• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.197-206
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• 2003

It is intended to retrieve the time history of displacement from measured acceleration signal. In this study, the word retrieving means reconstructing the time history of original displacement signal from already measured acceleration signal not just extracting various information using relevant signal processing techniques. Unlike extracting required information from the signal, there are not many options to apply to retrieve the time history of displacement signal, once the acceleration signal is measured and recorded with given sampling rate. There are two methods, in general, to convert measured acceleration signal into displacement signal. One is directly integrating the acceleration signal in time domain. The other is dividing the Fourier transformed acceleration signal by the scale factor of - $\omega$$^2$and taking the inverse Fourier transform of it. It turned out both the methods produced a significant amount of errors depending on the sampling resolution in time and frequency domain when digitizing the acceleration signals. A simple and effective way to convert the time history of acceleration signal into the time history of displacement signal without significant errors is studied here with the analysis on the errors involved in the conversion process.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2009년도 학술대회
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• pp.227-231
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• 2009

The aim of the research is to focus on the cognitive principles and to achieve human-level intelligence in referring context based browser history and the Windows history. One of the major problems faced by today's computer users is insufficient and single exclusive context based reference of the browser history and the Windows history. Today we search for the browser history and Windows history in different places even though the context is the same. For e.g., When working on a research paper or preparing a business presentation, a user may require to refer many web sites on the internet and various documents on the local computer. The browser can provide only time based history. The windows document history is also time based and limited to list only few documents. Hence, we propose a tool "Cognitive Based Context Aware Reference History Management Tool" which helps to access the exclusive reference of context and time based history in one place. The tool also proposes to store image history with urls and classifies images of a specific topic accessed in different time, bookmarks management and cross browser history management. These features are very useful as we can access all related documents (doc, docx, ppt, pptx, pdf, txt, and html), web pages, images and bookmarks in one place. The tool uses the cognitive principles like classification and association to achieve the purpose.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.304-311
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• 1998

An algorithm to enhance spectra matching of acceleration time history used in the seismic analysis of nuclear power plants(NPP) is proposed. The new scheme provides the solution on the highly fluctuating and over conservatism problems that happened in order to satisfy design spectrum enveloping criteria in the traditional method. To obtain optimized spectrum for a time history, a spectrum matching procedure that adapts a system identification technique is also developed. The algorithm also introduces maximum displacement control, baseline correction, clipping and raising of maximum peak of time history, and power spectral density (PSD) control of time history. It is verified through numerical examples that this new scheme can definitely generate acceleration time history, closely matching the target spectra and satisfying other stipulated requirements.

• 한국지반공학회논문집
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• 제19권1호
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• pp.143-150
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• 2003

과압밀점토의 응력-변형 거동에 중요한 영향을 미치는 변형률 속도에 관하여 다루었다. 본 연구에서는 응력경로 회전각, 과압밀비 그리고 접근길이를 포함한 응력이력과 재하속도 이력 및 재하속도를 포함한 시간이력을 변화시켜 압밀-배수 응력경로 삼축 실험을 수행하였다. 실험 결과 모든 영향인자에 대하여 시간이 증가할수록 변형률 속도 역시 증가하였다. 또한, 회전각의 정의에 따라 상이한 변형률 속도의 값을 보였고, 과압밀비와 재하속도가 증가할수록 변형률 속도 역시 증가하였다. 응력이력에서는 응력-변형 거동과 변형률 속도간의 상관성이 존재하였지만 시간이력에서는 응력-변형-변형률 속도의 상관성을 보이지 않았다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.41-47
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• 2004

The objective of this paper is to monitor damage in beam-type structures by using time history of natural frequencies. First, numerical experiments on test beams are described, Dynamic responses of the test structures are obtained for several damage scenarios in a consequent order. Next, the time history of natural frequencies are extracted for the first four modes from the dynamic responses of the test structures. Finally, damage detection in the test structures is performed using the time-history of natural frequencies.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.831-839
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• 2016

Seismic qualification by test is widely used as a way to show the integrity and functionality of equipment that is related to the overall safety of nuclear power plants. Another means of seismic qualification is by direct integration analysis. Both approaches require a series of time histories as an input. However, in most cases, the possibility of using real earthquake data is limited. Thus, artificial time histories are widely used instead. In many cases, however, response spectra are given. Thus, most of the artificial time histories are generated from the given response spectra. Obtaining the response spectrum from a given time history is straightforward. However, the procedure for generating artificial time histories from a given response spectrum is difficult and complex to understand. Thus, this paper presents a simple time-domain method for generating a time history from a given response spectrum; the method was shown to satisfy conditions derived from nuclear regulatory guidance.

