• Structural Engineering and Mechanics
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• 제83권5호
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• pp.593-607
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• 2022

To solve the problem of detecting structural damage, a two-stage method using the Kalman filter and Particle Swarm Optimization (PSO) is proposed. In this method, the first PSO population is enhanced using the Kalman filter method based on dynamic responses. Due to noise in the sensor responses and errors in the damage detection process, the accuracy of the damage detection process is reduced. This method proposes a novel approach for solve this problem by integrating the Kalman filter and sensitivity analysis. In the Kalman filter, an approximate damage equation is considered as the equation of state and the damage detection equation based on sensitivity analysis is considered as the observation equation. The first population of PSO are the random damage scenarios. These damage scenarios are estimated using a step of the Kalman filter. The results of this stage are then used to detect the exact location of the damage and its severity with the PSO algorithm. The efficiency of the proposed method is investigated using three numerical examples: a 31-element planer truss, a 52-element space dome, and a 56-element space truss. In these examples, damage is detected for several scenarios in two states: using the no noise responses and using the noisy responses. The results show that the precision and efficiency of the proposed method are appropriate in structural damage detection.

• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.289-307
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• 2010

We developed a photometric pipeline to be used for a wide field survey. This pipeline employs the difference image analysis (DIA) method appropriate for the photometry of star dense field such as the Galactic bulge. To verify the performance of pipeline, the observed dataset of the open cluster M11 was re-processed. One hundred seventy eight variable stars were newly discovered by analyzing the light curves of which photometric accuracy was improved through the DIA. The total number of variable stars in the M11 observation region is 335, including 157 variable stars discovered by previous studies. We present the catalogue and light curves for the 178 variable stars. This study shows that the photometric pipeline using the DIA is very useful in the detection of variable stars in a cluster.

• Journal of Communications and Networks
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• 제5권2호
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• pp.124-134
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• 2003

In this paper, we investigate the error probability performance of noncoherently detected orthogonal modulation combined with Alamouti space-time block coding. We find that there are two types of pair-wise error probabilities that characterize the performance. We employ methods that allow a direct evaluation of exact, closed-form expressions for these error probabilities. Theoretical as well as numerical results show that noncoherent orthogonal modulation combined with space-time block coding (STBC) achieves full spatial diversity. We derive an expression for approximate average bit error probability for-ary orthogonal signaling that allows one to show the tradeoff between increased rate and performance degradation.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.127-130
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• 2007

화상 통신과 보안 시스템에서 얼굴 인식을 위한 얼굴영역을 검출하는 연구가 대두되며, 이러한 연구의 전 처리 단계로써 YCbCr 색 좌표계에서 색 정보를 이용하여 피부영역만을 검출하는 알고리즘을 제안한다. CbCr 색 정보를 이용한 기존의 피부 영역 검출 알고리즘의 경우, 실외나 카메라 풀래시를 사용하였을 때 반사광에 의해 밝게 나타난 피부 영역에서 검출 손상이 발생하는 문제점이 나타났다. 따라서 본 논문에서는 어떠한 환경에서도 피부색만을 정확하게 검출하기 위해 기존의 알고리즘을 개선하여 Cb, Cr 뿐만 아니라 Y(Luminance) 값까지 모두 고려한 3-channel 구조의 피부 검출 시스템을 제안한다.

• Smart Structures and Systems
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• 제31권1호
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• pp.13-27
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• 2023

Fatigue crack is a fatal problem for steel structures. Early detection and maintenance can help extend the service life and prevent hazards. This paper presents the ultrasonic guided waves-based (UGWs-based) fatigue crack detection of a steel I-beam. The semi-analytical finite element model has been built to obtain the wave propagation characteristics. Damage indices in both time and frequency domains were analyzed by considering the characteristic variations of UGWs including the amplitude, phase angle, and wave packet energy. The pulse-echo and pitch-catch methods were combined in the detection scheme. Lab-scale experiments were conducted on welded steel I-beams to verify the proposed method. Results show that the damage indices based on the characteristic variations in the time domain can identify and localize the fatigue crack before it enters the rapid growth stage. The damage severity can be reasonably evaluated by analyzing the time-domain damage indices. Two nonlinear damage indices in the frequency domain give earlier warnings of the fatigue crack than the time-domain damage indices do. The identification results based on the above two nonlinear indices are found to be less consistent under various excitation frequencies. More robust nonlinear techniques needed to be searched and tested for early crack detection in steel I-beams in further study.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2004년도 한국우주과학회보 제13권2호
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• pp.52-52
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• 2004

