Nonlinear programming techniques have recently been used rather extensively in conjunction with automated design and optimization of ship structures. This paper presents an introduction to the field and discusses the methods used, with special emphasis on the sequential unconstrained minimization technique (SUMT).
In practical design problems the number of free variables easily becomes high and the structural analyses may also become complex and time consuming. Large computer times are a consequence. Various methods by which the required number of redesigns during the search for optimum, as well as the computer work involved in each such redesign may be reduced are discussed. Approximate behaviour and constraint models in terms of simple polynomials have been used with considerable success and may be combined with an extrapolation technique that allows one to reduce significantly the number of response _ surfaces. The application of gradient methods of search combined with finite difference approximations of the gradients is demonstrated to yield efficient algorithms. Sequences of suboptimizations have also been tried with considerable success. In this manner the required computer time may by reduced to only a fraction of that previously experienced..
A few examples of typical applications to practical ship design problems are presented, viz. :
a) Optimum design of the midship section of an OBO-carrier.
b) Minimum weight design of grillages and transverse frames of tankers.