System dynamics models have been used in legal disputes since the late 1970s to prove and quantify damages. But such use of these models to support expert witness testimony presents challenges generally not encountered in non-dispute applications of system dynamics. Perhaps the most important such challenge is establishing admissibility of expert testimony supported by system dynamics models under the prevailing standards laid down by the US Supreme Court (Daubert standards) that lean heavily on the scientific method. Best-practice system dynamics work adheres to the scientific method and should prove admissible. Work that does not adhere to the scientific method or uses less stringent standards is vulnerable to being ruled inadmissible in such challenges. In particular, use of system dynamics work as a basis for opposing expert testimony must improve significantly, to meet the current admissibility standards. The stakes are high because current and future cases are likely to set precedents that will significantly affect future use of system dynamics in the legal arena, and because legal admissibility will doubtless impact the broader perception of the legitimacy of system dynamics analysis.

A cryogenic test article, the Generic Research Cryogenic Tank, was designed to qualitatively simulate the thermal response of transatmospheric vehicle fuel tanks exposed to the environment of hypersonic flight. One-dimensional and two-dimensional finite-difference thermal models were developed to simulate the thermal response and assist in the design of the Generic Research CryogenicTank. The onedimensional thermal analysis determined the required insulation thickness to meet the thermal design criteria and located the purge jacket to eliminate the liquefaction of air. The two-dimensional thermal analysis predicted the temperature gradients developed within the pressure-vessel wall, estimated the cryogen boiloff, and showed the effects the ullage condition has on pressure-vessel temperatures. The degree of ullage mixing, location of the applied high-temperature profile, and the purge gas influence on insulation thermal conductivity had significant effects on the thermal behavior of the Generic Research Cryogenic Tank. In ad- "'Consulting engineer, member AJAA.

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