최근 대기환경 및 난류해석분야에 관심을 받고 있는 대와류모사(LES)는 그 적용분야도 다양하다. 특히 LES를 이용한 난류 유동장 해석 시, 실제와 유사한 난류의 특성을 지니고 있는 입구조건을 부여하면 해석 도메인 내에서 실제 난류를 보다 빠르게 생성시 킬 수 있다. 본 연구에서는 LES를 이용한 해석으로 난류경계층을 수치해석 도메인 내에 빠르게 생성시킬 수 있도록 하기 위해 입구 조건으로 기존에 많이 적용하는 방법 중 하나인 합성법(synthesis method)이 이용되었고, 수치해석 도메인 내에 만들어진 난류특성들을 기존의 연구결과들과 비교하였다. 입구에 유입되는 몇몇 유동특성들은 기존의 연구결과와 동일한 값을 입력할 수 있으나 유동방향의 길이크기는 쉽지 않다. 그로인해 기존의 연구결과들과 비교하였을 때, 채널 내에서 발달한 난류특성들은 약간의 차이를 나타내지만 유입데이터와 큰 차이는 나타나지 않았다. 또한, 본 합성법을 통한 난류 입구유동의 길이크기에 따른 응답특성을 확인하기 위하여, 폭방 향으로 다양한 길이스케일 변화를 주어 그 특성을 확인하였다. 그 결과, 폭방향의 길이스케일이 커질수록 벽면의 전단응력의 회복이 빨라졌으며, 이는 난류경계층의 발달이 빨라지는 것을 의미한다.

PURPOSES: In this paper, the applicability of DEM to a coarse graining method was evaluated by simulating a series of minicone tests for cement pasteMETHODS: First, the fundamental physical quantities that are used in a static liquid bridge model were presented with three basic quantities based on the similarity principle and coarse graining method. Then, the scale factors and surface tensions for six different sizes of particles were determined using the relationship between the physical quantities and the basic quantities. Finally, the determined surface tensions and radii were utilized to simulate the fluidal behavior of cement paste under a minicone test condition, and the final shape of the cement paste with reference DEM particle radii was compared with the final shape of the others.RESULTS : The simulations with adjusted surface tensions for five different radii of particles and surface tension showed acceptable agreement with the simulation with regard to the reference size of the particle, although disagreement increases as the sizes of the particle radii increase. It seems reasonable to increase the particle radii by at least 0.196 cm considering the computational time reduction of 162 min.CONCLUSIONS: The coarse graining method based on the similarity principle is applicable for simulating the behavior of fluidal materials when the behavior of the materials can be described by a static liquid bridge model. However, the maximum particle radius should be suggested by considering not only the scale factor but also the relationship of the particle size and number with the radius of the curve of the boundary geometry.

평관형 알루미나 세라믹 멤브레인을 적용한 실험실 규모의 단독 혐기성 유동상 멤브레인 생물반응기에서 알루미나 세라믹막과 비흡착성 PET구형입자를 유동메디아로 적용하여 평균 유입 COD 250 mg/L를 포함하는 합성폐수를 적용하여 상온에서 유기물 제거효율과 파울링 현상을 관찰하였다. 약 250일 연속운전에서 약 10 L/m2.hr 투과플럭스가 달성되었다. 운전기간 동안 약 80% COD 제 거율을 나타내었고 0.075 kWh/m3 운전에너지가 요구되었고 이는 생산되는 메탄발생 전기에너지의 약 30%에 해당되었다. 실험결과는 GAC를 유동메디아로 사용한 동일 반응기의 결과와 비교분석하였다.

The planetary gearing system is compact and lightweight. The performance of planetary gearing system which uses floating intermediate rings have been found to be very good for practical systems. To apply this system for the reduction of rotation of an engine, in designing stage, the quantitative estimate of the load sharing factors is required for understanding the performance. The method widely used for this purpose is to make use of elastic deformation of components of the structure or to utilize hydrodynamic oil film. This paper shows the way how to analyze the static load sharing factors by using the coefficient ''. This method can be applied for non-linear systems such as oil film bearing. The influences of various factors on '' of oil film spring are also shown. Furthermore, It is established in this study that the use of floating intermediate ring in designing the planetary gearing system has a very high reliability.

