• Title/Summary/Keyword: Numerical inversion

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Adaptive Output Feedback Control of Unmanned Helicopter Using Neural Networks (신경회로망을 이용한 무인헬리콥터의 적응출력피드백제어)

  • Park, Bum-Jin;Hong, Chang-Ho;Suk, Jin-Young
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.11
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    • pp.990-998
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    • 2007
  • Adaptive output feedback control technique using Neural Networks(NN) is proposed for uncertain nonlinear Multi-Input Multi-Output(MIMO) systems. Modified Dynamic Inversion Model(MDIM) is introduced to decouple uncertain nonlinearities from inversion-based control input. MDIM consists of approximated dynamic inversion model and inversion model error. One NN is applied to compensate the MDIM of the system. The output of the NN augments the tracking controller which is based upon a filtered error approximation with online weight adaptation laws which are derived from Lyapunov's direct method to guarantee tracking performance and ultimate boundedness. Several numerical results are illustrated in the simulation of Van der Pol system and unmanned helicopter with model uncertainties.

A Numerical Sensitivity Experiment of the Downslope Windstorm over the Yeongdong Region in Relation to the Inversion layer of Temperature (역전층이 영동 지역의 활강풍에 미치는 영향에 관한 민감도 수치실험 연구)

  • Lee, Jae Gyoo;In, So-Ra
    • Atmosphere
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    • v.19 no.4
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    • pp.331-344
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    • 2009
  • A sensitivity study has been performed using ARPS (Advanced Regional Prediction System) version 5.2.10 in a downslope windstorm case of 12-13 February 2006. The purpose of this study was to find out the role of the inversion layer of temperature mainly in relation to the strength of the downslope winds over the Yeongdong region located downstream of the Taebaek mountains. Under the conditions of N (Brunt-$V{\ddot{a}}is{\ddot{a}}la$ frequency)=0.008 and N=0.016, the effects of the presence of the inversion layer, its variation of height of the layer, and the depth of the layer were identified. The sensitivity experiments suggested that the inversion layer effected the downstream wind speed of the mountains under both conditions of N=0.008 and N=0.016, and notably when the inversion layer was located near the mountain crest the downstream wind speed of the mountains was strong (~ $27ms^{-1}$) only under the condition of N=0.016. In addition, when the atmosphere was rather stable (N=0.016) and the depth of the layer was relatively thin (765 m) the downstream wind speed of the mountains was the strongest (~ $30ms^{-1}$) among the sensitivity experiments.

Numerical forecasting of sea fog at West sea in spring (봄철 서해안 해무의 수치예보)

  • Han, Kyoung-Keun;Kim, Young-Chul
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.14 no.4
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    • pp.94-100
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    • 2006
  • The purpose of this case study is to determine the possibility of Numerical Forecasting of sea fog at West Sea in spring time. For practical method of analyzing the data collected from 24th to 26th March 2003, Numerical Weather Prediction model MM5(Mesoscale Model Version 5) and synoptic field study using synoptic chart, upper level chart, and sea surface temperature were employed. The results of synoptic field analysis summarized that sea fog at West sea in spring is intensified by the inflow of the warm flow from west or southwest, low sea surface temperature to increase the temperature difference between air and sea surface, and inversion layer to disturb the disperse. It appears that the possibility of sea fog forecasting by MM5, in view of the result that the MM5 output is similar to the synoptic fields analysis.

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Frequency Domain Waveform Inversion Using $l_1$ -norm ($l_1$-norm을 이용한 주파수 영역 파형역산)

  • Pyun, Suk-Joon;Shin, Chang-Soo
    • 한국지구물리탐사학회:학술대회논문집
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    • 2007.06a
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    • pp.118-123
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    • 2007
  • A robust objective function in the frequency domain is applied to the acoustic full waveform inversion. The proposed objective function is defined as $l_1$-norm of residual wavefields in the frequency domain. Generally, the full waveform inversion is extremely sensitive to a number of factors such as parameterization, initial model, noise and so on. The numerical tests were performed for checking the sensitivity to attenuation and several noises. For the comparison with other objective functions, the conventional least-squares method and the logarithmic method were tested under the same condition. The synthetic data examples show that the proposed algorithm is more robust than the well-known methods.

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Development of an Inversion Analysis Technique for Downhole Testing and Continuous Seismic CPT

  • Joh, Sung-Ho;Mok, Young-Jin
    • Geotechnical Engineering
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    • v.14 no.3
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    • pp.95-108
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    • 1998
  • Downhole testing and seismic CPT (SCPT) have been widely used to evaluate stiffness profiles of the subgrade. Advantages of downhole testing and SCPT such as low cost, easy operation and a simple seismic source have got these testings more frequently adopted in site investigation. For the automated analysis of downhole testing and SCPT, the concept of interval measurements has been practiced. In this paper. a new inversion procedure to deal tilth the interval measurements for the automated downhole testing and SCPT (including a newlydeveloped continuous SCPT) is proposed. The forward modeling in the new inversion procedure incorporates ray path theory based on Snell's law. The formulation for the inversion analysis is derived from the maximum likelihood approach, which estimates the maximum likelihood of obtaining a particular travel time from a source to a receiver. Verification of the new inversion procedure was performed with numerical simulations of SCPT using synthesized profiles. The results of the inversion analyses performed for the synthetic data show that the new inversion analysis is a valid procedure which enhances Va profiles determined by downhole testing and SCPT.

