Date of Award

3-23-2017

Document Type

Thesis

Degree Name

Master of Science in Operations Research

Department

Department of Operational Sciences

First Advisor

James W. Chrissis, PhD.

Abstract

Due to the rising cost and scarcity of helium, new methods to ensure buoyancy for lighter-than-air vehicles (LTAVs) are being sought. One alternative under study uses an internal vacuum to reduce the weight to buoyancy ratio. It's a novel approach; however, the vacuum presents challenges for the vehicle's structure. The structure must have minimum mass while preventing buckling and excess stress throughout the frame and membrane. The structure under analysis is a hexakis icosahedron with a membrane covering. Achieving minimum mass involves optimizing the structure under the loading conditions. Finite-element analysis (FEA) and direct-search methods are employed, providing an optimal design under various regimes. Specifically, ABAQUS R is used as a FEA modeler, and mesh-adaptive direct search (MADS) is the optimization procedure. The goal of this research is to reduce the diameter of the vehicle using optimization techniques to a goal size of 31 inches (0.7874 meters). The smallest design to date has a diameter of 20 feet (6.096 meters). This research demonstrates the feasibility of two designs, one at 15 feet (4.572 meters) and another at 4 feet (1.2192 meters). The problem formulation includes multiple black-box objectives and constraints. Results for a number of designs are presented and compared.

AFIT Designator

AFIT-ENS-MS-17-M-158

DTIC Accession Number

AD1051601

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