• The Journal of the Acoustical Society of Korea
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• 제32권6호
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• pp.484-493
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• 2013

Typical underwater acoustic sensors can measure the scalar quantity of sound-pressure-magnitude with the limitation of being unable to identify the direction of an incoming wave. This paper proposes a method to detect the direction of the sound wave with a ring sensor. The sensor of the proposed structure has a piezoceramic ring divided into eight elements, and distinguishes the direction of the sound wave by properly combining the output voltages of the piezoceramic elements. Further, through the analysis of the effects of the structural parameters like the ring radius and length, and piezoceramic thickness, we have suggested the way to improve the sensitivity of the vector sensor.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제20권3호
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• pp.519-526
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• 2016

As marine accidents happen frequently, it is required to establish a marine traffic monitoring system, which is designed to improve the safety and efficiency of navigation in VTS (Vessel Traffic Service). For this aim, recently, X-band marine radar is used for extracting the sea surface information and, it is necessary to retrieve wave information correctly and provide for the safe and efficient movement of vessel traffic within the VTS area. In this paper, three different current estimation algorithms including the classical least-squares (LS) fitting, a modified iterative least-square fitting routine and a normalized scalar product of variable current velocities are compared with buoy data and then, the iterative least-square method is modified to estimate wave information by improving the initial current velocity. Through several simulations with radar signals, it is shown that the proposed method is effective in retrieving the wave information compared to the conventional methods.

• Journal of the Korean Institute of Telematics and Electronics D
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• 제35D권1호
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• pp.8-15
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• 1998

An analysis of the microstripline is started as an assumption of the axial & transveral current distribution. Applying the boundary conditions to the scalar wave equations of a electric & magnetic potential, the two simultaneous coupled integral equations are produced. The electronmagnetic fields in microstrip line can be obtained by solving these two coupled integral equaltion. In general, either a numerical analysis method or a Galerkin method was used to solve them. In this paper, a residue theorem is proposed to solve them. The electromagnetic fields are expressed as integral equations for LSE and LSM mode in the spectral domain. Applying a residue theorem to the Fourier transformed equation and Fourier inverse transformed equation which is necessary for interchanging the space domain and the spectral domain, the electromagnetic fields are expressed as algebraic equations whichare relatively easier to handle. the distributions of the electromagnetic field are shown at the range of -5w/2.leq.x.leq.5w/2, 0.lep.y.leq.4h for z=0. It agrees well with the results of the Quasi-TEM mode analysis.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.239-243
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• 2005

Fully three-dimensional Large Eddy Simulation calculations of the flow past 2D cavity are conducted to study the purging of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity. The length to depth ratio(L/D) is 2 and Reynolds number based on the depth is 3,360. Fully developed turbulent inflow are fed at the inlet from precursor simulation of channel flow. Mean flow pattern and unsteady features are investigated based on the experimental data of Pereira and Sousa. From the study of mass exchange processes, it is found that the mechanism of removal of the contaminant is very different between the non-buoyant and buoyant cases. In the buoyant case, internal wave motion which interacts with a strong cavity vortex is dominant in the ejection mechanism of the contaminants.

• The Transactions of the Korean Institute of Electrical Engineers
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• 제33권11호
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• pp.425-432
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• 1984

This paper is to propse a new self-excitation method of synchronous generator. Instead of conventional exciter of synchronous generator, the additional winding which is arranged in addition to the armature winding, is used in this generator. The output terminal of the additional winding is connected to a capacitor and to a full wave rectifier in series. In this configuration, one source double excitation which is composed of capacitor-self-excitation by lead urrent and direct current excitation by rectifier, is induced. The result is that` The excetation efficency is improved greatly and output waveform is improved also. In three-phase synchronous generator using the new method of the one source double excitation, voltage element (shunt characteristics) and current element (series characteristics)are compounded in scalar by adapting star-point-open-rectifier system. The result is as following` The effect of load power factor angle on voltage regulation is reduced greatly, compound characteristics is become manifold by controlling capacity of capacitor, and transient response is improved.

• The Journal of the Acoustical Society of Korea
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• 제14권2E호
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• pp.87-90
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• 1995

A new solution to the two-dimensional scalar wave equation is presented, which descries a diffraction-limited beam maintaining the lateral field response expressed by the sinc function. Physically, it is a superposition of plane waves having different wavelengths traveling in different directions. The beam can attain a line focus with one-dimensional array transducer in ultrasonic medial imaging.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.475-480
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• 2007

For the propagation of elastic waves in unbounded domains, absorbing boundary conditions at the fictitious numerical boundaries have been proposed. In this paper we focus on both first- and second-order paraxial boundary conditions(PBCs) in the framework of variational approximations which are based on paraxial approximations of the scalar and elastic wave equations- We propose a penalty function method for the treatment of PBCs and apply these into finite element analysis. The numerical verification of the efficiency is carried out through comparing PBCs with Lysmer-Kuhlemeyer' s boundary conditions.

• Journal of the Korean Institute of Telematics and Electronics
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• 제3권4호
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• pp.16-24
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• 1966

The LASER Amplifier is treated in the manner of a Fabry-Perot Resonator with an active media, five layers are considered: air, reflector, active medium(ruby), reflector and air. One dimensional scalar wave equations are derived using the method of boundary value probrems in which it is assumed that incident coherent radiation falls normally on the surface wall. All equations are treated from the transient analysis point of view using the Laplace transform nethods, and are arranged steady state region as an amplifier and transient region as a self excited oscillator. Also some remarks are given on the design problem of LASER amplifier in connection with the transient terms involved.

• Journal of Ocean Engineering and Technology
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• 제7권1호
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• pp.99-106
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• 1993

The use of Hermite cubic element, as a possible finite element computation of transport equations containing shocks, has been invesigated. In the present paper the hermite cubic elements are applied to both linear and nonlinear scalar one and two dimensional equations. In the one dimensional problems, numerical results by the hermite cubic element show better than those by the linear element, and the steady state solution by the hermite cubic element yields result with good resolution. This fact proves the superiority of the hermite cubic element in space differencing. In two dimensional case, the results by the hermite cubic element shows a boundary instability, and the use of higher order time differencing method may be necessary for fixing the problem.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2010년도 학술발표회
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• pp.546-550
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• 2010

흐름과 장파에 의하여 발생되는 난류의 subgrid scale mixing effects를 고려할 수 있는 수심적분형 모형(depth-integrated model)을 제시하였다. 완전비선형의 수심적분형 모형은 약분산(weakly dispersive) 환경에서 흐름의 회전성(rotational)을 고려하도록 perturbation approach를 이용하여 유도되었다. 동일한 방법을 이용하여 수심적분형 이송확산방정식(depth-integrated scalar transport equation)을 유도하였다. 방정식은 4차정확도의 유한체적기법을 이용하여 해석하였으며, 다양한 혼합양상을 보이는 흐름에 대한 수치모의를 수행하였다.