An existing nonlinear ship design optimization program designated SHIPDOC has been extended and a new surface effect ship (SES) description input file is being developed under the sponsorship of the Naval Sea Systems Command's surface ship concept formulation (CONFORM) program. SHIPDOC is currently being used in support of several feasibility and preliminary level SES designs.
The program has several novel features including an open‐ended, user‐created ship description and the potential to model all types of ships both enhanced and conventional, surfaced and submerged. This capability has been combined with a nonlinear optimization algorithm that solves for the minimum weight ship subject to user controlled constraints.
This paper presents a brief overall description of SHIPDOC and its current capabilities followed by a synopsis of ship types, both surface and submerged, which have been designed with the program in order to illustrate SHIPDOC's practical design capability.
Rationales for using reliability based techniques for technology evaluation and design are presented. The use of a method for estimating lifetime loads, applicable to any ship type, is presented using primary structural load estimation as an example. The sequence leading from model design considerations and testing through the formulation of structural criteria is explained and illustrated using SES examples. The principal emphasis is upon overall or global loads although the method can be applied to local loads. The method provides a means of quantifying load differences due to variations in a commonly used structural load probability distribution, mission requirements, operating environment, vessel lifetime, and service life reliability. An example showing the effect upon displacement for changes in primary load exceedence is shown. The method of load estimation used here, once experimental (or theoretical) data are available, is shown to be no more difficult to apply than currently used deterministic methods, thus allowing quantitative estimates of certain technology changes to be made quickly.
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