Hydrodynamic Performance Research Articles

A Novel Semi-Spar Floating Wind Turbine Platform Applied for Intermediate Water Depth

For the exploitation of offshore wind resources in areas with intermediate water depths, a novel semi-spar floating foundation is introduced to combine the superiority of the conventional semisubmersible and spar-type floater. It consists of an upper floater and a hanging weight, which are connected through 12 suspension ropes. Such a floating foundation can be wet-towed as a semisubmersible floater, which features a large waterplane moment of inertia to increase stability and reduce transportation costs. After being anchored on site, it behaves as a spar floater with moderate draft and superior hydrodynamic characteristics. The stability of the proposed semi-spar platform during wet towage is analyzed. Afterward, a fully coupled aero-hydro-servo-elastic simulation is conducted to evaluate its hydrodynamic responses in comparison with the responses of the well-acknowledged OC3-spar and OC4-semisubmersible platforms. Then, the ultimate strength of the mooring lines and suspension ropes under extreme conditions was numerically investigated, as well as the relationship between the ropes’ tension and wave direction. Eventually, a cost-effectiveness analysis is conducted in terms of power generation and steel mass. The results demonstrate that the proposed semi-spar design meets the safety criteria in transportation and exhibits a smaller response in surge and pitch motions. In addition, the ultimate strength of mooring lines and suspension ropes satisfies the safety requirements, and simulation reveals that the lateral suspension ropes parallel to the propagation direction are sensitive to the environmental conditions of winds and waves. This study confirms that the newly proposed floating wind turbine exhibits excellent hydrodynamic and power generation performance, which is of great significance for the sustainability of the energy and electricity industry.

Study on the Hydrodynamic Performance of Swing-Type Flapping Hydrofoil Bionic Pumps Affected by Foil Camber

The flapping hydrofoil bionic pump is an innovative hydrodynamic device that utilizes flapping hydrofoil technology. Flapping hydrofoil bionic pumps are crucial in addressing issues like inadequate river hydropower and limited water purification capabilities in flat river network regions. Optimizing the foil characteristics is essential for enhancing the hydrodynamic efficiency of the flapping hydrofoil bionic pump. This study investigates the impact of foil camber parameters on the hydrodynamic performance of swing-type asymmetric flapping bionic pumps. The NACA series standard foils with varying cambers are analyzed using the overlapping grid technology and finite volume method. The thrust coefficient, flow rate, pumping efficiency, and flow field structure of the flapping hydrofoil bionic pump are examined under pressure inlet conditions with the foil camber. The findings indicate that increasing the foil’s curvature within a specific range can greatly enhance the maximum values of thrust coefficient, propulsive efficiency, and pumping efficiency of the flapping hydrofoil bionic pump. Specifically, when the foil curvature is 6%c, the maximum value of the instantaneous thrust coefficient of the flapping hydrofoil bionic pump is significantly improved by 31.25% compared to the symmetric foil type under the condition of an oscillating frequency of f = 1 HZ. The flapping hydrofoil bionic pump achieves its maximum pumping efficiency when the oscillation frequency is within the range of f ≤ 2.5 Hz. This efficiency is 11.7% greater than that of the symmetric foil, and it occurs when the foil curvature is 8%c. Within the frequency range of f > 2.5 Hz, the flapping hydrofoil bionic pump that has a foil curvature of 6%c exhibits the highest enhancement in pumping efficiency. It achieves a maximum increase of 12.8% compared to the symmetric foil type. Nevertheless, the average head was less than 0.4 m, making it suitable for ultra-low-head applications.

Flowing Liquid-Based Triboelectric Nanogenerator Performance Enhancement with Functionalized Polyvinylidene Fluoride Membrane for Self-Powered Pulsating Flow Sensing Application.

