Integrators DsiplacementControl and ArcLength

laskar · Post by **laskar** » Thu May 08, 2008 11:03 am

Is the arc length scheme implemented in the DisplacementControl Integrator in OpenSees?

If so what is the difference between the Integrators DispacementControl and ArcLength available in OpenSees.

silvia · Post by **silvia** » Thu May 08, 2008 12:25 pm

i don't think it is.

laskar · Post by **laskar** » Thu May 08, 2008 12:46 pm

I checked the source code for DisplacementControl Integrator on OpenSees. The description of DisplacementControl Integrator given in the code is as follows:

// Description: This file contains the class definition for DisplacementControl.
// DisplacementControl is an algorithmic class for perfroming a static analysis
// using the arc length scheme, that is within a load step the follwing
// constraint is enforced:
// i=1 delta U^T delta U + alpha^2 delta lambda^2 = delta s^2
// i>1 dU^T delta U + alpha^2 dLambda delta lambda = 0
// where dU is change in nodal displacements for step, dLambda is
// change in applied load and DisplacementControl is a control parameter.
//

Due to this I am confused about the difference between the DisplacementControl and ArcLength Integrators. I am also wondering how a user can perform analysis using DisplacementControl without arc length scheme?

mhscott · Post by **mhscott** » Thu May 08, 2008 1:16 pm

It's very likely the documentation was copied from ArcLength eventhough the implementations are different. The DisplacementControl in OpenSees is "iteration at constant displacement" in the following reference.

@article{Clarke:1990,
author = {M. J. Clarke and G. J. Hancock},
title = {A Study of Incremental-Iterative Strategies for Non-Linear Analyses},
journal = {International Journal for Numerical Methods in Engineering},
volume = {29},
pages = {1365--1391},
year = 1990
}

laskar · Post by **laskar** » Thu May 08, 2008 1:32 pm

Thank you for your reply. Could you please tell me if it is possible to perform analysis using DisplacementContol in OpenSees along with the ArcLength Scheme?
If yes, please let me know how it can be done? Do we need to simultaneously use the two integrators in that case:
i.e first Integrator DisplacementControl ....
then Integrator ArcLength ....

Could you also let me know what inputs need to given for the $arclength and $alpha parameters needed to create an ArcLength Integrator?

mhscott · Post by **mhscott** » Thu May 08, 2008 6:49 pm

The parameters come straight from the paper. You can only use one integrator at a time, so you should stick with arc-length.