• 한국항행학회논문지
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• 제17권4호
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• pp.429-434
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• 2013

본 논문에서는 모서리 경계조건을 만족하는 접지된 2개의 유전체층 위의 완전도체띠 격자구조에 의한 TM(Transverse Magnetic) 산란 문제를 수치해석 방법인 FGMM (Fourier Galerkin Moment Method)를 이용하여 해석하였다. TM 산란에 대하여 도체띠에 유도되는 표면 전류밀도는 스트립 양 끝에서 매우 큰 값이 예측되므로, 이때 도체띠에 유도되는 표면 전류밀도는 1종 Chebyshev 다항식과 적절한 모서리 경계조건을 만족하는 함수의 곱의 급수로 전개하였다. 전반적으로, 접지평면 위에 유전체층의 비유전율의 값이 증가하면, 반사전력의 급변점에 대한 스트립 폭은 더 큰 값으로 이동하였다. 수치결과들은 기존 논문들과 비교하여 급속한 수렴해와 좋은 일치를 보였다.

• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 1995년도 정기학술강연회 발표논문 초록집
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• pp.66-70
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• 1995

The oscillatory boundary layer that develops when surface waves propagate over the sea bottom affects many flow-pendent phenomena in the coastal zone. Examples of such phenomena are wave energy dissipation due to bottom friction and the initiation and transport of sediment (Grant and Madsen 1986). In nature the boundary layer under waves will almost always be turbulent (Nielsen 1992). (omitted)

• 대한수학회논문집
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• 제38권1호
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• pp.299-318
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• 2023

This article devises an exponentially fitted method for the numerical solution of two parameter singularly perturbed parabolic boundary value problems. The proposed scheme is able to resolve the two lateral boundary layers of the solution. Error estimates show that the constructed scheme is parameter-uniformly convergent with a quadratic numerical rate of convergence. Some numerical test examples are taken from recently published articles to confirm the theoretical results and demonstrate a good performance of the current scheme.

• Smart Structures and Systems
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• 제20권3호
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• pp.311-328
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• 2017

The characteristics of boundary layers have significant effects on the aerodynamic forces and vibration of the wind turbine blade. The incorporation of active trailing edge flaps (ATEF) into wind turbine blades has been proven as an effective control approach for alleviation of load and vibration. This paper is aimed at investigating the effects of external trailing edge flaps on the flow pattern and velocity distribution within a boundary layer of a NREL 5MW reference wind turbine, as well as designing a new type of velocity sensors for future validation measurements. An aeroelastic-aerodynamic simulation with FAST-AeroDyn code was conducted on the entire wind turbine structure and the modifications were made on turbine blade sections with ATEF. The results of aeroelastic-aerodynamic simulations were combined with the results of two-dimensional computational fluid dynamic simulations. From these, the velocity profile of the boundary layer as well as the thickness variation with time under the influence of a simplified load case was calculated for four different blade-flap combinations (without flap, with $-5^{\circ}$, $0^{\circ}$, and $+5^{\circ}$ flap). In conjunction with the computational modeling of the characteristics of boundary layers, a bio-inspired hair flow sensor was designed for sensing the boundary flow field surrounding the turbine blades, which ultimately aims to provide real time data to design the control scheme of the flap structure. The sensor element design and performance were analyzed using both theoretical model and finite element method. A prototype sensor element with desired bio-mimicry responses was fabricated and validated, which will be further refined for integration with the turbine blade structures.

