Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Assessment of the roughness effect for a high-speed catamaranusing full-scale and model-scale CFD simulations
Guangyu Shi1,2, Alexandros Priftis1, Evangelos Boulougouris1 and Haibin Wang1
1

Maritime Safety Research Centre (MSRC), Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde
Glasgow, Scotland, United Kingdom
2College of Shipbuilding Engineering, Harbin Engineering University, Harbin, People’s Republic of China(CFD) simulation (Speranza et al., 2019). This method has theadvantage of considering the heterogeneous distribution of the shear
stress on the hull surface, which cannot be accounted for by empiricalor theoretical approaches.

ABSTRACTIn the present paper, the hull roughness effects on the calm water
resistance of a medium-sized high-speed catamaran are assessed using
the CFD method. The simulations are carried out using both the modelscale and ship-scale geometries. The model-scale resistance isextrapolated to the ship-scale using the ITTC recommended procedure(including the resistance increment due to the hull roughness) and thencompared with the data obtained from the ship-scale CFD simulation,
where the hull roughness effects are evaluated using the modified wall
function approach. The results show that the resistance increment
predicted from the model-scale simulation is significantly larger thanthat of the ship-scale calculation, especially at higher speeds. Besides, it
is found that the increase of the resistance is primarily attributed to thefrictional resistance component. Finally, the effects of the hullroughness on the flow field are also analysed.

Therefore, the CFD calculation has been widely used in the evaluationof ship resistance with the hull roughness in past decades. Demirel et al.
(2014) developed a new roughness function that was used in a CFD
solver to predict the resistance due to the antifouling coatings. The
method was validated using the towing test results of a flat plate fromliterature and good agreement was accomplished. Later, Demirel et al.
(2017) modified their roughness function model which was proposed intheir early paper and applied this modified model to investigate theroughness effect on the resistance of the full-scale KRISO Container
Ship (KCS) hull. They found that the wave resistance and the wave
system could also be significantly affected if the hull was in heavy
calcareous fouling condition. Song et al. (2020a) validated a CFD
method to calculate the hull roughness effect by comparing thesimulation results with those from the towing tank tests and goodagreement was achieved. As expected, a significant increase infrictional resistance was observed. Besides, increases in viscouspressure resistance and decreases in wave-making resistance were also
noticed. Later, Song et al. (2021a, 2021b) investigated the effect of theheterogeneous roughness distribution on the hull resistance using bothexperimental and numerical methods. It was found that the added
resistance due to the bow-rough condition was higher than that of theaft-rough condition, suggesting that the forward part of the hull
generated more added resistance than the other parts. Andersson et al.
(2020) reviewed the existing methods to model the hull roughness
using various roughness functions. No convergence within the researchcommunity towards specific roughness functions of calculating theroughness length scales was found, indicating that to properly model
the hull roughness effect, more details regarding the rough hull surface
such as the type of the coatings should be considered in the CFD
calculation. Mikkelsen and Walther (2020) compared the full-scale
CFD simulation with the speed trial measurements. They found that thepower consumption estimated using an empirical formula that modelled
the roughness effect as a point force was considerably lower than theKEY WORDS: Fast catamaran, hull roughness, resistance, CFD.
INTRODUCTION
Ship resistance can be considerably increased by the roughness of thehull surface, which could be caused by coatings, corrosion andbiofouling etc. Therefore, the hull roughness effects must be taken into
account when evaluating the ship’s power consumption andenvironmental influence. Accordingly, there have been many studies topredict the resistance increase due to hull roughness using various
methods. The traditional approach is to use empirical formulas(Bowden and Davidson, 1974; Townsin and Mosaad, 1985) to estimate
the resistance increment and then apply it as a concentrated point force.
These formulas are usually fitted from experimental and sea-trial
results and can be used for extrapolating the model test resistance to thefull-scale one. Theoretically, the roughness effect can be taken into
account by using the similarity law scaling procedure proposed byGranville (Granville, 1978), which, however, is limited by the flat plate
simplification. An alternative method to include the roughness effect isto employ a modified wall function in the computational fluid dynamics

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