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In the frame of inviscid and incompressible fluids without taking into consideration of surface tension effects, the axisymmetric evolution of two buoyancy-driven bubbles in an infinite and initially stationary liquid are investigated numerically by VOF method. The numerical experiments are performed for two bubbles with same size, with the following one being half of the leading one, and with the leading one being half of the following one, and for different bubble distances. The ratio of gas density to liquid density is 0.001. It is found by numerical experiment that when the distance between the two bubbles is greater than or equal to one and half of the bigger bubble radius, the interaction is very weak and the two bubbles evolute like isolated ones rising in an infinite liquid. When the two bubbles come closer, the leading bubble itself evolutes like an isolated one rising in an infinite liquid. However, due to the smaller distance between the two bubbles, large pressure gradient forms in the liquid region near the top of the following bubble, which causes the upward stretch of its top part no matter what sizes of the two bubbles are. When the distance between the two bubbles is less than or equal to three-tenth of the bigger bubble radius, before the liquid jet behind the leading bubble fully developed, the top part of the following bubble has already been sucked into the leading one, giving a pear-like shape. Soon after the following bubble merges with the leading one. It is also found that for the smaller bubble, its transition to toroidal is always faster than that of the bigger one because of its smaller size. The mechanism of the above phenomena has been analyzed numerically.

This paper aims to develop the simulated numerical methodology for sloping beach with nonlinear free-surface waves of sloshing water in a 2D rectangular tank. The current computational tool would be the first step in accurately modeling wave energy converters. The 2D tank model was developed by ANSYS FLUENT software, and Navier–Stokes equations are discretized on a regular structured grid based on the finite volume method (FVM). The model is validated for nonlinear sloshing cases. In addition, tank flexibility is analyzed for its impact on liquid sloshing. The test was conducted in five different wave steepness conditions. There were five conditions of wave steepness used in the test. This study looked at fluid–structure interaction around moving plates. The output power of the plate wave energy converter for different plate heights and streamline motion around the plate are important studies in the flow field. Variations of drag coefficient with the wave steepness are the important study in this paper. It shows that the drag coefficient increases with the increase in wave steepness and plate length. In particular, the new structure can give a new, highly accurate formula for determining the wave power of the ocean structures. Its application is seen in wave energy converter (WEC), where the interaction of solid objects, such as wind turbines with water waves, extracts renewable wave energy from the ocean. A highly efficient CFD approach method is introduced to capture the interaction of solid object with a two-phase flow. The effect of wave steepness using second-order stokes wave theory on a moving thin plate in intermediate water is a new discussion. This research is a highly relevant source of information in the development of many practical systems and has direct employment in the design of WEC in order to extract ocean energy.

A two-dimensional model is developed to numerically study the water flow boiling through a tree-shaped microchannel by VOF method. In this work, the bubble dynamics and flow patterns along the channel are examined. Additionally, the pressure drop, heat transfer performance and the effects of mass flow rate and heat flux on the heat transfer coefficient are analyzed and discussed. The numerical results indicate that, there are three main bubble dynamic behaviors at the wall, namely coalesce-lift-off, coalesce-slide and coalesce-reattachment. At the bifurcation in high branching level, the slug bubbles may coalesce or breakup. The flow patterns of bubbly, bubbly-slug flows occur at low branching level and slug flow occurs at high branching level. The passage of bubbles causes the increasing of fluid temperature and local pressure. Additionally, the pressure drop decreases with the branching level. The flow pattern and channel confinement effect play a vital role in heat transfer performance. The nucleate boiling dominant heat transfer is observed at low branching level, the heat transfer performance is enhanced with increasing branching level from $k=0$ to 2. While, at high branching level, the heat transfer performance becomes weaker due to the suppression of nucleate boiling. Moreover, the heat transfer coefficient increases with the mass flow rate and heat flux.

This paper investigates the wave-induced flow field and water particle movement inside and around a vertical permeable structure, which is affected by the interaction between water waves and porous media. A three-dimensional fully nonlinear numerical model is developed to study the interaction between water waves and permeable structures. Modified resistance terms inside the equations of motion are proposed, which are able to consider the size of porous material directly inside the governing equations. It is understood that the wave-induced flow field and water particle movement inside and around the permeable structure are strongly influenced by the wave period or relative width of the permeable structure (structure width to wavelength ratio). Other parameters such as porous material size, porosity, and resistance coefficients affect the flow field. However, their degree of influence differs depending on the wave period.