Pulsating flow, a common term in industrial and medical contexts, necessitates precise water flow measurement for evaluating hydrodynamic system performance. Addressing challenges in measurement technologies, particularly for pulsating flow, we propose a flowing liquid-based triboelectric nanogenerator (FL-TENG). To generate sufficient energy for a self-powered device, we employed a fluorinated functionalized technique on a polyvinylidene fluoride (PVDF) membrane to enhance the performance of FL-TENG. The results attained a maximum instantaneous power density of 50.6 µW/cm2, and the energy output proved adequate to illuminate 10 white LEDs. Regression analysis depicting the dependence of the output electrical signals on water flow revealed a strong linear relationship between the voltage and flow rate with high sensitivity. A high correlation coefficient R2 within the range from 0.951 to 0.998 indicates precise measurement accuracy for the proposed FL-TENG. Furthermore, the measured time interval between two voltage peaks precisely corresponds to the period of pulsating flow, demonstrating that the output voltage can effectively sense pulsating flow based on voltage and the time interval between two voltage peaks. This work highlights the utility of FL-TENG as a self-powered pulsating flow rate sensor.

Hydrodynamics and mass transfer performance of microbubble flow in the bubble column with a contraction section

Bubble columns have many applications in the biochemical, petrochemical, and metallurgical industries. The gas-liquid system composed of microbubbles is characterized by significant phase interfacial area, high mass transfer efficiency, fast dissolution rate, strong adsorption capacity, and long self-sustaining time. This paper investigated the performance of pressurized dissolved gas microbubble generation (PDG) using a Venturi tube as the releaser using a plug-in online imaging instrument. The hydrodynamic and mass transfer characteristics of the microbubble flow generated by PDG in a bubbling column with a contraction section (BCS) were then investigated. One of the primary studies was the effect of the contraction section on the flow performance of the bubbles, the mass transfer performance, and the aeration efficiency of the PDG versus the throat inlet Venturi bubble generator (VBG). The results show that the initial bubble Sauter mean diameter is essentially constant with dissolved gas pressure, and the bubble size distribution(BSD) is similar. The bubble stream passing through the contraction section exhibits two different BSD at the center and side walls of the BCS outlet section. Microbubbles in the inlet section in the absence of external forces almost do not occur in bubble coalescence. The flow of bubbles in the contraction section is subject to a slight coalescence effect. The diameter of bubbles in the contraction section is mainly larger than 20 μm. In the contraction section, coalescence occurs mainly at the side wall. The way of occurrence is adsorption coalescence and collision coalescence. The bubbles move in a gradually confined space with a high degree of interference with each other's bubbles, and the liquid linear velocity acts as an ‘external force’ that benefits the flow of the bubbles out of the confined space. The standard aeration efficiency of PDG is 3–11 times higher than that of the VBG. At 0.3 MPa, the highest standard aeration efficiency for the PDG method was between 0.18 and 0.64 kgO2/kW∙h.

A Numerical Investigation of the Hydrodynamic Performance of a Pitch-Type Wave Energy Converter Using Weakly and Fully Nonlinear Models

In this study, the performance of a wave energy converter (WEC) rotor under regular and irregular wave conditions was investigated using 3D nonlinear numerical models. Factors such as the power take-off (PTO) load torque, wave periods, spacing of multiple WEC rotors, and wave steepness were analyzed. Two models were employed: a weakly nonlinear model formulated by incorporating the nonlinear restoring moment and Coulomb-type PTO load torque based on the potential flow theory, and a fully nonlinear model based on computational fluid dynamics. The results show that the average power estimated by both numerical models is consistent, with a wave steepness of 0.03 for the range of one-way and two-way PTO load torques, except for the deviations observed in the long range of the one-way PTO load torque. Furthermore, the average power of the WEC rotor under the applied PTO load torque exhibits a quadratic dependency, regardless of the wave steepness. In addition, adopting a one-way PTO load torque was more efficient than adopting a two-way PTO load torque. Therefore, the fully nonlinear model demonstrated its ability to handle a high degree of nonlinearity, surpassing the limitations of the weakly nonlinear model, which was limited to moderate wave steepness.

