Earticle

본 연구에서는 건물협곡에서 형성되는 연직발달형 소용돌이에 대해 전산유체역학(CFD) 모델을 이용하여 건물 외관비 에 따른 소용돌이 현상의 발달 양상 및 바람속도성분을 수치적으로 해석하였다. 이를 위하여 건물협곡의 폭(Width, W) 을 기준으로 건물의 높이(Height, H)를 증가시키는 조건하에서 수치실험을 수행하였다. H/W=1.0 및 H/W=2.0의 경우에 는 건물협곡 내에서 풍하측 건물 쪽에서는 하강기류가 나타났고, 풍상측 건물 쪽에는 상승기류가 발생하는 1차적인 연직 소용돌이의 패턴이 관찰되었다. H/W=3.0 및 H/W=4.0의 경우에는 건물협곡 내의 풍하측 건물 쪽에는 상승기류가 나타 났고 풍상측 건물 쪽에는 하강기류로 변화하는 2차적인 역회전 패턴이 추가적으로 형성되었다. 또한, H/W=5.0 및 H/ W=6.0에서는 소용돌이의 연직기류의 방향이 또다시 역전되는 현상이 나타났다. 결과적으로 건물협곡 내에서 형성되는 연직기류는 건물 높이의 증가에 따라 ‘S’자 형태로 발달하는 양상을 보였으며, 이러한 역전양상은 연직속도성분 및 수평 속도성분의 변화로부터 확인되었다.

In this study, the effect of obstacle aspect ratio on vertical vortex patterns and wind velocity components in building canyon was numerically investigated using a computational fluid dynamics (CFD) model. As the experimental conditions, the building height (H) was gradually increased based on the width (W) of the building canyon. In the cases of H/W=1.0 and H/W=2.0, a descending (an ascending) air current was presented at leeward (windward) building side as the primary vertical vortex pattern. In the cases of H/W=3.0 and H/W=4.0, the secondary reverse pattern was additionally developed that an ascending (a descending) air current was presented at leeward(windward) building side. The flow pattern in vertical vortex was reversed again in the cases of H/W=5.0 and H/W=6.0. As a result, the vertical flow in building canyon was developed as ‘S’ shape, according to the building height increase. The reverse patterns were also determined from the changes in the vertical and horizontal wind velocity components in building canyon.

Air flow field characteristics in a compact chamber system are indispensable for the efficient development of vehicle aerodynamic performance. In this study, air flow and velocity uniformity in the chamber system were numerically analyzed using the CFD method. Air flows at a uniform velocity from the outlet of the blower, passes fast through the heat exchanger with partial pressure difference, and then moves into the blower inlet. Overall pressure drop through the fan gradually increases with the flow rate. The uniformity varies along the test section, decreasing by 5-10% with distance from the nozzle. These predicted results can be widely used as basic conceptual design data for an efficient vehicle chamber system.

In this study, a numerical analysis study was conducted on the flow characteristics according to the internal flow path change and differential pressure of the hydrogen shut-off valve, and through this, the pressure loss characteristics and flow coefficient of the hydrogen shut-off valve were predicted. ANSYS CFX program was used to predict the flow characteristics of the hydrogen shut-off valve. When the flow path gap was 1.3 mm, the design conditions of the hydrogen shut-off valve were satisfied, and the value of the flow coefficient of the valve was about 1.53. As the inlet pressure of the hydrogen shut-off valve increases, the outlet flow rate increases, but regardless of the inlet pressure, the flow coefficient of the valve is almost constant, ranging from 1.53 to 1.56, indicating that it is the inherent flow coefficient of the designed hydrogen shut-off valve.

최근 실내에서 생활하는 시간이 증가됨에 따라 실내공기질의 중요성을 인식하고 있다. 또한, 에너지 절감 및 효율을 높이기 위해 실내공간은 점점 밀폐화 되고 있어 실내공기질에 대한 개선 요구가 증가하고 있다. 실내공 기질 개선을 위한 공기정화기에서 미세먼지 제거를 위해 주로 사용되는 EPA(Efficient Particulate Air Filter) 필 터와 실내 유해가스 제거를 위해 주로 사용되는 ACF 필터의 여과성능을 비교하고자 본 연구를 시작하였다. 각 섬 유상 필터를 통한 공기 흐름과 압력 강하를 유동해석을 통해 수치해석 방식으로 도출하여 제시하였다. 결론적으로, ACF 필터를 구성하고 있는 섬유는 EPA 필터를 구성하고 있는 지지층 섬유보다 얇고 EPA 필터의 여과층 섬유보 다는 굵은 특성이 있어 형성되는 기공이 상대적으로 크게 형성되는 특성이 있어 EPA 필터에 비해 공기투과도과 높으면서, 압력손실도 낮게 나타나는 것을 공기의 흐름을 통해 확인하였다. 또한, 여과속도는 여과재 전단에 절곡된 각도에 따라 유속의 특성이 달라지는 것을 확인할 수 있었으며, 이는 공기정화기 효율향상의 측면에서 절곡형 필터 적용시, 여과효율과 압력강하 간의 영향을 고려한 최적의 필터 특성을 확인하여야 하는 것으로 보인다. 본 연구를 향후 실내공기질 개선을 위한 EPA 필터와 ACF 필터를 효과적으로 융합하는 방안으로 활용하고자 한다.

