There are a few different ways to create a grid refinement zone in a region where you feel the cell size needs to be smaller in order to better capture the flow.



As you can see, the user has the option to create a user-defined refinement zone. The process, which has to be performed in SimericsMP (not in Orca3D), is summarized below. Start by creating a "User Defined Zone" refinement zone and set the cell size like you normally would. To define the zone shape, you have to specify some expression in terms of x, y, and z. In this example, we created an expression variable called CustomZone, defined as shown below. The expression for x and y is pretty straightforward: If x is between 5 and 11 and y is between -2 and 0. The z part of the expression is a little more complicated. We defined a value that is a straight line that varies with y along a slope that matches the vessel deadrise angle (at least approximately, the deadrise varies along the length). This helps to keep the zone following the hull in station view. Of course you could also have it vary in height longitudinally with x. When all of the x, y, z conditions are met for a given point in the mesh, CustomZone returns a value of 0 which indicates the point is in the refinement zone, but for values that don't meet the conditions it returns 1 which indicates the point is outside the refinement zone and no refinement should occur there.



Below is a OneDrive link to a sample where you can have a closer look at how this is done.

Custom Refinement Zone.zip 


It is much easier to know the X, Y, and Z values to use in the definition of the custom refinement zone if the model in Rhino/Orca3D is in the same orientation as the model in Simerics. This is not always the case because you can enter a weight and CG in Orca3D and it will compute the sinkage and trim for the equilibrium flotation. The model is then sent to Simerics in this equilibrium condition. In this case, where you need to be able to enter coordinates in Simerics, it makes sense to first transform the Rhino model so that it is in the same orientation as it will be SimericsMP so that measurements are transferrable. This is easily achieved in Orca3D as follows:

1. Run the OrcaHydrostatics command and select the same geometry that you would select for the Orca3D CFD command input.
2. Enter the same weight/CG or sinkage/trim/heel input as you do in the CFD command and click the "Transform Model to Resultant Condition" checkbox as below.



When you click Calculate, it should create a new layer with the transformed geometry in static equilibrium (relative to the Rhino z=0 plane) that matches the SimericsMP starting condition. Now any measurements you take relative to that geometry should match the SimericsMP model.