This paper on "Dynamic Analysis for Inertial Measurement Electronics" was presented at the NAFEMS World Congress on Effective Engineering Analysis - 25-28 April 1999, Newport, Rhode Island, USA.

Summary

By combining SDRC solid modeling and FEM construction capabilities with MSC/NASTRAN computing capability we are able to solve frequency domain problems much faster and more accurately than ever before. An acceptable alternative to contour plots is to use some of the FE Tools utility programs for calculating and sorting von Mises stresses based on the NASTRAN .xdb file results.
Our experience in the laboratory with Pyrotechnic shock testing has been that we have never broken or cracked a structural element in a chassis. But when we use Sol 111 to solve for Shock Response Spectra (SRS) the rms value of stresses are many times the ultimate strength of the material. Furthermore, and not surprising, the larger the bandwidth of frequencies we consider, the larger the overstatement of the stresses. By approximating the effect of slip at the interfaces, attenuation at right angle turns in the structure, and limiting the number of modes allowed to participate, we believe we are getting stress values that are closer to the real values and do identify the weaker areas of the design. These so-called “knock down” factors are based on test measurements from similar equipment, and if anyone else wants to use this method, it is recommended they establish their own “knock down” values for their type of hardware.