• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.245-253
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• 2020

In this study, natural frequencies are compared using several pile-soil interaction (PSI) models to evaluate the effects of each model on resonance safety checks for a monopile type of wind turbine structure. Base spring, distributed spring, and three-dimensional brick-shell models represented the PSIs in the finite element model. To analyze the effects of the PSI models on a natural frequency, after a stiffness matrix calculation and Winkler-based beam model for base spring and distributed spring models were presented, respectively; natural frequencies from these models were investigated for monopiles with different geometries and soil properties. These results were compared with those from the brick-shell model. The results show that differences in the first natural frequency of the monopiles from each model are small when the small diameter of monopile penetrates hard soil and rock, while the distributed spring model can over-estimate the natural frequency for large monopiles installed in weak soil. Thus, an appropriate PSI model for natural frequency analyses should be adopted by considering soil conditions and structure scale.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.47-50
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• 2015

Speech Signals consist of signals of consonants and vowels, but the lasting time of vowels is much longer than that of consonants. It can be assumed that the correlations between signal blocks in speech signal is very high. Each speech signal is divided into blocks which have 128 speech data. FFT is applied to each block. Low frequency areas of the results of FFT is taken and Covariance matrix between blocks in a speech signal is extracted and finally eigenvalues of those matrix are obtained. It is studied that what the distribution of eigenvalues of various speech files is. The differences between speech signals and noise signals from cars are also studied.

• Proceedings of the Korean Society of Computer Information Conference
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• 2021.07a
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• pp.221-222
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• 2021

본 논문에서는 HFS+ 파일시스템의 클러스터의 상태를 분석하여 디지털 포렌식에 활용하기 위한 기법을 제안한다. 이 방법은 파일시스템의 클러스터 안에 들어있는 정보를 텍스트 형식과 GUI 형식으로 표시하하여 포렌식을 수행하기 위한 정보를 제공하는 것을 목표로 개발한다. 이 기법에서 적용되는 파일시스템은 macOS에서 사용하는 HFS+ 파일시스템으로 파일/디렉토리에 대한 클러스터의 수, 클러스터의 연속정보, 클러스터에 연관된 파일/디렉토리의 고유정보와 시간정보를 표시한다. 이 기법을 위한 도구는 C/C++와 Python언어로 macOS 환경에서 동작하도록 개발된다. 일반적으로 Windows 환경에 비하여 macOS 환경에서 사용할 수 있는 포렌식 분석을 소프트웨어들이 상대적으로 많지 않아서 이 도구에서 제공하는 디스크 클러스터의 할당상태와 그것과 연관된 포렌식 정보를 얻는데 효과적으로 사용될 수 있는 점이 이 연구가 기여하는 바이다.

• The Journal of the Korea Contents Association
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• v.16 no.8
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• pp.90-96
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• 2016

The 3390 million people, around 83% of the adult population in Korea use smartphone. Although the safety problem of the certificate has been occurred continuously, most of these users use the certificate. These safety issues as a solution to 'The owner of a mobile phone using SMS authentication technology', 'Biometric authentication', etc are being proposed. but, a secure and reliable authentication scheme has not been proposed for replace the certificate yet. and there are many attacks to steal the certificate and private key. For these reasons, security experts recommend to store the certificate and private key on usb flash drive, security tokens, smartphone. but smartphones are easily infected malware, an attacker can steal certificate and private key by malicious code. If an attacker snatchs the certificate, the private key file, and the password for the private key password, he can always act as valid user. In this paper, we proposed a safe way to keep the private key on smartphone using smartphone's unique information and user password. If an attacker knows the user password, the certificate and the private key, he can not know the smart phone's unique information, so it is impossible to use the encrypted private key. Therefore smartphone user use IT service safely.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.11a
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• pp.349-352
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• 2017

