• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.6
• /
• pp.860-873
• /
• 1998

In a low speed open-type wind tunnel, a group of parallel wakes downstream of two dimensional grid model consisting of several circular cylinders were experimentally investigated to study the response of the wake flows to the acoustic excitation, in hoping to promote the understanding of the underlying mechanism behind the gross flow change due to artificial excitation. In the unexcited wake flows, the development of the individual wakes behind cylinders was almost uniform for the ratio of the spacing to the cylinder diameter of s/d.geq.1.5. For smaller s/d, however, the jet streams issued through the gaps between the cylinders became biased in one side and the cylinders had wakes of different sizes. At s/d=1.25, the gap flow directions change in time, leading to unstable wake patterns. Further reduction in s/d made this unstable flip-flopping of the jets stable. The most effective excitation frequency was found to be in the Strouhal number range of St=0.5-0.6. This frequency was related to the vortex shedding. At s/d=1.75, the excitation frequency was 2 or 4 times the vortex shedding frequency. When the flow was excited at this frequency, the vortex sheddings were energized, and pairings between neighboring vortices were generated. Also, the merging process between individual wakes was accelerated. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. For smaller spacing of s/d .leq,1.0, the acoustic excitation became less effective in controlling the flow.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.3 no.2
• /
• pp.18-24
• /
• 2000

A two-dimensional numerical method for inviscid two-fluid flows with a significant entrainment into both directions is established, and the oil leakage from a non-pressurized underwater pipe is studied. The interface between two fluids is modeled at a vortex sheet. The flow field and the subsequent interface evolution are solved by using the vortex-in-cell method. For longer flow simulation with a realistic two fluids interaction, an efficient merging scheme is introduced. In the Boussinesq limit, the speed of the external fluid intrusion into the pipe is very close to the existing mathematical models, and the lock exchange is observed in spite of a significant roll-up of the interface and entrainments. It is believed that the developed method can be utilized effectively for further detailed studies on various two-fluid flows which are encountered in many different marine oil spill problems.

• Journal of Korean Society of Transportation
• /
• v.29 no.3
• /
• pp.123-137
• /
• 2011

In general, flow propagation has been explained using the shock wave theory which is expressed as a function of variations in volume and density. However, the theory has certain limitation in portraying heterogeneous flow, e.g., flow propagation between lanes. Motivated by this fact, this study seeks a new measure for analyzing the propagation characteristics of traffic flow at three sections of highway (i.e., merging area, weaving section, and basic section) from temporal and spatial perspectives, and then develops a model for estimating the measure for the flow propagation. The "shock wave speed" which is the measure widely adopted in literature, was first applied to describe the propagation characteristics, but it was hard to find distinct characteristics in the propagation. This finding inspires to develop a new measure named "Impulse Volume". It is shown that the measure better explains the propagation characteristics at the three study sections of highway. In addition, several models are also developed by performing multi-regression analyses to explain the flow propagation between lanes. The models proposed in this paper can be distinguished in three sections and the lane placement.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.6
• /
• pp.786-798
• /
• 2001

This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.46 no.12
• /
• pp.66-72
• /
• 2009

This paper proposes an efficient binary arithmetic encoder for CABAC which is used one of the entropy coding methods for H.264/AVC. The present binary arithmetic encoding algorithm requires huge complexity of operation and data dependency of each step, which is difficult to be operated in fast. Therefore, renormalization exploits 2-stage pipeline architecture for efficient process of operation, which reduces huge complexity of operation and data dependency. Context model updater is implemented by using a simple expression instead of transIdxMPS table and merging transIdxLPS and rangeTabLPS tables, which decreases hardware size. Arithmetic calculator consists of regular mode, bypass mode and termination mode for appearance probability of binary value. It can operate in maximum speed. The proposed binary arithmetic encoder has 7282 gate counts in 0.18um standard cell library. And input symbol per cycle is about 1.

