Circulating Water Channel Research Articles

Scale-Model Experiments for the Surface Wave Influence on a Submerged Floating Ocean-Current Turbine

In order to harness the kinetic energy of marine currents, we propose a novel ocean-current turbine with a horizontal axis. The turbine can be moored to the seabed and function similarly to kites in a water flow. To operate such turbines in a marine current, the resulting rotor torque needs to be canceled. Therefore, the proposed turbine is designed with a float at its top and a counterweight at its bottom. Thus far, we have verified the turbine stability and blade performance through towing experiments. As the next step, we constructed a scale-model turbine to confirm the mooring system. This experiment was performed at a circulating water channel with wave-making facilities. The influence of waves on the floating body was also investigated. In this paper, we report the behavior of the scale-model turbine moored to the tank bottom and discuss the influence of surface waves.

Ship–bank interaction of a VLCC ship model and related course-keeping control

ABSTRACTTo assess the influence of ship-bank interactions on the course keeping ability of ships, Planar Motion Mechanism (PMM) tests on a scale model of the KVLCC2 tanker were conducted in a circulating water channel (CWC) at different ship-bank distances and speeds. To characterize the asymmetric hydrodynamic features, the asymmetric hydrodynamic derivatives are defined and are measured by the straight towing test with off-centerline displacements. The change in the linear hydrodynamic derivatives due to ship-bank interactions is discussed. The state-space equations are derived from the linear equations of maneuvering motion, which include the asymmetric hydrodynamic derivatives. The Linear Quadratic Regulator (LQR) is adopted to provide the rudder angle and the variation in forward speed during the course keeping process. The simulation results with varying ship-bank separations show that the LQR is more suitable than the classical proportional–integral–derivative (PID) controller for the course keeping of the KVLCC2 in the scenario discussed.

Experimental study on inertial hydrodynamic behaviors of a complex remotely operated vehicle

This paper presents an experimental study on inertial hydrodynamic behaviors of an open-frame remotely operated vehicle (ROV) that has a complex open-frame hull but a large capacity to hold more instruments on board than those of other ROVs. A 1:4 scaled model was tested by a vertical planar motion mechanism in a circulating water channel of Harbin Engineering University. The inertial coefficients, which can be used for the simulation of motions and therefore for the maneuverability of the ROV, were calculated. Particular attention was paid to discuss the properties of the cross-inertial coefficients, which are related to the inertial forces/moments induced by the motion in other directions.

The Design and Evaluation of Vertical Flow Circulating Water Channel for Flow Visualization Considering the Easiness and Safety of Experiment in Laboratory

The Design and Evaluation of Vertical Flow Circulating Water Channel for Flow Visualization Considering the Easiness and Safety of Experiment in Laboratory

Numerical simulation of PMM tests for a ship in close proximity to sidewall and maneuvering stability analysis

As the maneuverability of a ship navigating close to a bank is influenced by the sidewall, the assessment of ship maneuvering stability is important. The hydrodynamic derivatives measured by the planar motion mechanism (PMM) test provide a way to predict the change of ship maneuverability. This paper presents a numerical simulation of PMM model tests with variant distances to a vertical bank by using unsteady RANS equations. A hybrid dynamic mesh technique is developed to realize the mesh configuration and remeshing of dynamic PMM tests when the ship is close to the bank. The proposed method is validated by comparing numerical results with results of PMM tests in a circulating water channel. The first-order hydrodynamic derivatives of the ship are analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure and the variations of hydrodynamic derivatives with the ship-sidewall distance are given. The straight line stability and directional stability are also discussed and stable or unstable zone of proportional-derivative (PD) controller parameters for directional stability is shown, which can be a reference for course keeping operation when sailing near a bank.

Experimental and numerical characterization of a full-scale portable hydrokinetic turbine prototype for river applications

A preliminary hydrokinetic turbine prototype for river applications was built for experimental testing at the circulating water channel at the Naval Surface Warfare Center, Carderock Division. The prototype was designed based on numerous blade characterization and optimization analyses conducted using computational fluid dynamics (CFD) simulations. Testing was conducted for channel flow speeds ranging from 1.0 m/s to 1.7 m/s. At each tested flow speed, the generator loading was manually adjusted to produce a performance curve based off the power output from the prototype unit. In addition to manual generator loading, a solar charging unit was used to simulate turbine operation while adjoined to the ground renewable energy system (GREENS). CFD predictions were produced for the prototype using the k-ω SST turbulence model for the purpose of validation. A peak power coefficient of 0.37 was measured at a tip speed ratio of 2.50 during manual generator loading. Relative error between numerical predictions and experimental results was less than 3.0% when generator, transmission, gearbox, and other losses of selected components were applied to the numerical predictions. The solar charging converter improved prototype operation by conditioning the power output, indicating that the prototype could successfully be integrated with GREENS for portable applications.

