• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.8
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• pp.3374-3383
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• 2011

In this study, numerical analyses for slamming impact phenomena have been carried out using a 2-dimensional wedge shaped structure having finite deadrise angles. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct(or PLIC-VOF) scheme is used for the tracking of the deforming free surface. Numerical analyses are carried out for the deadrise angles of $10^{\circ}$, $20^{\circ}$ and $30^{\circ}$. For each deadrise angle, variations are made for the grid size on the wedge bottom and for the entry speed. The magnitude and the location of impact pressure and the total drag force, which is the summation of pressure distributed at the bottom of the structure, are analyzed. Results of the analyses are compared with the results of the Dobrovol'skaya similarity solutions, the asymptotic solution based on the Wagner method and the solution of Boundary Element Method(BEM).

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.454-459
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• 2013

Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.6
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• pp.879-885
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• 2018

The highway weaving section is a point where there is a conflict caused by entry and exit vehicles. In order to minimize the impact on the main line, an accumulation line should be installed. The design speed of the collecting part is 50 km/h, but the actual driver does not have proper deceleration according to the design speed. In this study, considering the driving behaviors, the design specification, and the driver 's viewing angle, the appropriate separation distance for safe entry and exit of collecting, connecting, and collecting roads was examined. As a result of the analysis, it is found that a distance of 60m is required from the point where the merging starts. The results of this study are expected to contribute to the improvement of driver safety due to the conflict between entry and exit vehicles when applied to the weaving section where collecting roads are installed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.725-730
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• 1987

An experimental study of the air flow through inlet pipe of reciprocating two-cycle engine was investigated under motored condition. Measurements of the two components of velocity, velocity fluctuation, and the other behavior of inlet flow have been obtained by laser Doppler anemometer system. The research engine comprised the cylinder head of a two-cycle engine which mounted on optical spacer with measuring window and glass inlet entry for laser anemometer measurement. A dual beam laser Doppler anemometer was used with conventional forward scattered method and comprised argon-ion laser, frequency shifter with Bragg cell module, and the signal processor. Measurements of mean velocity fluctuation of inlet flow for different engine speeds, measuring positions, and the changes in cylinder volume are investigated. The results presented show that the changes in engine speed is shown to be strongly influenced on the mean velocity of inlet air. The effect of measuring position and cylinder volume on the inlet velocity was also investigated for the inlet port entry and is shown to be small compared to the engine speed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.10-17
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• 2013

This thesis proposes an automatic embedded core generator system that supports branch prediction. The proposed system includes a dynamic branch prediction module that enhances execution speed of target applications by inserting history/direction flags into BTAC(Branch Target Address Cache). Entries of BHT(Branch History Table) and BTAC are determined based on branch informations extracted by simulation. To verify the effectiveness of the proposed branch prediction module, ARM9TDMI core including a dynamic branch predictor was described in SMDL and generated. Experimental results show that as the number of entry rises, area increase up to 60% while application execution cycle and BTAC miss rate drop by an average of 1.7% and 9.6%, respectively.

• Journal of computational fluids engineering
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• v.19 no.1
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• pp.7-14
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• 2014

Aerothermodynamic characteristics of re-entry vehicles in hypersonic speed regimes are investigated by applying CFD methods based on the Navier-Stokes-Fourier equations. A special emphasis is placed on the effects of high temperature chemically reacting gases on shock stand-off distance and thermal characteristics of the flowfields. A ten species model is used for describing the kinetic mechanism for high temperature air. In particular, the hypersonic flows around a cylinder are computed with and without chemically reacting effects. It is shown that, when the chemically reacting effects are taken into account, the shock stand-off distance and temperature are significantly reduced.

• 연구논문집
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• s.25
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• pp.13-22
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• 1995

At the running speed higher than 250 km/h, several aerodynamic problems such as the increase of aerodynamic resistance, aerodynamic noise, pressure fluctuation at the tunnel entry, impulsive wave at the tunnel exit bring about the power consumption, deterioration of riding quality, and severe environmental noise. To solve these aerodynamic problems, the flow phenomena around the high speed train have to be analyzed in detail. In this study, the flow around the train is modelled as the 2-dimensional viscous compressible flow and the flow field is calculated numerically for the three different types of geometry and running speed. The aerodynamic drag coefficient and the pressure coefficient are evaluated each case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2169-2177
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• 2015

This paper proposes a new pattern matching module to overcome the increased runtime of previous algorithm using RAM, which was designed to overcome cost limitation of hash-based algorithm using CAM (Content Addressable Memory). By adopting Merge FSM algorithm to reduce the number of state, the proposed module contains state block and entry block to use in RAM. In the proposed module, one input string is compared with multiple entry strings simultaneously using entry block. The effectiveness of the proposed pattern matching unit is verified by executing Snort 2.9 rule set. Experimental results show that the number of memory reads has decreased by 15.8%, throughput has increased by 47.1%, while memory usage has increased by 2.6%, when compared to previous methods.

• Journal of Korean Society of Transportation
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• v.28 no.3
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• pp.29-37
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• 2010

Ramp metering control is the most representative strategy of uninterrupted flow control and management system. Ramp metering is to adjust vehicles entering an expressway in such a way that expressway mainline maintains flow stability by regulating ramp vehicles. The effect of two metering strategies, single-entry metering and platoon metering, on mainstream under the same metering rate with pre-timed metering are analyzed by micro-simulation. Platoon metering shows lower performance than single-entry metering under the same metering rate in terms of speed, density, and delay, causes earlier breakdown than single-entry metering. It indicates that the selection of metering type has critical importance as the flow of mainline is high.

• Journal of Internet Computing and Services
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• v.20 no.1
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• pp.57-65
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• 2019

In the case of Domeggook B2B online shopping malls, it has a market share of over 70% with more than 2 million members and 800,000 items are sold per one day. However, since the same or similar items are stored and registered in different catalog entries, it is difficult for the buyer to search for items, and problems are also encountered in managing B2B large shopping malls. Therefore, in this study, we developed a catalog entry auto classification and recommendation system for products by using semi-supervised machine learning method based on previous huge shopping mall purchase information. Specifically, when the seller enters the item registration information in the form of natural language, KoNLPy morphological analysis process is performed, and the Naïve Bayes classification method is applied to implement a system that automatically recommends the most suitable catalog information for the article. As a result, it was possible to improve both the search speed and total sales of shopping mall by building accuracy in catalog entry efficiently.