DAA modal analysis for parametric investigations of fluid-structure interaction in underwater shock, revision 2

A program is initiated with the goal of developing a simulation of the underwater shock response of submarines. This capability is to be employed for systems analysis studies of a variety of tactical parameters, especially the orientation of the shock wave relative to the structure. It is deemed acceptable to develop generic analytical models that avoid the details of specific structures, and the number of degrees of freedom is limited by the need for computational efficiency. These objectives were met by using the modal expansion version of the doubly asymptotic approximation. This technique is implemented in a modular form that permits progressive enhancements of a basic model. The concept is to partition the system into substructures that are not inertially coupled. Based on these concepts three varients on a basic model are described; each modification provides the capability to evaluate different aspects of the system. The basic model consists of a rigid cylinder capped by hemispheres subjected to a shock wave arriving from an arbitrary heading angle. The REFLECT model extends this fundamental model to treat multiple shock waves associated with reflections from the surface and bottom. This analysis employs a vectorial superposition of the CAPS response for each incident wave. To assess the importance of an internal dead load, such as a reactor, the CAPS model is extended. The new version includes a large internal mass suspended from the cylinder by four springs that give equivalent axial, transverse and rotational suspension stiffnesses. The center of mass of this dead load can be located arbitrarily along the axis of symmetry of the cylinder.