Tuesday, September 29, 2020
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Project Outputs - Large time steps

For many fluid dynamics simulations, low viscosities allow for the usage of fast fractional step schemes. Computing the velocity explicitely allows for an important reduction in the computational time required per time step. However, one of the main limitations of Eulerian explicit fractional step solvers is the presence of the non-linear convective term. This factor reduces the maximum possible time step, increasing the number of steps needed and therefore the total time required for the simulation. Also the linearization of the equations translates into poor solutions.

In the RealTime project, a new strategy was developed to tackle this problem. By using a Lagrangian formulation, the convective term vanishes, therefore allowing for an explicit treatment of the pressure without the limitations of Eulerian counterparts. Moreover, integrating the forces along the streamlines of the material points that define the continuum, it was possible to provide a better aproximation to the non-linear convective movement in a single, explicit step. This allowed for a fast solver that is accurate even for very large time steps, requiring only the pressure to be calculated implicitely. The result of this work lead to the creation of the Particle Finite Element Method , second generation (PFEM2). Two implementations were developed, fixed mesh strategy (using projection) and a moving mesh strategy (using remeshing). Below several examples can be seen.

Koshizuka dam break experiment in 2D
Koshizuka dam break experiment in 3D
High speed jet
Rayleigh instability in 2D
Rayleigh instability in 3D
Turek Benchmark at RE=200
Detail of a FSI simulation using fixed mesh PFEM-2


       Debris Flow Simulation with a fixed and a tracking mesh

CIMNE, Campus Nord UPC, Edifici C1, C/ Gran Capità, s/n, 08034 Barcelona
Tel:93 401 0796 / Fax.93 401 6517 Email: projectes@cimne.upc.edu