• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.411-418
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• 2018

This paper introduces a new method of ice load generation in the time domain for the station-keeping performance evaluation of Arctic offshore structures. This method is based on the ice load spectrum and mean ice load. Recently, there has been increasing interest in Arctic offshore technology for the exploration and exploitation of the Arctic region because of the better accessibility to the Arctic ocean provided by the global warming effect. It is essential to consider the ice load during the development of an Arctic offshore structure. In particular, when designing a station-keeping system for an Arctic offshore structure, a consideration of the ice load acting on the vessel in the time domain is essential to ensure its safety and security. Several methods have been developed to consider the ice load in the time domain. However, most of the developed methods are computationally heavy because they consider every ice floe in the sea ice field to calculate the ice load acting on the vessel. In this study, a new approach to generate the ice load in the time domain with computational efficiency was suggested, and its feasibility was examined. The ice load spectrum and mean ice load were acquired from a numerical analysis with GPU-event mechanics (GEM) software, and the ice load with the varying heading of a vessel was reconstructed to show the feasibility of the proposed method.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2149-2151
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• 2004

The time-frequency domain reflectometry(TFDR) is well known to detect and locate a fault in a coaxial cable[3]. Traditional reflectometry methods have been achieved in either the time domain or frequency domain only. However, the time-frequency domain reflectometry utilizes time and frequency information of a reflected signal passed through a cable to detect and locate the fault. The purpose of this paper is to find appropriate time-frequency distribution function suitable for a TFDR system. Choosing the appropriate time-frequency distribution function implies one can detect the fault and estimate the location accurately. We consider and compare adequate time-frequency distribution function on the basis of experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.903-904
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• 2013

• Journal of Korea Multimedia Society
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• v.7 no.12
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• pp.1665-1670
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• 2004

The general fractal image compression provides a high compression rate, but it requires a large encoding time. In order to overcome this disadvantage, many researchers have introduced various methods that reduce the total number of domain blocks considering their block similarities or control the number of searching domain block depending on its distribution. In this paper, we propose a method that can reduce the number of searching domain blocks employing the variance coherence of intensity values and also the number of range blocks requiring the domain block search through the classification of range blocks. This proposed method effectively reduces the encoding time and also a negligible drop of the quality as compared with the previous methods requiring the search of all range blocks.

• Journal of Information Technology Applications and Management
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• v.12 no.1
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• pp.111-123
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• 2005

Many indexing methods were proposed so that process moving object efficiently. Among them, indexing methods like the 3D R-tree treat temporal and spatial domain as the same. Actually, however. both domain had better process separately because of difference in character and unit. Especially in this paper we deal with limited region such as indoor environment since spatial domain is limited but temporal domain is grown. In this paper we present a novel indexing structure, namely STS-tree(Separation of Time and Space tree). based on limited region. STS-tree is a hybrid tree structure which consists of R-tree and one-dimensional TB-tree. The R-tree component indexes static object and spatial information such as topography of the space. The TB-tree component indexes moving object and temporal information.

• Honam Mathematical Journal
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• v.37 no.3
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• pp.299-315
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• 2015

In this paper, we study the first-order system least-squares (FOSLS) spectral method for parabolic partial differential equations. There were lots of least-squares approaches to solve elliptic partial differential equations using finite element approximation. Also, some approaches using spectral methods have been studied in recent. In order to solve the parabolic partial differential equations in parallel, we consider a parallel numerical method based on a hybrid method of the frequency-domain method and first-order system least-squares method. First, we transform the parabolic problem in the space-time domain to the elliptic problems in the space-frequency domain. Second, we solve each elliptic problem in parallel for some frequencies using the first-order system least-squares method. And then we take the discrete inverse Fourier transforms in order to obtain the approximate solution in the space-time domain. We will introduce such a hybrid method and then present a numerical experiment.

• Journal of Advanced Navigation Technology
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• v.7 no.1
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• pp.38-50
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• 2003

In this paper, a new high resolution reflectometry scheme, time-frequency domain reflectometry (TFDR), is proposed to detect and locate fault in wiring. Traditional reflectometry methods have been achieved in either the time domain or frequency domain only. However, time-frequency domain reflectometry utilizes time and frequency information of a transient signal to detect and locate the fault. The time-frequency domain reflectometry approach described in this paper is characterized by time-frequency reference signal design and post-processing of the reference and reflected signals to detect and locate the fault. Design of the reference signal in time-frequency domain reflectometry is based on the determination of the frequency bandwidth of the physical properties of cable under test. The detection and estimation of the fault on the time-frequency domain reflectometry relies on the time-frequency domain reflectometry is compared with commercial time domain reflectomtery (TDR) instrument. In these experiments provided in this paper, TFDR locates the fault with smaller error than TDR. Knowledge of time and frequency localized information for the reference and reflected signal gained via time-frequency analysis, allows one to detect the fault and estimate the location accurately.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.6-10
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• 1996

This paper presents an overview of research results obtained by the authors in a series of publications. Methods are developed both for time-varying and time-invariant for linear and nonlinear. for time domain and frequency domain . and for discrete-time and continuous-time systems. Among the topics presented are: 1. Learning control based on integral control concepts applied in the repetition domain. 2. New algorithms that give improved transient response of the indirect adaptive control ideas. 4. Direct model reference learning control. 5 . Learning control based frequency domain. 6. Use of neural networks in learning control. 7. Decentralized learning controllers. These learning algorithms apply to robot control. The decentralized learning control laws are important in such applications becaused of the usual robot decentralized controller structured.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.8
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• pp.627-638
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• 2017

Expecting fatigue life of mounted radar in aircraft is very important when designing, because the mounted radar in aircraft is exposed to long-term external random vibration. Among the methods of predicting the fatigue life, Fatigue analysis method in frequency domain has continuously been proposed in this field. In this paper, four fatigue analysis methods in frequency domain, which are widely used, have been selected and compared with the results for Specimen fatigue test. As a result, Dirlik and Benascicutti-Tovo methods have been matched better with fatigue analysis in time domain than the method in frequency method through the comparison between the fatigue analysis method in time domain and the method in frequency domain by conducting the specimen fatigue test with strain gage. Based on the results of the specimen fatigue test, We have conducted fatigue analysis of mounted radar in aircraft with Dirlik and Benasciutti-Tovo methods in the finite element model, and confirmed that the required life was satisfying.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.1
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• pp.78-92
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• 2001

In this paper, several dynamic systems are modeled using the time domain finite element method. Galerkins' Weak Principle is used to model the general second-order mechanical system, and is applied to a simple pendulum dynamics. Problems caused by approximating the final momentum are also investigated. Extending the research, some dynamic analysis methods are suggested for the hybrid coordinate systems that have both slew and flexible modes. The proposed methods are based on both Extended Hamilton's Principle and Galerkin's Weak Principle. The matrix wave equation is propagated in space domain, satisfying the geometric/natural boundary conditions. As a result, the flexible motion can be obtained compatible with the applied control input. Numerical example is shown to demonstrate the effectiveness of the proposed modeling methods for the hybrid coordinate systems.