• Title/Summary/Keyword: Hydrodynamic pressure

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Flying Characteristics of Running Tape above Rotating Head (I) (회전헤드에 대한 주행테이프의 부상특성 ( I ))

  • 민옥기;김수경
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.523-536
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    • 1991
  • This dissertation analyzes the running mechanism of flexible and thin tape above rotating head through the numerical simulation and the experiment. The scope of analysis is confined to the phenomena of two dimensional elasto hydrodynamic lubrication between the protruded bump on a rotating cylinder and the running tape. This model is based on the elastic deformation equation of plate and shell and Reynolds equation. Finite difference method is employed as a numerical technique to calculate (1) the distribution of pressure between the running tape and rotating bump and (2) the vertical deformation of elastic thin tape over he rotating bump under hydrodynamic pressure. In numerical analyses, the effects of bump size on flying characteristics of the tape were evaluated and examined considering the influence of tension and stiffness of tape.

A Study on the Vibration Control Using Magnetic Bearings of the Flexible Shaft Supported by Hydrodynamic Bearings (동수압 베어링으로 지지되는 연성축의 자기 베어링을 이용한 진동제어에 관한 연구)

  • 정성천;장인배;한동철
    • Tribology and Lubricants
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    • v.10 no.2
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    • pp.43-50
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    • 1994
  • The hydrodynamic bearing is accepted in many rotating systems because it has a large load carrying capacity. But the anisotropic pressure distribution of the bearing can arise the unstable vibration phenomenon over a certain speed. The magnetic bearing is an active element so that the unstable phenomenon of the hydrodynamic bearing, which is induced by the anisotropic support pressure of the oil film, can be controlled if the control algorithm and the controller gains are chosen appropriately. In this study, we investigate the stabilization method of the hydrodynamic bearing system composing the hybrid bearing which is the single unit of hydrodynamic bearing and magnetic bearing. The load carrying conditions of the hybrid bearing is modelled by the sum of the stiffness and damping coefficients of the hydrodynamic and the magnetic bearings in each direction. The dynamics of the rotor is analyzed by the Finite Element Method and the stability limit is determined by the eigenvalues of the hybrid bearings and shaft system. The eigenvalue study of the system shows that the stability limit of the hybrid bearing is increased compared to that of the hydrodynamic bearing. A Small increment of the stiffness and damping coefficient of the hybrid bearings by the magnetic actuators can increase the stability limit of the system. In this paper we tried to show the design references of the hybrid bearings by using the nondimensional bearing parameters. The analysis results show the possibilities of the stability limit increment of the hydrodynamic bearing system by combining the magnetic bearing.

Integrated Analysis of Hydrodynamic Motions and Structural Behavior of Large-Scaled Floating Structures using AQWA-ANSYS Coupling (AQWA-ANSYS 연계에 의한 대형 부유구조체의 파랑운동-구조거동 통합해석)

  • Lee, Du-Ho;Jeong, Youn-Ju
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.24 no.6
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    • pp.601-608
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    • 2011
  • In order to design floating structures, it should be required to evaluate hydrodynamic motions and structural behavior under the wave loadings. Then, structural behavior of floating structures should be evaluated including the effects of wave-induced hydraulic pressure subjected to floating structures. However, there has been a problem to exactly evaluate structural behavior of floating structures since it was difficult to directly connect wave-induced hydraulic pressure resulting from hydrodynamic analysis with structural analysis model. In this study, in order to exactly evaluate structural behavior of floating structures under the wave loading, integrated analysis of hydrodynamic motion and structural behavior was carried out to the large-scaled floating structure. The wave-induced hydraulic pressure resulting from hydrodynamic analysis AQWA were directly mapped to structural analysis model ANSYS bia Workbench interface of ANSYS Inc.. As the results of this study, it was found that the integrated analysis of this study evaluate exactly structural behavior of floating structures under the wave loadings since this method can directly reflect wave-induced hydraulic pressure resulting from hydrodynamic analysis to structural analysis model. Also, as the results of structural behavior evaluation, it was found that the tensile stress on the top slab was maximized at the wave direction of $0^{\circ}$, and tensile stress on the bottom slab was maximized at the wave direction of $45^{\circ}$, respectively.

An Basic Estimation for the Mutual action of Seismic load-Pore Pressure about Fill dam (필 댐에 관한 지진하중-간극수압의 상호작용 평가를 위한 기초연구)

  • Jeung, Eu-Jung;Baek, Sung-Chu;Nam, Yel-Woo;Lee, Seom-Beom;Park, Inn-Joon;Kim, Hong-Taek
    • 한국방재학회:학술대회논문집
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    • 2007.02a
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    • pp.275-278
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    • 2007
  • In case of having no consideration for pore pressure, we may underestimate earthquakes in seismic analysis of fill dam. because we can not consider hydrodynamic pressures induced by earthquakes. Nevertheless, there are few actual results on hydrodynamic pressures variation due to the principal variables of seismic analysis of fill dam. So, in this study we study earthquake-pore pressure interaction performing divers variable analysis, as considering Sesimic load-Pore Pressure.

