• 제목/요약/키워드: closed boundary layer

검색결과 35건 처리시간 0.024초

TIME PERIODIC SOLUTIONS TO A HEAT EQUATION WITH LINEAR FORCING AND BOUNDARY CONDITIONS

  • In-Jee Jeong;Sun-Chul Kim
    • 대한수학회지
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    • 제60권2호
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    • pp.465-477
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    • 2023
  • In this study, we consider a heat equation with a variable-coefficient linear forcing term and a time-periodic boundary condition. Under some decay and smoothness assumptions on the coefficient, we establish the existence and uniqueness of a time-periodic solution satisfying the boundary condition. Furthermore, possible connections to the closed boundary layer equations were discussed. The difficulty with a perturbed leading order coefficient is demonstrated by a simple example.

A CLOSED-FORM SOLUTION FOR TURBULENT WAVE BOUNDARY LAYERS

  • Larson, Magnus
    • 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)

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INFLUENCE OF CONSTANT HEAT SOURCE/SINK ON NON-DARCIAN-BENARD DOUBLE DIFFUSIVE MARANGONI CONVECTION IN A COMPOSITE LAYER SYSTEM

  • MANJUNATHA, N.;SUMITHRA, R.;VANISHREE, R.K.
    • Journal of applied mathematics & informatics
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    • 제40권1_2호
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    • pp.99-115
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    • 2022
  • The problem of Benard double diffusive Marangoni convection is investigated in a horizontally infinite composite layer system consisting of a two component fluid layer above a porous layer saturated with the same fluid, using Darcy-Brinkman model with constant heat sources/sink in both the layers. The lower boundary of the porous region is rigid and upper boundary of the fluid region is free with Marangoni effects. The system of ordinary differential equations obtained after normal mode analysis is solved in closed form for the eigenvalue, thermal Marangoni number for two types of thermal boundary combinations, Type (I) Adiabatic-Adiabatic and Type (II) Adiabatic -Isothermal. The corresponding two thermal Marangoni numbers are obtained and the essence of the different parameters on non-Darcy-Benard double diffusive Marangoni convection are investigated in detail.

계층적인 메쉬 구조를 이용한 영상분할 방법 (Image Segmentation Using Hierarchical Meshes)

  • 임동근;호요성
    • 한국방송∙미디어공학회:학술대회논문집
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    • 한국방송공학회 1999년도 학술대회
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    • pp.9-14
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    • 1999
  • The object boundary of an image plays an important role for image interpretation. In this paper, we introduce a concept of hierarchical mesh-based image segmentation for finding object boundaries. In each hierarchical layer, we employ neighborhood searching and boundary tracking methods to refine the initial boundary estimate. We also apply a local region growing method to define closed contours. Experimental results indicate that reliable segmentation of objects can be accomplished by the pro-posed tow complexity technique.

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대기경계층 내에 놓인 자유단 원주의 형상비가 후류유동에 미치는 영향에 관한 연구 (Effect of cylinder aspect ratio on wake structure behind a finite circular cylinder located in an atmospheric boundary layer)

  • 박철우;이상준
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집E
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    • pp.247-252
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    • 2001
  • The flow around free end of a finite circular cylinder(FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wake structures behind a 2-D cylinder and a finite cylinder located in a uniform flow were also measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency is decreased and the vortex formation length is increased compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, in the region near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly established. In the wake center region, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit, compared to that of uniform flow.

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구에 설치한 딤플과 표면 거칠기에 의한 항력 감소 메커니즘 (Mechanism of Drag Reduction by Dimples and Roughness on a Sphere)

  • 최진;전우평;최해천
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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    • pp.191-194
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    • 2006
  • In this paper, we present a detailed mechanism of drag reduction by dimples and roughness on a sphere by measuring the streamwise velocity above the dimpled and roughened surfaces, respectively. Dimples cause local flow separation and trigger the shear layer instability along the separating shear layer, resulting in generation of large turbulence intensity. With this increased turbulence, the flow reattaches to the sphere surface with high momentum near the wall and overcomes strong adverse pressure gradient formed in the rear sphere surface. As a result, dimples delay main separation and reduce drag significantly. The present study suggests that generation of a separation bubble, i.e. a closed-loop streamline consisting of separation and reattachment, on a body surface is an important flow-control strategy for drag reduction on a bluff body such as the sphere and cylinder. In the case of roughened sphere, the boundary layer flow is directly triggered by roughness and changes to a turbulent flow. Due to this change, the drag significantly decreases. As the Reynolds number further increases, transition to turbulence occurs earlier on the sphere surface. Because of faster growth of turbulent boundary layer by roughness, earlier transition thickens the boundary layer, resulting in earlier separation and drag increase with increasing Reynolds number

