• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.121-128
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• 1999

This paper presents a time domain method for soil-structure interaction analysis for seismic loadings. It is based on the finite element formulation incorporating analytical frequency-dependent infinite elements for the far field soil. The dynamic stiffness matrices of the far field region formulated using the present method in frequency domain can be easily transformed into the corresponding matrices in time domain. At first, the equivalent earthquake forces are evaluated along the interface between the near and the far fields from the free-field response analysis carried out in frequency domain, and the results are transformed into the time domain. An efficient procedure is developed for the convolution integrals to evaluate the interaction force along the interface, which depends on the response on the interface at the past time instances as well as the concurrent instance. Then, the dynamic responses are obtained for the equivalent earthquake force and the interaction force using Newmark direct integration technique. Since the response analysis is carried out in time domain, it can be easily extended to the nonlinear analysis. Example analysis has been carried out to verify the present method in a multi-layered half-space.

• 한국문헌정보학회지
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• 제39권4호
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• pp.89-104
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• 2005

디지털 보존 주제분야를 중심으로 지식영역 비주얼화(knowledge domain visualization)를 시도하였다. 분석을 위한 데이터는 1990년부터 2005년까지의 기간 동안의 Web of Science DB를 중심으로 총 74건의 문헌을 추출하여 활용하였다. 지식영역 비주얼화를 위하여 사용한 툴은 서지DB를 중심으로 비주얼 데이터마이닝 결과를 제공하는 Java 어플리케이션인 CiteSpace이다. 분석 결과, 디지털 보존 분야의 핵심적인 지식 영역은 최신정보기술을 중심으로 한 디지털 보존전략, 정보네트워크와 보존시스템, 전자정부와 지식관리의 세 영역인 것으로 나타났다.

• 전기학회논문지P
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• 제65권4호
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• pp.316-320
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• 2016

This paper proposes an alternate time-switched multiplexed space-frequency block coding technique for single-carrier modulation with frequency domain equalization. The traditional multiplexed space-frequency block coding technique for single-carrier modulation uses multiple groups of two transmitters and suppresses the interference signals of other SFBC groups at the receiver. In this paper, we reconfigure transmit signals to adapt them for alternate time-switched multiplexed SFBC for single-carrier modulation with frequency domain equalization and receiver structures and propose a structure for transmitter and receiver, show that its performance is better than the traditional algorithm by simulations.

• 한국전산구조공학회논문집
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• 제37권2호
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• pp.85-93
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• 2024

이 논문에서는 파랑 하중을 받는 부유식 구조체의 운동 해석에 있어서 시스템 식별 방법을 이용한 상태공간방정식 모델을 수립하고 해석하는 방법을 제안하였다. 상태공간방정식 모델의 수립 방법으로는 주파수영역에서 하중-변위 입출력 관계에 대한 목표 전달함수를 구하고 이에 가장 근접하는 상태공간방정식을 구하는 절차를 제시하였다. 전통적으로 부유식 구조체 운동의 시간영역 해석은 지연함수의 합성곱적분을 포함하는 Cummins 방정식을 시간적분하여 이루어진다. 상태공간방정식 모델은 이러한 시간영역해석을 효과적으로 수행하기 위한 방법의 하나로서 연구되어 왔다. 제안하는 방법에서는 시스템 식별방법인 N4SID 와 전달함수의 분모 및 분자 다항식의 계수를 설계변수로 하는 최적화방법을 사용하여 목표 전달함수에 상응하는 상태공간방정식을 구한다. 제안하는 방법의 적용성을 보이는 예제로서 단자유도 수치모델 및 6자유도 바지의 운동을 해석하였다. 제시하는 상태공간방정식 모델은 주파수영역 및 시간영역에서 모두 기존의 해석결과와 잘 일치하고 시간영역해석에서는 계산의 정확도를 확보하면서 계산 시간을 크게 줄일 수 있음을 확인하였다.

