Faux Contact Sport

In a similar take on sprung masses and friction, it turns out that ENT+InitStrain in a zero length element is also an easy way to fake one-dimensional contact and impact. Consider Problem 14-23 from Hibbeler 14th edition. An 8 kg block, 2 m from a spring of stiffness 200 N/m, is given an initial velocity … Continue reading Faux Contact Sport →

Two Sprung Masses and Some Friction Force

In Problem 13-13 from Hibbeler 14th edition, blocks A and B, of weight 8 lb and 6 lb, respectively, rest on a flat surface. A spring of stiffness 20 lb/ft is placed between the blocks. The blocks are pushed together, compressing the spring 0.2 ft, then the blocks are released to slide along the surface. … Continue reading Two Sprung Masses and Some Friction Force →

Centripetal Acceleration

How can you induce element forces without defining loads or straining effects due to thermal expansion, residual stress, initial strain, or differential support motion? Centripetal acceleration! Get a mass revolving in a plane about a fixed point and a force directed radially (toward the center of revolution) is required to keep the mass from flying … Continue reading Centripetal Acceleration →

Minimal Thermal Example

For verification purposes, I needed to come up with the fixed-end axial force for a beam subjected to uniform thermal expansion. It's not rocket science, nowhere near an LPU, but a little pencil and paper and the free end axial deflection is $latex \alpha (\Delta T) L$. The fixed-end axial force, to push the free … Continue reading Minimal Thermal Example →

Projectile OpenSeesing

Growing up in the Pine State, you were either a fan of NASCAR or college basketball, and in some cases both. I leaned heavily toward the latter. The hard dynamics underpins the physics of both sports--and most others. Centripetal forces act on race cars going around turns and projectile motion is a simplified description of … Continue reading Projectile OpenSeesing →

How to Use with with OpenSeesPy

The with command offers a clean approach to manage Python resources, particularly file streams. Without going into detail, the with command is a shortcut for exception handling. The nice thing about reading and writing files using the with command is you don't have to worry about closing the file stream. Immediately after the with block … Continue reading How to Use with with OpenSeesPy →

No Element Required

Simulating basic particle motion raises subtle, often overlooked points about OpenSees. For example, consider problem 12-1 from Hibbeler's Engineering Mechanics: Dynamics, 14th edition. A particle moves along a straight line with acceleration a=(2t-6) m/s2. What is the velocity at t=6 s and displacement at t=11 s? Assume at rest initial conditions. By integration, the exact … Continue reading No Element Required →

The Hard Dynamics

I am confident that you can use OpenSees to solve all reasonable problems from textbooks on statics, structural analysis, finite elements, structural dynamics, and (most of) strength of materials. But what about engineering dynamics? The rigid body dynamics that's way more difficult than deformable body dynamics. You know, kinematics and kinetics of particles and rigid … Continue reading The Hard Dynamics →

2023 In Review

WordPress put together a year-in-review summary of blog statistics, but the automated report had a couple errors--namely reporting that April 24, 2023 accounted for 817% of all blog visits for the year and that the high number of referrals from Facebook was "a nod to our [WordPress's] targeted SEO and marketing efforts." Despite the error … Continue reading 2023 In Review →

A Better Way to Find Memory Leaks in OpenSees

In a previous post, I explained how to find a memory leak in OpenSees. The basic idea was to put the analysis inside a loop, run the loop a million times, and monitor your operating system for increasing memory usage. A perfectly fine leak hunting approach--as long as you are willing to monitor your operating … Continue reading A Better Way to Find Memory Leaks in OpenSees →