiple time series as input
to the recorder command.

[oleviuqserh]

Hi Frank. Thanks for the reply. I understand your point. My approach would only work if a seismic simulation is the intended case. However, in seismic simulations it would be very useful if a new recorder option is added to the interpreter to handle the absolute and relative accelerations as different queries. Similarly, the same could be done for the case of absolute/relative velocities, and the case of absolute/relative displacements.

For example,

recorder Node -file output1.out -time -absolute -node 1 -dof 1 2 3 accel
recorder Node -file output2.out -time -absolute -node 1 -dof 1 2 3 vel
recorder Node -file output3.out -time -absolute -node 1 -dof 1 2 3 disp

If the simulation is not a seismic one, then the interpreter would ignore the -absolute option that was defined in the recorder. Otherwise, it would compute the absolute response by summing the relative calculated response with the ground motion one.

The advantage of using this syntax is that the user will not have to deal with the time series tag anymore.

What do you think?

Thank you.

[fmk]

won't work .. it's too messy to implement for all possible cases, e.g. user requests absolute but only uniform provided in 1 dirn?, user requests relative in multi-support?? .. it's timeSeries or nothing (aka user does it himself externally)

[oleviuqserh]

I see. It is a challenging problem. In such a case, would you implement a -timeSeries option for the case of querying absolute displacements and absolute velocities. For the time being I guess it has not been implemented yet. Thank you.

[fmk]

it's there but it only takes 1 timeSeries at the moment .. i have to modify it to allow ndof timeSeries.

[arbarbosa]

Maybe what may be useful is something like the following command to output absolute accelerations (velocities and displacements, also) in X, Y and Z, for example:

recorder Node -file output.out -timeSeries $IDloadTagX $IDloadTagY $IDloadTagZ -time -node 1 -dof 1 2 3 accel

Thanks