• 한국소음진동공학회논문집
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• 제15권10호
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• pp.1137-1147
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• 2005

The dynamic response due to the unbalance and crack and the quasi-static response due to gravity are analytically derived based on the complex transfer matrix. The additional slope is expressed as function of the bending moment at crack position based on the fracture mechanics concept, and inversely the bending moment is expressed as function of the additional slope at the crack Position. At each angle step during the shaft revolution, the additional slope and bending moment are calculated by an iterativemethod. The transient behavior is considered by introducing Fourier series expansion concept for the additional slope. Simulation is carried out for a simple rotor similar to those available in the literature and comparison of the basic crack behavior is shown. Using the additional slope, the cracked rotor behavior is explained with the crack depth increased: the magnitude of the additional slope increases and the closed crack duration during a revolution decreases as the crack depth increases. The direction of unbalance is also shown as a factor to affect the crack breathing. Whirl orbits are shown near the sub-critical speed ranges of the rotor.

• 전자공학회논문지S
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• 제36S권11호
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• pp.128-139
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• 1999

본 논문은 6-스텝까지 인버터의 선형제어영역을 넓히기 위한 공간전압 변조방법의 선형화 기법에 대해 제안하였다. 이 방법은 인버터에서 발생시키고자 하는 전압을 연속모드에서는 보상각을 얻기 위해서 6스텝 모드를 포함하는 불연속모드에서는 불연속 스위칭이 이루어지도록 하는 유지각을 얻기 위해서 퓨리에 급수를 이용하고 있다. 이 각들의 근사화 수식들을 과변조 영역에서 기본파 전압을 보상하기 위해 사용하였다. 따라서, PWM 인버터 출력전압의 최대 활용과 선형 제어를 이룰 수 있다.

• 한국수학사학회지
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• 제21권3호
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• pp.67-96
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• 2008

19세기에 푸리에와 디리클레가 한 개의 식으로 표현되지 않을 수도 있는 "임의의" 함수를 삼각급수로 표현하는 것과 관련하여 연속함수의 적분을 다루었던 코시의 적분보다 더 일반적인 적분의 필요성을 제기하여 리만적분론으로 이끌었다. 한동안 리만적분이 가장 일반적인 적분으로 간주되었고, 이 적분론이 집중적으로 다루어진 결과 리만적분의 약점들이 보였으나, 적어도 초기에는 이것들이 리만적분에 대한 비판으로 보이지 않았다. 그러나 죠르단이 1892년에 용량개념을 소개하며 리만적분론을 측도론적 배경에서 다루었고, 이로부터 몇 년 후에 보렐이 죠르단의 용량론을 측도론으로 발전시킨 후에 르베그가 이 둘의 이론을 합쳐서 지금 "르베그적분"으로 알고 있는 적분의 새 개념을 얻게 되었다.

• 한국해양공학회지
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• 제18권5호
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• pp.7-14
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• 2004

The interaction of incident manochromatic waves with an array of N surface-piercing porous dual cylindrical structures is investigated in the frame of three-dimensional linear potential theory. The dual cylindrical structure is camposed of concentric two cylinders. The exterior cylinder is porous and the interior cylinder is impermeable. The fluid domain is divided into N+1 regions i.e. a single exterior region and N interior regions. The diffraction potentials in each region representing the scattering of incident waves by an array of porous cylindrical structures are expressed by the Fourier Bessel series. The unknown coefficients in each region are determined by applying the porous boundary condition and continuity of mass flux at the matching boundary. It is found that an array of porous cylindrical structures reduces both the wave forces and the wave run-up, and shows the excellent performance of wave blocking. The results show that various types of breakwater exchanging seawater are prospective by controlling the porosity and the configuration of cylindrical structures.

