A Multi-Attribute Decision Process for Structural Material Assessment and Selection of Light-Weight

The U.S. Navy is actively exploring the use of lightweight materials for the next generation of warships, including high-strength steels, lightweight aluminums, and non-metallic fiber-reinforced plastic (FRP) composites. High strength steels often result in heavy ship designs which compromise the ship speed and range. Aluminum alloys offer an advantage in weight but with a limited ship hull fatigue life. FRP composites are corrosion and fatigue resistant and have other payoffs including light weight, reduced radar and acoustic signatures, and are therefore a more attractive and survivable material choice. Proper selection of lightweight materials and structural assessment of high-performance ships, for the U.S. Navy, is therefore a complicated decision making process which must be carried out in a systematic and methodical approach. In this dissertation a unique multi-attribute decision process model is developed to identify, describe, analyze, and evaluate key attributes to aid the selection of light-weight, high-performance naval ships. The ship decision process is focused on the structural design and assessment of alternative lightweight materials and generalized to aid the Navy research development test and evaluation (RDT&E) community to confirm the use of advanced materials for future ships that have the greatest improvement in structural performance and most affordable cost. A nested, additive linear utility function is developed to compute the total value or utility of a proposed ship concept in terms of a set of 3 ship performance attributes, a set of 3 design impacts on operation attributes, and a set of 5 ship cost impact attributes. The overall merit of the proposed ship concept is determined by adding and weighting the ship's performance, design impact operation, and cost level utilities. Three sets of expert opinions were collected and applied to determine the relative importance of the individual performance, operation and cost attributes and the Bradley-Terry statistical scaling model was used to determine the weighting factors for the 11 individual attributes. The appropriate weights can be modified to reflect different types of ships satisfying different requirements and operation schemes for future naval needs and threats. The decision process model is exercised to assess and compare four ship concept variants of a 3,000-ton notional littoral combat ship (LCS) that the U.S. Navy is considering. The four ship variants compare the steel baseline, the light-weight aluminum, the fiber glass composite and the advanced carbon-fiber composite ships. The relative rank order of the LCS ship variants is discussed and demonstrated the usefulness of the developed decision aid model. The stability of the model is also assessed by performing sensitive analyses using the 90% confidence values for the dominating attributes weights. The results show that the model is stable based on the attribute weights developed. It is also relatively easy to use and apply to naval or commercial ship selection processes.