• International Journal of Naval Architecture and Ocean Engineering
• /
• 제12권1호
• /
• pp.755-767
• /
• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• 한국음향학회지
• /
• 제18권1호
• /
• pp.25-31
• /
• 1999

본 연구에서는 음향측정 목적의 선형배열에 가우시안 가중치를 적용시킨 광대역 단일 빔형성 알고리듬을 제안한다. 제안 알고리듬은 배열 내의 모든 센서를 동시에 사용하여 1회에 광대역 수신 빔을 형성시킨다. 여기서 주파수 종속 함수의 가우시안 가중치는 각 센서의 수신 주파수 범위를 제어하도록 시간지연 보상 전에 적용된다. 시뮬레이션 결과, 제안 알고리듬에 의해 형성된 광대역 단일빔의 지향지수 및 빔패턴 특성이 광대역 음향신호 측정에 가용함을 확인하였다.

• 전자공학회논문지B
• /
• 제32B권1호
• /
• pp.127-135
• /
• 1995

The diffusion neural network forms a Gaussian distribution by transferring an excitation to the surround. A DOG(difference of two Gaussians) is obtained by the diffusion neural network. This type of the DOG, which can detect the intensity changes of an image, has the same shape as a LOG(Laplacian of a Gaussian:${\Delta}^2$G) and narrow band pass characteristics. In this paper we show that another type of the DOG which has a very narrow Gaussian for the excitatory and a very wide Gaussian for the inhibitory, can be formed by the diffusion process of this network, This type of the DOG has a wide band width in spatial frequency domain and can be used efficiently in detecting special type of edges.

• 대한조선학회논문집
• /
• 제55권6호
• /
• pp.466-473
• /
• 2018

Most frequency domain-based approaches assume that structural response should be a Gaussian random process. But a lot of non-Gaussian processes caused by multi-excitation and non-linearity in structural responses or load itself are observed in many real engineering problems. In this study, the effect of non-Normality on fatigue damages are discussed through case study. The accuracy of four frequency domain methods for non-Gaussian processes are compared in the case study. Power-law and Hermite models which are derived for non-Gaussian narrow-banded process tend to estimate fatigue damages less accurate than time domain results in small kurtosis and in case of large kurtosis they give conservative results. Weibull model seems to give conservative results in all environmental conditions considered. Among the four methods, Benascuitti-Tovo model for non-Gaussian process gives the best results in case study. This study could serve as background material for understanding the effect of non-normality on fatigue damages.

• 대한조선학회논문집
• /
• 제52권1호
• /
• pp.88-95
• /
• 2015

For the frequency-domain spectral fatigue analysis, the probability density function of stress range needs to be estimated based on the stress spectrum only, which is a frequency domain representation of the response. The probability distribution of the stress range of the narrow-band spectrum is known to follow the Rayleigh distribution, however the PDF of wide-band spectrum is difficult to define with clarity due to the complicated fluctuation pattern of spectrum. In this paper, efforts have been made to figure out the links between the probability density function of stress range to the structural response of wide-band Gaussian random process. An artificial neural network scheme, known as one of the most powerful system identification methods, was used to identify the multivariate functional relationship between the idealized wide-band spectrums and resulting probability density functions. To achieve this, the spectrums were idealized as a superposition of two triangles with arbitrary location, height and width, targeting to comprise wide-band spectrum, and the probability density functions were represented by the linear combination of equally spaced Gaussian basis functions. To train the network under supervision, varieties of different wide-band spectrums were assumed and the converged probability density function of the stress range was derived using the rainflow counting method and all these data sets were fed into the three layer perceptron model. This nonlinear least square problem was solved using Levenberg-Marquardt algorithm with regularization term included. It was proven that the network trained using the given data set could reproduce the probability density function of arbitrary wide-band spectrum of two triangles with great success.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2003년도 하계종합학술대회 논문집 V
• /
• pp.2641-2644
• /
• 2003

Recently, TRAO Taeduk Radio Astronomy Observatory is developing wide-band digital spectrometer for radio astronomy, which will be used as back-end signal processing unit of Dual channel SIS receiver. So in this paper, we performed development of high speed digitizing sampler for the wide-band digital autocorrelator, which can perform sampling and quantization on pseudo-random gaussian noise with the maximum conversion speed of 1.5 Gsps..

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 1998년도 추계종합학술대회 논문집
• /
• pp.1267-1270
• /
• 1998

This paper analyzes the characteristics of wide-band one-shot beam formed by using all sensors of array at once, as variation of weighting width. Gaussian function is applied to each sensor as a role of weighting. As the results of the simulation for nested linear array having 17 sensors for each octave, as the width goes wider the directivity index(DI) becomes lower but more even and the variation of beamwidth becomes smaller. It is confirmed, therefore, that weighting width is carefully decided in consideration of DI level, DI stability and the beamwidth.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 1998년도 하계종합학술대회논문집
• /
• pp.639-642
• /
• 1998

This paper proposes a new wide-band beamforming which has guassian weighting. For the prupose of measurement this beam is formed by using all sensors toghether, not octave-by-octave. Weighting is applied to each sensor before time-delay compensation as a frequency-dependent function. As the resutls of the simulation of the proosed algorithm for nested linear array having 17 sensors for each octave, it is confirmed that beam can be formed with all sensors together and uniform directivity index can be achieved by proposed algorithm.

• 대한조선학회논문집
• /
• 제49권4호
• /
• pp.359-366
• /
• 2012

This is the final one of the two companion papers dealing with accuracy of accumulated fatigue damage estimation under wide band process. It is stated that four kinds of wide band models exist: typed of equivalent stress, combined PDF, correction factor, and damage combination. For the idealized ESDs from full scale measurement data on an 8100TEU container vessel, fatigue damages are compared for a narrow band prediction model based on Rayleigh PDF and five wide band fatigue prediction models of Dirlik, Wirsching-Light, Jiao-Moan, Benasciutti and DNV. DNV model consistently overestimates fatigue damages regardless of variation of ESDs. Predictions by Jiao-Moan model, which is understood as standard method for design of offshore platforms, are also in conservative side. Best accuracy is found from the results by Dirlik and Benasciutti models, but Benasciutti model is preferred since it can easily combined with narrow band fatigue damage based on Rayleigh PDF.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2003년도 추계종합학술대회
• /
• pp.133-136
• /
• 2003

초광대역(Ultra-WideBand) 시스템은 1nsec 이하의 매우 짧은 펄스폭을 갖는 가우시안 모노펄스를 이용하여 전송한다. 따라서, 전송 신호는 매우 낮은 전력의 수 GHz에 이르는 초광대역 스펙트럼을 갖게 되며, 기존의 통신 시스템에 거의 간섭을 미치지 않는 것으로 알려져 있다. 반송파를 사용하지 않는 초광대역 시스템에서 다중 경로 전파의 충돌은 일반적인 무선 통신시스템과는 매우 다르다. 이 논문은 다중 경로 채널하에서 BPSK, QPSK, 16-QAM 변복조 기술들을 적용한 초광대역 시스템을 컴퓨터 시뮬레이션을 이용하여 BER(Bit Error Rate) 성능을 비교 분석하고자 한다.