• Journal of Sensor Science and Technology
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• v.11 no.2
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• pp.67-76
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• 2002

We have presented a 2-dimensional fluxgate sensor with ferrite core, excitation, and pick-up coil. This fluxgate sensor system consists of a sensing element, driving circuits for excitation coil and signal processing for detecting second harmonic frequency component which is proportional to the DC magnetic to be measured. The sensor core is excited by a square waveform of voltage through the excitation coil of 80 turns. The second harmonic output of pick-up coil(x and y axis: 100 turns) is measured by FFT spectrum analyzer. This result is compared with output of PSD(phase sensitive detector) unit for detecting the second harmonic component. The measured maximum sensitivity is about 1580 V/T at driving frequency of 1.5 kHz and excitation current of 2 App. The nonlinearity of this system is measured about 2.3%(PSD) and about 1%(second harmonics of the pick-up). The angle error of the system is ${\pm}2$ %/FS.

• Journal of The Korean Society of Grassland and Forage Science
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• v.21 no.4
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• pp.225-232
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• 2001

In order to identify the optimum seeding rate of Jeju barnyard grass (Echinochloa crusgalli var. fiurnentacea(Roxb) Wight), 15, 20, 25, 30, 35 and 40 kilograms per a hectare were planted in April 16, 2000, respectively. The growth characterization, the yield and chemical composition were then investigated in June 28(1st cutting) and August 30(2nd cutting), 2000. According to increasing the seeding rate, plant height(155.5 to 162 cm), the yield of fresh forage(61 to 73 MT/ha), dry matter forage(11.9 to 16.9 MT/ha), crude protein(0.9 to 1.6 MT/ha), and TDN(6.1 to 9.7 MT/ha) were gradually increased until the seeding furrow, 35 kg/ha. In 40 kg/ha of seeding furrow, however, those results were decreased than that of the former seeding furrow. The contents of crude protein(7.4 to 10.4%), ether extract(3.3 to 5.2%), nitrogen free extract(46.4 to 47.8%), and TDN(52.1 to 60.4%) were also similar to those of the plant heights and the each yield excepted the seeding furrow, 40 kg/ha. Namely, the each results about the contents increased in 40kg/ha of seeding furrow. According to increasing the seeding rate, the stem diameter, number of leaves, number of withering leaves, and fresh weight were gradually decreased. The contents of crude fiber(30.3 to 27.5%) and crude ash(12.7 to 9.0%) were also decreased These results showed that the optimum seeding rate for the best of the feed production was the seeding furrow, 35 kg/ha.

• Korean Journal of Environmental Agriculture
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• v.18 no.3
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• pp.229-235
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• 1999

To identify the differences on plant growth and yield of two rice cultivars among direct water-seeding methods broadcasting on flooded paddy surface(BF), drilling on flooded paddy surface(DF), and puddled-soil drill seeding(PD) under markedly different weather condition between 1995 and 1996. The mean air temperature for duration from May to June, early growth stage of rice in 1995 was lower $1{\sim}3^{\circ}C$ than that in normal or 1996. In 1995 the respiratory consumption index during panicle formation stage and early ripening stage was higher than those of in 1996 or normal year. Number of seedling stand among the methods of direct seeding rice appeared slightly higher in order of BF>DF>PD. Properly in Nonganbyeo, the number of seedling stand was much low in 1995 compared with in 1996. The leaf area index and shoot dry weight at early growth stage of rice plant and culm length at mature in 1995 were larger in direct water seeding rice than those of machanical transplanting rice, but in 1996. Faster ripening speed and shorter ripening period of rice crop appeared in 1996 compared to in 1995. It was due to higher growing degree-days, sunshine hours and solar radiation during rice growing season in 1996. Dongjinbyeo rice showed higher yield than Nonganbyeo which had lower ripened grains especially in 1995.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.287-296
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• 2020

The wave-impact load on offshore structures can be divided into green-water and wave-slamming impact loads. These wave impact loads are known to have strong nonlinear characteristics. Although the wave impact loads are dealt with in the current classification rules in the shipping industry, their strong nonlinear characteristics are not considered in detail. Therefore, to investigate these characteristics, wave-impact loads induced by a breaking wave on a circular cylinder were analyzed. A model test was carried out to measure the wave-impact loads due to breaking waves in a two-dimensional (2D) wave tank. To generate a breaking wave, the focusing wave method was applied. A series of 2D tank tests under a horizontal wave impact was carried out to investigate the structural responses of the cylindrical structure, which were obtained from the measured model test data. According to the results, we proposed a structural damage-estimation procedure of an offshore tubular member due to a wave impact load. Furthermore, a recommended wave-impact load is suggested that considers the minimum required thickness of each member. From the experimental results, we found that the required minimum thickness is dependent on the impact pressure located in a three-dimensional space on the surface of a tubular member.

• Korean Journal of Plant Resources
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• v.22 no.1
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• pp.37-41
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• 2009

In order to find out the optimum compost powder, fertilizer level and planting method of high yielding F1 variety, Cheongpungyuchae, this experiment was conducted with 2 compositions of compost powder level and 3 different planting method at the experiment paddy field of Mokpo Experiment Station, National Institute of Crop Science, RDA. Cheongpungyuchae, rapeseed variety was grown under different compost powder level and planting method with the highest yielding variety. Yield components such as ear length, total branch, number of pods per ear and oil content were highest at the plots with compost powder 1,500 kg/10a at level and planting method, Oct.30, transplanting with 50 ${\times}$ 30 cm. Judging from the results reported above, at optimum compost powder level and planting method of rapeseed seemed to be 1,500 kg/10a compost powder and transplanting method with 50 cm row spacing and 30 cm planting space.

