• Smart Structures and Systems
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• 제21권5호
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• pp.591-600
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• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• 한국컴퓨터정보학회논문지
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• 제23권11호
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• pp.85-93
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• 2018

In recent years, there has been an increasing number of ways to distribute document-based malicious code using vulnerabilities in document files. Because document type malware is not an executable file itself, it is easy to bypass existing security programs, so research on a model to detect it is necessary. In this study, we extract main features from the document structure and the JavaScript contained in the stream object In addition, when JavaScript is inserted, keywords with high occurrence frequency in malicious code such as function name, reserved word and the readable string in the script are extracted. Then, we generate a machine learning model that can distinguish between normal and malicious. In order to make it difficult to bypass, we try to achieve good performance in a black box type algorithm. For an experiment, a large amount of documents compared to previous studies is analyzed. Experimental results show 98.9% detection rate from three different type algorithms. SVM, which is a black box type algorithm and makes obfuscation difficult, shows much higher performance than in previous studies.

• 한국음향학회지
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• 제20권5호
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• pp.100-109
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• 2001

부레를 가진 어류의 산란 강도를 조사하기 위하여 길이가 다른 참돔 (red seabream, pagrus major)을 이용한 음향 실험을 실시하였다. 대상 어류를 살아 있는 상태로 - (1) 망 내에 각각 넣은 후, (2) 자유 유영 상태로 놓은후 - 3개의 음향센서 (38, 120, 200kHz)를 이용하여 길이에 따른 산란강도를 측정하였다. 실험 결과 길이에 따른 참돔의 산란 강도는 각 주파수별로 TS/sub 38㎑/＝20 log/sub 10(l)/ -66.41, TS/sub 120㎑/＝20 log/sub lo(1)/ -71.80, TS/sub 200㎑/＝20 log/sub 10(1)/ -73.94로 나타났다. 실험 결과와 이론 모델을 비교하기 위하여 어류의 형태를 근거로 한 Helmholtz-Kirchhoff 음선 근사법을 사용한 결과, 산란강도는 어류 몸체보다는 부레에 의한 효과가 95%이상으로 나타났다. 한편, 수신된 산란강도 자료를 이용한 확률밀도 함수로부터 어류의 행태에 따른 산란강도 변위는 망 내의 산란체에서는 가우스 확률밀도함수 (Gaussian PDF)로, 자유 유영 상태에서는 레일리 확률밀도함수 (Rayleigh PDF) 특성을 나타냈다.

• 대한안전경영과학회지
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• 제16권2호
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• pp.217-230
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• 2014

The purpose of this study is to develop the Generalized Depreciation Function (GDF) and Winfrey Depreciation Function (WDF) by reviewing methods for the depreciation accountings. The Depreciation Accounting Models (DAM), including straight-line model, declining-balance model, sum-of-the-year-digit model and sinking fund model presented in this paper, are reclassified into the charging pattern of increasing type, decreasing type and constant type. This paper also discusses the development of the GDFs based on convex type, concave type and constant type according to the demand pattern of product, frequency of plant usage, deterioration of time, relative inadequacy, Capital Expenditure (CAPEX) and Operating Expenditure (OPEX) of the Total Productive Maintenance (TPM). The WDFs presented in this paper depict a sudden degradation of plant performance by measuring the change of TPM activity at the midpoint of useful life of asset. The WDFs are classified into left-modal type, symmetrical type and right-modal type by varying the value of skewness and kurtosis. Moreover, three increasing patterns, such as convex, concave and linear types, are used in this paper to present the distinct identification of WFDs by using Instantaneous Depreciation Rate (IDR) in terms of Performance Depreciation Function (PDF) and Depreciation Density Function (DDF). In order to have better understanding of depreciation models, the numerical examples are used for evaluating the Net Operating Less Adjusted Tax (NOPLAT) and Economic Value Added (EVA). It is concluded that the depreciation models showing a large dispersion of EVA require the adjustment of NOPLAT and Invested Capital (IC) based on the objective cash basis and net operating activity for reducing the variation of EVA.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.254-263
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• 2015

In this study, numerical simulations are carried out to investigate the dynamic SGS model effects in a Kerosene-LOx coaxial swirl injector under high pressure conditions. The turbulent model is based on large-eddy simulation (LES) with real-fluid transport and thermodynamics. To assess the effect of the dynamic subgrid-scale (SGS) model, the dynamic SGS model is compared with that of the algebraic SGS model. In a swirl injector under supercritical pressure, the characteristics of temporal pressure fluctuation and power spectral density (PSD) present comparable discrepancies dependant on the SGS models, which affect the mixing characteristics. Mixing efficiency and the probability density (PDF) function are conducted for a statistical description of the turbulent flow fields according to the SGS models. The back-scattering of turbulent kinetic energy is estimated in terms of the film thickness of the swirl injector.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2007년도 제34회 KOSCO SYMPOSIUM 논문집
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• pp.118-125
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• 2007

The firtst-order conditional moment closure (CMC) model is applied to CH4/air swirl diffusion flame in a gas turbine model combustor. The flow and mixing fields are calculated by fast chemistry assumption with SLFM library and a beta function pdf for mixture fraction. RNG k-e model is used to consider the swirl flame in a confined wall. Reacting scalar fields are calculated by elliptic CMC formulation with chemical kinetic mechanism, GRI Mech 3.0. Validation is done against measurement data for mean flow and scalar fields in the model combustor [1]. Results show reasonable agreement with the mean mixture fraction and its variance, while temperature is overpredicted as the level of local extinction increases. The second-order CMC model is needed to consider local extinction with considerable conditional fluctuations near the nozzle.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.50-55
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• 2001

