• Weed & Turfgrass Science
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• v.2 no.3
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• pp.322-326
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• 2013

This study was tried to control the weedy rice using minimum tillage direct seeding of rice on dry paddy. Minimum tillage direct seeding on dry paddy is tilled with 4 cm in width at 27 cm intervals by 1-shaped rotary blade. Using this cultivation method can control weedy rice effectively by minimizing the soil disturbance. In this study, weedy rice was firstly emerged at April 28 in 2012. After 11 days emergence rate of weedy rice at May 9 was 61.9%. At this time rice was sown and then herbicides was treated at 10 and 15 days after sowing. When herbicides was treated at 10 days after sowing the control effect was 89-96%, and when treated at 15 days the control effect was 97-99%. However emergence of weedy rice differ according to the year and year. It was thought to be affected by April average temperature and total precipitation. So, for effective weedy rice control and stable rice yield, it was considered that irrigation at April 15-20 to induce the emergence of weedy rice is required.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.360-369
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• 2008

The solar cells should be operated at the maximum power point because its output characteristics were greatly fluctuated on the variation of insolation, temperature and load. It is necessary to install an inverter among electric power converts by means of the output power of solar cell is DC. The inverter is operated supply a sinusoidal current and voltage to the load and the interactive utility line. In this paper, the proposes a photovoltaic system is designed with a step up chopper and single phase PWM voltage source inverter. Synchronous signal and control signal was processed by one-chip microprocessor for stable modulation. The step up chopper is operated in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature for solar cell has typical dropping character. The single phase PWM voltage source inverter is consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be develop continuously by connecting with the source of electric power for ordinary using. It can be cause the efect of saving electric power, from 10 to 20%. The single phase PWM voltage source inverter operates in situation, that its output voltage is in same phase with the utility voltage. The inverter are supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.39 no.3
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• pp.205-210
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• 1994

This experiment was conducted to investigate of soil hardening degree before sowing, furrow depth at sowing and flooding time after sowing at furrowing in flooded rice paddy field that many people have an interest in as direct sowing method most recently. As hardening period was increased, the percentage of seedling stand and seed floating at flooding were increased slightly, while buried depth of stem at maximum tillering stage and cone penetration depth were decreased, respectively. Therefore, optimum degree of soil hardening was about 3 days after draining, at this time, cone penetration degree was about 6~7cm. According to furrow depth was more and more deep, buried depth of stem was increased gradually, but percentage of seedling stand was decreased considerbly. Also, root distribution ratio on surpace horizon and lodging degree were increased gradually according to furrow depth become more and more shallow. As flooding time after sowing was late, percentage of seedling stand and panicle number per $m^2$ were decreased slightly. These results apparently indicated that sowing after 3 days hardening when cone penetration degree was 6~7cm, furrow depth 3~4cm degree and flooding time just after sowing the best method to good establish of seedling stand.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.114-131
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• 1992

In the present work, a two-dimensional boundary-value problem for a large amplitude motion is treated as an initial-value problem by satisfying the exact body-boundary and nonlinear free-surface boundary conditions. The present nonlinear numerical scheme is similar to that described by Vinje and Brevig(1981) who utilized the Cauchy's theorem and assumed the periodicity in the horizontal coordinate. In the present thesis, however, the periodicity in the horizontal coordinate is not assumed. Thus the present method can treat more realistic problems, which allow radiating waves to infinities. In the present method of solution, the original infinite fluid domain, is divided into two subdomains ; ie the inner and outer subdomains which are a local nonlinear subdomain and the truncated infinite linear subdomain, respectively. By imposing an appropriate matching condition, the computation is carried out only in the inner domain which includes the body. Here we adopt the nonlinear scheme of Vinje & Brevig only in the inner domain and respresent the solution in the truncated infinite subdomains by distributing the time-dependent Green function on the matching boundaries. The matching condition is that the velocity potential and stream function are required to be continuous across the matching boundary. In the computations we used, if necessary, a regriding algorithm on the free surface which could give converged stable solutions successfully even for the breaking waves. In harmonic oscillation problem, each harmonic component and time-mean force are obtained by the Fourier transform of the computed forces in the time domain. The numerical calculations are made for the following problems. $\cdot$ Forced harmonic large-amplitude oscillation(${\omega}{\neq}0,\;U=0$) $\cdot$ Translation with a uniform speed(${\omega}=0,\;U{\neq}0$) The computed results are compared with available experimental data and other analytical results.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.147-151
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• 2007

