• Title/Summary/Keyword: temperature gradients

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NOAA영상자료에 의한 한국 남해안연안수 조사연구 (Study on the Southern Coastal Waters of Korea by NOAA Image)

  • 김복기
    • 대한원격탐사학회지
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    • 제5권1호
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    • pp.57-67
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    • 1989
  • 1987년 10월부터 1988년 8월까지의 한국남해안에서 시험조사선에 의한 현장조사와 NOAA 영상자료로써 남해안연안수의 소장에 관하여 분석 고찰한 결과는 다음과 같다. $\circled1$ 동계의 층별 수온분포는 0m층 6.07~18.62$^{\circ}C$, 30m층 6.02~18.54$^{\circ}C$, 50m층 7.19~18.69$^{\circ}C$로 상.하층간의 수직분포는 거의 균일한 현상이었고 0m층 남해안연안수와 대마난류간의 수평수온경도는 0.28$^{\circ}C$/mile로 년중 최대였다. $\circled2$ 하계의 층별 수온분포는 0m층 19.37~29.92$^{\circ}C$, 30m층 13.26~27.11$^{\circ}C$, 50m층 7.36~26.6$0^{\circ}C$로서 상.하층간의 수직분포는 성층구조로서 30~50m층의 수직수온경도는 0.44$^{\circ}C$/m로 년중 최대였다. $\circled3$ NOAA영상에서 남해안연안수의 분포는 현장자료와 비교적 일치되고 있으나 SST는 현장수온에 비하여 동계는 2~4$^{\circ}C$, 하계는 4~6$^{\circ}C$ 저온분포였다.

기후변화 조건에서 수분구배 및 영양소 구배에 따른 굴참나무와 상수리나무 잎 형태적 특성의 생태지위 변화 (Variations in Ecological Niche of Quercus variabilis and Quercus acutissima Leaf Morphological Characters in Response to Moisture and Nutrient Gradient Treatments under Climate Change Conditions)

  • 박여빈;김의주;박재훈;김윤서;박지원;이정민;유영한
    • 한국환경복원기술학회지
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    • 제27권2호
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    • pp.43-53
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    • 2024
  • This study attempted to elucidate the ecological niches and influencing environmental factors of Quercus variabilis and Quercus acutissima, which are representative deciduous broad-leaved trees in Korean forests, taxonomically close and genetically similar, under climate change conditions. Under climate change conditions induced by increased CO2 and temperature, soil moisture and nutrient environments were manipulated in four gradients. At the end of the growing, plants were harvested to measure growth responses, calculate ecological niches, and compare them with those of the control. Eperimental plants were grown for 180 days in a glass greenhouse designed with four gradients each for soil moisture and nutrient environments under climate change conditions induced by increased CO2 and temperature. After harvesting, growth responses of leaf traits were measured, ecological niches were calculated, and these were compared with those of the control groups. Furthermore, the responses of the two species' populations were interpreted using principal component analysis(PCA) based on leaf trait measurements. As a result, under climate change conditions, the ecological niche breadth for moisture environment was broader for Quercus variabilis than Quercus acutissima, whereas for the nutrient environment, Quercus acutissima exhibited a broader niche breadth than Quercus variabilis. And the rate of change in ecological niche breadth due to climate change decreased for Quercus variabilis in both moisture and nutrient environments, while for Quercus acutissima, it increased in the moisture environment but decreased in the nutrient environment. Additionally, in terms of group responses, both Quercus variabilis and Quercus acutissima expanded their ecological niches under climate change conditions in both soil moisture and nutrient conditions, with Quercus acutissima exhibiting a broader niche than Quercus variabilis under nutrient conditions. These results indicate that the changes in leaf morphological characteristics and the responses of individuals reflecting them vary not only under climate change conditions but also depending on environmental factors.

연료희석이단면확대채널에형성된삼지화염의전파속도에미치는영향에관한실험적연구 (An Experimental Study on the Effect of Fuel Dilution on the Propagation Velocity of Triple Flames in a Diverging Channel)

  • 서정일;신현동;김남일
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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    • pp.13-18
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    • 2007
  • When triple flames propagated in a diverging channel, the effects of fuel dilution on the lift-off characteristics of triple flames were investigated. A multi-slot burner was used to stabilize the lift-off flame especially at weak fuel concentration gradients. It was reported that there is a maximum propagation velocity at a critical concentration gradient in an open jet regardless of fuel dilution. The enhancement of a diffusion flame affected to increase the propagation velocity around critical concentration gradients. However, the influence of a confined channel on the structure of triple flames according to fuel dilution needs to be investigated compared with an open jet case. This study aimed to examine the effect of a confined channel on the structure and the propagation velocity of the triple flames according to fuel dilution. Lift-off height and propagation velocity of triple flames were investigated by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% $N_2$), Fuel dilution reduced the propagation velocity of triple flame in a confined channel mainly due to the decrease of flame temperature in premixed branch. Despite the difference in fuel dilution, the propagation velocity has a maximum value at a specific fuel concentration gradient even though the critical concentration gradient increases with fuel dilution. And the critical concentration gradient in a confined channel is larger than that in an open jet due to enhancement of convective diffusion.

