Search Results (8)

In this paper, the hydrodynamic characteristics of a rim-driven thruster (RDT) behind the hull of an underwater vehicle are investigated. The studied underwater vehicle is the benchmark DARPA (Defense Advanced Research Projects Agency) suboff model, with and without full appendages. In order to verify and validate the numerical model, a grid sensitivity analysis is made for the AFF-1, AFF-8 and the ducted propeller cases, respectively. Then, the resistance and pressure distribution over the surface of the suboff with and without appendages are compared with available experimental measurements and good correlations were observed. As for the propeller, a well-studied ducted propeller, the 19A duct in combination with Ka-47 blades, is employed, and the numerical results exhibit a close relationship with the available experimental data under a wide range of advance coefficients. Afterwards, the self-propulsion characteristics of the suboff models propelled by RDTs using different duct configurations are studied, more specifically, the unsteady effects of the flow field induced by the interactions between propeller and hull under various working conditions. The results indicate that due to the influence of the hull, the RDTs operate in different working conditions compared to open water and exhibit distinct hydrodynamic characteristics. Moreover, the duct profile can have a significant effect on the unsteady pressure fluctuations in the flow field, especially in the vicinity of the propeller. Full article

In order to develop a reliable numerical method to investigate the effects of ship-generated waves on a moored ship in restricted waterways, this paper takes the MASHCON2022 benchmark model test case as the study object and simulates the whole process of a ship passing a moored ship by using the unsteady Reynolds-Averaged Navier-Stokes (URANS) method coupled with the dynamic overset mesh technique. The initial acceleration process of the passing ship before approaching the moored ship is considered in the numerical simulations to reproduce the benchmark model tests more realistically. The numerical simulations with four acceleration modes are conducted. The comparisons among the numerical results and the test data verify that the prediction accuracy considering the acceleration process is obviously higher than that without the acceleration process, especially for the solitary wave system, and the results based on the linear acceleration agree with the test data best. The flow field results indicate that the impacts of the solitary wave system and the primary wave system on the moored ship are different: the solitary wave system induces significant positive pressures on the hull, while the primary wave system leads to remarkable negative pressures; both result in pronounced attitude variations of the moored ship, but the hydrodynamic forces and moments affected by the primary wave system are more pronounced. Full article

The consideration of shallow water effects has gained in importance regarding inland operations. The interaction between the keel and the riverbed affects the hydrodynamic characteristics of marine vessels. The highly complex nature of the interference phenomenon in catamarans makes the shallow water problem more complicated as compared to monohulls. Hence, catamarans are very sensitive to speed changes, as well as to other parameters, such as the shallow water effects. This makes the design of catamarans more challenging than their monohull equivalents. At lower Froude numbers, the higher importance of the frictional resistance makes the greater wetted surface of the catamaran a disadvantage. However, at higher speeds, there is the potential to turn their twin hulls into an advantage. This study aims to investigate the wave-making resistance of a zero-carbon fast passenger ferry operating in shallow water. The URANS (unsteady Reynolds-averaged Navier–Stokes) method was employed for resistance simulations. Then, the double-body approach was followed to decompose the residual resistance into viscous pressure and wave-making resistance with the help of the form factors of the vessel calculated at each speed. The characteristics of the separated wave-making resistance components were obtained, covering low, medium, and high speeds. Significant findings have been reported that contribute to the field by providing insight into the resistance components of a fast catamaran operating in shallow waters. Full article

Due to the interference between the main hull and the outrigger of the pentamaran, resistance is greatly affected. Therefore, research on the pentamaran front outrigger inclination angle has further practical significance for reducing resistance. In this study, the pentamaran front outrigger inclination angle was analyzed by CFD method, the ship motion in waves was simulated by overlapping grid technology, and the resistance of the pentamaran in static water and waves was predicted by using the unsteady RANS equation. First, a series of validation studies were carried out for the numerical methods used in the study. Then, the influence of the front outrigger inclination angle on the pentamaran resistance performance under different working conditions is calculated and discussed. In order to analyze the influence of the change of the front outrigger inclination angle on the resistance, free surface wave-making and hull pressure are further discussed. The results show that the influence of the front outrigger inclination angle change on the resistance of the pentamaran has a certain rule, and the resistance of the pentamaran can be reduced by adjusting the front outrigger inclination angle. Full article