Recently, as people spend more time indoors, the importance of indoor air quality is recognized. In addition, in order to save energy and increase efficiency, the indoor space is becoming more and more airtight, and the demand for improvement of indoor air quality is increasing. In this study, the filtration performance of the EPA filter, which is mainly used to remove fine dust, and the ACF filter, which is mainly used for removing harmful gases, in an air purifier for improving indoor air quality was compared. In addition, the results were derived and presented in a numerical analysis method through flow analysis of the air flow and pressure drop through each fibrous filter. In conclusion, the fibers constituting the ACF filter are thinner than the support layer fibers constituting the EPA filter and thicker than the filter layer fibers of the EPA filter. It was confirmed through the flow that the air permeability and pressure loss were low compared to the EPA filter because the pores formed by this were relatively large. In addition, it was confirmed that the filtration rate varies according to the pleated angle at the front end of the filter medium. This means that it is necessary to check the optimal filter characteristics in consideration of the effect between filtration efficiency and pressure drop when applying a bending type filter in terms of improving the efficiency of the air purifier. This study is intended to be used as a method for effectively converging EPA filters and ACF filters to improve indoor air quality in the future.

The enhancement of heat transfer in cooling system of cylindrical lithium-ion battery pack is numerically investigated by installing fins on the cooling plate. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery and the conjugated heat transfer is analyzed with the commercial package STAR-CCM+. The result shows that installing fins on the cooling plate increases the convective heat transfer on the surface and thus lowers the maximum temperature of the battery pack. As the length and thickness of the fins increase, heat transfer in the battery pack improves. Considering the geometry and airflow of the battery pack, the optimal values for the length and thickness of the fin are both 2mm. As the convective heat transfer coefficient of the surface increases, the maximum temperature of the battery pack is greatly reduced and the temperature gradient is greatly improved.

본 연구에서는 도심지에 위치한 숭례문을 중심으로 유입류 풍향 조건에 따라 변화되는 풍환경을 수치해석하였다. 이를 위해 지리정보시스템 자료와 전산유체역학 모델을 이용하여 대상영역의 상세 바람장을 수치모의하였으며, 벡터장, 3차원 바람속도성분, 풍속장 등에 대한 흐름특성을 분석하였다. 대상영역에서는 건물협곡을 따라 흐르는 바람길의 형성과 건물에 의한 바람의 회전 및 와류 등 급격한 풍향의 변화가 모의되었으며, 그 영향으로 숭례문 주변에서는 유입류의 풍향에 의존하지 않는 복잡한 흐름의 양상이 나타났다. 숭례문 지점에서의 풍속은 지표풍(지상 2 m)과 비교하여 상층마루 높이(지상 14 m)에서 평균 3배 이상 강하게 형성되었고, 유입류가 동풍인 경우에 전반적으로 높게 나타났으며, 숭례문의 남동 측면이 상대적으로 바람 에 의한 영향이 클 것으로 예측되었다. 본 연구를 통하여, 고층건물 및 고밀도 건물군 등 인공구 조물에 의한 바람길 및 빌딩풍 등의 형성이 도심지에 위치한 건축문화재에 미치는 영향을 파악 하고 대책을 마련하기 위한 상세 풍환경 평가의 필요성이 제시되었다.

In this study, the wind environment in an urban area near Sungneymun gate was numerically investigated in the cases of inflow directions. The wind fields for the target area were simulated using Geographic Information System data and Computational Fluid Dynamics model. Results, including vector fields, three-dimensional wind velocity components, and wind speeds, were analyzed to examine flow characteristics. Wind direction variability affected by buildings was shown in the target area. The complex flows around Sungneymun did not depend on the inflow direction as a boundary condition. The wind speed around Sungneymun was generally 3 times stronger at 14 m above ground level (AGL) compared to the surface wind at 2 m AGL and relatively high in the case of easterly inflow. The effect of wind was also analyzed to be relatively significant at the southeast side of Sungneymun. Thus, it was suggested that the assessment of wind environment affected by high-rise and high-density buildings should be necessary for the architectural heritage in urban areas.