It is necessary to develop a device for the design of wet scrubber with a more efficient deodorization performance in order to enhance the odor reducing effect of the wet scrubber. Therefore in this study, the superiority of the new wet scrubber with the centrifugal separation function different from the conventional wet scrubber was analyzed by the computational fluid dynamics. From CFD analysis, the pressure and velocity distribution, the peak vorticity, the retention time and the flow uniformity were calculated and compared with the performance characteristics of the centrifugal separator. As the results of CFD analysis, the peak vorticity and retention time of the gas flow were increased about 22% and the flow uniformity was improved about 7.2% by the centrifugal separator. Therefore the centrifugal separator in the wet scrubber will improve the deodorizing effect and the cleaning condition of the gas.

현장에서 양생 또는 고형화 과정을 거치는 일반 시멘트 콘크리트, 자가다짐 시멘트 콘크리트, 아스팔트 콘크리트, 고분자 개질 혼합물과 같은 도로포장 재료의 유동 특성은 시공시점에서의 환경조건과 함께 도로포장 구조물의 초기 성능을 결정하는 중요한 요소이다. 따라서 재료의 양생이 완료되는 시점까지 포설 및 다짐에 영향을 미치는 재료의 유동 특성을 검토하는 것은 기존 혼합 및 포설 장비의 개선뿐만 아니라 새로운 장비의 개발을 통한 시공과정 개선 및 최적화를 위해서도 매우 중요한 과정이라 할 수 있다. 또한 건축 또는 토목 구조물의 시공 및 유지관리에 활용되는 건설정보 모델링이 향후 부재의 역학적 거동과 연계된 시공 및 유지관리를 포함하는 통합적인 수준으로 발전될 것임을 고려할 때, 경험에서 벗어나 실험적으로 검증된 역학적 기반의 설계 및 시공 방법을 제시하는 것은 매우 중요한 의미를 갖는다. 건설재료의 유동은 그 최종 형태에 따라 순수전단 유동, 신장유동, 이들의 중간 정도에 해당하는 유동의 3가지로 구분하여 분석적 해를 유도할 수 있다. 그러나 분석적 해를 활용하는 방법은 비교적 단순한 경계조건에 대한 재료의 유동적 특성을 예측하는데 유용하게 활용될 수는 있으나, 경계조건이 복잡해질수록 해를 계산하는 것이 거의 불가능하여 컴퓨터를 활용한 수치해석 기법을 적용하는 것이 합리적이다. 한편 유동성 재료의 동적 거동을 해석하는 방법으로는 이산요소법이나 전산유체역학(computational fluid dynamics, CFD)을 활용할 수 있는데, 입자형 재료 사이에 존재하는 유체의 양이 상대적으로 적어 입자와 입자 사이 또는 입자와 경계조건과의 상호작용이 중요하게 고려되어야 할 경우에는 이산요소법이 바람직한 반면, 시멘트 페이스트와 같이 균질의 재료로서 연속체의 특성을 나타내는 경우에는 CFD를 활용하는 것이 바람직한 것으로 알려져 있다. 본 연구에서는 연속체로 가정할 수 있는 유동성 재료의 시간에 따른 거동을 예측하기 위한 CFD의 활용성을 평가하고자 하였다. 이를 위하여 미니콘 실험에 대하여 분석적 해와 CFD를 활용한 결과를 비교하여 수치해석에 활용된 가정과 모형의 타당성을 검증하였으며, 검증된 모형을 활용하여 주요 입력변수에 대한 민감도 분석을 수행하여 시간에 따른 재료의 슬럼프와 퍼진 정도의 변화를 확인하였다.

To improve dispersibility of cereal powder without additives, granulation of cereal powder was conducted using fluidized- bed granulator. Operation condition was sample 300 g, internal temperature 40°C, ventilation speed 30-90 m3/ h, inlet temperature 90°C and spray pressure 2.5 bar. The amount of distilled water (20-45%) as binder, granulation time (10-15 min) and drying time (3-10 min) were controlled. Mean diameter over volume (Brouckere mean, D4,3) was increased from 123 μm to 263 μm and dispersibility was improved from 73% to 92.25% at experiment conditions. Wettability (wetting time) was drastically decreased from 5,000 second to 7 second. Granulation of cereal powder did not affect sinkability and mean diameter over volume as wet analysis was about the same between raw and granulated cereals. Such phenomenon means that granulation with only water as binder enables cereal powder to disperse in water or milk without rapid sedimentation.