인위적인 온실가스 증가의 영향으로 지구의 기온이 상승하고 있으며, 우리나라에서도 이러한 전 지구적인 온난화 추세를 상회하는 경향을 보이고 있다. 20세기 후반부터 기후변화에 따른 강수량 및 집중호우의 증가 추세가 보고되고 있으며, 이에 따른 피해 또한 증가하고 있다. 이러한 이상기후 현상이 전 세계적으로 빈번히 발생하여 가용 수자원의 변동이 커지고 있다. 추가적인 댐 건설이 어려운 상황이고, 댐 운영의 불확실성에 의한 현실적인 운영의 어려움으로 인하여 보수적인 댐 운영이 이루어지고 있는 실정이므로, 한정된 수자원의 효율적인 이용과 예측이 요구되고 있다. 본 연구에서는 기상연구소에서 개발된 A2, B2 기후변화 시나리오에 따른 다목적댐에서의 용수공급능력의 변화에 대한 평가를 수행하였다. 대규모 유역의 대표적인 다목적댐을 선정하고 기후변화 시나리오별 유입량을 분석하였으며, 이를 저수지 모의운영 기법을 이용하여 기후변화 시나리오에 따른 각 댐의 신뢰도 95% 용수공급능력과 예상발전량을 산정함으로써 가용수자원을 평가하였다. 또한 다목적댐의 과거 실적 유입량 자료를 이용한 모의운영 결과와 비교하여 제시하였다. 과거 실적에 의한 결과와 비교할 때, 기후변화 시나리오에 따른 향후 국내 가용 수자원량에도 큰 변화가 있을 것으로 예측되었다. 이로부터 댐 운영에 있어서 홍수기의 안정적인 댐관리와 갈수기의 적절한 수자원 분배를 위한 방향을 제시할 수 있다. 본 연구의 결과는 향후 기후변화에 따른 저수지의 효율적인 운영을 위한 유역의 수자원 영향 평가에 활용할 수 있을 것으로 기대된다.댐의 순기능에 대한 정량적인 분석을 수행하였다. 또한 댐별 방류량을 변동하여 하류 주요지점에 미치는 유황개선효과를 정량화하였다. 마지막으로 댐의 효율을 최대화한 하류확보가능하천유지유량을 월별평균량으로 산정하였다. 이는 향후 오염총량제 기준유량 및 환경용수의 법제화를 통한 하천유지용수의 증가시 비구조적 대책의 공급가능 최대량으로 활용가능할 것으로 사료된다.원에서 인위적으로 방류한 양이 많았기 때문으로 추정할 수 있다. 두 지점의 1월 유출이 100 % 이상인 것은 동절기 하천 결빙으로 인한 유량파악이 힘든 것으로 나타났다. 1월의 하천수위는 계측기에 기록된 수위값으로 유량을 산정한 것이다. 3월, 10월, 12월의 유출이 많은 것은 전월말 발생한 강우의 영향으로 크게 나타났다.다. 5. 초장의 절대치는 품종간에 차이는 있으나 비교적 조파구간에는 초장에 큰 변이가 없었고 파종기가 늦어짐에 따라 짧아졌다. 초장의 신장속도는 파종기가 늦어짐에 따라 현저하게 빨라지고 특히 조생종이 만생종보다 더욱 가속적인 경향이었다. 따라서 최고초장과 최저초장과의 절대치의 차이는 조생종일수록 적고 만생종일수록 큰 격차를 보이었다. 6. 간직경에 있어서도 만생종은 일반적으로 조기파종할수록 굵고, 조생종과 중생종은 4월 25일 파종기가 가장 굵은 편이며 이보다 파종기가 지연 가늘어지는 경향이었다. 7. 간중은 품종의 조만생에 따라 약간의 차이는 있으나 대체로 적기(4월 25일~5월 15일)보다 조기 혹은 만기 파종하면 작아지나 파종기 이동에 따른 간중의 변화는 품종의 조만성에 따라 양상을 달리하여 조생종은

• Korean Journal of Medicinal Crop Science
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• v.5 no.1
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• pp.67-71
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• 1997

Bupleurum falcatum is one of the oldest medicinal crop spontaneously generated as well as cultivated by man and successfully grown during the summer season in Korea. This study was conducted to examine the effect of planting density in the row spacing and hill spacing system using machine seeder on major agronomic traits, yield and labor saving. In 1993 and 1994, a spilt plot design was used with row spacing as the main plot and hill spacing as subplot. Labor saving efficency of the machine seeder reduced 96% than the hand seeding in sowing time required. Number of seeding stand increased, but stem height and number of nodes did not affect with different density in each row and hill spacing. There were reduced with narrow hill spacing on stem diameter, number of branches, shoot weight and root traits. There was no significant interaction between row and hill spacing for any major traits studied except shoot weight. Yield was more increase at 20cm than at 30cm row spacing. For these studies the optiomum density appears to be between drilling or 5cm hill spacing with 20cm row spacing. A highly significant positive correlation was appeared between number of seedling stand and root yield.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.52 no.3
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• pp.325-333
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• 2007

