Enabling efficient hull optimisation for wind-assisted cargo ships: The VPP derivative method based on Ranse CFD

Kurzfassung

Wind Assisted Ship Propulsion (WASP) technologies represent a means to adhere to decarbonisation regulation, while ensuring an economic ship operation less dependent on future volatilities in fuel prices. As wind-assisted operation differs from conventional operation with constant drift, heel and resultant induced resistance, optimising hulls for sail-assistance unlocks significant potential. The performance evaluation of a sail-assisted ship involves balancing all aerodynamic and hydrodynamic forces, for which, typically, a Velocity Prediction Program (VPP) is used. For accurate predictions, a range of RANSECFD calculations is necessary, making performance evaluation computationally costly. Consequently, hull optimisation becomes a costly nested process with the VPP analysis as the inner loop. This paper presents, the VPP derivative method, which enables a more efficient hull optimisation through quicker evaluation of the objective function. The method focuses on specific operation conditions and employs RANSE-CFD simulations replicating these. To employ a VPP speed derivative, selected key performance drivers are monitored. In this way, performance implications of hull variants can be evaluated efficiently by a gradient approach. The objective function may be evaluated quicker and the nested process is converted to a single-loop optimisation. The influence of the performance drivers is discussed using the case study of a 130 m sail-assisted tanker vessel. Through a sequential design space exploration, considerable performance gains are illustrated, while maintaining satisfactory accuracy and dramatically reducing computational time per hull variation. The VPP derivative method proves to be a valuable tool to speed up the optimisation of a WASP ship hull.