본 연구는 경주 중·저준위처분장 2단계 표층처분시설의 폐쇄 후 안전성에 대한 불확실성을 예측·평가하기 위하여 수행되 었다. 다중덮개와 처분고의 건전/열화를 고려한 총4가지의 시나리오를 도출하여 강우침투 시 예상되는 처분시설 내부의 유 체 이동을 모사하였다. 강우 조건은 총 30년(1985~2014) 간의 월평균 데이터를 적용하였으며, 시뮬레이션 기간은 제도적 관 리기간인 300년으로 설정하였다. 처분덮개와 처분고 콘크리트 모두 건전성을 유지하는 조건의 기본 시나리오 평가 결과, 처 분시설 내부의 처분고를 완전히 포화시키지 못하는 것을 확인할 수 있었다. 다중 덮개층을 구성하는 8개 층의 각 매질의 모 세관 압력과 투과도 차이로 인하여 다중 덮개층이 효과적으로 차수·배수 역할을 하는 것으로 나타났다.

In this study, the heat flow characteristics of wave heat exchanger was investigated by being applied to the white smoke reduction system. Through numerical analysis, the heat transfer and flow characteristics of the wave heat exchanger with the change of inlet condition of air-side and water-side were analyzed. To investigate the temperature, the absolute humidity, heat transfer rate, pressure drop and turbulence characteristics of the wave heat exchanger, the simulation analysis was conducted by using the commercial computational fluid dynamics software (Solidworks Flow Simulation) under uniform flow conditions. As the inflow rate of air decreased and the inflow temperature of water increased, the heat transfer coefficient of the wave heat exchanger decreased. When the experimental conditions of water-side were the same, the air outlet temperature and absolute humidity of the wave heat exchanger increased with increasing inflow rate of air. To reduce the white smoke, the air outlet temperature and absolute humidity of the wave heat exchanger must be reduced. Therefore, the lower the air velocity and the water inflow temperature into the wave heat exchanger, the more effective it is.

PURPOSES :In this paper, the flow of construction material was simulated using computational fluid dynamics in a 2D axisymmetric condition to evaluate the effect of initial or varying material properties on the final shape of a specimen.METHODS :The CFD model was verified by using a well-known analytical solution for a given test condition followed by performing a sensitivity analysis to evaluate the effect of material properties on the final shape of material. Varying dynamic viscosity and yield stress were also considered.RESULTS :The CFD model in a 2D axisymmetric condition agreed with the analytical solution for most yield stress conditions. Minor disagreements observed at high yield stress conditions indicate improper application of the pure shear assumption for the given material behavior. It was also observed that the variation of yield stress and dynamic viscosity during curing had a meaningful effect on the final shape of the specimen.CONCLUSIONS :It is concluded that CFD modeling in a 2D axisymmetric condition is good enough to evaluate fluidal characteristics of material. The model is able to consider varying yield stress and viscosity during curing. The 3D CFD-DEM coupled model may be required to consider the interaction of aggregates in fluid.

The diffuser is effective in closed systems, however, its effect is weaken in open or free flow situations. This can be solved by modifying the rear-end of the diffuser in a manner that enables the formation of strong vortex. By doing that, a large portion of fluid's energy is converted to vortex's dynamic energy, which results in the deduction of static component, or in other words, the decrease of pressure. This study involved the design of rear-end part for efficient hydrodynamic performance of shroud diffusers, and demonstrated with numerical simulation by computational fluid dynamics (CFD). This study focuses on the use of brim end for the shroud where the effect of brim's length and attaching angle are analyzed.

According to the structure, solenoid valve can be categorized as spool valve or poppet valve. While various research on spool valve which has simple structure and fine susceptibility to contamination has been conducted, poppet valve which has less susceptibility to contamination and advantage in a long time operation still need much research because of its complicated structure. In order to design the poppet valve, various parameters such as the diameter of the poppet, the angle of the poppet, the diameter of the disk, the spring stiffness, the spring preload and flow path structure should be considered. Conventional studies on poppet valve usually take only one design parameters and did not much focused on the effect of the parameters on flow characteristics. In this paper, the change of the flow characteristics according to the design parameters of the poppet valve for 3/2Way solenoid valve is analyzed. The previous studies and the results of initial model analysis was referred for the selection of the design parameters. The effects of design parameters on maximum pressure, minimum pressure, and pressure drop was examined using analysis of means(ANOM).