Surface-specific Moody-diagrams: A new paradigm to predict drag penalty of realistic rough surfaces with applications to maritime transport

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment


The sea-water that flows over a ship hull forms a turbulent boundary layer that is responsible for the skin-friction drag incurred by the ship. This boundary layer is influenced by the "roughness'' of the hull surface, which increases the drag penalty by up to 80% compared to a smooth surface in some applications. This highlights the urgent need to understand the "roughness'' effects of surface coatings and their degradation on the efficiency, economy and emissions of ship transportation. In this project, we propose a transformative approach where we tackle this pressing problem using three complementary methods. First, we will carry out Direct Numerical Simulations (DNS) of turbulent flow over surfaces that have been obtained from surface scans of various ship hulls. These results will be complemented by laboratory experiments and measurements in a towing tank of flows over replica of the same scanned surfaces. Finally, a DNS-Embedded Large Eddy Simulation (DELES) methodology will be developed and used to predict the influence of realistic topographies on drag.This holistic approach will provide the necessary data to gain fundamental understanding of the flows over such rough surfaces and enable development of a new data-rich paradigm for predicting the effects of roughness. We will specifically focus on maritime transport by developing a new surface-specific Moody-diagram approach that can be used by coatings manufacturers and ship operators to generate a realistic estimate of the drag penalty of coatings and fouling. This information can then be used to make operational decisions such as duration between dry-docking, quality of surface finish when in dry-dock, choice of specific coatings for specific surface finish and the variations in performance during service. This new approach can easily be extended to different sectors and new surface-specific Moody-diagrams can be developed for a whole range of applications including oil, gas and water transport pipelines, aircraft fuselage, trains, propellers etc. This project has financial support from a leading antifouling coatings manufacturer as well as collaborators at the University of Melbourne and the US Naval Academy who share our mutual interest in this research area.

Planned Impact

In this project, a new paradigm for the prediction of roughness effects will be developed, focussing on roughness types prevalent in the marine environment (knowledge). The new surface-specific Moody-diagrams that will emerge from this project will enable both civil and military ship operators to make well-informed decisions on scheduling of ship dry-docking maintenance cycles and accurate predictions for the roughness induced variations of ship performance (economy). Optimal scheduling of maintenance cycles will lead to significant reductions in fuel consumption by ships and commensurate lowered emissions of greenhouse gases and particulate matter. This will contribute to achieving the UK's goals under the Climate Change Act 2008 (society). Since particle pollution exposure has been linked to health conditions such as decreased lung function, aggravated asthma and heart attacks, a reduction in particulate matter emissions by ships will help in improving the health of people living in coastal areas (society). The PDRAs involved in this project will gain new skills in experiments and simulation, international collaboration and public outreach (people). In addition, the project will be communicated to people who operate small vessels such as motorboats and yachts for leisure activities with the aim to raise their awareness of the impact of marine roughness on fuel consumption and emissions, improving their skills in assessing roughness impact on vessel performance and encouraging them to adopt better maintenance practices (people).
Description We have developed a methodology to determine the drag of surface based on the surface scans taken from it. This is novel and new way to predicting the drag incurred by a rough surface.
Exploitation Route Yes. We are in discussion with AkzoNobel about using our methods.
University of Melbourne has won a follow-up award to this where they would make direct measurements in a ship hull and complement this with wind tunnel experiments.
We are also taking steps towards setting an international database that can be used to identify the drag penalty of rough surfaces.
Sectors Aerospace, Defence and Marine

Description We have proposed a new method to determine the drag produced by a rough surface. We are collaborating with different people, especially with coatings manufacturers to determine the baseline drag of a ship hull before the coating. This information will be useful to them to determine what the effect of a coating is on changing the roughness of the ship hull and how it affects the drag produced.
First Year Of Impact 2018
Sector Aerospace, Defence and Marine
Impact Types Societal,Economic

Description Collaboration with Glasgow 
Organisation University of Glasgow
Department MRC - University of Glasgow Centre for Virus Research
Country United Kingdom 
Sector Academic/University 
PI Contribution We are doing the experimental work for a roughness project
Collaborator Contribution They are doing the numerical simulations for a roughness project
Impact Several conference abstracts
Start Year 2017
Description Collaboration with Melbourne 
Organisation University of Melbourne
Country Australia 
Sector Academic/University 
PI Contribution We carried out collaborative experiments at Southampton of flows over smooth and rough surfaces. The rough surfaces were manufactured in Melbourne and shipped to Southampton for the measurements.
Collaborator Contribution The collaborators allowed access to their unique wind tunnel facility as well as provided the rough surfaces for measurements in Southampton.
Impact We have published 2 papers as a result of the collaboration with Melbourne. We are currently working on further publications.
Start Year 2009
Description International Paint 
Organisation AkzoNobel
Department AkzoNobel UK
Country United Kingdom 
Sector Private 
PI Contribution We carry out experiments based on the information on the surface roughness provided by the partners.
Collaborator Contribution The partner will provide us with surface scans of roughness form ship hulls.
Impact Currently, we are in the process of finalising this collaboration.
Start Year 2018