Effect of construction process on displacement reduction of aluminium high speed craft

Effect of construction process on displacement reduction of aluminium high speed craft

Bouhuys, C.W.

Kaminski, M.L. (mentor)

Mechanical, Maritime and Materials Engineering

Marine and Transport Technology

2017-03-03

On one hand, welded hulls of aluminium high speed craft are found to have a decreased displacement. On the other hand, ship stability is determined based on an inclination test and the design lines plan. The combination of reduced displacement, results of an inclination test and the design lines plan reduce the stability. This reduction is undesired and should be controlled during hull construction. The following research question was formulated in order to allow this control: How does the construction process of high speed craft effect displacement of aluminium hulls? The literature study has confirmed that welding produces relatively large deformations of thin aluminium panels. These deformations can be split into out-of-plane and in-plane deformation. Out of plane deformations are caused by asymmetric shrinkage of a weld with respect to the middle of the plate in the thickness direction. In-plane deformations result from in-plane shrinkage of a weld and surrounding material. Both types of deformations contribute to transverse and lengthwise reduction of plate dimensions. A little has been found on quantitative prediction of these deformations. Analytical prediction models as function of material properties and welding parameters exist, but they are mainly applicable for steel structures. Also some empirical models have been found for steel. This has led to the following research program. Assuming that physical phenomena responsible for deformation of steel and aluminium structures are the same, it has been decided to tune coefficients for these models based on deformations measured during construction process of aluminium structures. Three measurement campaigns were carried out. The first campaign was focused on selection of a method to measure relatively small panel distortions. Different methods were considered. Finally a 3D scanner provided by FARO and software provided by Polyworks were chosen because this method allows for measurements at different stages of panel construction in laboratory and shipyard conditions, see Figure 1. It has been found that the method is accurate enough providing that fixed reference blocks are used. The second and third measurement campaigns consisted of measurement of a deck panel and T-frames. During production of the panel, multiple scans were performed to capture evolution of deformations. Processing the results revealed that in-plane deformations dominate in-plane shortening of the panel and that the out-of-plane deformation can be disregarded. Production of the T-frames consisted of joining the flange to the web of the frame. This was done by means of a double sided fillet weld. Scans were performed before and after welding. In this case it has been concluded that the out-of-plane deformation cannot be disregarded. The obtained analytical and empirical formulations have been used to develop a method which is capable to quantify shrinkage of aluminium structures depending on welding sequence. The method is relatively simple but resembles the observed phenomena. Finally, the method has been implemented in a computer tool. The validity range of the method is limited to structures similar to those measured. The tool is capable to predict displacement changes of aluminium high speed craft caused by welding during the engineering stage so that some measure can be undertaken to mitigate these effects.

http://resolver.tudelft.nl/uuid:49f3f2fe-a792-46b3-bddc-6fdaad413882

2022-03-03

Student theses

master thesis

(c) 2017 Bouhuys, C.W.