Experimental studies toward the characterization of Inmetro's circulating water channel

Circulating water channels are facilities which can be used for conducting environmental, metrological and engineering studies. The Brazilian National Institute of Metrology-INMETRO has a water channel of innovative design, and the present work deals with the prior experimental investigation of its hydrodynamics performance. By using the optical technique PIV - Particle Image Velocimetry, under certain conditions, the velocity profile behavior in a region inside the channel was analyzed in order to evaluate the scope of applicability of such bench.

An experimental study of a circular cylinder's two-degree-of-freedom motion induced by vortex

This paper presents results of an experimental investigation of vortex-induced vibration (VIV) of a flexibly mounted and rigid cylinder with two-degrees-of-freedom with respect to varying ratio of in-line natural frequency to cross-flow natural frequency, f∗, at a fixed low mass ratio. Combined in-line and cross-flow motion was observed in a sub-critical Reynolds number range. Three-dimensional displacement meter and tension meter were used to measure dynamic responses of the model. To validate the results and the experiment system, x and y response amplitudes and ratio of oscillation frequency to cross-flow natural frequency were compared with other experimental results. It has been found that the higher harmonics, such as third and more vibration components, can occur on a certain part of steel catenary riser under a condition of dual resonance mode. In the present work, however, due to the limitation of a size of circulating water channel, the whole test of a whole configuration of the riser at an adequate scale for VIV phenomenon was not able to be conducted. Instead, we have modeled a rigid cylinder and assumed that the cylinder is a part of steel catenary riser where the higher harmonic motions could occur. Through the experiment, we have found that even though the cylinder was assumed to be rigid, the occurrence of the higher harmonic motions was observed in a small reduced velocity (Vr) range, where the influence of the in-line response is relatively large. The transition of the vortex shedding mode from one to another was examined by using time history of x and y directional displacement over all experimental cases. We also observed the influence of in-line restoring force power spectral density with f∗.

A Study on the Development of Low Speed Twin-Hull Form for Seabed Organic Sediment Collection

In this study, conceptual design of the fore-body hull form of catamaran type dredging vessel was performed that can effectively remove the contaminated sediments in coastal seabed. The hull form was simpled for the easy hull construction and the resistance performance was investigated to find out the effect of hull form parameters between variation of waterline and angle of entrance, etc. The relation between resistance performance and characteristics of free surface flows according to variation of bow forms was investigated by model testing in the circulating water channel and using Ansys CFX. The improvement of ship resistance performance to the wave resistance decrease due to improved wave pattern has been verified according to move the stem and the volume of the shoulder to the fore part of the vessel.

가변형 이중 날개를 갖는 수직축 수류터빈에 대한 연구

In this paper, we propose a vertical axis water turbine with dual blades. A parametric study was conducted using numerical analyses. First, a two-dimensional finite-volume analysis with a commercial code was used to find the pitch angle of the main blade under different tip speed ratio conditions. Second, we developed a potential-based panel method to find the best configuration of the inner blades. Experimental tests were conducted at the circulating water channel of Chungnam National University. Various configurations of the dual blades were considered, and their performances were comparatively investigated. The results showed that the turbine with movable dual blades produces a constant torque and tip speed ratio at various flow rates.

Shape Design of the Duct for Tidal Converters Using Both Numerical and Experimental Approaches (pre-2015)

Recently, focus has been placed on ocean energy resources because environmental concerns regarding the exploitation of hydrocarbons are increasing. Among the various ocean energy sources, tidal current power (TCP) is recognized as the most promising energy source in terms of predictability and reliability. The enormous energy potential in TCP fields has been exploited by installing TCP systems. The flow velocity is the most important factor for power estimation of a tidal current power system. The kinetic energy of the flow is proportional to the cube of the flow’s velocity, and velocity is a critical variable in the performance of the system. Since the duct can accelerate the flow velocity, its use could expand the applicable areas of tidal devices to relatively low velocity sites. The inclined angle of the duct and the shapes of inlet and outlet affect the acceleration rates of the flow inside the duct. In addition, the volume of the duct can affect the flow velocity amplification performance. To investigate the effects of parameters that increase the flow velocity, a series of simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS-CFX. Experimental investigations were conducted using a circulation water channel (CWC).

