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Adjusting a vessel's trim and draught to enhance resistance characteristics is a promising strategy to improve the energy efficiency of maritime transport. However, the vast majority of scientific effort has been directed at such gains in deep, unrestricted waters. Shallow and confined waters modify the flow and pressure distribution around a ship, altering considerably the resistance curve. This study aims to elucidate trim and draught increase effects on a ship's resistance while advancing through a restricted waterway using Computational Fluid Dynamics. The results show that increasing the draught of a benchmark hull magnifies the hydrodynamic resistance by approximately 10% to 15% depending on the ship speed. This added hydrodynamic resistance may be compensated by adjusting the vessels’ trim, but the ability to compensate the added hydrodynamic resistance is sensitive to ship's speed. At low speeds, the numerical model predicts the increase in resistance due to a 10% higher draught can be reduced by varying the trim angle leaving the total resistance 0.87% higher than at the design draught and zero trim angle condition. On the other hand, higher speeds offer a greater potential for resistance reduction through trim.

According to the Food and Agriculture Organization, fishing at sea is a risky activity with the highest mortality rate due to accidents. Many ship accidents are experienced by small ships, especially on boats with a length of smaller than 24 metres. With a large number of small fishing boats in Indonesia, the risk of potential ship accidents is high. Therefore, an operability analysis must be carried out for various loading conditions to address any safety issues due to severe vessel motion in advance. The operation of fishing vessels is different from that of merchant ships. The net cargo of merchant ships tends to remain unchanged during a voyage. By contrast, the net cargo of a fishing boat, which is fish caught, will change during its operation at sea. This change will also affect the ship’s seakeeping characteristics. This study aims to determine the effect of changes in load and their effect on a traditional fishing boat’s operability in Indonesia, taking into account the ship’s intact stability. In addition, this study also highlights the response of the ship roll motion to prevent stability failure. The stability curve is used to relate ship stability analysis to seakeeping analysis. Percentage operability and Operability Robustness Index are used to assess the root mean square (RMS) roll response and the ship's expected maximum roll motion. In this study, it is shown that the percentage operability of the fishing boat satisfying all pre-determined seakeeping criteria varies between 61% to 74%. Among all criteria, the limiting boundary for RMS roll motions and RMS pitch motion are relatively low, affecting the overall operability.

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.

Shallow water studies of ship hydrodynamics typically examine a single, constant underwater canal cross-section at a time. In practice, the underwater cross-sectional area and shape of the waterway is rarely, maintained constant over long distances. This study presents an attempt to quantify the effects of an abruptly varying water depth by numerically modelling such a condition using CFD. The results show that waves propagate and refract in the numerical towing tank in a physically consistent manner showing less than 0.1% error in the dissipation of a solitary wave when compared to analytical relations. A strong boundary layer is formed on the canal bottom almost as soon as the ship enters the shallower region. The resistance increase, resulting from the depth change is up to approximately 226% of the initial value near critical speeds.

Historically, the field of naval architecture has relied on a combination of model testing and scaling laws, known as extrapolation procedures, to predict full-scale power requirements. Numerous problems with extrapolation procedures were identified almost as soon as they were proposed, but since there were no alternative scaling laws their use persisted. This review article explores the cause of these uncertainties, the attempts to circumvent or correct them, and the current efforts to reduce and even eliminate the need for extrapolation of ship resistance through the use of full-scale Computational Fluid Dynamics. We find that while there are a number of developments and accomplishments in achieving robust and reliable full-scale numerical simulation, the research community is not yet ready to replace experimentation and extrapolation. The principal bottlenecks are the availability of open full-scale data, including ship geometries, and computational power to predict full-scale flows with the necessary accuracy.

The problem of predicting a ship’s form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship’s speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-ω, k-ω SST, and k-e models). The results show that at very low speeds (Froude numbers in the range of 0.02–0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.

The increased availability of computational resources has transformed the prediction of engineering quantities of interest at the design stage. For ship hydrodynamics, this means analysts are now able to predict the power requirements of a vessel at model-scale with good accuracy, routinely. As ever more intricate analysis methods and tools are developed, it has become apparent that modelling all physical phenomena at full-scale remains unattainable both presently, and in the near future. The difficulty in accounting for the full-scale performance frequently limits analysis to model-scale, causing scale effects. Scale effects arise due to the discrepancy in force ratios a model and the prototype will experience. One main consequence of the presence of scale effects is the difficulty in demonstrating the efficacy of new technologies, such as novel energy saving devices. The naval architecture community is therefore not ready to shed many of the historic assumptions made in the design of vessels. A prime example of this is the hydrodynamic modelling of a ship’s full-scale power requirements. Performing solely numerical simulations to obtain such data is considered risky, and is typically accompanied by model-scale experimentation and/or simulations. This work will focus on scale effects encountered when modelling the towed resistance of a ship at model and full-scale. The reasons scale effects are in many cases tolerated, and the problems they may cause are also reviewed. The only remedy to circumventing the presence of scale effects is to work in full-scale at the design stage, but there are a number of problems in doing so. These issues are also explored in this work, with special emphasis on the bottlenecks in adopting full-scale Computational Fluid Dynamics (CFD) numerical simulations as the only prediction tool used in the design process.

