부유식방파제의 수리특성 및 와 상호작용에 관한 실험적 연구

윤재선,손혁준,전시영,조용식,Yoon. Jae-Seon,Son. Hyok-Jun,Chun. Si-Young,Cho. Yong-Sik 한국방재학회 2010 한국방재학회논문집 Vol.10 No.6

본 연구에서는 LDV시스템을 이용하여 부유식 방파제 주변의 유동장의 변화를 수리모형실험을 통해 분석하였다. LDV시스템은 유체의 유속을 측정하기 위해 다양한 수리모형실험에서 폭넓게 사용되어왔다. LDV시스템을 이용하면 측정시간이 오래 걸리는 단점이 있지만, 측정한 자료를 가공하지 않고 정확한 유속장을 제시할 수 있다는 장점이 있다. 방파제의 형상과 흘수를 달리하여 수리모형실험을 수행하였으며, 유동장과 와류의 상관관계를 분석하였다. 또한, 연직 2차원 Navier-Stokes 방정식 모형을 이용하여 수치모형실험을 수행하였으며, 수치모형실험 결과와 수리모형실험 결과를 비교분석하였다. In this study, laboratory experiments are conducted to investigate flow-fields around floating breakwaters by using the LDV(Laser Doppler Velocimetry) system. The LDV system is a well-known equipment to measure fluid particle velocities in laboratory experiments. Although the system requires great efforts and enormous time for measurements, it can provide precise velocity fields comparing to other available equipments. Various types of drafts and shapes for breakwaters are employed in laboratory experiments to analyze a relation between flow-fields and vorticity. A series of numerical experiments are also carried out by using a two-dimensional Navier-Stokes equations model. Numerically predicted results are compared with laboratory measurements.

장주기 및 유동성분을 고려한 부유식방파제의 방파성능 개선

윤재선,조용식 한국방재학회 2011 한국방재학회지 Vol.11 No.1

본 연구에서는 단독형 및 2열형(multi-arranged (2 pieces)), 3열형(multi-arranged) 부유식방파제에서의 구조물간 거리와 흘수,형상을 변화시키고 파의 주기와 파형경사를 변화시키며, 다양한 변수변화에 따른 영향을 분석하였다. 부유식방파제의 흘수변화는전달계수에 직접적인 영향을 주며, 비교적 장주기에 해당하는 조파조건에선 단독형과 2열형 부유식방파제보다 3열형 구조에서높은 방파효율을 나타내었다. 수리모형실험의 결과 검증을 위하여 수치모형과 동일한 조건하에 실험을 하고 LDV시스템을 이용하여 각 부유식방파제에서의 유동장을 측정하였으며, 수리모형실험을 통하여 그에 따른 전달계수을 분석하였다. In this study, a series of laboratory experiments are carried out to analyze fluid behaviors around multi-arranged (2 pieces) float-ing breakwaters with various parameters such as distance between structures, wave periods and steepness. The rate of wave trans-mission is shown to be affected directly by wave periods of incident waves and the breakwaters with multi-arranged structuresshow the highest rate of wave protection compared with other cases. The velocity fields around the breakwaters are measured byusing the Laser Doppler Velocimetry system. The transmission coefficients are also measured in laboratory experiments. Finally,laboratory observed data are compared with numerical experimental results and analyzed in detail.

