• 터널과지하공간
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• 제12권3호
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• pp.220-228
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• 2002

절리암반에서의 열유동을 수치해석적으로 분석하였다. 1차원 모델 해석을 통하여 한 조의 절리군이 열전도에 미치는 영향을 비교 분석하고, 이론해와 비교하였다. 절리 내에 물이 전혀 없는 경우, 절리는 열 차단제의 역할을 하며 정상상태에서도 온도의 불연속이 관찰되었다. 따라서 암반 내 존재하는 절리가 완전 건조상태인 경우에는 개별적인 절리의 열차단 효과를 일일이 고려하여야 정확한 결과를 얻을 수 있다 그러나 절리 내에 물이 부분적으로 혹은 완전히 포화된 경우에는 열차단 효과가 현저히 줄어들어 온도 분포에 미치는 영향이 현저히 감소하였다. 따라서 절리 암반을 통한 열전도는 암반을 무결암의 열적 성질과 불연속면의 열적 성질을 포함한 열적 이방성 연속체로 가정함으로써 가능하다 할 수 있다. 절리의 포화 정도가 증가할수록 절리가 열유동에 미치는 영향이 감소하므로 암반의 열전달 특성은 등방에 가까워지며, 따라서 복잡한 모델을 이용한 해석보다는 현지 암반의 열물성을 정확히 측정하는 것이 더욱 중요함을 알 수 있었다.

• Membrane and Water Treatment
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• 제1권3호
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• pp.171-179
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• 2010

The transport of selected salts of sulphuric acid (cobalt, copper, iron(II), manganese, nickel and zinc sulphate) through an anion-exchange membrane Neosepta-AFN was investigated in a counter-current continuous dialyzer at various salt concentrations and volumetric liquid flow rates. The basic transport characteristics - the rejection coefficient of salt and the permeability of the membrane - were calculated from measurements at steady state. The salt concentration in model mixtures was changed in the limits from 0.1 to 1.0 kmol $m^{-3}$ and the volumetric liquid flow rate of the inlet streams was in the limits from $8{\times}10^{-9}$ to $24{\times}10^{-9}m^3\;s^{-1}$. Under the experimental conditions given, the rejection coefficient of salts tested was in the range from 65% to 94%. The lowest values were obtained for iron(II) sulphate, while the highest for copper sulphate. The maximum rejection of salt was reached at the highest volumetric liquid flow rate and the highest salt concentration in the feed. The permeability ($P_A$) of the Neosepta-AFN membrane for the individual salts was in the range from $0.49{\times}10^{-7}m\;s^{-1}$ to $1.8{\times}10^{-7}m\;s^{-1}$ and it can be described by the following series: $P_{FeSO_4}$ < $P_{NiSO_4}$ < $P_{ZnSO_4}$ < $P_{CoSO_4}$ < $P_{MnSO_4}$ < $P_{CuSO_4}$. The permeability of the membrane was strongly affected by the salt concentration in the feed - it decreased with an increasing salt concentration.

• KSBB Journal
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• 제17권2호
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• pp.182-188
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• 2002

푸마르산으로부터 숙신산 생물전환을 위하여 E. faecalis RKY1을 HFBR에 친정화하여 연속생산 공정에 대한 가능성을 모색하였다. E. faecalis RKY1은 실관의 spongy 부분에 효과적으로 고정화되었으며, transverse mode로 HFBR 조업시 실관가닥이 50개 및 200개일 경우 거의 비슷한 경향을 나타냈다. 또한 배지의 공급속도를 0.25, 0.5, 1.0 mL/min로 증가시키면서 조업한 결과, 정상상태에 도달하는 시간이 각각 24, 12, 9시간으로서 유속이 증가할수록 정상상태에 도달하는 시간은 단축되었지만, 반응기 내의 기질 및 생성물 분포는 그 변화가 심하였다. 실관 생물반응기를 이용하여 숙신산 생물 전환시 배지의 공금 유속이 증가할수록 숙신산 생산성은 증가하였지만 전환수율이 감소하여 미반응 푸마르산은 증가하였다. 최대 숙신산 생산성 및 이 때의 수율은 푸마르산염 농도 80 g/L 및 배지 공금 유속 2.0 mL/min일 때 17.1 g/L ·hr 및 0.54 g/g이었으며, 최적 숙신산 생산성 및 이 때의 수율은 푸마르산염 농도 50 g/L 및 배지 공급 유속 1.0 mL/min일때 9.0 g/L · 및 0.90 g/g으로서 회분식 생물전환의 경우보다 더 우수하였다.

