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If a layer of low-density water settles on top of higher density water, such as fresh water melting from a glacier and settling on top of colder seawater, a body of water can stratify into stable, distinct layers. A vessel advancing in such a stratified fluid can generate internal waves between these layers. The generation of internal waves requires energy and thus increases the resistance experienced by the vessel, a phenomenon known as the dead water effect which can result in a severe reduction in speed and loss of steering power. This study uses Computational Fluid Dynamics (CFD) to investigate the increase in ship resistance caused by the dead water effect. The results show that the presence of a stratified flow can increase total resistance approximately sixfold in extreme conditions. At standard operating conditions, total resistance may increase by approximately 6% as a result of flow stratification. [ABSTRACT FROM AUTHOR]

Ship hydrodynamics in a constant waterway have been well studied. With a coordinate system fixed on the moving ship, the boundary value problem (BVP) is usually treated as a steady one. However, the hydrodynamics of a ship moving in confined waterways with abrupt changes in width or depth are complex due to their unsteady nature. The studies on such unsteady problems are insufficient. In the engineering practice, the hydrodynamic unsteadiness can be fully reflected by a scenario when a ship enters a lock. Prior studies have predominantly focused on predicting the ships' hydrodynamic forces without considering the unsteady terms on the free-surface boundary conditions. Obviously, such steady or quasi-steady methods overlooked the crucial unsteady phenomena on free water surface. To address this gap, the present study introduces a novel three-level difference scheme to discretize the free surface condition, preserving unsteady terms while maintaining temporal continuity of cells on the free surface. With the implementation of such fully unsteady BVP, we observed some interesting unsteady free surface motions, which were not well documented in the existing literature. To verify our new observations, as well as to validate the numerical method proposed in this study, two physical model tests were designed and conducted in a towing tank: a submerged ellipsoid enters a deep lock at relatively high speeds, and a box enters a shallow and narrow lock at very low speeds. The discussion is highlighted on the unsteady waves in front of the moving bodies, as well as the unsteady resistance induced by such waves. [ABSTRACT FROM AUTHOR]

This document discusses the importance of verification and validation in computational simulations, particularly in the field of marine applications. Verification involves evaluating the precision of a computational model's solution, while validation involves comparing the simulation with experimental data to assess accuracy. The document highlights the significance of uncertainty estimation in verification and validation studies and provides examples of recent studies in marine hydrodynamics. The document also presents five contributions that demonstrate the application of verification and validation analysis in various numerical modelling cases related to high-speed craft hydrodynamics, added resistance in waves, cavity formation during water exit, and super-cavitating flow modelling. [Extracted from the article]

Many ship accidents are experienced by small boats. With a large number of small fishing boats in Indonesia, the risk of potential ship accidents is high. Therefore, an operability analysis must be conducted for various loading conditions to address any safety issues due to severe vessel motion. The net cargo of a fishing boat will change during its operation at sea and then will affect the vessel'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, considering 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 equations. In ship hydrodynamics, this has been particularly difficult to resolve due to the complex nature of the problem. The present study aims to alleviate the ambiguity inherent in the field. This is done by performing a series of tests on turbulence models and comparing the outcomes with experimental results. The results are analysed via a modified bivariate plot, which reveal a strong candidate for the optimum choice of turbulence modelling. 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. [ABSTRACT FROM AUTHOR]