The improvement of heat transfer in water cooling passage of lithium-ion battery is numerically studied by employing trapezoidal vortex generators. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery. The conjugated heat transfer is analyzed with the commercial package STAR-CCM+ in terms of inlet flow velocities. The result shows that vortex generator enhances the convective heat transfer by developing thermal boundary layers and secondary flows in downstream, which results in reducing the average temperature of the battery by about 1℃. The heat transfer is enhanced for the whole inlet velocity, while the pressure loss sharply increases at more than inlet velocity of 0.1m/s. The optimum inlet velocity is around 0.1m/s for in terms of the heat transfer and pressure loss.

본 논문에서는 원전 증기발생기세관 진단을 위한 와전류탐상의 전자기 수치해석을 수행하였다. 전자 기적 특성을 해석하기 위하여 맥스웰 방정식을 이용하여 지배방정식을 유도하였고, 3차원 전자기 유한요소 프로그램인 OPERA 3D를 이용하여 전자기 수치 해석을 수행하였다. 신호해석을 위해 사용된 프로브의 종류는 배열와전류프로브이며, FBH 결함의 신호를 해석하였다. 결함의 깊이는 세관 두께의 40[%], 60[%] 및 100[%]로 하였다. 시험주파수는 100[kHz], 300[kHz], 400[kHz]를 사용하였고, 각각의 결함 및 시험주파수에 대한 결과를 비교분석하였다. 본 논문의 결과는 앞으로 배열와전류프로브를 이용하여 원전 증기발생기세관 진단을 할 경우 신호 해석에 도움이 될 것으로 사료된다.

In this study, numerical analysis was carried out to develop low-noise axial fans, which are often used for ventilation in houses. A commercial program and the turbulence models are used for the analysis of internal fan. Proudman acoustic power model and the Curle surface acoustic power model were used for analysis. As a result, the distribution of flow velocity and pressure around the blade and guide of the fan was high, and low in the center of the fan. Noise from the inner wall of the fan case and the blade surface was the highest at the body and vane connections of the blade, and low at the center of the vane and the center of the body.

본 연구는 도심지 지하 굴착에 따른 배면 지반의 침하 거동을 정량적으로 분석하고, 이에 따른 인접 구조물의 안정성을 평가하기 위해 수행되었다. 수치해석은 Mohr–Coulomb 모델을 적용하여 굴착심도별 변형 특성을 도출하였으며, 이를 현장 계측 결과와 비교·검증하였다. 해석 결과, 최대 침하는 굴착벽 뒤 약 0.6H 지점에서 발생하였으며, 굴착심도 증가에 따라 비선형적인 침하 거동을 보였다. 벽체 형식별 비교에서 CIP 벽체가 가장 우수한 변위 제어 능력을 나타냈다. 모든 해석 결과는 Sowers(1962) 및 Skempton(1956)의 허용 한계 기준을 충족하여 인접 구조물의 손상 가능성이 매우 낮은 것으로 평가되었다. 본 연구는 배면 지반 침하 예측 및 구조물 영향평가에 대한 신뢰성 향상에 기여하며, 향후 도심지 굴착공사 설계 시 기초자료로 활용 가능하다.

This study was conducted to quantitatively analyze the settlement behavior of the ground behind urban excavations and to evaluate the stability of adjacent structures. Numerical analyses applying the Mohr –Coulomb model were performed to derive deformation characteristics according to excavation depth and were verified through field monitoring data. The results indicated that the maximum settlement occurred at approximately 0.6H behind the retaining wall and exhibited nonlinear behavior with increasing excavation depth. Among wall types, the CIP wall showed the most effective displacement control performance. All analytical results satisfied the allowable limits proposed by Sowers (1962) and Skempton (1956), confirming that potential structural damage to adjacent buildings was minimal. The findings of this study contribute to improving the reliability of settlement prediction and deformation assessment and can serve as fundamental data for future urban excavation design and safety management.

A computational analysis was performed to study the thermal characteristics within the injection molding process of polygon mirrors in LiDAR systems. Such polygon mirrors are significantly influenced by the geometric shape of the injection mold as well as temperature and operating conditions. The analysis included the temperature distribution, heat flux, and variations in heat transfer rate of the polygon mirror from initial conditions. From the beginning of the injection process, temperature of the polygon mirror changes rapidly, leading to conductive heat transfer to the mold. There are large variations in the mirror temperature change depending on local position, and surface heat flux are affected by internal cooling path. These results are expected to be used as thermal design data for various polygon mirror processes.

