• Journal of radiological science and technology
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• v.3 no.1
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• pp.81-86
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• 1980

To compare three-phase 12-pulse full-wave X-ray generators with single-phase full-wave X-ray generators on their performance of outputs, authors studied the generating X-ray by means of exposure dose and radiographic density. The results were as follows; 1. The exposure doses of three-phase full-wave X-ray generators showed a 30%-60% increase as compared against of single-phase full-wave generators. 2. The transmitted doses of three-phase full-wave generators were more increased than single-phase full-wave X-ray generators. 3. To obtain the same density, 60kVp in three-phase full-wave generators were equivalent to $60{\sim}65kVp$ in single-phase full-wave generators, and 100kVp in those generators were equivalent to $100{\sim}125kVp$ in these generators.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.97-102
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• 2013

Frequency tuning characteristics of a THz-wave by varying phase-matching angle and pump wavelength in a noncollinear phase-matching THz-wave parametric oscillator (TPO) are analyzed. A novel scheme to realize the tuning of a THz-wave by moving the cavity mirror forwards and backwards is proposed in a noncollinear phase-matching TPO. The parametric gain coefficients of the THz-wave in a $LiNbO_3$ crystal are explored under different working temperatures. The relationship between the poling period of periodically poled $LiNbO_3$ (PPLN) and the THz-wave frequency under the condition of a quasi-phase-matching configuration is deduced. Such analyses have an impact on the experiments of the TPO.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.299-310
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• 2003

In the evaluation of the subgrade stiffness structure by the SASW method, the calculation of the phase velocities is the important task controlling the reliability of the result. The interpretation of the phase spectrum should precede the phase-velocity calculation in the current practice of the SASW method. The difficulty involved in the interpretation prohibited the SASW method from being spread over to the industry. This study proposed a new method called the frequency-wave number technique, which is based on the frequency-wave number relationship of the surface wave in the multi-layered system. The frequency-wave number technique eliminates the expertise in the interpretation of the phase spectrum, automates the phase-velocity calculation and expedites the determination of the phase-velocity dispersion curve. To verify the validity of the proposed frequency-wave number method, the transfer function determined from the numerical simulation of the SASW measurements was used fir the calculation of the automatic calculation of the phase velocities and compared with the phase velocities by WinSASW employing the phase-unwrapping method. Also, the proposed method was applied to the real SASW measurements performed at$\bigcirc$$\bigcirc$area in GyeongGi-Do to see how the proposed method works with the real measurements.

• Ocean Systems Engineering
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• v.2 no.3
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• pp.189-203
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• 2012

New experiments focusing on the evolution characteristics of nonlinear wave trains were conducted in a large wave flume. A series of wave trains with added sidebands, varying initial steepness, perturbed amplitudes and frequencies, were physically generated in a long wave flume. The experimental results show that the increasing wave steepness, increases the speed of sidebands growth. To study the frequency and phase modulation, the Morlet wavelet transform is adopted to extract the instantaneous frequency of wave trains and the phase functions of each wave component. From the instantaneous frequency, there are local frequency downshifts, even an effective frequency downshift was not observed. The frequency modulation increases with an increase in amplitude modulation, and abrupt changes of instantaneous frequencies occur at the peak modulation. The wrapped phase functions show that in the early stage of the modulation, the phase of the upper sideband first diverges from that of the carrier waves. However, at the later stage, the discrepancy phase from the carrier wave transformed to the lower sideband. The phase deviations appear in the front of the envelope's peaks. Furthermore, the evolution of the instantaneous frequency exhibits an approximate recurrence-type for the experiment with large imposed sidebands, even when the corresponding recurrence is not observed in the Fourier spectrum.

• Structural Engineering and Mechanics
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• v.25 no.2
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• pp.181-200
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• 2007

A decoupling technique for simulating near-field wave motions in two-phase media is introduced in this paper. First, an equivalent but direct weighted residual method is presented in this paper to solve boundary value problems more explicitly. We applied the Green's theorem for integration by parts on the equivalent integral statement of the field governing equations and then introduced the Neumann conditions directly. Using this method and considering the precision requirement in wave motion simulation, a lumped-mass FEM for two-phase media with clear physical concepts and convenient implementation is derived. Then, considering the innate attenuation character of the wave in two-phase media, an attenuation parameter is introduced into Liao's Multi-Transmitting Formula (MTF) to simulate the attenuating outgoing wave in two-phase media. At last, two numerical experiments are presented and the numerical results are compared with the analytical ones demonstrating that the lumped-mass FEM and the generalized MTF introduced in this paper have good precision.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.145-152
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• 2001

