• 비파괴검사학회지
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• 제34권6호
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• pp.457-466
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• 2014

This paper presents an analytic and numerical simulation of the generation and propagation of pico-second ultrasound with nano-scale wavelength, enabling the production of bulk waves in thin films. An analytic model of laser-matter interaction and elasto-dynamic wave propagation is introduced to calculate the elastic strain pulse in microstructures. The model includes the laser-pulse absorption on the material surface, heat transfer from a photon to the elastic energy of a phonon, and acoustic wave propagation to formulate the governing equations of ultra-short ultrasound. The excitation and propagation of acoustic pulses produced by ultra-short laser pulses are numerically simulated for an aluminum substrate using the finite-difference method and compared with the analytical solution. Furthermore, Fourier analysis was performed to investigate the frequency spectrum of the simulated elastic wave pulse. It is concluded that a pico-second bulk wave with a very high frequency of up to hundreds of gigahertz is successfully generated in metals using a 100-fs laser pulse and that it can be propagated in the direction of thickness for thickness less than 100 nm.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 춘계학술대회
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• pp.180-185
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• 2009

우주비행체의 정밀 자세제어에 있어서 자세지향 및 안정성을 저해하는 구동기 교란의 효과는 매우 중요한 요소 중 하나라 할 수 있다. 최근 CMG는 그 구조의 복잡성에도 불구하고 반작용휠에 비교할 때 고출력 저중량이라는 장점에 근거하여 인공위성의 차세대 구동기로 많은 연구가 진행되고 있다. 정밀자세제어가 요구되는 인공위성의 구동기로 이용되기 위해서는 CMG가 위성 동체에 주게 될 교란력의 특성을 파악하는 것이 필수적이다. 본 논문에서는 CMG의 교란토크 및 교란력를 분석하기 위해 정적 동적 불균형을 가정하고, 라그랑지안 방법을 이용하여 해석적 모델을 유도하고 휠을 제작하여 진동을 분석하였다.

• 지구물리와물리탐사
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• 제25권4호
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• pp.242-251
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• 2022

자동 미분은 컴퓨터를 이용한 미분 계산시 함수의 전방향 연산만 정의하면 연쇄법칙을 이용해 함수의 미분을 자동으로 계산해주는 기능이다. 최근 자동 미분을 지원하는 계산 라이브러리들의 발달에 따라 지구 물리 역산 문제에 자동 미분 기술을 도입하는 사례가 증가하고 있다. 본 연구에서는 탄성파 탐사 전파형 역산 목적함수의 그래디언트 계산시 자동 미분을 도입하였을 때의 장단점과 성능을 분석하였다. 목적함수의 그래디언트 계산은 연쇄법칙을 이용해 매개변수 미분, 파동장 미분과 목적함수 미분의 곱으로 나타낼 수 있다. 수치 예제를 통해 매개변수 미분과 목적함수 미분 계산은 자동 미분으로 수행하고 파동장 미분은 해석적 방법으로 수행함으로써 해석적 미분의 장점인 빠른 성능과 자동 미분의 장점인 복잡한 그래디언트 계산의 편리성을 함께 얻을 수 있음을 보였다.

• 한국정보통신학회논문지
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• 제13권9호
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• pp.1737-1744
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• 2009

본 연구에서는 3C_D_T 웹사이트 평가모델의 항목 구성을 접목시켜, 현재 운영되고 있는 J지역 내 문화 관광 웹 사이트 평가 요소들에 대하여 중요하게 생각하는 상대적인 중요도를 계층적 분석과정(AHP: analytic hierarchy process)을 적용하여 네티즌들이 우선적으로 고려하는 평가요소들의 상대적인 비중과 우선순위를 산출하였다. 분석 결과, 콘텐츠(Contents) 요인이 가장 중요한 요소로 나타났으며, 민감도 분석 등을 추가로 실시하여 개선 방안에 대해 제시하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 Proceedings of the Korea Automatic Control Conference, 11th (KACC); Pohang, Korea; 24-26 Oct. 1996
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• pp.177-180
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• 1996

The purpose of this paper is to design a robust adaptive control algorithm for a class of systems having continuous relay nonlinearity. This continuous relay nonlinearity can be defined as an analytic nonlinear function having unknown parameters and bounded unmodeling part. By this mathematical modeling, the whole system can be considered as a nonlinear system having unknown parameters and bounded perturbation. The control algorithm of this paper, RALC, can be constructed by robust adaptive law, feedback linearization, and indirect robust adaptive control. By this RALC, we can obtain that the output of given system can follow that of a stable reference linear model made by designer and the boundedness of all signals in closed-loop system can be maintained. Therefore, we can confirm a robust adaptive control for a class of systems having continuous relay nonlinearity.