장주기 및 유동성분을 고려한 부유식방파제의 방파성능 개선

윤재선,조용식,Yoon. Jae-Seon,Cho. Yong-Sik 한국방재학회 2011 한국방재학회논문집 Vol.11 No.1

In this study, a series of laboratory experiments are carried out to analyze fluid behaviors around multi-arranged (2 pieces) floating breakwaters with various parameters such as distance between structures, wave periods and steepness. The rate of wave transmission is shown to be affected directly by wave periods of incident waves and the breakwaters with multi-arranged structures show the highest rate of wave protection compared with other cases. The velocity fields around the breakwaters are measured by using the Laser Doppler Velocimetry system. The transmission coefficients are also measured in laboratory experiments. Finally, laboratory observed data are compared with numerical experimental results and analyzed in detail. 본 연구에서는 단독형 및 2열형(multi-arranged (2 pieces)), 3열형(multi-arranged) 부유식방파제에서의 구조물간 거리와 흘수, 형상을 변화시키고 파의 주기와 파형경사를 변화시키며, 다양한 변수변화에 따른 영향을 분석하였다. 부유식방파제의 흘수변화는 전달계수에 직접적인 영향을 주며, 비교적 장주기에 해당하는 조파조건에선 단독형과 2열형 부유식방파제보다 3열형 구조에서 높은 방파효율을 나타내었다. 수리모형실험의 결과 검증을 위하여 수치모형과 동일한 조건하에 실험을 하고 LDV시스템을 이용하여 각 부유식방파제에서의 유동장을 측정하였으며, 수리모형실험을 통하여 그에 따른 전달계수을 분석하였다.

스월유동이 분무특성에 미치는 영향에 관한 연구

최숭환 ( S. H. Choi ),전충환 ( C. H. Jeon ),장영준 ( Y. J. Chang ) 한국분무공학회 2002 한국액체미립화학회지 Vol.7 No.1

N/A It is well known that the flow and spray characteristics is critical factor on the performance and emission of a direct injection diesel engine. So this study aims to investigate the interaction of flow and spray characteristics. At first, in cylinder flow distributions in swirl adaptor for 4-valve cylinder head of DI Diesel engine were investigated under steady conditions for different SCV angles mounted on the cylinder head with steady rig test and 2-D LDV. And the in-cylinder flow was quantified in terms of mean flow coefficient and swirl ratio/tumble ratio. It was found that the swirl ratio is controlled between 2.3 and 3.8. Then spray characteristics of the intermittent injection were investigated. PDA system was utilized for measurement of a droplet size and velocity. The analyses of the PDA results are carried out with Time Dividing Method. It was found that there is a correlation between the swirl flow and SMD. The droplet size and the velocity were nearly constant value with each SCV angle. And the swirl ratio is higher, SMD smaller. The swirl ratio was helpful factor to the atomization of droplet.

IN-CYLINDER FLOW ANALYSIS USING WAVELET ANALYSIS

D. PARK,P. E. SULLIVAN,J. S. WALLACE 한국자동차공학회 2006 International journal of automotive technology Vol.7 No.3

Better fundamental understanding of the interactions between the in-cylinder flows and combustion process is an important requirement for further improvement in the fuel economy and emissions of internal combustion (IC) engines. Flow near a spark plug at the time of ignition plays an important role for early flame kernel development (EFKD). Velocity data measurements in this study were made with a two-component laser Doppler velocimetry (LDV) near a spark plug in a single cylinder optical spark ignition (SI) engine with a heart-shaped combustion chamber. LDV velocity data were collected on an individual cycle basis under wide-open motored conditions with an engine speed of 1,000 rpm. This study examines and compares the flow fields as interpreted through ensemble, cyclic and discrete wavelet transformation(DWT) analysis. The energy distributions in the non-stationary engine flows are also investigated over crank angle phase and frequency through continuous wavelet transformation (CWT) for a position near a spark plug. Wavelet analysis is appropriate for analyzing the flow fields in engines because it gives information about the transient events in a time and frequency plane. The results of CWT analysis are provided and compared with the mean flows of DWT first decomposition level for all cycles at a position. Low frequency high energy found with CWT corresponds well with the peak locations of the mean velocity. The high frequency flows caused by the intake jet gradually decay as the piston approaches the bottom dead center (BDC).