본 연구에서는 GIS 자료를 기반으로 해안지역의 대규모 건축물이 해륙풍에 미치는 영향에 대하여 비교·평가하였다. 이 를 위해, 대규모 건축물의 높이 조정 및 통경축에 변화를 CFD모델에 반영하고, 해풍 및 육풍 조건에서 수평 및 연직 바 람성분과 풍속에 대하여 분석하였다. 대규모 건축물이 건설됨에 따라, 건물 주변에서는 와류 형성 등의 영향으로 풍속이 약화되었다. 풍하측 지역에서는 수렴현상이 나타났으며, 해풍조건에는 육상, 육풍조건은 해상에서 나타났다. 이에 따라, 수평 및 연직 바람성분의 변화를 보였으며, 풍하측 지역과 건축의 측면부에서는 풍속이 다소 강화되었다. 특히, 수렴현상 및 풍속강화현상은 건물 높이가 일정한 건축물에서 상대적으로 넓은 범위에 강하게 나타났다. 본 연구를 통하여, 대규모 건축물 건설에 있어 건물의 높이 조정과 통경축을 고려한 외관은 풍환경의 변화를 완화시킬 수 있음을 확인하였으며, 실 제 건설에 있어 풍환경 영향평가를 기반으로 한 설계가 필요할 것으로 생각된다.

This study evaluated the effects of large-scale buildings construction on sea-land winds in coastal area using a CFD model based on GIS data. The analysis included changes in horizontal and vertical flow and wind speed depending on adjustments to the height and wind-corridor of building facade. In sea wind conditions, the flow tended to converge behind the building (the downwind area of land) and vortices were formed around the building. The wind speed around the building weakened due to vortices and other influences, while it strengthened somewhat at the western boundary. Convergence and increased wind speed were more pronounced and affected a wider area behind the building when the building facade height was constant. In land wind conditions, the flow tended to converge on the sea (the downwind area of building), and the wind speed weakened around the building due to the formation of vortices. However, the wind speed increased somewhat on the sides of a building and the sea. Especially, the convergence and increased wind speed on the seaward side were more pronounced and covered a relatively wide range in buildings with a constant height of facade. It is also suggested that in actual construction, designs based on wind environment impact assessments should be considered, as adjusting the height and wind-corridor of buildings can alleviate changes in the wind environment.

Seawater flow and turbine torque in a lab-scale tidal power generation system have been analyzed with CFD method. Its power generation is largely influenced by hydraulic flow characteristics of pressure variation and mechanical turbine torque in the system caused by vertical flow field including tangential rotation. Pressure drop through the turbine was gradually increased with flow rate by seawater level difference, and it depends on the turbine blade and system geometry. And curl was severely varied along the flow direction with more than about 8 times increase through the flow system. There was also turbine torque change with pressure inlet due to the water level. Those predicted results can be widely used as basic concept design data for efficient tidal power generation system development.

In this paper, based on the existing research, we define the parameters for the number of ignition devices to be applied to the pyrovalve, the operation and airtightness according to the temperature, the material of the nipple and the thickness of the fractured part, and ANSYS Ver. 19.2 was used to analyze the FEA model, and a comparative analysis was conducted through structure analysis according to the piston shape of the pyrovalve. In addition, an experimental study was conducted by manufacturing a prototype according to the design variables. As a result, high-strength pyrovalves can stably supply working fluids such as fuel and oxidizer for space launch vehicle propulsion engines, as well as precisely control flow path switching was confirmed.

In this study, magnetic characteristics of two models of permanent magnet actuator applied and used in the Recloser were studied, and the new model design was verified using numerical analysis on the operation and current characteristics of the magnet actuator accordingly. Such as the Recloser require fast operation characteristics to open the fault current, so when the moving and fixed contacts of a magnet actuator with permanent magnets that generate holding force come into contact, a high holding force is required, and when it open to circuit, the magnetic force is rapidly reduced. It demands very high performance. Therefore, the speed characteristics and current characteristics of the contact points of the magnet actuator for which the design was completed were compared.