Experimental and CFD investigation on resistance reduction of hydrofoils for amphibious vehicles

ABSTRACT Resistance characteristics of amphibious vehicles are crucial for their sailing speed and battlefield survivability. This study proposes the installation of hydrofoils at the wheel cavity to reduce resistance and enhance performance. Two hydrofoil designs and four shapes are analyzed to determine the optimal drag reduction design. Towing tests and numerical simulations are employed to investigate and evaluate the hydrodynamic performance of amphibious vehicles. The impact of hydrofoils on resistance reduction is analysed and elucidated through a comprehensive analysis of surface pressure distribution, sailing attitude, and energy consumption in the flow field. Results demonstrate that, except for the elongation-hydrofoil, the other three shapes all show significant performance optimisation at medium to high speeds Fr > 0.5 , with improved effectiveness as speed increases. Among the four shapes, the curve-hydrofoil exhibits the best overall drag reduction effect (18%) and resistance peak compression ability (6.68%), owing to its ample lift force and optimal trim capability.

Performance analysis of two generations of heaving point absorber WECs in farms of hexagon-shaped array layouts

ABSTRACT Numerical analyses are presented for two generations of a floating heaving point absorber wave energy converter (WEC) installed with different farm array layouts. The wave farm configurations are based on WECs developed by Waves4Power. The numerical models are developed in the DNV software package, Sesam. Parametric studies of the isolated WEC configurations and farm array layouts are conducted under typical environmental conditions and various incident wave directions to understand the hydrodynamic power performance and the levelised cost of energy (LCoE). Hexagonal layouts are proposed for deploying the WEC units and compared with a 10-unit layout termed StarBuoy, which has been reported in previous work. The results of the present study confirm that the interactions between arrayed units in a farm can have either positive or negative effects on the LCoE, which is dependent on the array layout and environmental conditions. The hexagonal array layouts lead to lower LCoE owing to constructive interaction effects.

Assessment of Hydrodynamic Performance and Motion Suppression of Tension Leg Floating Platform Based on Tuned Liquid Multi-Column Damper

To address the unstable motion of a tension leg platform (TLP) for floating wind turbines in various sea conditions, an improved method of incorporating a tuned liquid multi-column damper (TLMCD) into the TLP foundation is proposed. In order to evaluate the control effect of TLMCD on the motion response of the floating foundation, a multiphase flow solver based on a viscous flow CFD method and overlapping grid technique is applied to model the coupled multi-body dynamics interaction problem involving liquid tanks, waves, and a spring mooring system. This method has been proven to accurately capture the high-frequency motions of the structure and account for complex viscous interferences affecting the geometric motions. Additionally, the volume of fluid (VOF) method and the first-order linear superposition method are used to model the focused wave, enabling a simulation of the effects of transient wave loads on the floating foundation. The results show that the tuned damping effect of TLMCD on the TLP is mainly in the pitch motion, with the maximum pitch amplitude control volume ratio of TLMCD reaching up to 86% and the maximum surge amplitude control volume ratio of TLMCD reaching up to 25.2% under the operating conditions. These findings highlight the potential for additional research on and implementation of TLMCD technology.

Hydrodynamics, mass transfer, and hydrogenation performance of a HiGee‐aided fixed bed reactor

AbstractMicrobubble shows great potential for hydrogenation reaction in fixed bed reactors (FBRs). However, the lack of understanding of the hydrodynamic behaviors of microbubble swarm in FBR limits the reactor design. In this work, a pilot‐scale HiGee‐aided fixed bed reactor (HFBR), including a HiGee microbubble generator (HMG) and a catalyst bed, has been developed and then applied for poly alpha olefin 4 (PAO 4) hydrogenation. An empirical correlation of Sauter mean diameter (d32) of microbubbles at the inlet and outlet of catalyst bed was established. The gas holdup (φb) of catalyst bed with HMG was 5–10 times higher than that without HMG. Based on d32 and φb, the effective interfacial area in HFBR was calculated as 2000–6000 m2/m3. Compared with static mixer‐aided fixed bed reactor, the aromatic content of PAO 4 hydrogenated in the HFBR was 56%–69% lower, which shows bright future for industrial application.

