• 제목/요약/키워드: Density Variation

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남부지방에 있어서 수도수량구성요소 및 수량해석 제 3 보 재식밀도에 따른 주요형질 및 수량의 변이 (Analytical Studies on the Rice Yield Components and Yield in South Region of Korea III. Variation in the Rice Yield Component and Yield under the Different Planting Density)

  • 김용재
    • 한국작물학회지
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    • 제31권1호
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    • pp.104-111
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    • 1986
  • 남부 난지 다모작지대의 도작 증수재배의 기초자료를 얻고자 재식밀도를 3.3$m^2$당 50, 70, 90, 110주로 하고 이앙시기를 5월 20일부터 7월 5일까지 15일 간격, 4시기로 하여 수량형질의 변이 및 수량을 검토한 결과를 요약하면 다음과 같다. 1. 줄기의 중기는 밀식보다 소식에서 컸고 이앙기가 빠를수록 가늘었다. 2. 이앙기 이동에 따른 적정 재식밀도는 서광벼의 경우 5월 20일 및 6월 5일 이앙구에서는 3.3$m^2$당 90주였으며 만식구인 6월 20일 및 7월 5일 이앙에서는 110주였고 동진벼는 5월 20일, 6월 5일, 6월 20일 이앙까지 90주였으며 7월 5일 이앙에서는 110주였다. 3. 등숙율은 재식밀도증가에 따른 변이가 크지 않았으나 다만 만식에서 그 효과가 인정되었다. 4. 재식밀도에 따른 1, 2차 지경 및 영화의 퇴화는 밀식할수록 적어지며 서광벼가 동진벼보다 뚜렷한 경향을 보였다. 5. 단위면적당 수수는 재식밀도 증가에 따라 직선적인 증가현상을 보였고 이앙기의 조만에 따른 변이폭은 동진벼보다 서광벼에서 더 컸다.

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Adaptive Link Voltage Variation (ALVV) Control for High Efficiency in High Power Density Adapter

  • Kim, Bong-Chul;Lee, Byoung-Hee;Park, Ki-Bum;Kim, Chong-Eun;Ryu, Byoung-Woo;Moon, Gun-Woo;Youn, Myung-Joong
    • 전력전자학회:학술대회논문집
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    • 전력전자학회 2008년도 하계학술대회 논문집
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    • pp.508-510
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    • 2008
  • In designing a LLC resonant converter, the ratio of magnetizing inductance ($L_M$) to resonant inductance ($L_R$), the inductor ratio (K) is usually considered. In high power density adapter, both adapter size and efficiency are important factors. Considering the size of adapter, high K design can be more attractive. But, wide frequency variation of high K design results in design difficulty of magnetic elements and decrease in efficiency. To solve these drawbacks, an adaptive link voltage variation (ALVV) control is proposed. With the proposed control method, the LLC resonant converter can be operated at the resonant frequency despite the output voltage variation. The control strategy and schematics are presented, and verified experimentally.

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AF궤도회로에서 세라믹 코팅재에 의한 자계의 세기 변화에 대한 연구 (A Study on the Variation of Magnetic Field Intensity by Ceramics Coating Material in AF Track Circuits)

  • 김민규;김선동;고영환;김민석;이종우
    • 한국철도학회:학술대회논문집
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    • 한국철도학회 2010년도 춘계학술대회 논문집
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    • pp.1656-1662
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    • 2010
  • Automatic train control systems are divided into ATC, ATP and ATS systems etc. The ATP and ATS systems offer discontinuous information for train control. While the ATC systems provide continueous information for train control. There is a method for offering continuous information by AF track circuits. Magnetic fields are formed by current through rails in the AF track circuit systems. So, the continuous information is received by the magnetic fields on a on-board antenna. Coating materials on rails are researched to decrease defects such as head check, shelling, corrugation, squats and so on in Germany. Currently, a coating method of rail construction is proposed by using the ceramics in Korea. When deciding physical characteristic of ceramics, researches are required about variation of flux density by the ceramics. In case that the flux density is much lower than existing value, the information for train control is not transmitted to the on-board antenna. In this paper, inductance on rails is calculated and a model is presented about variation of the magnetic field intensity in the AF track circuit. Standard permeability of ceramics is proposed by analyzing the variation of magnetic field intensity. It is demonstrated by using Maxwell and Matlab program.

