A comparison of theoretical investigation and numerical simulation of a single bubble oscillation is carried out in this paper. The theoretical research is based on solving Rayleigh-Plesset (R-P) equation and Keller-Miksis (K-M) equation using Runge-Kutta method. The numerical method focuses on the two discrete methods in the volume of fluid (VOF) method, geometric reconstruction (GR) and modified

The performance and flow field of hydropower turbine in shallow water can be affected by the presence of free surface. Therefore, the influence of free surface on the turbine performance was studied through transient computational fluid dynamics (CFD) analysis. The turbine included three blades made of NACA0018 hydrofoil. Submerged depths and different tip speed ratio (TSR) were two main variables

To enable a virtual design and optimization process of partially filled coolant tanks a reliable numerical approach is needed to predict the liquid and gas two phase flow inside the tanks. In this study numerical results are validated by experimental data to examine the suitability of the method for the tank design process. The liquid motion inside the tanks can be described as sloshing with high amplitude

Wave overtopping at a sea dike was observed using video images during a storm in July 2018 at Rizhao Coast, China. A shore-based video monitoring system was mounted to collect coastal images with a sample frequency of 1 Hz in the beginning 10 min of each hour during daylight. A method to extract the frequency, location, width and duration of individual overtopping events based on the shore-based video

The energy transfer and dissipation as well as the turbulent structures in a lid-driven cavity flow with porous walls are investigated via the lattice Boltzmann method, with direct numerical simulation (DNS) for an isothermal incompressible flow for which the Reynolds number (Re) is 50 000. A generalized Navier-Stokes equation with the Brinkman-Forchheimer-extended Darcy model is implemented, in which

The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the downstream centerline of the bluff cylinder at a distance of 4 diameters away from the center of the cylinder. To simulate the fish body undulation and movement, the moving mesh is generated

The internal flow field of an axial-flow pump under low flow rate conditions is extremely turbulent. The unstable flow region is formed due to the tip leakage and the rotating stall, and is distinguished by a saddle patterned zone in its flow-head curve that demonstrates restrictions in its workable flow range. It is therefore important to understand and improve the operational characteristics of an

The shallow water flow through and around a patch of rigid emergent vegetation was investigated numerically. The mean flow field and turbulent structures were studied, especially their dependence on the solid volume fraction (SVF) of the patch and the bed friction. Two streamwise velocity scales, U1s at the starting point of the steady wake and U1e at the downstream end of the steady wake, and the

The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteristics. The internal flow field is simulated via the shear stress transport turbulence model to analyze the influence of the T-shaped blade on the performance of a centrifugal pump. It is

With the development of ocean engineering and demand for safety of the ship and offshore structures, the transportation and storage of liquid have become an important issue nowadays. Furthermore, in order to improve the hydrodynamic performances of the ship and offshore structures, the anti-rolling liquid tanks are often taken into consideration. The internal-external coupling flow effect is vital

This paper presents a numerical study of the hydroelastic coupling during the free-surface water entry of deformable spheres of different material densities. The focus is on the hydrodynamic forces, the stress loads, the sphere deformations, the wetted areas of the sphere and the cavity dynamics, including the impacting of the elastic spheres and the hydroelastic coupled behaviors in the free surface

A numerical study was performed on the embankment weir overflows with various surface roughness and tailwater submergence, to better understand the effects of weir roughness on discharge performances under the free and submerged conditions. The variation of flow regime is captured, from the free overflow, submerged hydraulic jump, to surface flow with increasing tailwater depth. A roughness factor

In this paper, the large eddy simulation (LES) method in conjunction with the Zwart cavitation model is adopted for the assessment of the erosion risk on a hydrofoil surface. The numerical results are in good agreement with the experiments. On this basis, three methods, namely the intensity function method (IFM), the time-averaged aggressiveness indicators (TAIs) and the gray level method (GLM), are

The vortex-based propulsive systems’ enhanced performance greatly contributes to the vortex added-mass effect, which was initially developed to explain the added drag when a solid body accelerates in fluids. However, the solution of the instantaneous vortex added-mass coefficient is still remaining a question because vortices always do not have a stable geometric shape like solid bodies. In this paper

In this paper, Liutex similarity is extended and revised in channel turbulence. Liutex similarity is free from viscous dissipation, relaxing the very high Reynolds number assumption of K41. Liutex similarity hypothesis in 2-D channel turbulence is first proposed and estimated, which denotes that the statistical properties of Liutex field are uniquely and universally determined by the scale l, Liutex

