Experimental Investigation and Numerical Modeling of Hydrodynamic Characteristics of a Heaving Sea Cage

2009 ◽  
Author(s):  
Sho Ito ◽  
Tomoyuki Tsunoda ◽  
Hiroshi Itakura ◽  
Weiguang Bao ◽  
Daisuke Kitazawa ◽  
...  
Keyword(s):  
Wave Amplitude ◽  
Forced Oscillation ◽  
Oscillation Amplitude ◽  
Exciting Force ◽  
Hydrodynamic Characteristics ◽  
Offshore Area ◽  
Aquaculture System ◽  
Cultured Fish ◽  
Offshore Aquaculture ◽  
Sea Cage

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. In the present study, therefore, we investigated hydrodynamic property of a heaving sea cage as the first step. Forced oscillation tests and wave exciting force tests have been carried out, and numerical modeling have also been made to estimate hydrodynamic characteristics theoretically and to estimate the drag and mass coefficients. Results of the forced oscillation tests show that the added mass and damping coefficient of sea cage models depend on forced oscillation amplitude. This dependence may be mainly attributed to the deformation of net, and we successfully reduce the dependence on the forced oscillation amplitude in the result of reanalysis which takes into account the deformation of net. Results of measured wave exciting force show that wave exciting forces are not linear in wave amplitude. This may be due to the viscous drag effects as well as the deformation of net. On the other hand, we calculated the flow around a sea cage. This is based on velocity potential and supplemented the effect of viscosity by equivalent linearization. In the boundary condition on the sea cage surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface. This permeate coefficient is a function of wave amplitude, wave period and porosity of the net. In the future works, deformation of net should be also taken into account in this calculation.

Experimental Investigation and Numerical Modeling of Hydrodynamic Force Characteristics of a Heaving Net

2010 ◽  
Author(s):  
Sho Ito ◽  
Takeshi Kinoshita ◽  
Daisuke Kitazawa ◽  
Weiguang Bao ◽  
Hiroshi Itakura ◽  
...  
Keyword(s):  
Hydrodynamic Force ◽  
Fundamental Problem ◽  
Exciting Force ◽  
Water Current ◽  
Plate Model ◽  
Offshore Area ◽  
Aquaculture System ◽  
Cultured Fish ◽  
Offshore Aquaculture ◽  
Sea Cage

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore sea cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. We investigated the hydrodynamic force properties of a heaving sea cage in the previous work and its results proved that the deformation of net much affects on sea cage’s motion characteristics. To study the most fundamental problem, we investigated the hydrodynamic force properties of an undeformable net in the present study. Nine net models are arranged. These models have square-shaped frame and its inner dimensions are 216 × 216 mm. In these net models, three different twine diameters and three different twine intervals are arranged. The porosities of these models are in the range of 0.39 to 0.91. In addition, an impermeable plate model is also arranged. Forced heaving tests and wave exciting force tests are carried out on each net and plate model. Added mass and damping coefficients, as obtained by forced heaving tests, differ according to porosity of net and oscillation frequency and amplitude. Wave exciting forces, as obtained by wave exciting force tests, also differ according to porosity of net and wave slope and the forces increase with wave amplitude in higher order than one. To compare with experimental results, we theoretically calculate the hydrodynamic forces from a linearized potential flow approach supplementing the effect of porosity. In the boundary condition on the net surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface.

Hydrodynamic Forces and Motion Responses of Feeding Platform and Sea Cages

2008 ◽  
Author(s):  
Sho Ito ◽  
Takeshi Kinoshita ◽  
Daisuke Kitazawa ◽  
Tomoyuki Tsunoda ◽  
Weiguang Bao ◽  
...  
Keyword(s):  
Forced Oscillation ◽  
Damping Coefficient ◽  
Initial Tension ◽  
Offshore Area ◽  
Aquaculture System ◽  
Cultured Fish ◽  
The Difference ◽  
Offshore Aquaculture ◽  
Sea Cage ◽  
The Relationship

