Full scale finite element modelling and analysis of the 17th-century warship Vasa: A methodological approach and preliminary results

Aging wooden structures in cultural heritage will inevitably need an improved support. A sensible design necessitates a numerical model of the structure to estimate stresses and displacements in order to evaluate a support design. In the present work a full-scale finite-element model of the 17th-century warship Vasa has been developed. Experiences from this exercise may be of use in making choices in the development of numerical models for other complex wooden structures of significance in cultural heritage. A geometrical model of the ship was provided by the museum as a wireframe model, consisting of only lines, points and curves. It was developed based on geodetic measurements using a total station and hand measurements of details with tapes and rules. From this wireframe model, a three-dimensional model comprising solid bodies for solid-like parts (i.e. the three-layer main hull and keel), surfaces for the shell-like components (deck planks) and lines for beam-like constituents (deck beams) was developed. This geometric model was then imported into finite-element software ANSYS, for further development of the stiffeners (knees, riders), pillars and masts as one-dimensional elements, adjustment of the correct location of deck beams and, finally, structural analyses of the entire ship. Since only the deformed geometry of the ship is known, the stresses and displacements were determined as a result of the self-weight and boundary conditions at support contacts only. The stresses in the three-layer main hull are lower than those in the other members. The displacements are determined from the reference state with zero gravity to the situation where the self-weight and the reaction forces from the support structure give rise to stresses and additional deformations. According to the geodetical measurements, visual observations and calculation of the centre of mass distribution, the maximum movement of the ship is at the stern. The displacements from the finite-element model are in general agreement with the observations, with the more pronounced displacement field towards the heavier stern of the ship. In addition, the highest stresses at the keel, the three-layer main hull and pillars in the orlop and storage decks appear to be at the stern in the numerical model.