In view of the frequent occurrence of floods due to climate change, and the fact that a large calculation domain, with complex land types, is required for solving the problem of the flood simulations, this paper proposes an optimized non-uniform grid model combined with a high-resolution model based on the graphics processing unit (GPU) acceleration to simulate the surface water flow process. For the

This paper applies the Flow-3D to investigate the impacts of different flow discharge and vegetation scenarios on the flow velocity (including the longitudinal, transverse and vertical velocities). After the verification by using experimental measurements, a sensitivity analysis is conducted for the vegetation diameter, the vegetation height and the flow discharge. For the longitudinal velocity, the

The acoustic propagation characteristics of the cavitating flow are essential for the noise suppression, but were not well studied. In the current paper, a new technique concerning the propagation path of the monopole acoustic energy is presented and two typical thermodynamic cavitation modes (the inertial and thermal modes) are selected to investigate the effect of the cavity shedding dynamics on

Recently, the Liutex-based force field models are proposed and applied to some two-dimensional flows to explore the possibility of direct vortex control strategies. In this paper, we applied the Liutex-based centripetal force model to three-dimensional flow around a circular cylinder at Re = 3 900 . The turbulent flows around the three-dimensional cylinder are modeled by the delayed detached-eddy simulations

This paper presents experimental measurements by the time-resolved particle image velocimetry (TR-PIV) for the turbulent boundary layer (TBL) over the smooth surface, the superhydrophobic (SH) surface, and the superhydrophobic-riblets (SR) surface in an open-surface recirculating water channel. The Reynolds number based on the wall friction velocity and the thickness of the TBL over the smooth surface

The incompressible unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are performed for a free-running container ship in maneuvering conditions: the starboard and portside turning circle simulations with 35° rudder deflection. The validation variables include trajectory, motions, and propeller performances, and the prediction shows acceptable agreements against the experimental data. During

The Gymnarchus niloticus fish can swim in surging and heaving directions only with a long undulating ribbon fin while keeping its body along almost straight line. These features substantially inspire the design of underwater vessels with high maneuverability and station keeping performance, which is characterized by peculiar vortex structures induced by undulating fin propulsion. To reveal the propulsion

Vortical structures of a submarine with appendages are fully turbulent and complex. Thus, flow control and vortex manipulation are of great importance for the hydrodynamic performance and acoustic characteristics. Take the generic submarine model DARPA Suboff as the test case, a vortex tuning method based on the Liutex force field is proposed to manipulate the vorticity field. Viscous flow past the

The Knowledge of turbulent flow developing inside and around the bottom trawl net is of great importance not only for improving the hydrodynamic performance of the gear but also for the selectivity via the fish response, such as the herding response or escape behavior. The 3-D Electromagnetic Current Velocity Meter (ECVM) measurements were performed to investigate the effect of turbulent flow on the

Part 2 reports the validation, local force and local flow study results for the free-running added power simulations whose conditions are the same as the self-propulsion test except for the increased propeller rotational speed and the presence of wave. When targeting the same mean Froude number in the wave condition, the propeller requires the increased propeller rotational speed for the operation

Hydrodynamic cavitating flows usually consist of 3-D intense vortical flows that are detached from solid boundaries. Detached vortical flows normally generate heaps of cavitating flow structures, which, in turn, govern the location of cavitation erosion before collapse. Thus, this study introduces a new numerical approach based on the improved delayed detached eddy simulation (IDDES) turbulence modeling

When studying the flow dynamics and the characteristics of fluid motion, vortex structure with their interactions is the key issue. In the present work, a vortex control method is investigated based on the vortex identification system of Liutex. The numerical study is carried out in OpenFOAM by directly adding a source term to the Navier-Stokes equations, which is called the centripetal force model

An iterative time-marching scheme is developed to investigate the hydrodynamic interactions between multiple ships. Such an unsteady interactive effect could be magnified in restricted waterways, e.g., a channel or harbor area. To the author’s knowledge, nearly all the research on the ship-to-ship interaction neglecting the free surface effects. The free surface is usually treated as a rigid wall.