• 한국압력기기공학회 논문집
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• 제17권2호
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• pp.137-144
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• 2021

The mode superposition time history analysis method is commonly used in a seismic analysis. The maximum response in the time history analysis can be derived by combining the responses of individual modes. The residual mode response is the response of the modes which are not considered in the time history analysis. In this paper, the residual vector method to consider the residual mode response in the time history analysis is introduced and evaluated. Seismic analyses for a sample structure model and a reactor vessel model are performed to evaluate the residual vector method. The analysis results show that residual mode response is well calculated when the residual vector method is used. It is confirmed that the residual vector method is useful and acceptable to consider the residual mode response in a seismic analysis of the nuclear power plant equipment.

• Structural Engineering and Mechanics
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• 제41권5호
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• pp.675-689
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• 2012

Most connections of steel structures exhibit flexible behaviour under cyclic loading. The flexible connections can be assumed as nonlinear rotational springs attached to the ends of each beam. The nonlinear behaviour of the connections can be considered by suitable moment-rotation relationship. Time-history analysis by direct integration method can be used as a powerful technique to determine the nonlinear dynamic response of the structure. In conventional numerical integration, the response is evaluated for a series of short time increments. The limitations on the size of time intervals can be removed by using Chen and Robinson improved time history analysis method, in which the integrated displacements are used as the new variables in integrated equation of motion. The proposed method permits longer time intervals and reduces the computational works. In this paper the nonlinearity behaviour of the structure is summarized on the connections, and the step by step improved time-history analysis is used to calculate the dynamic response of the structure. Several numerical calculations which indicate the applicability and advantages of the proposed methodology are presented. These calculations illustrate the importance of the effect of the nonlinear behaviour of the flexible connections in the calculation of the dynamic response of steel frames.

• Structural Engineering and Mechanics
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• 제69권3호
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• pp.293-306
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• 2019

In current seismic design codes, various elastic design acceleration spectra are defined considering different seismological and soil characteristics and are widely used tool for calculation of seismic loads acting on structures. Response spectrum analyses directly use the elastic design acceleration spectra whereas time history analyses use acceleration records of earthquakes whose acceleration spectra fit the design spectra of seismic codes. Due to the fact that obtaining coherent structural response quantities with the seismic design code considerations is a desired circumstance in dynamic analyses, the response spectra of earthquake records used in time history analyses had better fit to the design acceleration spectra of seismic codes. This paper evaluates structural response distributions of multi-story reinforced concrete frames obtained from nonlinear time history analyses which are performed by using the scaled earthquake records compatible with various elastic design spectra. Time domain scaling procedure is used while processing the response spectrum of real accelerograms to fit the design acceleration spectra. The elastic acceleration design spectra of Turkish Seismic Design Code 2007, Uniform Building Code 1997 and Eurocode 8 are considered as target spectra in the scaling procedure. Soil classes in different seismic codes are appropriately matched up with each other according to $V_{S30}$ values. The maximum roof displacements and the total base shears of considered frame structures are determined from nonlinear time history analyses using the scaled earthquake records and the results are presented by graphs and tables. Coherent structural response quantities reflecting the influence of elastic design spectra of various seismic codes are obtained.

• Earthquakes and Structures
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• 제8권3호
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• pp.639-663
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• 2015

Time history dynamic structural analysis is a time consuming procedure when used for large-scale structures or iterative analysis in structural optimization. This article proposes a new methodology for approximate prediction of extremum point of the response history via wavelets. The method changes original record into a reduced record, decreasing the computational time of the analysis. This reduced record can be utilized in iterative structural dynamic analysis of optimization and hence significantly reduces the overall computational effort. Design examples are included to demonstrate the capability and efficiency of the Reduced Record Method (RRM) when utilized in optimal design of frame structures using meta-heuristic algorithms.