• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.305-312
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• 2023

Physics-Informed Neural Network (PINN) is used to invert bubble size distributions from attenuation losses. By considering a linear system for the bubble population inversion, Adaptive Learned Iterative Shrinkage Thresholding Algorithm (Ada-LISTA), which has been solved linear systems in image processing, is used as a neural network architecture in PINN. Furthermore, a regularization based on the linear system is added to a loss function of PINN and it makes a PINN have better generalization by a solution satisfying the bubble physics. To evaluate an uncertainty of bubble estimation, deep ensemble is adopted. 20 Ada-LISTAs with different initial values are trained using the same training dataset. During test with attenuation losses different from those in the training dataset, the bubble size distribution and corresponding uncertainty are indicated by average and variance of 20 estimations, respectively. Deep ensemble Ada-LISTA demonstrate superior performance in inverting bubble size distributions than the conventional convex optimization solver of CVX.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.590-590
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• 2006

• Water for future
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• v.17 no.4
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• pp.269-272
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• 1984

우선 홍수유량은 강우가 수문유출계를 통하여 변환된 것이므로, 원리적으로는 유량데이터만으로, 즉 강우데이터 없이도 홍수예측이 가능함을 기술한다. 다음에는 강우유출계의 강한 비선형성은 유량을 수치휠터에 의해 2~3의 성분으로 분리할 때 각성분계부터는 제거되는 것(단, 강우의 분리법칙이 비선형이 된다. "휠터 분리 AR법")에 대하여 기술한다. 제삼으로, 실측유량과 예측유량의 오차가 가장 신뢰도가 높은 정보임을 지적하고, 이 오차를 이요하는 휠터링의 방법으로서 세가지의 고찰법이 있음을 제시한다. 마지막으로 역산강우에 칼만.휠터를 적용하는 방법을 제안하고, 그 방법을 효과적으로 하는 여러 가지 기법을 기술한다. 기법을 기술한다.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.421-424
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• 2002

소나선배열 신호처리에 있어서 일반적으로 사용하는 빔형성기법은 환경에 대한 정보를 사용하지 않으나, 정합장처리 기법은 해양환경 정보를 사용함으로써 소음원의 추적 및 환경정보의 역산에 이용될 수 있다. 본 연구에서는 2001년도에 동해에서 수행된 실험 자료에 대한 정합장처리 실험과 결과에 대해서 소개한다.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1995.03a
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• pp.92-100
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• 1995

최근 지하 공간의 활용이 증대되는 추세에 이와 관련되어 지하 구조물의 시공전 또는 시공 중에 있어 시공 전략 수립, 장비 결정, 안정성 및 경제성 등을 위해 암반 내의 파쇄대나 균열대의 발달 및 분포에 대한 탐사는 필수적으로 선행되어야 한다. 이러한 탐사에는 분해능이 매우 높은 탐사 기술이 요구되며, 일반적으로 시추공이나 지하 갱도를 이용한 탄성파 탐사나 지오레이다(georadar) 탐사를 많이 사용하고, 자료해석을 위한 역산 기법으로는 지오토모그래피(geotomography)가 필수적인 기법으로 인식되고 있다. (중략)

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.141-146
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• 1998

동해 울릉분지에서 해양내부에 수온구조 파악을 위하여 수중 폭발성 음원인 SUS를 이용한 해양음향 토모그래피 실험을 1998년 8월에 실시하였다. 토모그래피 실험은 30, 60 km 반경으로 36개의 지점에서 항공기를 이용하여 SUS를 투하하고 관측해역 중앙에 위치한 선박에서 선배열수신기 (10개의 수신기 배열)로 수신하였다. 토모그래피 실험에 의한 역산 결과를 비교하기 위하여 AXBT를 이용한 수온관측이 동시에 수행되었다. AXBT 관측으로 울릉분지에서 자주 나타나는 난수성 소용돌이가 관측되었으며 이는 관측해역의 남동쪽에 위치하고 있으며 남서방향에서 북동방향으로 진행하는 형태를 보이고 있다. 음파의 도달시간 차이를 이용한 역산결과는 해양내부의 수온분포를 보여주는데 오차가 커서 새로운 해양음향 토모그래피 기법의 도입 필요성을 제시한다.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.5-17
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• 2007

