• Journal of applied mathematics & informatics
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• v.17 no.1_2_3
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• pp.1-23
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• 2005

The shortest-paths problem is a fundamental problem in graph theory and finds diverse applications in various fields. This is why shortest path algorithms have been designed more thoroughly than any other algorithm in graph theory. A large number of optimization problems are mathematically equivalent to the problem of finding shortest paths in a graph. The shortest-path between a pair of vertices is defined as the path with shortest length between the pair of vertices. The shortest path from one vertex to another often gives the best way to route a message between the vertices. This paper presents an $O(n^2)$ time sequential algorithm and an $O(n^2/p+logn)$ time parallel algorithm on EREW PRAM model for solving all pairs shortest paths problem on circular-arc graphs, where p and n represent respectively the number of processors and the number of vertices of the circular-arc graph.

• Journal of Magnetics
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• v.21 no.3
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• pp.374-378
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• 2016

The transformer used in an inverter type arc welding machine is designed to use high frequency in order to reduce its size and cost. Also, selecting core materials that fit frequency is important because core loss increases in a high frequency band. An inrush current can occur in the primary coil of transformer during arc welding and this inrush current can cause IGBT, the switching element, to burn out. The transformer design was carried out in $A_P$ method and amorphous core was used to reduce the size of transformer. In addition, sheet coil was used for primary winding and secondary winding coil considering the skin effect. This paper designed the transformer core with an air gap to prevent IGBT burnout due to the inrush current during welding and proposed the optimum air gap length.

• Korean Management Science Review
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• v.15 no.2
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• pp.229-237
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• 1998

This paper presents a new algorithm for the K Shortest Paths Problem which is developed with a Double Shortest Arborescence and an inward arc breaking method. A Double Shortest Arborescence is made from merging a forward shortest arborescence and a backward one with Dijkstra algorithm. and shows us information about each shorter path to traverse each arc. Then K shorter paths are selected in ascending order of the length of each short path to traverse each arc, and some paths of the K shorter paths need to be replaced with some hidden shorter paths in order to get the optimal paths. And if the cross nodes which have more than 2 inward arcs are found at least three times in K shorter path, the first inward arc of the shorter than the Kth shorter path, the exposed path replaces the Kth shorter path. This procedure is repeated until cross nodes are not found in K shorter paths, and then the K shortest paths problem is solved exactly. This algorithm are computed with complexity o($n^3$) and especially O($n^2$) in the case K=3.

• Journal of Magnetics
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• v.21 no.2
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• pp.204-208
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• 2016

This paper demonstrates the key parameter detection for smelting of submerged arc furnace (SAF) based on magnetic field radiation. A magnetic field radiation model for the inner structure of SAF is established based on relative theory of electromagnetic field. A simple equipment of 3D magnetic field detection system is developed by theoretical derivation and simulation. The experiments are carried out under the environment of industrial field and AC magnetic field generated by electrode currents and molten currents in the furnace is reflected outside of the furnace. The experimental results show that the key parameters of smelting including the position of electrode tip, the length of electric arc, and the liquid level of molten bath can be achieved. The computed tomography for SAF can be realized by the detection for smelting.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.2
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• pp.207-213
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• 2001

Welding variables and condition in gas metal arc welding (GMAW) effect on the weld quality and productivity, extensive research efforts have been made to analyze the welding variables and conditions. In this study dynamic behavior of GMAW system is investigated using the chararcteristic equations of the power supply. wire and welding arc. Characteristic equation of wire is modified to include the effect of droplets attached at the electrode tip. The dynamic characteristics of arc length, current, voltage with respect to the step, ramp inputs of CTWD was simulated. From results of simulation, some predictions about dynamic characteristics of GMAW and welding process are available. The proposed simulator and results appear to be utilized to determine the proper welding conditions, to be improved by considering power supply dynamic characteristics.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.293-300
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• 1999