• 한국항공우주학회지
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• 제37권11호
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• pp.1055-1065
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• 2009

경계층 안정성 방정식인 PSE를 이용하여 익형 표면에 형성되는 경계층의 안정성 해석을 수행하였다. 압축성 비점성 유동 해석으로 경계층 가장자리 조건을 얻고, 일반좌표계에서의 압축성 경계층 방정식을 4차 정확도로 계산하여 층류 경계층 유동장을 얻었다. 층류 경계층 데이터를 PSE의 입력으로 하여 안정성 해석을 수행하고 교란의 증폭률을 얻어 안정성 특성을 고찰 하였다. 마하수 0.5의 NACA0012 및 HSNLF(1)-0213 익형에 대한 해석을 수행하여 교란 주파수에 따른 증폭률 및 위치에 따른 교란의 진폭 분포 특성을 파악하였다. 익형의 윗면과 아랫면에서 받음각에 따른 안정성 특성을 각각 증폭률의 크기와 주파수 범위에 대해 분석하였다. 또한 중립안정성 곡선, 마하수에 따른 안정성 특성을 살펴보았으며 익형의 종류에 따른 안정성 특성 차이를 분석하였다.

• Wind and Structures
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• 제8권6호
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• pp.455-467
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• 2005

The effects of upstream velocity profiles on the flow around a low-rise rectangular prism submerged in a turbulent boundary layer have been investigated. Three different boundary layer profiles are generated, which are characterized by boundary layer height, displacement thickness, and momentum thickness. Flow characteristics variations caused by the different layers such as those in turbulent kinetic energy distribution and locations of re-circulating cavities and reattachment points have been precisely measured by using a PIV (Particle Image Velocimetry) technique. Observations were made in a boundary layer wind tunnel at $Re_H$=7900, based on a model height of 40 mm and a free stream velocity of 3 m/s with 15 - 20% turbulence intensity.

• Structural Engineering and Mechanics
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• 제12권2호
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• pp.135-156
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• 2001

Analytical solutions and finite element results of laminated composite plates with smart material layers embedded in them are presented in this study. The third-order plate theory of Reddy is used to study vibration suppression characteristics. The analytical solution for simply supported boundary conditions is based on the Navier solution procedure. The velocity feedback control is used. Parametric effects of the position of the smart material layers, material properties, and control parameters on the suppression time are investigated. It has been found that (a) the minimum vibration suppression time is achieved by placing the smart material layers farthest from the neutral axis, (b) using thinner smart material layers have better vibration attenuation characteristics, and, (c) the vibration suppression time is larger for a lower value of the feedback control coefficient.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.306-311
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• 2001

Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer$(\delta=270mm)$ was the natural turbulent boundary layer at the test section with fully long developing length(18m). The thin boundary layer with 36.5mm thickness was generated by on a smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity and the height of the model was $7.9{\times}10^3$. The mean velocity vector fields and turbulent kinetic energy distribution were measured and compared. The effect of boundary layer thickness is clearly observed not only in the length of separation bubble but also in the reattachment points. The thinner boundary layer thickness, the higher turbulent kinetic energy peak around the model roof. It is strongly recommended that the height ratio between model and approaching boundary layer thickness should be a major parameter.

• Journal of applied mathematics & informatics
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• 제22권1_2호
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• pp.49-65
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• 2006

A robust numerical method for a singularly perturbed second-order ordinary differential equation having two parameters with a discontinuous source term is presented in this article. Theoretical bounds are derived for the derivatives of the solution and its smooth and singular components. An appropriate piecewise uniform mesh is constructed, and classical upwind finite difference schemes are used on this mesh to obtain the discrete system of equations. Parameter-uniform error bounds for the numerical approximations are established. Numerical results are provided to illustrate the convergence of the numerical approximations.

• Advances in nano research
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• 제8권2호
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• pp.103-114
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• 2020

In this research, buckling and free vibration of rectangular polymeric laminate reinforced by graphene sheets are investigated. Various patterns are considered for augmentation of each laminate. Critical buckling load is evaluated for different parameters, including boundary conditions, reinforcement pattern, loading regime, and laminate geometric states. Furthermore, vibration analysis is investigated for square laminate. Elastic properties of the composite are calculated using a combination of both molecular dynamics (MD) and the rule of mixture (MR). Kinematics of the plate is approximated based on the first shear deformation theory (FSDT). The current analysis is performed based on the energy method. For the numerical investigation, Ritz method is applied, and for shape functions, Chebyshev polynomials are utilized. It is found that the number of layers is effective on the buckling load and natural frequency of laminates which made from non-uniform layers.