Damping Is a Sensitive Subject

Dynamic response sensitivity analysis by the direct differentiation method (DDM) works pretty well in OpenSees, minus a couple limitations. First, not all element and material models implement the methods necessary to compute response sensitivity with respect to model parameters. And second, even fewer element and material models implement the methods necessary to compute the sensitivity … Continue reading Damping Is a Sensitive Subject →

A Return to FORM

The structural reliability modules Terje Haukaas implemented in OpenSees comprised one of the last groups of commands to be ported from Tcl to Python. So, performing reliability analysis in OpenSeesPy has been slow to catch on. But the porting is done and there are some slight differences between Tcl and Python. This post shows basic … Continue reading A Return to FORM →

The Sensitivity Is in the Details

Although the Hardening and Steel01 uniaxial materials can be calibrated to give the same response, the DDM response sensitivity with respect to the same parameter can be different due to how the material models are implemented. Consider the truss model from a previous post on minimal DDM examples. The stress-strain response shows the elastoplastic tangent … Continue reading The Sensitivity Is in the Details →

You Never Forget

My first journal article was not without some minor drama. Another group of researchers was also in pursuit of the direct differentiation method (DDM) formulation for force-based frame elements. Mutually aware of the parallel efforts, one of those researchers went so far as to call me on a public landline in Davis Hall with a … Continue reading You Never Forget →

Minimal DDM Examples

Although it was the subject of my first journal article and has been a welcome diversion since, other than one post, the direct differentiation method (DDM) has not seen much action on the blog. With the DDM, you can compute accurate and efficient derivatives of the structural response with respect to various model and load … Continue reading Minimal DDM Examples →

Finite Differences

A previous post showed how to compute response sensitivity by the DDM, or direct differentiation method. Comparisons with finite difference calculations verified that the DDM results were correct. In this post, I'll dig a little deeper into finite differences. The advantage of the finite difference method (FDM) is it will work for any model parameter--you … Continue reading Finite Differences →

Sensitivity Training

Sensitivity of structural response with respect to modeling parameters provides search directions for gradient-based algorithms in reliability analysis, optimization, and system identification. In addition to these applications, stand-alone sensitivity analysis gives useful information about the effect of parameters on the structural response. There are three methods to compute response sensitivity for nonlinear, path-dependent analysis of … Continue reading Sensitivity Training →