| Shafting vibration characteristics mainly depend on the supporting stiffness.Traditionally, marine propulsion shafting supporting stiffness consists of bearing stiffness, thestiffness of bearing seat and the hull structure rigidity. And these stiffness can be got bynumerical methods or experimental formula. However, because of the hydrodynamiclubrication, when shafting is working, fluid film will be occurring between the shafting andbearing. This fluid film has stiffness and damping, and also supports the shafting. The fluidfilm stiffness will change the original shafting supporting stiffness, and it will change theshafting vibration characteristics too. So, in order to get the accurate shafting vibrationcharacteristics in the condition of shafting rotating, the fluid film stiffness needs to be takeninto account.This paper used finite difference method to calculate the2D Reynolds equation, so as toget the fluid film pressure distribution in the bearing. And then, the influence of journaleccentricity and bearing aspect ratio to the fluid film thickness and pressure distribution isanalyzed.According to the previous research results, this paper presented a new method tocompute journal balance position based on secant method. Owing to the superlinearconvergence rate of secant method, the compute accuracy is higher and the compute time isshorter. And then, the influence of journal eccentricity and bearing aspect ratio to the journalattitude angle, bearing carrying capacity, side leakage flow, and journal drag coefficient isanalyzed.Load increment method and the force disturbing method were used to calculate fluid filmstiffness and damping respectively. Then the influence of bearing load, journal rotating speed,and lubricant viscosity to the fluid film stiffness and damping is analyzed.This paper proposed a new method to calculate the fluid film stiffness and damping,which can take journal arbitrary tilt and bearing elastic deformation into account. And then, itanalyzed the influence of Young’s modulus to the fluid film thickness and pressuredistribution, as well as the influence of bearing elastic deformation to the bearing static anddynamic coefficients.According to exist research results, this paper analyzed the effect of fluid film stiffnesson the shafting vibration characteristics. A simulated marine propulsion shafting test bench was built up, and both the simulation and experimental shafting modals has been done toensure that the model, which was built in ANSYS, is correct. And then, each bearing’s loadwas measure to calculate the fluid film stiffness under a certain shafting working condition.The impact of fluid film stiffness on the shafting inherent characteristics and shaftingvibration response was analyzed. The results show that, when bearings are under goodhydrodynamic lubrication condition, it is necessary to consider the impact of the liquid filmstiffness, so as to get the accurate shafting vibration characteristics. |
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