LS-DYNA offers several ways to prescribe a motion to a rigidbody using *BOUNDARY_PRESCRIBED_MOTION keyword. To prescribe a motion to a rigidbody along a local coordinate system, LS-DYNA offers two method to accomplish this. To demonstrate the differences in these two methods, we will consider a rigidbody that has initial rotational velocity and a prescribed displacement.…
Over the years, spotweld representation for crash and NVH applications have evolved from a crude to a detailed modeling resulting in reduced pre-processing effort while greatly enhancing the accuracy of numerical models. Here is link that gives a brief overview of spotwelding process in LS-DYNA. Please note that the document is over 2 years old…
In many designs, parts are often press-fitted as part of an assembly which causes an initial stress condition that is important to consider in simulations. To induce initial stresses that occur in such press-fit conditions, one can either linearly/non-linearly scale the overlap (penetration) or the contact stiffness over a certain interval depending on the following…
When running explicit simulations in LS-DYNA, it is very important to understand the total CPU clock and the total Elapsed time used by the solver. This information is available at the bottom of every D3HSP file written by LS-DYNA as shown below. The total elapsed time reported in the file is the difference between the…
When running problems using Implicit solution sheme in LS-DYNA, the default iterative non-linear solver used is the BFGS method that employs a ‘Quasi-Newton’ method in which the global stiffness matrix is reformed only every ILIMIT steps and in between these a relatively inexpensive update to the stiffness matrix is performed. This default stiffness matrix update…
When simulating airbag deployment, using the classical uniform-pressure (CONTROL VOLUME) or non-uniform-pressure (ALE, Particle), users frequently encounter oscillations. These oscillations are generally categorized as local and global. To reduce both forms of oscillations, LS-DYNA provides two types of damping that are briefly discussed here. 1. Mass-Weighted-Damping The parameter MWD in *AIRBAG_{OPTION} keyword provides a means…
LS-DYNA is a general purpose finite element software and is designed for use in various applications. Based on the use of the software for a specific application, LS-DYNA offers several parameters that can be changed from their default values to improve the accuracy, robustness, and stability of the simulation. For performing crash analysis using LS-DYNA,…
Memory in LS-DYNA is specified in “words” at the execution time. The term “word” refers to the amount of data that can be written to or read from a memory in one operation. The following figure will aid in the relationships of bits, the most basic data type, to words on various computers. One bit…
Discrete springs provide a easy way to model complicated systems by using their responses in the material definitions. This post brings attention to the way LS-DYNA handles the default behavior in tension or compress when the material input does not pass through the origin (0,0) but simply begins from origin. When only one of either…
LS-DYNA supports various joint definition types such as spherical, cylindrical, etc (please refer to the LS-DYNA User’s manual for a complete list). Irrespective of the joint definition type and the elements associated, translational constraints are applied to the joint nodes to model appropriate behavior. The constraints are applied using the default penalty formulation whose stiffness…
