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

Viewed as sinews and muscles of fluid motion, coherent vortical structures with their interactions are key to understanding the flow dynamics. Based upon this observation, we explore the possibility of efficient flow control by directly manipulating vortices numerically inside the flow field based on the vortex definition and identification system of Liutex. The objective is twofold: (1) to study the

A new approach referred as “the network modeling method” was developed by the authors to analyze the behaviors of marine structures. In this paper the method is briefly described and applied to predict the loads acting on the connectors between the two modules of the Scientific Research and Demonstration Platform (SRDP), which was deployed in a complicated wave environment near islands and reefs in

The flocculation and the settling of the cohesive sediment play an important role in the sediment transport process, and they are affected by many factors. On the coasts and in the estuaries, the organic matter and the salinity are two significant factors. In this study, experiments are carried out to evaluate the flocculation and the settling of the kaolinite in cases of various organic matter and

To accurately determine the shedding frequency of the cavitation cloud in a submerged cavitation jet, the spectral analysis and the proper orthogonal decomposition (POD) for high-speed photography images are performed. The spectrums of 6 different kinds of image signals (the area-averaged gray level, the line-averaged gray level, the point gray level, the cavitation length, width, and area) are calculated

The motion of fluid consists of different scales of coherent vortical structures. These vortical structures determine the characteristics of fluid motion and are key to understand fluid dynamics. In this paper, we study the fine control method of vortical structures based on the Liutex force field model. This is achieved by constructing a source term using Liutex and directly add it to the Navier-Stokes

This paper presents a developed new coupled method which combined our in-house CFD solver naoe-FOAM-SJTU and naoe-FOAM-os with a potential theory High Order Spectral method (HOS). A parametric study of nonlinear wave propagation in computational fluid dynamics (CFD) zone is considered. Mesh convergence, time step convergence, time discretization scheme and length of relaxation zone are all carried

This paper numerically investigates the self-propelled swimming of a flexible filament driven by coupled pitching and plunging motions at the leading edge. The influences of bending rigidity and some actuation parameters (including the phase offset between pitching and plunging, and the amplitudes of pitching and plunging motions) on the swimming performance are explored. It is found that with increasing

The hydrodynamics and locomotion mechanism of Euglena Gracilis (E. Gracilis) is investigated using microscopic shadow imaging and micro particle image velocimetry (MicroPIV). Three distinct locomotion modes were observed: translation, spin, and left/right turn. Since the flagellum was not possible to image, the strokes were identified by evaluating the flow field around the protist. The flow field

Along with the anti-cavitation performance, the high speed and the high power density, are the main trends in the development of centrifugal pumps. At present, the most effective method is to install an inducer in front of the impeller. However, the tip leakage of the inducer results in the vortex cavitation at the blade leading edge of the inducer, and the cavitating flow inside the inducer seriously

The drag and side force coefficients of a half-submerged cylinder in a free-surface flow were calculated through numerical simulations, with the aim of supporting the numerical modelling of log transport in rivers. The variability of these coefficients with the yaw angle with respect to the flow direction and with the ratio between the flow depth and the diameter of the cylinder were investigated.

Droplet breakage is a common phenomenon in converting a pipe flow to a swirl flow in a vane-type pipe separator (VTPS)’ inlet. The evaluation of the dispersed droplet sizes after breakage is crucial to the optimum design of the inlet structure and the estimation of the oil-water separation performance. This paper studies the droplet behavior in a swirl flow produced by guiding vanes. Experiments are

The large eddy simulation (LES) is used to resolve the flow structure in the cavitating turbulent flow around the Clark-Y hydrofoil coupled with a homogeneous cavitation model. A new method is proposed in this paper to calculate the LES error of the time-averaged streamwise velocity for the LES verification and validation (V&V). From the instantaneous cavity patterns, it is demonstrated that the predicted

In this paper, the flow field around NACA0015 hydrofoil is calculated under the condition of two-phase cavitating flow to provide a theoretical guidance for reducing the cavitation noise. A modified turbulence model coupled with the Zwart cavitation model is used to calculate the flow field. According to the computed sound source data, the dipole sound pressure distribution diagrams for the extremely

In this paper, a modified Rayleigh-Lamb equation is derived that takes into account the radial vibrations of a gas bubble coated with a viscoelastic shell and located in an elastic medium. For small oscillations of inclusion, the problem of heat exchange between a gas, a liquid phase, a viscoelastic shell, and an elastic medium is solved. The energy integral is determined. In the case of small disturbances

The bubble drag force correlation plays an important role in the numerical simulation accuracy of gas/liquid flows. In order to systematically investigate the interphase drag force of non-buoyancy driven bubbly flows, a dynamic-positioning body force (DPBF) method is developed in this study. It is proved that this method has an enough computation precision. Using this method, a series of direct numerical

Vortex dynamics, with the possibility of efficient flow control, is explored in this study based on the new introduced vortex definition and identification system of Liutex. With the six core elements of vortex identification, including (1) absolute strength, (2) relative strength, (3) local rotational axis, (4) global rotational axis, (5) vortex core size and (6) vortex boundary, provided by the Liutex

In order to study the flow characteristics in water bodies with rigid aquatic vegetation, series of laboratory experiments are carried out in an open channel, in which glass rods are used as plants with diameters of 6mm, 8mm and 10mm, respectively. For each diameter of glass rods, four typical cases are considered with various densities and arrangements of glass rods. The flow velocities in the four

