• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.109.4-109
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• 2001

We have developed a laser ultrasonic system for visualization of elastic waves propagating on a solid surface, in order to visualize ultrasonic waves propagating on opaque media. This system can produce a series of successive images as an animation of wave propagation, because of scanning an optical heterodyne probe to measure surface transient displacements. Using this visualization technique, we observed the scattering and diffraction of ultrasonic waves around various shapes of artificial defects, and examined its application to nondestructive inspection. This imaging system provides various kinds of visualization images such as propagation image, amplitude image, arrival time image and velocity image. We have been confident that this technique is available for nondestructive inspection and materials ...

• KSTLE International Journal
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• 제7권1호
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• pp.10-13
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• 2006

In this work, imaging and study of elastic property of the living cell was performed. The motivation of this work was to seek the possibility of exploiting Young's modulus as a disease indicator using Atomic Force Microscope (AFM) and also to gain fundamental understanding of cell mechanics for applications in medical nanorobots of the future. L-929 fibroblast adherent cell was used as the sample. Imaging condition in cell culturing media environment was done in very low speed ($20{\mu}m/ s$) compared to that in the ambient environment. For measuring the Young's modulus of the living cell, AFM indentation method was used. From the force-distance curve obtained from the indentation experiment the Young's modulus could be derived using the Hertz model. The Young's modulus of living L-929 fibroblast cell was $1.29{\pm}0.2$ kPa.

• Structural Engineering and Mechanics
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• 제31권2호
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• pp.117-135
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• 2009

The reflection and transmission of micropolar thermoelastic plane waves at the interface between an elastic solid and micropolar generalized thermoelastic solid is discussed. The interface boundary conditions obtained contain interface stiffness (normal stiffness and transverse stiffness). The expressions for the reflection and transmission coefficients which are the ratios of the amplitudes of reflected and transmitted waves to the amplitude of incident waves are obtained for normal force stiffness, transverse force stiffness and welded contact. Numerical calculations have been performed for amplitude ratios of various reflected and transmitted waves. The variations of amplitude ratios with angle of incident wave have been depicted graphically. It is found that the amplitude ratios of reflected and transmitted waves are affected by the stiffness, micropolarity and thermal distribution of the media.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.103-109
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• 2007

With the increase of track density, high rotational speed and the compatibility for various media in optical disk drives, the effective design to vibration reduction is very important for robust operation. Especially when a slim optical disk drive for a notebook PC is excited by a mass-unbalanced disk, internal vibration and its transmission to external case bring about severer problem than that of conventional one. In this paper a design process of a rubber mount in a slim optical disk drive for vibration reduction is presented. The characteristics of rubbery materials - hyper-elastic and visco-elastic - are measured with standard specimens. The static stiffness of a rubber mount was calculated by FEM and the dynamic stiffness is predicted with the static stiffness and the impedance test data of the standard specimen. The transmissibility tests are performed for the purpose of verification of the design process.

• 한국지반공학회지:지반
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• 제13권1호
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• pp.101-110
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• 1997

본 논문에서는 무한영역에서 발생하는 임의의 1$1/r^n$변위감쇠특성을 해석할 수 있는 p-버전 정적 무한요소를 연구하였다. 무한요소를 개발하기 위하여 이론해를 근사화한 형상함수를 사용하였다. 균질한 무한 탄성체내의 공동변형문제와 반무한탄성체위에 놓인 강성기초의 거동해석을 통하여, 본 연구에서 개발된 무한요소가 무한영역을 효율적으로 묘사할 수 있음을 검토하였다.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.425-437
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• 2021

Under foundation shock mats have been used in the current practice in order to reduce/damp vibrations received by buildings through the surrounding environment. Although some investigations have been made on under foundation shock mats performance, their effectiveness in the reduction of railway induced-vibrations has not been fully studied, particularly with the consideration of underneath soil media. In this regard, this research is aimed at investigating performance of shock mat used beneath building foundation for reduction of railway induced-vibrations, taking into account soil-structure interaction. For this purpose, a 2D finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a shock mat, and the building. The model results were validated using an analytical solution reported in the literature. The performance of shock mats was examined by an extensive parametric analysis on the soil type, bedding modulus of shock mat and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, a better performance of shock-mats is observed. A simplified model/method was developed for prediction of shock mat effectiveness in reduction of railway-induced vibrations, making use of the results obtained.