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Simplified Analysis of Rectangular Liquid Storage Tanks Considering Fluid-Structure Interaction (유체-구조물 상호작용을 고려한 직사각형 액체저장탱크의 단순해석법)

  • Lee, Jin Ho;Cho, Jeong-Rae
    • Journal of the Earthquake Engineering Society of Korea
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    • v.26 no.5
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    • pp.203-209
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    • 2022
  • A simplified method for earthquake response analysis of a rectangular liquid storage tank is proposed with fluid-structure interaction considered. In order to simplify the complex three-dimensional structural behavior of a rectangular liquid storage tank, it is assumed that structural deformation does not occur in the plane parallel to the direction in which the earthquake ground motion is applied but in the plane perpendicular to the direction. The structural deformation is approximated by combining the natural modes of the simple beam and the cantilever beam. The hydrodynamic pressure, the structure's mass and stiffness, and the hydrodynamic pressure's added mass are derived by applying the Rayleigh-Ritz method. The natural frequency, structural deformation, pressure, effective mode mass, and effective mode height of the rectangular liquid storage tank are obtained. The structural displacement, hydrodynamic pressure, base shear, and overturning moment are calculated. The seismic response analysis of an example rectangular liquid storage tank is performed using the proposed simplified approach, and its accuracy is verified by comparing the results with the reference solution by the finite element method. Existing seismic design codes based on the hydrodynamic pressure in rigid liquid storage tanks are observed to produce results with significant errors that cannot be ignored.

Split Hopkinson Pressure Bar(SHPB)에 의한 고 변형률 재료의 구성방정식 시뮬레이션

  • 이억섭;정주호;김종호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.10a
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    • pp.724-727
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    • 1995
  • Dynamic deformation behavior under the high strain rate loading condition obtained with the aid of Split Hopkinson Pressure Bar(SHPB) technique is simulated by DYNA2D (an hydrodynamic code). A constitutive equation such as Johnson-Cook model is used by adjusting various parameters to fit experimentally determined dynamic stress-strain relationship.

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Hydrodynamic pressure distribution between a piston and cylinder - Experiment (1) (피스톤과 실린더 사이에서의 압력분포-실험(1))

  • 김영환;박태조
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2001.11a
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    • pp.304-309
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    • 2001
  • In this paper, the hydraulic oil pressure distributions are measured in the clearance gap between a stationary piston and moving cylinder apparatus. The results showed that the hydrodynamic pressure distributions are highly affected by the speed of cylinder and further experimental and analytical studies are required to obtain more accurate results. Therefore present experimental method can be used to enhance the performance of various hydraulic components adopting the piston-cylinder mechanism.

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Study of modified Westergaard formula based on dynamic model test on shaking table

  • Wang, Mingming;Yang, Yi;Xiao, Weirong
    • Structural Engineering and Mechanics
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    • v.64 no.5
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    • pp.661-670
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    • 2017
  • The dynamic model test of dam-reservoir coupling system for a 203m high gravity dam is performed to investigate effects of reservoir water on dynamic responses of dam during earthquake. The hydrodynamic pressure under condition of full reservoir, natural frequencies and acceleration amplification factors along the dam height under conditions of full and empty reservoir are obtained from the test. The results indicate that the reservoir water have a stronger influence on the dynamic responses of dam. The measured natural frequency of the dam model under full reservoir is 21.7% lower than that of empty reservoir, and the acceleration amplification factor at dam crest under full reservoir is 18% larger than that under empty reservoir. Seismic dynamic analysis of the gravity dams with five different heights is performed with the Fluid-Structure Coupling Model (FSCM). The hydrodynamic pressures from Westergaard formula are overestimated in the lower part of the dam body and underestimated in its upper part to compare with those from the FSCM. The underestimation and overestimation are more significance with the increase of the dam height. The position of the maximum hydrodynamic pressure from the FSCM is raised with the increase of dam height. In view of the above, the Westergaard formula is modified with consideration in the influence of the height of dam, the elasticity of dam on the hydrodynamic pressure. The solutions of modified Westergaard formula are quite coincident with the hydrodynamic pressures in the model test and the previous report.

On the Hydrodynamic Forces acting on a Partially Submerged Bag (부분적으로 물에 잠긴 백에 작용하는 유체역학적 힘)

  • G.J. Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.29 no.4
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    • pp.104-113
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    • 1992
  • The hydrodynamic problem is treated here when a pressurized bag is submerged partially into water and the end points of it oscillate. SES(Surface Effect Ship)has a bag filled with pressurized air at the stern in order to prevent the air leakage, and the pitch motion of SES is largely affected by the hydrodynamic force of the bag. The shape of a bag can be determined with the pressure difference between inside and outside. Once the hydrodynamic pressure is given, the shape of a bag can be obtained, however in order to calculate the hydrodynamic pressure we should know the shape change of the bag, and vice versa. Therefore the type of boundary condition on the surface of a bag is a moving boundary like a free surface boundary. In this paper, the formulation of this problem was done and linearized. The calculation scheme for the radiation problem of an oscillating bag is shown in comparison with the case that the bag is treated as rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

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Fluid-structure interaction system predicting both internal pore pressure and outside hydrodynamic pressure

  • Hadzalic, Emina;Ibrahimbegovic, Adnan;Dolarevic, Samir
    • Coupled systems mechanics
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    • v.7 no.6
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    • pp.649-668
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    • 2018
  • In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy's law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot's porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.