• Journal of the Korea Organic Resources Recycling Association
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• v.25 no.4
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• pp.23-29
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• 2017

This experiment was carried out to compare the productivity and feed value between standard cultivation and organic mixed expeller cake fertilizer cultivation to develop organic cultivation technology except from standard cultivation using chemical fertilizers in the field of forage production. This study was conducted in the rice field of Livestock Research Institute Jacheon-myeon, Gangin-gun Jellanam-do. Organic mixed expeller cake fertilizer consists of 4.0% nitrogen, 65% castor, 30% seeds and 5% fish meal. Sorghum-Sudangrass Hybrids(SX17) was sowed 40kg per hectare on May 25. Test group formation was consisted of a standard group and test treatment. The standard group(Con.) was fertilized chemical fertilizer according to the N-P-K kg/ha, 200-150-150 (basal 100kg, uptake 100kg). Test treatment was carried out organic fertilizer 100%(T1), organic fertilizer 150%(T2) and organic fertilizer 200%(T3) according to the nitrogen content of standard group(Con.). Plant height of harvest time depending on the treatment was that Con was 317cm, T1 was 252cm, T2 was 269cm and T3 was 293cm. Dry matter yield was that Con was 11,386kg/ha, T1 was 6,015kg/ha, T2 was 6,799kg/ha, T3 was 7,627kg/ha. In the test treatment, plant height and dry matter yield increased with increasing fertilizer. Crude protein was the height in Con(7.0%) and Crude protein of test treatment was T1(5.7%), T2(6.3%), and T3(5.1%). As a result of this study, T2 was recommended.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.27-39
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• 1996

The effects of free surface and a strut on the lifting characteristics on a fin attached at the mid-chord of the strut are investigated experimentally in a circulating water channel. Variation of lift force on the fin is investigated with respect to free stream velocity(V), angle of attack of the fin(${\alpha}$) and ratio of the submergence depth of the fin to the chord of the fin(H/C). Attentions are focused on the lifting characteristics of the fin at shallow depths of submergence. Visualization of the free surface deformation along the strut and of the streamline about the fin is made in order to examine the inflow angle to the fin. Lift force on the fin alone i.e. in absence of the strut is also measured to investigate the difference in lifting characteristics of the fin caused by the strut. The results show that lift forces over the fin are largely affected by a free surface in the case of small submergence ratios(HiC<3.0). For HiC>5.0, the effects of the free surface are negligibly small. The inflow angle to the fin is significantly influenced by the strut and flow speed at the shallow depths of submergence. The deformation of the free surface is largely governed by the waves generated by the strut. However, for small submergence depths, the effects of the fin are found also significant.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.11a
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• pp.158-161
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• 2018

In this paper, the towing force is calculated for the LNG bunker barge. LNG bunkering barge is being developed as an infrastructure for the bunkering of LNG(Liquefied Natural Gas), an eco-friendly energy source. In the case of the LNG bunker barge, a self-propulsion is considered through retrofit from an operating point. Therefore, the LNG bunker barge is similar to the shape of the ship as compared to a towed barge, so a rule of the towed barge overestimates the towing force. In order to improve accuracy, the calm water resistance is calculated according to the ITTC 1978 method considering the wave resistance by the Rankine source method. The added resistance in waves is calculated using the modified radiated energy method considering the shortwave correction method of NMRI. The performance of the towing resistances through the calm water resistance and the added resistance in waves was compared with rules of the towed barge.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.3
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• pp.1-13
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• 1998

In the present paper, the hydrodynamic characteristics of three dimensional hydrofoils moving with a constant speed below the free surface using a higher-order boundary element method based on 9-node Lagrangian curvilinear elements are investigated. A bi-quadratic spline scheme is employed to improve the numerical results on the free surface. To validate the present scheme, the calculated results are compared with the analytic solutions for a submerged sphere and a spheroid showing a good agreement. For the validation of the hydrofoil study, the computed lift and drag of a hydrofoil having $NACA64_{1}A412$ section with aspect ratio(A.R.) of 4 are compared with the experimental data by Wadlin et al.[28]. The comparison covers a number of variations of angle of attack and submergence depth. Then, using an A.R. hydrofoil with NACA0012 section, the free surface on the lift and drag are investigated and these are compared with the previous results. The wave elevations and patterns created by the aforementioned submerged bodies are also investigated with Froude numbers and submergences.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.208-215
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• 2017

When persistent oil, such as crude oil or Bunker C oil, is spilled at sea, viscosity increases through the weathering process. Equipment that can collect this oil when mixed with floating marine debris is very limited. In this study, devices that can be attached to the outside of existing oil skimmers have been applied to the inside of the main body, to develop an unmanned conveyor belt type floating marine debris and high viscosity oil recovery skimmer, which is composed of a conveyor belt, a sweeper with a forced inflow device, and a collection tank equipped with a buoyant body. The resulting skimmer was operated at a speed of 1.2 knots at a distance of 30 m in a sea area test. It was stable when moving laterally in any direction. An oil recovery performance test was conducted using a portable storage tank, and oil was recovered from a minimum of $7.8k{\ell}/h$ to a maximum of $23.3k{\ell}/h$. Moreover, recovery of $7.7k{\ell}/h$ was obtained in a wave water tank test with floating marine debris such as PET bottles and oil mixed. If the equipment developed in this study was used in the field for oil pollution accidents, it could be expected to contribute to improved response capability. We believe our equipment could be used in further studies to improvement the performance of existing portable oil skimmers.