• Advances in concrete construction
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• 제14권1호
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• pp.35-43
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• 2022

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases.

• 소음진동
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• 제11권1호
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• pp.156-166
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• 2001

This work uses tensor calculus to derive a complete set of three-dimensional field equations well-suited for determining the behavior of thick shells of revolution having arbitrary curvature and variable thickness. The material is assumed to be homogeneous, isotropic and linearly elastic. The equations are expressed in terms of coordinates tangent and normal to the shell middle surface. The relationships are combined to yield equations of motion in terms of orthogonal displacement components taken in the meridional, normal and circumferential directions. Strain energy and kinetic energy functionals are also presented. The equations of motion and energy functionals may be used to determine the static or dynamic displacements and stresses in shells of revolution, including free and forced vibration and wave propagation.

• 한국소음진동공학회논문집
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• 제17권1호
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• pp.41-47
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• 2007

Scattering fields of two dimensional acoustic waves by a circular cylinder are investigated. The present numerical approach for the acoustic scattering problem has difficulties of numerical robustness, long-time stability and suitability of far-field boundary treatments. The time-dependent periodic acoustic source is used to analyze Interference patterns between incident waves and waves reflected by the cylinder. Characteristic boundary algorithms coupled with 4th order Modified-Flux-Approach ENO(essentially non-oscillatory) schemes are employed in generalized coordinates to examine the effect of the wane frequency on the interference patterns. Non-reflecting boundary conditions, which is crustal for accurate computations of aeroacoustic problems, are used not to contaminate scattering fields by reflected waves at the outer boundary. Computed scattering fields show the circumferential acoustic modes generated by interacting between acoustic sources and scattered waves. At a lower frequency, the wave passes almost straight through the cylinder without Interacting with circular cylinder. Simulation results are presented and compared with the analytic solution. Computed RMS-pressure distribution on the cylinder wall is good agreement with exact solution.

• Steel and Composite Structures
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• 제38권1호
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• pp.47-66
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• 2021

This work addresses the free vibration analysis of Functionally Graded Porous (FGP) nanocomposite truncated conical shells with Graphene PLatelet (GPL) reinforcement. In this study, three different distributions for porosity and three different dispersions for graphene platelets have been considered in the direction of the shell thickness. The Halpin-Tsai equations are used to find the effective material properties of the graphene platelet reinforced materials. The equations of motion are derived based on the higher-order shear deformation theory and Sanders's theory. The Fourier Differential Quadrature (FDQ) technique is implemented to solve the governing equations of the problem and to obtain the natural frequencies of the truncated conical shell. The combination of FDQ with higher-order shear deformation theory allows a very accurate prediction of the natural frequencies. The precision and reliability of the proposed method are verified by the results of literature. Moreover, a wide parametric study concerning the effect of some influential parameters, such as the geometrical parameters, porosity distribution, circumferential wave numbers, GPLs dispersion as well as boundary restraint conditions on free vibration response of FGP-GPL truncated conical shell is also carried out and investigated in detail.

• 한국압력기기공학회 논문집
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• 제6권1호
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• pp.16-22
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• 2010

Cast austenitic stainless steel(CASS) is used in the primary cooling piping system of nuclear power plant for it's relative low cost, corrosion resistance and easy of welding. However, the coarse-grain structure of cast austenitic stainless steel can strongly affect the inspectability of ultrasonic testing. The major problems encountered during inspection are beam skewing, high attenuation and high background noise of CASS component. So far, the best inspection performance involving CASS components have been achieved using low frequency TRL(Transmitter/Receiver side-by-side L wave) angle beam probe. But TRL technique could not detect shallow defect and it contains an uncertainty for sizing capability. Currently, most of researchers are studying to overcome these challenge issue. In this study, low-frequency phased array TRL technique used to detect and sizing the flaws in CF8A cast austenitic stainless steel.As conclusion, we could detect and size not only axial flaw but also circumferential flaw using low frequency phased array technique.

