No abstract

No abstract

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING/MONITORING AGENCY REPORT NUMBER(S) AFRL-RB-WP-TR-2008-3090 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTESPAO Case Number: WPAFB 08-1717, 27 Mar 2008. Report contains color. ABSTRACTA thermal protection system (TPS) is responsible for protecting a spacecraft's components from melting due to high reentry temperatures. In the design of TPS, both maximum thermal stress and minimum natural frequency must be considered due to the combined thermoacoustic environment inherent in high-speed vehicle applications. A multiobjective structural optimization method for the three-dimensional acreage TPS design is developed using an evolutionary structural optimization (ESO) algorithm. The static control parameter used to find the optimum in minimum thermal stress design is modified to address an irregular mode-switching phenomenon, as well as to improve the modal stiffness in dynamic analysis. Two objectives are optimized simultaneously, namely, the maximization of fundamental natural frequency and the minimization of maximum thermal stress. The proposed modified control parameter is demonstrated in the design of a metallic TPS using the method of weighted objectives. The results are then compared with the conventional ESO sensitivity approach. This work concludes by applying the methodology which makes use of both topology and shape optimization in the design of an acreage TPS.