Experimental investigation of the near wake of a horizontal axis tidal current turbine

A scaled-model of an HATCT (Horizontal Axis Tidal Current Turbine) was tested in the CNR-INSEAN Circulating Water Channel. Two different analyses were performed during the experiments: preliminary investigation of the performances of the turbine in different working conditions and LDV (Laser Doppler Velocimetry) measurements in the near wake. Velocity measurements are performed in phase locking to the rotor, in order to resolve the blade wake structure at different working regimes. Indeed, the knowledge of all three velocity components (tangential, axial, radial) allows to evaluate through energy balance concerns, the transfer of inflow kinetic energy into mechanical work of the rotor and into different energy contributions in the wake. The LDV analysis of the near wake also contributes to understand some of the most important fluid dynamics aspects related to the design of the rotor and to the different working conditions, and can be used as a preliminary study for understanding the wake evolution and the interaction between two or more turbines in a farm.

回流水槽における操縦流体力の計測精度について

In this paper it is reported the possibility of the maneuvering test of the model ship in Circulating Water Channel (CWC). The wall effect on the model ship with the drift angle in CWC is researched by using model test and Computational Fluid Dynamics (CFD) analysis. Then a condition/criterion is studied for drift angle of the model and the distance between ship model and the side wall of CWC. Hydrodynamic force acting on the turning hull is measured in Yawing test by Planar Motion Mechanism (PMM)．The frequency dependency is shown in the test data result from the setting condition (period and r’). To avoid the frequency dependency, reasonable period range is proposed. Oblique towing test and Yawing test are carried out with keeping the above criterion. The analyzed data agrees with the results by towing tank. Then the maneuvering test in CWC has enough accuracy for course stability criterion of the ship practically.

シーラカンス胸鰭の受動的撓みがその流体力学的性能に及ぼす影響

Open water characteristics are measured in a circulating water channel with four model pectoral fins with different bending stiffness of Coelacanth. Open efficiencies reach highest value in the range of Strouhal numbers between 0.2 and 0.4 and maximum value of open efficiency increases with reducing bending stiffenss.

어선원 복지공간 확보를 위한 5톤급 쌍동형 연안어선 선형개발에 관한 연구

This paper reports the hull form development and resistance performance of a 5-ton-class catamaran-type coastal fishing boat. The weight estimation and preliminary design were basically extracted from existing coastal fishing vessels. In addition, the resistance performance was investigated using a model test in a high-speed circulating water channel and was analyzed in comparison to an existing catamaran fishing vessel. As a result, the modified hull achieved an approximately 30% reduction in resistance compared to the previous hull. The stability or boarding sensitivity of the modified hull form was more stable or comfortable than the original hull form based on a trim and sinkage comparison between the two boats.

An improved wake description by higher order velocity statistical moments for single screw vessel

Unfavorable wake and separated flow from the hull might cause a dramatic decay of the propeller performance in single-screw propelled vessels such as tankers, bulk carriers and containers. For these types of vessels, special attention has to be paid to the design of the stern region, the occurrence of a good flow towards the propeller and rudder being necessary to minimize fuel consumption and avoid excessive vibratory shaft loads and risk for cavitation erosion. The present work deals with the analysis of the propeller inflow in a single-screw chemical tanker vessel affected by massive flow separation in the stern region. Detailed flow measurements by Laser Doppler Velocimetry (LDV) were performed in the propeller region at model scale, in the large Circulating Water Channel of CNR-INSEAN. These tests were undertaken with and without the propeller in order to investigate its effect on the inflow characteristics and the separation mechanisms. In this context, the study also concerned a phase locked analysis of the propeller perturbation at different distances upstream of the propulsor. The study shows the effectiveness of the 3rd order statistical moment (i.e., skewness) for describing the topology of the wake and accurately identifying the portion affected by the detached flow. The skewness coefficient also suggests that a better physical representation of the propeller inflow is provided by the mode value of the velocity, which is the maximum of the probability density function, rather than the mean velocity.

