Hull Roughness Research Articles

The impact of roughness on the resistance of full-scale ships

Abstract This study aims to explore the impact of hull roughness on ship resistance, which provides a reference for enhancing the operational efficiency and energy-saving levels of ships. Initially, the development and accuracy of Computational Fluid Dynamics (CFD) numerical simulations are elucidated through literature, and the current state of research on hull roughness by scholars both domestically and internationally is introduced. Subsequently, taking the 2000 TEU container ship SITCCAGAYAN as the object of study, a CFD simulation is performed based on the unsteady Reynolds-averaged Navier-Stokes equations in Star CCM+ software. An improved wall function method and roughness function are used to design the simulation experiments, conducting the resistance prediction under various conditions, including the fully smooth hull, fully rough hull, and different levels of roughness at various parts of the hull. The experiment, based on results such as the increase in resistance, roughness impact factor, and roughness Reynolds number, demonstrates that the surface roughness of the hull significantly affects the magnitude of ship resistance. An increase in local and overall roughness leads to an increase in total resistance, but the roughness at the bow part of the ship has the greatest impact on resistance.

Evaluation of the powering extrapolation of a ship with a gate rudder system, including ageing and fouling effects

This paper is based on the evaluation results of the calm water powering extrapolation of a 90-m general cargo vessel, originally built with a conventional rudder system (CRS) and later retrofitted with an innovative energy-saving device (ESD) known as the Gate Rudder System® (GRS), as part of the EU H2020 Project GATERS. The power estimation of the vessel was conducted using an adapted extrapolation procedure based on the scaled model tests of the vessel in a towing tank, validated by the three sets of sea trials. The first sea trial was performed when the ship was new, while the latter two were conducted during the project timeline, before and after the GRS retrofit. This paper aims to adapt the ITTC-78 power extrapolation method to predict the power performance of a ship retrofitted with the GRS for the first time in the maritime industry. Within this framework, the specific objectives of the paper are to describe and validate the proposed method using relevant power-speed data of the GATERS project target vessel (M/V ERGE) initially equipped with the CRS and later replaced by the retrofit GRS to achieve the project objective. Due to the real-world circumstances of retrofitting a 13-year-old ship with a novel energy-saving device, investigating the effects of ageing, hull roughness, and fouling has also become one of the key objectives of the paper. The findings demonstrate the ageing effect on the target ship's powering performance after retrofitting with GRS, highlighting the need for special consideration of power extrapolation alongside the hull fouling effects. The paper also demonstrates that the GRS is an emerging ESD, as a retrofit beside newly built ships with GRS, which improved the powering performance of the project target vessel, achieving a remarkable 25% power saving based on the comparative full-scale sea trials.

Effects of Homogeneous and Inhomogeneous Roughness on the Ship Resistance

Ship hull roughness can significantly increase the ship resistance. The roughness caused by biofouling attached to the ship hull is not uniform but has a random distribution. The purpose of this study is to investigate how the inhomogeneous surface roughness distribution affects the ship resistance and the various resistance components. The KRISO container ship (KCS) is considered as a case study. To model the inhomogeneous surface roughness, the ship hull is divided into three segments with equal wetted surface area. Combinations of three roughness heights, denoted as P, Q, and R with ks values of 125 μm, 269 μm, and 425 μm, respectively, are considered to obtain homogeneous and inhomogeneous roughness arrangements (PPP, QQQ, RRR, PQR, PRQ, QPR, QRP, RPQ, and RQP). CFD method is utilized in this study, utilizing RANS equations and k-ω SST turbulence model. A VoF method is used to model the free surface. CFD simulation results show that for the homogeneous roughness, the total resistance coefficient CT increases with increasing ks (PPP < QQQ < RRR), as expected. For the inhomogeneous roughness, the friction resistance coefficient CF increases in the order PQR < PRQ < QPR < QRP < RPQ < RQP, consistent with results from earlier studies. In all the cases, the friction resistance (CF) is the dominant component of the total resistance. As Re increases from 2.2 x 109 to 2.7 x 109, the percentage of the friction resistance decreases, while the percentage of the wave resistance increases. The viscous-pressure resistance decreases slightly as Re increases from 2.2 x 109 to 2.7 x 109.