• Wind and Structures
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• 제5권2_3_4호
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• pp.379-392
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• 2002

Numerical flow computations around an aeroelastic 3D square cylinder immersed in the turbulent boundary layer are shown. Present computational code can be characterized by three numerical aspects which are 1) the method of artificial compressibility is adopted for the incompressible flow computations, 2) the domain decomposition technique is used to get better grid point distributions, and 3) to achieve the conservation law both in time and space when the flow is computed a with moving and transformed grid, the time derivatives of metrics are evaluated using the time-and-space volume. To provide time-dependant inflow boundary conditions satisfying prescribed time-averaged velocity profiles, a convenient way for generating inflow turbulence is proposed. The square cylinder is modeled as a 4-lumped-mass system and it vibrates with two-degree of freedom of heaving motion. Those blocks which surround the cylinder are deformed according to the cylinder's motion. Vigorous oscillations occur as the vortex shedding frequency approaches cylinder's natural frequencies.

• Journal of applied mathematics & informatics
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• 제25권1_2호
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• pp.269-282
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• 2007

In this paper, we consider a two-dimensional fractional space-time diffusion equation (2DFSTDE) on a finite domain. We examine an implicit difference approximation to solve the 2DFSTDE. Stability and convergence of the method are discussed. Some numerical examples are presented to show the application of the present technique.

• Journal of Astronomy and Space Sciences
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• 제36권2호
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• pp.97-103
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• 2019

An automated signal-acquisition method for the NASA's space geodesy satellite laser ranging (SGSLR) system is described as a selection of two system parameters with specified probabilities. These parameters are the correlation parameter: the minimum received pulse number for a signal-acquisition and the frame time: the minimum time for the correlation parameter. The probabilities specified are the signal-detection and false-acquisition probabilities to distinguish signals from background noise. The steps of parameter selection are finding the minimum set of values by fitting a curve and performing a graph-domain approximation. However, this selection method is inefficient, not only because of repetition of the entire process if any performance values change, such as the signal and noise count rate, but also because this method is dependent upon system specifications and environmental conditions. Moreover, computation is complicated and graph-domain approximation can introduce inaccuracy. In this study, a new method is proposed to select the parameters via a conditional equation derived from characteristics of the signal-detection and false-acquisition probabilities. The results show that this method yields better efficiency and robustness against changing performance values with simplicity and accuracy and can be easily applied to other satellite laser ranging (SLR) systems.

• 한국정보통신학회논문지
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• 제2권4호
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• pp.653-660
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• 1998

본 연구는 시간영역 유한 차분법(finite difference-time domain method:FDTD)을 이용하여 마이크로스트립 배열 안테나의 전자계 특성들을 해석한다. 직각좌표계에서 맥스웰 방정식의 유한차분 방정식을 정의하였으며, 자유공간과 같은 무한영역해석을 위해서 Mur의 흡수경계조건을 이용하였다 마이크로스트립 배열 안테나를 단위격자 구조로 모델링한 후 시간영역에서 필드분포를 도시하였다.

• International journal of advanced smart convergence
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• 제9권3호
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• pp.137-140
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• 2020

Orthogonal time frequency space (OTFS) modulation is considered as one of the solutions to cope with high mobility channel environments. It converts the time-varying channel to the near-constant channel response in the delay-Doppler domain. This modulation scheme also benefits from the diversity in two-dimensional modulation. According to recent researches, this method outperforms the conventional OFDM modulation, especially in high-speed channel conditions. In this paper, to investigate the performance of OTFS in a practical system, channel estimation in the delay-Doppler domain is compared with the conventional method in the time-frequency domain at different mobile speeds. Simulation results confirm that the delay-Doppler domain channel estimation brings a better performance compared to the conventional one under the same overhead rate.

• ETRI Journal
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• 제39권4호
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• pp.493-501
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• 2017

This paper introduces a new motion-synthesis technique for animating multiple characters. At a high level, we introduce a hub-sub-control-point scheme that automatically generates many different spline curves from a user scribble. Then, each spline curve becomes a trajectory along which a 3D character moves. Based on the given curves, our algorithm synthesizes motions using a cyclic motion. In this process, space-time warp curves, which are time-warp curves, are embedded in the 3D environment to control the speed of the motions. Since the space-time warp curve represents a trajectory over the time domain, it enables us to verify whether the trajectory causes any collisions between characters by simply checking whether two space-time warp curves intersect. In addition, it is possible to edit space-time warp curves at run time to change the speed of the characters. We use several experiments to demonstrate that the proposed algorithm can efficiently synthesize a group of character motions. Our method creates collision-avoiding trajectories ten times faster than those created manually.