• 한국정밀공학회지
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• 제23권6호
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• pp.119-127
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• 2006

A non-destructive time domain approach to examine structural damage using parameterized partial differential equations and Galerkin approximation techniques is presented. The time domain analysis for damage detection is independent of modal parameters and analytical models unlike frequency domain methods which generally rely on analytical models. The time history of the vibration response of the structure was used to identify the presence of damage. Damage in a structure causes changes in the physical coefficients of mass density, elastic modulus and damping coefficients. This is a part of our ongoing effort on the general problem of modeling and parameter estimation for internal damping mechanisms in a composite beam. Namely, in detecting damage through time-domain or frequency-domain data from smart sensors, the common damages are changed in modal properties such as natural frequencies, mode shapes, and mode shape curvature. This paper examines the use of beam-like structures with piezoceramic sensors and actuators to perform identification of those physical parameters, and detect the damage. Experimental results are presented from tests on cantilevered composite beams damaged at different locations and different dimensions. It is demonstrated that the method can sense the presence of damage and obtain the position of a damage.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.20-26
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• 2011

A weakly nonlinear seakeeping methodology for predicting motions and loads is presented in this paper. This methodology assumes linear radiation and diffraction forces, calculated in the frequency domain, and fully nonlinear Froude-Krylov and hydrostatic forces, evaluated in the time domain. The particular approach employed here allows to overcome numerical problems connected to the determination of the impulse response functions. The procedure is divided into three consecutive steps: evaluation of dynamic sinkage and trim in calm water that can significantly influence the final results, a linear seakeeping analysis in the frequency domain and a weakly nonlinear simulation. The first two steps are performed employing a three-dimensional Rankine panel method. Nonlinear Froude-Krylov and hydrostatic forces are computed in the time domain by pressure integration on the actual wetted surface at each time step. Although nonlinear forces are evaluated into the time domain, the equations of motion are solved in the frequency domain iteratively passing from the frequency to the time domain until convergence. The containership S175 is employed as a test case for evaluating the capability of this methodology to correctly predict the nonlinear behavior related to wave induced motions and loads in head seas; numerical results are compared with experimental data provided in literature.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.200-204
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• 2005

The use of beamforming method and de-Dopplerization technique was applied in studying the rotating sound sources. Acoustic analysis of a moving sound source required that the measured sound signals be do-Dopplerized and restored as of the original emission signals. Two main issues of the signal reconstruction in time domain are addressed herein: First, to remove Doppler effect from the measured data and to restore the original emission data of the moving source. The difference of the time domain beamforming from the frequency domain beamforming was mentioned. Also, the time domain beamforming method is deployed in the test and the comparisons were made to the frequency domain results. The time domain signal reconstruction was numerically simulated prior to the application. To validate the de-Dopplerization Performance, the rotating Point sources were examined and localized by the use of a phased array of microphone. The application of prop-rotor was conducted in a hovering condition. The results of reconstructing time signals of rotating sources and its locations were shown in the power distribution maps. In the prop-rotor measurements, the acoustic source locations were successfully verified in varying positions for different frequencies of interest.

• 지구물리와물리탐사
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• 제22권4호
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• pp.225-238
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• 2019

최적의 심도 영역 속도를 도출하기 위한 구조보정 속도분석(MVA, migration velocity analysis) 기법을 해양에서 취득한 원거리 다중채널 탄성파 자료에 적용하여 그 효용성을 확인한다. 지금까지 통상적으로 수행된 시간 영역 자료처리 결과는 지질학적 층서해석에는 무리 없는 결과이나, 어느 정도 가능성이 있는 플레이나 리드 지역에서의 유가스 탐사에서는 저류층 지질모델 구축, 시추 설계, 매장량 계산에서 반드시 심도 영역 속도 구조와 영상이 필요하다. 데이터 영역에서 근사 방식을 사용한 공통 중간점 기반 속도 분석으로부터 도출한 속도는 처음부터 오차를 내재하여 불확실성이 높다. 반면에, 이를 보완해 줄 검층 자료가 없는 상황에서 실측 규모의 속도 구조를 도출하는데 있어 이미지 영역 구조보정 속도분석 기법은 상당히 효율적인 방법이다. 이 연구에서는 해양에서 취득한 다중 채널 탄성파자료에 대해 합리적인 결과를 도출하기 위해 시간 영역에서 신호의 품질을 최적화하고, 이 자료에 대하여 반복적으로 MVA 기법을 적용함으로써 심도영역 속도 및 구조보정 단면도를 도출하였다. 시간 영역 속도를 단순히 Dix 방정식에 의해 심도영역으로 변환한 속도를 이용하여 생성한 결과(공통 수신점 모음도 및 중합 단면도)와 MVA 기법을 이용한 심도영역 자료처리를 통해 도출된 속도를 이용하여 생성한 결과를 비교함으로써, 심도영역 결과가 보다 합리적임을 확인하였다. 심도 영역으로 도출된 속도는 중합전 심도 구조보정에 바로 사용될 수 있을 뿐만 아니라, 현장 자료의 파형역산 적용 시 초기 모델로 활용함으로써 역산 수행 과정에서 발생할 수 있는 국부 최소(local minima) 문제를 최소화할 수 있다.