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링레이저 자이로의 출력오차 최소화를 위한 불규칙 몸체진동잡음 연구 (A study on the dither random noise to minimize the output error of ring laser gyroscope)

  • 심규민;손승현
    • 한국광학회지
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    • 제14권6호
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    • pp.649-656
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    • 2003
  • 본 논문에서는 몸체진동형 링레이저 자이로에서 레이저 공진기에 인가되는 입력 각속도가 lock-in 영역에 있을 때 발생하는 맥놀이신호 위상오차의 크기는 맥놀이신호의 위상에 관계된다는 것을 수치해석적인 계산을 통하여 확인하였다. 그리고 그 오차가 누적되지 않고 통계적 평균값이 영이 되도록 하기 위하여 몸체진동의 진폭을 변화시키는 몸체진동잡음 인가방식에 대한 요구조건을 연구하였다. 그 결과 몸체진동잡음에는 진폭을 증가시키고 감소시키는 진폭경사가 필요하고 여기에 유사 백색잡음을 첨가해주어야 하며 진폭경사의 기울기 및 진폭의 최대값과 최소값을 불규칙적으로 변화시켜야 됨을 알 수 있었다. 그리고 이러한 조건을 만족하는 것과 그렇지 않은 몸체진동잡음을 이용하여 자이로를 동작시키면서 주변온도의 변화에 의하여 나타나는 출력변화를 비교함으로서 몸체진동잡음에 의하여 오차가 누적되는 특성을 확인하였다.

Theoretical buckling analysis of inhomogeneous plates under various thermal gradients and boundary conditions

  • Laid Lekouara;Belgacem Mamen;Abdelhakim Bouhadra;Abderahmane Menasria;Kouider Halim Benrahou;Abdelouahed Tounsi;Mohammed A. Al-Osta
    • Structural Engineering and Mechanics
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    • 제86권4호
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    • pp.443-459
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    • 2023
  • This study investigates the theoretical thermal buckling analyses of thick porous rectangular functionally graded (FG) plates with different geometrical boundary conditions resting on a Winkler-Pasternak elastic foundation using a new higher-order shear deformation theory (HSDT). This new theory has only four unknowns and involves indeterminate integral variables in which no shear correction factor is required. The variation of material properties across the plate's thickness is considered continuous and varied following a simple power law as a function of volume fractions of the constituents. The effect of porosity with two different types of distribution is also included. The current formulation considers the Von Karman nonlinearity, and the stability equations are developed using the virtual works principle. The thermal gradients are involved and assumed to change across the FG plate's thickness according to nonlinear, linear, and uniform distributions. The accuracy of the newly proposed theory has been validated by comparing the present results with the results obtained from the previously published theories. The effects of porosity, boundary conditions, foundation parameters, power index, plate aspect ratio, and side-to-thickness ratio on the critical buckling temperature are studied and discussed in detail.

열 기울기를 고려한 클락 스큐 최소화 기법 (A Clock Skew Minimization Technique Considering Temperature Gradient)

  • 고세진;임재호;김기영;김석윤
    • 대한전자공학회논문지SD
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    • 제47권7호
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    • pp.30-36
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    • 2010
  • 발달로 인해 칩의 집적도가 향상되고, 그에 따라 칩 내의 전류밀도가 증가하게 되었다. 이는 칩의 온도가 상승하는 효과를 가져오게 되고, 또한 거리에 따른 온도의 변화를 증가시키는 요인이 된다. 본 논문은 칩 내의 온도의 기울기 때문에 발생되는 클락의 스큐를 최소화하기 위한 균형 스큐 트리를 생성하는 기법을 제안한다. 제안한 기법은 Elmore 지연 수식을 이용하여 연결선의 지연을 구하고 DME(Deferred Merge Embedding) 알고리즘을 통해 만들어진 클락 트리를 변형시키면서 최적의 균형 스큐 트리를 찾는다. 제안한 기법의 성능 평가를 위하여 C 언어로 제안된 기법을 구현하였고, 온도의 기울기 때문에 발생한 클락 삽입 지점을 평균 약 54%이하로 수축시킬 수 있다는 것을 시뮬레이션 결과로 보였으며, 스큐가 현저히 낮아지는 것을 확인하였다.

