A Few “Words” on Memory Settings in 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…

October 27, 2006 | by

Best Practices for Modeling Recoverable Low Density Foams – By Example

Attachments:mat57_default.k Modeling recoverable foams poses several challenges in crash worthiness as well as in low-to-medium impact velocity conditions. This is due to its relatively low stiffness when compared with structural materials which has an indirect effect on its contact-impact interactions with other materials. To review the best practices when modeling such components, we can consider…

October 12, 2006 | by

Storing Re-Usable Models in a Central Location with *INCLUDE_PATH

Beginning version 971 and later, LS-DYNA allows easy way to store models in a central location for use at run time. This feature can be turned on using *INCLUDE_PATH which takes unlimited number of absolute directory names. When INCLUDE_PATH is used, LS-DYNA first checks the file, specified using *INCLUDE keyword, in the local directory and…

October 12, 2006 | by

Simulation Based Product Design Using LS-DYNA – Single Code & Single Model Benefits

Over the past decade, the ability of simulations driving the design has grown rapidly and today’s confidence in simulations results is a good testament to it. Two significant areas that have contributed to this is the “Numerical Modeling Awareness” and “Design Domain Knowledge” gained over the years by design and analysis community. Numerical modeling awareness…

October 6, 2006 | by

Implicit Dynamics – Now with Birth, Death, and Burial Properties

When solving static or quasi-static type problems, the default Implicit Static solver (IMAS=0 in CONTROL_IMPLICIT_DYNAMICS) requires a well-conditioned model, with no rigidbody modes, to get good convergence behavior. It is often difficult to prevent rigidbody modes especially when its dependent on contact-impact conditions. In such cases, use of Implicit Dynamics solver (IMAS=1) can help us…

October 3, 2006 | by

Overview of Mass-Scaling in LS-DYNA

Mass-scaling is a term that is used for the process of scaling the element’s mass in explicit simulations to adjust its timestep. The primary motivation is to change (usually increase) the global compute timestep which is limited by the Courant’s stability criteria. LS-DYNA allows two different types of mass-scaling using the DT2MS parameter from *CONTROL_TIMESTEP…

October 2, 2006 | by

Identifying Problem Areas for Poorly Converging Implicit Solutions

For non or poorly converging implicit solutions, the parameter D3ITCTL parameter in *CONTROL_IMPLICIT_SOLUTION may come handy to isolate regions of interest. When D3ITCTL is non-zero, LS-DYNA outputs the model information at each Iterative step into a binary file named D3ITER which is in the same format as D3PLOT. The number of steps for which the…

September 21, 2006 | by

Use of *SENSOR in LS-DYNA 971

A powerful new feature available in LS-DYNA version 971 is the *SENSOR keyword. To briefly summarize the Keyword Manual description, *SENSOR allows boundary conditions and various model entities to be activated/deactivated based on element, force, and/or node based criteria. Options are available for modeling very elaborate systems, but we will focus on a very simple…

September 10, 2006 | by

LS-DYNA Simulation Template

Using the newly implemented feature of embedding FORTRAN type expressions in LS-DYNA using the *PARAMETER_EXPRESSION keyword, it is becoming easier to develop analysis templates that can provide flexible ways of changing analysis settings. A partial input file highlighting the possibilities is shown below, and the full file is available here: main.k. Using this as a…

September 8, 2006 | by

Ensuring Stable, Robust, and Accurate LS-DYNA Models

LS-DYNA simulation models, both large and small, frequently suffer from undetected modeling errors that can cause runs to die prematurely. Sometimes even minor model changes can introduce stability issues indicating a lack of robustness. Runs that die prematurely squander significant resources, something which I generally refer to as “simulation wasteâ€?. A recently developed procedure that…

August 31, 2006 | by