Comparison study on mooring line models for hydrodynamic performances of floating offshore wind turbines

The mooring system plays a crucial role in the seakeeping ability of floating offshore wind turbines (FOWTs) but complicates the overall dynamics of the system. Many quasi-static (QS) and dynamic models for mooring analysis exist but a comprehensive comparison among open-source or semi open-source codes in various scenarios is rare. In the present study, six mooring models including three dynamic and three QS ones are assessed. The three dynamic models are the local discontinuous Galerkin (LDG) finite element method (FEM), the lumped mass (LM) method and the finite different method (FDM), and the three QS models are the piecewise extrapolation method (PEM), the catenary and the QS of MAP. Three groups of tests involving catenary line under fairlead excitation, hanging line with axial excitation and FOWT in waves are conducted. The first two test groups focus on single line dynamics to assess among the three dynamic models while the third test group focuses on coupled hydro-mooring modeling with the FEM, PEM, catenary and QS coupled to OpenFOAM. The test results show that there are substantial differences among the models in various scenarios. And the LDG FEM and LM models are recommended to be applied in realistic FOWT hydrodynamics problems.

Simulation Analysis and Experimental Study on Airfoil Optimization of Low-Velocity Turbine

By combining computational fluid dynamics (CFD) and surrogate model method (SMM), the relationship between turbine performance and airfoil shape and flow characteristics at low flow rate is revealed. In this paper, the flow velocity tidal energy airfoil model is designed based on the Kriging model, and the original airfoil with a relative thickness of 12% and a relative curvature of 2.5% is obtained. The parameter optimization is carried out by setting the 4th CST equations through the surrogate model; the maximum lift-drag ratio is the optimization goal, the optimization design variable is 10, the maximum number of iterations is 100, and the maximum number of sub-optimization iterations is 200. The results show that the hydrodynamic performance of the airfoil with thinner thickness and more curvature is better, the maximum thickness part is shifted forward by 4.58%, and the lift-drag ratio is improved by 4.03%. The flow field and the efficiency are more stable, which provides an engineering reference for the optimal design of hydraulic turbine airfoils under low flow velocity. It supplements the research on the performance of turbine blades in low velocity.

Experimental Study on the Hydrodynamic Performance of a Flexible Connected Double-Module Floating Structure

Abstract A flexibly connected double-module floating structure can be used as the primary component unit of a large multi-module floating structure, revealing some basic principles regarding the interaction of multiple modules and connectors to the same extent. This study investigated the hydrodynamic characteristics of a double-module floating structure with cable–fender connectors and connector loads through an experimental model test. Due to the weak coupling strength of the connector, the motion response of each unit of the double-module floating structure mainly responds to the wave frequency, and the resonance frequency of the floating unit is close to that of the single floating module. The magnitude of the connector load is related to the relative pitch motion of the two modules. The increased stiffness of the connector can limit the pitch motion of the modules but can also lead to higher forces on the connector. The load acting on the fender in the cable–fender connector is strongly nonlinear, and the shear force on the fender is large; this may be the control load causing fender damage.

Hydrodynamic performance optimization and adjustment prediction of a novel deep-sea towed body with adjustable hydrofoils

The towing stability of the towed body has an important impact on the data collection quality of the mounted sensors. In this paper, a novel deep-sea towed body control technology based on adjustable hydrofoils is proposed, and a hydrodynamic performance optimization and adjustment prediction strategy is established. Through computational fluid dynamics (CFD) simulation, the effectiveness of the adjustable hydrofoils in improving the towing stability of the towed body is verified, and the hydrodynamic mechanism of the adjustable hydrofoils is analyzed. The influence weight and influence law of the hydrofoil structural parameters on adjusted variables are determined by sensitivity analysis and main effect analysis, and the hydrodynamic performance optimization of the adjustable hydrofoil is completed based on the fast elitist Non-dominated Sorting Genetic Algorithm III (NSGA-III). A bidirectional Gaussian Process (GP) prediction model with respect to the angle of attack of hydrofoils and adjusted variables is established. The prediction model shows high prediction accuracy and strong generalizability, with the prediction error within 4%. The effectiveness of the novel towed body control technology is verified through sea trials. This paper provides reference and guidance for the development and engineering application of the towed body control technology.