• 디지털콘텐츠학회 논문지
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• 제16권4호
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• pp.605-613
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• 2015

본 논문은 패턴인식에서 자주 사용되는 투영행렬을 희소화하는 문제를 다룬다. 최근 임베디드 시스템이 널리 사용됨에 따라 탑재되는 프로그램의 용량이 제한받는 경우가 빈번히 발생한다. 개발된 프로그램은 상수 데이터를 포함하는 경우가 많다. 예를 들어, 얼굴인식과 같은 패턴인식 프로그램의 경우 고차원 벡터를 저차원 벡터로 차원을 축소하는 투영행렬을 사용하는 경우가 많다. 인식성능 향상을 위해 영상으로부터 매우 높은 차원의 고차원 특징벡터를 추출하는 경우 투영행렬의 사이즈는 매우 크다. 최근 라소 회귀분석 방법을 이용한 RSR(rotated sparse regression) 방법론[1]이 제안되었다. 이 방법론은 여러 실험을 통해 희소행렬을 구하는 가장 우수한 알고리즘 중 하나로 평가받고 있다. 우리는 본 논문에서 RSR을 개선할 수 있는 세 가지 방법론을 제안한다. 즉, 학습데이터에서 이상치를 제거하여 일반화 성능을 높이는 방법, 학습데이터를 랜덤 샘플링하여 희소율을 높이는 방법, RSR의 목적함수에 엘라스틱 넷 회귀분석의 패널티 항을 사용한 E-RSR(elastic net-RSR) 방법을 제안한다. 우리는 실험을 통해 제안한 방법론이 인식률을 희생하지 않으며 희소율을 크게 증가시킴으로써 기존 RSR 방법론을 개선할 수 있음을 보였다.

• 한국음향학회지
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• 제41권2호
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• pp.174-183
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• 2022

본 논문에서는 내부 유체를 갖는 수중에 몰수된 탄성 쉘이 기포층으로 둘러싸여 있을 때의 음향 방사를 모드 이론을 이용해 연구했다. 전 방향성의 점음원이 내부 유체의 중심에 위치해 있고 음향 소음원으로서 사용되었다. 모드 해의 미지수는 매질 사이의 경계조건으로부터 계산된다. 넓은 주파수 대역에서 모드 해의 안정성을 유지하기 위해, 모드 해의 규격 기법이 사용되었다. 기포 층은 Commander와 Prosperetti의 유효 매질 이론에 기반하여, 단일 모드 분포, 균일 분포, 정규 분포, 멱함수 분포를 이용해 각각 모의되었다. 각각의 기포 분포에 대해 삽입손실이 주파수에 대해 계산되었다. 추가적으로 공극비, 탄성 쉘의 매질 특성, 탄성 쉘과 기포층의 간극의 영향에 대한 수치해석을 수행했다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1989년도 봄 학술발표회 논문집
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• pp.22-27
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• 1989

This paper presents a study of soil-structure interaction problems using infinite elements. The infinite elements are formulated for homogeneous and layered soil media, based on approximate expressions for three components of propagating waves, namely Rayleigh, compressive and shear waves. The integration scheme which was proposed for problems with single wave component by Zienkiewicz is expanded to the multi-wave problem. Verifications are carried out on rigid circular footings which are placed on and embedded in elastic half space. Numerical analysis is performed for a containment structure of a nuclear power plant subjected seismic excitation.

• 비파괴검사학회지
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• 제23권6호
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• pp.635-644
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• 2003

To ensure the reliability of ultrasonic nondestructive testing techniques for modern structural materials, the effects of anisotropy and inhomogeneity and the influence of non-planar component geometries on ultrasonic wave propagation have to be taken into account. In this article, fundamentals and applications of two analytical approaches to three-dimensional elastic beam field calculation are presented. Results for both isotropic materials including curved interfaces and for anisotropic media like composites are presented, covering field profiles for various types of transducers and the modeling of time-dependent rf-signals.