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
Means and Ends
OpenSees is often a means to an end, or an instrument, with the end being an advanced degree. There is nothing wrong with that! But OpenSees can also be an end in itself. You can learn to automate workflows, to think algorithmically, and to manage data structures--all in the context of earthquake engineering. That end … Continue reading Means and Ends
Five Tweets from the Bot
The OpenSees Twitter bot is almost two years old. The bot has 356 followers, compared to 200 followers a year ago. Impressive OpenSees work continues to be tweeted. Here are five of the most recent tweets gleaned by @OpenSeesTweets. https://twitter.com/NHE_SimCenter/status/1460763867047501831 https://twitter.com/ccaprani/status/1459045946159812608 https://twitter.com/mikusscott/status/1451608792135651330 https://twitter.com/SilviaMazzoni_/status/1450195727783641088 https://twitter.com/6icees2021/status/1447127835261480960
Repeated Section Modes
If you use a section with linear-elastic response in the displacement-based, force-based, and mixed beam-column elements in OpenSees, you will get the same response from all three elements. TrueFalseIt depends The answer is it depends on the type of "section with elastic response" you use. Also, I wouldn't include "It depends" as a possible answer … Continue reading Repeated Section Modes
Trying to Get a Reaction
OpenSees does not compute reactions automatically because this can be a time consuming process--OpenSees assembles reactions over all nodes in a model, not just over the nodes that are constrained. When performing response history analysis, assembling reactions is likely not something you want or need to do at every time step. You probably just want … Continue reading Trying to Get a Reaction
RBOC: Influence Lines
Searching for books recently, this title caught my eye. I do not plan to read the book, but I bet the message goes something like this: Instead of posting the latest notch on your CV and/or flashy results that no one can comprehend, post useful content in order to get leads and customers instead of … Continue reading RBOC: Influence Lines
Inerters Everywhere
Vibration control devices based on relative acceleration, or inerters, are all the rage these days. So it's no surprise that inerter models are making their way into OpenSees. As far as I know, two inerter elements are available: InertiaTruss and Inerter. There has also been a third attempt at inerters, but via a material model. … Continue reading Inerters Everywhere
Portwood Digital 