An optimal flattening algorithm for ship hull plate fabricated by thermal forming

Normally, ship hull plates contain compound curvature distributions and they can only be fabricated by integrating mechanical rolling with bending and following them with regional heating to achieve required configuration. This paper mainly proposes a comprehensive flattening process to determine optimal planar shape, shrinkage strain distribution and mapping relation for three typical ship hull plates by thermal forming, which practically benefit for automatic forming. An innovative geometric method is first presented to obtain initial planar approximation and strain square sum subject to negative principal strain constraints within each element from planar to desired surface is formulated based on nonlinear kinetic analysis. Then, we employ area equivalent method through transforming spatial quadrilateral into planar quadrilateral to simplify optimization model. Finally, initial planar approximations are regarded as iteration initial points to solve the model based on sequential quadratic programming. The results indicate that the proposed process can effectively achieve optimal planar shape, mapping relation and negative principal strain to help achieve all heating paths and heat source parameters at one time, thus automation.