The Society of Naval Architects Ano Marine Engineers

Major changes in the size, shape and performance of ships will create a severe challenge to the technical skills of ship structural designer. Fortunately, the groundwork has alreadY been laid for the technology required to support him. The na~;re and quality of this technical base is discussed and gaps are identified. The serious need for closing the interface between researcher and designer is noted. References were selected to give a broad background in progress to date, and an easy initiation into all facets of the topic . INTRODUCTION THE DESIGN PROCESS The practicing structural naval architect is at once blessed and cursed by the thousands of years of experience garnered by his precursors -blessed, because few professions enjoy the benefits of so many thousands of fullscale experiments which led to todayr s empirical design methods, and cursed, because in the face of such soundly– based tradition, it is vet’ydifficult to promote innovation. However, innovation is required, and must be promoted, to meet tomorrow’ s design challenge. Empiricism, which served us well for millenia, has been stretched to the breaking point by our recent exponential Increases in the speed and size of $hips Further, empiricism based on experience cannot safely deal with new concepts in hull form, propulsion technology and dYnamic lift. Development of completely ritional structural d~sign method; is essential to insure that structural efficiency and reliability will keep pace with other performance parameters in the rapidly-developing field of marine technology. Since the 1920’s, major impFowments have been made in the structure of ships, including the introduction and refinement of welding and the development of many excellent highstrength steels and marine aluminums Even more important, the theoretical ground-work has been laid for a tOtallY rational process of ship structural design, with the potential for optimization and lifetime reliability prediction. Between the development of a theoretical concept and its practical application in a design office, however, there is a great gulf which can be spanned only by hard work. The nature and scope of this work, and the new design methods which will hopefully result, will be the principal subjects of this paper. Before discussing the future of the ship structural design process, it is necessary to outline briefly the present nature of the process, and the environment In which it operates . The process of overall ship design is an iterative one, proceeding cyclically to resolve the conflicts among the many systems which comprise the ship, each of which has its own separate objective and constraints, but with each contributing to the overall goals of ship performance . These conflicts are often serious, and difficult to resolve, and the compromises which must be made sometimes produce marked changes in the objectives of individual systems . The system designer may find that he has developed two or three completely different systems for the same ship, with only the last representing a tOtallY acceptable compromise in itself, and with other systems The key words in the ship design process are “time” and “cost”, and the usual demand for speed and productivity leaves little opportunity for any system designer to advance the state of his art. The structural design process itself is also an iterative one, since direct structural synthesis has been achieved only for very simple structural systems Tbe core of this ite~ative cycle contains these steps: postulation of a geometry; analysis of the response under applied loads; comparison of calculated response against an established standard; and return to the geOmetry, revising it for an improvement in response. Other peripheral steps are required to support the cycle, including