Better than Ideal Conditions

In simulating the nonlinear response of structural models, the Newton-Raphson algorithm converges quadratically as the iterations approach equilibrium at a time step. Quadratic convergence means the error at the current iteration is less than some constant times the square of the error at the previous iteration, e.g., the error is on the order of $latex … Continue reading Better than Ideal Conditions

Incompetence, Not Malice

"Never attribute to malice that which can be explained by incompetence" is a form of Hanlan's razor, an aphorism that explains many actions in academia and elsewhere. For example, we often perceive omissions of important details in published work as intentional acts to prevent reproduction of the research. In some cases, this is true, while … Continue reading Incompetence, Not Malice

Non-Convergence Does Not Mean OpenSees Crashed

I once had the following conversation with a concerned user (CU) of OpenSees: CU: "I was running a response history analysis, then all of a sudden OpenSees crashed."PD: "Really, it crashed? Did you get the blue screen of death?"CU: "No. The analysis stopped and I saw 'Failed to converge'. It crashed."PD: "Oh, I see. What … Continue reading Non-Convergence Does Not Mean OpenSees Crashed

Be Careful with Modal Damping

Modal damping is kind of the it-spell in the dark art that is modeling viscous damping in structures. Although modal damping is pretty straightforward, you should be aware of an important aspect of its implementation in OpenSees. The issue is that OpenSees assembles the dynamic tangent in to the matrix storage scheme you choose via … Continue reading Be Careful with Modal Damping