1534. Cut and Splice a Method of Weight Estimating for Naval Ship Design

Paper

Abstract

During Preliminary Design Session of the 1983 SAWE International Conference, the Algorithm Mass-
Factoring Method (AM-FM)*, for determination of realistic weights from the theoretical weights of
any finite element model (FEM) structural optimization and analyses program (SOAP), was presented.
The algorithmic method is based on the premise that for any structure, when reduced to elementary
components as in a finite element model, the elements can be described in terms of simple functions.
These functions are easily determined. For example – a plate (cover, web, membrane) element; is
capable of carrying and transferring certain tupes of loads; may be stiffened in some manner to
yield a valid realistic weight for that element. In a similar manner, the weight of beam elements
can be determined. It was noted, based on the above premise, that the AM-FM is applicable to any
type of structure (aircraft, missile, space vehicle, automobile, buildings, etc.) that may be analyzed
by FEM-SOAP’s.
One of the major areas of concern was the unknown effect of FEM grid-density on both the SOAP sizing
and the AM-FM weights. The purpose of this paper is to present the results of an analyses of a wing
box using three levels of element grid-density. Further, a modeling technique variation was included.
The variable technique studied was the modeling of plate stiffeners as beam or rod elements versus the
effect of being modelled as lumped stiffeners. The study shows that the AM-FM method of finite element
model weight determination is self-adapting and insensitive to grid-density variations.