• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.73-80
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• 2016

To reduce the mechanical energy loss and to get the high energy efficiency, an apparatus of wave power generation inducing a consistent one way rotating motion from the wave reciprocation motions was developed and the hydraulic experiments for the real electric power production were conducted and the results were discussed. In the experiments for the shape of the buoyant tank, the efficiency of the fixed 9 cm diameter type enduring the wave plate weight was 14.6% and this was the best result for all shapes. But although the free sliding type was expected to represent a high efficiency, the experiments did not show a good result as 8.5% efficiency. Therefore, the shape of buoyant tank was decided as the fixed 9 cm diameter type in the next all tests. In the experiments for the various incident waves, when the water depth was 90 cm, the average efficiencies were measured as 3.9% in the 2nd gear, 4.9% in the 3rd gear, 4.9% in the 4th gear, 12.0% in the 5th gear, 10.0% in the 6th gear, 3.1% in the 7th gear, and 3.0% in the 8th gear. Also, when the water depth was 80 cm, the average efficiency was shown as 15.0% with 5th gear condition. Therefore the high average efficiency as 13.5% was given with 80~90 cm water depth and the 5th gear in the model.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.3
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• pp.189-202
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• 2012

An Oscillating Water Column (OWC) wave generation system uses the air flow induced by the vertical motion of water column in the air chamber as a driving force of turbine. It is well known that OWC is one of the most efficient devices to harness wave power. This study estimated the air flow velocity from the time variation of the water level fluctuation in the air chamber under regular wave conditions using 3-dimensional numerical irregular wave tank (3D-NIT) model that can simulate the 3-dimensional irregular wave field. The applicability of the 3D-NIT model was validated by comparing numerically predicted air flow velocities with hydraulic experimental results. In addition, the characteristics of air flow frequency spectrum variation due to the incident frequency spectrum change, and the variations of frequency spectrum and wave reflection due to the existence of converter inside the air chamber were discussed. It is found that the phase difference exists in between the air flow velocity and the water level fluctuation inside the air chamber, and the peak frequency of the spectrum in water level fluctuation is amplified by the resonance in the air chamber.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.3
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• pp.200-213
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• 1993

A model experiment on a midwater rope trawl net which is used in the North Pacific to catch alaska pollack is carried out in the circulating tank to examine the basic efficiency of the net. The prototype is the net used by M/S Hanil(1, 179GT, 2, 700PS), a Korean trawler. The model net was made according to the Tauti's Similarity Law of Fishing Gear in 1/100 scale by considering the condition of the tank. To measure the basic efficiency of the standard model net, the vertical opening and width between some points marked on the net were measured, and the hydrodynamic resistance were determined. Then the constructive conditions of the net were varied as follows and the factors were measured again to compare the efficiency of those nets with that of the standard net(A-1 type) front weight multiplied 1.5 times: A-2 type. buoyancy and depressing force multiplied 1.7 times: A-3 type. front weight multiplied 1.5 times on A-3 type: A-4 type. depressors rigged at ground rope: B type. cod-end stuffed with cashmylon wad: C type. The results obtained can be summarized as follows: 1. The vertical opening at the center of head rope was steeply decreased with the flow velocity increasing and the vertical opening H(m) can be expressed in H=1.2v super(-1.2)(v : flow velocity in m/sec). The width of the net varied a little when the flow velocity was over 0.4m/sec, and the width of net mouth showed about 37% of the distance between the fore tips of net pendant. The shape of net mouth was almost a circle at 0.2m/sec and then steeply flatted elliptically with the flow velocity increasing and the area of mouth S(m super(2)) can be expressed in S=(1.65-2.3v)$\times$10 super(-2). The hydrodynamic resistance of the net increased almost linearly with the flow velocity increasing and the resistance R(kg) can be expressed in R=3.2$\times$d/l$\times$abv. where d/l denotes the mean of d(diameter of netting twine) and l(length of a leg in a mesh) from wing tip to the end of bag-net except cod-end on the side pannel, and a denotes the strectched circumference of the net at the fore end of a meshed part and b the stretched length of the whole net from wing tip to the end of cod-end. 2. In the condition-varied nets, the vertical opening of head rope showed some increase in every type net except the C type, and the increase showed the greatest in the B type by 30~54%, whereas it showed decrease in the C type by 5~10%. Variation of the area of net mouth showed almost the same tendency as the vertical opening and the increase showed the greatest in the B type by 20%, whereas it showed decrease in the C type by 12%. Hydrodynamic resistance showed some increase in every type compared with the standard net, and the rate of increase indicated 5~10% in the A-2, A-3 and A-4 type, 22% in the B type and 3% in the C type.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.71-80
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• 1992