• 대한전기학회논문지
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• 제33권5호
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• pp.167-172
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• 1984

This paper describes the finite element analysis of magnetostatic field problems with permanent magnets. Two kinds of algorithms, one using the magnetic vector potential and the other using the magnetic scalar potential, are introduced. The magnetization of the pemanent magnet is used as the source instead of the magnetic equivalent current in both of the formulations using the magnetic vector potential and the magnetic scalar potential. A simple functional, which has only the region integral instead of the region integral and boundary integral, is derived in the formulation using the magnetic scalar potential. These make the formulation of the system equations simpler and more convenient than the conventional methods. The numerical results by the two proposed algorithms for a C-type permanent magnet model are compared with the analytic solutions respectively. The numerical results are in good agreement with the analytic solutions.

• 한국조리학회지
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• 제12권1호
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• pp.203-215
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• 2006

This study tried to develop an estimation model on the competitive power as a method to understand a practical index on the competitive power in order to improve the competitiveness of domestic bakery corporations and look into their internal structure. The results of the practical analysis are summarized below. First, eight critical success factors, which are considered important in competitive power in bakery corporations, were derived from preceding studies and an expert meeting. Second, this study performed a questionnaire with eight derived factors for bakery managers and employees. Seven critical success factors suitable for bakery corporations were chosen through validity and reliability tests. Third, this study performed an AHP(Analytic Hierarchy Process) analysis in order to establish preference according to each factor and weight. The importance of factor concerned with the competitive power of bakery corporations according to the result of weight analysis appeared in order of customer resources, personnel resources, corporate images, material resources and qualities, technical capability, financial factors and pliability(time).

• 한국대기환경학회지
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• 제19권6호
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• pp.733-743
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• 2003

The flow field in multiple fluid sphere systems was studied analytically. The expanded zero vorticity cell model based on Kuwabara's theory (1959) was applied and the effects of gas slippage at the collecting surface were considered. Also, the solid sphere system was extended to fluid sphere including the effects of the induced internal circulation inside the liquid droplet spheres or gas bubble systems. As a result, the obtained analytic solution was converged to the existing solutions for flow field around solid and bubble sphere systems with proper boundary conditions. Based on the resolved flow field, the terminal velocity around the collecting fluid spheres was obtained. Subsequently, this study evaluated the most general solution for flow field around the multiple fluid sphere systems. The obtained flow field in multiple fluid sphere could be used as a fundamental consideration of wet scrubber design and devices for removing particles by fluid-fluid interactions.

• Nuclear Engineering and Technology
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• 제28권5호
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• pp.488-499
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• 1996

We have extended the source projection analytic nodal discrete ordinates method (SPANDOM) for more flexible applicability in analysis of hexagonal assembly cores. The method (SPANDOM-FH) does not invoke transverse integration but instead solves the discrete ordinates equation analytically after the source term is projected and represented in hybrid form of high-order polynomials and exponential functions. SPANDOM-FH which treats a hexagonal node as one node is applied to two fast reactor benchmark problems and compared with TWOHEX. The results of comparison indicate that the present method SPANDOM-FH predicts accurately $k_eff$ and flux distributions in hexagonal assembly cores. In addition, SPANDOM-FH gives the continuous two dimensional intranodal scalar flux distributions in a hexagonal node. The reentering models between TWOHEX and SPANDOM were also compared and it was confirmed that SPANDOM's model is more realistic. Through the results of benchmark problems, we conclude that SPANDOM-FH has the sufficient accuracy for the nuclear design of fast breeder reactor (FBR) cores with hexagonal assemblies.

• 산업공학
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• 제12권4호
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• pp.602-616
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• 1999

Recently, due to the primary emphasis of environmental problem, the proper selection of the membrane systems necessary for waste water treatment has been one of the critical issues in the industrial sector. This paper shows how an Analytic Hierarchy Process (AHP) model can be used for assessing the performance of selected membrane systems: ultrafiltration, microfiltration, reverse osmosis, and electrodialysis essential for waste water treatments. The final results show that ultrafiltration is the most attractive membrane system to use in a water recycling system, followed by microfiltration, reverse osmosis and electrodialysis. This is consistent with the information that we found with respect to the elements that were taken into consideration. Sensitivity analysis is also provided here.