The six numbers define two points in 3D with lower and upper coordinates.
#GMSH RULED SURFACE VS PLANE SURFACE FULL#
It is possible to edit the BB array in order to restrict the simulation volume to a fraction of the mesh geometry, but we will use the full volume, here. Next, the bounding box coordinates are shown within the array BB. Thus, it is required to change the length UNIT to 0.001. Our geometry model uses mm as length unit, while the default setting in the parameter file is m. First, we have to define the length unit, which is used within the mesh file. the simulation volume and its cell resolution. The next section of the parameter file deals with the bounding box, i.e. In the next lines of the parameter file, the desired output of the simulation run is specified: P0_Ar = 0.5 # Default pressure of initial Ar distribution NREAL_Ar = 1.2e13 # Default scale factor for Ar Thus, the lines within the parameter file should be edited as follows: Accordingly, the resulting value for NREAL_Ar is 1.2 x 10 13. To transfer this to the case with a pressure 0.5 Pa with 10 mm cell dimension, we need to keep in mind that NREAL_Ar scales reciprocally with the square of the pressure 6). In section statistical constraints, for Argon with a pressure of 1.0 Pa, a cell dimension of 5 mm and a value of NREAL_Ar=3e12 is suggested, which leads to an average of 10 simulation particles per cell. Since we assume that the pressure in the tube will be significantly lower, we will start with a homogeneous pressure distribution of 0.5 Pa and use 1.0 cm as appropriate cell dimension. 6 mm, thus a cell dimension of about 0.5 mm would be required close to the gas inlet.
#GMSH RULED SURFACE VS PLANE SURFACE FREE#
For Argon with a pressure of 1 Pa, the mean free path is approx. This means, that the pressure will reach 1 Pa close to the gas inlet but will be significantly lower in the major part of the simulation volume. In our test case, we will define a gas inlet operating with Argon at a pressure of 1.0 Pa and a pumping surface. The next lines within the parameter file deal with the selection of gas species, their initial distribution and their statistical weight. WALL = 10 // Tube orientation along x axis // Center point at left tube edge Tube3d.geo LC = 10 // characterictic mesh size
For definition of the geometric points, we use the following GMSH script (click name to download): First, the geometric points have to be defined, second, the points are connected with lines and finally, surfaces are defined by line loops. The coordinate origin (0,0,0) is located at the left end of the tube, centralized within the circular cross sectionĪ geometric model always consists of points, lines, and surfaces.