Numerical Studies of Propeller Exciting Bearing Forces under Nonuniform Ship’s Nominal Wake and the Influence of Cross Flows

Huilan Yao,Huaixin Zhang

doi:10.1155/2017/4319260

Abstract

Propeller exciting forces are the main causes of stern vibrations. In this paper, three-dimension exciting bearing forces of one blade and the whole propeller under nonuniform ship’s wake were predicted, and the influence of cross flows on these exciting forces was studied. All simulations were carried out using a commercial solver, STAR-CCM+. To obtain the nominal wake for studying propeller exciting forces, flow field around a bare hull was simulated. Numerical results were widely validated by measured data, especially the velocity field at the propeller plane. Harmonic characteristics of the nonuniform ship’s wake were studied. Then, a propeller under uniform inflow and nonuniform ship’s wake with/without cross flows was simulated. Free-water surface and hull boundary were considered using a specially designed dummy stern. Results show that the influence of cross flows on propeller exciting forces is obvious. As for the exciting forces of one blade, the cross flows have greater influence on the axial force. As for the exciting forces of the whole propeller, the cross flows have greater influence on the transverse and vertical forces, and if the cross flows in ship’s wake are not considered, the amplitudes of the main harmonics of transverse and vertical forces increase obviously.

Highlights

With the increasing pressure of market competition, both the load capacity of the ship and the main engine power are increased
The present study focused on predicting three-dimension exciting bearing forces of one blade and the whole propeller under nonuniform ship’s wake using numerical methods and studying the influence of cross flows on these exciting forces
It is clear that the predicted ship resistances by unsteady Reynolds-averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) are close to the experimental data, and all deviations are within 6% (Table 3)

Summary

Introduction

With the increasing pressure of market competition, both the load capacity of the ship and the main engine power are increased. Under the influence of nonuniform ship’s wake, propeller exciting forces, including bearing forces and surface forces, may cause severe structural vibrations. The nonuniform ship’s wake is needed for measuring propeller exciting forces. The entire ship model with a model-sized propeller can be used in large cavitation tunnels or depressurized tanks to perform the measurement experiments. If the wire grid is used alone, only the axial velocity is simulated, and the measured results need to be revised to consider the cross flows. If the wire grid is used with a dummy stern, the simulated cross flows may still be different from that in the actual ship wake. It is important to study the influence of cross flows in the wake field on propeller exciting forces [2]

Methods

Results

Conclusion