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SH-wave in a piezomagnetic layer overlying an initially stressed orthotropic half-space

  • Kakar, Rajneesh;Kakar, Shikha
    • Smart Structures and Systems
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    • 제17권2호
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    • pp.327-345
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    • 2016
  • The existence of SH-wave in a piezomagnetic layer overlying an initially stressed orthotropic half-space is investigated. The coupled of differential equations are solved for piezomagnetic layer overlying an orthotropic elastic half-space. The general dispersion equation has been derived for both magnetically open circuit and magnetically closed circuits under the four types of boundary conditions. In the absence of the piezomagnetic properties, initial stress and orthotropic properties of the medium, the dispersion equations reduce to classical Love equation. The SH-wave velocity has been calculated numerically for both magnetically open circuit and closed circuits. The effect of initial stress and magnetic permeability are illustrated by graphs in both the cases. The velocity of SH-wave decreases with the increment of wave number.

Single-Layer 포텐셜과 가중함수를 이용한 응력강도계수의 계산 (Calculation of Stress Intensity Factors Using Single-Layer Potential and Weight Function)

  • 이형연;홍창선
    • 대한기계학회논문집
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    • 제19권4호
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    • pp.981-989
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    • 1995
  • A new weight function approach to determine SIF(stress intensity factor) using single-layer potential has been presented. The crack surface displacement field was represented by one boundary integral term whose kernel was modified from Kelvin's fundamental solution. The proposed method enables the calculation of SIF using only one SIF solution without any modification for the crack geometries symmetric in two-dimensional plane such as a center crack in a plate with or without an internal hole, double edge cracks, circumferential crack or radial cracks in a pipe. The application procedure to those crack problems is very simple and straightforward with only one SIF solution. The necessary information in the analysis is two reference SIFs. The analysis results using present closed-form solution were in good agreement with those of the literature.

대기경계층 내에 놓인 실린더의 자유단 형상변화가 후류유동에 미치는 영향에 관한 연구 (Effect of Free End Shape on Wake Structure Around a Finite Cylinder Located in an Atmospheric Boundary Layer)

  • 박철우;이상준
    • 대한기계학회논문집B
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    • 제27권1호
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    • pp.105-116
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    • 2003
  • The flow structure around the free end of a finite circular cylinder (FC) embedded in an atmospheric boundary layer (ABL) over open terrain was investigated experimentally with varying the free end shape. The experiments were carried out in a closed-return type subsonic wind tunnel. A finite cylinder with an aspect ratio (L/D) of 6 was mounted vertically on a long flat plate. The Reynolds number based on the cylinder diameter is about Re=7,500. The velocity fields near the FC free end were measured using the single-frame double-exposure PIV method. As a result, for the FC with a right-angled free end, there is a peculiar vortical structure, showing counter-rotating twin vortices near the FC free end. It is caused by the interaction between the entrained irrotational fluids from both sides of FC and the downwash flow from the FC free-end.

폐쇄형 시험부에서 케블라 덮개가 장착된 마이크로폰 어레이의 주파수 특성에 대한 실험적 연구 (An Experimental Study on Frequency Characteristics of the Microphone Array Covered with Kevlar in Closed Test Section Wind Tunnel)

  • 황은수;최영민;김양원;조태환
    • 한국소음진동공학회논문집
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    • 제25권3호
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    • pp.150-159
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    • 2015
  • An experimental study on frequency characteristics of the microphone array covered with Kevlar sheet was conducted in the closed test section. Microphones that were flush-mounted in the wall of wind tunnel were subjected to very high flow noise resulting from the turbulence in the wall boundary layer. This noise interference by the boundary layer was referred as 'a microphone self-noise' and various approaches were studied to reduce this interference. Recessed microphone array with high tensioned cover was one of the good approaches to reduce this self-noise. But, the array cover could cause an unexpected interference to the measuring results. In this paper the frequency characteristics of the microphone array with Kevlar cover was experimentally studied. The white noise was used as a reference noise source. Three kinds of tensions for the Kevlar cover were tested and those results were compared with the test results without the Kevlar cover. The gap effect between the cover and microphone head was also tested to find out the proper position of microphone in the array module. Test results show that the mid-tension and 10mm gap was the best choice in the tested cases.