After reading through the Introduction to GUMBO and the Frequently Asked Questions, the objective of this tutorial is to familiarize the user on the use of GUMBO, the boundary condition, connectivity, and general grid manipulator software of USS_UNCLE.
This tutorial is an aide to familiarize the user with the steps to prepare a problem for USS_UNCLE:
Read in the grid data set, gumbo_tutorial_1.grud which should be bundled with USS_UNCLE. The file can be read through the Read Data Panel. (The filename can be typed into the GridFile field or selected via the browser. The GridFile toggle must be active, then depress the Read Data button to actually read the data file.)
The grid is the domain around a ship hull which is composed of three blocks. The inner or second block contains the ship hull on the kmin face in the region 1<=i<=85, 21<=j<=41. Blocks 1 and 3 are the forward and aft of the ship, respectively. The free surface should be a jmax face. Figure 1 shows the three initial blocks read.
Once the grid has been read, the user should orient themselves on how to manipulate the graphical image and to be able to select the blocks, faces, edges, etc.
Calculate the Load Balance Efficiency. This current value should be 0.576471. It is desired to have a value between 0.9-1.0 to be highly effective. The following steps will provide insight into the procedure to make the blocking more efficient.
| In this particular case it will be easier to specify the boundary conditions on the initial blocks rather than the concatenated block. In general, it is easier to apply boundary conditions to the largest blocks that are created by concatenation, then subdivide into smaller regions. This needs to be evaluated on a case-by-case basis and there is no right procedure. It is really a user preferrence and which is more comfortable. The user should proceed to the BC & Connectivity Panel. The boundary conditions to apply are free surface (should always be a jmax face), far field, symmetry, and solid surface. Figure 2 displays the solid surface boundaries. |
| The blocks will be merged or concatenated into the largest blocks possible. In this case it is trivial, other cases will be a little more tricky. Select the three blocks in the increasing I direction (as Block 1, 2, then 3). Concat the blocks together in the I direction. Figure 3 displays the solid surface boundary conditions of the block. The user should visually inspect the boundary conditions. Now check the boundary conditions. All the faces should have been specified. GUMBO should have merged all the previously defined boundary conditions. |
| The next step is to repartition the grid so that it will be balanced efficiently. See Grid Math Options to help determine how to repartition the grid. But for now, split the block into three regions in the I direction. There will be three equally sized blocks, Figure 4, and the load balance efficiency is 1. The boundary conditions can be checked again. There should be no problems indicated. This is due to the fact that GUMBO automatically created the block connectivity upon splitting. |
At this point the grid is ready be saved as input for the solver; however, the blocks should be renumbered sequentially from 1. This will synchronize the boundary condition, connectivity, and grid files, since the grid files have an implied order.
The next steps will go through creating a full geometry by mirroring the given blocks.
Select the three blocks in order (this will save renumbering the blocks again) and mirror them about the XY plane. The K direction of the mirrored blocks will need to be reversed to keep the grid right-handed.
| If the boundary conditions are displayed, the inner faces are still marked as symmetry. The user can change the symmetry boundary condition and replace it with an unspecified boundary condition. Once the symmetry boundary conditions have been removed, the block connectivities can be determined automatically. Figure 5 displays the solid surface boundary conditions of the full grid. |
Check the faces to ensure that boundary conditions and connectivities exist and do not overlap.