A mathematical model for the analysis of roll gap phenomena in strip temper rolling process is described. The mechanical peculiarities of temper rolling process, such as high friction value and non-circular contact arc, low reduction and non-negligible entry and exit elastic zones as well as central restricted deformation (preliminary displacement or sticking) zone etc., are all taken into account. The deformation of work rolls is calculated with the influence function method and arbitrary contact arc shape is permitted. The strip deformation is modeled by slab method and the entry and exit elastic deformation zones are included. The restricted deformation zone near the neutral point is also considered. The concept and the calculation method of limiting preliminary displacement are used to determine the length of the central restricted deformation zone. The comparison of the model results with the measured mill data is also made.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.129-138
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• 2012

This paper deals with geometrical non-linear analyses of the tapered variable-arc-length beam, subjected to the combined load with an end moment and a point load. The beam is supported by a hinged end and a frictionless sliding support so that the axial length of the deformed beam can be increased by its load. Cross sections of the beam whose flexural rigidities are functionally varied with the axial coordinate. The simultaneous differential equations governing the elastica of such beam are derived on the basis of the Bernoulli-Euler beam theory. These differential equations are numerically solved by the iteration technique for obtaining the elastica of the deformed beam. For validating theories developed herein, laboratory scaled experiments are conducted.

• Journal of Sensor Science and Technology
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• v.25 no.3
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• pp.208-212
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• 2016

In this work, a loop sensor for Arc-Flash detections has been developed in order to trip a circuit breaker within 2.5 ms after an Arc-Flash event. For an efficient capturing of the flash light, plastic optical fibers, where light attenuations are larger than those in silica-based ones, with different diameters and surface conditions were utilized. The performance was comparatively analyzed with those of a point sensor and a commercialized product. The point sensor module was designed for hemisphere-like capturings of Arc-Flashes larger than 3 kA at 2 meters from the sensor. On the other hand, the loop sensor allowed 360-degree-detections around the fiber axis and the measurement range was dependent on the length of the fiber connected to the sensor module. The trip-level-dependent brightness measurement results showed that the fabricated point sensor and loop sensor satisfied a brightness condition, 10~40 klux, and the responses of the system to Arc-Flashes were completed within 2.5 ms.

• 연구논문집
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• s.30
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• pp.147-157
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• 2000

The filtered vacuum arc source (FVAS), which is adopted by magnetic filtering methode to remove the macro-particle in vacuum arc plasma, was composed of a torus structure with bending angle of 60 degree. The radius of torus was 266 mm, the radius of plasma duct was 80 mm and the total length was 600 mm. The magnet parts were consisted of one permanent magnet, one magnetic yoke and five solenoid magnets. The plasma duct was electrically isolated from the ground so that a bias voltage could be applied. The baffles inside plasma duct were installed in order to prevent the recoil effect of macro-particles. Graphite was used as the cathode material to coat the amorphic diamond film and its diameter was 80 mm. The amorphic diamond film attracts much attention due to its excellent mechanical, optical and tribological properties suitable for wide range of applications. The effects of solenoid magnet in plasma extraction were studied by computer simulation and experiment using Taguchi's method. The source and extraction magnet affected the arc stabilization. The extraction beam current was maximized with low value of the source magnet current and high value of the filtering magnet current. Optimum deposition condition was obtained when the currents of arc discharge, source, extraction, bending, deflection and outlet magnet were 30 A, 1 A, 3 A, 5 A, and 5 A, respectively.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.972-974
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• 2005

The present work deals with the theoretical study of the effects of copper vapours resulting from the erosion of the electrodes on the properties of a SF6 arc in a Laval nozzle. Computations have been done for a DC arc of 1000A with upstream gas pressure of 3.75MPa. The arc plasma is assumed to be in local thermodynamic equilibrium(LTE). The sheath and non-equilibrium region around the electrodes are not considered in this model. However, its effects on the energy flux into the electrodes are estimated from some experimental and theoretical data. The turbulence effects are calculated using the Prandtl mixing length model. A conservation equation for the copper vapour concentration is solved together with the governing equations for mass, momentum and energy of the gas mixture. Comparisons were made between the results with and without electrodes erosion. It has been found that the presence of copper vapours cools down the arc temperature due to the combined effects of increased radiation and increased electrical conductivity. The copper vapour distribution is very sensitive to the turbulent parameter. The erosion of upstream electrode(cathode) has larger effects on the arc compared to the downstream electrode(anode) as the copper vapour eroded from the anode cannot diffuse against the high-speed axial flow.