Question

FEA

d) Provide an example of when you would use the explicit dynamics analysis system. e) Describe adaptive meshing.

Answer 1

Answers:

d)

An explicit dynamic analysis is computationally efficient for the analysis of large models with relatively short dynamic response times and for the analysis of extremely discontinuous events or processes and it allows for the definition of very general contact conditions. It uses a consistent, large-deformation theory—models can undergo large rotations and large deformation. It can use a geometrically linear deformation theory—strains and rotations are assumed to be small. It be used to perform an adiabatic stress analysis if inelastic dissipation is expected to generate heat in the material. It be used to perform quasi-static analyses with complicated contact conditions and allows for either automatic or fixed time incrementation to be used—by default, Abaqus/Explicit uses automatic time incrementation with the global time estimator.

The explicit dynamics procedure is ideally suited for analyzing high-speed dynamic events, but many of the advantages of the explicit procedure also apply to the analysis of slower (quasi-static) processes. A good example is sheet metal forming, where contact dominates the solution and local instabilities may form due to wrinkling of the sheet.

Explicit dynamics computationally attractive for problems where the total dynamic response time that must be modeled is only a few orders of magnitude longer than the stability limit. For example, wave propagation studies or some “event and response” applications.

e) Adaptive meshing:

In many nonlinear simulations the material in the structure or process undergoes very huge deformations. These deformations distort the finite element mesh, often to the point where the mesh is unable to provide accurate results – or the analysis terminates for numerical reasons. In such simulations, it is essential to use adaptive meshing tools to intermittently minimize the distortion in the mesh. Adaptive mesh domains define the regions of the model where the mesh can move independently of material deformation.

The primary characteristics of the adaptive meshing capability are:

• The mesh is smoothed at regular intervals to reduce element distortion and to maintain good element aspect ratios.
• The same mesh topology is maintained i.e. the number of elements and nodes and their connectivity do not change.