MASTODON Newsletter (Spring 2019)
Explicit Integrator in MOOSE
Made progress in implementing an explicit solver that will significantly reduce runtime. The explicit solver is benchmarked by comparing results of simple problems with the corresponding implicit, Newmark-Beta solution. The explicit solver is expected to be merged into the MOOSE framework in Summer, 2019 after thorough testing and will include both consistent and lumped-mass matrix options.
The implementation comprises changes to the MOOSE framework and includes a new, CentralDifference TimeIntegrator. The implementation includes several other changes that make the usage of the explicit solver extremely easy to use. The user is simply required to change the TimeIntegrator in the Executioner and add the input statement, implicit = false, in the strain kernels. Sample results for a single solid element problem are presented in Figure 1.
Figure 1: Comparison of the results of the implicit and explicit integration for a single solid element problem.
Beam Mesh Generator
A beam mesh generator has been created and is currently under testing. The mesh generator will input nodal co-ordinates and beam connectivity information through csv files and will create a mesh automatically. This circumvents the usage of a meshing software and provides a much easier way to import meshes from traditional structural engineering software like SAP2000 or GTStrudl. Figure 2 shows an L-shaped mesh and the corresponding input csv files created for testing. More tests and examples will follow. This will be merged with MASTODON in Summer, 2019.
Figure 2: Illustration of a beam mesh generator example.
Shell Element Implementation
A 4-noded shell element is being implemented in MOOSE based on the Dvorkin and Bathe (1984) formulation. This shell element can be used for problems that involve small or finite rotations. An initial tested version of this element would be available in MASTODON by end of Summer, 2019.
Figure 3: Illustration of the Dvorkin and Bathe (1984) 4-noded shell element.
MASTODON VectorPostProcessors
Extended the ResponseHistoryBuilder, ResponseSpectraCalculator and HSICalculator vectorpostprocessors to accept sets of nodes, or boundaries at input. Users do not have to create an individual VPP block for history, or spectrum at each node anymore. This makes these VPPs more user friendly. Illustrations and examples of the updated VPPs are provided in the corresponding documentation pages.
Figure 4: Response histories of two nodes calculated from a single ResponseHistoryBuilder block.
References
- E Dvorkin and K Bathe.
A continuum mechanics based four-node shell element for general non-linear analysis.
Engineering Computations, 1(1):77–88, 1984.[BibTeX]