• 항공우주기술
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• 제8권2호
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• pp.140-148
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• 2009

발사체 추진시스템에서 CC(Combustion Chamber) 산화제 개폐밸브는 액체산소를 연소기로 공급 및 차단함으로써 연소를 개시 및 중단시킬 뿐만 아니라, 정상운영 상태에서는 연소기 내 안정된 연소가 가능하도록 일정한 유량의 액체산소를 공급한다. CC 산화제 개폐밸브 개발과 관련하여, TM(Technology Model)의 극저온 산화제 개폐밸브를 제작하여, 밸브의 정상적인 작동성능을 이미 확인한 바 있다. 반면 TM의 유량계수, Cv가 설계기준 값보다 상당히 작았기 때문에, 차기 개발 단계인 CC 산화제 개폐밸브 EM(Engineering Model)의 설계/제작을 통해 충분히 개선된 Cv 특성을 확보하기 위해 CFD 해석을 수행하였다. CFD 해석 결과, 밸브 출구 각도를 120o로 변경하고, 밸브의 부분적인 크기 증가와 스트록 길이를 증가시킴으로써 EM의 Cv를 상당히 향상시킬 수 있는 것으로 확인되었다. 유량시험을 통해 측정된 EM의 개선된 Cv는 최소 212로써, 기존 TM의 Cv값인 161보다 32%가량 증가된 것을 확인하였다.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.340-349
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• 2016

A coupled room system consists of adjacent rooms and apertures where the sound energy is exchanged between the two rooms. Acoustically, a coupled room system shows a non-exponential decay profile. Most of the related researches have been to analyze the acoustic properties of two-room coupled system so far whereas three-room coupled system were seldom studied. In this regard, this paper aims to analyse the distribution of sound pressure level, sound decay curve of three-room coupled system and sound energy flow between them by using the acoustic diffusion model and to further verify them through experiments. Firstly, the sound pressure level distribution and mean sound pressure level in the steady-state condition are analyzed at various frequencies and source locations. Good agreements are observed in both experiments and analysis results. Secondly, two double slope effect quantifiers of sound attenuation, LDT/EDT and LDT/T10 are compared at various frequencies and for different source locations. The result indicates that LDT/T10, less affected by the early reflection patterns than LDT/EDT, is more suitable to the analysis and experiments of a multi-slope sound decay curve. Lastly, the sound energy flow in each room is analyzed based on the acoustic diffusion model. After the early decay stage, the sound energy is observed to flow from the room with a long reverberation time to the room with a short one.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2007년도 학술발표회 논문집
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• pp.8-14
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• 2007

Water quality in Lake Rotorua, New Zealand, deteriorated since the 1960s because of excessive phytoplankton growths due principally to increasing nitrogen and phosphorus in the lake waters. Nutrient concentrations in eight of the nine major streams feeding Lake Rotorua have increased since 1965. The groundwater system has a key role in the hydrology of the Lake Rotorua catchment and the groundwater system is probably the control on the time delay between intensification of agricultural land use and response of surface water quality. All major, and many minor streams, in the catchment are fed by springs. Two lithological units are most important to groundwater flow in the Lake Rotorua catchment: Mamaku Ignimbrite, erupted in about 200,000 years ago and Huka Formation sediments which filled the caldera left by the Mamaku Ignimbrite eruption. Rainfall recharge to groundwater in the groundwater catchment of Lake Rotorua is estimated as approximately 17300 L/s. A calibrated steady-state groundwater flow model estimates that approximately 11100 L/s of this flow discharges into streams and then into the lake and the balance travels directly to Lake Rotorua as groundwater discharge through the lake bed. Land use has impacted on groundwater quality. Median Total Nitrogen (TN) values for shallow groundwater sites are highest for the dairy land use (5.965 mg/L). Median TN values are also relatively high for shallow sites with urban-road and cropping land uses (4.710 and 3.620 mg/L, respectively). Median TN values for all other uses are in the 1.4 to 1.5 mg/L range. Policy development for Lake Rotorua includes defining regional policies on water and land management and setting an action plan for Lake Rotorua restoration. Aims in the action plan include: definition of the current nutrient budget for Lake Rotorua, identification of nutrient reduction targets and identification of actions to achieve targets. Current actions to restore Lake Rotorua water quality include: treatment of Tikitere geothermal nitrogen inputs to Lake Rotorua, upgrade of Rotorua City sewage plant, new sewage reticulation and alum dosing in selected streams to remove phosphorus.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권3호
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• pp.41-50
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• 2015