Low Rayleigh number thermal convection in a fluid layer confined between two-infinite horizontal walls kept at spatially sinusoidal temperature distributions, T_L=T_m+\Delta T\sin \kappax,\;T_U=T_m+\Delta T\sin(\kappax-\beta)$, is theoretically investigated by a regular perturbation expansion method. For small wave numbers, an upright cell is formed between the two walls at $\beta$=0. The cell is tilted, as the phase difference increases, and a flow with tow counter-rotating eddies occurs at $\beta=\pi$. when the wave number is large, isolated eddies are formed near the lower and upper walls, for all the phase differences. There exists a wave number at which maximum heat transfer rate at the walls occurs, at each of the phase differences. And the wave number increases with increase of the phase difference. for a fixed wave number, the heat transfer rate decrease with increase of the phase difference.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.576-585
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• 2016

The current control methods of Y-connected 7 Phase BLDC motor are sine wave current control and square wave control. The sine wave current control method needs dq axis transformation of $7{\times}7$ matrix for current control and very complex. Also this method is not suitable for multi Phase BLDC motor of trapezoidal back emf wave. Therefore, in Y connected multi phase BLDC motor, the square wave current control methods are required. Generally, in the 3Phase BLDC system, Average current control method is used for current control. The average current is obtained that the summation of absolute value of each phase current magnitude is divided by the number of conduction phase. However, if average current control method is applied to multi-phase system, there is a problem that each phase currents are different. This problem affects unbalance of each phase torque and fluctuation of total torque. This paper proposed each phase current control method of Y connected 7Phase BLDC system. Proposed method is used for PI controller of each phase for each phase current control. This method can perfect square wave current control. Also, configuration of the method is easier than DQ axis transformation. Proposed method is verified through simulation and experiments.

• Structural Engineering and Mechanics
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• v.85 no.5
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• pp.645-654
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• 2023

Based on first-order shear deformation theory, a wave propagation model of graphene platelets reinforced metal foams (GPLRMFs) circular plates is built in this paper. The expressions of phase-/group- velocities and wave number are obtained by using Laplace integral transformation and Hankel integral transformation. The effects of GPLs pattern, foams distribution, GPLs weight fraction and foam coefficient on the phase and group velocity of GPLRMFs circular plates are discussed in detail. It can be inferred that GPLs distribution have great impacts on the wave propagation problems, and Porosity-I type distribution has the largest phase velocity and group velocity, followed by Porosity-III, and finally Porosity-II; With the increase of the GPLs weight fraction, the phase- and group- velocities for the GPLRMFs circular plate will be increased; With the increase of the foam coefficient, the phase- and group- velocities for the GPLRMFs circular plate will be decreased.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.115-119
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• 2009

We numerically investigated propagation of various waves in the two-phase flows such as sound wave, shock wave, rarefaction wave, and contact discontinuity in terms of pressure, void fraction, velocity and density of the two phases. The waves have been generated by a hydrodynamic shock tube, a pair of symmetric impulsive expansion, impulsive pressure and impulsive void waves. The six compressible two-fluid two-phase conservation laws with interfacial friction terms have been solved in two fractional steps. The first PDE Operator is solved by the HLL scheme and the second Source Operator by the semi-implicit stiff ODE solver. In the HLL scheme, the fastest wave speeds were estimated by the analytic eigenvalues of an approximate Jacobian matrix. We have discussed how the interfacial friction terms affect the wave structures in the numerical solution.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.10a
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• pp.95-104
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• 2006

A floating-type wave power pump is a device which sends air into water by using wave power. The floating-type wave power pump has the new configuration composed of a curved surface reflection board, a slope, and phase plates. As a result of a water-tank experiment it turned out that the floating-type wave power pump with a curved surface reflection board and a slope raised power and efficiency in the wide wavelength waves. The result of a marine experiment was also preferable. The floating-type wave power pump sends air into the sea by using wave power, so it can be used for the improvement of marine environment. In addition, the floating body constituted of a curved surface reflection board, a slope, and phase plates, is effective as a device to utilize the energy of a wave. Therefore, it can be widely used for a wave power generation, pumping up deep seawater.