jaabell

Paper04 - Modelling the cyclic ratcheting of sands through memory-enhanced bounding surface plasticity.

This is the first paper fruit of the on-going collaboration with Federico Pisanò at TU Delft. Here we tackle the problem of formulating a constitutive model, derived from the SAniSand framework by Yannis Dafalias, which can replicate the ratcheting phenomenon on sands.

What is ratcheting?

Large earthquake in Mexico triggers tsunami warnings

The magnitude I gave came from the Tsunami threat record. pic.twitter.com/2h5dppVLLQ

— José A. Abell 🇻🇦🇨🇱 (@jose_abell) June 23, 2020

#EngineeringWizardry | 00 | new series

Stuck teaching during COVID-19 lockdowns in Chile has reminded me one crucial thing about statics (the class I'm teaching this first semester in the southern hemisphere): it can be very frustrating for students. This frustriation comes from unmet expectations. They're just finishing their early maths and physics formation (Calculus, Linear Algebra, Differential Equations, physics etc. ), an ideal world where problems have nice answers such as \(\sqrt{2} \pi\) or no answer at all. Then, along comes statics, and the world seems upside down.

Using my gmshtranslator python tool to interface gmsh with opensees.

I wrote the gmshtranslator tool a while back during my …

Paper03 - Earthquake Soil Structure Interaction of Nuclear Power Plants, differences in response to 3-D, 3 × 1-D, and 1-D excitations

Summary: Finally! First paper since PhD was accepted for publication …

Video of 2-D SSI model of an RC Shear Wall Building

The RC shear-wall building is modeled in OpenSees using non-linear fiber based beam column elements. Soil is modeled as a continuum using quad elements and linear stress-strain relationship. Soil shear wave-speed is varied in depth such as to obtain a \(V_{s30}\) consistent with a class B site according to chilean seismic code. Lysmer-Kulhemeyer dashpots are used along the soil boundary to model seismic radiation and earthquake wave-field input.

The performance of the building will be assessed for varying site fundamental periods. This is an aspect of SSI that is not covered by the chilean seismic code, and has been shown to be a problem in past earthquakes.

This is part of an on-going study with Prof. Carolina Magna from Adolfo Ibañez Unversity and her MS student Miguel Ángel Rodriguez from UDP.

New cable element in OpenSees

With my student, Pablo Ibañez, we implemented a new catenary cable element in OpenSees. This element is based on the work by Salehi et al[1].

The stiffness of this element is obtained using a flexibility formulation. Basically the shape of the cable is determined by the integral:

Where \(\vect{x_1}\) is the position of the first node of the cable, \(\vect{w}\) is the weight vector in each direction, \(EA\) is the stiffness, \(\alpha \Delta T\) is the change in strain due to temperature and \(\vect{f}\) is the force vector at the start node. This equation is iterated (with the forces as variable) upon until the the shape of the cable matches the nodal postiions imposed by the finite element program (trial displacements). Then it is used to derive a stiffness matrix.

The element, as is, passes all our static verification tests. With the additional assumption of a lumped-mass matrix, we're currently working on a dynamic verification suite as well as some validation experiments.

The animation above was created using OpenSees to simulate the cable and Blender to render it.

Reference

[1] Salehi Ahmad Abad, M., Shooshtari, A., Esmaeili, V., & Naghavi Riabi, A. (2013). Nonlinear analysis of cable structures under general loadings. Finite Elements in Analysis and Design, 73, 11–19. https://doi.org/10.1016/j.finel.2013.05.002

OpenSees coming to python!

One of the gripes a lot of people have with …

Finite Elements for Shallow Water Equations

Talk Given at IngeoKring 2016 - Physics-Based Earthquake-Soil-Structure Interaction for Near-Field Induced Seismicity

This is a talk given at the IngeoKring 2016 Autumn …

NTS-02. On Rayleigh damping coefficients for FE analysis

Testing IPython Notebook integration into Pelican

SNE # 01. Example of ESSI simulation and visualization with visitESSI

These are the results of a simple elastic-domain simulation. Mesh …

NTS (Note-To-Self): Creating dynamically linked libraries

A nice extensive tutorial can be found here.

In a …

SNE # 0. Stochastic inverse pendulum

This is the first installment of "Small Numerical Experiments" (SNE …