A numerical study to analyse the effects of a micro-sized antifouling topography applied on a ship’s hull with the aid of computational fluid dynamics (CFD)

Abstract

Biofouling is the unwanted attachment of microorganisms on surfaces that are exposed or submerged under water. Biofouling has caused many serious problems especially the marine industry. The operational performance of marine vehicles such as ships will be negatively affected because of the build-up of biofouling organisms on the ships surface causing hydrodynamic drag. Several antifouling methods such as using toxic chemical coatings and manually removing the fouling organisms have been implemented but were unsustainable and costly. This leads to the investigation of natural and biomimetic surfaces that can solve complex engineering challenges such as drag reducing and antifouling surfaces that can save money and time. CFD analysis has shown that microorganisms on patterned surfaces will experience complex micro-hydrodynamic environment such as inconsistent velocity distribution, different strain rates, recirculation and distribution pattern of wall shear. Moreover, high shear bounded zones and steep fluctuating stress strain rate are microfluidic conditions that can inhibit the attachment of biofouling organisms. Many living sea creatures exhibit drag reducing and antifouling capabilities such as the shark skin riblet surface. The wall shear stress, fluid flow velocity and the development of vortices are useful in predicting the location of biofouling occurrence. Simulations on the shark skin surfaces shows the average velocity around the topography is 7.213 x 10-3 ms-1 and vortices were present between the gaps. The peak of each topography developed high wall shear stress but the bed of the topography experienced low wall shear stress which could lead to the potential build-up of biofouling. The investigation of the antifouling shell surface includes six different shell surface geometries that are simplified as V-shape riblet, U-shape riblet, space V-shape riblet, blunt V-shape riblet, L-shape riblet and ∩-shaped riblet. The velocity and shear stress analysis above the different shaped riblet surfaces were included. Moreover, the influence on the flow by different riblet shapes were also discussed. The knowledge gained from the discussion can aid to determine the optimal design of topography that can be applied to the ship’s hull. ANSYS fluent will be used to create the design for the ship’s surface. The ideal combination of size and geometry of topography based on literature will be selected. The 3D model of a few micro-sized topography surface will be produced. Tetrahedron method for meshing will be used for high accuracy. The analysis of hydrodynamic variations like wall shear stress, shear strain rates and flow velocity around the selected topographies will be determined. CFD simulations will be used to verify the antifouling performance of the topographies. The optimally designed micro-sized topographies that are simulated are expected to reduce the biofouling occurrence on a ship’s hull and reduce frictional drag during the sailing of ships.