• Structural Engineering and Mechanics
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• 제17권5호
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• pp.641-654
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• 2004

This paper presents a theoretic model of a smart structure, a transversely isotropic piezoelectric thick square plate constructed with three laminas, piezoelectric-elastic-piezoelectric layer, by adopting the first order shear deformation plate theory and piezoelectric theory. This model assumes that the transverse displacements through thickness are linear, and the in-plane displacements in the mid-plane of the plate are not taken to be account. By using Fourier's series expansion, an exact Navier typed analytical solution for deflection and electric potential of the simply supported smart plate is obtained. The electric boundary conditions are being grounded along four vertical edges. The external voltage and non-external voltage applied on the surfaces of piezoelectric layers are all considered. The convergence of the present approach is carefully studied. Comparison studies are also made for verifying the accuracy and the applicability of the present method. Then some new results of the electric potentials and displacements are provided. Numerical results show that the electrostatic voltage is approximately linear in the thickness direction, while parabolic in the plate in-plane directions, for both the deflection and the electric voltage. These results are very useful for distributed sensing and finite element verification.

• 대한기계학회논문집
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• 제11권3호
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• pp.362-367
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• 1987

본 연구에서는 위의 인자들 중 .int.Pdt대신에 계산의 편의상 .int.Pd.theta.로, .DELTA.P는 최고압력차의 영향이 가장 크다고 생각되어 (.DELTA.P)$_{max}$를 대상으로 하여 이들 제인 자와 각 주파수성분과의 상관관계에 대하여 검토하고, 주파수역에 대하여 미치는 영향 을 정량적으로 해석하기 위하여 보조 프로그램을 작성하였다.

• 한국소음진동공학회논문집
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• 제18권1호
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• pp.123-130
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• 2008

An analytical method for the free vibration of a flexible rectangular plate in contact with water is developed by the Rayleigh-Ritz method. The plate clamped along the edges is partially contacted with water at both sides. It is assumed that the contained water is incompressible and inviscid. The wet mode shape of the plate is assumed as a combination of the dry mode shapes of a clamped beam. The liquid motion is described by using the liquid displacement potential and determined by using the compatibility conditions along the liquid interface with the plate. Minimizing the Rayleigh quotient based on the energy conservation gives an eigenvalue problem. It is found that the theoretical results can predict excellently the fluid-coupled natural frequencies comparing with the finite element analysis result.

• Structural Engineering and Mechanics
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• 제70권5호
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• pp.525-534
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• 2019

An analytical research on buckling of simply supported thin plate with variable thickness under bi-axial compression is presented in this paper. Combining the perturbation technique, Fourier series expansion and Galerkin methods, the linear governing differential equation of the plate with arbitrary thickness variation under bi-axial compression is solved and the analytical expression of the critical buckling load is obtained. Based on that, numerical analysis is carried out for the plates with different thickness variation forms and aspect ratios under different bi-axial compressions. Four different thickness variation forms including linear, parabolic, stepped and trigonometric have been considered in this paper. The calculated critical buckling loads and buckling modes are presented and compared with the published results in the tables and figures. It shows that the analytical expressions derived by the theoretical method in this paper can be effectively used for buckling analysis of simply supported thin plates with arbitrary thickness variation, especially for the stepped thickness that used in engineering widely.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.765-779
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• 2020

This article presents a nonclassical size dependent model based on the modified couple stress theory to study and analyze the bending behavior of perforated microbeams under different loading patterns. Modified equivalent material and geometrical parameters for perforated beam are presented. The modified couple stress theory with one material length scale parameter is adopted to incorporate the microstructure effect into the governing equations of perforated beam structure. The governing equilibrium equations of the perforated Timoshenko as well as the perforated Euler Bernoulli are developed based on the potential energy minimization principle. The Poisson's effect is included in the governing equilibrium equations. Regular square perforation configuration is considered. Based on Fourier series expansion, closed forms for the bending deflection and the rotational displacements are obtained for simply supported perforated microbeams. The proposed methodology is validated and compared with the available results in the literature and an excellent agreement is detected. Numerical results demonstrated the applicability of the proposed methodology to investigate the bending behavior of regularly squared perforated beams incorporating microstructure effect under different excitation patterns. The obtained results are significantly important for the design and production of perforated microbeam structures.

