Vibrartion Analysis of Fibre Glass Contra Rotating Propeller of Fishing Vessel

Abstract

Conventional marine propeller remains the standard mechanism for ship propulsion however the blade material of a marine propeller is very significant in reducing the noise and vibration. The efficiency of a marine propeller mainly depends on blade material due to the marine corrosive environment, scaling and marine aquatic growth on the blade surface. The propeller efficiency depends on blade shape, size, density, and strength of the material. A suitable blade material should have low density, high strength and long fatigue life. At the same time the blade material should with stand large hydrodynamic inertia, fatigue load, sustain the sea environmental effects like accumulation of silts, sediments, algae, calcium deposits etc. Due to the increase in weight of the propeller due to these deposits and also designing a larger size propeller becomes more important. Indeed, optimising the weight of the propeller blades are of great importance since this would lower the forces transferred on to the propeller hub. These factors demand the selection of new and innovative materials for blade manufacturing to sustain above environmental conditions and required mechanical properties. Fibre glass appears to be a promising material for marine propellers being well known for its low weight, high strength and stiffness. It is highly flexible and low-cost material and acts as a protective barrier from corrosion and rust in saline environment and found to be a promising propeller material for small craft fishing vessels. To control the noise and vibration and improve the onboard comfort level on small fishing vessel contra rotating propeller made from fibre glass was proposed in the present research work. For this propeller made from 3 different materials such as fibre glass, Carbon Epoxy and Aluminium were chosen and modelled for different geometries. A contra rotating propeller comprises two coaxial propellers sited one behind the other and rotating in opposite directions. The forward propeller diameter is bigger in diameter has 4 blades while aftermost propeller is smaller in diameter have 3 blades only both of them made from fibre glass material. This present CAD model was designed using FUSION 360 software. The purpose of the contra rotating propeller is to ensure that the design of the propeller is tuned according to the above needs. The vibration simulation studies are carried using Ansys FEM analysis software. In this work the modal analysis was done without considering the damping for different thrust loads using Fluent software 16. 0. The blade is assumed like a cantilever beam subjected to loading. A higher section modulus is taken which can be achieved if more mass/fibre is distributed towards the root of the blade as opposed to the tip, as more distribution of mass away from the neutral axis. The simulation results obtained were compared with respect to the other materials. In the present simulation fixed boundary conditions are assumed at the two propeller shafts with total number of elements as 4548 and 8436 nodes. The results show that the mode shapes for above modelled fibre made glass contra rotating propeller regarding 1st, 2nd & 3rd order frequencies occur at of 52.815Hz, 78.42Hz & 116.96Hz respectively. The results confirms that fibre glass material would be a promising material for contra rotating propellers suitable to small craft marine fishing vessels.