Analysis of Local Vibration and Strength of Water Jet Propulsion Unit of High Speed Ship

In recent years, water jet propulsion unit has been widely used in the field of high speed ship. Compared with traditional propeller, water jet propulsion unit has excellent maneuverability with high speed, and lateral force generated by water jet propulsion unit can reduce the radius of turning. High speed ship with water jet propulsion has higher efficiency, lower noise. However, water jet propulsion unit needs to be opened in stern transom plate, and it causes the water jet force when ship is operating, all of these will affect the local strength of stern. It remains to be researched whether the vibration generated by water jet excitation force has a significant influence. These problems are designers worried about. To solve these problems, this paper builds the finite element model of stern contains water jet propulsion unit, considering hull deck load, broadside load, bottom load, bulkhead load and water jet load, checking the local strength of stern. Analysis of vibration problem, considering the influence of added mass of entrained water, dividing stern into deck, bottom, water jet propulsion unit, stern transom plate and other local structure, calculating natural frequencies of plate, panel and grillage of each local structures. Comparing the results with shaft frequency and blade frequency, checking the reserve frequency, judging whether water jet propulsion unit on vibration problem meets standards, providing reference for the following hull design.