• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1610-1615
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• 2007

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.2
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• pp.167-178
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• 1997

It has been expected not only for crew but also for passengers to realize a ship whose rolling and other motions are small as much as possible. Restricting our consideration to the roll reduction, the conventional roll stabilization system, fins or anti-rolling tanks hve been utiized as the actuator. Excessive motions would interfere with the recreational activities of passengers on a cruise ship. Often more than half of the load of a containership is stowed above deck where it is subjected to large acclerations due to rolling. In some situations this may cause some internal damage to the contents of the containers; in more severe situations failure of the lashing can occur and containers may be lost over-board. Underdeck cargo in ordinary cargo ships and bulk commodities in colliers, ore ships and grain ships can shift if the motions become too severe. The purpose of this study is to concentrate on the additions. either internal or external to the hull, that reduce or otherwise improve the motion responses of the hull. It is assumed that the additions are such that their benefit to the motions of the ship outweights any impact on the ability of the ship to perform its assigned task. It is particularly challenging to obtain large improvements in the motion characteristics of existing ships that are being rebuilt or modified for some task not anticipated in their original design. Further the authors will statistically analyze the influence of ruder-roll-yaw coupling motion in the case of application of this advanced control method to various kinds of ship.

• Journal of the Korea Society for Simulation
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• v.17 no.3
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• pp.1-8
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• 2008

It is essential to maintain constant QoS despite of cell overload or erroneous wireless link during transmission because QoS of a multimedia service may be severely degraded by small delay or packet loss. This paper deals with a cell selection method for supporting the QoS of multimedia services over heterogeneous networks. The proposed scheme is based on Fuzzy Multi-Criteria Decision Making (FMCDM), in which uncertain parameters such as user system preference, the communication cost and cell load, and the transmission delay are used in the decision process using the aggregation function in fuzzy set theory. In this scheme, errors in the evaluation parameters impose milder changes on the total evaluation value than in binary logics. Simulation is focused on the average delay and packet loss rate, and the simulation results show that our proposed method provides mobile terminals the optimal performance.

• Journal of Power System Engineering
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• v.19 no.3
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• pp.16-21
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• 2015

Nitrous oxide($N_2O$) concentration in the atmosphere has been constantly increased by the human activities with industrial growth after the industrial revolution. One of factors to increase $N_2O$ concentration in the atmosphere is the $N_2O$ emission caused by the combustion of marine fuel. Especially, a sulfur component included in marine fuel oils is known as increasing the $N_2O$ formation in diesel combustion. Form this point of view, $N_2O$ emission from a ship is not negligible. On the other hand, Exhaust gas recirculation(EGR) that have thermal, chemical and dilution effect is effective method for reducing the NOx emission. In this study, an author investigated $N_2O$ reduction by using EGR on a direct injection diesel engine. The test engine was a 4-stroke diesel engine with maximum output of 12 kW at 2600rpm, and operating condition of the engine was a fixed load of 75%. The experimental oil was a blend-fuel that were adjusted with sulfur ratio of 3.5%, and EGR ratio of 0%, 10%, 20% and 30%. In conclusion, diesel fuel that contained 3.5% sulfur component increased $SO_2$ emission in exhaust gas, and increment of EGR ratio reduced NO emission. Moreover, $N_2O$ emission was decreased as over 50% at EGR ratio of 10% and reduced 100% at EGR ratio of 30% compared with $N_2O$ emission of 0% EGR ratio.

• Journal of Korean Society of Transportation
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• v.33 no.5
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• pp.431-440
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• 2015

This study aims to quantify the railway freight performance using various indicators, to compare it over many countries, and to evaluate efficiency of railway freight in Korea. The indicators developed in this study was classified into two categories; country-specific and company-specific indicator. The former includes freight train density, average gross train load and average haul while the latter contains revenue/ton-km, ratio of operating costs to revenue, revenue per employee, ton-km per employee, costs per ton-km and ratio of labor costs to total operating costs. The results of this study shows that Korail performance is in low efficiency due to multi-frequency small amounts transport. The productivity of railway freight in Korea represented as ton-km per employee appears to be lower than that of other oversea companies considered in this study.

• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.769-782
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• 2006

As the ambient vibration test (AVT) of railway bridges has a limited range of speed, it has a limitation in examining the dynamic behavior of bridges accordingto speed. Thus, in order to analyze the correlation between the speed of a train passing over a bridge and the bridge's dynamic response, we conducted a speed-increasing experiment using a real diesel locomotive. To analyze the acceleration response characteristics, we attached seven vertical accelerometers at equal intervals throughout the entire section of the bridge except the supports, and one horizontal accelerometer to the middle span. Linear variable differential transformers (LVDT) were installed at the bridge's center in both vertical and horizontal directions to investigate the vertical and horizontal behaviors. The test train was statically loaded at the center and at the end of the bridge. And its speed was increased from 5 km/h to 90 km/h. With data obtained from the experiment, the vibration level was evaluated in each direction by the filtering frequency, and the level of horizontal vibration was examined in comparison with vertical vibration. The displacement and wheel load variation was analyzed by speed.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.3
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• pp.51-58
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• 2008

This paper is a study of a prevention of power folding controller's thermal degradation. Power folding technology has been applied for many fields such as side rear vision mirror of vehicles, windshield wiper, antenna, power window. These controllers have been comprised with traditional DC moors, Switching electronic devices, and relays. But this methods have a limitation to overcome such problems of product reliability, endurance, noise margins. Therefore on this paper, to detect the movement of motor, sensing motor brush noise on a load sensing part has been used and controlling a precise RC timing control minimizes the thermal deterioration of motor. And using MOS FETs as a electronic switching device increases life-time and liability of control circuit. After testing such circuit and control method, repetition of operating time, cut-off time, wide operation voltage, power noise margin ware increased over eleven-fold.

• Journal of Environmental Science International
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• v.11 no.12
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• pp.1205-1215
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• 2002

To evaluate the change for water quality after the water gate operation in Shiwha lake, in situ survey were conducted on september in 2000 and January, march, jane in 2001. Chemical characteristics and eutrophication level was estimated from the survey data. The water quality of the Shihwa lake was greatly affected by pollutant load from rainfall, and formation of stratification in summer and winter was increased to effect on nutrient release from sediment. Especially, high concentration of chlorophyll-a was occurred in autumn, due to increased nutrient, high water temperature and low salinity after rainfall runoff. The mean concentration of DIN, DIP were 0.346mg/L, 0.0217mg/L in surface water and 0.826mg/L, 0.0415mg/L in bottom water, respectively, which were over III grade of seawater standard. Also high percentage of ammonia nitrogen to DIN in bottom water for autumn and winter was affected by released nutrient from sediment. Correlation analysis of chlorophyll-a versus TSS was shown that organic matter was affected by autochthonous organic matter stem from the algae, these factor showed reverse correlation about salinity. Closely correlations among to the water quality constituent in continuity survey was appeared. The results of eutrophication index estimation showed the high potentiality of red tide occurrence in Shiwha lake, particularity in summer or fall. Overall water quality was greatly improve to compared with measuring data during 1997~1998 at the beginning water gate operation, which reported by KORDI. Therefore, to improve of water quality in Shiwha lake, we need to establish of management plan about nutrient release from sediment, rainfall runoff, maximum of seawater exchange.

• Convergence Security Journal
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• v.13 no.3
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• pp.47-54
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• 2013

Ad-hoc network is composed of mobile nodes and has a vulnerability of attack like on conventional wire networks. So, many studies have been conducted to apply the traceback mechanism on wire network to Ad-hoc network. In this paper, a new mechanism that can trace back to IP source of spoofing DDoS packet using iTrace message on Ad-hoc network is proposed. The proposed mechanism implements ICMP Traceback message and the traceback path between agents allocated in local network and a server located in management network. Also the proposed mechanism can trace the position of attacker even after an attack is over and has extendability through standardization by using a mechanism that IETF proposed. Result of performance evaluation shows a great improvement in terms of load, integrity, safety, traceback function as compared with conventional mechanisms.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.2
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• pp.261-270
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• 1989

Bend test is one of the methods comparing the physical properties of the clasp wires. The type of bend test used in this investigation was the cantilever loading of a wrought wire. The purpose of this study was to compare the flexibility of a number of commonly used clasp wires, in according to gauge, alloy and heat treatment, under specific condition of load and deflection. Seven noble and one base metal wires were tested under three conditions as follows: (1) as received, (2) quenched (placed in an over at $700^{\circ}C$ for ten minutes and immediately quenched in water at room temperature.), (3) oven cooled (quencned as described, then placed in an oven at $450^{\circ}C$ for two minutes and uniformly slowly cooled to $250^{\circ}C$ in thirty minutes.) The basic test specimen consists of a sample 25 mm in length and 19, 18 gauge in diameter (17 gauge also in two alloys), and the wire was loaded in the form of straight cantilever beams. Force at 0.25 mm (0.01 inch) and 0.5 mm (0.02 inch) deflections for all samples were recorded. The results were as follows ; 1. Ticonium was least flexible and No. 2 was most flexible in according to gauge, alloy and heat treatment. 2. In most of precious wrought wire, the flexibility was increased, but there was no statistically significant differences between as-received and softened condition. 3. There was no statistically differences between as-received and hardened condition. 4. For each alloy, there were statistically significant differences in flexibility due to clasp diameter.