The Effects of Hydrodynamic Forces on Maneuvrability Coefficients for Wind-Assisted Ships

Abstract

Assessing the manoeuvring performances of a ship at a design stage is becoming more important, especially when trying to improve shipping efficiency to reduce fuel consumption. When designing a hull with appendages, it is necessary to balance hydrodynamic efficiency with manoeuvrability. Therefore, the possibility of simulating a captive test at a design stage will increase the chances of understanding the behaviour of a ship from an early stage in the design process. The current research is based on the evaluation of hydrodynamic efficiency of a hull and appendages in a pure resistance, self-propulsion and in a wind-assisted mode. The forces and moments acting on the hull and appendages are then analysed and used as inputs for a Virtual Captive Test (VCT) [1]. In order to correctly perform a VCT and further analyse the performances of a ship with a Velocity Prediction Programme (VPP), particular care has been put in correctly capturing the manoeuvrability coefficients. Those are derived with polynomial fittings once the forces and moments acting on the ship are extracted from the Computational Fluid Dynamics (CFD) simulations. Many CFD simulations were performed to assess the hydrodynamic characteristics of the hull and appendages in a range of flow directions, rudder angles and rotating flow. Those simulations encompass the whole range of datapoints needed to describe a wind-assisted ship during manoeuvring. Taking into consideration both hydrodynamic characteristics and manoeuvrability effects at an early design stage can reduce model tests costs and will allow to inspect a larger number of hull-appendages scenarios when analysing the final VPP results.