Classical fluid kinematics or Cauchy-Stokes decomposition mistreated vorticity as fluid rotation and mixed flow stretching with shearing. Classical fluid dynamics or Navier-Stokes (N-S) equations are based on the classical kinematics and treated vorticity as null in contribution of forces and mixed the stretching force with the shearing force, which is not consistent with the Galilean invariancy. N-S

This paper proposes a 3-D non-hydrostatic free surface flow model with a newly proposed general boundary-fitted grid system to simulate the nonlinear interactions of the bi-chromatic deep-water gravity waves. First, the monochromatic bidirectional and bi-chromatic bidirectional waves of small wave steepness are successively simulated to verify the abilities of the numerical model. Then, a series of

In this paper, cross-flow vortex-induced vibration (VIV) responses of a circular cylinder surrounded with different control rods have been investigated in a wind tunnel. The number of rods n is set equal to 3 and 6, and the ratios of diameters d / D (where d is the diameter of small rods, D is the cylinder diameter) are assumed to 0.10, 0.16 and 0.20. The spacing ratios of s (s = G / D, where G is

For complex aerodynamic and hydrodynamic problems, the analysis of vortex is very important. The Liutex method is an eigenvalue-based method which is local, accurate, and unique, which can give an accurate definition of vortex, so the control of vortex can be implemented and effectively guaranteed. Based on Liutex method, two methodologies of centripetal force model and counter-rotation force model

The transition in the boundary-layer flow affects the hydrodynamic performances of hydraulic machineries, as the key components in the ship propulsion system. The shear stress transfer (SST) γ-Reθt transition model is an important prediction tool in the boundary layer simulation for hydrofoils. The present paper improves the prediction accuracy of the SST γ-Reθt model for the boundary layers along

The computational fluid dynamics (CFD) approach can be used to obtain both internal and external characteristics of centrifugal pumps, and the variations of the hydrodynamic force, the pressure and the torque on the blades acquired by the CFD are highly associated with the safety of the pumping system. Based on the CFD simulations, this paper investigates the stopping characteristics of multiple pumps

The significance of riparian vegetation on river flow and material transport is not in dispute. Conveyance laws, sediment erosion and deposition, and element cycling must all be adjusted from their canonical rough-wall boundary layer to accommodate the presence of aquatic plants. In turn, the growth and colonization of riparian vegetation are affected by fluvial processes and river morphology on longer

The mechanism of the flow resistance in open channels and pipelines is of vital importance for various critical issues related to the water flow. The Nikurade’s method of calculating the friction factor is not applicable in some cases. It is necessary to consider the influence of the vortex volume surrounding the vegetation and to study the hydrodynamic characteristics of the vegetated channels. This

The vortex rope usually occurs in the draft tube of the Francis turbine operated under part-load conditions, to induce strong low-frequency pressure vibrations, and therefore, is very harmful to the safety of the hydropower unit. In the present work, three kinds of strategies are extensively investigated, i.e., the installations of the ventilation and the fin, as well as the hybrid strategy of the

Fluid kinematics describes the fluid motion without consideration of any force. Classical fluid kinematics adopts Helmholtz velocity decomposition, which is equivalent to Cauchy-Stokes (CS) velocity gradient tensor decomposition. CS decomposes the velocity gradient tensor into a strain-rate (symmetric) tensor and a vorticity (anti-symmetric) tensor. However, several questions arise: (1) since vorticity

The destabilization of an erodible sediment bed by a reproducible impulsive phenomenon is studied experimentally. For this, a specific setup is designed to produce a well-controlled isolated vortex, advected over a uniform sand bed. Particle image velocimetry (PIV) measurements are performed to get fluid flow information; suspended particles images are also recorded. A new measurement technique, based

Design of floating offshore wind turbines (FOWTs) needs reliable and innovative technologies to overcome the challenges on how to better predict the dynamic responses in terms of aero-hydro-servo-elastic disciplines. This paper aims to demonstrate the optimized prediction of the dynamic response of FOWTs by Simulation annealing diagnosis algorithm (SADA). SADA is an Artificial Intelligence technology-based

Vortical structures and wakes of bluff bodies in homogenous and stratified environment are common and important in ocean engineering. Based on the Boussinesq approximation, a thermocline model is proposed to deal with the variable density stratified fluid, and implemented in the commercial software Simcenter STAR-CCM+ framework. The improved delayed detached eddy simulation (IDDES) modeling method

By impacting a concave dual-layer liquid (with the oil and the dyed water) surface in a test tube, a compound jet with a water core and an oil shell is generated. The velocities of the jet’s head (V)j and the oil-water interface (V′j) are experimentally determined against the initial thickness and the viscosity of the upper layer liquid. The results show that the oil-water interface can be roughly

The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding, where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity. Therefore, it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise. This paper first compares the Omega vortex

A thermal-hydrodynamic coupling model is used to investigate the interplay between the wall temperature distribution and the bubble departure during the nucleate boiling process. The boiling process is modeled as the combination of three subprocesses: the transient heat conduction process in the solid heater, the evaporation of the microlayer underneath the bubble, and the bubble dynamics in the two-phase

Generating body-fitted particle distribution for arbitrarily complex geometry underpins the applications of particle-based method to engineering and bioengineering and is highly challenging, and thus hinders the potential of particle methods. In this paper, we present a new computer-aided design (CAD) compatible body-fitted particle generator, termed as CAD-BPG, for arbitrarily complex 3-D geometry