The airwake behaviour around a ship provides useful information for the safe operation of helicopters on naval ships as well as in helicopter pilot training. This study investigates the impact of ship motions on the airwake behind the superstructure of a naval ship using Detached Eddy Simulation. A full-scale simplified frigate geometry is analysed stationary and in head waves at three different wavelengths under a uniform wind field and in the presence of an atmospheric boundary layer. The results reveal that an atmospheric boundary layer impacts significantly the airwake, as well as the vertical wave-induced motions of the ship, which reduce in amplitude by between 20.9% and 22.39% in heave, and up to approximately 38% in pitch. Moreover, the results show that the presence of an atmospheric boundary layer impacts the ship's heave and pitch motion periods. The flow field is also significantly altered depending on the ambient wavelength and period of motion, particularly in the case where an atmospheric boundary layer is modelled.

With the increasing demand for the autonomous ship, a fast planning method for long-distance ship routes is needed. In this paper, a multi-scale Visibility Graph (VG) method is proposed for long-voyage route planning, as a solution to the problems of the slow planning and poor route accuracy. First, polygon data of obstacles are extracted from an electronic chart. In order to reduce the number of Visibility Points (VPs), the VPs are expanded from the convex points of these polygons. The small-scale, medium-scale, and large-scale VG models are established respectively. Second, this paper proposes the Local Planning Window (LPW) method, which greatly reduces the complexity of the VG models. The great circle route method is used to decompose the longer route, which further shorten the search time of the VG. The route planning process is designed for the multi-scale VG method. Finally, a long-voyage route planning example is carried out, in which, the utilization rate of the number of obstacle polygons and the number of VPs are analyzed. The data results show that: the complexity of VG models can be reduced greatly, and the search time of the VG will be shortened, by using the multi-scale VG method.

In this study, the forces and moments acting on the KCS ship model as a result of oblique towing at 10 and 20 degrees drift angles are evaluated experimentally and numerically via a commercial Reynolds averaged Navier-Stokes solver. For the purposes of this work, the KCS hull is modelled both experimentally and numerically at a scale factor of 1:75. The adopted case-studies feature both horizontal and vertical restrictions. Thus, the subject of this work is the oblique motion of a ship in a narrow canal with a depth of h/T = 2.2. The relative impact of turbulence modelling is assessed by comparing the computed integral quantities via several eddy-viscosity closure strategies. These include significant variants of the k-ϵ and k-ω models as well as a widely used one-equation closure. Multiphase numerical simulations are performed at several of the experimentally investigated depth Froude numbers for each drift angle condition in order to fully capture the physics of the problem at hand. The present study aims to provide a quantitative evaluation of the performance of the adopted turbulence models and recommended the best closure strategy for the class of investigated problems.

The increasing relevance of simulation-based design has created a need to accurately estimate and bind numerical errors. This is particularly relevant to full-scale computational ship hydrodynamics, where measurements are difficult and expensive, simultaneously requiring a high degree of predictive accuracy even in early design stages. However, the field of ship hydrodynamics has yet to fully exploit the enhanced capabilities and potential benefits numerical verification methods have to offer. The present study presents a detailed application of numerical verification procedures in CFD as applied to local parameters, such as free surface elevation and skin friction. This is done in order to pinpoint specific locations in the computational domain responsible for heightened levels of error and uncertainty. Relationships between different parameters are demonstrated and discussed based on a set of full-scale simulations of the KCS advancing through a canal using CFD.

With the rapid advent of computational methods in all fields of engineering, several areas have emerged as significant sources of ambiguity. Among these is the selection of a turbulence model to close the Reynolds averaged Navier-Stokes equation. In ship hydrodynamics, this has been particularly difficult to resolve due to the complex nature of the problem. Furthermore, there are a wide variety of turbulence models all claiming superiority. Thus, navigating to the correct choice is a subject of experience. The present study aims to alleviate the ambiguity inherent in the field. This is done by performing a series of tests on the turbulence models and comparing the integral outcomes with experimental results. Specifically, shallow water cases are chosen due to the additional layer of complexity associated in the prediction of parameters of interest. The results are analysed via a modified bivariate plot, which reveals a strong candidate for the optimum choice of turbulence modelling. The assessment simultaneously takes into account resistance and sinkage, in addition to consistency across different case studies. The time per iteration also points towards the same candidate, identified as the standard k-ω model, as a good choice within the software used to perform the analysis. The results also suggest that pressure resistance and its constituent components are not coupled with the turbulence model. On the other hand, frictional resistance is highly dependent on the closure selected and is identified as the main contributor to deviations with regards to experimental values.

