• 전자공학회논문지
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• 제51권6호
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• pp.271-275
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• 2014

회전하는 동기 좌표계 d-q 변환을 이용한 단상 능동 전력 필터의 새로운 제어기를 제안하였다. 힐버트 변환기를 사용하여 $90{\circ}$의 위상차를 가지는 두 개의 교류 신호를 만든다. 이 신호들을 회전하는 동기 좌표계 d-q 변환을 이용하여 기본파 성분을 직류로 변환할 수 있고 따라서 고조파 검출이 용이하다. 순시 유효 전력의 평균값을 구한다. 역률 보상을 하므로 전원 전류는 전원 전압과 동위상이다. 단상에서의 전력 공식으로부터 전원 전류의 크기를 알 수 있다. 능동 전력 필터의 보상 전류의 기준 신호는 전원 전류의 기준신호에서 부하 전류를 빼주면 구할 수 있다. 새롭게 제안된 제어기에 히스테리시스 전류 제어기를 적용하여 시뮬레이션 하였다. 능동 전력 필터가 부하전류의 고조파와 무효전력을 보상하여 전원 전류가 전원전압과 동위상이 되고 전원전류가 정현파에 가깝게 되는 것을 확인하였다. 힐버트 변환기는 전대역 여파기를 사용하여 구현하였다.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제28권3호
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• pp.321-338
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• 2014

본 원고에서는 수학자 족보 프로젝트(MGP, Mathematics Genealogy Project)의 과거와 현재에 대해 소개하고, 힐베르트와 저자의 경우를 예를 들어, 우리가 MGP를 어떻게 활용할 수 있을지 연구한다. MGP를 통하여 한국의 주요 수학자들(한국 수학사에 기여한 5명, 역대 한국과학상 수학부문 수상자, 대한수학회 학술상 수상자 등)의 뿌리에 대해 조사해 본 결과 MGP의 데이터베이스에는 그들의 기록이 누락되었거나 부실한 경우가 대부분이었다. 따라서 본 논문에서는 자신의 수학적 뿌리에 대한 정보를 프로젝트에 입력하는 방법을 구체적으로 소개하였다. 이 작업은 한국인 수학자들 자신의 학문적 뿌리를 정리하고 또한 한국 근대 수학사의 이해 및 한국 수학의 미래를 전망하는 데 도움이 된다.

• Smart Structures and Systems
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• 제14권4호
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• pp.595-615
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• 2014

This study aims to investigate the relationship between structural damage and sensitivity indices using the Hilbert-Huang transform (HHT) method. Two damage detection indices are proposed: the ratio of bandwidth (RB), and the ratio of effective stiffness (RES). The nonlinear four bays multiple degree of freedom models with various predominant frequencies are constructed using the SAP2000 program. Adjusted PGA earthquake data (Japan 311, Chi-Chi 921) are used as the excitations. Next the damage detection indices obtained using the HHT and the fast Fourier transform (FFT) methods are evaluated based on the acceleration responses of the structures to earthquakes. Simulation results indicate that, the column of the 1 st floor is the first yielding position and the RB value is changed when the RES<90% in all cases. Moreover, the RB value of the 1 st floor changes more sensitive than those from the top floor. In addition, when the structural response is nonlinear (i.e., RES<100%), the RB and the RES curves indicate the incremental change in the HHT spectra. However, the same phenomenon can be found from FFT spectra only when the stiffness reduction is large enough. Therefore, the RB estimated from the smoothed HHT spectra is an effective and sensitive index for detecting structural damage.

• 한국음향학회지
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• 제30권7호
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• pp.402-407
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• 2011

물리현상의 인과성에 대한 필요충분조건은 Kramers-Kr$\ddot{o}$nig (K-K) 관계식으로 표현된다. 음파에 대한 Kramers-Kr$\ddot{o}$nig 관계식은 음파의 위상속도 분산식과 감쇠계수 분산식 사이의 힐버트 변환 쌍으로 나타난다. 본 연구에서는 400 kHz-1.1 MHz의 고주파 영역에서 물이 찬 다공성 유리구슬 매질에서 측정된 p파 음속 및 감쇠계수를 Waters 등에 의해 얻어진 미분 형태의 Kramers-Kr$\ddot{o}$nig 관계식과 정량적으로 비교했다. 감쇠계수는 주파수의 거듭제곱형태를 따르며, 이때 실험값은 Kramers-Kr$\ddot{o}$nig 관계식과 비교적 정확히 일치한다.

