• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제21권4호
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• pp.225-244
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• 2017

The natural convective nanofluid flow and heat transfer inside a square enclosure with a center heater in the presence of magnetic field has been studied numerically. The vertical walls of the enclosure are cold and the top wall is adiabatic while the bottom wall is considered with constant heat source. The governing differential equations are solved by using a finite volume method based on SIMPLE algorithm. The parametric study is performed to analyze the effect of different lengths of center heater, Hartmann numbers and Rayleigh numbers. The heater effectiveness and temperature distribution are examined. The effect of all pertinent parameters on streamlines, isotherms, velocity profiles and average Nusselt numbers are presented. It is found that heat transfer increases with the increase of heater length, whereas it decreases with the increase of magnetic field effect. Furthermore, it is found that the value of Nusselt number depends strongly upon the Hartmann number for the increasing values of Rayleigh number.

• Journal of applied mathematics & informatics
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• 제37권3_4호
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• pp.177-182
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• 2019

This study is about the number expressed and the number not expressed in terms of the sum of consecutive natural numbers with a difference of 2k. Since it is difficult to generalize in cases of onsecutive positive integers with a difference of 2k, the table of cases of 4, 6, 8, 10, and 12 was examined to find the normality and to prove the hypothesis through the results. Generalized guesswork through tables was made to establish and prove the hypothesis of the number of possible and impossible numbers that are to all consecutive natural numbers with a difference of 2k. Finally, it was possible to verify the possibility and impossibility of the sum of consecutive cases of 124 and 2010. It is expected to be investigated the sum of consecutive natural numbers with a difference of 2k + 1, as a future research task.

• 한국산림과학회지
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• 제99권4호
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• pp.553-558
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• 2010

본 연구는 산불피해 후 자연복원과 소나무 조림을 실시한 지역에서 서식환경과 설치류 개체군의 밀도 차이를 파악하기 위해 강원도 삼척시 검봉산 일대의 2000년도 산불피해 지역에서 2008년 3월에서 12월까지의 기간 동안 수행되었다. 자연복원지과 소나무 조림지에서 각각 3개씩 1 ha 크기의 조사지를 선정하여 2개월 간격으로 각각 4일간의 포획조사 및 서식환경조사를 실시하였다. 서식환경 조사 결과, 하층 피도량 및 치수의 수는 조림지가 자연 복원지에 비해 높은 값을 나타낸 반면, 중층 피도량, 중상층 피도량, 상층 피도량, 교목, 관목의 수, 고사목의 수, 수목잔존물의 양 등은 자연복원지에서 더 높은 값을 나타냈다. 포획 조사 결과 등줄쥐(Apodemus agrarius), 흰넓적다리 붉은쥐(Apodemus peninsulae), 대륙밭쥐(Eothenomys regulus), 다람쥐(Tamias sibiricus) 등 총 4종 688개체가 포획되었다. 설치류의 포획 개체수는 조림지보다 자연복원지가 더 높게 나타났으며, 흰넓적다리붉은쥐, 대륙밭쥐, 다람쥐 등 3종이 조림지보다 더 높은 포획 개체수를 보였다. 이에 비해 등줄쥐는 조림지에서 많이 포획되었다. 등줄쥐와 흰넓적다리붉은쥐는 4월과 12월에 최대 포획개체수를 나타내었으며, 대륙밭쥐는 4월과 6월에, 다람쥐는 6월과 10월에 가장 많은 개체수가 포획되었다. 수목잔존물 제거 및 조림으로 인해 수관층과 하층식생이 개방된 서식 환경은 설치류의 서식에 적합하지 않은 것으로 판단된다. 그러므로 산불 피해 발생후 하층식생 및 수관층이 유지될 수 있도록 산림을 관리하는 것이 설치류의 다양성 유지에 필요할 것으로 생각된다.

• 한국전산유체공학회지
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• 제16권3호
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• pp.66-74
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• 2011

A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

• The Korean Journal of Ecology
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• 제8권1호
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• pp.31-37
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• 1985

The decomposition rate of litter and the number of soil microorganisms were measured on various slope directions in deciduous oak forest in Mt. Yongam. And the chemical constitutents of litter and soil were analyzed. The decomposition rate by slope directions followed the order east facing slope>south-east facing slope>north-west facing slope>north-east facing slope>north facing slope>south facing slope>south-west facing slope>west facing slope. Of the chemical constituents analyzed, original concentrations of Ca and carbohydrate were closely correlated with the decomposition rate. There was a close relation between the number of fungi and decomposition rate by slope directions. However, a little relationship existed between the number of bacteria and decomposition rate by slope directions. The number of fungi and concentrations of Ca and carbohydrate correlated to each other. And the number of bacteria is related to concentrations of phosphorus.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.294-301
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• 2004

