F-DEMPack2 manual

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Contents

General Application Data

DEM 2 manual swimming general application data.png

Project information

The user can fill here several fields with information related to the current simulation.

Toggle debug/release

Here the user can choose the Debug option in order to see the complete menu despite a possible loss of robustness.

Simulation Options

It consists of a few settings concerning the whole simulation, in particular the simulation duration, the output delta time and the number of threads to use in the simulation. At the moment the code runs only in OpenMP, MPI is currently under development.

Physical Options

It deals with general physical settings. At this moment it consists only of the gravity value.

Coupling Parameters

It refers to those parameters concerning the inter-component coupling.

Coupling level

It has 4 possible values: No interactions, One way, Soft two-way and full two-way, which correspond, respectively, to no-interactions, only fluid to DEM, to unmodified fluid equations or to averaged Navier-Stokes.

Time averaging mode

  • Take newest values: Take the present value of the hydrodynamic forces from DEM for the fluid integration.
  • Take uniform average over DEM substeps: Average values of the hydrodynamic force over all substeps within one fluid step.

Interaction start time

The user can set here the time to start the interaction between DEM and fluid.

Hydrodynamic Force Model

  • Pick each individual force: Pick specific expressions for the usual terms, one at a time, even though compatibility may be not guaranteed.
  • Buoyancy Force type: Here the desired buoyancy law for the DEM particles can be chosen.
  • Maxey-Riley Equations: To use these equations for the simulation, even though they are addressed to

small Reynolds numbers.

  • Drag Modifier Type: The user can choose between different drag laws available.
  • Include Faxen terms: Including them may improve the accuracy of the results. Nevertheless, they require the calculation of the local laplacian and its derivative, which involves a certain overhead.

Post-Processing variables

Those are options concerning variables that are calculated by post-processing the fluid-field solution. Here the user can choose the Gradient and the Velocity Laplacian Calculation Modes. Both are computed as a post-process from the fluid solution.

Results

This section contains the options concerning the results to be post-processed. It allows the printing of many nodal values for both DEM elements and fluid mesh nodes. Discretion is advised when printing results in postprocess, because much memory may be needed to be allocated, harming performance in many cases.

Fluid DEM 2 manual swimming full menu.png Analysis Data: Solver Type: Choose between Monolithic and Fractional Step. The monolithic solver is slower, but remarkably more accurate than the fraction step solver. Turbulence Model: The user can decide to use no turbulence model or to choose between Smagorinsky-Lilly or Spalart-Allmaras. In general, Smagorinsky-Lilly gets better results for separated boundary layers but needs finer meshers. Solution Strategy: It has many options to adjust the behaviour of the solver. The user should not bother to change those default values. Problem Parameters: the user can enter here the delta time to use in the computations of the fluid part as well as the step for the divergence clearance. Properties: The user can create as many Fluid Properties as desired. The standard Propertry, for example, is that related to the Water Material. So the user, when later creating the different Fluid Elements, will have to assign every Element to their corresponding Property. Elements: Fluid: The user must assign here the properties of the existing fluid groups. First of all, the Element Type that will be used in the computations, in this case the Tetrahedra element being the only available for 3D, and the corresponding Property for the group. Initial Conditions: Initial Velocity: The user can assign here an initial velocity field for a given mass of fluid. Initial Pressure: Here an initial pressure field can be assigned to the desired fluid group. Boundary Conditions: Inlet Velocity: Here a fluid inlet entity can be assigned to a given group. The user must assign the group an inlet velocity field for the group as well as its fixity depending on the three axis. Outlet pressure: The user can assign here an outlet pressure for a given group representing an outlet of fluid. Is-Slip: When assigning this condition to a solid boundary group, the fluid will have in general a non-zero velocity relative to the boundary. No-Slip: On the contrary, when assigning this condition to a boundary, the fluid will have a null velocity in relation to the boundary. Flag Variable: Not active at this moment.

DEM 2 manual swimming fluid menu.png

3. DEM Please, refer to Manual2_whatever for a full description of the menus in this section.

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