Hydrogeologic environment of the Mega City such as Seoul, suffers from rapid changes caused by urbanization, construction of underground subway or buildings, and contaminant loading by diverse anthropogenic activities. Understanding the present condition of groundwater environment and water budget is necessary to prevent natural and manmade disasters and to prepare for sustainable water resource management of urban environment. In this study, regional groundwater flow and water budget status of Seoul was analyzed using numerical simulation. Modeling result indicated that groundwater level distribution of Seoul generally followed the topography, but the significant decreases in groundwater level were observed around the subway network. Steady-state water balance analysis showed groundwater recharge by rainfall and leakage from the water supply network was about 550,495 m³/day. Surface water inflow and baseflow rate via Han River and major streams accounted for 799,689 m³/day and 1,103,906 m³/day, respectively. Groundwater usage was 60,945 m³/day, and the total groundwater leakage along the subway lines amounted to 114,746 m³/day. Modeling results revealed that the subway could decrease net groundwater baseflow by 40%. Our study result demonstrated that the subway system can have a significant influence on the groundwater environment of Seoul.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.941-951
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• 2016

The aim of this work is to simulate the thermohydraulic consequences of a main steam line break and to compare the obtained results with Rossendorf Coolant Mixing Model (ROCOM) 1.1 experimental results. The objective is to utilize data from steady-state mixing experiments and computational fluid dynamics (CFD) calculations to determine the flow distribution and the effect of thermal mixing phenomena in the primary loops for the improvement of normal operation conditions and structural integrity assessment of pressurized water reactors. The numerical model of ROCOM was developed using the FLUENT code. The positions of the inlet and outlet boundary conditions and the distribution of detailed velocity/turbulence parameters were determined by preliminary calculations. The temperature fields of transient calculation were averaged in time and compared with time-averaged experimental data. The perforated barrel under the core inlet homogenizes the flow, and therefore, a uniform temperature distribution is formed in the pressure vessel bottom. The calculated and measured values of lowest temperature were equal. The inlet temperature is an essential parameter for safety assessment. The calculation predicts precisely the experimental results at the core inlet central region. CFD results showed a good agreement (both qualitatively and quantitatively) with experimental results.

• Journal of Pharmaceutical Investigation
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• 제41권3호
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• pp.161-171
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• 2011

The objective of the present study is to systematically characterize a linear viscoelastic behavior of petroleum jelly in small amplitude oscillatory shear flow fields correspondent to the rheological ground state. With this aim, using a strain-controlled rheometer, the dynamic viscoelastic properties of commercially available petroleum jelly have been measured at $37^{\circ}C$ (body temperature) over a wide range of angular frequencies at an extremely small strain amplitude of 0.1 %. In this article, the linear viscoelastic behavior was reported in detail and then explained from a structural view-point of petroleum jelly and discussed in depth with respect to the consumer's requirements. Main findings obtained from this study can be summarized as follows : (1) The storage modulus is always greater than the loss modulus over an entire range of angular frequencies studied, meaning that the linear viscoelastic behavior of petroleum jelly is dominated by an elastic nature rather than a viscous nature. (2) Petroleum jelly shows a desirable linear viscoelastic behavior with respect to the consumer's requirements because it is undesirable for the product to flow down from the skin at an initial stage upon contact with the human skin. (3) A fractional derivative model shows an excellent applicability to describe a linear viscoelastic behavior of petroleum jelly. However, this model should be used with a special caution because there exists no physical meaning for the model parameters. (4) A modified form of the Cox-Merz rule gives a good ability to predict the relationship between steady shear flow properties (nonlinear behavior) and dynamic viscoelastic properties (linear behavior) for petroleum jelly.

• 한국수소및신에너지학회논문집
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• 제27권6호
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• pp.764-772
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• 2016

This paper presents on the evaluation of numerical analysis model of a ball valve used for a gas pipeline. The ball valve has important role to control the gas flow of the pipeline as well as safety operation to prevent gas explosion at the emergency. For the validation of numerical simulation, the computational domains are introduced three different types: a hexahedron chamber connected to a pipeline outlet without considering the geometry of pressure tubes, a pipeline only considered the geometry of pressure tubes, and a pipeline connected both of the a hexahedron chamber and pressure tubes. The commercial code, SC/Tetra, is introduced to solve the three-dimensional steady-state Reynolds-averaged Navier-Stokes analysis in the present study. The valve flow coefficient and valve loss coefficient with respect to the valve opening rate of 30%, 50%, and 70% are compared with experimental results. Throughout the numerical analysis for the three analysis domains, pressure computed along the pipeline is affected by computational domains. It is noted pressure obtained by the computational model considering both of the a hexahedron chamber and pressure tubes has a relatively good agreement to the experimental data.