• 한국산림과학회지
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• 제106권4호
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• pp.480-486
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• 2017

본 연구는 국내 소나무, 잣나무, 낙엽송을 대상으로 입목의 총재적 중 상부직경 혹은 상부수고까지의 재적을 예측하는 이용재적모델을 개발하고자 수행되었다. 모델개발을 위하여 사용된 자료는 강원 및 경북지역의 소나무림, 잣나무림, 낙엽송림에서 수집한 총 131본의 수간석해목이었으며, 이용재적비율, 단순비율형태, 지수비율형태의 6개 이용재적식을 검토하여 최종모델을 개발하였다. 본 연구의 분석결과, 상부직경까지의 이용재적예측은 지수비율형태인 $V_d=V_t\{{\exp}[{\alpha}_1(d^{{\alpha}_2}/D^{{\alpha}_3})]\}$ 이 상부수고까지의 이용재적예측은 단순비율형태인 $V_h=V_t\{1+{\beta}_1(P^{{\beta}_2}/H^{{\beta}_3})\}$이 최종모델로 선정되었다. 본 연구에서 선정된 2개의 최적모델식을 정리하여 내재간곡선식을 도출하였으며, 이를 활용해 상부직경에 따른 상부수고와 상부수고에 따른 상부직경 예측이 가능하였다. 본 연구결과에서 개발된 모델은 높은 정확도뿐만 아니라 임업현장에서 편리하게 사용할 수 있어 활용도가 높을 것으로 판단된다.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.352-357
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• 2016

An investigation of ribbed divergent channel was undertaken to determine the effect of rib pitch to height ratio on total friction factor and heat transfer results in the fully developed regime. The ribbed divergent rectangular channel with the channel exit hydraulic diameter ($D_{ho}$) to inlet channel hydraulic diameter ($D_{hi}$) ratio of 1.16 with wall inclination angle of 0.72 deg, at which the ratios (p/e) of 6,10, and 14 are considered. The ribbed straight channel of $D_{ho}/D_{hi}=1.0$ were also used. The ribbed divergent wall is manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (p) to height 6, 10, and 14. The measurement was run with range of Reynolds numbers from 24,000 to 84,000. The comparison shows that the ratio of p/e=6 has the greatest thermal performance in the divergent channel under two constraints; identical mass flow rate and identical pressure drop.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.361-364
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• 2002

This paper discusses the influencing factors such as coring position, height to diameter ratio of core specimen(h/d) and coring torque on the strength estimation of concrete by small site coring method in order to verify the validities of small size core method. According to results, as for the influence of drilling position, when core specimens are obtained from the place parallel to placing direction, compressive strength of core specimens are higher than those perpendicular to placing direction. This is due to the loss of the area of core specimen perpendicular to plating direction by bleeding. And in case of $\phi$ 24mm core specimen, when vertical drilling against placing direction is taken. compressive strength of core specimen obtained at the bottom of the structure is higher than that at the top of the structure. As for the influence of height to depth ratio, as h/d ratio increases compressive strength shows to be decreased. As for the influences of rotation speed of drilling machine, as its speed goes up, compressive strength decreases, regardless of core diameter.

• 한국전산유체공학회지
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• 제15권3호
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• pp.16-23
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• 2010

Shape optimization of an upper plenum of a PBMR type gas cooled nuclear reactor has been performed by using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) analysis and surrogate modeling technique. The objective function is defined as a linear combination of uniformity of flow distribution in the core and pressure drop in the upper plenum and the core. The ratio of thickness of slot to diameter of rising channels, ratio of height of upper plenum to diameter of rising channels, and ratio of height of the slot at inlet to outlet, are used as design variables for optimization. Design points are selected through Latin-hypercube sampling. The optimal point is determined through surrogate-based optimization method which uses 3-D RANS analyses at design points. The results show that the optimum shape represent remarkably improved performance in flow uniformity and friction loss than the reference shape.

• Journal of the Korean Wood Science and Technology
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• 제43권2호
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• pp.145-155
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• 2015

Fiber morphology and basic characteristics of Legi bamboos (Gigantochloa atter) growing on Yogyakarta were studied considering their age and height positions in the culms. Culms of 4, 16, and 40 months were harvested, and their total lengths were measured. The length, diameter, and wall thickness of each internode were measured. All the sample culms were divided into three different parts along the height, and their fiber dimension and physical properties were observed. The data obtained were analyzed by analysis of variance. The results showed that the culms had a diameter of 5.8 to 10.8 cm. The lowest internodes always showed the shortest length and the thickest wall. The culms had an average fiber length of 2.41 mm and Runkel ratio of 0.61. Fiber length was affected by the height, while fiber diameter, lumen diameter, and fiber wall thickness were affected significantly by the age of the culms. The culms had high green moisture content (GMC) of 157.89%, and basic density (BD) of $456.67kg.m^{-3}$, a total longitudinal shrinkage of 0.35%, and relatively low R/T shrinkage ratio. The interactions between age and height were affected GMC and BD.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2211-2218
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• 2003

The present study investigates heat/mass transfer characteristics in a rotating two-pass duct for smooth and ribbed surfaces. The duct has an aspect ratio of 0.5 and a hydraulic diameter of 26.67 mm. 70-angled rib turbulators are attached on the leading and trailing sides of the duct in parallel and cross arrangements. The pitch-to-rib height ratio is 7.5 and the rib height-to-hydraulic diameter ratio is 0.075. The Reynolds number based on the hydraulic diameter is constant at 10,000 and the rotation number ranges from 0.0 to 0.2 Detailed local heat/mass transfer coefficients are measured using a naphthalene sublimation technique. The results show that the secondary flows generated by the $180^{\circ}-turn$, rib turbulators, and duct rotation affect the wall heat/mass transfer distribution significantly, As the duct rotates, the rotaion-induced Coriolis force deflects the main flow and results in differences on the heat/mass transfer distribution between the leading and trailing surfaces. Its effects become more dominant as the rotaion number increases. Discussions are presented describing how the rib configuration and the rotaion speed affect the flow patterns and local heat/mass transfer in the duct.