The Seakeeping committee of Korea Towing Tank Conference executed the cooperative experimental study on deck wetting phenomena using S-175 contatiner model ships. Two members, Korea Research Institute of Ships and Ocean Engineering(KRISO) and Hyundai Maritime Research Institute(HMRI) participated in the study. This study was initiated by the ITTC(International Towing Tank Conference) Seakeeping Committee as the cooperative study of the 19th ITTC aiming at the establishement of the model test procedure on the deck wetting phenomena. Special emphasis was made on the determination of reliable record length for experimental measurement on rarely occurring events(such as deck wetness, slamming etc). Comparisons were made on both the test results and the test procedrues in this research. The measured frequencies of deck wetting show remarkable deviations between the runs. This fart implies that sufficiently long record length is required in the deck wetness measurement compared to the conventional ship motion tests. Careful considerations were made on the physical interpretation of the deck wetting phenomena, the correlation between the measured relative motion at stemhead and the measured deck wetness, and the estimation of deck wetting frequencies by Poisson process.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.255-265
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• 1991

In order to find the excavating performance of water-jet nozzle on the sand, the authors were carried out the excavating experiment with the model nozzles which were semi circular sectioned nozzles and rectangular nozzle in water tank. The results were as follows. 1) Excavating maximum depth and width on the sand by the water jet were straightly increased in proportion to the velocity of water jet and the section area of nozzle, and that, by the nozzle distance from the excavating point on the sand, the depth was decreased, while the width was increased straightly. 2) Rectangular nozzle which the thick of hole is 1mm, was a little bit better than the circular nozzle of the same sectioned area on the excavating performance. 3) Empirical equations between the velocity of water jet, the distance of nozzle, and the maximum excavating depth and width by angle of nozzle were expressed as linear, they were as follows on the 45$^{\circ}$ angle of the rectangular nozzle(1$\times$12mm); D=0.0093V sub(0)-0.23H+5.7. W=0.0147V sub(0)+1.06H+10.2. where, D is the maximum excavating depth(cm), W is the maximum excavation width(cm), V sub(0) is the velocity of water jet(cm/s); 926$\leq$V sub(0)$\leq$1504, H is the distance(cm) from nozzle tip to water-jetted point on the surface of sand.

• Journal of agriculture & life science
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• v.44 no.6
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• pp.171-182
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• 2010

Water demand and resource at a watershed scale were investigated to prepare for long-term water planning of the Namgang sub-basin. The quantity of water resource was defined as average annual runoff by a simple Tank model with three serial tanks, and water demand for public, industrial, agricultural and the other uses was determined using the per-unit method employed in the Water Vision 2020, the Ministry of Construction and Transportation. The results showed that total amount of water resources in the Namgang sub-basin was estimated as about $935,414{\times}10^{3}m^3/yr$ for a 10-year period from 2000 to 2009 and the water withdrawals in public, industrial, agricultural and other sector were derived as $105,493{\times}10^{3}m^3/yr$, $32,686{\times}10^{3}m^3/yr$, $243,194{\times}10^{3}m^3/yr$, and $81,615{\times}10^{3}\;m^3m^3/yr$, respectively. In addition, the Namgaram Inno-city project could increase the overall water demand by $17,156{\times}10^{3}\;mm^3/yr$ due to the population influx.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.620-631
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• 2022

This paper shows the numerical prediction of the change in oil outflow rate according to the orifice shape of a damaged ship by using the computational fluid dynamics (CFD) analysis method. It also provides discharge coefficients for various orifice shapes to be used in theoretical prediction approaches. The oil outflow from the model ship was analyzed using a multiphase flow method under the condition that the Froude and Reynolds number similitudes were satisfied. The present numerical results were verified by comparing them with the available experimental data. Along with the aspect ratio of the orifice and the wall thickness of the cargo tank, the effects of the orifice shapes defined by mathematical figures on the oil outflow were investigated. To consider more realistic situations, the investigation of the ef ect of the crushed iron plate around the damaged part was also included. The numerical results confirmed the change in oil outflow time for various shapes of the damaged part of the oil tank, and discharge coefficients that quantify the viscous effects of those orifice shapes were extracted. To verify the predicted discharge coefficients, they were applied to an oil spill estimation equation. As a result, a good agreement between the CFD and theoretical results was obtained.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.196-205
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• 2004