The natural convective heat transfer in a rectangular enclosure with a heating source has been studied by experiment and numerical analysis. The governing equations were solved by a finite volume method, a SIMPLE algorithm was adopted to solve a pressure term. The parameters for the numerical study are positions and surface temperatures of a heating source i.e., Y /H =0.25, 0.5, 0.75 and 11$^{\circ}C$ $\leq$ΔT$\leq$59$^{\circ}C$. The results of isotherms and velocity vectors have been represented, and the numerical results showed a good agreement with experimental values. Based on the numerical results, the mean Nusselt number of the rectangular enclosure wall could be expressed as a function of Grashof number.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제26권2호
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• pp.205-220
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• 2012

이 연구에서는 수렴하는 자연 수 수열의 사례를 구성하는 것을 목표로 특별한 패턴의 자연수 수열을 찾아 연구하였다. 자연수 수열의 수렴과 관련하여 다음 두 가지를 조사 분석하였다. 첫째, 극한에 대한 일상의 언어지만 수학적 의미를 내포한 고등학교 직관적 정의를 자연수 수열의 수렴성에 대한 이해의 토대가 되는 상수 수열을 포함한 기본적인 수열들에 어떻게 적용하는지를 수학교육전공의 대학생을 중심으로 살펴보았다. 둘째, 자명하지 않으며 특수한 패턴을 가진 수렴하는 자연수 수열의 사례로 전자항의 각 자릿수의 제곱의 합이 후자항을 결정하는 자연수 수열들에서 찾았다. 이 수열들의 탐구를 위해 꼬리의 개념을 사용하였고, 지필의 환경에서 이 수열들의 극한과 관련된 속성들이 쉽게 관찰되지 않아 원활한 탐색을 위해 스프레드시트를 활용하였다. 여기서 스프레드시트는 실험과 관찰을 도모하고 수학적 패턴의 발견을 도울 뿐 아니라 추론과 증명을 뒷받침하는 자료 추출의 도구가 될 수 있다는 시사점올 준다.

• Journal of Forest and Environmental Science
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• 제36권4호
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• pp.290-297
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• 2020

This study analyzed and compared the damage rate, natural parasitic rate, and the morphological characteristics of Thecodiplosis japonensis larvae, which inhabit forest areas as control areas to large urban areas in 2018 and 2019. This research was conducted to provide basic data for the management of Thecodiplosis japonensis, which harm pine needles, and the results were as follows. First, the gall formation rate of Thecodiplosis japonensis collected from urban areas was upper-crown 35.59% and 34.25%, mid-crown 25.57% and 27.95%, and lower-crown 25.34% and 26.61%; the gall formation rate of Thecodiplosis japonensis was in the order of upper-crown>mid-crown>lower-crown in 2018 and 2019, respectively. In the control areas, the gall formation rates of Thecodiplosis japonensis in mountain villages in 2018 and 2019 were upper-crown 17.72% and 21.78%, mid-crown 13.85% and 16.97%, and lower-crown 15.12% and 15.79%; thus, in the order of upper-crown>lower-crown>mid-crown. The number of larvae in the galls of needles damaged by Thecodiplosis japonensis was as follows: the average number of larvae in the pine trees of urban areas was 9 and 8 in the upper-crown, 7 and 8 in the mid-crown, and 6 and 7 in the lower-crown respectively. This shows that the number of larvae was fewer in the lower-crown than the upper-crown, and that the number of larvae was higher in 2018 than in 2019. For natural parasitic rate of Thecodiplosis japonensis, the gall formation rate and natural parasitic rate of Thecodiplosis japonensis were surveyed; the natural parasitic rate was 12.5% and 11.8% in urban areas while the rate was 21.7% and 20.9% in mountain villages in respectively in 2018 and 2019.

• 대한기계학회논문집
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• 제17권9호
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• pp.2304-2314
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• 1993

Natural convective flow and heat transfer in a two-dimensional square enclosure fitted with a horizontal partition are investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was situated perpendicularly at the one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were carried out with the variations of length, position and thermal conductivity of the partition, and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). As the results, an oscillatory motion of natural convection is resulted in a sudden rise of overall heat transfer, but the increase of length of partition is significantly restrained the increase of Nusselt number. The maximum heat transfer was shown just before the transition of the direction of oscillating flow. An oscillatory motion of flow was perfectly shown the stability with the decrease of the length of partition and Rayleigh number. Also, the heat transfer was raised with the increase of the thermal conductivity in proportion to the increase of the length of partition. The stability and oscillation of flow are affected by the position of partition.

• 설비공학논문집
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• 제18권9호
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• pp.722-728
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• 2006

Natural convection flows in a cubical air-filled slanted cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$, respectively, the remaining four faces having a linear variation from $T_c\;toT_h$ are numerically simulated by a solution code (PowerCFD) using unstructured cell-centered method. Special attention is paid to three-dimensional flow and thermal characteristics according to a new orientation (diamond type) for the cubical-cavity benchmark problem in natural convection. Comparisons of the average Nusselt number at the cold face are made with experimental benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the laminar convection in a cubical air-filled slanted cavity with differentially heated walls.