Various field setup and filtering criteria have been suggested to avoid the near field effects in surface wave methods. Unlike other surface wave methods HWAW method uses the near field component positively. It is possible by using maximum energy point based on time-frequency map and inversion method to consider receiver locations from the source point and body wave component. To verify the HWAW method in the near field numerical study was performed and the wave propagation in the stratified soil media was simulated due to a surface point load. All of five representative soil models were used. The experimental dispersion curves, determined by HWAW method at the various receiver distances in the region of near field, all coincided well with the theoretical dispersion curves determined by 3D forward modeling (Kausel's method). Consequently, it was considered that the HWAW method can provide reliable $V_s$ profiles effectively in the near field.

• Journal of the Korean Geophysical Society
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• v.3 no.4
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• pp.251-260
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• 2000

Applicabilities of two numerical methods, the 2-dimensional and the 3-dimensional method, are evaluated to inverse test results obtained from the underwater SASW(Spectral -Analysis-of-Surface-Waves) method. As a result of this study, it has been found that the 2-dimensional method can supposed to be applicable for the cases where stiffness of soil layer increases gradually with depth, and the stiffness is relatively low. For the other cases, however, it has been concluded that the 3-dimensional method needs to be applied to determine realistic theoretical dispersion curves. An example is also shown that in situ soil profile underwater is estimated from experimental dispersion curves using the 3-dimensional method. As a results, it can be concluded that the underwater SASW method can be effectively applied to explore the underwater soil condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1C
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• pp.45-51
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• 2010

In urban area, design and construction of civil engineering structures such as subway tunnel, underground space and deep excavation is impeded by unreliable site investigation. Variety of embedded objects, electric noises and traffic vibrations degrades the quality of site investigation, whatever the site-investigation technique would be. In this research, a preliminary research was performed to develop a dedicated site investigation technique for urban geotechnical sites, which can overcome the limitations of urban sites. HiRAS (Hybrid Integration of Surface Waves and Resistivity) technique which is the first outcome of the preliminary research was proposed in this paper. The technique combines surface wave as well as electrical resistivity. CapSASW method for surface-wave technique and PDC-R technique for electrical resistivity survey were incorporated to develop HiRAS technique. CapSASW method is a good method for evaluating material stiffness and PDC-R technique is a reliable method for determination of underground stratification even in a site with electrical noise. For the inversion analysis of HiRAS techniuqe, a site-specific relationship between stress-wave velocity and resistivity was employed. As for outgrowth of this research, the 2-D distribution of Poisson's ratio could be also determined.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.85-98
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• 2009

The tau-p inversion algorithm is widely employed to generate starting models with most computer programs, which implement refraction tomography. This algorithm emphasises the vertical resolution of many layers, and as a result, it frequently fails to detect even large lateral variations in seismic velocities, such as the decreases which are indicative of shear zones. This study demonstrates the failure of the tau-p inversion algorithm to detect or define a major shear zone which is 50m or 10 stations wide. Furthermore, the majority of refraction tomography programs parameterise the seismic velocities within each layer with vertical velocity gradients. By contrast, the Generalized Reciprocal Method (GRM) inversion algorithms emphasise the lateral resolution of individual layers. This study demonstrates the successful detection and definition of the 50m wide shear zone with the GRM inversion algorithms. The existence of the shear zone is confirmed by a 2D analysis of the head wave amplitudes and by numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, an analysis of the shot record amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients, occurs in the weathered layers. The major conclusion reached in this study is that while all seismic refraction operations should aim to provide as accurate depth estimates as is practical, those which emphasise the lateral resolution of individual layers generate more useful results for geotechnical and environmental applications. The advantages of the improved lateral resolution are obtained with 2D traverses in which the structural features can be recognised from the magnitudes of the variations in the seismic velocities. Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features such as faults which do not display any intrinsic variation or 'signature' in seismic velocities.