A VPP Derivative Optimisation Method for Wind-Assisted Cargo Ships Based on RANSE-CFD

Abstract 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 significantly from conventional operation with constant drift, heel and resultant induced resistance, there is significant potential in optimising hulls for sail-assistance. The evaluation of the performance of a sail-assisted ship involves balancing all aerodynamic and hydrodynamic forces. Typically, a Velocity Prediction Program (VPP) is used for this task. For accurate predictions, a large amount of RANSE-CFD calculations is necessary, which makes performance evaluation and hull optimisation computationally costly. In this paper, the VPP derivative method, is developed, which enables a far more efficient hull optimisation. 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 may be evaluated in a very time efficient manner by a gradient approach. Influence of the performance drivers is discussed and considerable performance increases are illustrated using a case study of a 130 m sail-assisted tanker vessel. Computational time per hull variation was cut down dramatically, while maintaining a satisfactory accuracy. The VPP derivative method proves to be a valuable tool to speed up the optimisation of a WASP ship hull.