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Density distributions and Power spectra of outflow-driven turbulence

  • Kim, Jongsoo;Moraghan, Anthony
    • 천문학회보
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    • 제39권1호
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    • pp.57.2-57.2
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    • 2014
  • Protostellar jets and outflows are signatures of star formation and promising mechanisms for driving supersonic turbulence in molecular clouds. We quantify outflow-driven turbulence through three-dimensional numerical simulations using an isothermal version of the total variation diminishing code. We drive turbulence in real space using a simplified spherical outflow model, analyze the data through density probability distribution functions (PDFs), and investigate density and velocity power spectra. The real-space turbulence-driving method produces a negatively skewed density PDF possessing an enhanced tail on the low-density side. It deviates from the log-normal distributions typically obtained from Fourier-space turbulence driving at low densities, but can provide a good fit at high densities, particularly in terms of mass-weighted rather than volume-weighted density PDF. We find shallow density power-spectra of -1.2. It is attributed to spherical shocks of outflows themselves or shocks formed by the interaction of outflows. The total velocity power-spectrum is found to be -2.0, representative of the shock dominated Burger's turbulence model. Our density weighted velocity power spectrum is measured as -1.6, slightly less that the Kolmogorov scaling values found in previous works.

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BLDC 전동기의 정현적 공극 자속밀도 구현에 의한 코깅 토크 저감 (Reduction of Cogging Torque of BLDC Motor by Sinusoidal Air-Gap Flux Density Distribution)

  • 김사무엘;정승호;류세현;권병일
    • 전기학회논문지
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    • 제56권1호
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    • pp.57-65
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    • 2007
  • Along with the development of power electronics and magnetic materials, permanent magnet (PM) brushless direct current (BLDC) motors are now widely used in many fields of modern industry BLDC motors have many advantages such as high efficiency, large peak torque, easy control of speed, and reliable working characteristics. However, Compared with the other electric motors without a PM, BLDC motors with a PM have inherent cogging torque. It is often a principle source of vibration, noise and difficulty of control in BLDC motors. Cogging torque which is produced by the interaction of the rotor magnetic flux and angular variation in the stator magnetic reluctance can be reduced by sinusoidal air-gap flux density waveform due to reduction of variation of magnetic reluctance. Therefore, this paper will present a design method of magnetizing system for reduction of cogging torque and low manufacturing cost of BLDC motor with isotropic bonded neodynium-iron-boron (Nd-Fe-B) magnets in ring type by sinusoidal air-gap flux density distribution. An analytical technique of magnetization makes use of two-dimensional finite element method (2-D FEM) and Preisach model that expresses the hysteresis phenomenon of magnetic materials in order for accurate calculation. In addition, For optimum design of magnetizing fixture, Factorial design which is one of the design of experiments (DOE) is used.

3차원 공동의 폭변화에 따른 초음속 유동에 대한 수치분석연구 (NUMERICAL ANALYSIS OF THREE DIMENSIONAL SUPERSONIC CAVITY FLOW FOR THE VARIATION OF CAVITY SPANWISE RATIO)

  • 우철훈;김재수;최홍일
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2006년도 추계 학술대회논문집
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    • pp.181-184
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    • 2006
  • High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation and reattachment, shock and expansion waves. The general cavity flow phenomena include the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity' flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions, The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio(L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyized and compared with the results of Rossiter's Eq.

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공동의 폭 변화에 따른 3차원 초음속 공동 유동연구 (NUMERICAL ANALYSIS OF THREE DIMENSIONAL SUPERSONIC CAVITY FLOW FOR THE VARIATION OF CAVITY SPANWISE RATIO)

  • 우철훈;김재수
    • 한국전산유체공학회지
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    • 제11권4호
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    • pp.62-66
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    • 2006
  • High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation, reattachment, shock waves and expansion waves. The general cavity flow phenomena includes the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio (L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyzed and compared with the results of Rossiter's Eq.

