• 한국도로학회논문집
• /
• 제14권6호
• /
• pp.131-138
• /
• 2012

PURPOSES : Two-lane highways have one lane in each direction, and lane changing and passing maneuvers take place in the opposing lane depending on the availability of passing sight distance. 2001 Korea Highway Capacity Manual (KHCM) is classified into two classes of two-lane highways (Type I, II), and average travel speed and time-delayed rate are used as measures of effectiveness (MOEs). However, since existing two-lane highways have both uninterrupted and interrupted traffic flow-system elements, a variety of free-flow speeds exhibits in two-lane highways. In addition, it is necessary to check if the linear-relationship between volumes and time-delayed rate is appropriate. Then, this study is to reestablish the relationship between average travel speed, time-delayed rate, and flow. METHODS : TWOPAS model was selected to conduct this study, and the free-flow speeds of passenger cars and the percentage of following vehicles observed in two-lane highways were applied to the model as the input. The revised relationships were developed from the computer simulation. RESULTS : In the revised average travel speed vs. flow relationship, the free-flow speed of 90km/h and 70km/h were added. It shows that the relationship between time delayed-rate and flow appeared to be appropriate with the log-function form and that there was no difference in time-delayed rate between the free flow speeds. In addition to revise the relationships, the speed prediction model and the time-delayed rate prediction model were also developed. CONCLUSIONS : The revised relationships between average travel speed, time-delayed rate, and flow would be useful in estimating the Level of Service(LOS) of a two-lane highway.

• 한국인쇄학회지
• /
• 제23권2호
• /
• pp.129-141
• /
• 2005

The liquid film behavior between two rotating rollers has been analyzed for many years. Their contributions were, however, limited almost within the areas of polymer laminar flow in there. When the slip contact of two rotating rollers is used as a role of vehicle to distribute the liquid discharged on to each roller after splitting from the nip, there was few available relationship to control the roller speed and to design system. On this work it was possible to get out a certain relationship between the discharged film thickness ratio and the roller surface seeds without any help of pressure limit at the splitting point. The hydrodynamic analyzation of Newtonian liquid behavior around the point was well proved on some manipulative experiment. The thickness ratio increases along with the roll surface speed ratio increases. And the discharged volume flow rate ratio on each roller surface varies with square of the speed ratio. Both of these relationship have a decision factor also made up by the speed ratio.

• Journal of Biosystems Engineering
• /
• 제14권1호
• /
• pp.33-40
• /
• 1989

The flow properties of water added com-cob-mix(CCM) were studied in order to provide basic information for designing its pumping system. For the study, a model system similar to actual situation was constructed. From the experiment, it can be concluded that the flow properties of the water added CCM has close relationship with its moisture content as follows; 1. The pressure drop caused by friction was very low when the moisture content of water added CCM was more than 70%. However, when the moisture content of the material is about 60%, the pressure drop increases up to 10 kPa/m at low pumping speed, and 20 kPa/m at high pumping speed, respectively. 2. The water added CCM having about 65% moisture content showed pseudo-plastic flow characteristics. 3. As the moisture content of the material decreases, the shear stress increases more rapidly than the shear rate does. Finally, below approximately 60% moisture, the shear stress becomes a linear relationship with the shear rate. 4. It was possible to pump the material having the moisture content down to 58% through a pipe having 80 mm diameter by a pump operating at 234 rpm. However, by either increasing the diameter of the pipe or decreasing the pumping speed, it can be possible to pump the material having lower moisture content than 55%.

• International Journal of Fluid Machinery and Systems
• /
• 제6권3호
• /
• pp.144-151
• /
• 2013

In this paper, the design method of a low-head propeller-type hydro turbine is studied for various numbers of blades on an axial propeller. We also investigate the relationship between geometrical parameters and internal performance parameters, such as angular velocities (100, 200, 300, 400 rpm) and 2.5~4m low heads through a three-dimensional numerical method with the SST turbulent model. The numerical results showed that the blade number had a more dominant influence than the change in heads and rotational speed on the flow characteristics of the turbine. The distributions of pressure and velocity in the streamwise direction of the propeller turbine were graphically depicted. Especially, the relationship among dimensionless parameters like specific speed ($N_s$), flow coefficient (${\phi}$) and power coefficient (P) were investigated.

• International Journal of Fluid Machinery and Systems
• /
• 제8권1호
• /
• pp.46-54
• /
• 2015

Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

• 대한교통학회지
• /
• 제24권2호
• /
• pp.31-41
• /
• 2006

본 논문은 전통적인 경제학적 개념의 수요함수와 비용과의 관계로서 혼잡비용을 추정할 때 어려움을 극복하고 실제 적용 가능한 혼잡비용을 추정하는 것이다. 본 논문에서는 속도-밀도 곡선을 이용한 공학적인 방법론을 이용하여 속도에 대한 탄력성을 통해 도로의 소통상황에 따른 실질적으로 적용 가능한 혼잡통행료를 산출하기 위해서 실질 교통량자료를 이용하여 속도, 밀도 및 교통량 관계에 따른 이론적인 혼잡요금을 추정하였다. 또한, 본 논문은 장래 전자통행료징수시스템의 도입을 전제로 속도에 따른 적정혼잡통행료를 산정 하였다 특히 연구대상 지역(강변북로)의 자료를 이용하여 다양한 분석결과 Drake모형이 가장 적합한 것으로 분석되었으며, 산정된 모형을 이용하여 통행속도의 변화에 따른 적정 혼잡통행료를 추정하였다. 본 논문의 분석결과를 임금율법에 적용하여 혼잡통행료를 부과할 경우 44km/h-68krn/h일 때 최적의 혼잡 통행료는 94원에서 3,255원으로 추정되었다. 한계대체율법을 적용한 경우에는 속도가 44km/h-68km/h일 때 최적의 혼잡 통행료는 107원에서 6,381원으로 추정되었다.