• Steel and Composite Structures
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• 제7권6호
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• pp.457-468
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• 2007

Analytical and experimental investigation on dynamic properties of extra lightweight concrete sandwich beams reinforced with various lay ups of carbon reinforced epoxy polymer composites (CFRP) are discussed. The lightweight concrete used in the core of the sandwich beams was made up of extra lightweight aggregate, Lica. The density of concrete was half of that of the ordinary concrete and its compressive strength was about $100Kg/cm^2$. Two extra lightweight unreinforced (control) beams and six extra lightweight sandwich beams with various lay ups of CFRP were clamped in one end and tested under an impact load. The dimension of the beams without considering any reinforcement was 20 cm ${\times}$ 10 cm ${\times}$ 1.4 m. These were selected to ensure that the effect of shear during the bending test would be minimized. Three other beams, made up of ordinary concrete reinforced with steel bars, were tested in the same conditions. For measuring the damping capacity of sandwich beams three methods, Logarithmic Decrement Analysis (LDA), Hilbert Transform Analysis (HTA) and Moving Block Analysis (MBA) were applied. The first two methods are in time domain and the last one is in frequency domain. A comparison between the damping capacity of the beams obtained from all three methods, shows that the damping capacity of the extra lightweight concrete decreases by adding the composite reinforced layers to the upper and lower sides of the beams, and becomes most similar to the damping of the ordinary beams. Also the results show that the stiffness of the extra lightweight concrete beams increases by adding the composite reinforced layer to their both sides and become similar to the ordinary beams.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권10호
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• pp.1862-1878
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• 2011

With the advances in wireless communication technology and the advent of smartphones, research on location-based services (LBSs) is being actively carried out. In particular, several spatial index methods have been proposed to provide efficient LBSs. However, finding an optimal indexing method that balances query performance and index size remains a challenge in the case of wireless environments that have limited channel bandwidths and device resources (computational power, memory, and battery power). Thus, mechanisms that make existing spatial indexing techniques more efficient and highly applicable in resource-limited environments should be studied. Bitmap-based Spatial Indexing (BSI) has been designed to support LBSs, especially in wireless broadcast environments. However, the access latency in BSI is extremely large because of the large size of the bitmap, and this may lead to increases in the search time. In this paper, we introduce a Selective Bitmap-based Spatial Indexing (SBSI) technique. Then, we propose an Adaptive Bitmap-based Spatial Indexing (ABSI) to improve the tuning time in the proposed SBSI scheme. The ABSI is applied to the distribution of geographical objects in a grid by using the Hilbert curve (HC). With the information in the ABSI, grid cells that have no objects placed, (i.e., 0-bit information in the spatial bitmap index) are not tuned during a search. This leads to an improvement in the tuning time on the client side. We have carried out a performance evaluation and demonstrated that our SBSI and ABSI techniques outperform the existing bitmap-based DSI (B DSI) technique.

• 한국광학회지
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• 제29권3호
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• pp.99-103
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• 2018

동적 광단층 탄성영상법은 광 결맞음 단층촬영법을 기반으로 하여 위상차에 의해 조직의 기계적 성질 중 하나인 탄성도를 측정하기 위한 기법이다. 광 결맞음 단층촬영법은 마이켈슨 간섭계를 기반으로 한 비침습적 고해상도 단면 촬영기법이다. 본 논문에서는 광단층 탄성영상법을 생체 조직에 적용하기 전에 실행가능성을 판단하고자 강도를 쉽게 구분할 수 있는 지우개, 스펀지, 샤프심으로 샘플을 제작하여 실험을 진행하였다. 샘플에 사인파의 일정한 진동자극을 가하기 위해 압전액추에이터를 샘플의 아래쪽에 위치시켰으며 위쪽에서 광 결맞음 단층촬영법으로 스캔하였다. 깊이마다 횡방향에 대한 변형속도를 힐버트 변환하여 포락선을 검출한 후 포락선의 높낮이를 색깔로 표현하여 이미지 상에서 샘플 내의 상대적인 강도를 비교할 수 있었다. 또한, 샘플단과 참조단 사이의 간섭을 이용하는 것보다 샘플단 내의 자기간섭을 이용할 경우 변형속도 계산에 있어 장점이 있음을 제시하였다.

