Isogeometric Tribodynamics of a Radial Piston Fluid Power Motor

Abstract

In recent times the radial piston principle has been found particularly suitable for hydrostatic fluid power transmission systems for renewable energy applications. This forms an incentive to design these units for high efficiency. At present only little work has been dedicated to modeling of losses in radial piston units. The focus of this paper is an isogeometric tribodynamics model of a radial piston fluid power motor, which connects the rigid body dynamics with the models of hydrodynamic lubrication pressure in the sliding parts. The use of CAD models in the formulation of the tribodynamics eliminates the time and effort needed to manually parameterize the interface geometry. A NURBS-based isogeometric analysis approach is considered for the modeling of pressure dynamics of the fluid film lubrication. Isogeometric analysis is considered superior in terms of accuracy and efficiency compared to standard finite element methods, as it needs lesser degrees of freedom to produce same order of error. Moreover, it renders an exact representation of the lubrication domains in fluid power machinery possible. This makes isogeometric analysis very much convenient for boundary value problems on surfaces, such as hydrodynamic lubrication in joint clearances of fluid power machines. The paper explains the isogeometric tribodynamics model structure and gives a detailed description of the modeling of the piston-cylinder interface of a Calzoni type radial piston motor using the isogeometric approach.