Two-Dimensional Meshing

Although the material and element models are there, OpenSees is not well known for solid finite element analysis. Creating a good mesh is key to solid FEA and there aren't many meshing tools implemented in OpenSees. The OG block2D and block3D commands work fine, but you have to manually join or tie adjacent meshes with … Continue reading Two-Dimensional Meshing →

Work on Your Cliches

Before you tell your supervisor what you've done with OpenSees, you gotta work on your cliches. Cliches don't come from nowhere. For instance, Nuke learned his cliches from Crash before he used them in The Show. https://youtu.be/SB_LjL0lUJ4 Cliches for baseball, OpenSees, and life: Play them one day at a timeI'm just happy to be hereHope … Continue reading Work on Your Cliches →

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 →

Full Credit

I've been reading the Austin Kleon "trilogy on creativity" and making connections with OpenSees. In the second book, Show Your Work!, Kleon explains why and how you should always credit the creators of work you share. Or, in the world of OpenSees, the creators of work you remix then share. Sure, the creators of the … Continue reading Full Credit →

Happy Franksgiving

OpenSees is the result of Frank's giving. So send him an e-mail to say thank you. I knew this portmanteau would not be novel. After a quick Google search, I was surprised to learn that Franksgiving was an episode in United States history, ultimately leading to the holiday being celebrated on the fourth, instead of … Continue reading Happy Franksgiving →

Tips for Squandering OpenSees

I recently came across a blog post by Prof. Amy J. Ko on how tenured faculty can accelerate the demise of tenure. Applying the same sardonic tone, here are five ways you can ensure OpenSees will also be gone sooner rather than later. 1. Don't learn - A firm grasp of linear analysis is sufficient … Continue reading Tips for Squandering OpenSees →

Cable Analysis

Analyzing cables subject to transverse loads is straightforward in OpenSees. Use a mesh of corotational truss elements with elastic uniaxial material. Of course, you can use any uniaxial material you like. The only trick is you have to scramble the nodes up a little bit--if you try to analyze a perfectly straight cable, you'll get … Continue reading Cable Analysis →

Make a Pull Request

If a tree falls in a forest and no one is around to hear it, does the tree make a sound? If a model is coded in OpenSees and no one pushes it upstream on GitHub, does the model exist? Is there only the perception that the tree makes a sound and that the model … Continue reading Make a Pull Request →

Initial Conditions

There are a couple ways to set initial conditions for nodal displacements and velocities in OpenSees. If you look at the end of this post, you'll see the hard way to do it: set initial displacements as single point (sp) constraints in a load pattern, do one analysis step, then remove the load pattern prior … Continue reading Initial Conditions →

Monte Carlo Simulation

The uncertainty associated with a finite element analysis is as important, if not more important, than the results of the analysis itself. Thanks to Terje Haukaas, OpenSees has several modules for finite element reliability analysis: FORM, FOSM, SORM, and several other methods to quantify uncertainty. Unfortunately, those methods have not yet made their way into … Continue reading Monte Carlo Simulation →