To simulate the combustion process under stratified charged conditions, like GDI engines, the new combustion model is proposed, which is based on Welter's FAE model and Peters' PDF model for considering primary reactions. In addition to these models, the new laminar burning velocity correlation and diffusion flame model are also included in the proposed model. The former can be applicable to much wider range of equivalence ratio, pressure and temperature than the others, such as Keck's and Guilder's models, and the latter has been derived from water-gas shift reaction and hydrogen oxidation, by which the secondary reactions can be considered after primary reactions. 3-D computation has been performed by using STAR-CD v3.05 in the simple cylindrical geometry under stratified charged condition. Judging from the calculated results, the present model proves to be reasonable to simulate the characteristics of flame propagation and concentrations of products in burned regions.

• 한국음향학회지
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• 제21권4호
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• pp.380-386
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• 2002

Rahim의 논문 (M.G. Rahim, et al., PROC. of ICASSP96, 1996)과 같은 기존의 후처리 방법은 음소 모델과 반모델 (anti-model)의 유사도를 이용하여 음소 단위 신뢰도를 계산하고, 이들의 평균을 단어 단위 신뢰도로 정의한다. 그런데 음소단위의 신뢰도가 동일한 확률밀도함수를 갖는 것이 아니기 때문에 특정단어의 경우 계산된 신뢰도는 대체로 낮은 값을 갖는다. 이를 극복하기 위한 방법으로서, 본 논문에서는 기존의 신뢰도를 통계적으로 정규화한 신뢰도를 제안한다. 즉 음소단위의 신뢰도가 가우시안 분포를 갖는다고 가정한 후 트라이 폰(sri-phone) 단위로 정규화하여 동일한 정규분포를 갖도록 한다. 본 논문에서는 제안된 방법의 검증을 위하여 문맥종속 핵심어 모델과 문맥독립 필러 모델을 이용한 일반적인 핵심어 검출기를 사용하였다. 실험결과 제안된 정규화 신뢰도 (NCM: Normalized Confidence Measure)가 불검출율 (WDR: Missed Detection Rate) 8%정도에서 오검출율 (PAR: false alarm rate)을 0.44에서 0.33 FA/KW/HR (false alarm/keyword/hour)로 저하시켰다. 이것은 오검출율에서 성능이 25% 향상된 것이다.

• 한국통신학회논문지
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• 제26권11B호
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• pp.1546-1555
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• 2001

일반적으로 CDMA 시스템의 해석에서 시스템의 대역폭에 관계없이 한 칩 구간 내에 일정한 평균 전력을 갖는 한 개의 다중 경로 성분만을 고려하고 있다. 그러나 본 논문에서는 고정된 채널 모델에서 시스템의 대역폭에 따라 한 칩 구간 내의 다중 경로 성분들의 수를 달리하고, 이 다중경로 성분들에 자기 상관 함수의 기울기와 상대적인 위상을 고려하여 페이딩의 영향을 해석하였다. 이러한 페이딩이 시스템에 미치는 영향을 알아보기 위해 출력 신호의 통계적 분포를 나타내는 출력 신호의 확률 밀도 함수를 구하였다, 그리고 이 출력 신호에 대한 조건부 에러 확률을 이용하여 사용자 수에 대한 평균 에러 확률을 유도하였다. 광대역 다중 경로 채널 모델로 실측 채널 모델인 JTC 채널 모델을 사용하고, 시스템의 성능 개선을 위해 MRC 레이크 수신기를 사용하였다. 그리고 W-CDMA 시스템의 대역폭에 따른 성능을 공정하게 비교하기 위해 사용자 수를 성능비교의 파라미터로 설정하고 동일한 주파수 대역폭 내에서 hybrid FDMA/CDMA 시스템을 가정하여 비교하였다. 모의 실험의 결과로부터 이용 가능한 많은 다중 경로 성분이 존재할 때 고정된 채널 모델에서 시스템의 분해능이 좋을수록 성능이 우수함을 알 수 있었다.

• International Journal of Computer Science & Network Security
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• 제22권5호
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• pp.225-233
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• 2022

Due to the large number of documents that are important to people and many of their requests from time to time to perform an essential official procedure, this requires a practical arrangement and organization for them. When necessary, many people struggle with effectively arranging official documents that enable display, which takes a lot of time and effort. Also, no mobile apps specialize in professionally preserving essential electronic records and displaying them when needed. Dataset consisting of 10,841 rows and 13 columns was analyzed using Anaconda, Python, and Mito Data Science new tool obtained from Google Play. The research was conducted using the quantitative descriptive approach. The presented solution is a model specialized in saving essential documents, categorizing according to the user's desire, and displaying them when needed. It is possible to send in an image or a pdf file. Aside from identifying file kinds like PDFs and pictures, the model also looks for and verifies specific file extensions. The file extension and its properties are checked before sharing or saving it by applying the similarity algorithm (Levenshtein). Our method effectively and efficiently facilitated the search process, saving the user time and effort. In conclusion, such an application is not available, which facilitates the process of classifying documents effectively and displaying them quickly and easily for people for printing or sending to some official procedures, and it is considered one of the applications that greatly help in preserving time, effort, and money for people.