Parametric hull shape variations by Reduced Order Model based geometric transformation

The representation and the variation of hull shapes are two challenging problems in naval architecture due to the complexity of the geometry and to the need to ensure the fairness of the surfaces. Conventional CAD techniques are widely used to accurately describe the hull shape. However, they are rather complex to be easily used to generate hull shape variations due to the great number of variables involved. We propose a study to highlight the pro and cons of the application of space reduction techniques, usually referred to as Reduced Order Models (ROMs), to create a parametric model for both global and local hull shape variations. A geometric transformation relying on the Proper Orthogonal Decomposition (POD) method is applied on top of a combined subdivision surface — Free Form Deformation (FFD) approach conceived for modeling and variation of hull shapes. The analysis focuses on highlighting the geometric meaning of the new POD basis functions and on how this model affects the variability of the explored design space. Two studies are developed in order to show possible applications of this technique. In the first one a new set of selection criteria for the POD modes based on geometric considerations are proposed to use it on uncorrelated geometric domains. In the latter the large-dimensional space of the so-called Design Velocities (DV), related to the shape sensitivity, is reduced by using the POD approach to create a new transformation of the hull shape.