engleski

A numerical analysis of the ship's propeller shrink fitting

In merchant marine ships of nowadays, propellers play a significant role in their propulsion systems. Propellers are used to convert the shaft's rotation into the thrust force that is transmitted to the hull, causing the ship's motion. The most common junction between the propeller and the shaft is the conical keyless shrink-fit junction. This junction is of particular importance when applied on large merchant ships. Therefore, this shafting detail deserves a particular attention in design, construction, manufacture and assembly, as well as in the exploitation surveys. Owing to the fact that there were many failures of this important junction part reported, the In-ternational Association of Classification Societies (IACS) dealt with this problem since 1978, establishing the common Unified Requirement UR K3. However, neither the all IACS societies have implemented this UR completely, nor the problem has completely been solved. This was the reason why this problem was assigned to the IACS Working Party on Machinery, with the main focus on improving the existing UR. The development of numerical tools, particularly the simulation of contact problems using the Finite Element Method, enabled more detailed analysis that was not possible in the early eighties. The conical keyless shrink-fit junction of an 8, 3 m diameter propeller of the 166.300 tdw oil tanker, presently being built in Croatia, was modelled by using the non-linear finite element package ADINA. The fitting process and the conditions met in exploitation were simulated for various operating temperatures that are strongly effecting the junction. Analytical results are based on the pressure-axial displacement relation during the fitting process, the push-up force relation, and the relation describing the thermal pressure changes in exploitation. The obtained results are presented in tabular and chart forms and compared with the analytical ones obtained by the IACS UR. The analytical and numerical results show a very good agreement. A simple analytical method and a numerical finite element approach have been implemented to the calculation of keyless shrink-fit of the propeller to its shaft. The analytical method is based on the simple analytical calculations, as stated in CRS rules and IACS UR K3. The numerical modelling uses a rather complicated non-linear approach, especially when modelling the contact. The most important conclusion is that the value of the simple analytical method has been proved, by comparing its results to the ones obtained by numerical modelling in the presented case of a real practical situation, i.e. the 166.300 tdw oil tanker. This fact is of great importance for the future development of the IACS UR K3. Further work is going to be focused on the improvement of the analytical method, taking into account the unequal pressure distribution along the junction. Numerical results and feedback ob-tained during the assembly process in a shipyard will be used to evaluate the worth of the analytical approach. The final goal is to obtain a comprehensive, robust, fast and verified method, which may be easily implemented in a classification society surveyor's everyday work.

ship; keyless propeller; shrink-fitting; nonlinear FE analysis

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