First International Symposium on Marine Propulsors Smp’09, Trondheim, Norway, June 2009 Some Unsteady Propulsive Characteristics of a Podded Propeller Unit under Maneuvering Operation Pengfei Liu 1 , Mohammed Islam 2 and Brian Veitch 3 1 National Research Council Canada, Institute for Ocean Technology, St. John’s, NL Canada 2 Oceanic Consulting Corporation, St. John's, NL Canada 3 Faculty of Engineering & Applied Science, Memorial University of Newfoundland, St. John’s, NL Canada ABSTRACT Propulsion dynamics of a podded propulsor unit in steering motion at fixed azimuth angles were investigated numerically. Unsteady forces, torques and bending moments were predicted for a model podded propulsor unit at various azimuth angles. Analysis was performed for averaged forces and their fluctuations as well. A time- domain unsteady multi-body panel method code, PROPELLA, was further developed for this work. Predictions were compared with a set of time averaged in- house experimental data for a puller type podded propulsor configuration in the first quadrant operation. Unsteady fluctuations of forces were predicted numerically. Analysis was made for the bending moment on propeller blades, shaft and the propulsor unit stock shaft for azimuth angles from 0 to 45 degrees. It indicates that the magnitude and fluctuation of the forces are significant and they are essential for structural strength and design optimization. The predicted bending moment and global forces on the propulsor unit provide some useful data for ship maneuvering motion and simulation at off design conditions. Keywords Podded propulsor; Propulsor Simulator; Propeller unsteady loads; Panel Methods 1 INTRODUCTION Research and development on propulsion hydrodynamics prediction, design optimization and performance evaluation for traditional marine propellers are extensive in the literature. Among these, the first attempt of using panel method for a propeller was made in the mid 1980’s (Hess and Valarezo 1985), and examples of panel method application to marine propellers include the work by Kerwin and others (Kerwin et al. 1987) and some work at Mitsubishi (Hoshino 1993) to name a two. However, R&D activities for the podded propulsor units became noticeable only since around 2000. With a dramatic increase in application and installation of podded propulsors, structural and bearing failures became prevalent and hydrodynamic design optimization became important. Therefore, systematic research and development work, both experimentally and numerically became necessary. Prior to mid 2000’s, R&D work on podded propulsors was mostly performed by individual shipbuilders internally. Published results were rare. To address these issues, a collaborative R&D program was initialized in 2001 among Memorial University of Newfoundland (MUN), Institute for Ocean Technology (IOT) of National Research Council Canada (NRC), Oceanic Consulting Corporation and Thordon Bearing Ltd. The podded propeller research program contains both experimental and numerical components. The goal of the numerical work is to develop a robust and reliable numerical tool with a suite of capabilities to perform tasks such as propulsive characteristics and unsteady structural load prediction, and performance evaluation and design optimization of podded propeller units. In the past seven years, a propeller panel method code, PROPELLA, was adopted and used as the main prediction tool to address the needs for podded propulsor simulations. Numerical tools need verification and validation before they can be used but verification and validation with a good agreement with analytical and experimental measurements are not the ultimate goal of a numerical work. This numerical tool, in addition to being able to produce the same kind of results as from experimental measurements in a cost effective and timely fashion, was used to produce important results that are impossible or difficult to obtain from experimental measurements. These results include unsteady propeller blade spindle torque, in-plane and out-of-plane bending moments about arbitrary axes, and the propulsor unit’s transient global force and moments with respect to any arbitrary axes. The hydrodynamics kernel of the code is a classical panel method. It is a low order time-domain panel method formulated similar to many other panel methods, such as PMARC developed at NASA Ames Research Centre (Katz and Plotkin 1991). The backbone of the current panel method code was initially developed to simulate marine swimmers with lunate tails (Liu 1996a, Liu & Bose 1997, and Liu & Bose 1999). The code PROPELLA was then developed for an ice-class propeller research program (Liu 1996b and Veitch et al. 1997). Inflow wake and hyperboloid panel algorithm were studied and implemented as well (Liu & Bose 1998), followed by a semi-empirical cavitation model to predict propeller cavitation performance (Liu et al. 2001a). In the Copyright NRC. Printed with permission.