Methods for computing stiffness and damping properties of main propulsion thrust bearings¹

Article type: Research Article

Authors: Vassilopoulos, L.

Affiliations: Maritech, Inc., Belmont, U.S.A.

Note: [1] Paper presented before The New England section Society of Naval Architects and Marine Engineers, U.S.A.

Abstract: The study of longitudinal shaft vibrations of propulsion shafting systems requires knowledge of the thrust bearing stiffness and damping properties. The paper presents a step-by-step engineering procedure for determining these parameters using simplified structural model and elementary lubrication theory, but the utility of finite element and finite difference methods for more refined assessments is also mentioned. The paper deals only with integral bearings of the hydrodynamic, tilting-pad type. The net bearing stiffness is obtained by linearizing the behavior of its various elements, such as the collar, oil film, pads, buttons, links, rings, shims, housing and flanges. The derived analytical expressions for structural component flexibilities are based on existing, closed-form solutions for circular plates, beams, Hertzian contact stresses, cylindrical shells and compression members. The oil film stiffness is based on a simplified treatment of a two-dimensional thrust pad. Bearing damping is made up of structural damping which is based on empirical data and film damping which is taken to be caused primarily as a result of squeeze film action. Two modern bearings of different design are used to illustrate the methods discussed in this paper and to offer example calculations that should aid those wishing to make similar predictions for other bearings.

DOI: 10.3233/ISP-1982-2932903

Journal: International Shipbuilding Progress, vol. 29, no. 329, pp. 13-31, 1982