THE APPLICATION OF MODELLING AND SIMULATION TO SHIP DESIGN FOR HELICOPTER OPERATIONS

Modern combat ships, such as frigates and destroyers, routinely operate with maritime helicopters. The challenge of landing the helicopter in bad weather is acknowledged as being both demanding and dangerous; moreover, if the flying conditions are too difficult the helicopter will not be cleared to take off, and an important component of the ship’s capability will be lost. The unsteady air flow over the ship, particularly in the vicinity of the flight deck, is a significant factor that limits the helicopter’s operational envelope. The characteristics of the air flow, known as the ship’s airwake, depend on the wind speed and direction relative to the ship, and the geometry of the ship’s superstructure. The aerodynamics of the ship’s superstructure does not receive much attention at the design stage, compared to, for example, its radar cross-section. This thesis presents an investigation where modelling and simulation has been used to assess and inform the aerodynamic design of a modern warship. The modelling techniques that have been applied are time-accurate computational fluid dynamics, to compute the complex three-dimensional unsteady flow field over the full-size ship, and the mathematical modelling of a helicopter’s flight dynamics, to compute how a helicopter will respond to the unsteady air flow. These modelling techniques have then been used in two simulation applications; one is the Virtual AirDyn, to assess the unsteady loads applied to the helicopter by the ship’s airwake, and the second is piloted flight simulation in a motion-base flight simulator, to assess the effect of the airwake on a pilot’s workload while conducting a deck landing. Collectively the modelling and simulation techniques have been used to assess different design options for a ship’s superstructure. The techniques have also been applied investigate how the ship’s size affects the airwake and the ship’s motion, and how these affect the helicopter and the pilot workload when operating over the landing deck. Air flow modelling has also been used to predict how a ship’s hot engine exhaust gases mix with the airwake to cause fluctuating elevated temperatures over and around the flight deck. It has been demonstrated how relatively small changes to the geometry of the ship’s superstructure ahead of the flight deck can affect the aerodynamic loads on the helicopter, and that these effects can be detected and quantified to provide guidance to the ship designer. It has also been shown that while larger ships create larger and more aggressive airwakes that perturb the helicopter and increase the pilot workload during a landing. Smaller ships, on the other hand, have a more dynamic motion in rough seas, and smaller decks with a closer superstructure. Simulation has been used to show how these different effects combine and how ship size affects the pilot workload during a deck landing. The study has also identified that while offshore oil rig helicopter operators have clear guidelines on limits for air temperature increases, there are no such guidelines when operating a helicopter to a ship, and that the range of temperature increases that can occurs over the flight deck are sufficient to affect the helicopter performance. A significant contribution made by this study has been to inform the design of a real ship, so demonstrating the potential of modelling and simulation in the design of ships for helicopter operations.