The effect of submerged vertical breakwater dimension on wave hydrodynamics and vortex generation around the breakwater is investigated with numerical modeling via two dimensionless parameters: the breakwater dimensionless submergence depth (a/H_i; a-the breakwater depth of submergence) and the Keulegan–Carpenter number (KC = H_iπ/L_bw; H_i-incident wave-height and L_bw-breakwater width). In the numerical model, Reynolds Averaged Navier–Stokes (RANS) equations with a standard k–ε turbulence closure model were implemented; the free surface was traced using the VOF method. A total of 10 different simulations with different KC number and breakwater submergence depth were conducted for this study. The results revealed that the transmission coefficient increases with increasing a/H_i and KC number, but that the effect of the KC number is not linear like the relation to a/H_i. For the waves modeled, the transmission coefficient increases dramatically with increasing the KC number until the KC number reaches a critical value, this critical value is observed when breakwater width is equal to a quarter of wavelength. This gives a hint in design of breakwater width. Turbulence intensity decreases with increasing a/H_i and KC on the seaside of the breakwater while it increases especially near the bed on the leeside of the breakwater; this can increase scour risk on the leeside of the breakwater. The optimum a/H_i for both, high-energy dissipation rate and low risk of scour tends to 3.5 for KC ≈ 1.0.

A numerical wave model for two-dimensional wave field in the vertical plane is proposed in this study. The model combines a VOF method with a non-reflective wave generator in addition to the open boundary treatment based on an added dissipation zone to achieve stable computations. Not only wave breaking due to a submerged breakwater, but also post-breaking wave deformation are numerically investigated using the proposed model. Extensive laboratory experiments were also conducted to verify the validity of the model. The breaking characteristics and the frequency spectra of wave amplitude are examined for various incident wave conditions and breakwater configurations. The computed and measured results have revealed that second harmonic free wave component is generated in the region of non-breaking reformed wave, and that a breaking wave-induced circulating flow is formed at the onshore side of the submerged breakwater. It is demonstrated that the proposed numerical wave model can reproduce well the wave deformation before and after wave breaking through comparison with the experimental results.

In this paper, the atomization characteristics of Si₃N₄ ceramic dry granulation affect the performance of Si₃N₄ ceramic bearing balls. In order to improve the dry granulation characteristics and the comprehensive performance of Si₃N₄ ceramic bearing balls, the atomization mechanism of the spinning nozzle used for Si₃N₄ dry granulation was studied in detail. The interaction between air and binder in the pressure-swirl nozzle is analyzed based on VOF method, the modified realizable $k-𝜀$ turbulence model is used to simulate the flow field inside and outside the pressure-swirl nozzle, the effects of nozzle inlet parameters including the number of tangential inlets and the deflection angle of tangential inlets on the binder volume fraction, velocity distribution and pressure distribution are analyzed. The results show that when the number of tangential inlets increases from 1 to 4, the swirl strength of gas–liquid two-phase in the nozzle increases, the mean diameter of air core increases from 1.51mm to 2.01mm, and the spray cone angle increases from 18.5${}^{\circ }$ to 26.4${}^{\circ }$. Besides, when the deflection angle of tangential inlet increases from 0${}^{\circ }$ to 15${}^{\circ }$, the swirl strength of gas–liquid two-phase in the nozzle with the deflection angle of tangential inlet of 10${}^{\circ }$ is the largest, and the mean diameter of air core and spray cone angle is 3.04mm and 30.7${}^{\circ }$, respectively. Based on the atomization experiment platform of the electric control fuel system, the mean diameter of air core and spray cone angle are measured, the micromorphology of Si₃N₄ particles is observed, which verifies the correctness of numerical simulation. When the Si₃N₄ particles are prepared by dry granulation, taking the atomization performance of nozzle into consideration, the pressure-swirl nozzle with 4 tangential inlets and 10${}^{\circ }$ deflection angle should be selected.

Various new types of seawalls have been adopted instead of existing seawalls such as vertical and block mound seawalls, from the comprehensive viewpoints of disaster prevention, coastal environment and utilization. However, a practical estimation procedure for wave overtopping rate of complex-shaped seawalls has not been established yet. The purpose of this study is, therefore, to numerically examine countermeasures against wave overtopping around road revetment in Okinawa Main Island by conducting numerical simulation using a two-dimensional numerical wave flume 'CADMAS-SURF'. As a result, it is revealed that the CADMAS-SURF can represent wave overtopping phenomena at actual fields. Moreover, numerical computations with the CADMAS-SURF are found to be useful in comprehensively discussing the prevention of wave overtopping disaster.