IN-CYLINDER FLOW ANALYSIS USING WAVELET ANALYSIS

Park, D.,Sullivan, P.E.,Wallace, J.S. The Korean Society of Automotive Engineers 2006 International journal of automotive technology Vol.7 No.3

Better fundamental understanding of the interactions between the in-cylinder flows and combustion process is an important requirement for further improvement in the fuel economy and emissions of internal combustion(IC) engines. Flow near a spark plug at the time of ignition plays an important role for early flame kernel development(EFKD). Velocity data measurements in this study were made with a two-component laser Doppler velocimetry(LDV) near a spark plug in a single cylinder optical spark ignition(SI) engine with a heart-shaped combustion chamber. LDV velocity data were collected on an individual cycle basis under wide-open motored conditions with an engine speed of 1,000rpm. This study examines and compares the flow fields as interpreted through ensemble, cyclic and discrete wavelet transformation(DWT) analysis. The energy distributions in the non-stationary engine flows are also investigated over crank angle phase and frequency through continuous wavelet transformation(CWT) for a position near a spark plug. Wavelet analysis is appropriate for analyzing the flow fields in engines because it gives information about the transient events in a time and frequency plane. The results of CWT analysis are provided and compared with the mean flows of DWT first decomposition level for all cycles at a position. Low frequency high energy found with CWT corresponds well with the peak locations of the mean velocity. The high frequency flows caused by the intake jet gradually decay as the piston approaches the bottom dead center(BDC).

Steady-Flow Characteristics and Its Influence on Spray for Direct Injection Diesel Engine

Jeon, Chung-hwan,Park, Seung-hwan,Chang, Young-june The Korean Society of Mechanical Engineers 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.7

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of DI (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70° and 90°. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

LDV 시스템을 활용한 SI 엔진의 유동 및 연소 특성 상관 관계 분석

이승일(Seung-il Lee),고인석(Insuk Ko),김우재(Woojae Kim),송세진(Sejin Song),민경덕(Kyoungdoug Min),이종혁(Jonghyeok Lee),오희창(Heechang Oh),손진욱(Jinwook Son),김영남(Youngnam Kim) 한국자동차공학회 2020 한국자동차공학회 학술대회 및 전시회 Vol.2020 No.11

흡기 포트 형상에 대한 모터링 엔진의 실린더내 텀블유동 계측에 대한 실험적 연구

박정규 건국대학교 산업기술연구원 2005 건국기술연구논문지 Vol.30 No.-

Many researches of in-cylinder flow have been carried out, which played a large role in engine combustion. In this study the measurements of tumble flow were made for motoring condition(1000rpm) using laser Doppler velocimetry to investigate the in-cylinder flow with the change of intake port and compression ratio especially, during the intake and compression process. To further consider the tumble structures developed and decayed inside cylinder, several parameters were introduced which consisted of tumble averaging velocity, tumble area ratio, tumble moment and the eccentricity of tumble center. In this research available results about the optimal intake port configuration are obtained, which can be suitable guide line in the analysis of the tumble flow characteristics.

Design of a bubble collecting section in a high speed water tunnel for ventilated supercavitation experiments

백부근,박일룡,김기섭,이건철,김민재,김경열 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.9

The main objective of the present study is to design a bubble collecting section for use in ventilated supercavitation experiments. The large amounts of air ventilated around a cavitator split into small bubbles that follow the water’s passage through the water tunnel. The presence of these bubbles in the test section of the water tunnel prevents effective observation of supercavitation. To enable the clear observation of cavitation shape, a bubble collecting section with large volume is necessary upstream of the test section to collect bubbles. The buoyancy of bubbles provides a simple means for their collection. However, the bubbly flows in such systems have rather high velocities and a non-uniform velocity distribution, which degrades the buoyancy effect. In the present study, a bubble collecting section with three porous plates that produce a uniformly low velocity distribution is designed and analyzed with numerical methods. The effectiveness of this approach is assessed experimentally with the 1/10 miniature model. The reduction of the void fraction downstream of the bubble collecting section was also assessed in the test section. The bubble collecting section in the full-scale water tunnel was also eventually found to be well designed through flow speed measurements and bubble visualization in the test section.