Data-driven approach to evaluate the impact of hull roughness on main engine load of river-sea ships

Hull roughness increases the ship's resistance during navigation, significantly increasing fuel consumption and emissions. The study proposed the hull fouling factors (HFFs) to evaluate the time-varying impact of hull roughness on main engine load (MEL) for the three bulk carriers. Initially, ships' Automatic Identification System data, operational data, and weather and sea state data were fused to develop predictive models for MEL. Specifically, the Random Forest (RF) model outperformed others in predicting MEL. Then, by adopting a controlled variable experiment, the RF model was utilized to evaluate the impact of hull roughness on MEL as the days since clean (DSC) increased. Hull roughness analysis results showed that the HFFs of ship operated primarily on sea routes showed an increasing trend with the increasing DSCs. In contrast, the HFFs of ships primarily operated on the river-sea routes did not change significantly. The approach revealed significant temporal variations in hull roughness for ships operating in different routes. Besides, the proposed HFFs could capture the impact of sea temperature, salinity, current velocity and ship speed on hull roughness. Overall, the finding provides new insights into the time-varying hull roughness impacts on sea-to-river ships, and supports hull cleaning strategies, energy management and emission estimates.

Resistance and speed penalty of a naval ship with hull roughness

Hull roughness, attributed to factors such as corrosion, the degradation of marine coatings, and, notably, biofouling colonisation, leads to increased fuel consumption, thus entailing significant environmental and economic penalties. While this issue on commercial ships is well documented in recent studies, the specific impact on the speed of warships has received limited attention. To fill this gap, this research quantifies the resistance and power penalties, as well as the speed reduction under various fouling scenarios, and explores the resultant changes in flow characteristics around the hull. For this purpose, full-scale simulations of a naval ship, specifically the DTMB 5415, utilise the unsteady Reynolds Averaged Navier-Stokes (URANS) method. A modified wall function model was incorporated into the numerical model to accurately simulate the effects of surface roughness.

Numerical investigations on Hydrofoil Performance due to Homogeneous Roughness

Adding a foil system to catamaran shups, also known as Hydrofoil Supported Catamarans (hysucat), is one method of reducing energy consumption and carbon emissions. By taking advantage of the lifting force of the foil, the implementation of a foil system can efficiently decrease a vessel’s draft and consequently reduce the ship’s resistance. However, continually submerged areas of the ship’s hull will be vulnerable to biofouling. As biofouling grows, the hull becomes rough. As a result of increased frictional resistance, rough surfaces may lower the performance of a system, according to fluid mechanics. This study aims to investigate the impact of foil roughness on its work performance. To achieve this, a computational fluid dynamics (CFD) numerical method will be set up with a modified wall function employed for roughness modelling in simulation. The specified roughness height values (ks ) values, which range from 81.25 to 325.00 to 568.75 in µm, represent the general hull roughness. The results reveal that a rough surface may negatively affect the hydrofoil’s operational performance by raising the resistance significantly.

Frictional Resistance Increase Due to Hull Roughness: An Analysis of the Hull Form Parameters Influence

An awareness of the drag increase brought on by biofouling's roughness on the ship hull is one technique to cut emissions aboard ship. However, predicting the increased drag on ships poses significant challenges. When predicting the rise in frictional resistance brought on by roughness, the hull is considered flat. In fact, ship hulls have a variety of shapes, and it is not certain whether this is a factor influencing the magnitude of the increase in resistance due to roughness. In this article, the effect of the hull's form parameters— (ratio of length per breadth), (coefficient block), and (Length of center buoyancy)—on the increase in frictional resistance brought on by roughness have been investigated. The method used to calculate the ship resistance is Computational Fluid Dynamics (CFD) simulation, complemented by roughness modelling using the wall function approach method. The Design of Experiment (DOE) method has been used to vary the shape of the hull model as a variation of the test specimen in this study. The verification and validation tests have been carried out on the CFD simulation results, where the results have been compared with proven empirical methods. Based on the study results, the value of frictional resistance and increased frictional resistance () of all specimens has shown no significant difference in value, evidenced by the variance values, ranging only 1.57-2.1%. Thus, these results prove that the increase in frictional resistance due to roughness is sufficient to assume the ship's hull as a flat plate. The other finding is that roughness can also increase the pressure resistance, and hull shape parameters also contribute towards changes in the value of resistance.

