In the area of numerical simulations involving the use of airbags to absorb impact energy, passively or actively, accurate definitions of airbag leakage parameters play a crucial role in predicting the response of impacting objects (ex. occupants). LSDYNA provides various options for airbag leakage modeling that may appear overwhelming at first but are actually quite…
Element count in finite element simulations are increasing faster than the “Moores law” used in chips. There are several reasons for this increase among which the single-model-multi-loadcase philosophy is certainly one of them. Earlier approach of building load-case-dependent models were both cumbersome, data duplication and big challenges for design change integrations. In today’s simulations, one-model…
This post will give you a brief summary of one-way and two-way contact definitions. The one-way/two-way refers to the treatment of slave nodes impacting the master segments. One-Way Contacts One-way was one of the first implementations in contact treatment and was done so such that it is computationally efficient. In the one-way contact treatment, the…
The known advantage with implicit simulations is that the solution is unconditionally stable allowing larger values of timestep. In implicit static simulations (IMASS=0 in *CONTROL_IMPLICIT_DYNAMICS), the simulation time has no real significance but is rather an indication of the applied load magnitude. For example if we have a simulation where a load is applied linearly…
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…
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…
Under-integrated elements are widely popular in the explicit field for their robustness and computational efficiency. However, their use in Implicit without appropriate stabilization methods can cause singularities and may result in poor convergence behavior. LS-DYNA offers parameters such as ISHELL, ISOLID, and IBEAM in the keyword *CONTROL_IMLPICIT_EIGENVALUE which can be used to switch to an…
When migrating input files or using internal switching from Explicit to Implicit solution type, the influence of strain-rate effects, if defined for the materials used, should always be considered. If the problem is intended to be static or quasi-static during the implicit solution, it is recommended that strain-rate effects be ignored. LS-DYNA now offers a…
There are two classical solution methods available in LS-DYNA to solve a given problem. The widely popular “Explicitâ€? solution scheme, using the central-difference method, is applied to short-duration transient dynamic problems while the “Implicitâ€? solution scheme is used for static problems. Both of these methods have their advantages and disadvantages which depend entirely on the…
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…
