My Dear Expert and colleagues
I would like to describe 3D irregular targets as shown in figure below … Where can I find advices about the topic in our FLUKA program cards?
Also in previous How to import GDML to FLAIR topic Duarte Guerreiro refer to a GDML file. it is needed for my case? and How I could generate such a file and what is its importance?
Assuming you have a CAD description of this mask, you can use FluDAG, which is an integration of DAGMC within FLUKA. It supports the decomposition of your CAD surfaces into high resolution tessellation primitives. More info on FluDAG at , and on its installation here.
The GDML format is used as geometry input description by e.g. Geant4. You cannot use it as an intermediate step into FLUKA here, as complex shapes would not be supported by the conversion process.
Hope this helps,
 Andrew Davis, Janet Barzilla, Alfredo Ferrari, Kerry T. Lee, Vasillis Vlachoudis, Paul P.H. Wilson (2019). FluDAG: A CAD based tool for high energy physics. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. Volume 915, Pages 65-74. https://doi.org/10.1016/j.nima.2018.10.117
Many Many Thanks for this full explanation and the valuable advice to my problem. Really this will help me a lot to understand this interesting field it will guide me to the correct way to start.