The purpose of this study is to apply the cumulant lattice Boltzmann method (LBM) to simulate high Reynolds number free surface flows. The single-phase cumulant LBM is extended to solve the free surface flows by using the phase-field method as the interface capturing scheme. Numerical simulations are performed on an experimental problem of dam break flow impact on a vertical cylinder. Important numerical

A two-dimensional computational fluid dynamics (CFD) numerical model is developed to study the power takeoff (PTO) efficiency of an Edinburgh duck wave energy converter (WEC) device by using the OpenFOAM source package. After the numerical validations and the convergent verifications, the characteristics of the duck WEC device for the power takeoff in various incident wave periods are examined. The

The interactions between the bubbles and the particles near structures are important issues for the applications of the cavitation in the fluid machinery. To study the hidden microscopic mechanisms, a numerical method for simulating the laser-generated bubble between the solid wall and a particle is developed in this paper with considerations of the viscosities and the compressibility of the gas and

When the ice-going ships advance in the polar region, the navigation in the floe ice region is often encountered, the hull will suffer the high-frequency contact force produced by the floe ice, which will affect the navigation performance of the ship. Therefore, it is necessary to predict the water and ice force acting on the hull accurately. In this paper, the numerical simulation and experimental

The flow-induced motion (FIM) of an elastically mounted square-section cylinder is experimentally investigated over a wide range of Reynolds numbers (1.5 × 104 < Re < 7.0 × 104). A 14 m long towing tank water channel and a carrier are designed to facilitate the investigation of FIM at high velocities. The cylinder is limited to a transverse oscillation and is carried inside the water channel. The effect

A method is proposed to investigate the steady deformation and the drag of a single droplet in a flowing gas at a high Reynolds number. The volume of fluid (VOF) method is used to model the droplet surface structure. The direct numerical simulation (DNS) method is used to model the gas flow field. In order to avoid the effect of the droplet acceleration on the drag and reduce the computation cost,

Stopping maneuver is an important research topic in ship maneuverability. The stopping ability of ship is not only related to the hydrodynamic characteristics of hull, rudder and propeller, but also related to the capacity of main engine. However, there are few researches on the capacity of main engine under reversed propulsion condition. In the paper, a numerical water tank is established to simulate

The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river. So far, few studies have been conducted to investigate the suspended sediment transport capacity in the vegetated sediment-laden flow. In this study, a new formula is derived to predict the sediment transport capacity in a vegetated flow by considering

The tip-leakage vortex (TLV) cavitation is a challenging issue for a variety of axial hydraulic turbines and pumps from both technical and scientific viewpoints. The flow characteristics of the TLV cavitation were widely studied in the past decades, but the knowledge about the tip-leakage cavitating flow is still limited. The present paper reviews the progresses in the researches of the TLV cavitation

The vortex-induced vibration may lead to a premature failure of hydraulic mechanical systems, especially under the resonance condition in the torsional mode. To predict the structural fatigue life, a careful consideration of the dynamic response to the hydraulic excitations is essential in the design phase. This study focuses on the numerical investigation of the relationship between the flow velocity

To make the Kaplan turbine technology comparable to both the Pelton and the Francis turbine, the master equation for the Kaplan turbine has been established by analyses similar to that-for the Francis turbine. The analysis begins with the descriptions of free vortex flows at the runner inlet and the swirl flow at the impeller exit. By considering the Euler equation for specific work and by further

Design of a very large floating structure (VLFS) deployed near islands and reefs, different from those in the open sea, inevitably faces new technical challenges including numerical analysis methods. In this paper, a direct coupling analysis method (DCAM) has been established based on the Boussinesq equations and the three-dimensional hydroelasisity theory with Rankine source method to analyze the

In 2019 a Scientific Research & Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China. It is a simplified small model of a two-module semi-submersible-type VLFS. The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for

Due to the inference of the uneven shallow water seabed and the surrounding islands, the wind-generated waves around or in a reef lagoon are rather complicated, and critical to the safety of floating structures deployed near islands or inside a lagoon. This paper aims to find a feasible analysis tool for the wave simulations near islands and reefs. The proposed three methods of grid techniques of WAVEWATCH

With the large-scale density stratified tank and the numerical flume proposed, series of numerical cases in line with the experiments are carried out to investigate the interaction between the tension leg platforms (TLPs) and the internal solitary waves (ISWs). The waveforms, and the loads and the torques on the TLP obtained by the experiments and the simulations agree well with each other. Experimental