Adding monitor points
To add a new monitor point, pressin the section of the CASD scenario menu. Double-click the monitor point (or press ) to enter the point’s position. If you intend to simulate a fire scenario, you also have to assign a direction to the monitor point. This is the direction along which the incident radiative flux is calculated, and it is specified as a vector. If you do not specify a direction then the maximum value of all directions will be output.
Where to place monitor points
Avoid putting monitor points exactly on a grid line or within fractions of a grid cell size from a wall. Usually it is best to enter monitor points according to the grid, not according to the geometry. For example, if you place two monitor points close to both sides of a solid wall they may not even be in two different control volumes. Further, during the porosity calculation, Flacs may adjust the wall to the nearest control volume face (grid line) and therefore the wall may move to the wrong side of a monitor point! Also, ensure that none of the monitor points is inside a fully blocked control volume.
Verifying monitor point locations
Check monitor point locations visually in Flowvis 2D and 3D plots: to show the monitor points, tick off thecheckbox in the section of the properties sidebar. Monitor points that are placed outside the simulation domain will be red. Monitor points that are too close to or inside obstructing geometry will also be red. These monitor points will not give results in the r1-file.
Selecting output variables
Select the output variables to be written for a monitor point by editing the monitor point in CASD. If you want to edit several monitor points at the same time, mark them and click. Typically, you would like the same set of variables to be output at all monitoring locations; you can achieve this by selecting all monitor points, right-clicking and selecting in the context menu. When editing monitor points, you can choose one or several variables by left-clicking or dragging.
Which variables to output
The most commonly used monitor point variables for explosion simulations are pressure (P), dynamic pressure (DRAG), panel pressure (PP), pressure impulse (P_IMP) and sometimes flow velocity (UVW). For dispersion calculations, you would typically require the volume gas concentration (FMOLE) and flow velocity (UVW).
Output frequency and file
Flacs writes monitor point data to the scalar-time output file (r1-file, e.g. r1000000.dat3) once every MODD time steps (default: MODD=1, i.e. every time step). You can set MODD in the section of the CASD scenario menu, or in the scenario file (cs-file). Normally you want the monitor point output very often, e.g. in every time step for an explosion simulation, while 3D field data is sufficient to have much less often.