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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.

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 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.

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.

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.

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.