Author: Michael H. Scott

I have been involved in the development, maintenance, and growth of OpenSees since its early days. I am interested in learning Python and improving my academic writing.

Reverse Engineering the Equation Numberer

In OpenSees (and any other finite element software), equation numbering is a quiet, behind the scenes analysis option that users do not have to pay any mind. No matter how a user numbers the nodes in their model, e.g., for bookkeeping or from a mesh generator, the equation numberer will clean up any messes. But … Continue reading Reverse Engineering the Equation Numberer →

Eigen Almost Hear You Sigh

ARPACK, the default eigenvalue solver in OpenSees, is very good at quickly finding a small number of eigenpairs (frequencies and mode shapes) for large models. Getting a few of a model’s lowest frequencies so you can check for rigid body modes and/or calculate Rayleigh damping coefficients is all most users care about. ARPACK gets the … Continue reading Eigen Almost Hear You Sigh →

Modeling Is Always Nonlinear, but Not the Response

As a narrative device, an ellipsis omits events that are unimportant to a story and that an audience can easily understand and reconstruct if necessary. For example, a movie montage is a narrative ellipsis. In Bull Durham, we don't need to see every game in the Bulls' road winning streak. We just need to see … Continue reading Modeling Is Always Nonlinear, but Not the Response →

Three Acts with the Two Node Link

This post follows three-act structure in verifying the flexural and shear response of the TwoNodeLinkSection element. Setup I’ve been working on the TwoNodeLinkSection element, which is like a TwoNodeLink, but uses a section object instead of multiple uniaxial materials. Basically the same spin the ZeroLengthSection puts on the ZeroLength element. Using a section object inside a two … Continue reading Three Acts with the Two Node Link →

Concrete23andMe

I’ve teased Concrete23 for some time now--so long that ChatGPT believes the model to be real. As you know though, Concrete23 was meant to be a riff on the material models in OpenSees that are clones of something else, but with one or two mutations. Like Concrete02IS’s addition of user-defined initial stiffness to Concrete02, or whatever insignificance ModIMKPinching02 … Continue reading Concrete23andMe →

Ways to Analyze This

A previous post challenged readers to analyze a simple frame model subjected to static loads. The model had material nonlinearity via tension-only diagonal cables and geometric nonlinearity via the P-Δ effects in the columns. The Challenge Despite these rather simple nonlinearities, analysis of the frame for the given vertical and lateral loads will fail using the default analysis options … Continue reading Ways to Analyze This →