• Journal of Biosystems Engineering
• /
• 제36권6호
• /
• pp.444-452
• /
• 2011

In this study the characteristics of natural ventilation of Venlo-type greenhouse with continuous roof vents were analyzed using commercial computational fluid dynamics (CFD) code. Developed CFD simulation model was verified by comparison with experimental data. Simulation errors were 1.9-46.0% for air velocity and 1.7-11.2% for air temperature at each measurement point. CFD simulations were conducted to estimate the effect of roof vents opening direction, opening angle, outside wind velocity and wind directions on ventilation rate and climate condition in greenhouse. The results of this study showed that ventilation rate of the present greenhouse was increased linearly in proportion to the increase of roof vent opening angle and outside wind velocity over 2.0 m/s. According to the analysis on the effects of different roof vent opening direction, simultaneous opening of wind and leeward vents showed the highest ventilation rate and lowest mean temperature in greenhouse.

• 한국구조물진단유지관리공학회 논문집
• /
• 제15권2호
• /
• pp.179-188
• /
• 2011

강부재의 피로가 주요원인이 되어 구조물이 붕괴되거나 교체되는 사례를 찾아보기 어렵다. 이처럼 사실상 피로에 대해서는 손상을 허용하고 있지만, 발견되는 피로균열에 대한 직접적인 상태평가는 이루어지지 않고 있다. 피로균열에 대한 진전 비진전성의 판단 및 균열진전속도의 평가가 이루어져야만, 합리적인 보수 보강 공법의 선정과 시행시기가 결정될 수 있을 것이다. 본 연구에서는 측정되는 COD(Crack Opening Displacement)를 통한 피로균열진전속도 평가법을 검토하기 위하여, 2종류의 관통 균열 시험편과 면외거셋 용접이음 시험편의 균열진전시험을 실시하였다. 그리고 실용적인 COD의 측정을 위해 변형률 게이지를 이용하는 방법에 대해 검토하였다. 그 결과, COD 측정을 통한 균열진전속도의 합리적인 평가법을 제안하였고, 변형률 게이지를 이용한 성공적인 COD 측정을 실험적으로 증명하였다.

• 한국수소및신에너지학회논문집
• /
• 제29권4호
• /
• pp.370-377
• /
• 2018

Ball valve has been widely used in the field of high-pressure gas pipeline as an important component because of its low flow resistance and good leakage performance. The present paper focuses on the flow nature at the downstream of the ball valve used for gas pipelines according to valve opening rates. Steady 3-D RANS equations, SC/Tetra, have been introduced to analyze the flow characteristics inside the ball valve. Numerical boundary conditions at the inlet and outlet of the valve system are imposed by mass flow-rate and pressure, respectively. Velocity distributions obtained by numerical simulation are compared with respect to the valve opening rates of 30, 50, and 70%. Cavity distributions, asymmetry flow velocity and the flow stabilization point at each opening rate are also compared. When the valve opening rates are 30 and 50%, the flow stabilization requires the sufficient length of 10D or more due to the influence of the recirculation flow at the downstream of the valve.

• 대한기계학회논문집
• /
• 제19권4호
• /
• pp.908-917
• /
• 1995

The constant .DELTA.K fatigue tests are performed in SS41 and its weldments to investigate crack opening behavior and fatigue crack propagation behavior at each parts of weldment and its boundary layer. The weldments were annealed after welding for the purpose of relieving residual stress. Every weldments has notch at weld metal zone, and fatigue crack propagates from weld metal zone to vase metal zone perpendicular to weld line. The Laser ISDG method is used in order to determine the crack opening ratio, this method is more precise than indirect measurement method, and faster and easier than other direct measurement method.

• 설비공학논문집
• /
• 제20권2호
• /
• pp.121-127
• /
• 2008

This paper investigates the effects of outdoor pressure fluctuations on natural ventilation through an opening on a building envelope. The ventilation airflow rate depends on the magnitude and the period of the pressure fluctuations, the size of the opening relative to the space volume, and the resistance characteristics of the opening. Non-dimensional parameters have been derived, which determine indoor pressure responses due to outdoor pressure fluctuations. The flow regions are categorized into (1) synchronized region, (2) opening resistance region, and (3) transition region depending on the non-dimensional parameter derived. Pressure fluctuations and flow characteristics are investigated numerically using the 4th order Runge-Kutta method.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2020년도 봄 학술논문 발표대회
• /
• pp.216-217
• /
• 2020

As the fire inside the building grows rapidly, ejected flame from an opening occurs due to flashover. As a result, the number of cases where the flame spreads to the exterior of the building and rapidly expands to the upper floor is increasing. In particular, in the case of the fire in the Daebong Green Apartment, Uijeongbu in 2015, it was a case where the flame spread to adjacent buildings due to the opening eruption flame from the first ignited building, causing great damage to three apartments. Therefore, this study is to introduce an international standard under development that estimates the shape and properties of the ejected flame from an opening and quantitatively evaluates the radiant heat flux received by the exterior wall of the building by assuming the occurrence of the ejected flame from an opening.