• 동력기계공학회지
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• 제15권6호
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• pp.27-34
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• 2011

The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.

• Structural Engineering and Mechanics
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• 제21권4호
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• pp.437-450
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• 2005

In this study, a complete analysis of soil-structure interaction problems is presented which includes a modelling of the near surrounding of the building (near-field) and a special description of the wave propagation process in larger distances (far-field). In order to reduce the computational effort which can be very high for time domain analysis of wave propagation problems, a special approach based on similarity transformation of the infinite domain on the near-field/far-field interface is applied for the wave radiation of the far-field. The near-field is discretised with standard Finite Elements, which also allows to introduce non-linear material behaviour. In this paper, a new approach to calculate the involved convolution integrals is presented. This approximation in time leads to a dramatically reduced computational effort for long simulation times, while the accuracy of the method is not affected. Finally, some benchmark examples are presented, which are compared to a coupled Finite Element/Boundary Element approach. The results are in excellent agreement with those of the coupled Finite Element/Boundary Element procedure, while the accuracy is not reduced. Furthermore, the presented approach is easy to incorporate in any Finite Element code, so the practical relevance is high.

• 대한조선학회논문집
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• 제45권2호
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• pp.168-174
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• 2008

To calculate the fluid-structure interaction(FSI) problem rationally, it should be the basic technology to analyse each domain of fluid and structure accurately. In this paper, a new FSI analysis algorithm was introduced using the 3D solid finite element for structural analysis and CFD code based on the HCIB method for viscous flow analysis. The fluid and structural domain were analysed successively and alternatively in time domain. The structural domain was analysed by the Newmark-b direct time integration scheme using the pressure field calculated by the CFD code. The results for example calculation were compared with other research and it was shown that those coincided each other. So we can conclude that the developed algorithm can be applied to the general FSI problems.

• 한국산학기술학회논문지
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• 제11권3호
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• pp.1053-1058
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• 2010

지반과 구조물의 상호작용을 해석하는 한 방법으로 지반을 무한의 영역으로 가정하여 이를 무한요소로 모델링한 후 구조물과 연동하여 해석하는 기법이 사용되었으나 하지만 기존의 동적 무한요소는 대부분 시간영역이 아닌 주파수 영역에서 정식화되었고 중첩의 원리가 적용되어 구조물이나 지반의 비선형 거동을 해석에 포함하기 어렵다. 본 연구에서는 시간영역에서 정식화가 가능하고 비선형 거동해석도 가능한 무한 요소를 개발하였다. 개발된 무한요소를 다량의 유한요소를 사용한 결과와 비교하여 정확도를 검증하였고, 비선형 지반모델을 적용하여 비선형해석이 가능함을 확인하였다. 따라서 개발된 무한요소를 지반-구조물 상호작용에 적용할 수 있으며, 이를 바탕으로 구조물내진 설계에도 활용할 수 있을 것으로 판단된다.

• International Journal of Aerospace System Engineering
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• 제2권1호
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• pp.43-46
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• 2015

Aeroelastic gust response analysis plays an important role in design of aircrafts. For gust response analysis, frequency domain aerodynamics method has been typically used with generalized aerodynamic influence coefficient matrices at various reduced frequencies. However, it cannot be applied to the aeroservoelastic analysis, such as gust alleviation control. Time-domain state space (SS) models must be built. It attacks little attention that gust response analysis relies on continuous gust time-domain input signal in terms of its PSD function. The aim the current study is to provide a reduced-order modeling (ROM) method based on CFD to model gust responses for continuous gust responses for continuou gust inputs in time domain. The paper analyzed the gust response of AGARD445.6 wing subjected to the Dryden gust with ROMs and compared the difference between the rigid structure and elastic one. The results demonstrate that structure elastic effect effect should be considered in the design of aircraft.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.263-268
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• 2008

The measurement of magnetic field is performed AC magnetic field emission density in driver cab and saloon's compartment of rolling stock. In order to measure magnetic-field emission, a three-axial magnetic-field sensor is used and connected to data process system. The AC magnetic field is checked and analysis through BNC output, DAQ cad and notebook PC. The spectral analysis is performed by short time Fourier transform(STFT) for time-domain emission signal.