Validation of a full scale CFD simulation of a self-propelled ship with measured hull roughness and effect of welding seams on hull resistance

This study presents the verification and validation of a full scale self-propulsion computational fluid dynamics (CFD) model including measured hull roughness and welding seams. The reference for validation is comprised of speed trial data from five sister ships. To ensure numerical accuracy, resistance and propeller open-water CFD simulations are verified and validated against model tests from two different towing tanks and discrepancies are found to be within the experimental uncertainty of model scale testing. The self-propulsion CFD results emphasise the necessity of measuring hull roughness for accurate performance calculations with discrepancies less than 3.4% on the delivered power relative to the fitted speed trial results. It is found that the empirical Townsin/Mosaad roughness formulation with measured average hull roughness, as recommended by ITTC, provides similar results, as modifying the wall functions using the Colebrook/Grigson roughness function. Homogeneous and heterogeneous roughness modelling methods are found to provide similar results for the studied ship. Modelling of the transverse welding seams on the hull surface is found to increase the total resistance by approximately 0.1% per seam, resulting in a total estimated increase in resistance of 1.5–1.8%. Finally, adding a fairing is found to significantly reduce the resistance penalty from welding seams.

Ship energy-saving device: Influence of the scale effect and hull roughness on the resistance reduction effect of an interceptor

Saving energy of ships are key research topics in the shipping industry, and the scale effect of energy-saving devices is a critical issue. Based on the Reynolds-averaged Navier–Stokes method, free-surface and double-body simulations of model- and full-scale ships were performed in this study. The resistance reduction effect and interceptor mechanism were analyzed. In addition, the influence of the scale and roughness effects on the resistance reduction performance of the interceptor was studied. The results showed that the stern flow field was significantly improved after the interceptor was installed, which was mainly responsible for the ship resistance reduction. When the Froude number ≥0.334, the average resistance reduction rates of the model- and full-scale interceptors were 5.67% and 8.71%, respectively. Some differences were observed between the extrapolated results of the resistance reduction effect of the interceptor and the results of the full-scale simulation; therefore, the change in the form factor and the scale effect of the wave-making resistance were considered in the extrapolated method. In addition, with increasing hull roughness, the frictional, viscous pressure, and total resistances of the ship increased, which decreased the resistance reduction rate of the interceptor by 1%–3% and shortened the resistance reduction speed range of the interceptor.

An advanced prediction method of ship resistance with heterogeneous hull roughness

Despite the ongoing efforts for predicting the effect of hull roughness on ship resistance, the majority of the studies have been treating the hull surfaces as uniformly (i.e., homogeneously) rough. This can be a limiting factor since the real ships’ hulls are not uniform due to various reasons such as the heterogeneous accumulation of biofouling. The current study aims to propose a new prediction method for added resistance due to heterogeneous hull roughness. This newly proposed method incorporates the similarity law scaling and the Roughness Impact Factor to consider the relative impacts of hull roughness in different regions. Two separate case studies involving recent Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) results were used to assess the newly proposed method, which showed better prediction performance compared to the conventional method.

Impacts of different characteristics of marine biofouling on ship resistance

Ship resistance research on marine biofouling is an old but hot topic which invokes plenty of studies recently. Previous studies on the surface roughness of ship hulls mainly focus on the height of micro-organisms or macro-organisms adhered to ship hulls without considering other components which may indeed play an important role in generating additional resistance. Many authors attempt to use a single parameter, for example, height of the biofoulers, to describe the hull roughness. Our research indicate that any single factor affecting ship hull roughness can not completely reflect the compositions of ship resistance. Here we propose a novel numerical model which enables more precise estimates of the contribution of each single component involving in the marine biofouling.The standard k−ε model of FLUENT is modified by considering the possible rotating, jetting, surging and swirling of fluid flowing over ship hulls due to characteristics of the marine biofoulers. Simulated results using the modified model at various speeds are compared with that using the original model, and an improvement of ship resistance is evident, quantitatively consistent with measured, indicating that the modified model behaves in a reasonable manner in simulating the relationship between ship resistance and ship surface roughness.The marine biofoulers affect ship resistance primarily by increasing the tangential surface shear stresses. Simulated results demonstrate that additional resistance caused by height, shape, hardness and density of the biofoulers accounts for up to ∼80% of total resistance in the heavy fouling condition (taking vessel “YOURIXX” as an example), implying an economic demand for good hull performance.

Effect of Hull and Propeller Roughness during the Assessment of Ship Fuel Consumption

The effects of hull and propeller roughness are presented over ten years of operation on ship performance. The developed model used in this study is a combination of NavCad and Matlab to perform the resistance and propulsion computations of the selected ship as well as the processing of input and output data. By considering the ship hull, the engine installed and an optimized propeller, the ship performance is computed for a different combination of hull and propeller roughness according to the ITTC recommendations and the opinion of experts in the marine field. Twelve cases are simulated over the selected years of operations and compared to the new ship performance. The hull roughness has the dominant effect on the performance of the ship due to its large area. However, by adding the effect of propeller roughness, an increment is noticed in the loading ratio and fuel consumption by 1–4% and 2–4%, respectively, in addition to the hull roughness. From this study, it is concluded that the roughness of both the hull and propeller is important consider to achieve more accurate results than just considering the hull roughness.