• 한국분무공학회지
• /
• 제21권1호
• /
• pp.20-28
• /
• 2016

This paper presents an experimental study on the GDI injector with Bosch method. The injection characteristics, such as the injection quantity, the injection rate, the maximum velocity of the nozzle exit and the injection delay were studied through the change of the injection pressure, the tube pressure and energizing duration in injection rate measurement device using nheptane. The injection quantity is increased by increasing injection pressure, decreasing tube pressure or increasing energizing duration. As the difference of the injection quantity changed, the shape of injection rate was moved with a constant form. The maximum velocity of the nozzle exit showed a tendency to increase as the injection pressure is increased. However, tube pressure did not affect. Overall, it was confirmed that the closing delay is longer than the opening delay in all conditions. As the injection pressure increased, the result has a tendency to decrease the closing delay, it did not affect the opening delay. Reduction of the closing delay showed the reduction of the injection duration. the tube pressure and energizing duration did not affect the injection delay (opening delay, closing delay).

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2001년도 추계학술대회 논문집
• /
• pp.263-268
• /
• 2001

The constant .DELTA. K fatigue tests are performed in SS41 and its weldment. The LASER ISDG method is used in determination of crack opening ratio. This method is more precise than indirect measurement method, faster and easier than other direct measurement method. And obtained results are followed 1) Crack opening ratio U is proportional to fatigue crack growth rate da/dN at constant .DELTA. K 2) Fatigue crack growth rate da/dN in weldment increases in weld metal and heat affected zone, decreases in base metal as crack grows.

• 한국응용곤충학회지
• /
• 제56권3호
• /
• pp.253-259
• /
• 2017

이산화염소 훈증 처리는 저곡해충에 대한 방제 가능성을 가지고 있다. 특히 체내로 독성 가스의 침투력을 높이기 위해 기문의 개방화를 유도하면 이 훈증 가스 처리 효과를 증가시킬 수 있다. 이 가설을 증명하기 위해 본 연구는 이산화염소 훈증 처리에 감수성을 보이는 화랑곡나방(Plodia interpunctella)을 대상으로 기문 개방 활동을 분석하였다. 화랑곡나방 유충의 기문은 모두 9쌍으로 앞가슴에 1쌍 그리고 복부에 8쌍을 각각 지니고 있다. 이들은 몸 내부에 가로 및 세로기관지와 연결된 구조를 지녔다. 기문 개방 유무는 염색액 침투 방법으로 판정하였으며 이를 토대로 분석한 결과 주변 온도 증가에 따라 기문 개방화는 약 60% 까지 증가하였다. 특히 이산화탄소에 노출되면 기문개방화는 약 95%까지 증가하였다. 반면에 이산화염소에 노출되면 화랑곡나방 유충의 기문은 대부분 닫혀 기문개방율이 약 25%로 줄었다. 이산화염소 처리에 이산화탄소를 추가한 결과 기문개방율은 이산화탄소 단독 처리만큼 크게 증가하였다. 이를 토대로 두 혼합 가스를 처리하여 살충효과를 분석한 결과 이산화염소 단독 처리에 비해 혼합처리가 현격하게 높은 살충력을 나타냈다.

• 환경생물
• /
• 제20권4호
• /
• pp.386-390
• /
• 2002

소나무 구과의 열개현상을 비교형태학적 형질을 통해 관찰하였다. 어린 구과에서는 조직의 분화가 완전하게 일어나지 않았지만 각 기관으로 분화되는 과정임을 알 수 있었다. 성숙한 구과와 동일 크기의 녹색 구과에서 유관속다발과 보강조직의 수축률은 각각 1.0∼l.5%와 14.0∼l6.0%였다 실편의 종단부는 유조직과 보강세포로만 구성되어 있었고, 중앙부는 종단부와 기부 두께가 비슷하였다. 기부는 실편과 실편 받침이 있어 더욱 두꺼웠으며, 유관속다발보다 보강조직이 2배 이상 두껍게 나타났다. 결론적으로 구과가 완전 성숙하여 건조됨에 따라, 종단부는 보강조직으로만 구성되어있어 조직내 수축만 일어나고 중앙부는 두 조직간 두께가 비슷해 밖으로 휘지 않는다. 그러나 실편내 기부에서 배축면에 위치한 보강조직이 두껍고, 유관속다발보다 보강조직에서 수축률이 훨씬 크므로 실편의 기부가 밖으로 펴지게 되어 구과는 열개된다.