A tunneled planing craft is a high-speed boat with two tunnels over the hull bottom that are designed to improve the vessel’s performance. Hydrodynamic performance of tunneled planing hulls in calm-water is well-known, however, current information on wave conditions is limited. In this study, two different tunneled planing hulls with two degrees of freedom in heave and pitch motions are studied in regular waves by using the computational fluid dynamics (CFD) method based on the Unsteady Reynolds Averaged Navier-Stokes Equations (URANSE) in conjunction with k−ϵ turbulence model. The results demonstrate that tunneled planing hull motions in waves are nonlinear. In addition, it is found that the dynamic responses of heave and pitch motions as well as occurrence portability of the fly-over phenomenon significantly increases as the Froude number grows. Fly-over motions resulted in vertical motions and acceleration up to 5g, high impact pressure, and large induced drag. At a very high planing speed, after flying over the water surface, when the vessel re-enters the water, the resulting hydrodynamic load leads to a second fly-over motion. Since the fly-over is an unwanted movement with adverse effects, these results can provide a better understanding of the fly-over motion that one may consider in future design for improving the planing hull performance. Full article

This study deals with wave-induced unsteady pressure on a ship moving with a constant forward speed in regular head waves. Two different numerical methods are applied to solve wave–ship interaction problems: a Rankine panel method which adopts velocity potential, and a Cartesian-grid method which solves the momentum and mass conservation equations under the assumption of inviscid and incompressible fluids. Before comparing l1ocal pressure distributions, the computational methods are validated for global quantities, such as ship motion responses and added resistance, by comparison with available experimental data. Then, the computational results and experimental data are compared for hydrodynamic pressure, particularly focusing on the magnitude of the first-harmonic component in different sections and vertical locations. Furthermore, the Cartesian-grid method is used to simulate the various wave-amplitude conditions, and the characteristics of the zeroth-, first-, and second-harmonic components of wave-induced pressure are investigated. The nonlinearity of pressure distribution is observed mostly from the pressure near the still-water-level of the ship bow and the normalized first-harmonic component of wave-induced pressure decreases as the wave steepness increases. Lastly, to understand the local characteristics of wave-induced unsteady pressure, the time-averaged added pressure and added local force are analyzed. It is found that the major contribution of the time-averaged added local force that occurs around the ship stem above the design waterline. Full article

Reducing the on-board noise and fluctuating pressures on the ship hull has been challenging and represent added value research tasks in the maritime industry. Among the possible sources for the unpalatable vibrations on the hull, propeller-induced pressures have been one of the main causes due to the inherent rotational motion of propeller and its proximity to the hull. In previous work, a boundary element method, which solves for the diffraction potentials on the ship hull due to the propeller, has been used to determine the propeller induced hull pressures. The flow around the propeller was evaluated via a panel method which solves in time for the propeller loading, trailing wake, and the sheet cavities. In this article, the propeller panel method is extended so that it also solves for the shape of developed tip vortex cavities, the effects of which are also included in the evaluation of the hull pressures. The employed unsteady wake alignment scheme is first applied, in the absence of cavitation, to investigate the propeller performance in non-axisymmetric inflow, such as the inclined-shaft flow or the flow behind an upstream body. In the latter case, the propeller panel method is coupled with a Reynolds-Averaged Navier–Stokes (RANS) solver to determine the effective wake at the propeller plane. The results, including the propeller induced hull pressures, are compared with those measured in the experiments as well as with those from RANS, where the propeller is also simulated as a solid boundary. Then the methods are applied in the cases where partial cavities and developed tip vortex cavities coexist. The predicted cavity patterns, the developed tip vortex trajectories, and the propeller-induced hull pressures are compared with those measured in the experiments. Full article

The numerical simulation of propeller cavitation benchmark tests of YUPENG ship model is studied based on OpenFOAM, an open-source CFD (Computational Fluid Dynamics) platform, and the benchmark tests are introduced as well. The propeller cavitation shape and the hull pressure fluctuation are measured and predicted, respectively. The uncertainty in hull pressure fluctuation measurement is also analyzed, and the analysis showed the uncertainty is below 10%. The cavitation shape and the hull pressure fluctuation predicted show quite good agreement with the observations and measured data, and the influences of the grid resolutions on the unsteady propeller cavitation and the hull pressure fluctuation are investigated as well. The monotonic convergence achieved and the quite small grid uncertainty illustrate the reliability of the numerical simulation methods. Full article