• 한국토양비료학회지
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• 제23권2호
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• pp.87-93
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• 1990

토양(土壤)의 깊이별 지온(地溫)을 예측(豫測)하기 위한 통계모형(統計模型)을 설정(設定)하기 위하여 1979년(年)부더 1988년(年)까지 중앙기상태(中央氣象台) 수원측후소(水原測候所)에서 관측(觀測)된 지온자료(地溫資料)와 평균최고(平均最高), 최저(最低), 기온(氣溫), 강수량(降水量), 풍속(風速) 및 최심적설량등(最深積雪量等) 기상자료(氣象資料)에 대(對)한 통계분석(統計分析)을 하였다. 통계분석(統計分析)은 지온(地溫)을 Fourier 급수(級數)에 의한 년주기함수(年週期函數)와 년주기함수(年週期函數)에서의 잔차(殘差)는 대기(大氣)의 기상조건(氣象條件)의 변화(變化)에서 오는 노이지(nuise)로 보고 이에 대한 상관분석(相關分析)을 stepwise backward elimination법(法)에 의하여 각(各) 계수(係數)를 찾는 방법(方法)으로 하였다. 깊이별(別) 지온(地溫)의 년주기함수(年週期函水)로 Fourier급수(級數)의 8항(項)을 사용(使用)하였을 때 지면온도(地面溫度)의 평균평방오차(平均平方誤差)가 2.30, 토심(土深) 50 cm에서 1.13, 500 cm에서 0.42로 토심(土深)이 깊을수록 작아졌고, $r^2$는 0.913~0.988이었다. 주기함수분석(週期函數分析)에서 잔차(殘差)에 대한 독립변수(獨立變數)로서 평균(平均), 최고(最高), 최저기온(最低氣溫), 강수량(降水量), 최심적설(最深積雪) 및 풍속등(風速等) 기상요소(氣象要素)와의 상관분석(相關分析)을 위한 지연일수검출(遲延日數檢出)에 따르면, 기온(氣溫)은 토탐(土深) 0 cm와 5 cm에 대하여 0일(日), 30 cm까지는 -1일(日), 50 cm에서는 -2일(日)이었다. 강수량(降水量)의 지연일수(遲延日數)는 30 cm까지 -1일(日), 50 cm에서 -2일(日), 최심적설(最深積雪)과 풍속(風速)은 10 cm까지가 -1일(日), 30 cm까지 -2일(日), 50 cm에서는 -3일(日)이었다. 지연일수(遲延日數)를 고려(考慮)한 잔차분석(殘差分析)에 의한 지온예측(地溫豫測) 통계모형(統計模型)의 평균평방오차(平均平方誤差)는 토심(土深) 0 cm에서 1.64, 50 cm에서 0.97로 주기함수(週期函數)의 평균평방오차(平均平方誤差)보다 작아졌으며, $r^2$값은 높아져 통계모형(統計模型)의 정도(精度)가 높아졌다. 계수(係數)의 크기로 보아 년주기함수(年週期函數)에 독립적(獨立的)인 대기(大氣) 기상요소(氣象要素)가 지온(地溫)의 결정(決定)에 크게 영향(影響)을 주는 깊이는 30 cm이며, 기온(氣溫)은 50 cm깊이까지도 영향(影響)을 주는 것으로 나타났다. 이 통계모형(統計模型)의 검정결과(檢定結果) $r^2$값이 0.976~0.996으로 예측치(豫測値)와 실측치간(實測値間)에 고도(高度)의 유의성(有意性)이 있어 실용성(實用性)이 있었다. 한편, 토양표면(土壤表面)의 최고지온(最高地溫)과 최고기온(最高氣溫)의 차(差)(${\Delta}T_{ms}$)를 옥수수포장(圃場)에서 조사(調査)한 결과(結果), ${\Delta}T_{ms}$와 일사량(日射量)($R_s;J_m{^{-2}}$)과 직선적(直線的)인 관계(關係)로 엽면적지수(葉面積指數)가 그 이하(以下) 일 때에는 $${\Delta}T_{ms}=0.902+1.924{\times}10^{-3}R_s $$엽면적지수(葉面積指數)가 그 이상(以上)일 때에는 $${\Delta}T_{ms}=0.274+8.881{\times}10^{-4}R_s$$ 의 관계(關係)가 있었다.