Interpretation of Physical Properties of Marine Sediments Using Multi­Sensor Core Logger (MSCL): Comparison with Discrete Samples

  • Kim, Gil-Young;Kim, Dae-Choul
    • Journal of the korean society of oceanography
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    • 제38권4호
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    • pp.166-172
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    • 2003
  • Multi­Sensor Core Logger (MSCL) is a useful system for logging the physical properties (compressional wave velocity, wet bulk density, fractional porosity, magnetic susceptibility and/or natural gamma radiation) of marine sediments through scanning of whole cores in a nondestructive fashion. But MSCL has a number of problems that can lead to spurious results depending on the various factors such as core slumping, gas expansion, mechanical stretching, and the thickness variation of core liner and sediment. For the verification of MSCL data, compressional wave velocity, wet bulk density, and porosity were measured on discrete samples by Hamilton Frame and Gravimetric method, respectively. Acoustic impedance was also calculated. Physical property data (velocity, wet bulk density, and impedance) logged by MSCL were slightly larger than those of discrete sample, and porosity is reverse. Average difference between MSCL and discrete sample at both sites is relatively small such as 22­24 m/s in velocity, $0.02­-0.08\;g/\textrm{cm}^3$ in wet bulk density, and 2.5­2.7% in porosity. The values also show systematic variation with sediment depth. A variety of factors are probably responsible for the differences including instrument error, various measurement method, sediment disturbance, and accuracy of calibration. Therefore, MSCL can be effectively used to collect physical property data with high resolution and quality, if the calibration is accurately completed.

고효율, 고전력밀도 아답터를 위한 도통밴드 제어 AC-DC 벅 컨버터 (A Conduction Band Control AC-DC Buck Converter for a High Efficiency and High Power Density Adapter)

  • 문상철;정봉근;구관본
    • 전력전자학회:학술대회논문집
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    • 전력전자학회 2017년도 전력전자학술대회
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    • pp.38-39
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    • 2017
  • This paper proposes a new control method for an AC-DC Buck converter which is utilized as a front-end converter of a 2-stage high power density adapter. In the conventional adapter applications, 2-stage configuration shows higher power transfer efficiency and higher power density than those of the single stage flyback converter. In the 2-stage AC-DC converter, the boost converter is widely used as a front-end converter. However, an efficiency variation between high AC line and low AC line is large. On the other hand, the proposed conduction band control method for a buck front-end converter has an advantage of small efficiency variation. In the proposed control method, switching operation is determined by a band control voltage which represents output load condition, and an AC line voltage. If the output load increasesin low AC line, the switching operation range is expanded in half of line cycle. On the contrary, in light load and high line condition, the switching operation is narrowed. Thus, the proposed control method reduces switching loss under high AC line and light load condition. A 60W prototype which is configured the buck and LLC converter with the proposed control method is experimented on to verify the validity of the proposed system. The prototype shows 92.16% of AC-DC overall efficiency and 20.19 W/in 3 of power density.

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한국수영만에서 잔차류장의 운동 .위치에너지의 계절변화 (Seasonal Variation of Kinetic and Potential Energy of Residual Flow Field in Suyoung Bay, Korea)

  • 김동선;유철웅
    • 한국환경과학회지
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    • 제6권4호
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    • pp.313-322
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    • 1997
  • 한국수영만에서 잔차류장의 운동 위치에너지의 계절변화를 연구하기 위하여 우리는 에너지의 수지를 계산하고 조석에너지와 비교했다. 위치에너지는 겨울과 봄철에 크며, 밀도성층이 형성된 여름과 초가을에 작게 나타났다. 잔차류의 운동에너지는 계절적인 변화를 보이고 있으며, 단위면 적당 잔차류의 평균 운동에너지는 6.4$\times$$10^{-4}ergs s^{-1}cm^{-}2$이다. 수영 만에서 잔차류장의 계절변동은 조석잔차류의 운동에너지가 밀도류나 취송류의 운동에너지보다 큰 11월을 제외하고는 밀도류가 지배하고 있다. 잔차류의 주성분인 조석잔차류, 취송류 및 밀도류의 운동에너지의 평균백분율은 잔차류의 운동에너지에 대하여 각각 29.1%, 3.4%, 67.5% 이다. 단위면적당 잔차류의 운동에너지, 위치에너지 및 조석에너지의 비는 각각 1.0 : 6.7$\times$$10^3$ : 8.2$\times$$10^4$ 이다.

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