As far as I know, OpenSees has no Easter eggs. But perhaps we should hide a few, e.g., to congratulate users who reach exactly zero for the norm of the residual or to deride those who use more than two integration points in a dispBeamColumn element. While you're waiting for OpenSees Easter eggs to be … Continue reading Egg-Centric OpenSees Jokes
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.
Statically Equivalent Loads
When it comes to numerical integration, OpenSees users either pay too much, or too little, attention. Me? I pay way too much attention to the topic. How else did OpenSees end up with so many integration methods for frame elements? But numerical integration is one of the concepts that users of OpenSees, or any other finite element analysis software, must understand. … Continue reading Statically Equivalent Loads
Apples and Oranges
Good articles on finite element formulations combine accessible theory with reproducible examples. One such article, Alemdar and White (2005), balances theory and examples for distributed plasticity frame element formulations quite well. I never did more than skim the article and give indirect, second hand citations over the years. So, when I recently rolled up my sleeves … Continue reading Apples and Oranges
Section Warping Analysis
Loading a ZeroLengthSection element is the easiest approach to compute the moment-curvature and shear force-shear deformation response of fiber sections in OpenSees. However, we cannot do a section warping analysis with a zero length element like we can with non-warping sections--at least not without modifying the ZeroLengthSection element to handle seven DOFs per node. That source code modification is … Continue reading Section Warping Analysis
OpenSees Blogs Well
You know the active voice, where the subject performs an action. The graduate student analyzed the model. Here the subject is the graduate student. And you also know the passive voice, where the subject is affected by an action. The model was analyzed by the graduate student. Now the subject is the model. But do … Continue reading OpenSees Blogs Well
OpenSees Coming and Going
Years ago, one of those shows like Diners, Drive-Ins, and Dives featured a greasy spoon somewhere in middle America famous for its eggs and fried chicken meal known as the “Coming and Going”–the boundary conditions of a chicken’s life on a single plate. This quarter in Eastchester, I am teaching the introductory undergraduate course in structural analysis and the … Continue reading OpenSees Coming and Going
One Is All You Need
It is fairly well known that you can use a single force-based element to simulate the material nonlinear response of a frame member. Likewise, using a corotational mesh of displacement-based elements is an effective approach to simulate combined material and geometric nonlinearity. A previous post looked at geometric nonlinearity with linear-elastic response in a single … Continue reading One Is All You Need
Two Node Link’s Awakening
The twoNodeLink, implemented by Andreas Schellenberg, is one of the lesser utilized general purpose elements in OpenSees. In simple terms, the twoNodeLink element is a zeroLength element with length. And the element is not dis-similar to the link elements you will find in SAP. Like the zeroLength element, the twoNodeLink element uses uncoupled uniaxial materials to define force-deformation response between two nodes where the deformation … Continue reading Two Node Link’s Awakening
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
Which Noun Are You Modifying?
Thanks to Google Scholar citation alerts, I see all the published articles that cite OpenSees. Most of the titles make no sense and on the rare occasion that a title looks interesting, I'll click the link and read the abstract. Today's citation alert delivered to my inbox an article whose title stood out, not for … Continue reading Which Noun Are You Modifying?
Portwood Digital 