• Journal of information and communication convergence engineering
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• 제15권4호
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• pp.244-249
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• 2017

Wearable sensor-based gait analysis has been widely conducted to analyze various aspects of human ambulation abilities under the free-living condition. However, there have been few research efforts on using wearable sensors to analyze human walking on an unstable surface such as on a ship during a sea voyage. Since the motion of a ship on the unstable sea surface imposes significant differences in walking strategies, investigation is suggested to find better performing wearable sensor-based gait analysis algorithms on this unstable environment. This study aimed to compare two representative gait event algorithms including time domain and frequency domain analyses for detecting heel strike on an unstable platform. As results, although two methods did not miss any heel strike, the frequency domain analysis method perform better when comparing heel strike timing. The finding suggests that the frequency analysis is recommended to efficiently detect gait event in the unstable walking environment.

• International Journal of Control, Automation, and Systems
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• 제5권1호
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• pp.1-7
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• 2007

In this paper, the necessary and sufficient conditions for strict positive realness of the rational transfer functions directly from basic definitions in the frequency domain are studied. A new frequency domain approach is used to check if a rational transfer function is a strictly positive real or not. This approach is based on the Taylor expansion and the Maximum Modulus Principle which are the fundamental tools in the complex functions analysis. Four related common statements in the strict positive realness literature which is appeared in the control theory are discussed. The drawback of these common statements is analyzed through some counter examples. Moreover a new necessary condition for strict positive realness is obtained from high frequency behavior of the Nyquist diagram of the transfer function. Finally a more simplified and completed conditions for strict positive realness of single-input single-output linear time-invariant systems are presented based on the complex functions analysis approach.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.29-35
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• 1997

This research presented a frequency analysis method to analyze NRRO in a computer hard disk drive. RRO was proved to be the harmonics of rotational frequency. The frequency components of NRRO is the subtraction of the harmonics from TIR in frequency domain, so that NRRO in time domain can be obtained by Fourier inverse transformation of NRRO in frequency domain. This method can make the experiments simple without the index signal indispensable to time domain analysis. This research also shows that NRRO is caused by the defect frequencies of ball bearing. Even though the excitation force of ball bearing is independent of the rotational speed, the amplitude of NRRO is magnified near the resonance frequencies of the spindle motor. NRRO in axial direction is almost twice bigger than that in radial direction, because the spindle motor has smaller stiffness in axial direction.

• 한국해양공학회지
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• 제20권5호
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• pp.30-35
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• 2006

In tire presence of incident waves with different frequencies, there are second order sum and difference frequency wave exciting forces due to the nonlinearity of tire incident waves. Although the magnitude of these nonlinear wave forces are small, they act on TLPs at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency waveexciting forces occurring close to tire natural frequencies of TLPs often give greater contributions to high and law frequency resonant responses. Nonlinear motion responses and tension variations in the time domain are analyzed by solving the motion equations with nonlinear wave exciting forces using tire numerical analysismethod. The numerical results of time domain analysis for the nonlinear wave exciting forces on the ISSC TLP in regular waves are compared with the numerical and experimental ones of frequency domain analysis. The results of this comparison confirmed tire validity of the proposed approach.

• 한국구조물진단유지관리공학회 논문집
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• 제11권3호
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• pp.87-94
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• 2007

구조물의 동적해석은 크게 시간영역과 주파수영역해석으로 나눌 수 있다. 시간영역해석은 직접적분법과 모드중첩법 등을 사용하며 주파수영역해석은 DFT법을 적용하고 있다. 일반적으로 DFT법은 주기함수에 대한 응답을 산정할 경우 효과적인 해석방법이지만 비주기함수인 경우 정확한 해석결과를 얻을 수 없어 주기를 크게 하거나 응답을 수정하여 해의 정확성을 향상시키고 있다. 따라서 본 연구는 비주기함수인 이동하중을 받는 구조물에 대해 시간영역과 주파수영역에서 동적응답을 산정하였다. 그 결과 구조물의 자유진동주기를 크게 하거나 응답을 수정하여 DFT법을 적용한다면 주파수영역에서도 충분히 정확한 해석결과를 얻을 수 있을 것으로 판단된다.

• 한국해안·해양공학회논문집
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• 제28권1호
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• pp.27-33
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• 2016

불규칙 파랑 중에서 직접 예인하는 케이슨의 상판침수에 대한 수치해석을 수행하였다. 패널법을 이용하여 주파수 영역에서의 선형 운동해석을 수행하였고, 통계적 방법을 통해 상판침수를 예측하였다. 시간영역 해석에서는 예인시스템, 환경하중 등을 상세히 구현하여 운동해석을 수행하였고, 상판침수 결과를 주파수 영역에서의 결과와 비교하였다. 또한, 시간 영역 해석에서는 예인선의 수 및 배치에 대한 검토를 수행하여 상판침수 측면에서 예인시스템이 미치는 영향과 운송조건을 고찰하였다.

• 풍력에너지저널
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• 제14권1호
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• pp.29-36
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• 2023

The analysis of the floating offshore wind turbine platform is based on the procedures provided by the IEC including the International Classification Society, which recommends the analysis in the time domain. But time-domain simulation requires a lot of time and resources to solve tens of thousands of DLCs. This acts as a barrier in terms of floating structure development. For final verification, it requires very precise analysis in the time domain, but from an initial design point of view, a simplified verification procedure to predict the quantity of materials quickly and achieve relatively accurate results is crucial. In this study, a structural design procedure using a design wave applied in the oil and gas industries is presented combined with a conservative turbine load. With this method, a quick design spiral can be rotated, and it is possible to review FOWTs of various shapes and sizes. Consequently, a KRISO Semi-Submersible FOWT platform was developed using a simplified design procedure in frequency-domain analysis.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.760-765
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• 1993

A multivariable learning control is designed in frequency domain. A general to of feedback assisted learning scheme is considered and an inverse model based learning algorithm is derived through convergence analysis in frequency domain. Performance of the proposed control method is evaluated through numerical simulation.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.94-101
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• 2004

The purpose of this raper is to assess the benefits of frequency domain fatigue analysis and compare it with more conventional time domain techniques. The multi-body dynamic analysis, FE analysis and fatigue life prediction technique are applied for the frequency domain fatigue analysis. To obtain the dynamic load history used in the frequency domain fatigue analysis, the computer simulations running over typical road Profiles are carried out by utilizing vehicle dynamic model. The fatigue life estimation for the rear suspension system of small-sized passenger car is performed by using resonance durability analysis technique, and the estimation results are compared with the conventional quasi-static durability analysis results. For the pothole simulation, the percent changes, of the fatigue life between the two durability analysis techniques don't exceed 10%. But for the Belgian road simulation because of the resonance effect, the fatigue life using the resonance durability analysis technique are much smaller estimated than the quasi-static durability analysis results.

• 한국해양공학회지
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• 제3권2호
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• pp.526-526
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• 1989