Numerical analysis has been carried out to investigate the characteristics of seawater flow fields and turbine output in a compact double current tidal power generation system for various level differences. There are growing concerns for the development of efficient tidal power generation which is stable and less affected by environmental circumstances as ocean energy. Especially the flow field characteristics in the compact tidal power generation system have a large influence on the system power generation performance. Flow velocity, pressure, and streamline distributions are compared including vertical type turbine out, and it can be predicted that seawater is accelerated by vortex flow in front of the turbine and there is severe turbine output variation due to the water level difference with pressure difference. These results can be applied as basic data for the effective development of compact tidal power generation system.

The effect of flow direction on heat transfer in water cooling channel of lithium-ion battery is numerically investigated. Battery Design StudioⓇ software is used for modeling electro-chemical heat generation in the battery and the conjugated heat transfer is analyzed with the commercial package STAR-CCM+. The result shows that the maximum temperature and temperature difference of battery with Type 1 are the lowest because the heat transfer in the entrance region near the electrode is enhanced. As the inlet velocity is increased, the maximum temperature and temperature difference of battery decreases but the pressure loss increases. The pressure loss in Type 2 channel is the lowest due to the shortest channel length, while the pressure loss with Type 3 or 4 channel is the highest because of the longest channel length. Considering heat transfer performance and pressure loss, Type 1 is the best cooling channel.

Numerical analysis has been carried out to investigate the flow field characteristics for exhaust gas in automobile engine DPF system. The DPF system performance is largely affected by exhaust gas flow while it passes through the complicated geometry of DOC/DPF system, fan shape structure, and perforated can with air for fuel combustion. Hence the characteristics of fluid velocity, pressure, and streamline are analyzed with velocity uniformity in front of DOC and swirl flow near the fan. It can be seen that the velocity uniformity increases with the gas flow rate including flow acceleration near the lower area of the fan. The air flow also influences the gas flow distribution close to the impeller and fan structure with complicated swirl flow. These results are expected to be applicable as fundamental design data for automobile engine exhaust system.

본 연구에서는 도시(건물)지표에서 형성되는 지표흐름의 유형에 따른 건물협곡 내부에서의 상세흐름특성을 전산유체 역학(CFD) 모델을 이용하여 수치적으로 해석하였다. 이를 위하여, 건물의 높이(H)를 기준으로 건물 간의 간격인 건물협 곡의 폭(W)을 증가시키는 조건하에서 수치실험을 수행하였으며, 건물협곡 내에서의 벡터장 및 방향별 바람속도성분의 변동 양상에 대한 수치해석으로부터 W/H 비에 따른 지표흐름유형을 정량적으로 해석하였다. W/H=1.0 및 W/H=2.0의 경우에는 건물협곡 내에서 하강(풍하측)기류 및 상승(풍상측)기류가 뚜렷하게 구분되며, 협곡 내부를 가득 채운 단일 연 직소용돌이의 형성으로부터 Skimming Flow(SF)의 특징을 확인할 수 있었다. W/H=3.0 및 W/H=4.0의 경우, 풍하측 건 물의 최상층부(z/H=1.0)에서는 연직흐름이 분리되어 상승기류가 발생하였고, 건물협곡의 중층부에서는 x방향의 수평흐 름이 풍하측 건물 쪽으로의 양의 흐름과 풍상측 건물 쪽으로의 음의 흐름으로 분리되어 양방향 수평흐름이 나타났으며, 이는 Wake Interference Flow(WIF)의 경우에 해당하는 것으로 해석되었다. W/H=5.0 및 W/H=6.0의 경우에는 건물협곡 내 부의 x방향 수평흐름의 양방향(양/음) 분리영역이 하층부까지 확장되어, Isolated Roughness Flow(IRF)의 특징을 보였다.

In this study, the flow characteristics in building canyon by the surface flow regimes associated with air flow over buildings were numerically investigated using a computational fluid dynamics (CFD) model. The experimental conditions were constructed with the building arrays of increasing W (width of building canyon) / H (building height) ratios. The numerical analysis was conducted with vector fields and wind velocity components in building canyon. In the cases of W/H=1.0 and W/H=2.0, the vertical descending air current at leeward building side and the ascending air current at windward building side were distinctly presented with a single vertical vortex in building canyon, as the characteristics of the skimming flow (SF). In the cases of W/H=3.0 and W/H=4.0, the wake interference flow (WIF) was developed that the vertical ascending air current at the top (z/H=1.0) of leeward building and the separated horizontal flow with the positive/negative values for the wind velocity of x-direction at the middle layers were presented in building canyon. In the cases of W/H=5.0 and W/H=6.0, the separated horizontal flow of x-direction was expanded to the bottom of building canyon, as the characteristics of the isolated roughness flow(IRF).