Finite Element Modeling And Fluid-structure Interaction Vibration Analysis Of Main Engine And Double Bottom

Engine room double bottom is an important structural component of ship hull, its main function is to guarantee the transverse, longitudinal and local strength of a ship and isolate engine room with sea water. The vibration generated by main engine and other mechanical equipment in operation is passed to double bottom through supporting system. The stimulated vibration of double bottom may cause vibration of other ship structures and radiate noise to surrounding sea water. Excessive vibration may not only cause structure fatigue, but also affect normal operation of other equipment and physical mental health of seafarers. Therefore, the research on local vibration of ship, engine room double bottom included, has been one of the focus of work on vibration and noise reduction of ship. Liquid tanks between inner bottom and outer bottom of double bottom hold liquid such as lubricating oil, fuel oil and sewage. At the same time, the outer bottom contact with sea water. As the fluid-structure interaction largely changes inherent characteristic of structure, the effect of fluid in liquid tank and surrounding sea water on results cannot be ignored when vibration characteristic and vibration response stimulated by main engine of double bottom is analyzed.According to the research status, the paper firstly establishes FSI model of main engine lubricating oil tank in double bottom in ADIN A software. The influence of fluid on inherent characteristic of lubricating oil tank is analyzed and different boundary conditions of free surface of fluid is discussed, which lays the foundation for latter analysis. Secondly, the effect of fluid on natural frequency and modal shape of double bottom is further analyzed by the modal analysis of double bottom in different case (dry, fulfilling and contacting with surrounding sea water). Thirdly, the finite element model of MAN6S35MC diesel engine is established and connected to double bottom, the change of modal shape of coupled model is acquired. Finally, transient analysis is used to acquire the vibration response of coupled model. The effect of fluid in liquid tank and outboard sea water on vibration response is analyzed. This paper has some reference value on further research of coupled vibration of ship’s local structure and power equipment.