• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.2
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• pp.41-48
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• 2023

In this study, simplified linear numerical method that can simulate wave generation and transformation by a moving bottom is introduced. Numerical analysis is conducted in wave number domain after continuity equation, linear dynamic and kinematic free surface boundary conditions and linear kinematic bottom boundary condition are Fourier transformed, and the results are expressed in space domain by an inverse Fourier transform. In the wavenumber domain, the dynamic free water surface boundary condition and the kinematic free water surface boundary condition are numerically calculated, and the velocity potential in the mean water level (z = 0) satisfies the continuity equation and the kinematic bottom boundary condition. Wave generation and transformation are investigated when the triangular and rectangular shape of bottoms move periodically. The results of the simplified numerical method are compared with the results of previous analytical solutions and agree well with them. Stability of numerical results according to the calculation time interval (Δt) and the calculation wave number interval (Δk) was also investigated. It was found that the numerical results were appropriate when Δt ≤ T(period)/1000 and Δk ≤ π/100.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.225-230
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• 1992

An attempt is made to assemble and synthesize recent publications which may contribute to our capability for understanding the transformation of wave spectra in finite-depth water or in the presence of current. This review is limited essentially to the effects of shoaling and current on one-dimensional transformation of wave spectra and examining the adequacy of the approximation of irregular waves by a monochromatic wave in modeling of wave transformation in coastal areas.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.65-73
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• 2007

In the inverse perturbation method, enormous computational resource was required to obtain reliable results, because all unspecified DOFs were considered as unknown variables. Thus, in the present study, a reduced system method is used to condense the unspecified DOFs by using the specified DOFs, and to improve the computational efficiency as well as the solution accuracy. In most of the conventional reduction methods, transformation errors occur in the transformation matrix between the unspecified DOFs and the specified DOFs. Thus it is hard to obtain reliable and accurate solution of inverse perturbation problems by reduction methods due to the error in the transformation matrix. This numerical trouble is resolved in the present study by adopting iterative improved reduced system(IIRS) as well as by updating the transformation matrix at every step. In this reduction method, system accuracy is related to the selection of the primary DOFs and Iteration time. And both are dependent to each other So, the two level condensation method (TLCS) is selected as Selection method of primary DOFs for increasing accuracy and reducing iteration time. Finally, numerical verification results of the present iterative inverse perturbation method (IIPM) are presented.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.60-67
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• 1994

This is the first of two companion papers which suggests the algorithm of the combined Finite Element Method and Infinite Element Method for the analysis of the axi-symmetric acoustic transducer in the open boundary. Using the algorithm, the numerical analysis for the transducer radiation impedance, directivity, and coupling effect between transducer elements are also conducted. In the second paper, the wideband array transducer is designed and its acoustic characteristics are examined on the basis of the results of the first paper.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.1
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• pp.1-8
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• 1990

In this paper, the transient electromagneti wave scattering at dielectric cylinder is studied by new numerical analysis method. Basic formulation of boundary integral equation (BIE) for numerical method is started weighted residual technique. BIE is made to two simultaneous equation at surface inner and outside point of dielectric cylinder in extended boundary condition (EBC) and surface boundary condition (SBC). Numerical method is used Boundary element method (BEM) that is two form, one is direct method and the other is indirect method, so that this method that transformes operator inversion martics is used numerical analysis. A good agreement of this numerical solution and the other results is obtained.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.270-270
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• 2020