To find out the planting times for the economic yield of a super sweet corn hybrid, "Cambella 90" was planted from 1 April of 2003 and 2004 at the 10 days intervals under black polyethylene (P. E.) film mulch and in bare soil in Gyeongsan. Daily maximum soil temperature under black P. E. film mulch was lower, while daily minimum soil temperature was higher compared to bare soil. Soil moisture content under black P. E. film mulch maintained optimum level longer than in bare soil. Emergence rate, percent stand, culm length, and the number of marketable ears were higher under black P E. film mulch compared to bare soil. Silking date under black P. E. film mulch was earlier compared to bare soil by $4{\sim}6$ days at April plantings, while only 1 day earlier at June plantings. Silking date of individual plants in a plot ranged $3{\sim}5$ days depending on planting dates and soil mulch in the same plot. The number of large ears decreased as planting dates delayed. Considering emergence rate and the number of marketable ears, the planting time for the economic yield of a super sweet com hybrid, "Cambella 90" ranged 1 April to 20 June in the southern part of Korea.

• Journal of The Korean Society of Grassland and Forage Science
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• v.6 no.3
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• pp.164-168
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• 1986

This study was conducted at the forage experiment field of SNU, Snweon to investigate effects of sowing time and seeding rate on growth characteristics, winter survival and dry matter yield of forage rye (Secale cereale L.) as fresh-cut forage. Treatments involved 9 combinations of sowing times (September 8, 28 and October 18) and seeding rates(80, 130 and 180kg $ha^{-1}$). Plant height was not influenced by the time of sowing, but forage rye had a tendency to be taller as increasing seeding rate when sown on September 8 and October 28 and harvested in fall and spring, respectively, Winter survival was reduced by fall harvesting in the plot sown on September 8, however, total dry matter yield was increased by the fall harvesting. Average dry matter yields of 5884, 4993 and 3525kg $ha^{-1}$ were obtained when forage rye was sown on September 8, 28 and October 18, respectively. Dry matter yield was decreased as delaying the time of sowing, but a tendency toward higher yield of forage rye by increasing seeding rate was observed. Yield difference by seeding rates was markedly larger when forage rye was sown on October 18 than September 8 and 28. Based on the results of this study, it appears that the dry matter yield of forage rye could be enhanced by sowing early to late September under upland condition in the middle plain are of Korea. The seeding rates of 80 to 130 kg $ha^{-1}$ and 180kg $ha^{-1}$ would be suitable for early to mid fall and late fall sowings, respectively.

• Journal of The Korean Society of Grassland and Forage Science
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• v.34 no.2
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• pp.81-86
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• 2014

This study was conducted to evaluate the effect of different seeding dates on agronomic characteristics, forage quality, dry matter (DM) and dry matter digestible (DDM) yields of sudangrass hybrid (Sorghum bicolor(L.) Moench) and oat (Avena sativaL.) at Seongju in Kyeongbuk from 2012 to 2013. The experiment was arranged in randomized complete block design with three replications. Sudangrass was seeded five times seeding dates of 10 days interval ranging from $1^{th}$ August to $10^{th}$ September in 2012 and 2013. Oat was seeded three times seeding dates of 10 days interval ranging from $20^{th}$ August to $10^{th}$ September in 2013. Sudangrass was harvested on $26^{th}$ October, 2012 and $2^{nd}$ November, 2013. Plant length and DM content decreased with delaying seeing date. The DM and DDM yields of sudangrass were higher (P<0.05) in first seeding date than all other seeding dates and decreased with delaying seeding dates (P<0.05). The DM and DDM yields of oat were higher (P<0.05) in first and second seeding dates than third seeding date. The results of this study indicated that early seeding of sudangrass would be a recommended than late seeding after $20^{th}$ of August, and late seeding of oat after $30^{th}$ August would be recommened for DM and DDM yields in the Southern Korea.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.649-655
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• 2006

Waves progressing into the coastal area can be amplified, swashed and overtopped by a wave overtopping control structure, and it converts the kinetic energy of the waves to the potential energy with a hydraulic head above the mean sea level by conserving the overflow in a reservoir. Then the potential energy in the form of hydraulic head can be converted to electric power utilizing extremely low-head hydraulic turbine. This study aims to find the most optimal shape of wave overtopping structure which maximizes overtopping volume rate of sea water. Laboratory experiments for the performance evaluation of wave overtopping control structures were carried out in three dimensional wave tank, and the three dimensional structure models with planar wave concentration shapes(B/b) were manufactured into five classes, which were optimized by cross sectional parameters of the structure, ie, length of ramp(l), gradient of inclined ramp($cot{\phi}$) and freeboard height of the wave overtopping structure($h_e$) proposed by Shin and Hong(2005). The wave overtopping discharges were investigated with 20 incident wave conditions and wave directions of $0^{\circ},\;15^{\circ},\;30^{\circ}$.