Experimental validation of an inverse method for the determination of ice loads on a ship hull

• Main Author: Veltheim, Oskar
• Other Authors: Suominen, Mikko, Ikonen, Teemu, Insinööritieteiden korkeakoulu, Kujala, Pentti, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2022
• Subjects: inverse method; FEM; experimental measurements; experimental validation; ropax; Baltic Sea; Arctic; Arktis*
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/114526

The decrease of the Arctic ice coverage enables increasing number of ships to operate in new shipping routes. To ensure safe operation in Arctic conditions safe and efficient ship designs are required. One important aspect of current ship-ice interaction studies is the determination of the extend of the ice load area, which is especially interesting in terms of structural design. The aim of this thesis is to develop and validate an inverse load determination method. The method is validated using experimental data, which was measured during the building phase of the ropax ferry Aurora Botnia. The data consists of measured strains and loads from sets of experimental loadings of the hull. This thesis presents an inverse method, which uses an influence coefficient matrix to represent the strain response of the structure to the unit pressure applied to discretization areas of a selected load discretization. The matrix is constructed based on the strain response of a finite element model, which is verified using the collected experimental data. The method determines the loading from the measured strains in the structure using the influence coefficient matrix and a simplified Tikhonov regularization equation. Based on the results, the inverse method succeeds to locate the load in a 3-by-3 grid load discretization in 42 of 46 loading events. The average relative error of determined load magnitude is 13.5 %. Three major sources for uncertainty are the inaccuracies of the experimental measurements, inaccurate finite element presentation of the real structure and the drift of the experimental strain data. These sources and possible solutions are discussed. Arktisen jääpeitteen kutistuminen mahdollistaa kasvavissa määrin laivaliikenteen uusilla laivaväylillä. Laivojen turvallisen operoinnin takaamiseksi laivat on suunniteltava turvallisiksi. Erityisen tärkeä osa nykyistä jään ja laivan vuorovaikutustutkimusta on jääkuormien vaikutusalueen määrittäminen. Tämä on erityisen tärkeää rakennesuunnittelun kannalta. Tämän ...