G-DEMPack Tutorial 2: DemPack 2.0
This tutorial assumes that both the D-DEMPack and the GiD Pre and Postprocessor are installed, otherwise please follow the instructions in D-DEMPack installation. Please check the D-DEMPack manual page for a detailed explanation of all the fields and concepts present in this tutorial as well as for how to load the Problem Type.
Creating the Geometry of the Domain and the DEM Objects
In general, the process should start by creating a new geometry from scratch or by modifying or using an already existing one. For this tutorial, a group of simple entities were created which try to represent a simplified example of most of the capabilities of the program. The main objective of this document is to understand all the steps involved in assigning the corresponding properties and boundary conditions to a model and how to run a DEM simulation using the D-DEMPack package. The GiD geometry of this tutorial is available for downloading here: File:Dempack tutorial.zip. On the other hand, the user is strongly encouraged to follow any of the GiD Tutorials available here.
We will start by assigning the corresponding group properties. In this tutorial, a very easy geometry was created for the sake of simplicity. The next figure shows the geometry chosen, a very simple but representative enough one.
We follow by assigning groups to the geometry. To do this, we must open the Group Editor window by clicking on the icon showing in the next figure:
Once the window is opened, we have to create the groups representing our domain. To do so, we have to click on the New icon to start adding entities. The next figure shows its location. When the New icon is pressed, an automatically named group will be created. To rename it, just click on it, modify the name and press enter to finish. Do this process as many time as needed to create the necessary groups.
In this sample case, seven groups were created: two FEM walls (the floor and a box), two different inlets (one creating spheres and the other clusters) and three initial volumes of spheres. The list of group entities should be similar to the one that follows:
We must start assigning entities to the groups. To do this, just right-click on the corresponding layer, go to assign, choose the geometry type (in general surfaces or volumes), choose the appropriate geometry in the GiD drawing and click Finish when done. The next figure shows the result of correctly assigning entities to their corresponding groups.
To do the previous operation, the user must first select the appropriate group and press the 'Draw groups by colour' icon to confirm the correct assignation. Press Finish when done. The next figure shows the location of the corresponding icon.
Setting the DEM Materials
We will continue by defining the properties of the DEM elements in the simulation. We just have to click on the Materials tab at the top of the tree to access the Materials section. The user can modify already existing materials in the tree by double clicking on the corresponding material. He can also create new materials by right-clicking on DEM and selecting New Material. The next figure shows the window.
To create or modify the material properties, we go to the desired material and unfold its properties by clicking on the plus sign on the right of its name. A list of parameters to fill in will unfold. To edit the value of the parameters, just double-click on its corresponding current data and insert the new data.
Assigning the DEM Element Entities
It is possible to create initial volumes composed of DEM spheres. To assign these volumes, the user must first double-click the DEM > Elements > DEM_Element section inside the Model tab. A window will open up at the bottom of the tree where the user will be able to insert the group associated with this DEM entity. The next figure shows this section in the tree.
On the other hand, details on the assignation of materials and their associated groups are shown in the figure that follows. The user must click Ok when finished.
Setting the Conditions
Creating Inlet Objects
We now proceed to set the boundary conditions, which consist in the inlet and DEM-FEM entities. We will first start with the inlet feature. To begin filling this section, we just double-click on the Inlet label and all its properties will show up. Apart from setting the value of the different parameters that will show up, again we have to relate this inlet condition with its corresponding group at the bottom and click Ok when done. The next figure shows the details.
Creating DEM-FEM Wall Entities
We follow by settting and assigning the properties of the DEM-FEM entities. In this case, a set of three subsections will unfold: the ‘Linear velocity’, the ‘Angular velocity’ and the 'Settings'. The next capture shows this menu and the particular settings for this simulation.
Both ‘Linear velocity’ and ‘Angular velocity’ parameters can be set to be periodical, assuming that the group starts at the center of the motion with maximum speed equal to the imposed value. Motionless properties are imposed bu default. In case of imposing both linear and angular velocities, the linear velocity only affects the center of rotation, while the rotation is around the updated position of the center of rotation. Finally, in the 'Settings’ section a very useful option exists, the 'Update velocity, not Displacements', which is being used in this tutorial. When this feature is activated, the corresponding DEM-FEM entity will have a certain velocity field assigned to its nodes but no displacement will occur. As said, this option will be active for the conveyor belt layer.
Prescribing and restricting the motion of Elements
Setting Initial Conditions on Elements
Setting up the General Options
The next step is to set the values of several DEM general parameters. Check the DEM Manual Page for a detailed explanation for each of the sections. The next figure shows the chosen values of those variables for the current simulation.
Choosing the Solution Strategy
This item has two subsections. On the first subsection, the user can set the type of parallel computing to use as well as the number of threads. The second subsection is devoted basically to time parameters, where the calculation delta time and the total time of the simulation can be entered. The user can also set the DEM neighbours search frequency and how often he gets information output on screen. The next figure shows the concrete values in this case.
In this last section the user can set the values of several parameters in relation to Results. The next figure shows the chosen values for the present simulation, as well as how the Force integration group subsection works referring to the Graphs item. Please check the D-DEMPack manual for a detailed review of all fields in this section.
Meshing and Running the Simulation
Finally, the last step before launching the calculation is to mesh the whole domain. To use the sphere mesher for the DEM volumes, the user must first select the corresponding entities. This is done by going to Mesh > Element_type > Sphere, selecting the desired volume and pressing Esc when done. Secondly, an average radius must be chosen for the mesh by clicking on Mesh > Unstructured > Assign_sizes_on_volumes, inserting the desired size in the window that will open, clicking on Assign to select the volume and pressing Esc and Close to finish assignation.
Additional meshing settings can be set on the Preferences window. This window is accessible by clicking on Utilities>Preferences. The options are available clicking on the tree option ‘Meshing’, tree sub-option ‘Sphere Mesher’.
An analogous procedure can be followed for meshing the FEM entities, in this case though by going to Mesh > Unstructures > Assign sizes on Surfaces, selecting the corresponding surfaces, inserting the desired value and pressing Esc when done. The next figure shows the chosen sizes for each of the entities in the simulation. Layers with no assigned size will take as mesh size the value given just before meshing. In our case, a global mesh size of 0.4 was used.
To mesh, we have to go to Mesh > Generate Mesh, insert the desired value and click OK. A mesh like the one showing in the figure that follows should be obtained.
Finally, we save the model and launch the calculation by clicking on Calculate>Calculate. The user can follow the state of the simulation by going to Calculate>View_process_info. Once the calculation is finished, we can examine the results by shifting to the GiD Postprocess.
Please check the GiD help documentation or the GiD tutorials for a quick view on Post-Process basic features. The next figures show some snapshots of the resulting simulation.