Hydrodynamic performance and wake study of an UUV sailing near the free surface

In this study, the SUBOFF UUV is numerically modelled in order to investigate the hydrodynamic features and effects of submerged navigation near the free surface. At various speeds and depths below the surface, the hydrodynamic behaviors of the SUBOFF UUV are examined. From the CFD results, we can deduce that submergence depth significantly affects total resistance of SUBOFF navigation nearby free surface. Because the Kelvin wake of SUBOFF creates wave-making resistance when approaching the open surface head-on, the fraction of pressure difference resistance becomes dramatically with an increase in Fr. The principle of superposition of the divergent wave system and the transverse wave system gradually reveals the divergent wave system as Fr grows larger. The wave making energy is greater, and the UUV needs more power to overcome the wave making resistance.

Design Process and Advanced Manufacturing of an Aquatic Surface Vehicle Hull for the Integration of a Hydrogen Power Plant Propulsion System

This article presents the design and manufacturing of a hydrogen-powered unmanned aquatic surface vehicle (USV) hull. The design process comprised three stages: (1) defining the requirements for a preliminary geometry, (2) verifying the hydrodynamic hull performance using computational fluid dynamics (CFD) simulations, and (3) experimentally validating the hydrodynamic hull performance and CFD analysis results through experimental fluid dynamics in a calm water towing tank. The manufacturing process utilized additive manufacturing technologies, such as fused granular fabrication and selective laser sintering, to produce the hull and other components, including the propeller and the rudder; thermoplastic materials with carbon fiber reinforcement were employed. The experimental results demonstrate that the optimized trimaran hull exhibited low hydrodynamic resistance (7.5 N), high stability, and a smooth flow around the hull (up to 2 m/s). The design and manufacturing of the USV hull met expectations from both hydrodynamic and structural perspectives, and future work was outlined to integrate a power plant, navigation system, and scientific equipment.

Investigation of hydrodynamic performance in a staggered multistage internal airlift loop reactor

The multistage internal airlift loop reactor (MIALR) has shown promising application prospects in gas–liquid–solid reaction systems. However, traditional MIALRs have a global circulation with strong interstage liquid-phase exchange. This paper proposes a staggered multistage internal airlift loop reactor (SMIALR) that incorporates special guide elements to create a staggered flow. Both experiments and computational fluid dynamics-population balance model simulations were conducted to investigate the hydrodynamic performances of MIALR and SMIALR. The results demonstrate that SMIALR exhibits a local circulation at each stage. Bubbles have a longer residence time in SMIALR, resulting in a 28.35%–55.54% increase in gas holdup and a 7.27%–13.69% increase in volumetric mass transfer coefficient. The gas–liquid mass transfer coefficient of SMIALR was improved by increasing the gas–liquid interfacial area. Additionally, the radial distribution of solids was found to be more uniform. This study offers insights for optimizing MIALR and provides a theoretical foundation for the design and scale-up of SMIALR.

Realizing the multifunctional microfluidic flow manipulation based on hydrodynamic metamaterials

From their initial application to the fields of chemistry and biology, microfluidic chips used as micro total analysis systems have developed into new technologies to satisfy the requirements of various societal industries. Microchannels are essential components of microfluidic chips; they play a vital role in connecting the inlet and outlet as well as determining the flow distribution and reagent mixing. Microfluidic research has always been devoted to minimizing energy dissipation, fluid resistance, and pressure drop to realize energy-efficient microfluidic chips. This study proposes a new theory for manipulating the flow in microchannels based on hydrodynamic metamaterials according to the spatial transformation theory. In particular, hydrodynamic metamaterials are specifically designed to construct flow shifters, flow splitters, and flow combiners, and theoretical and numerical simulations are performed to assess their hydrodynamic performance. The systematic design of hydrodynamic metamaterial devices proposed in this work establishes a theoretical framework to achieve a steady flow state without inducing unstable flow disturbances in complex-shape microchannels.

