• Title/Summary/Keyword: Vertical Cylinder

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New analytical solutions to water wave diffraction by vertical truncated cylinders

  • Li, Ai-jun;Liu, Yong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.11 no.2
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    • pp.952-969
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    • 2019
  • This study develops new analytical solutions to water wave diffraction by vertical truncated cylinders in the context of linear potential theory. Three typical truncated surface-piercing cylinders, a submerged bottom-standing cylinder and a submerged floating cylinder are examined. The analytical solutions utilize the multi-term Galerkin method, which is able to model the cube-root singularity of fluid velocity near the edges of the truncated cylinders by expanding the fluid velocity into a set of basis function involving the Gegenbauer polynomials. The convergence of the present analytical solution is rapid, and a few truncated numbers in the series of the basis function can yield results of six-figure accuracy for wave forces and moments. The present solutions are in good agreement with those by a higher-order BEM (boundary element method) model. Comparisons between present results and experimental results in literature and results by Froude-Krylov theory are conducted. The variation of wave forces and moments with different parameters are presented. This study not only gives a new analytical approach to wave diffraction by truncated cylinders but also provides a reliable benchmark for numerical investigations of wave diffraction by structures.

The Expressions of Vector Gravity and Gravity Gradient Tensor due to an Elliptical Cylinder (타원 기둥에 의한 벡터 중력 및 중력 변화율 텐서 반응식)

  • Hyoungrea Rim
    • Geophysics and Geophysical Exploration
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    • v.26 no.1
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    • pp.1-7
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    • 2023
  • This study derives the expressions of vector gravity and gravity gradient tensor due to an elliptical cylinder. The vector gravity for an arbitrary three-dimensional (3D) body is obtained by differentiating the gravitational potential, including the triple integral, according to the shape of the body in each axis direction. The vector gravity of the 3D body with axial symmetry is integrated along the axial direction and reduced to a double integral. The complex Green's theorem using complex conjugates subsequently converts the double integral into a one-dimensional (1D) closed-line integral. Finally, the vector gravity due to the elliptical cylinder is derived using 1D numerical integration by parameterizing a boundary of the elliptical cross-section as a closed line. Similarly, the gravity gradient tensor due to the elliptical cylinder is second-order differentiated from the gravitational potential, including the triple integral, and integrated along the vertical axis direction reducing it to a double integral. Consequently, all the components of the gravity gradient tensor due to an elliptical cylinder are derived using complex Green's theorem as used in the case of vector gravity.

Wide FOV Panorama Image Acquisition Method (광각 파노라마 영상획득 방법)

  • Kim, Soon-Cheol;Yi, Soo-Yeong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.3
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    • pp.2117-2122
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    • 2015
  • Wide FOV(Field-of-View) is required to contain much more visual information in a single image. The wide FOV imaging system has many industrial applications such as surveillance, security, tele-conference, and mobile robots. In order to obtain a wide FOV panorama image, an imaging system with hyperbolic cylinder mirror is proposed in this paper. Because the horizontal FOV is more important than the vertical FOV in general, a hyperbolic cylinder mirror is designed in this paper, that has a hyperbolic curve in the horizontal surface and is the same as a planar mirror in the vertical axis. Imaging model of the proposed imaging system is presented by ray tracing method and the hyperbolic cylinder mirror is implemented. The imaging performance of wide FOV is verified by experiments in this paper. This imaging system is cost-effective and is possible to acquire a wide panorama image having 210 degree horizontal FOV in real-time without an extra image processing.

Heat Transfer Characteristics for Inward Melting in a Paraffin-Filled Vertical Cylinder (파라핀을 채운 수직원관 내에서의 열전달 특성)

  • Yum, Sung-Bae;Hong, Chang-Shik
    • Solar Energy
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    • v.12 no.3
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    • pp.60-69
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    • 1992
  • Heat transfer characteristics and heat storage rate for vertical cylinder packed with paraffin as a latent heat storage material were theoretically studied. Conduction and convection mechanism were applied to the solid and liquid phase, respectively, and the results were compared with that of pure conduction model. The effects of heating temperature, initial solid temperature and aspect ratio on rate of storage were also studied. In the initial stage of melting, the natural convection is nearly restricted by the friction at the wall and the phase boundary. But it is generated when about 40% of solid melts and again it shrinks by the hot liquid situated on the upper part of the cylinder. So overall melting rate is higher then that for pure conduction model. The increase in heating temperature and aspect ratio activates the natural convection, so melting rate becomes higher. And the larger the aspect ratio, the greater the difference between upper and lower size of the solid. In the initial stage of melting, the initial temperature of solid paraffin has great effect on the melting rate, but as melting proceeds its effect lessens gradually.

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Natural convection heat transfer in a horizontal annulus from an inner tube with two vertical fins (2개의 수직휜이 부착된 내관으로부터 환상공간내의 자연대류 열전달)

  • 정태현;정한식;권순석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.654-660
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    • 1991
  • Natural convection heat transfer in a horizontal annulus from an inner tube with two vertical fins has been studied for the effects of dimensionless fin length and Rayleigh number. The maximum local Nusselt number of inner tube was obtained at .theta. = 145.deg. and that of outer cylinder at .theta. = 0.deg. for the case of $l_{F}$=0.3 Local Nusselt number distributions for the lower fins show higher values than that of the upper fins. The mean Nusselt number of inner tube was increased with the values of dimensionless fin length. The mean Nusselt number can be represented in an exponential function of Grashof number at various fin lengths. As compared with experimental and numerical results, isotherms and local Nusselt number show good agreement.t.

