F-DEMPack Tutorial 2: Annular pipe
Before starting with this tutorial, the user is strongly encouraged to follow the D-DEMPack Tutorial 2: Conveyor belt to get a feeling of how the problem type works, and in particular the DEM section. This tutorial will focus mainly in the Fluid section and its particularities.
The process should start by creating a new geometry from scratch, by modifying an existing one or by opening a finished one. It is assumed that the user already knows how to do this procedure so no details will be given about it.
In this tutorial, a simple geometry was created for the sake of simplicity. The idea is to understand all the steps involved in the problem type. The user must start by downloading the file [File:F_DEMPack_Tutorial_1.gid.zip], which contains the geometry and mesh of the proposed geometry. This file has already created the groups that will be used in the simulation.
The geometry of study consists of an annular tube through which a flux of an intermediate viscosity mud passes. An inlet creating DEM particles with time is located in the base of the annular pipe.
The downloaded file has already created the groups that will be used in the simulation.
In this sample case, the following five groups were created: Dem_inlet, Fluid, Inlet, No_slip and Outlet. The lower circle (surface) would be the Inlet, the smaller one just on top of it was the DEM_Inlet, the circle at the top would represent the Outlet, the No_slip would be the walls of the cylinder and, finally, the volume named Fluid would constitute the mass of fluid.
We will continue by defining the properties of the fluid in the simulation. We just have to click on the icon showing in the next figure to open the menus and in particular the Materials tab:
To begin inserting the fluid properties, we click on Fluid and then on the plus button at the bottom of the window to add a new Fluid material.
The next figure shows the details of the fluid material parameters that have been used in this example. To fill in or modify the value of the parameters, just unfold the General and Fluid submenus and double-click on the corresponding current data. The following data corresponds to an intermediate viscosity mud.
The same process can be followed, in this case, for the DEM material. We unfold the DEM-Defaultmaterial submenu at the bottom of the same window and fill the fields with the appropriate data. See Figure 6.
General Application Data
We now need to tell the program the model characteristics: boundary and initial conditions, inlet options, time considerations, etc. To begin filling all this data, we just click on the Model menu located at the left of the Materials tab and the Model Properties window will show up. This menu can be accessed also by clicking on the icon showing in the next figure:
The first section of the menu is General Application Data. Within this section the user can specify the simulation parameters, the coupling parameters between both subdomains -fluid and DEM particles-, and some postprocess results options. A deeper explanation of those parameters can be found in F-DEMPack2 manual.
The previous screenshot shows the reference parameters that have been used in this particular case.
The entities and conditions in relation to the DEM part of the problem are already preassigned so the user does not have to bother and can concentrate on the fluid aspects and details of the simulation. Nevertheless, figures showing the details on the DEM parts will be added here for the sake of completion and as a reference should the user lose these settings or in the case of have any problem when loading the file.
DEM-FEM wall group
The outer and inner cylinders are defined as walls in this section (No-Slip group). No motion is imposed on any of them.
Inlet DEM group
The annular surface over the base of the annurar pipe is set as the inlet of DEM particles. A total of 1000 particles per second are generated with an initial velocity of 1.5 m/s on the longitudinal direction of the pipe. The DEM material of the particles is specified in this submenu, as well as their diameter.
This section is devoted to set the limits of the bounding box, the gravity vector and some advanced features. The figure that follows shows the chosen parameters.
Other advanced options that the user can specify are those related to the Solution strategy and DEM-Specific Results. More information about these submenus can be found in F-DEMPack2 manual.
This section contains the information about the properties of the fluids, the different existing fluid elements and, when necessary, their assigned conditions. It also has some parameters in relation to the settings of the fluid solver.
The first two submenus are related to the solver type for the fluid part and its parameters, and the third sumbenu allows the user to enter the delta time to use in the computations of the fluid as well as the step for the divergence clearance.
The default parameters on the next figure gave good results in this particular case.
The user can set the fluid properties by assigning them to the Fluid material previously created. To do this, right-click on Properties and choose New. A New Property window will appear below. Fluid1 can be selected on the Material drop-down menu.
The next step is to identify the fluid elements amongst all the existing geometric entities. This can be done by going to Elements and right-click on Fluid. As before, if the user clicks on New a window will open at the bottom. The working fluid can be selected on the Group drop-down menu. The elements are properly assigned after clicking on Ok.
The same procedure is followed to assign the initial conditions to the problem. In this case, an initial vertical velocity field of 1.5 m/s is given to the mass of fluid. The picture that follows shows the process.
Regarding the boundary conditions, an inlet velocity of 1.5 m/s is proposed to be set in the entrance of the annular pipe. This can be done by right-clicking on Boundary_conditions > Inlet_velocity and creating the new inlet condition over the desired group. As seen in the next picture, a velocity of 1.5 is specified in the vertical direction.
A similar process is followed to impose the pressure boundary condition. In this example it is assigned a null pressure value at the top surface.
To finish with the boundary conditions, slip conditions are informed in the domain. In this case, no-slip conditions have been chosen on the cylinder walls. As shown in the figure that follows, the user must assign this property to the appropriate layer, in this case the outer and inner cylinders of the annular pipe.
Meshing and Running
The last step before launching the calculation is to mesh the domain. All the mesh characteristics are predefined on the downloaded model, so the user can proceed to mesh by typing Ctrl+G or by unfolding the Mesh menu on the top of GiD and clicking on Generate Mesh.... A size of 0.05 has been selected for the mesh.
After the geometry is successfully meshed and the case is saved, the user is now ready to launch the calculation. To do this, the user must go to Calculate > Calculate or press the Run the simulation button in the interface. The next figure shows the Process Management section of the interface.
The first button inside the red square opens the process control window, the second one runs the simulation, the third one gives information about the calculations and the last one stops the process.
Once the program starts writing results, the user can shift to the Postprocess in order to analyze the obtained results. After clicking on Open multiple files and selecting the desired group of files to be opened, the user can observe the sequence of results with time by using the Window > Animate utility. Next figures show a succession of results after running the sample case.
It is also possible to print several physical results as, for example, the velocity field of the particles or the fluid pressure distrubution on a determinated step of time. To do this, the user must click on View results > Display vectors > VELOCITY > |VELOCITY|, and View results > Contour Fill > PRESSURE > |VELOCITY|.