Hydrodynamic performance of a periodic array of flap-type devices installed on the stepped bottom topography in the front of the coastal wall

Harnessing wave energy stands as a promising method to mitigate carbon dioxide emissions and address the global energy shortage. The strategic placement of wave energy converters (WECs) in offshore areas is contingent upon the distinctive features of the coastline and the topographical layout. This study is dedicated to scrutinizing the hydrodynamic characteristics and the wave energy absorption of a periodic array of flap-type WECs situated on a stepped bottom topography, strategically positioned in front of a straight coast. The coastline is modeled as a fully reflecting vertical wall. To analyze the oblique wave interaction with this system, we have developed a semi-analytical solution grounded in the linear potential flow theory. We evaluated key performance metrics, including hydrodynamic efficiency, reflection coefficient, wave excitation torque, added inertia torque, and radiation damping. Case studies were conducted to assess the impacts of varying parameters, such as the distance between the flap and the wall, the wave depth above the step, the incident angle, and the step length on the hydrodynamic performance of the current system. The results underscore the substantial influence of the distance between the flap and the coastal wall on wave power efficiency. The trigger condition's frequency downshift, indicative of the standing wave field between the flap and the coastal wall, is observed with a reduction in the wave depth above the step, in contrast to scenarios without the step. In addition, wave resonance above the stepped bottom topography amplifies wave power extraction, albeit with the caveat of a diminished hydrodynamic efficiency due to the presence of Rayleigh–Bloch waves.

Hydrodynamic performance study of shore-based oscillating water column wave energy conversion device

Hydrodynamic performance study of shore-based oscillating water column wave energy conversion device

Micro Lubrication and Heat Transfer in Wedge-Shaped Channel Slider with Convex Surface Texture Based on Lattice Boltzmann Method

Hydrodynamic lubrication is widely used between two relatively moving objects, and the effect of fluid flow state and temperature distribution on lubrication performance in wedge-shaped gaps is a popular topic to study. In this paper, the incompressible double-distribution lattice Boltzmann method (LBM) is applied to study the effect of micro convex surface texture on micro lubrication and heat transfer in wedge-shaped channels. By comparing this model with the analytical solution of an infinitely wide wedge slider, the maximum pressure calculated by LBM is 0.1081 MPa, and the maximum pressure calculated by the Reynolds equation is 0.1079 MPa. The error of the maximum pressure is 1.11%, and the Reynolds equation result is slightly smaller. The reason is that the Reynolds equation ignores the influence of fluid inertia force on oil film pressure. The results indicate that the application of LBM can be used to study lubrication problems. Compared with the Reynolds equation, LBM can calculate the velocity field and pressure field in the film thickness direction, and can also observe precise flow field details such as vortices. Three micro convex texture shapes were established to study the effects of different convex textures on micro lubrication and oil film temperature distribution, and the velocity distribution, temperature distribution and oil film pressure along the oil film thickness direction were given. Under the same conditions, comparing the oil film pressure with and without surface texture, the results show that the maximum oil film pressure with surface texture 3 is increased by about 4.34% compared with that without surface texture. The slightly convex texture can increase the hydrodynamic lubrication effect and obtain greater load-bearing capacity, helping to reduce the possibility of contact friction. The results show that the convex surface texture can improve the hydrodynamic lubrication performance, increase the load carrying capacity and reduce the possibility of contact friction, and the convex surface texture can influence the temperature distribution of the oil film. At 3.6 mm in the slider length direction and 7.5 μm in the oil film thickness direction, the temperature of surface texture 1 is 402.64 K, the temperature of surface texture 2 is 403.31 K, and the temperature of surface texture 3 is 403.99 K. The presence of vortices is captured at a high convergence ratio.