• 생물환경조절학회지
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• 제16권2호
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• pp.142-145
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• 2007

몇 수종을 대상으로 한 용기 양묘에서 폐암면 혼합 배지 이용 시 폐암면과 다른 배지의 혼합 비율에 따른 생육 특성을 조사하였다. 폐암면 혼합 비율에 따른 소나무의 생육 특성에서 생체중, 건물중 및 수고는 50% 와 70% 혼합배지에서 기장 좋았지만 원줄기 직경은 차이를 나타내지 않았다. 비자나무에서 생체중과 수고는 70% 혼합배지에서 가장 많이 증가하였고 원줄기 직경과 신초수는 50% 와 70% 혼합배지에서 많이 증가하였다. 상수리나무에서 생체중, 수고 및 원줄기 직경은 50%와 70% 혼합배 지에서 좋았고, 건물중은 혼합배지와 대조구간 차이를 나타났으나 혼합 비율간에는 차이를 나타내지 않았다. 잎의 엽록소 함량도 70% 혼합배지에서 높게 나타났으며 이에 광합성도 가장 활발하였다. 들메나무에서 생체 중은 70% 혼합배지에서 월등히 많이 증가하였지만, 수고와 원줄기 직경은 폐암면 혼합배지와 대조구 간 차이만 나타나고 혼합 비율간에는 차이를 나타내지 않았다. 잎의 엽록소 함량은 처리 간 차이를 나타내지 않았지만 혼합 배지에서 다소 높은 경향을 나타내었지만, 광합성은 70% 혼합배지에서 아주 활발하였다.

• 공업화학
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• 제9권6호
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• pp.901-906
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• 1998

기체분산기로 단일노즐을 사용한 내부순환 공기리프트 반응기에서 기체 및 액체의 유동특성을 해석하였다. 실험은 공기-물계에서 하강관의 직경과 상승관의 높이가 다른 세 가지 반응기를 사용하여 기체속도와 반응기의 높이를 변화시키면서 각 유동지역의 기체체류량과 추적자의 충격-응답곡선을 측정하였다. 실험결과, 기포의 유동양상은 상승관에서 강한 기포합체를 일으키는 슬러그흐름을, 그리고 하강관에서는 직경의 크기에 따라 전이흐름 또는 균일상 기포흐름을 나타내었다. 그리고 동일한 반응기 상부지역의 높이비에서 각 유동지역과 반응기 전체의 평균 기체체류량은 하강관의 직경이 작을수록 상당히 증가하였다. 또한 혼합시간은 기체속도보다 반응기 상부지역의 높이에 크게 영향을 받으며 동일한 반응기 상부지역의 높이비에서는 하강관의 직경과 상승관의 길이가 클수록 상당히 큰 값을 나타내었다. 액체의 유동특성은 하강관에서 기포의 유동양상과 반응기 상부지역의 크기에 따라 크게 변화하였으며 상승관에서 액체의 순환속도는 기체속도와 반응기 상부지역의 크기가 증가할수록 증가하였고 동일한 반응기 상부지역의 높이비에서는 하강관의 직경과 상승관의 길이가 증가할수록 증가하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.270-273
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• 2003

The characteristic of constant volume micro combustor was investigated experimentally. The shape of micro combustor was cylindrical and has row aspect ratio or has relatively large diameter compared with chamber height. Diameter and chamber height was varied to investigate the geometric effect of combustor on the flame propagation. Diameter of 15 mm and 7.5 mm was designed while chamber height was designed to be 1mm, 2mm, and 3mm. The effect of initial pressure was also investigated parametrically from 1bar to 3bar. The gas used in this study was stoichiometric mixture of methane and air. The maximum pressure achieved in down scaled combustors was lower than that of conventional combustor because heat loss to wall was dominant as expected. The maximum pressure responded favorably with the change of height of combustor and the initial pressure, the maximum pressure was also increased. The flame propagation was possible when the specific condition was satisfied. Although the quenching distance of stoichiometric mixture of CH4 and Air is 2.5 mm, the flame could propagate even under quenching distance as the initial pressure increased.

• 대한기계학회논문집B
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• 제29권1호
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• pp.55-62
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• 2005

Combustion Characteristics and quenching criteria of micro combustor in various condition was exploited experimentally. Two different gases were used, and various geometric matrixes were considered to figure out quenching characteristic of micro combustor. The micro combustor studied in this study was constant volume, and has cylindrical shape. Geometric parameter of combustor was defined to be combustor height and diameter. The effect of height was exploited parametrically as 1 mm, 2mm and 3mm and the effect of diameter was parameterized to be 7.5mm and 15mm. Three different combustibles. (1) Stoichiometric mixture of methane and are, (2) Stoichiometric mixture of hydrogen and air and (3) Mixture of hydrogen and air with fuel stoichiometry of two were used. Pressure transition during combustion process was recovered. The ratio of maximum pressure to initial pressure responded favorably with the change of height of combustor and the initial pressure, the maximum pressure was also increased. The flame propagation was observed only when a specific condition was satisfied. From the experiment the condition that guarantees stable propagation of flame was tabulated. The tabulated results includes criteria of quenching according to combustor height, combustor diameter, species of fuel and initial pressure.