• 설비공학논문집
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• 제23권10호
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• pp.670-677
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• 2011

Direct numerical simulation are performed in order to investigate the effect of the circular cylinder shape on the forced convection around a circular cylinder at the Reynolds number of 300 and Prandtl number of 0.71. Three-dimensional characteristics of fluid flow and heat transfer around the smooth, wavy and torsional cylinders are investigated. A wavy cylinder has the sinusoidal variation in the cross sectional area along the spanwise direction with the wave length of ${\pi}/3$ and wavy amplitude of 0.1. A torsional cylinder has the twisted elliptic cross section with a torsional period of ${\pi}/2$ and an axis ratio of 1.35 corresponding to the major axis of 1.15 and the minor axis of 0.85. The value of time-and surface-averaged drag coefficient for the smooth cylinder is similar to that for the wavy cylinder, but larger than that for the torsional cylinder. The time and surface-averaged lift coefficient for the smooth cylinder is larger than that for the wavy and torsional cylinders. The time-averaged local heat transfer rate for the wavy and torsional cylinders shows different distribution along the circumferential direction, compared to that for the smooth cylinder because of the shape change in the spanwise direction for the cases of the wavy and torsional cylinders.

• 한국강구조학회 논문집
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• 제13권2호
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• pp.191-200
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• 2001

본 연구에서는 수치해석을 통하여 축하중을 받는 원통형 쉘의 좌굴해석을 수행하였다. 해석 식과의 비교를 통하여 수치모델 방법, 적절한 요소의 종류 및 요소의 개수등을 제시하였다. 매개변수 해석결과, 직경/두께비가 증가하면 좌굴응력은 크게 감소하나 높이/직경비가 증가하면 그 변화는 미세하며 이는 일반적인 기둥의 좌굴해석 결과와 상이하다. 높이/직경비가 커질수록 원주방향 좌굴모드의 파장수가 감소하였다. 바닥판의 두께가 증가하면 좌굴응력은 1~2% 증가한다. 따라서 그 영향은 거의 무시할 수 있다. 초기 형상결함의 크기가 증가하면 좌굴응력은 큰 감소를 보인다. 또한 회기분석을 통하여 좌굴응력을 간편하게 구할 수 있는 설계식을 도출하였으며, 수치해석 결과와 잘 일치하였다.

• 지구물리와물리탐사
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• 제9권1호
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• pp.73-85
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• 2006

상시진동의 수직 성분에 대한 배열 관측은 상시진동이 대부분 레일리파의 기본 모드로 이루어졌다는 가정하에 지하 층서구조를 추정하기 위해 자주 수행된다. 자료획득, 처리 및 분석의 유용한 도구로서 공간 자기상관(SPAC) 방법이 많이 사용되는데 이는 실제로 M개의 원형 수진기 배열과 중앙의 하나 측점으로 이루어진다 (M 측점 원형 배열). 이 논문에서는 분석 효율 및 현장 노력의 관점에서 효율적인 자료획득을 위한 원형 배열에 필요한 측점의 최소 수에 대해 연구하였다. 이 연구에서는 먼저 M 무한대의 원형 배열을 위한 SPAC 계수들이 단지 Bessel 함수 J0(rk)(r은 반지름, k는 파수)로서 표현되는 SPAC 알고리듬의 이론적 배경을 재정리하였다. 두번째로 M 측점 원형 배열에 대해 상시진동 에너지장과 무관한 오차항을 포함하는 SPAC 계수들을 배열을 가로지르는 파의 방향에 한해 해석적으로 유도해 내고 수치적으로 이들 오차항들에 대해서 평가하였다. 주요 평가 결과들은: 1) 만약 SPAC 계수들이, 계수가 첫번째 최소값을 갖는 주파수까지 이용되면 다른 4-, 5-, 9-측점 배열들에 비교했을 때 3-측점 원형배열이 상시진동의 관측에 효율적이고 유리하다. 2) 나이퀴스트 파수가 유효한 SPAC 계수가 평가될 수 있는 주파수의 상한선을 결정하는데 가장 영향을 끼치는 요소이다.