Lloyd (1983) described SLWIM, a new kind of mathematical model being developed at the Admiralty Research Establishment, Haslar, to predict the manoeuvnng qualities of deeply submerged submarines. The model uses a simulation of the changing flow around the manoeuvring submarine to predict the time history of the forces and moments experienced by the boat. These are then used to drive the standard equations of motion and predict the trajectory of the vehicle in response to movements of the control surfaces A related model called NUSIM is also being developed in parallel at ARE Haslar and forms the subject of another chapter in this volume (Tinker, 1988).
The main advantage of these models over conventional derivative based mathematical models is that they require no ad hoc model test data to provide information on the hydrodynamic characteristics of the particular submarine being simulated Predictions can therefore be made at an early stage in the design process without the need to build expensive physical models and test them over a long period of time.
The flow around a manoeuvring submarine is dominated by the vortices which are shed from the appendages and the hull (Fig 1) The characteristics of the appendage vortices may be predicted using lifting line or lifting surface theory The body vortices are influenced by the incidence and the rate of turn of the vehicle, and the timely prediction of their characteristics seems to be beyond the scope of any existing theory The SUBSIM program therefore makes use of empirical data to represent their effects The NUSIM program includes a prediction of the body vortices, but this is time consuming and is at present confined to rectilinear flow (1 e at a simple angle of incidence)
There exists a considerable mass of data on body vortices in the aeronautical literature Most of these data relate to the flow around missile-like bodies with pointed noses and blunt tails at supersonic speeds, although there are some subsonic data for airships Virtually all of these data seem to have been obtained in rectilinear flow, and any effects of flow curvature caused by manoeuvring have been ignored.
This dearth of information on submanne-like bodies (with blunt noses and pointed tails) in curved flow demanded that suitable experiments be conducted to provide empirical data for SWIM and validation of future developments of NUSIM Lloyd and Campbell (1986) described development work leading to suitable experiments and gave(Fig. 1 is available in full paper) some preliminary results Since that tune further experiments have been completed and a more detailed and sophisticated method of analysis has been developed. This chapter discusses the interpretation of selected results in detail and describes some of the difficulties encountered in the analysis.
The experiments were carried out in the Manoeuvring Tank at ARE(H) They were performed by the Wolfson Unit for Marine Technology and Industrial Aerodynamics (Southampton University) working under contract to ARE(H)