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There are multiple initiatives aimed at strengthening coastal communities against tsunami disaster risks, such as growing vegetation belts, construction of embankments, moats, and different hybrid alternatives. To find a solution for strengthening the coastal buildings themselves, we firstly reviewed the flow phenomena around a single emergent (circular and rectangular) cylinder (case C1), which was considered as a piloti-type column under different Froude conditions, and evaluated the formation of surface bow-waves, hydraulic jump detachment, and wall-jet-like bow-waves. Secondly, the flow characteristics were investigated under the same Froude conditions with side-by-side two-cylinder (case C2) and four-cylinder (case C4) arrays in an open channel. Surface bow-wave length (LBw) increased by 7–12% over the rectangular cylinders (RCs) compared to the circular cylinders (CCs) with a subcritical flow. For the supercritical flow with a 1/200 bed slope, hydraulic jump detachment was observed in relation to the Froude number. The observed length of the hydraulic jump detachment (Ljump) varied between 3.1–8.5% and 4.2–12.9% for the CCs and RCs in the supercritical flow with a 1/200 bed slope. In addition, the wall-jet-like bow-wave height (hjet) over the CCs was increased by 37% and 29% compared to the RCs with a supercritical flow and zero bed slope (orifice-type flow). For case C4, a hydraulic jump was observed for the supercritical flow over the horizontal channel bed. Finally, empirical equations were defined concerning the geometrical shape and arrangement based on the experiment data for the single and side-by-side configurations of the cylinders to validate the height of the wall-jet-like bow-wave as the most critical flow property.

Zheng, X.; Ma, Q.; Shao, S.; Hu, Z., and Gui, Q., 2019. An improved 2D + t incompressible smoothed particle hydrodynamics approach for high-speed vessel waves. Journal of Coastal Research, 35(5), 1106–1119. Coconut Creek (Florida), ISSN 0749-0208. The wave-generated resistance force is substantial for high-speed vessels. A thorough understanding of the wave pattern as well as its drag effect is important for improving vessel performance and optimal design. Owing to the existence of highly nonlinear waves and large deformations of the free surface, the mesh-free smoothed particle hydrodynamics (SPH) approach would provide a useful solution technique for such a practical problem. Based on the pioneering study on the combination of weakly compressible SPH with the two-dimensional (2D) + t (time) theory, the present paper carries out a further investigation on the complex wave patterns generated by a high-speed vessel, through coupling the 2D + t theory with an improved incompressible SPH (ISPH) solver. For the solid vessel boundary, a new treatment method of calculating the velocity and acceleration of the regenerated particles near the curved hull is proposed. In addition, a high accuracy numerical scheme based on the simplified finite difference interpolation (SFDI) approach is used to solve the pressure Poisson equation in the ISPH framework. The robustness of the proposed 2D + t ISPH model is demonstrated through the benchmark tests of water entry and practical applications to the self-designed laboratory experiment.

The bow wave breaking and the viscous interaction of stern wave are studied by simulating the free-surface flows. The Navier-Stokes equation is solved by a finite difference method in which the body-fitted coordinate system, the wall function and the triple-grid system are invoked. After validation, the calculations are extended to turbulent flows. The wave elevation at the Reynolds number of 10^sup 4^ is much less than that at 10^sup 6^ although the Froude number is the same. The numerical appearance of the sub-breaking waves is qualitatively supported by experimental observation. They are also applied to study the stern flow of S-103 for which extensive experimental data are available. Although the interaction between separation and the stern wave generation are not yet clear, the effects of the bow wave on the development of the boundary layer flows are concluded to be significant.[PUBLICATION ABSTRACT]

Ship bow wave breaking is a common phenomenon during navigation, involving complex multi-scale flow interactions. However, the understanding of this intense free surface flow issue is not sufficiently deep, especially regarding the lack of research on the impact of scale effects on bow wave breaking. This paper focuses on the benchmark ship model KCS and conducts numerical simulations and comparative analyses of bow wave breaking for three model scales under the condition of Fr = 0.35 . The numerical calculations were performed using the in-house computational fluid dynamics (CFD) solver naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM. Delayed detached eddy simulation (DDES) method is utilized to calculate the viscous flow field around the ship hull. The present method was validated through measurement data of wave profiles and wake flows obtained from model tests. Flow field results for three different scales, including bow wave profiles, vorticity at various sections, and wake distribution, were presented and analyzed. The results indicate that there is small difference in the bow wave overturning and breaking for the first two occurrences across different scales. However, considerable effects of scale are observed on the temporal and spatial variations of the free surface breaking pattern after the second overturning. The findings of this study can serve as valuable data references for the analysis of scale effects in ship bow wave breaking phenomena.

Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships, accompanied by complex flow field deformation. In this study, the smoothed particle hydrodynamics (SPH) method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model. In order to improve the computational efficiency, the inflow and outflow boundary model is used to establish a numerical tank of current, and a numerical treatment for free surface separation is implemented. Numerical simulations are carried out at Fr = 0.35, 0.40, 0.5, 0.6, and different types of wave breaking such as spilling breaker, plunging breaker, and scars are captured by the SPH method, which is consistent with the experimental result, demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships. Furthermore, the wave elevation and velocity field in the bow wave region are analyzed, and the evolution of the bow wave breaking is provided.

To reduce the resistance of high-speed displacement ships with Froude numbers (Fr) between 0.4 and 0.5, this paper proposes the installation of hydrofoils at the bow and stern of the ship. Firstly, starting from the bow wave, this paper proposes the installation of a flat plate appendage at the free surface of the ship’s bow to suppress the height of the bow wave and thus reduce the hull resistance. Taking the DTMB 5415 ship model as the research object, CFD calculation results show that installing a flat plate appendage at the free surface of the ship’s bow can effectively suppress the height of the bow wave, and the total resistance reduction ratio can reach 6.49% when Fr = 0.45. Then, the flat plate appendage was improved to a hydrofoil appendage, further reducing the hull resistance. As a result, the total resistance reduction rate can reach 9.15% at Fr = 0.45. Following this, hydrofoil appendages were installed simultaneously at the bow and stern. The drag reduction effect and mechanism were studied, and the results show that the hydrofoils at the bow and stern have a good drag reduction effect. Suppressing the bow and stern waves and improving the flow field are the main reasons for the drag reduction. Finally, the drag reduction effect of the hydrofoil appendages was verified through experiments, demonstrating its excellent drag reduction effect when Fr = 0.4–0.5 and a maximum total resistance reduction ratio of 14.552%.

The objective of this study is to design a hull-mounted sonar dome of a ship using OpenFOAM with a bulbous bow effect at cruise speed in calm water. Verification and validation for the original sonar dome simulation are conducted. Next, the 1.44 million grid size is selected to study different dome lengths. By protruding the dome forward 7.5% of the ship’s length, the optimal 17% resistance reduction is achieved and is mainly caused by the pressure resistance decrease. The optimal sonar dome not only functions in the same way as a bulbous bow, but the viscous flow behaviors are also improved. The protrusion corresponding to 90 deg phase lag reduces the bow wave amplitude. The flow acceleration outside the boundary layer and ship wake velocity are higher coinciding with the much lower total resistance. A smaller flow separation and thinner boundary layer are also observed behind the sonar dome because its back slope is less steep. The high pressure covers a smaller area around the bow, and the smaller bow wave crest does not hit the ship’s flare to form high pressure. Consequently, the lower high pressure on the dome front and higher low pressure on the dome back result in the decreases in pressure resistance. The vortical structures are also improved.

Divergent ship bow waves were simulated experimentally with a two-dimensional wavemaker that employs a flexible wave board. The wavemaker was programmed so that the wave board created a time sequence of shapes that simulated the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. The time history of the water surface shape was measured with a cinematic laser-induced fluorescence technique for eight Froude numbers (FD = U/, where U is the forward speed of the equivalent three-dimensional ship model, g the acceleration of gravity and D the ship model draft). The waves produced ranged from small-amplitude non-breaking waves at the lowest Froude numbers to plunging breakers at the highest Froude numbers. These waves are strongly forced and at the higher Froude numbers begin breaking before leaving the wave board. The time histories of various geometric characteristics of the water surface shape including the hull contact line, the wave crest, the plunging jet and the splash zone, which is here defined as both the turbulent zone on the front face of the wave in the spilling breakers and the turbulent zone generated ahead of the jet impact point in the plunging breakers, were measured. The phase speed of the primary wave generated during each run ranged from 2.56Uwl (where Uwl is the maximum speed of the wave board at the undisturbed water level in the tank) at the lowest Froude number to about 1.7Uwl at the three highest Froude numbers. The maximum heights of the primary wave, the contact point on the wavemaker and the splash zone increased in a nearly linear fashion with increasing FD. In the cases with plunging jets, the jet tip trajectory was parabolic with a vertical acceleration ranging from 0.6g at FD = 1.467 to 0.8g at FD = 1.817 (the highest Froude number).

Traditional benthic samplers such as box corers must be deployed with sufficient momentum to ensure penetration of the seabed. This creates a bow wave that disrupts the surface layer of the seabed before the corer is able to collect a full sample. The Multiple Corers available from world-leading seabed sampling experts Ocean Scientific International Ltd are able to overcome the traditional difficulties associated with benthic sampling and collect truly undisturbed sediment samples. The multiple corers are landed on the seabed at slow speed which, in combination with the minimal footprint of the corer, prevents a bow wave from forming and driving away the delicate flocculant material that forms on the surface layer of the seabed.