리기다소나무 고온건조 (High Temperature Drying of Pitch Pine Lumber)

  • 여환명;심상로
    • Journal of the Korean Wood Science and Technology
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    • 제32권4호
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    • pp.46-51
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    • 2004
  • 본 연구에서는 국산 리기다소나무의 대량 수요 창출과 이용기술 개발, 특히 구조용집성재 라미나로서의 이용 가능성 구명을 위해 고온에서 건조된 판재의 변형량과 변색정도를 조사 평가하였다. 함수율 분포시험을 통해 평가된 고온건조판재 내 적은 함수율 경사, 프롱테스트를 통해 확인된 적은 내부 잔류응력, 집성가공 가능한 적은 변형량 등은 본 연구에서 적용된 고온건조스케쥴이 구조용집성재용 라미나 건조조건으로 사용 가능성이 높다는 결과를 보여주었다. 예비실험을 통해 송진에 의한 접착장애는 발생하지 않는 것으로 확인 되었으나, 잔류수지에 의한 구조용집성재의 접착내구성 및 도장성능 감소현상 구명을 위한 수지정량 분석시험이 추후 요구되었다. 또한 최종 함수율이 집성재 라미나로서 이용 가능한 함수율보다 상당히 낮은 수준으로 건조되었으며 저온열기건조 판재에 비해 변색이 심하므로 함수율 제어 및 변색 억제를 위한 최적의 건조조건 구명에 대한 연구가 좀더 필요할 것으로 사료된다.

토양-대기의 수은 교환작용 -서울시 주거지역에 대한 예비측정- (Preliminary Measurements of Mercury Exchange Rates Across the Soil-Air Boundary in a Residential Area of Seoul)

  • 김기현;김민영
    • 한국대기환경학회지
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    • 제14권4호
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    • pp.369-377
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    • 1998
  • To examine various aspects of Hg exchange processes, we measured Hg$^{\circ}$concentration gradients over soil surfaces in a residential area of Seoul during Sept. 1997. From these measurements, we found that Hg$^{\circ}$concentrations in lower(20 cm) and upper(200 cm) levels varied in the range of 3.15~14.38 (5.30$\pm$1.88: N=236) and 2.07~15.10ng/m$^3$(4.06$\pm$1.69: N=236), respectively. When our data were divided into emission and dry deposition, emission of Hg$^{\circ}$was overwhelmingly dominant (up to 98% in frequency) over dry deposition. The concentration gradients for emission and deposition events were 1.29$\pm$0.86(N=231) and -1.0$\pm$1.27ng/m$^3$(N=5), respectively. The observation of excessively high concentrations in both levels and development of strong gradients suggest that our study site be greatly affected by certain pollution sources of mercury. In face, those data were quite comparable to that had previously been observed from highly contaminated soil environs of Tennessee, USA. To provide some insights into the processes governing the Hg$^{\circ}$exchange processes, we have conducted correlation analyses between Hg$^{\circ}$data and other concurrently determined meteorological plus chemical data. In general, Hg$^{\circ}$concentrations of both levels exhibited similarly the existence of strong correlations with parameters like windspeed, temperature, and relative humidity. Although its concentration gradient data showed similarly strong correlations with meteorological parameters, they showed somewhat unique patterns in that their correlations with Hg$^{\circ}$concentration were noticeably stronger for the lower level than the upper level. To provide rough estimates of Hg$^{\circ}$fluxes in this study, we computed its flux using our gradient data and the predicted K values from previous studies. According to this approach, Hg$^{\circ}$emissions were generally in the range of 103$\pm$80(N=231), while its depositions, being scarcely found, were on the similar magnitude of -92$\pm$128ng/m$^2$/hr(N=5). The findings of excessive emission of Hg$^{\circ}$in residential area of Korea suggests that contamination of mercury be a significant process and hence be dealt more seriously.

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디스크 브레이크의 적열점에 관한 3차원 시뮬레이션 (Three-dimensional Simulation of Hot spots in Disk Brakes)

  • 이일권;조승현;김청균
    • 한국윤활학회:학술대회논문집
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    • 한국윤활학회 2000년도 제31회 춘계학술대회
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    • pp.211-218
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    • 2000
  • Hot spot behaviors on the disk-pad contact surface during a braking operation have been analyzed for a ventilated disk brake using the finite element method. Hot spots which were studied using a coupled thermal-mechanical analysis technique are influenced by all of the mechanical, thermal, elastic and plastic processes that are involved in braking cycles, but their temperature gradients are most affected by rubbing speeds, braking forces, and design parameters between the disk and the pad. Undesirable hot spots that are generated by local thermoelastic instabilities are intended to be removed by optimized design parameters and material properties. In this study, a three-dimensional numerical method for the demonstration of hot spot behaviors has been applied to the rubbing surfaces between the disk and the pad.

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Numerical analysis of thermal and composite stresses in pre-stressed concrete pavements

  • Nejad, Fereidoon Moghadas;Ghafari, Sepehr;Afandizadeh, Shahriar
    • Computers and Concrete
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    • 제11권2호
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    • pp.169-182
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    • 2013
  • One of the major benefits of the pre-stressed concrete pavements is the omission of tension in concrete that results in a reduction of cracks in the concrete slabs. Therefore, the life of the pavement is increased as the thickness of the slabs is reduced. One of the most important issues in dealing with the prestressed concrete pavement is determination of the magnitude of the pre-stress. Three dimensional finite element analyses are conducted in this research to study the pre-stress under various load (Boeing 777) and thermal gradient combinations. The model was also analyzed under temperature gradients without the presence of traffic loading and the induced stresses were compared with those from theoretical relationships. It was seen that the theoretical relationships result in conservative values for the stress.