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Layered-earth Resistivity Inversion of Small-loop Electromagnetic Survey Data using Particle Swarm Optimization (입자 군집 최적화법을 이용한 소형루프 전자탐사 자료의 층서구조 전기비저항 역해석)

  • Jang, Hangilro
    • Geophysics and Geophysical Exploration
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    • v.22 no.4
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    • pp.186-194
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    • 2019
  • Deterministic optimization, commonly used to find the geophysical inverse solutions, have its limitation that it cannot find the proper solution since it might converge into the local minimum. One of the solutions to this problem is to use global optimization based on a stochastic approach, among which a large number of particle swarm optimization (PSO) applications have been introduced. In this paper, I developed a geophysical inversion algorithm applying PSO method for the layered-earth resistivity inversion of the small-loop electromagnetic (EM) survey data and carried out numerical inversion experiments on synthetic datasets. From the results, it is confirmed that the PSO inversion algorithm could increase the inversion success rate even when attempting the inversion of small-loop EM survey data from which it might be difficult to find a best solution by applying the Gauss-Newton inversion algorithm.

Resolution Limits of Cross-Well Seismic Imaging Using Full Waveform Inversion (전파형 역산을 이용한 시추공 영상의 분해능)

  • Cho, Chang-Soo;Lee, Hee-Il;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.5 no.1
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    • pp.33-45
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    • 2002
  • It was necessary to devise new techniques to overcome and enhance the resolution limits of traveltime tomography. Waveform inversion has been one of the methods for giving very high resolution result. High resolution image could be acquired because waveform inversion used not only phase but amplitude. But waveform inversion was much time consuming Job because forward and backward modeling was needed at each iteration step. Velocity-stress method was used for effective modeling. Resolution limits of imaging methods such as travel time inversion, acoustic and elastic waveform inversion were investigated with numerical models. it was investigated that Resolution limit of waveform inversion was similar tn resolution limit of migration derived by Schuster. Horizontal resolution limit could be improved with increased coverage by adding VSP data in cross hole that had insufficient coverage. Also, waveform inversion was applied to realistic models to evaluate applicability and using initial guess of travel time tomograms to reduce non-linearity of waveform inversion showed that the better reconstructed image could be acquired.

Inversion of spectral analysis of surface waves with analytic Jacobian (해석적 자코비안을 이용한 표면파 기법의 역산)

  • Ha, Hee-Sang
    • Journal of the Korean Geophysical Society
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    • v.5 no.3
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    • pp.233-245
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    • 2002
  • The spectral-analysis-of-surface-waves (SASW) method is a nondestructive testing method based upon generation and detection of elastic stress waves. SASW is widely used as one of the techniques to determine stiffness profile in engineering geophysics. The essential steps involved are construction of an experimental dispersion curve from data collected in situ, and inversion of the dispersion curve to determine the stiffness profile. The main object of this study is to derive an analytical Jacobian for the inversion. If we set the subsurface to N homogeneous layer, it could save 2N times Jacobian calculation compared to numerical jacobian calculation during inversion. To reconstruct a stiffness profile, constrained damped least square method was applied for the inversion. The algorithm was tested for the numerical data and for the real asphalt and tunnel data, which were able to verify the stiffness profile. The stiffness profile reconstructed by the algorithm showed the possibility to appraise the soundness of tunnel with applications SASW.

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Extraction of Flow Velocity Information using Direct Wave and Application of Waveform Inversion Considering Flow Velocity (직접파를 이용한 배경매질 유속정보 도출과 유속을 고려한 파형역산의 적용)

  • Lee, Dawoon;Chung, Wookeen;Shin, Sungryul;Bae, Ho Seuk
    • Geophysics and Geophysical Exploration
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    • v.20 no.4
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    • pp.199-206
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    • 2017
  • Field data obtained from marine exploration are influenced by various environmental factors such as wind, waves, tidal current and flow velocity of a background medium. Most environmental factors except for the flow velocity are properly corrected in the data processing stage. In this study, the wave equation modeling considering flow velocity is used to generate observation data, and numerical experiments using the observation data were conducted to analyze the effect of flow velocity on waveform inversion. The numerical examples include the results with unrealistic flow velocities. In addition, an algorithm is suggested to numerically extract flow velocity for waveform inversion. The proposed algorithm was applied to the modified Marmousi2 model to obtain the results depending on the flow velocity. The effect of flow velocity on updated physical properties was verified by comparing the inversion results without considering flow velocity and those obtained from the proposed algorithm.

A new algorithm for SIP parameter estimation from multi-frequency IP data: preliminary results (다중 주파수 IP 자료를 이용한 SIP 변수 추정)

  • Son, Jeong-Sul;Kim, Jung-Ho;Yi, Myeong-Jong
    • Geophysics and Geophysical Exploration
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    • v.10 no.1
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    • pp.60-68
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    • 2007
  • Conventional analysis of spectral induced polarization (SIP) data consists of measuring impedances over a range of frequencies, followed by spectral analysis to estimate spectral parameters. For the quantitative and accurate estimation of subsurface SIP parameter distribution, however, a sophisticated and stable inversion technique is required. In this study, we have developed a two-step inversion approach to obtain the two-dimensional distribution of SIP parameters. In the first inversion step, all the SIP data measured over a range of frequencies are simultaneously inverted, adopting cross regularisation of model complex resistivities at each frequency. The cross regularisation makes it possible to enhance the noise characteristics of the inversion by imposing a strong assumption, that complex resistivities should show similar characteristics over a range of frequencies. In numerical experiments, we could verify that our inversion approach successfully reduced inversion artefacts. As a second step, we have also developed an inversion algorithm to obtain SIP parameters based on the Cole-Cole model, in which frequency-dependent complex resistivities from the first step are inverted to obtain a two-dimensional distribution of SIP parameters. In numerical tests, the SIP parameter images showed a fairly good match with the exact model, which suggests that SIP imaging can provide a very useful subsurface image to complement resistivity.