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1998년도 한국우주과학회보 제7권1호
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• pp.15.2-15
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• 1998

No Abstract.See Full-text

• 한국정보과학회논문지:소프트웨어및응용
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• 제36권2호
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• pp.169-177
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• 2009

본 논문에서는 뉴스 기사 분할 관점에서, 뉴스 비디오 샷 경계 탐지 알고리즘의 특성을 고려한 다음과 같은 설계 기준을 제시하고, 이를 모두 만족하는 새로운 샷 경계 탐지 알고리즘을 제안하고자 한다. 1) 뉴스 비디오 샷 경계 탐지의 재현율을 높임으로써, 앵커 샷 탐지 단계에서 입력으로 사용될 데이타의 오류를 최소화한다; 2) 급격한 장면 변환과 점증적 장면 변환을 하나의 알고리즘으로 탐지함으로써 한번의 데이타 탐색으로 샷 분할을 수행한다; 3) 분할된 샷들을 정적 샷과 동적 샷으로 분류함으로써 앵커샷 탐지 단계의 탐색 공간을 축소한다. 제안된 뉴스 비디오 샷 경계 탐지 알고리즘은 특이간 분해를 기반으로 점증적 클러스터링 알고리즘과 머서 커널을 결합한 구조로서, 위에서 제시한 기준을 모두 만족하도록 설계되었다. 제안된 방법론은 특이간 분해를 통해 특징 벡터의 차원축소 뿐만 아니라, 뉴스 비디오를 구성하는 연속적인 프레임에서의 잡음과 아주 작은 변화를 제거함으로써 분류 성능을 높일 수 있다. 또한 머서 커널의 도입은 쉽게 분류되지 않는 데이타를 고차원 공간으로 매핑함으로써 구분하기 어려운 샷 경계의 탐지 가능성을 높여준다. 실험을 통하여 제안된 방법론이 매우 높은 재현율을 보이며, 앵커 샷 탐지를 위한 탐색 공간 축소를 효과적으로 수행함을 보인다.

• International Journal of Aeronautical and Space Sciences
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• 제17권4호
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• pp.535-550
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• 2016

Securing the safety and the reliability of liquid-propellant rocket engines (LREs) for space vehicles is indispensable as engines consist of many complex components and operate under extremely high energy-dense conditions. Thus, health monitoring has become a mandatory requirement, especially for the reusable LREs that are currently being developed. In this context, a dynamic simulation program based on MATLAB/Simulink was developed in the current research on the Space Shuttle Main Engine (SSME), a partly reusable engine. Then, a series of fault simulations using this program was conducted: at a steady state operating condition (104% Rated Propulsion Level), various simulated fault conditions were artificially injected into the simulation models for the five major valves, the pumps, and the turbines of the SSME. The consequent effects due to each fault were analyzed based on the time responses of the major parameters of the engine. It is believed that this research topic is an essential pre-step for the development of fault detection and diagnosis algorithms for reusable engines in the future.

• Journal of Astronomy and Space Sciences
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• 제27권3호
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• pp.221-230
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• 2010

A 4+12+16 amplitude phase shift keying (APSK) modulation outperforms other 32-APSK modulations in a nonlinear additive white Gaussian noise (AWGN) channel because of its intrinsic robustness against AM/AM and AM/PM distortions caused by the nonlinear characteristics of a high-power amplifier. Thus, this modulation scheme has been adopted in the digital video broadcasting-satellite2 European standard. And it has been considered for high rate transmission of telemetry data on deep space communications in consultative committee for space data systems which provides a forum for discussion of common problems in the development and operation of space data systems. In this paper, we present an improved bits-to-symbol mapping scheme with a better bit error rate for a 4+12+16 APSK signal in a nonlinear AWGN channel and propose a simple signal detection algorithm for the 4+12+16 APSK from the presented bit mapping.