An AVL research engine, type 520, is modified to adapt to the 3.5L four-valve SI engine. With these given engine configurations, a test rig is constructed which allows easy changing of the different pistons and engine heads with a motoring capacity up to 3500 rpm. Nearly complete optical access to the inside of the cylinder is obtained by installing a transparent quartz cylinder on an AVL single cylinder engine. To avoid lubrication and to minimize scratches in the quartz cylinder the piston rings are made of Rulon-LD. With this experimental engine, researches for the in-cylinder flow characteristics by changing the induction system have been carried out using the laser based flow diagnostic techniques. In accordance with the previous result, it is evident that larger sized particles would be required in order to observe the flow characteristics of interest. The flow visualization taken with microballoon particles shows significant improvement. This provide detailed information.

This paper presents the flow analysis of flow over a cylindrical helical-blade turbine to investigate its optimum performance by varying design parameters. For numerical investigations, shear stress transport (SST) turbulence model is used. This simulation is carried out using commercial code CFX by ANSYS Inc. In this paper, the shape optimization was of turbine blades with NACA0021 performed for the vertical-axis turbine having the cylindrical shape. The influences of blade angle of attack, helical angle, and solidity on each shape are grasped. From of the flow analysis, power coefficient decreased when the helical angle was 20 degrees or more, and no electricity is produced when the solidity of 0.1. As a result of the shape optimization, the cylindrical turbine showed the highest power coefficient of 0.2733 at 3° of the blade angle of attack, 10° of the helical angle, and 0.2 of the solidity at the tip speed ratio of 1.

기존의 한방향 펌프는 순환과 배수를 위해 각각의 모터를 사용하지만, 양방향 펌프는 하나의 모터로 모터의 회전 방향에 따라 배수와 순환이 모두 가능하므로 원가절감이 가능하다. 하지만 양방향 펌프는 배수와 순환 시 펌프 케이싱 내부에서 역류와 흡입이 발생하여 유입된 물이 각각 배출구와 순환구로 원활하게 유출되지 못하는 단점이 있다. 본 연구에서는 주효과 분석을 통해 배출과 순환 시 유출되는 유량과 토크에 주요한 영향을 미치는 인자를 설계변수로 선택하여 실험계획법, 근사 모델, 그리고 최적설계를 통해 펌프 케이싱 형상을 최적화함으로써 역류와 흡입은 개선하고 펌프의 토크 대비 배출구와 순환구의 유량을 증가시키는 효과를 거두었다.

본 논문에서는 과도한 계산용량이 필요한 초음속 비행체의 비정상 열응답 해석을 수행하기 위한 준-비정상해석 기법을 소개한다. 준-비정상해석 기법은 연성 연계 기법과 복합 열전달 해석기법을 통합한 방법으로 계산시간 단축시키면서 동시에 정확도를 향상시키기 위해 고안되었다. 또한 준-비정상해석 시, 해석 구간을 분할하기 위한 기준시간을 결정하는 알고리즘을 고안하여 준-비정상해석 기법의 정확도를 향상시키고자 하였다. 본 논문에서는 준-비정상해석 기법을 평가하기 위하여 가상의 비행 시나리오에서 열응답 해석을 수행하였으며, 비정상 해석 결과와 비교 검증을 수행하였다. 무딘 물체의 표면 온도 및 정체점의 온도를 통해 각각의 기법의 차이를 도출하였다. 비정상 해석을 통해 도출한 정체점의 온도와 준-비정상 해석을 통해 도출한 정체점의 온도 차이는 11.4% 이내로 높은 정확도를 확보함과 동시에 28배에 가까운 계산시간을 단축시켜 해석 기법의 효율성과 정확성을 확보하였다.

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.

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.

본 연구에서는 전산유체해석 기법을 이용하여 대용량 막여과 설비 유닛의 유량불균등 현상을 분석하고 이를 해결할 수 있는 개선방안을 도출하고자 하였다.

In this study, FLUENT v.16.1 was used to investigate the compressible flow generated by the supersonic jet spewed from a high pressure tube. As the boundary condition for CFD (Computational Fluid Dynamics) analysis, the inlet temperature of air was constantly 300 K and the variation of JPR (Jet Pressure Ratio) were 5, 50, 100, 150 and the variation of tube diameter were 10, 20, 30 cm. As a result, it was confirmed that the effective range was increased as the JPR was higher, but it was confirmed that the effective range was lower than the JPR rise, and that the effective range was increased as the diameter was larger. Therefore, it is found that the tube diameter is more sensitive than the JPR among the influence factors of jet, and if the result of this study were reflected in the design of high pressure system, it will contribute to the design of the system for preventing the second accident.

The refrigerant temperature of a compressor increases due to heat generated in the discharge chamber and the motor. The increase of the suction temperature raises the superheat resulting in EER reduction. Thus, accurate superheat prediction is needed for the design of an efficient compressor. In this paper, the unsteady flow analysis is performed using CFD to predict the superheat. The results show that the suction temperature increases by about 26 °C which agrees well with the experiments.

The brake systems are composed of brake disc, brake pad and caliper and, these three parts play an important role for braking. In this study, heat fluid analysis is conducted for five different ventilated disc models, and two piece brake disc model separated in rotor and housing is used. In this case, each model has a different number of holes and vent shape. The basic heat flux and braking power equations are applied for the heat fluid analysis. The cooling performance with/without the braking operation is also analyzed for given five models where the material properties and boundary conditions are set to be identical. From our analysis results, it is found that the number of disc holes and ventilated pins strongly influences on the cooling performance.