Concept Development and Verification of a Friction-Fastened Radial Support for Marine Propulsion Systems : Concept-Level Function Verification Using FEM, CFD and Tribological Assessment

Sammanfattning

This thesis concerns a radial support used in a CPP (controllable pitch propeller) system, for marine vessels. The existing radial support solution is fastened by a welded interface to the outside surface of the twin tube. This introduces weld-related risks such as over-stiffening and built in stresses in the joint between the twin tube surface and the support geometry. The thesis develops and evaluates a friction-fastened radial support concept without a welded interface to the twin tube. The developed support is intended as a possible replacement for the existing welded radial support design used in the current twin tube system. When the developed support was designed without a welded interface, it became dependent on the frictional interface between it and the twin tube. The new support therefore had to combine a high-friction inner interface, a low-friction outer interface and a load-carrying geometry with low stress concentrations and good stress flow. To balance these contradicting requirements, three regions with individual functional requirements were established. To define the design limitations and conduct a more efficient concept generation, requirement matrices were established for the three functional regions. Concepts were then generated through brainstorming and structured concept development based on those requirements. The concepts were compared using a weighted decision matrix, after which the selected concept was refined through FEM (finite element method) simulations to reduce stress concentrations and improve structural behavior. PLA prototype testing was then used to assess geometric behavior, mounting procedure complexity and qualitative geometric fit behavior, while CFD (computational fluid dynamics) screening was used to study how the lubricant flow interacted with the new support geometry. The final selected non-welded concept was based on a two sided split cone geometry that is contracted and kept in place around the twin tube using a compression ring on each side. The results indicate that the concept is a promising replacement candidate for the welded support at a concept-verification level. The FEM results showed that the iterative refinement improved stress distribution and reduced local stress concentrations, with version 3 showing the most favorable structural behavior. The CFD screening indicated that lubricant flows over the support and reaches the outer sliding interface in a desirable way. The main limitation of the thesis is that simulations and prototype evaluations do not provide full validation of the actual physical performance. Dedicated fretting and wear simulations were outside the scope of the study and real mechanical testing of a fully metallic prototype is still required before any conclusion can be drawn regarding the actual long-term performance of the non-welded hybrid clamped cone radial support.