Prediction of biological development effects on drag forces of ceramic hull coating using Reynolds-averaged Navier–Stokes-based solver

Ships in service feature surfaces that exhibit biofouling, which alters the hydrodynamics of the vessels, thus affecting their normal displacement and significantly increasing their fuel consumption. The application of three types of ceramic coatings as ecological, effective and durable alternatives to commercial silicone-based marine coatings is investigated in this study. Three different ceramic glazes and two control commercial paints are analysed in an actual environment during 20 months of exposure to simulate the navigation conditions such that growth and roughness data can be obtained and then applied to computational fluid dynamics (CFD) software using an open-source Reynolds-averaged Navier–Stokes solver. The CFD results are validated under smooth hull conditions with a full-scale Kriso Container Ship (KCS) model and with different levels of hull roughness. The developed approach shows that the drag in hulls coated with conventional paint is 19% greater than that in hulls with ceramic coating.

Assessment of Ship Fuel Consumption for Different Hull Roughness in Realistic Weather Conditions

This paper presents the effect of hull roughness over 10 years of operation on ship performance. The numerical model is developed by coupling NavCad and Matlab to perform the computation and the data processing. On the basis of a given hull, an engine, and an optimized propeller, the performance of the ship is computed for eight cases of hull roughness according to the ITTC recommendations in both calm waters and different weather conditions along the ship route. The effect of both wind and waves is considered for computing the added ship resistance along the route, thus requiring more power than just only the added resistance in waves. This provides a more accurate estimation of the ship’s performance along the different sea states. Lastly, a weighted average of the main ship parameters is estimated to evaluate better the ship’s performance. According to this study, the fuel consumption in calm water can be increased by around 20% after 10 years of ship operation based on the level of hull roughness. However, in the same weather conditions along the ship route, the ship’s fuel consumption can be increased by 10% compared to the same trip with a clean hull.

Predicting the Effect of Hull Roughness on Ship Resistance Using a Fully Turbulent Flow Channel

The consequences of poor hull surface conditions on fuel consumption and emissions are well-known. However, their rationales are yet to be thoroughly understood. The present study investigates the hydrodynamics of fouling control coatings and mimicked biofouling. Novel experimental roughness function data were developed from the “young” fully turbulent flow channel facility of the University of Strathclyde. Different surfaces, including a novel hard foul-release coating, were tested. Finally, the performance of a benchmark full-scale containership was predicted using Granville’s similarity law scaling calculations. Interestingly, the numerical predictions showed that the novel hard foul-release coating tested had better hydrodynamic performance than the smooth case. A maximum 3.79% decrease in the effective power requirements was observed. Eventually, the results confirmed the practicality of flow channel experiments in combination with numerical-based methods to investigate hull roughness effects on ship resistance and powering. The present study can also serve as a valuable guide for future experimental campaigns using the fully turbulent flow channel facility of the University of Strathclyde.

Roughness effect modelling for wall resolved RANS – Comparison of methods for marine hydrodynamics

This paper deals with several aspects of surface roughness modelling in RANS codes applied to full-scale ship simulations. To select a method that is suitable for wall-resolved RANS solvers and gives reliable results at high Reynolds numbers, five different roughness models are compared. A grid uncertainty analysis is performed and the sensitivity to the grid resolution close to the wall (y+) is investigated. The results are compared to extrapolated results of experiments carried out with rough plates with various heights and roughness types. A correlation factor between the Average Hull Roughness and the equivalent sand roughness height is investigated, and a value of five is deemed the most suitable. The work suggests that the Aupoix-Colebrook roughness model gives the best results for full-scale ship simulations, at least with the current code, and that the near-wall grid resolution required for smooth surfaces can be applied also for the rough case.