• Wind and Structures
• /
• 제13권3호
• /
• pp.275-292
• /
• 2010

Wind tunnel experiments were conducted to investigate the wind characteristics in the mountainous valley terrain with 4 simplified valley models and a 1:500 scale model of an existing valley terrain in the simulated atmospheric neutral boundary layer model. Measurements were focused on the mean wind flow and longitudinal turbulence intensity. The relationship between hillside slopes and the velocity speed-up effect were studied. By comparing the preliminary results obtained from the simplified valley model tests and the existing terrain model test, some fundamental information was obtained. The measured results indicate that it is inappropriate to describe the mean wind velocity profiles by a power law using the same roughness exponent along the span wise direction in the mountainous valley terrain. The speed-up effect and the significant change in wind direction of the mean flow were observed, which provide the information necessary for determining the design wind speed such as for a long-span bridge across the valley. The longitudinal turbulence intensity near the ground level is reduced due to the speed-up effect of the valley terrain. However, the local topographic features of a more complicated valley terrain may cause significant perturbation to the general wind field characteristics in the valley.

• 한국도로학회논문집
• /
• 제19권6호
• /
• pp.175-182
• /
• 2017

PURPOSES : Road sectors contribute approximately 16 % of total GHG emission rates in South Korea. Engineers and experts expend significant efforts to identify countermeasures for the reduction of carbon emission. This study aims to determine how total carbon emission rates change depending on whether or not there is speed limit enforcement. METHODS : In this study, Lamm's travel speed profile theory is first adopted to select the hazard road, which sections are designated as speed limit enforcement. Second, Motor Vehicle Emission Simulator (MOVES) was used to simulate the carbon emission on the road. RESULTS : The total carbon emission rate under speed limit enforcement was 10,773 g higher than the condition without speed limit enforcement in the designated road. This might affect acceleration, which can lead to increased emissions. CONCLUSIONS : There would be no researches about proving the relationship how speed limit enforcement has an effect on carbon emission. The result of our study can provide valuable guidelines regarding road safety and eco-friendly roads.

• 천문학회보
• /
• 제36권2호
• /
• pp.94.1-94.1
• /
• 2011

Recurrent substorms occur when high-speed solar wind streamers pass by Earth's magnetosphere. Most of the previous researches have been done using the observations obtained at the geosynchronous orbit focusing on the relationship between the solar wind disturbances and the occurrence of substorms. However, it is important to investigate the dynamics of the magnetotail because the magnetotail is the place where substorms develop. In this study we investigated the observations of recurrent dipolarizations in the near-Earth magnetotail that occurred during high-speed solar wind streamers. The dipolarizations and subsequent stretchings have occurred for more than three days with the average period of ~2 - 3 hours. The average period of ~2 - 3 hours is consistent with the average occurrence period of recurrent substorms. Also, the observed signatures on the geosynchronous orbit and the ground show recurrent substorms have occurred during the event. These suggest that the recurrent dipolarizations in the near-Earth magnetotail should be closely related to the recurrent substorms. On the other hand, there was no clear flow activities directly associated with the dipolarizations, except for some intermittent bursty flow activities. We will discuss the detailed characteristics of the dipolarizations and the relationship with recurrent substorms.

• 한국ITS학회 논문지
• /
• 제16권4호
• /
• pp.92-106
• /
• 2017

기상 악화 시 운전자의 시인성이 저하되어 교통 흐름에 영향을 미치며 이는 교통 정체나 교통사고를 유발시킨다. 특히, 안개가 발생할 경우 다른 기상 요인과는 달리 교통사고가 대형 교통사고로 이어지며 치사율도 높은 것으로 알려져 있다. 본 연구에서는 교통류에 영향을 미치는 가시거리 수준을 도출하기 위해 악천후 중 안개 발생 시 교통특성을 분석하였다. 연속류 도로를 대상으로 안개 발생 시와 미 발생 시의 교통량 및 속도 변화를 비교 분석하였으며, 가시거리 수준별 교통량-속도-밀도 관계를 분석하였다. 분석 결과, 동일시간대의 교통량 변화는 거의 없는 것으로 나타났으며 속도는 가시거리가 짧을수록 감소하는 것으로 나타났다. 또한, Q-U-K 관계에서 가시거리 200m 이하의 안개 발생 시 미 발생 시와 뚜렷한 차이를 보여 교통류에 영향을 미치는 것으로 분석되었다. 본 연구 결과를 기반으로 교통류에 영향을 미치는 가시거리 수준 판단이 가능하여 향후 안개 발생 시 제한 속도 제어, 교통량 제어 등 교통 운영 전략의 공학적 기초자료로 활용될 수 있을 것으로 기대된다.