자연재해저감종합계획의 주요 사항은 하천, 내수, 사면, 토사, 바람, 가뭄, 대설재해 등 자연재해로 인명피해나 재산피해가 발생할 수 있는 지역을 선정하고, 이에 적절한 저감대책을 수립하는 것이다. 다른 부분별 계획과 달리 자연재해저감종합계획은 다양한 자연재해를 대상으로 하므로 재해 유형별로 서로 다른 공학적 기법을 적용해야 한다. 실무에서는 자연재해저감종합계획 수립시 HEC-RAS, HEC-HMS(하천재해), XP-SWMM(내수재해), RUSLE(토사재해) 등 다양한 수치모형과 ArcGIS, QGIS 등 GIS 분석도구를 종합적으로 활용한다. 이 때, 모형별로 요구되는 입·출력 자료의 형식이 다양하다 보니 자료를 변환하는 등 번거로움이 발생한다. 이러한 배경에서 자연재해저감종합계획 수립에 GDP Tools의 적용가능성을 검토하고자 한다. GDP Tools는 방재설계 편의를 위해 개발된 도구로 자연재해저감종합계획에서 다루는 대부분의 재해유형에 대한 분석을 지원한다. GDP Tools를 이용하면 별도로 자료 형식을 변환할 필요가 없고, 분석 결과를 도면화하는 등 다양한 편의 기능을 활용할 수 있는 장점이 있다. 본 논문에서는 GDP Tools를 활용하여 자연재해 발생가능성을 검토하고, 그 결과를 기존 방법(상용 모형)의 결과와 비교하여 GDP Tools의 성능을 평가하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11C
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• pp.905-916
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• 2008

In this paper, we propose a new method which estimates and encrypts significant component of digital hologram using discrete wavelet packet transform (DWPT). After analyzing the characteristics of digital hologram in spatial and frequency domain, the required information for ciphering digital hologram was extracted. Based on this information an ciphering method was proposed with wavelet transform and packetization of subbands. The proposed algorithm can encrypt digital hologram in various robust from selecting transform-level and energy threshold. From analyzing the encryption effect numerically and visually, the optimized parameter for encryption is presented. Without additional analyzing process, one can encrypt efficiently digital hologram using the proposed parameter. Although only 0.032% among total data is encrypted, the reconstructed object dose not identified. The paketization information of subbands and the cipher key can be used for the entire secret key.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.1
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• pp.26-35
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• 1996

In this paper, characteristics of the electromagnetically coupled broadband microstrip antennas are analyzed by the Finite Difference Time Domain (FDTD) method, and antenna para- meters are optimized to get maximum bnadwidth. By using short radial tuning stub in microstrip feedline, electromagnetically coupled microstrip antenna shows broadband ($\simeq$13%) characteristics, and the characteristics are varied as a function of radius, radial angle, and position of the radial tuning stub. Operating frequency, return loss, VSWR and input impedance are calculated by Fourier transforming the time domain results. After optimization of the parameters, maximum bandwidth of the radial stub tuning microstrip antenna is about 15% and the ripple char- acteristic of the VSWR is better than the rectangular tuning stub microstrip antenna.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.11a
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• pp.75-78
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• 2013

최근 3D의 발전으로 다음 세대의 3D 기술로 디지털 홀로그램을 지목하고 있다. 본 논문에서는 프레넬릿 변환을 이용하여 디지털 홀로그램 압축을 위한 효과적인 양자화 방법에 대하여 제안하였다. 효과적인 양자화 방법을 위해 각각의 부대역의 특성에 고려하여 우선순위를 정하고 양자화를 적용하였다. 또한 PSNR을 높이고자 예외 인덱스를 적용하였다. 그 결과 2dB 정도 높아지는 것을 확인할 수 있었다. 실험결과에서는 최소 약 6:1부터 최대 약 181:1까지 압축을 수행하였고, PSNR을 이용하여 압축된 영상에 대하여 수치적인 결과를 분석하였다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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• pp.305-308
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• 2000

암의 진행 정도를 판단하기 위한 암세포 조직영상의 분석은 그 대상이 되는 영상의 다양성과 잡음으로 인해 정확한 분석이 어렵다. 특히, 암의 진행 정도를 판단하는데 있어서 중요한 요인인 세포핵의 variation에 따른 order/disorder 정도를 객관적 수치로 정량화하기 위해서는, 각 기(stage)에 따른 암의 진행정도를 가장 잘 나타낼 수 있는 특징값 추출이 필수적이다. 본 논문에서는 가장 유효한 특징값을 추출하기 위하여, 공간 영역과 주파수 영역에서 그 지역적 특징을 잘 나타내는 wavelet 변환을 적용한 후, 분할 된 서브 밴드 중 고대역 서브 밴드에서 질감 특징을 추출하고, 추출 된 질감 특징값들이 암의 진행 정도에 따른 각 집단간에 유의한 차이를 나타내는지에 대한 유의성을 검증하기 위하여, 다변량 통계학적 분석 방법을 사용하여 비교분석 하였다.