CFD analysis of the effect of heterogeneous hull roughness on ship resistance

Hull roughness significantly increases ship resistance, power, and fuel consumption. Although it is typically spatially heterogeneous, little research has dealt with heterogeneously distributed roughness on ship hulls. Therefore, this study investigates the heterogeneous hull roughness effect on ship resistance using Computational Fluid Dynamics (CFD). A series of CFD simulations were conducted on the KRISO Container Ship (KSC) hull model to accurately predict the effect of heterogeneous hull roughness on ship resistance. Specifically, the StarCCM + software package was adopted to develop Unsteady Reynolds Averaged Navier–Stokes (URANS)-based CFD simulations with a modified wall-function approach. Various surface coverage conditions were modelled, including homogeneous (i.e., smooth and full rough conditions) and heterogeneous conditions (i.e., different smooth/rough wetted surface ratios). Eventually, the present findings showed that increased roughness on the bulbous bow region has the most significant impact on ship resistance. Moreover, the introduction of a so-called roughness impact factor correlated the added resistance of the heterogeneous roughness scenarios to the corresponding rough wetted surface area. Accordingly, the rough bulbous bow scenario presented a higher roughness impact factor than the other rough hull cases.

Ship-scale CFD benchmark study of a pre-swirl duct on KVLCC2

Installing an energy saving device such as a pre-swirl duct (PSD) is a major investment for a ship owner and prior to an order a reliable prediction of the energy savings is required. Currently there is no standard for how such a prediction is to be carried out, possible alternatives are both model-scale tests in towing tanks with associated scaling procedures, as well as methods based on computational fluid dynamics (CFD). This paper summarizes a CFD benchmark study comparing industrial state-of-the-art ship-scale CFD predictions of the power reduction through installation of a PSD, where the objective was to both obtain an indication on the reliability in this kind of prediction and to gain insight into how the computational procedure affects the results. It is a blind study, the KVLCC2, which the PSD is mounted on, has never been built and hence there is no ship-scale data available. The 10 participants conducted in total 22 different predictions of the power reduction with respect to a baseline case without PSD. The predicted power reductions are both positive and negative, on average 0.4%, with a standard deviation of 1.6%-units, when not considering two predictions based on model-scale CFD and two outliers associated with large uncertainties in the results. Among the variations present in computational procedure, two were found to significantly influence the predictions. First, a geometrically resolved propeller model applying sliding mesh interfaces is in average predicting a higher power reduction with the PSD compared to simplified propeller models. The second factor with notable influence on the power reduction prediction is the wake field prediction, which, besides numerical configuration, is affected by how hull roughness is considered.

Full-scale ship stern wave with the modelled and resolved turbulence including the hull roughness effect

Stern wave flow phenomena are investigated in a full-scale Kriso container ship. The hull roughness effects are studied with and without propulsion. Reynolds-averaged Navier–Stokes (RANS) and detached eddy simulations (DES) are utilized with the ghost-fluid method (GFM). The DES is carried out with a submodel where a stationary RANS solution is used as a boundary condition. The surface roughness effect on the stern is significant due to the increased boundary layer thickness. The differences in the stern wave shape between RANS and DES become more pronounced with propulsion as DES resolves the turbulence and wave breaking. With the smooth hull, DES indicates transom wetting which RANS does not. For the heavy fouling condition RANS and DES predict a wetted transom. For the smooth hull, the DES results indicate 6.8% higher pressure (2.8% in total) resistance at the transom compared to the corresponding RANS. The resistance of the wetted transom correlates with the velocity change at the transom location. Heavy fouling does not cause pressure resistance although RANS and DES predict a wetted transom. We propose that the increased boundary layer should be taken into account in the after body design.

Biofouling dynamic and its impact on ship powering and dry-docking

Biofouling of ship hulls is a significant financial burden to shipping companies affecting ship performance and shipping costs through increased fuel consumption and associated maintenance costs. It also induces a serious environmental footprint through increased gas emissions. In addition, the application of antifouling coating harms marine life. It is, therefore, crucial to understand its dynamics enabling more reliable management of the overall ship operation expenses. A new methodology to evaluate the dynamic development of ship biofouling and its effects on ship powering demands and dry-docking costs is presented in this paper. The mathematical model is based on the well-known ITTC-1978 relationships which are uniquely combined with the stochastic modeling approach taking into account the reproductive potential and growth rate of marine organisms. The obtained results are successfully validated in the case of a typical Mediterranean fishing vessel using the full-scale measurements of the hull roughness as well as by the sophisticated computational fluid dynamic model. Such a model is further employed to select the most profitable hull maintenance schedule by taking into account maintenance intensity, fuel costs, maintenance costs, and ship idle costs. The developed approach proved to be efficient and of suitable accuracy equipping ship owners with a powerful support framework applicable in course of the challenging decision-making such as the evaluation of the dry-docking scheduling.