Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Agricultural and Biological Engineering

Committee Chair

Monika Ivantysynova

Committee Member 1

Andrea Vacca

Committee Member 2

Sadegh Dabiri

Committee Member 3

Dennis Buckmaster


Presently, axial piston machines of the swash plate type are commonly used in industry due to their many benefits. However, with recent technological advancements in hydraulic hybrid powertrains and displacement-controlled actuation, the application of such machines has been broadened demanding a more cost-effective reliable and efficient, yet versatile machine. The fluid film geometry of the lubricating interfaces is a very complex and sensitive phenomena that must simultaneously fulfill a competing bearing and sealing function. Therefore, the design process of such machines is a difficult process while tightly constrained manufacturing tolerances are essential thereby increasing the initial production costs. Accordingly, virtual prototyping through analytical simulation in this field has emerged as an ideal tool not only to improve the performance of existing units, but to also design new and innovative axial piston machines that fulfill the demands of advanced technology.

The aim of this dissertation is to investigate more efficient and reliable designs of the piston/cylinder interface of an axial piston machine over a broad range of operating conditions. Primarily, an extensive simulation study was conducted in which the design of a commercially available machine was modified to accommodate piston micro-surface shaping where the relative improvements were then quantified in comparison. This study utilizes a novel fully-coupled fluid structure interaction model considering both thermal and pressure deformations of the solid bodies to accurately predict the dynamic behavior of the lubricating interface. Having analyzed the phenomena of the lubricating gap and the effects of micro-surface shaping, an optimization technique was utilized to design this interface. The optimization scheme determines the best balance between improving the sealing function while maintaining or even improving the bearing function. A surface shaped piston was then measured and compared back to the simulation results realizing the capabilities of such a novel methodology. Ultimately, this cost-effective design process demonstrated that micro-surface shaping is beneficial as it allows for reduced clearances, achieving a reduction in volumetric losses, while increasing fluid film support, resulting in superior efficiency as well as enhanced reliability and overall performance.