Investigating strains on the Oseberg ship using photogrammetry and finite element modeling

• Main Authors: Eriksson, Andreas, Thermaenius, Erik
• Format: Others
• Language: English
• Published: Uppsala universitet, Tillämpad mekanik 2020
• Subjects: Oseberg ship; strain; strain analysis; mechano-sorptive strains; Delaunay triangulation; finite element analysis; Materials Engineering; Materialteknik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-412912

The Oseberg ship is known as one of the finest surviving artifacts from the Viking age, with origins dated back to the 800s. The ship has been displayed in the Viking ship museum in Oslo since 1926. The nearly 100 years on museum display along with the over 1000 years it was buried has weakened the structure of the ship. To slow down the deterioration, several research projects has been initiated, among them the project ''Saving Oseberg''. A part of ''Saving Oseberg'' is contributing to the planning of a new museum for the ship. As a basis for the planning, the ship has been monitored with photogrammetry. This is intended as a way to visualise the deformation and displacements of the ship due to seasonal changes in indoor temperature and humidity. In this thesis the photogrammetry data from the hull of the ship was used to make a finite element model, and through this model calculate the average strain on each element. The method was based on a previous research project conducted on the Swedish warship Vasa by a research group at the Division of Applied Mechanics at Uppsala University. The measurements of the ship was formed into a hull by Delaunay triangulation. The strain was approximated as a Green strain and evaluated using isoparametric mapping of the elements. Through the nodal displacements, the strain was evaluated by approximating the elements as tetrahedrons and calculating the average strain from these elements between the measurements. The result showed an oscillating behavior of the displacements, proving the proposal of seasonal depending displacements. The measured principal strains also matched to the corresponding relative humidity fluctuation during the year. The strain magnitude was relatively even throughout the ship, mostly varying between ±0.4% but certain areas were more subjected than others. A few elements on the starboard side showed very large strains through most of the measurements, this seemed very unusual and was probably the result of inaccuracies or errors in the data. Though the ship is subjected to relative small strains and permanent displacements after annual cycles, the mechano-sorptive strains may lead to accumulated deformation and eventually failure in the weak parts of the wood or at the high stress concentraion parts. In addition, the cyclic strain even in elastic range may cause fatigue failure in any material which could pose a large threat for the future conservation of the ship.