Influence of Pyrolyzing Fuel Disposition on Combustion Phenomena in a Cylindrical Enclosure (원형공간내 열분해 연료의 공간배치가 연소현상에 미치는 영향)

  • Han, Cho-Young;Kim, Jeong-Soo
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.680-685
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    • 2000
  • Investigation on ignition and flame propagation of pyrolyzing fuel in a cylindrical enclosure is accomplished. The pyrolyzing fuel of cylindrical shape is located in an outer cylinder sustained at high-temperature. Due to gravity, the buoyancy motion is inevitably incurred in the enclosure and this affects the flame initiation and propagation behavior. The radiative heat transfer plays an important role since a high temperature difference is involved in the problem. Numerical studies have been performed over overheat ratio, and vertical fuel eccentricity. The location of flame onset is affected by the vertical eccentricity of inner pyrolyzing fuel as well as thermal conditions applied.

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Three dimensional numerical simulations for non-breaking solitary wave interacting with a group of slender vertical cylinders

  • Mo, Weihua;Liu, Philip L.F.
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.1 no.1
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    • pp.20-28
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    • 2009
  • In thus paper we validate a numerical model for wave-structure interaction by comparing numerical results with laboratory data. The numerical model is based on the Navier-Stokes (N-S) equations for an incompressible fluid. The N-S equations are solved by a two-step projection finite volume scheme and the free surface displacements are tracked by the volume of fluid (VOF) method The numerical model is used to simulate solitary waves and their interaction with a group of slender vertical piles. Numerical results are compared with the laboratory data and very good agreement is observed for the time history of free surface displacement, fluid particle velocity and wave force. The agreement for dynamic pressure on the cylinder is less satisfactory, which is primarily caused by instrument errors.

Numerical Analysis on Combined Convection for a Vertical Cocentric Cylinder with External Fins (외부로 휜이 있는 수직이중관내의 조합대류 유동에 관한 수치적 연구)

  • Sohn, Sang-Suk;Lee, Chae-Moon;Yim, Jang-Soon
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.14 no.2
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    • pp.118-124
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    • 1985
  • The motion of a fluid in the closed annular cavity formed by two concentric vertical cylinders with externally finned tube has been analysed by a numerical solutions of the equation of momentum and energy. For the calculation procedure, the fluid is assumed to have constant thermo-dynamic and transporties except for the density, which is temperature-dependent in the buoyancy term of the vertical momentum equation (Boussinesq approximation). The govern ins equations for velocity and temperature are solved by a finite difference technique which incoorporates a scheme for treating the coupled variables. Results are presented for a range of the Rayleigh number and for various values of the fin height and the number of fins.

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Viscous Mean Drift Forces on a Floating Vertical Cylinder in Waves and Currents (파랑과 조류에 의한 부유식 수직 실린더 구조물에 작용하는 평균 점성 표류력)

  • Shin, Dong Min;Moon, Byung Young
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.3
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    • pp.503-509
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    • 2020
  • In offshore floating structures, the viscous mean drift force due to drag is considered a design part that has not been considered until recently. In this paper, an analytical solution for the viscous mean drift forces on a floating vertical cylinder considering the waves and currents was obtained. The area was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. In the case of waves, only the splash zone was considered; in the case of waves and currents, equations were obtained in both the splash zone and the submerged zone. The RAO results of previous studies were used to compare the calculated results with the drift forces acting on the fixed cylinder. Except for the case in only waves in the splash zone, the viscous mean drift force acting on the floating cylinder was larger than the drift force acting on the relatively fixed cylinder in most frequencies. In particular, the increase was greater when the currents were considered to be more important. Therefore, these results provide the inference for the viscous drift force due to drag in the design of floating offshore structures.

Numerical Analysis of Vortex Induced Vibration of Circular Cylinder in Lock-in Regime (Lock-in 영역에서 원형실린더의 와류유기진동 전산해석)

  • Lee, Sungsu;Hwang, Kyu-Kwan;Son, Hyun-A;Jung, Dong-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.1
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    • pp.9-18
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    • 2016
  • The slender structures such as high rise building or marine riser are highly susceptible to dynamic force exerted by fluid-structure interactions among which vortex-induced vibration(VIV) is the main cause of dynamic unstability of the structural system. If VIV occurs in natural frequency regime of the structure, fatigue failure likely happens by so-called lock-in phenomenon. This study presents the numerical analysis of dynamic behavior of both structure and fluid in the lock-in regimes and investigates the subjacent phenomena to hold the resonance frequency in spite of the change of flow condition. Unsteady and laminar flow was considered for a two-dimensional circular cylinder which was assumed to move freely in 1 degree of freedom in the direction orthogonal to the uniform inflow. Fluid-structure interaction was implemented by solving both unsteady flow and dynamic motion of the structure sequentially in each time step where the fluid domain was remeshed considering the movement of the body. The results show reasonable agreements with previous studies and reveal characteristic features of the lock-in phenomena. Not only the lift force but also drag force are drastically increasing during the lock-in regime, the vertical displacement of the cylinder reaches up to 20% of the diameter of the cylinder. The correlation analysis between lift and vertical displacement clearly show the dramatic change of the phase difference from in-phase to out-of-phase when the cylinder experiences lock-in. From the results, it can be postulated that the change of phase difference and flow condition is responsible for the resonating behavior of the structure during lock-in.