As far as an opening device of fishing gears is concerned, applications of a kite are under development around the world. The typical examples are found in the opening device of the stow net on anchor and the buoyancy material of the trawl. While the stow net on anchor has proved its capability for the past 20 years, the trawl has not been wildly used since it has been first introduced for the commercial use only without sufficient studies and thus has revealed many drawbacks. Therefore, the fundamental hydrodynamics of the kite itself need to ne studied further. Models of plate and canvas kite were deployed in the circulating water tank for the mechanical test. For this situation lift and drag tests were performed considering a change in the shape of objects, which resulted in a different aspect ratio of rectangle and trapezoid. The results obtained from the above approaches are summarized as follows, where aspect ratio, attack angle, lift coefficient and maximum lift coefficient are denoted as A, B, $C_L$ and $C_{Lmax}$ respectively : 1. Given the rectangular plate, $C_{Lmax}$ was produced as 1.46${\sim}$1.54 with A${\leq}$1 and 40$^{\circ}$${\leq}$B${\leq}$42$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 10.7${\sim}$1.11. Given the rectangular canvas, $C_{Lmax}$ was 1.75${\sim}$1.91 with A${\leq}$1 and 32$^{\circ}$${\leq}$B${\leq}$40$^{\circ}$. And when A${\geq}$1.5 and 18$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 1.24${\sim}$1.40. Given the trapezoid kite, $C_{Lmax}$ was produced as 1.65${\sim}$1.89 with A${\leq}$1.5 and 34$^{\circ}$${\leq}$B${\leq}$44$^{\circ}$. And when A=2 and B=14${\sim}$48, $C_L$ was around 1. Given the inverted trapezoid kite, $C_{Lmax}$ was 1.57${\sim}$1.74 with A${\leq}$1.5 and 24$^{\circ}$${\leq}$B${\leq}$36$^{\circ}$. And when A=2, $C_{Lmax}$ was 1.21 with B=18$^{\circ}$. 2. For a model with A=1/2, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Then there was a tendency of a gradual decrease in the value of $C_L$ and in particular, the rectangular kite showed a more rapid decrease. For a model with A=2/3, the tendency of $C_L$ was similar to the case of a model with A=1/2 but the tendency was a more rapid decrease than those of the previous models. For a model with A=1, and increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Soon after the tendency of $C_L$ decreased dramatically. For a model with A=1.5, the tendency of $C_L$ as a function of B was various. For a model with A=2, the tendency of $C_L$ as a function of B was almost the same in the rectangular and trapezoid model. There was no considerable change in the models with 20$^{\circ}$${\leq}$B${\leq}$50$^{\circ}$. 3. The tendency of kite model's $C_L$ in accordance with increase of B was increased rapidly than plate models until $C_L$ has reached the maximum. Then $C_L$ in the kite model was decreased dramatically but in the plate model was decreased gradually. The value of $C_{Lmax}$ in the kite model was higher than that of the plate model, and the kite model's attack angel at $C_{Lmax}$ was smaller than the plate model's. 4. In the relationship between aspect ratio and lift force, the attack angle which had the maximum lift coefficient was large at the small aspect ratio models, At the large aspect ratio models, the attack angle was small. 5. There was camber vertex in the position in which the fluid pressure was generated, and the rectangular & trapezoid canvas had larger value of camber vertex when the aspect ratio was high, while the inverted trapezoid canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the rectangular & trapezoid canvas had larger one when the attack angle was high.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1089-1096
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• 2015

A marine helicopter should remain sufficiently upright to permit safe evacuation of all personnel with a flotation system. And the rule requires that after ditching in water, the adequate flotation time will allow the occupants to leave the rotorcraft. To this end, stability test of the emergency flotation system for Korean marine helicopter was performed by using "Froude scaling method" in water tank. Test configuration and conditions were determined in consideration of the helicopter loading condition and related specifications. Test results meet the stability requirements at sea state code 4 and sea state code 2 with puncture conditions.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.11-20
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• 2000

The flow characteristics around the stern region of two VLCCs with the same forebody and slightly different afterbody are investigated along with propulsive performance of the ship. The local mean flow measurements and the resistance and self-propulsion tests are carried out in the towing tank for the two VLCC hull forms. The measured results clearly show the formation of bilge vortices and their effect on propulsive efficiency. The comparisons are made for the two VLCC hull forms and the relation between stern framelines and bilge vortex strength is explored. Experimental data can provide a good test case to validate the accuracy of numerical methods and turbulence model of CFD codes for ship flow calculation.