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the harsh natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are submerged every time around 10m below the sea surface to escape from high waves and strong currents. However, the safety of the sea cage against the incident wave has not been examined, while that against the water current has been analyzed by tank model test and numerical simulation. In the present study, therefore, the hydrodynamic forces on the submerged sea cage from the incident wave were investigated by the tank model test, and the motion of the submerged sea cage was observed. As a result of the forced oscillation test, the numerical values of the added mass and damping coefficient of the sea cage scatter according to the wave amplitude for the same frequency of the forced oscillation. The difference in the added mass may be attributed to the effects of ladder and the bending of the net. The current analysis is focused on modeling of the bending of the net. Then the difference was also found in the damping coefficient at the same frequency of the forced oscillation. The damping coefficient based on viscosity was separated by the equivalent linearization using the equation of Morison’s drag force. As a result, the scattering of the damping coefficient was reduced, adjusting the drag coefficient. It is a future study to examine the relationship between each mode of the motion of the sea cage and the adjusted drag coefficient. As for the experiment of the mooring system, the larger mooring force worked on the rope between the cushion float and anchor than that between the cushion float and frame rope of the sea cage. The motion of the submerged sea cage was suppressed so that the mooring force between the cushion float and frame rope was reduced. However, the mooring force depends on the initial tension of the mooring rope, therefore the relationship between the initial tension and the mooring force should be examined as future studies.

Experimental Investigation and Numerical Modeling of Hydrodynamic Force Characteristics and Deformation of an Elastic Net

2011 ◽  
Author(s):  
Sho Ito ◽  
Takeshi Kinoshita ◽  
Daisuke Kitazawa ◽  
Weiguang Bao ◽  
Hiroshi Itakura
Keyword(s):  
Hydrodynamic Force ◽  
Elastic Net ◽  
Water Current ◽  
Normal Velocity ◽  
Offshore Area ◽  
Aquaculture System ◽  
Cultured Fish ◽  
Offshore Aquaculture ◽  
Sea Cage ◽  
Force Characteristics

With the increasing worldwide demand of seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. An offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than a coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore sea cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. We investigated the hydrodynamic force properties of a heaving sea cage in the previous work and its results proved that the deformation of net much affects on sea cage’s motion characteristics. To study the most fundamental problem, we investigated the hydrodynamic force characteristics of a rigid net as a first step and explained that these relate to its porosity and wave conditions. As a second step, in the present study, we investigate hydrodynamic force properties of an elastic net. Six square-shaped textile net models which are made of elastic strings and metallic frame are arranged. Three different porosities (0.53, 0.64 and 0.74) and two different net’s tension (10 and 50 N/m) on each porosity are employed; that is, we arranged 6 elastic net models. Forced heaving tests and diffraction tests are carried out. In addition to measuring heave force, the deformation of net surface is measured by a video image analysis system. To compare with the experimental results, we calculate hydrodynamic forces and the deformation of net using a boundary element method. The boundary condition on elastic net is that the normal velocity to the surface is not zero but proportional to the pressure difference. The deformation is also taken into consideration.

Concept of an Offshore Aquaculture System With an Automated Feeding Platform

2008 ◽  
Author(s):  
Tomoyuki Tsunoda ◽  
Daisuke Kitazawa ◽  
Takeshi Kinoshita ◽  
Sho Ito ◽  
Weiguang Bao ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Model Test ◽  
Incident Wave ◽  
Natural Condition ◽  
Sea Surface ◽  
Tank Model ◽  
Offshore Area ◽  
Aquaculture System ◽  
Cultured Fish ◽  
Offshore Aquaculture

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The present study proposed the concept of an offshore aquaculture system with an automated feeding platform. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the cultured fish is starved during a few days before and after typhoon attack since the feeding ship is not able to approach the offshore sea cages, which is submerged every time around 10m below the sea surface to escape from high waves and strong currents. The automated feeding system should be therefore developed to enable the cultured fish to grow faster under the severe natural condition. The proposed system consists of several submerged fish cages and a feeding platform, which includes fuel tanks, feed storage silos, and an automated feeding machine. The feeding platform was designed by numerical analysis and tank model test in order to suppress its motion as small as possible. The motion of the feeding platform was first predicted by numerical analysis. The unmoved point was formed at each period of the incident wave. It moves upward as the period of the incident wave increases. Consequently, the point at 8m below the sea surface (3m above the bottom of the feeding platform) is the best one to attach the feeding hose. As a result of tank model test, pitch and heave motions of the feeding platform were dominant in the waves with short (1.5 seconds) and long (3.1 seconds) periods, respectively. An unmoved point was observed on the surface of the feeding platform as predicted by the numerical model, while the top of the feeding platform moved more largely. The unmoved point for the feeding hose was specified at above the bottom of the feeding platform.

scholarly journals Damping forced oscillations in power system via interline power flow controller with additional repetitive control

