10.3 Boolean operations on geometry

The Boolean operations are very common when preparing the structure of complicated geometry. The Boolean operations (Join operations) available in QuickWave have been in details described in Boolean Operations chapter of QW-Editor manual. Here, based on the examples from ..\Various\Joinex\ directory, we will only cite the basic information regarding the situations where the Boolean operations are not necessary:

An element inside another one

First of all note that the Join operations are being performed on slices in XY plane. Thus when deciding if such an operation is needed we should consider only if the intersection takes place in any of the XY plane slices. Let us consider example jo3.pro in which a quartz parallelepiped is partially inserted into a metal cylinder. Formally it is also an incorrectly defined structure. There is a part of the space attributed to both quartz and metal.

a) b)  c)

QW-Editor pictures of jo3.pro in 2D windows in horizontal XY-plane (a), in vertical XZ-plane (b) and QW-Simulator Test Mesh picture in the middle of the structure.

However, the SAT files Viewer and 3D windows of QW-Editor display the picture in accordance with presumed intentions that the part in question is filled with quartz. But the most important is that the QW-3D mesher always assumes that with one XY=plane contour completely included in another one, the medium of the inner contour prevails. As a result we have the correct meshing of the structure. We do not need to perform the Join operation in such a case.

a)b)c)

Pictures of jo3.pro in SAT files Viewer (a), 3D window with solid view (b) and 3D window with solid view with transparent covers (c).

An element internally tangential to another one

Let us now consider a structure of jo4.udo A block of quartz is internally tangential to the block of metal. The problem here is the left border in which there are conflicting declarations about medium visible on the right side. One element is supposed to enforce quartz and the second one to enforce metal. The software detects that the structure is internally tangential and assumes that the medium of smaller segment of common boarder is prevailing. That is why it is correctly meshed.

a)   b)    c) 

QW-Editor pictures of jo4.pro in 2D windows in horizontal XY-plane (a), in a 3D window (b) and QW-Simulator Test Mesh picture (c) after automatic meshing without Cut operation.

Note however that this criterion does not work in the case when both elements have in common an entire wall as exemplified by jo5.pro. In such a case the Cut operation is needed. Otherwise we may obtain incorrect meshing.

a)  b)      c)  

QW-Editor pictures of jo5.pro in 2D windows in horizontal XY-plane (a), in a 3D window (b) and QW-Simulator Test Mesh picture (c) after automatic meshing without Cut operation.

Intersecting elements made of the same medium

Let us consider now two intersecting elements made of the same medium considered in jo6.pro. The software makes a kind of “glue” operation on such elements prior to meshing. Thus the meshing result is fully correct without Glue operation enforced by the user.

a)b)  c) 

QW-Editor pictures of jo6.pro in 2D windows in horizontal XY-plane (a), in a 3D window (b) and QW-Simulator Test Mesh picture (c) after automatic meshing without Glue operation.

The above statement is an important indication on how to apply some of the library objects like for example the strip shapes of the library planar. It often happens that we want to put two strip segments adjacent to each other. An accidental microscopic slot in the junction can be very harmful to the meshing process and as a result to the accuracy of calculations. That is why whenever it is difficult to make the ends of the adjacent strips perfectly tangential, it is better to make them slightly overlapping then to risk appearance of some gaps between them.