Optimal design of a thin-wall diffuser for performance improvement of a tidal energy system for an AUV

The study presents an energy performance improvement measure for an Autonomous Underwater Vehicle (AUV) carrying oceanographic equipment for collecting scientific data from the ocean. The required electric energy for the on-board equipment is harvested from tidal energy by using twin horizontal axis turbines which are integrated with thin-wall diffusers to enhance their energy capturing performance. The main focus and hence objective of the paper is the optimal design of the diffusers by using Reynolds Average Navier–Stokes Equations (RANSE) based Computational Fluid Dynamics (CFD) method and the validation of the design using physical model tests.A goal-driven optimisation procedure is used to achieve a higher power coefficient for the turbine while keeping the size and the drag of the diffuser as practically minimum as possible. Two main parameters of the optimisation are selected, the outlet diameter and the expansion section length of the diffusers, which are optimised for the highest flow acceleration ratio at the diffuser throat and for the minimum drag of the integrated diffuser and turbine system which is called as “Diffuser Augmented Tidal Turbine” (DATT) system.The numerical optimisation is validated by two sets of physical model tests conducted with a single turbine without diffuser and the same turbine integrated with the diffuser (DATT) in a cavitation tunnel and a circulating water channel. These tests demonstrated a performance enhancement for the turbine with the optimal diffuser by almost doubling the power coefficient of the turbine without the diffuser. However, the performance enhancement was dependent upon the pitch angle of the turbine.

Evaluation of cavitation erosion of a propeller blade surface made of composite materials

Cavitation erosion strongly impacts the efficiency and strength of marine propellers. This is more important for propellers made from different types of composite materials. Thus, an investigation of cavitation erosion on the blade surface of composite ship propellers is necessary. A small three-blade propeller was made from fiberglass combined with epoxy, polyester and gelcoat resin. This propeller was tested in a circulating water channel and revolution speed and depth were determined by conditions of cavitation number. Cavitation erosion was observed and evaluated by images, weight loss and cavitation area. The results indicated that the cavitation erosion occurred at regions 0.4 R (Radius) and 0.7 R from the center, and cavitation also occurred randomly on pressure or suction surfaces and leading or trailing edges. Most damaged regions propagated along the circumferential direction of the propeller. Among the blade materials, the Ge-GF blade had the best property. This material had the smallest cavitation area and the most stable cavitation area rate. The Po-GF blade had the worst property with strong progression of the cavitation area, and the Ep-GF blade was of medium quality with a small reduction of the damage area rate. Besides, the depth of the damaged area of the Ge-GF blade was also lower than that of the Ep-GF and Po-GF blade.

Research on Disparity Map Generation Method of Underwater Target Based on the Improved SIFT Algorithm

In order to obtain the depth information of the underwater target, it’s necessary to generate the disparity map based on binocular vision stereo matching. In the circulation water channel, the stereo matching experiments with underwater target were carried out by using the BM algorithm, SGBM algorithms and SIFT algorithm respectively. Then the characteristics of the disparity maps were analyzed for the three kinds of stereo matching algorithms. Compared with the BM algorithm and SGBM algorithms, the SIFT algorithm has been proved to be more suitable for underwater stereo matching. In order to obtain more feature points of underwater image, it is necessary to improved SIFT algorithm parameter. Underwater image matching experiments were made to determine the principal curvature coefficientγ. The results illustrated that the improvedγis better than the original value for underwater disparity map generation.

전남 진도지역 낭장망의 유속에 따른 망구형상 변화에 관한 모형실험

A model net experiment of the gape net for anchovy in Jindo, Jeollanam-do was carried out to investigate the net shape and hydrodynamic resistance using circulating water channel. The model net was made 1/33 down scale by Tauti's similarity method and the range of experimental current speed was from 0.5 knot to 3.5 knot (increasing 0.5 knot interval). The net mouth height in 0.5 knot of the minimum experiment current speed was shown 26.0 cm (full-scale conversion value 8.58 m). The net mouth height and mouth area in 1.5 knot of the same current speed with a gape net fishing ground were shown 20.0 cm (full-scale conversion value : 6.60 m) and about 507.9 cm 2 (full-scale conversion value : 55.31 m 2 ). The net mouth height and area were decreased with increase the experimental current speed. The hydrodynamic resistance of the model net in 1.5 knot current speed was shown 1.11 kgf and the value of full-scale conversion by Tauti's method was shown 3.996 ton.