Characteristics of Field in Stern's Neighborhood under Maneuvering Motion

Abstract

The interference effects among hull, propeller and rudder have not been studied enough to establish the MMG type mathematical model for maneuvering motion of ships. An interference factor in the MMG model concerning inflow velocity to a propeller is calculated by applying the thrust identity method to measured propeller thrust under captive model tests. On the other hand, a factor concerning inflow velocity to a rudder is also calculated by applying the normal rudder force identity method to measured rudder force. In some published papers about the MMG model up to this time, the inflow velocity to a propeller under starboard side turning is different from one under port side turning whose turning rate is the same as the former's in an absolute value. And it is also shown that the inflow velocity to a propeller becomes increased by removing a rudder from an after body. Above mentioned facts seem so unreasonable that the following measures were taken. (1) Rotating fluid velocity around the longitudinal axis at a propeller disc which is generated around an after body under maneuvering motion is added to driving propller's revolution as increasing or decreasing relative propeller's revolution. (2) In order to derive the inflow velocity to a propeller before a rudder behind a ship, the K_T-J curve of a propeller with a rudder is used in applying the thrust identity method. Furthermore, in the latter part of this paper, measured velocity distribution at a propeller and a rudder are shown, and the characteristics of flow field in stern's neighborhood under maneuvering motion are described clearly.