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Shirui Feng ◽  
Xi Wu ◽  
Zhenquan Wang ◽  
Tao Niu ◽  
Qiong Chen
Keyword(s):  
Power Flow ◽  
Forced Oscillation ◽  
Control Method ◽  
Damping Ratio ◽  
Repetitive Control ◽  
Oscillation Amplitude ◽  
Reference Value ◽  
Forced Oscillations ◽  
Flow Controller ◽  
Power Flow Controller

AbstractWith the continuous expansion of power systems and the application of power electronic equipment, forced oscillation has become one of the key problems in terms of system safety and stability. In this paper, an interline power flow controller (IPFC) is used as a power suppression carrier and its mechanism is analyzed using the linearized state-space method to improve the system damping ratio. It is shown that although the IPFC can suppress forced oscillation with well-designed parameters, its capability of improving the system damping ratio is limited. Thus, combined with the repetitive control method, an additional repetitive controller (ARC) is proposed to further dampen the forced power oscillation. The ARC control scheme is characterized by outstanding tracking performance to a system steady reference value, and the main IPFC controller with the ARC can provide higher damping, and further reduce the amplitude of oscillations to zero compared with a supplementary damping controller (SDC). Simulation results show that the IPFC with an ARC can not only greatly reduce the oscillation amplitude, but also actively output the compensation power according to the reference value of the ARC tracking system.

Forced oscillation experiments

1991 ◽  
Vol 334 (1634) ◽  
pp. 199-211
Keyword(s):  
Numerical Methods ◽  
Water Depth ◽  
Forced Oscillation ◽  
Vertical Plane ◽  
Forced Oscillations ◽  
Hydrodynamic Characteristics ◽  
Scale Models ◽  
Ship Speed

Forced oscillation experiments with scale models are carried out to determine hydrodynamic characteristics of ships, with respect to motions in waves or steering and manoeuvring qualities. Depending on the considered motion components, in a horizontal or vertical plane, various methods are used to induce forced oscillations which are discussed briefly. Some results of forced oscillation experiments are presented as examples of this technique and compared with calculations based on numerical methods. The comparisons include, among others, the effects of ship speed and restricted water depth.

Study on the Hydrodynamic Characteristics for Heave Plate Structure of Truss Spar

2010 ◽  
Author(s):  
Wenjun Shen ◽  
Yougang Tang ◽  
Liqin Liu
Keyword(s):  
Numerical Simulations ◽  
Forced Oscillation ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Hydrodynamic Coefficients ◽  
Plate Structure ◽  
Plate Spacing ◽  
Mesh Method ◽  
Truss Spar ◽  
Heave Plate

The hydrodynamic characteristics of heave plates are studied in this paper. Firstly, different motion amplitudes and plate spacing influencing hydrodynamic coefficients are considered. Secondly, heave plates with different thicknesses are calculated, the case of edges with inclined form for heave plate is also taken into account. Numerical simulations are made for the plate forced oscillation, employing the dynamic mesh method and UDF (User defined functions). The values of Cm and Cd for heave plate are calculated. It is found that, in a certain amplitude range, Cm increases with increasing of amplitudes, Cd decreases with increasing of amplitudes. The values of Cm and Cd increase with increasing of plate spacing. Furthermore with the same effective thickness, the hydrodynamic performance of heave plate with inclined form is improved greatly.

scholarly journals Experimental Study of Heat Convection From Stationary and Oscillating Circular Cylinder in Cross Flow

2000 ◽  
Vol 123 (1) ◽  
pp. 51-62 ◽  
Author(s):  
H. G. Park ◽  
Morteza Gharib
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Particle Image ◽  
Forced Oscillation ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Digital Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

An experimental study is made on the processes of heat transfer from the surface of a forced oscillating cylinder in a crossflow. A range of oscillation amplitude A/D=0.1,0.2, forced oscillation frequency 0<Stc<1, and Reynolds number (Re=550, 1100, 3500) is covered in water Pr=6. Besides the increase at the natural vortex shedding frequency, large increases in the heat transfer are found at certain superharmonics. By using Digital Particle Image Velocimetry/Thermometry (DPIV/T), the increase in the heat transfer rate is found to correlate inversely with the distance at which vortices roll-up behind the cylinder, i.e., the distance decreases when the heat transfer increases. The cause of the increase is found to be the removal of the stagnant and low heat convecting fluid at the base of the cylinder during the roll-up of the vortices.

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