Hello Borzki,
VDI is an association of German Engineers:-
http://www.vdi.eu/. Probably you can know it better if you take a look at the link I've pasted up.
For your reply please refer the following points:-
1.) The analysis I'm doing is for Inter stage piping of a 6 stage centrifugal compressor.
2.) The compressor manufacturer has not provided me with the displacements at the suction and discharge nozzles of any of the stages
3.) I've modeled each stage of piping along with the inter coolers separately and then combined them using "include piping files" & defining the global co ordinates of the Inter coolers
4.) I've modeled the suction and discharge nozzles of the compressor as individual anchor points.
5.) As per default value of CAESAR-II the anchor point has a stiffness value of 1*10^12 N/mm. This value is not realisitc
6.) If I perform a calculation using this value the magnitude of imposed loads on the nozzle of the compressor is very high and it will fail in API 617 and NEMA SM-23 analysis.
7.) For this reason i need the realistic value of the stiffness of the suction and discharge nozzles of the compressor of each stages
8.) The VDI has done some work in calculation of the stiffness values for various flange sizes. i wanted to know them. But apparently no data is available on internet about it.
9.) Could you please provide me your suggestion weather my modelling strategy is correct or not. If required I can send you the CAESAR II file that I've modeled.