Sang-seok Han1*,
Ho-won Lee 2,
Saishuai Dai 1,
Momchil Terziev 1
1
Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, the United Kingdom
2
Department of Naval Architecture & Ocean Engineering, Inha University, Republic of Korea
Abstract
Traditional ship resistance models often assume uniform hull surface roughness, potentially misrepresenting the
heterogeneous fouling patterns observed in real-world operations. To address this limitation, we investigate the
hydrodynamic impact of spatially non-uniform roughness on a KRISO Container Ship (KCS) hull using Computational
Fluid Dynamics (CFD) simulations.
Seven hull surface conditions were investigated, including a smooth baseline and six types of roughness
distributions: uniform, linear gradient, non-linear gradient, random, direct-shear, and inverse-shear. All cases
were designed to have the same arithmetic mean hull surface roughness, allowing isolation of the effects of
spatial roughness distribution. Among the tested configurations, the linear gradient distribution exhibited the
most favourable resistance characteristics, whereas the shear-based and random distributions showed relatively
minor differences from the uniform case.
Spatial roughness patterns significantly influenced boundary layer growth and wake development. Uniform, random,
and shear-based distributions induced thicker boundary layers and delayed wake recovery, whereas the linear
gradient case resulted in weaker momentum loss and faster wake recovery.
These findings indicate that even under identical arithmetic mean roughness conditions, the spatial distribution
of hull surface roughness can significantly affect resistance characteristics. Explicit modelling of roughness
patterns is therefore essential for accurate performance prediction and motivates further experimental validation
and integration with propeller-hull interaction and free surface effects.
Figure 1. Visualisation of the spatially applied roughness height distributions on the KCS
hull surface.
This graphical representation illustrates the spatial distributions of the equivalent
sand-grain roughness height (ks) imposed on the hull surface to assess
their hydrodynamic impact. The cases comprise an ideal smooth surface, a spatially uniform
roughness field, linear and non-linear distributions, a statistically random distribution,
and wall-shear stress-based gradients (direct and inverse) prescribed according to the
local shear stress field.
Figure 2. Change in CT relative to uniform roughness for each distribution
and fouling level.
Spatial hull roughness leads to pronounced variations in the model-scale resistance
coefficient (CT), with longitudinally varying distributions producing
the most significant changes. In particular, linear and non-linear roughness patterns
induce substantially larger deviations compared to uniform or random cases, while
shear-stress-based configurations exhibit relatively minor effects. This behaviour underscores the importance of
roughness spatiality in model-scale resistance prediction.
Figure 3. Axial velocity contours (Vx / Vship) around the
KCS hull, extracted at y = 0.006Lpp, comparing the smooth hull surface and various
spatial roughness distribution cases, all sharing the same arithmetic mean roughness height equivalent to the
B20% condition.
The axial velocity contours show that the spatial distribution of hull roughness
alters boundary-layer development and modifies the wake structure. Longitudinally varying
roughness patterns lead to noticeable changes in boundary-layer growth and wake deficit
formation, whereas uniform or shear-based configurations produce comparatively milder
effects. These flow-field modifications underpin the resistance variations observed in
the preceding analysis, highlighting the hydrodynamic sensitivity to roughness spatiality.
