minimize W =W(b,h,ty,,O,tz,,,)
 such that

 a, (8-2)
 s, x c,
where N is the total number of failure modes, a, and c, is the allowable and response for

the its failure modes, and s, is the safety factor for the its failure mode. Deterministic

optimization use safety factors to account for uncertainties. A set of safety factor

typically used in the design of stiffened panel aerospace application (Lamberti et al.,

2003) is shown in Table 8-15.

Table 8-15. Safety factors used in deterministic design
General instability Local buckling Stiffener buckling Strength failure

 1.4 1.2 1.2 1.2


 The deterministic optimum found by using the global optimization capability in

PANDA2 software is shown in Table 8-16. The composite design is heavier than the

Aluminum designs in previous section, because composite design is substantially

penalized by thermal loading as shown in chapter four.

Table 8-16. Deterministic Optimum (inch, degree, lb)
 B h tl Bi tz 82 Weight

 9.999 1.583 0.02229 87.57 0.03950 14.84 3386


Analysis Response Surface Approximation

 The most critical safety margins of the two load cases are extracted from PANDA2

report. Two analysis response surfaces (ARS) were fitted to the critical margins of the

two load cases in terms of sixteen variables, which included six design random variables,

and 11 random variables. Statistical design of experiment is Latin Hypercube sampling

(LHS). The range of the design random variables for the ARS was chosen as +5% based