Methods for the Evaluation of Wingsails with a Crescent-Shaped Profile

Licentiate thesis, 2023

Seaborne transportation accounts for a large proportion of greenhouse gas (GHG) emissions. The International Maritime Organization (IMO) has stipulated that GHG emissions should be reduced by 50% before 2050 compared to 2018. The use of wind-assisted ship propulsion (WASP) is considered one of the most effective ways to reduce GHG emissions. Therefore, the present study aims to establish multidisciplinary numerical models for predicting and evaluating the propulsive performance and structural response of WASP systems. 

Conceptual designs of a set of telescopic wingsail rigs are generated. Numerical simulations, including computational fluid dynamics (CFD) simulations and finite element analysis, are performed for dimensioning and optimizing wingsail structures for ships to understand the fluid–structural interaction (FSI). Since the deformation of the wingsail structure that the surrounding flow excites is so large, the interaction between the flow and structure creates a coupled problem. Analysis of a crescent-shaped wingsail using an in-house software ShipCLEAN, which is based on a generic ship energy model, is conducted to evaluate this wingsail’s propulsive performance in comparison with other WASP concepts. 

It is concluded that wingsails with a sectional profile and significant camber have much better propulsive performance than those with conventional airfoil profiles because the potential thrust force coefficient is approximately 30% higher. It is also found that the external loads on the crescent-shaped wingsail show notable periodic oscillations due to strong flow separation, so it can be inferred that wingsails can suffer from remarkable vortex-induced vibration. This raises higher requirements on the strength and rigidity of the wingsail structure. Tip vortices are found to have negative impacts on thrust, and the sail can strongly influence the wake flow. It is also concluded from the structural analysis that the strength, especially the von Mises yield and compressive normal stress, is most critical among the assessment criteria that are considered when evaluating the wingsail structure. Using a strong frame to bear global bending and introducing a cubic-shaped mast prevents stress concentration and reduces the weight of the structures.