In international shipping, there are several waterways that are widely viewed as bottlenecks. Among these is the Suez Canal, where recent expansions have taken place. Although the Suez Canal has a high importance in international shipping, little research has been carried out in maximising the number of ships capable of traversing for a set period of time. The present study aims to examine hydrodynamic phenomena of ships advancing through the Suez Canal in the allowed speed range to determine the relative effects of the canal depth and/or width restrictions on the overall ship sailing performance. A rectangular canal is also included as a reference to gauge the effects of varying canal cross-section. The present study combines experimental, numerical, analytical and empirical methods for a holistic approach in calm water. As a case-study, the KCS hullform is adopted, and analysed experimentally, via Computational Fluid Dynamics, using the slender body theory, and empirical formulae. The results reveal strong coupling between the canal's cross section and all examined parameters.

A numerical simulation method is presented by integrating Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) solvers to predict ship wave loads and slamming loads taking into account hydroelastic effects. The interest of this study mainly lies in the slamming and green water pressures acting on a flexible ship investigated by the coupled CFD–FEA method. Firstly, verification and sensitivity analysis of the wave loads and slamming pressures on the S175 containership evaluated by the coupled CFD–FEA method is conducted by comparing the results using different mesh sizes and time step schemes. Discussion on the effect of hydroelasticity on impact pressures is also conducted. Then a comprehensive analysis on the global motions, wave loads, slamming and green water pressures of the ship in different regular wave conditions is undertaken. Finally, a simplified bow flare and bottom slamming pressure estimation method based on the seakeeping data of incident wave and ship global motions are proposed, which can reduce the computational burden of the two-way fluid-structure interaction simulations when impact pressure is concerned.

Although there is a significant body of research devoted to the shallow water hydrodynamic aspects of ships, several unexamined topics remain. Among these is that of critical outer flow in a dredged channel and its influence on parameters of interest. While empirical methods can be used with ease to resolve this, they can provide results with reliability sufficient only for an early design stage. On the other hand, more sophisticated potential flow theories are either inapplicable or do not perform well at the critical limit. However, RANS (Reynolds Averaged Navier-Stokes) – based tools can accurately capture all underlying phenomena without relying on limiting assumptions. This paper presents an attempt at comparing some results obtained via a CFD-based RANS solver and the slender body theory for critical outer flow in a dredged channel.

Restricted waters present several challenges for ship builders and operators. The proximity of the seabed and river or canal banks cause viscous effects to be more pronounced than in unrestricted waters. These effects do not follow a linear scaling law, which is typically assumed in terms of sinkage and trim. Moreover, the resistance of the ship is increased in a complex fashion, which has largely eluded researchers. The present study will aim to elucidate scale effects in shallow water performance predictions. Particular attention is placed on the form factor, wave resistance, and frictional resistance. Scale effects are confirmed in the two former parameters. Justification for the obtained results is sought in terms of flow properties. Specifically, the flow velocity and boundary layer thickness are examined in detail. The selected case-study reflects recent experimental work on the KCS hull form in restricted waters.

The numerical simulation of ship flows has evolved into a highly practical approach in naval architecture. In typical virtual towing tanks, the principle of Galilean relativity is invoked to maintain the ship as fixed, while the surrounding water is prescribed to flow past it. This assumption may be identified, at least partly, as being responsible for the wide-scale adoption of computational solutions within practitioners&rsquo, toolkits. However, it carries several assumptions, such as the levels of inlet turbulence and their effect on flow properties. This study presents an alternative virtual towing tank, where the ship is simulated to advance over a stationary fluid. To supplement the present work, the free surface disturbance is processed into Fourier space to determine the Kelvin half-angle for an example case. The results suggest that it is possible to construct a fully unsteady virtual towing tank using the overset method, without relying on Galilean relativity. Differences between theoretical and numerical predictions for the Kelvin half-angle are predominantly attributed to the assumptions used by the theoretical method. The methods presented in this work can potentially be used to validate free-surface flows, even when one does not have access to experimental wave elevation data.

Historically, the prediction ship resistance has received its fair share of attention by the scientific community. Yet, a robust scaling law still lacks, leaving testing facilities to rely on experience-based approaches and large datasets accumulated from years of operation. Academia's concern regarding this has not led to an extrapolation procedure, capable of bearing scrutiny adequately. One way to circumvent what has become the bane of the study of ship resistance is to perform Reynolds averaged Navier–Stokes (RANS) simulations directly in full-scale. The rapid advent of such methods has meant that confidence levels in predictions achieved by RANS simulations are low. This paper explores and demonstrates scale effects on the constituent components of ship resistance by performing a geosim analysis using a Computational Fluid Dynamics approach. Emphasis is placed on challenging the assumptions imposed as part of the currently accepted ship resistance extrapolation procedure. Our results suggest that a high degree of uncertainty exists in the calculated full-scale resistance depending on the approach taken towards its evaluation. In particular, scale effects are demonstrated in wave resistance, while free surface effects are palpable in the frictional resistance.