• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.18-23
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• 2002

Liquid phase mixing of impinging injector is a resultant byproduct from the momentum exchange between a pair of impinging jets and penetration of opponent jet. Principal aim of the present study is revealing the liquid phase mixing mechanism of split triplet impinging injection sprays, and thus extending our understanding on this particular injection element. Overall mixing extent is estimated from patternation tests by the use of purified tap water and kerosene to simulate the real propellant components, respectively, and with the liquid jet momentum ratio, a controlling mixing parameter, in the range of 0.5 to 6.0. Emphasis is placed on the effect of liquid sheet superposition and disintegration, and the results with detailed spray visualization revealed the fact that superposed liquid sheet disintegration is the main pathway of liquid phase mixing of split triplet impinging injector to yield enhanced mixing qualities.

• Structural Engineering and Mechanics
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• v.23 no.3
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• pp.233-247
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• 2006

Most codes of practice state that for large in-plane structures it is necessary to account for the spatial variability of earthquake ground motion. There are essentially three effects that contribute for this variation: (i) wave passage effect, due to finite propagation velocity; (ii) incoherence effect, due to differences in superposition of waves; and (iii) the local site amplification due to spatial variation in geological conditions. This paper discusses the procedures to be undertaken in the time domain analysis of a cable-stayed bridge under spatial variability of earthquake ground motion. The artificial synthesis of correlated displacements series that simulate the earthquake load is discussed first. Next, it is described the 3D model of the International Guadiana Bridge used for running tests with seismic analysis. A comparison of the effects produced by seismic waves with different apparent propagation velocities and different geological conditions is undertaken. The results in this study show that the differences between the analysis with and without spatial variability of earthquake ground motion can be important for some displacements and internal forces, especially those influenced by symmetric modes.

• Wind and Structures
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• v.9 no.3
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• pp.193-215
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• 2006

This paper presents an analysis of wind velocity measurements obtained from four ultrasonic anemometers arranged in a vertical formation. The anemometers were located in a rural environment with a view to providing detailed information on the flow statistics of the lower part of the atmospheric boundary layer, particularly for the extreme wind events that are important in loading calculations. The data is analysed using both conventional analysis and conditional sampling. The latter is combined with wavelet analysis in order to provide a detailed analysis of the energy/frequency relationship of the extreme events. The work presented in this paper suggests that on average the extreme events occur as a result of the superposition of two independent mechanisms - large scale events that scale on the atmospheric boundary layer thickness and small scale events a few tens of metres in size.

• Wind and Structures
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• v.8 no.1
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• pp.13-34
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• 2005

This paper presents an analysis of wind velocity and pressure data obtained in a rural environment with a view to identifying the vortex structures present within the flow and examining the relationship between pressure and dynamic pressure. The data is analysed using both conventional analysis and conditional sampling. A method examining the eigenvalues of a matrix formed by the addition of the square of the strain tensor and the square of the vorticity tensor is also investigated. This method illustrates that there are a number of vortex structures present in the flow. The work presented in this paper suggests that the extreme events occur as a result of the superposition of two independent mechanisms.

• Structural Engineering and Mechanics
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• v.31 no.6
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• pp.663-678
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• 2009

An exact solution is obtained for forced torsional vibration of a finite class 622 piezoelectric hollow cylinder with free-free ends subjected to dynamic shearing stress and time dependent electric potential at both internal and external surfaces. The solution is first expanded in axial direction with trigonometric series and the governing equations for the new variables about radial coordinate r and time t are derived with the aid of Fourier series expansion technique. By means of the superposition method and the separation of variables technique, the solution for torsional vibration is finally obtained. Natural frequencies and the transient torsional responses for finite class 622 piezoelectric hollow cylinder with free-free ends are computed and illustrated.

• Journal of the Korean Institute of Navigation
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• v.22 no.1
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• pp.79-89
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• 1998

When an automatic course-keeping is concerned , as is quite popular in modern navigation, the closed-loop steering system consists of autopilot device, power unit(or telemotor unit), steering gear, magnetic or gyro compass and ship dynamics. In order to estimate steering system of ship in open seas, we need to know the characteristics of each component of the system and also to know the characteristics of disturbance to ship dynamics. Calculation methods of irrgular disturbances are based on the linear superposition principle. In this paper, for the purpose of evaluation of automatic steering of ships , the influences of linear control constants of autopilot on propulsive energy loss are investigated bya performance index is introduced from the viewpoint of energy saving. Numberical calculations are carried out for an are carrier and for a fishing boat in multi-directional waves.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1251-1253
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• 2001

This paper presents on capacity design of DC-fed-traction system. The system is introduced including a characteristics of train, feeding network configuration, and design method of substation arrangements. Optimal design procedures is described, and program for capacity computation of the system is presented using the nodal equation, K.C.L, K.V.L, Ohm's law and superposition theory. For the proof of the proposed algorithm, we accomplished the simulation of DC traction system for HA-Nam LRT. By considering whole component in DC traction system the conclusion will be much precise.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.13-16
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• 1998

An anomalous current characteristics which show the superposition of a low current level and high current level at the subthreshold region when SONOSFETs are in memory states were investigated. We have assumed this phenomena were resulted from the effect of parasitic transistors by LOCOS isolation and were modeled to a parallel equivalent circuit of one memory transistor and two parasitic transistors. Theoretical curves are well fitted in measured log I$_{D}$-V$_{G}$ curves independent of channel width of memory devices. The difference between low current level and high current level is apparently decreased with decrease of channel width of devices because parasitic devices dominantly contribute to the current conduction with decrease of channel width of memory devices. As a result, we concluded that the LOCOS isolation has to selectively adopt in the design of process for charge-trap type NVSM.VSM.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1226-1228
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• 2001

In this paper, the modified simulation algorithms of the Auto Transformer (AT) feeding electric train were proposed. To obtain terminal voltage of train by using equivalent circuit of the AT feeding system, the iterative method is proposed for which determine the train voltages. The train voltages are iteratively calculated from the system voltage drop and line impedance. In the case study, the proposed method is verified from actual operation data of the Kwa-Chon line. Also it is verified that the proposed method can be extent to the multi-train simulation tool. The terminal voltage of the multi-train can be calculated by using superposition principle and it is easily applied to the proposed method. Therefore, the proposed method can be a solution for the complexity of the circuit analysis in the existing methods.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.5-6
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• 2006

Molecular motion at the surface of monodisperse polystyrene (PS) films with various chain end groups was studied by scanning probe microscopy. Surface glass transition temperature ($T_{g^s}$) of the PS films was much lower than the corresponding bulk value. And, the magnitude of $T_{g^s}$ was strongly dependent on chain end chemistry. This result can be explained in terms of the chain end concentration at the surface. Time-temperature superposition principle was applied to rheological analysis at the surface. The apparent activation energy of the surface ${\alpha}_{a}$-relaxation process was approximately a half of that for the bulk sample. This result clearly indicates that the cooperativity for the surface segmental motion was reduced in comparison with that in the bulk region.