파일시스템 포렌식으로 삭제된 파일을 복구할 수 있지만 데이터베이스에서 이용한 데이터 파일의 경우 레코드는 복구할 수 없다. 따라서 데이터베이스 포렌식이 연구되고 있다. 데이터베이스 포렌식은 각 데이터베이스 고유 저장 특성을 이용하여 데이터파일에서 삭제된 레코드를 추출하는 기법이다. 그러나 칼럼 정보를 얻지 못할 경우 기존 데이터베이스 포렌식으로는 레코드 복구가 불가능하다. 데이터 파일의 구성단위인 페이지를 읽어 칼럼구조를 유추하면 레코드를 복원할 가능성이 있다. 본 논문은 칼럼 정보 없이 데이터 파일에 레코드가 저장된 형태를 분석하여 삭제된 레코드를 포함한 파일에 잔존하는 레코드를 복구를 위한 분석과 실험을 하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.343-350
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• 2015

Extensive discussion on the optimal types of offshore wind turbine(OWT) among monopile, tripod and jacket in the intermediate depth of water has been actively carried out in worldwide wind turbine industry. Selecting the optimal types of OWT among several substructural types, it is required to consider the economic and technical feasibility including dynamically stable design of a wind turbine system. In this study, the effects of loading levels and uncertainties of soil properties on the natural frequency of OWT have been quantitatively investigated. In conclusion, the natural frequency of monopile-type OWTs has a significant level of uncertainty, hence it is very important to minimize the level of uncertainties in soil properties when the monopile is selected as a foundation for an OWT.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.2
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• pp.183-192
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• 2004

New dynamic analysis procedures lot the vertically drilled sea water pile are suggested and demonstrated by the typical design Problem. Pile structure submerged in the sea water as well as forces by the ocean waves and tidal currents are modeled and formulated by finite element method. To obtain wave forces for the finite element equation, Airy's wave theory is tested and selected among others. Lateral lifting forces induced by the vortex shedding of current flow is simply based on the harmonic function with the Strouhal frequency and lifting coefficient. Natural frequencies and frequency responses for the pile are calculated by NASTRAN using the results of the formulation. Dynamic displacement and stress results obtained by these procedures are shown to be applicable to predict the dynamic behaviors of the ocean pile by the wave and lifting forces as a preliminary design analysis.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.04a
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• pp.103-104
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• 2015

IoT의 주요 구성요소는 기존의 데스크 탑 외에 디바이스 즉, 단말 기기들이 주류를 이룬다. 이러한 IoT 디바이스들은 데이터의 유형이나 접근 방법이 다양하고, 실시간적 데이터 생산과 제어를 위한 양방향 데이터 접근 지원을 필요로 한다. 이러한 IoT 디바이스를 연결하여 클라우드 형 서비스로 개발하기 위해서는 디바이스 속성 관리가 용이한 도메인 관리 방법과 디바이스에 대한 일관된 접근 인터페이스를 제공하는 플랫폼이 필요하다. 이 논문에서는 리눅스 파일시스템 후면 즉, 사용자 영역에 리눅스 파일 시스템 스타일의 DB 기반 가상 파일시스템을 구축하여 IoT 디바이스를 연결하고 관리하는 프레임워크를 제시한다. 구현 가상 파일시스템은 계층적 디렉터리 체계를 DB에 유지하면서 단말 노드에는 지리적으로 산재한 IoT 디바이스들에 대한 속성 정보를 관리한다. 디렉터리 및 IoT 디바이스의 추가 삭제 검색 등 도메인 관리는 mkdir. mknod, ls, find 등 리눅스 고유 명령어로 이루어지고, 모든 IoT 디바이스에 대한 접근은 open(), read(), write(), close() 등 POSIX 인터페이스를 통해 가능하다.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.480-490
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• 2016

As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

• The Korean Journal of Applied Statistics
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• v.21 no.6
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• pp.981-996
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• 2008

Statistical matching techniques whose aim is to achieve a complete data file from different sources. Since the statistical matching method proposed by Rubin (1986) assumes the multivariate normality for data, using this method to data which violates the assumption would involve some problems. This research proposed the statistical matching method using robust regression as an alternative to the linear regression. Furthermore, we carried out a simulation study to compare the performance of the robust regression model and the linear regression model for the statistical matching.