• 한국전자파학회논문지
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• 제23권9호
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• pp.1100-1106
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• 2012

본 논문에서는 시간-주파수 동시 해석 기법 중 하나인 수정된 HHT 기법을 이용하여 회전하는 프로펠러의 날개에서 산란되는 마이크로 도플러 신호를 분석하였다. 프로펠러의 날개 모서리에 산란되는 산란파는 등가전류법(ECM)을 이용하여 구했다. 산란파의 시간 데이터를 얻은 후, 수정된 HHT 기법을 마이크로 도플러 신호의 해석에 적용하였다. 해석 결과는 실제 날개의 동특성에 잘 부합하였으며, 회전체로부터 발생하는 마이크로 도플러의 정편파적인 특성을 보였다. 수정된 HHT를 이용한 시간-주파수 동시 해석은 작은 레이더 단면적 값을 갖는 소형 비행체를 식별하기 위한 명확한 특성을 제공하였다.

• Smart Structures and Systems
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• 제25권1호
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• pp.65-80
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• 2020

In order to protect a structure over its full life cycle, a novel tuned mass damper (TMD), the so-called semi-active eddy current pendulum tuned mass damper (SAEC-PTMD), which can retune its frequency and damping ratio in real-time, is proposed in this study. The structural instantaneous frequency is identified through a Hilbert-Huang transformation (HHT), and the SAEC-PTMD pendulum is adjusted through an HHT-based control algorithm. The eddy current damping parameters are discussed, and the relationship between effective damping coefficients and air gaps is fitted through a polynomial function. The semi-active eddy current damping can be adjusted in real-time by adjusting the air gap based on the linear-quadratic-Gaussian (LQG)-based control algorithm. To verify the vibration control effect of the SAEC-PTMD, an idealized linear primary structure equipped with an SAEC-PTMD excited by harmonic excitations and near-fault pulse-like earthquake excitations is proposed as one of the two case studies. Under strong earthquakes, structures may go into the nonlinear state, while the Bouc-Wen model has a wild application in simulating the hysteretic characteristic. Therefore, in the other case study, a nonlinear primary structure based on the Bouc-Wen model is proposed. An optimal passive TMD is used for comparison and the detuning effect, which results from the cumulative damage to primary structures, is considered. The maximum and root-mean-square (RMS) values of structural acceleration and displacement time history response, structural acceleration, and displacement response spectra are used as evaluation indices. Power analyses for one earthquake excitation are presented as an example to further study the energy dissipation effect of an SAECPTMD. The results indicate that an SAEC-PTMD performs better than an optimized passive TMD, both before and after damage occurs to the primary structure.

• 전자공학회논문지A
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• 제30A권3호
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• pp.16-33
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• 1993

New decoding algorithm of double-error-correction Reed-Solmon codes over GF(2$^{8}$) for optical compact disks is proposed and decoding algorithm of RS codes with triple-error-correcting capability is presented in this paper. First of all. efficient algorithms for estimating the number of errors in the received code words are presented. The most complex circuits in the RS decoder are parts for soving the error-location numbers from error-location polynomial, so the complexity of those circuits has a great influence on overall decoder complexity. One of the most known algorithm for searching the error-location number is Chien's method, in which all the elements of GF(2$^{m}$) are substituted into the error-location polynomial and the error-location number can be found as the elements satisfying the error-location polynomial. But Chien's scheme needs another 1 frame delay in the decoder, which reduces decoding speed as well as require more stroage circuits for the received ocode symbols. The ther is Polkinghorn method, in which the roots can be resolved directly by solving the error-location polynomial. Bur this method needs additional ROM (readonly memory) for storing tthe roots of the all possible coefficients of error-location polynomial or much more complex cicuit. Simple, efficient, and high speed method for solving the error-location number and decoding algorithm of double-error correction RS codes which reudce considerably the complexity of decoder are proposed by using Hilbert theorems in this paper. And the performance of the proposed decoding algorithm is compared with that of conventional decoding algorithms. As a result of comparison, the proposed decoding algorithm is superior to the conventional decoding algorithm with respect to decoding delay and decoder complexity. And decoding algorithm of RS codes with triple-error-correcting capability is presented, which is suitable for error-correction in digital audio tape, also.