• The Journal of the Korea Contents Association
• /
• v.8 no.5
• /
• pp.94-103
• /
• 2008

In this paper, we adapt the $\kappa$-means clustering technique to segmenting a given 3D mesh. In order to avoid the locally minimal convergence and speed up the computing time, first we extract sharp vertices from the mesh by analysing its curvature and convexity that respectively reflect the local and global geometric characteristics from the viewpoint of cognitive science. Next the sharp vertices are partitioned into $\kappa$ clusters by iterated converging with the $\kappa$-means clustering method based on the geodesic distance instead of the Euclidean distance between each pair of the sharp vertices. For obtaining the effective result of $\kappa$-means clustering method, it is crucial to assign an initial value to $\kappa$ appropriately. Hence, we automatically compute a reasonable number of clusters as an initial value of $\kappa$. Finally the mesh segmentation is completed by merging other vertices except the sharp vertices into the nearest cluster by geodesic distance.

• International Journal of Highway Engineering
• /
• v.10 no.3
• /
• pp.47-56
• /
• 2008

Generally, accident exposure at intersections is relatively higher than that at roadway segments due to more possibility of merging, diverging, turning, crossing, and weaving maneuver. Furthermore, the traffic accident rate at intersections has been rapidly increasing since 1990's. Since there is more opportunity of conflict at unsignalized intersection, frequency and severity of traffic accident are more severe than signalized intersections. The purpose of the study is to analyze factors causing vehicle crashes and provide intersection design guidelines to improve intersection safety. For this study, vehicle to vehicle crash data of 116 rural 3 legs unsignalized were collected and field surveys were conducted for traffic and geometric conditions. Ordered probit models were developed to analyze the severity of crashes. It was found that weather, obstacles in minor roadsides, presence of major exclusive right lane, presence of major road crosswalk, difference between posted speed of major road and minor road, land-use around intersections, shoulder width of major road, ADT of major road are significant factors for intersection safety.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2003.05a
• /
• pp.192-197
• /
• 2003

A virtual vessel traffic control system is introduced to contribute to prevent a marine accident, e.g. ship collision or stranding. from happening. The system that comes from VTS limitaions, consists of both data acquisition by satellite remote sensing and a simulation of traffic environment stress (here, INOUE model used) based on the satellite data. Remotely sensed data cab be used to provide timely and detailed information about the marine safety, including the location, speed and direction of ships, and help us operate vessels safely and efficiently. If in the future, e.g. 5-minute after, environmental stress values that a ship may encounter on a voyage can be available, proper actions can be taken to prevent accidents. It lastly can be shown that JERS satellite data are used to track ships and extract their information.

• Journal of Korean Society of Transportation
• /
• v.34 no.4
• /
• pp.354-372
• /
• 2016

This study identified factors affecting the crash severity at freeway work zones. A nice feature of this study was to take into account the characteristics of work zone traffic management in analyzing traffic safety concerns. In addition to crash records, vehicle detection systems (VDS) data and work zone historical data were used for establishing a dataset to be used for statistical analyses based on an ordered probit model. A total of six safety improvement strategies for freeway work zones, including traffic merging method, guidance information provision, speed management, warning information systems, traffic safety facility, and monitoring of effectiveness for countermeasures, were also proposed.

• KIPS Transactions on Software and Data Engineering
• /
• v.2 no.1
• /
• pp.27-34
• /
• 2013

Background subtraction is one of the key techniques for automatic video content analysis, especially in the tasks of visual detection and tracking of moving object. In this paper, we present a new sample-based technique for background extraction that provides background image as well as background model. To handle both high-frequency and low-frequency events at the same time, multiple interval background models are adopted. The main innovation concerns the use of a confidence factor to select the best model from the multiple interval background models. To our knowledge, it is the first time that a confidence factor is used for merging several background models in the field of background extraction. Experimental results revealed that our approach based on multiple interval sampling works well in complicated situations containing various speed moving objects with environmental changes.