I have a structural system weighing approximately 40 kips that is to be accelerated axially to 18G's. The system is pushed by a propulsive structure that is aft of the main structure. In order to simulate the main structure as a "pushed" system, I applied sliding constraints on the bottom of the main structure, and fixed constraints on the aft portion of the structure (where it would mate with the propulsion structure). I then applied an 18G axial accel through the CG of the system (Simulation express this quantity as in/sec^2). No other loading is applied. This should result in axial reactions only at the constraints.
Now unless I've messed up my high school physics, I would expect to so a total reactive loading of 720 kips (18G's x 40kips) in the axial direction of my aft constraints. When I use the List Resultant Force tool, Simulation reports about 3,200 kips. This would suggest my system weighs around 177 kips, which is contrary to what mass properties reports. I do have some suppressed items, but they don't make up the difference in mass needed to achieve that kind of reactive loads.
I ran some smaller, simple assemblies and ran them against a hand check, and they computed fine. That might suggest something wrong with my model. Has anyone experienced something similar when applying accel loads? Any ideas on what I should look out for?
Unfortunately I can't provide a whole lot of detail or images of the system...
Thanks for the help,