Theoretical and computational analysis applied to a towfish design

Abstract

This thesis presents a preliminary design of a towfish structure which is done according to the European unfired pressure vessel code EN13445-3 [1]. The towfish is basically an underwater vessel which is equipped with sensors and cameras that are used to detect pollution and at the same time monitor plankton and jellyfish levels. The towfish is towed behind a surface ship using a towline and it is designed to dive to a depth of 50m below sea level. The depth of dive is controlled by means of hydroplanes. The towline permits also the transfer of data, control signals and electrical power between the towfish and the surface ship. From a structural point of view the towfish is a vessel acted upon by external pressure and local loads. Design by rule (DBR) was first used to calculate some of the various dimensions and thicknesses of the towfish components. The various components were designed mainly to prevent failure due to buckling. To this effect literature review and theory and methodologies in buckling are treated extremely in the thesis. Design by analysis (DBA) based on Annex B of the pressure vessel code EN13445-3 [1] was then used to carry out further buckling checks that were not possible to do using design by mile. It was concluded that the DBR resulted in a reliable towfish design and that the DBA was required to for designing certain components which were not covered in the DBR section.