The complicated flow structure around the pier threatens the safe navigation of ships. This paper studies the mechanism of the flow with a ship around the pier, passing or not passing and with consideration of the interval between the ship and the pier. The flow field model and the moving ship model are constructed by the six degrees of freedom (6DOF) solver combined with the virtual unit immersed

In this paper, the dynamic characteristics of the bubble in a broken confined domain are studied. The broken confined domain is composed of a solid wall and a plate that has a hole. The axisymmetric numerical model is established by combining the Eulerian finite-element method with volume of fluid (VOF) method, and is validated by comparing the results with those from an experiment. Then the influences

The bubble drag force correlation plays an important role in the numerical simulation accuracy of gas/liquid flows. In order to systematically investigate the interphase drag force of non-buoyancy driven bubbly flows, a dynamic-positioning body force (DPBF) method is developed in this study. It is proved that this method has an enough computation precision. Using this method, a series of direct numerical

To investigate the effects of the caudal fin deformation on the hydrodynamic performance of the self-propelled thunniform swimming, we perform fluid-body interaction simulations for a tuna-like swimmer with thunniform kinematics. The 3-D vortices are visualized to reveal the role of the leading-edge vortex (LEV) in the thrust generation. By comparing the swimming velocity of the swimmer with different

The water entry process associated with complicated unsteady structures, with consideration of the influence of the waves, is not well studied. In the present work, the oblique water entry of a cylinder under different regular waves is numerically investigated. The volume of fluid (VOF) method and the sub-grid scale (SGS) stress model based on the large eddy simulation (LES) method are adopted for

In this study, the new method of the vortex core line based on Liutex definition, also known as Liutex core line, is applied to support the hypothesis that the vortex ring is not a part of the Λ - vortex and the formation of the ring-like vortex is formed separately from the Λ - vortex. The proper orthogonal decomposition (POD) is also applied to analyze the Kelvin-VHelmholtz (K-H) instability happening

In order to compensate for the stochastic nature of the power grid due to the tremendous development and the integration of renewable energy resources and meet its other requirements, the hydraulic turbines are forced to operate more frequently under partial load conditions with singular and misaligned flows inevitably excited by the inter-blade vortex. This paper presents numerical investigations

Data assimilation (DA) refers to methodologies which combine data and underlying governing equations to provide an estimation of a complex system. Physics informed neural network (PINN) provides an innovative machine learning technique for solving and discovering the physics in nature. By encoding general nonlinear partial differential equations, which govern different physical systems such as fluid

The water contamination on the side windows of moving vehicles is a crucial issue in improving the driving safety and the comfort. In this paper, an effective optimization method is proposed to reduce the water contamination on the side windows of automobiles. The accuracy and the efficiency of the numerical simulation are improved by using the lattice Boltzmann method, and the Lagrangian particle

In this paper, the fluid transport in the interaction of two co-axial co-rotating vortex rings are investigated. Vortex rings are generated using the piston-cylinder apparatus, and the resulting velocity fields are measured using digital particle image velocimetry. The interaction process is analysed by means of vorticity contour, as well by investigation of the Lagrangian coherent structures (LCSs)

This study presents results of experiments where roughness applications are evaluated in delaying the tip vortex cavitation inception of an elliptical foil. High-speed video recordings and laser doppler velocimetry (LDV) measurements are employed to provide further details on the cavitation behavior and tip vortex flow properties in different roughness pattern configurations. The angular momentum measurements

In order to study the cavitation and hydrodynamic characteristics of propeller under uniform and non-uniform flows, numerical investigations are performed using interPhaseChangeDyMFoam in the open source computational fluid dynamics (CFD) software platform OpenFOAM with Schnerr-Sauer cavitation model. The simulation results can be used as a reference to evaluate the working ability of a propeller in

Energy dissipation and scour control are all the key issues for the design of hydraulic structures. On the basis of the high energy dissipation for the multiple slit-type energy dissipaters (M-STED) developed by the authors, in this work, the characteristics of the scour hole for the M-STED were experimentally investigated through three sets of those physical models with five cases and a scour hole

The turbulent cavitating flow around the propelling pump tip clearance is numerically simulated using the large eddy simulation (LES) method coupled with the Zwart-Gerber-Belamri (ZGB) cavitation model to investigate the cavitation-vortex interaction mechanism. The calculated cavitation structures around the blades are in a remarkable agreement with the experimental results. The distributions of the

Influenced by the fact that vorticity represents rotation for rigid body, people believe this idea also works for fluid flow. However, the vortex predictions by vorticity do not match experimental results, which drove scientists to look for more appropriate methods to identify vortex. All vortex identification methods can be categorized into three generations. The vorticity-based method is classified

The vortex-induced vibrations of a cylinder with two plates symmetrically distributed along the centerline of the wake are studied by using the fluid-structure interaction simulations on the Arbitrary Lagrangian-Eulerian method. In this study, the different geo-metrical distribution parameters of the splitter plates and inflow velocities are taken into account. The physical mechanisms of vortex-induced

A numerical model is proposed for analyzing the effects of added mass and damping on the dynamic behaviors of hydrofoils. Strongly coupled fluid-structure interactions (FSIs) of hydrofoils are analyzed by using the 3-D panel method for the fluid and the finite element method for the hydrofoils. The added mass and damping matrices due to the external fluid of the hydrofoil are asymmetric and computational

In this paper, the cavitating flow over a flexible NACA66 hydrofoil is studied numerically by a modified fluid-structure interaction strategy with particular emphasis on understanding the flow-induced vibration and the cavitating vortical flow structures. The modified coupling approaches include (1) the hydrodynamic solution obtained by the large eddy simulation (LES) together with a homogenous cavitation