• Title, Summary, Keyword: hydrodynamic pressure

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Minimization of Hydrodynamic Pressure Effect on the Ultraprecision Mirror Grinding

  • Lee, Sun-Kyu;Miyamoto, Yuji;Kuriyahawa, Tsunemoto;Syoji, Katsuo
    • International Journal of Precision Engineering and Manufacturing
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    • v.6 no.1
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    • pp.59-64
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    • 2005
  • This paper describes an investigation about the fluid delivering method that minimizes the generation of hydrodynamic pressure and improves the grinding accuracy. Traditionally, grinding fluid is delivered for the purpose of cooling, chip flushing and lubrication. Hence, a number of conventional investigations are focused on the delivering method to maximize fluid flux into the contact arc between the grinding wheel and the work piece. It is already known that hydrodynamic pressure generates due to this fluid flux, and that it affects the overall grinding resistance and machining accuracy. Especially in the ultra-precision mirror grinding process that requires extremely small amount of cut per pass, its influence on the machining accuracy becomes more significant. Therefore, in this paper, a new delivering method of grinding fluid is proposed with focus on minimizing the hydrodynamic pressure effect. Experimental data indicates that the proposed method is effective not only to minimize the hydrodynamic pressure but also to improve the machining accuracy.

Propeller Induced Pressure on Bottom Surface of Stern -A Method of Seperation from the Measured Pressure with Pressure Transducer attached on Hull Surface. (선미선저(船尾船底)에 미치는 추진기(推進器) 유기압력(誘起壓力) -선체표면(船體表面)에 붙인 압력변환기(壓力變換器)로 계측(計測)되는 압력(壓力)으로부터의 한 분리방법(分離方法)-)

  • Kyu-Jong,Cho
    • Bulletin of the Society of Naval Architects of Korea
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    • v.7 no.1
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    • pp.1-12
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    • 1970
  • The propeller induced pressure fluctuation around a ship's stern is one of the interesting problems from viewpoints of the noise and vibration. Most of the experimental works on the subject employ pressure transducer attached on hull surface near the propeller. In the technique, the measured pressure includes the hydrodynamic pressure transducer attached, if they exit. Hence, the separation of the additional pressure due to vibration from the measured pressure is essential for the determination of true values of the propeller induced pressure. In this paper, to contribute to the separation method, the author investigated the additional hydrodynamic pressure as below, based on the numerical calculation. (1) Hydrodynamic pressure on the body surface of two dimensional cylinders of some mathematical sections such as ellipse, rectangle, Lewis form of hypotrocoidal charactor and curvilinear-element section with chines oscillating vertically at high frequency in a free surface. (2) Hydrodynamic pressure on the surface of the shell plate in local vibration in an ideal fluid.

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On the Hydrodynamic Forces Acting on a Partially Submerged Bag

  • Lee, Gyeong-Joong
    • Selected Papers of The Society of Naval Architects of Korea
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    • v.2 no.1
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    • pp.140-155
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    • 1994
  • The hydrodynamic problem is treated here when a pressurized bag is submerged partially in the 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. The present paper describes the formulation of this problem and treats a linearized problem. The computations of the radiation problem for an oscillating bag are shown in comparison with the case that the bag is treated as a rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

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Measurement of Hydrodynamic Pressure Distribution between a Piston and Cylinder

  • Kim, Y.H.;Park, T.J.
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.419-420
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    • 2002
  • The piston-cylinder mechanism is widely adopted in the hydraulic machine components. In these cases, the hydrodynamic pressures are generated in the clearance gap between the piston and cylinder under lubrication action of the oils. Under the eccentric condition of the piston in the cylinder bore, the asymmetric pressure distributions in the circumferential direction result in lateral forces on the piston. When the lateral forces act as increasing the piston eccentricity, excessive wear can be occurs in the cylinder bore and piston. In this paper, the hydrodynamic pressures generated in the clearance are measured using a stationary piston and moving cylinder apparatus. The experimental results showed that the hydrodynamic pressure distributions are highly affected by the eccentricity of the piston.

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Dynamic analysis of water storage tank with rigid block at bottom

  • Adhikary, Ranjan;Mandal, Kalyan Kumar
    • Ocean Systems Engineering
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    • v.8 no.1
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    • pp.57-77
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    • 2018
  • The present paper deals with the finite element analysis of water tanks with rigid baffle. Fluid is discretized by two dimensional eight-node isoparametric elements and the governing equation is simulated by pressure based formulation to reduce the degrees of freedom in the domain. Both free vibration and force vibration analysis are carried out for different sizes and positions of block at tank bottom. The fundamental frequency depends on block height and it reduces with the increase of block height. The variation of hydrodynamic pressure on tank walls not only depends of the exciting frequency but also on the size and position of rigid block at tank bottom. The hydrodynamic pressure has higher value when the exciting frequency is equal and lower than the fundamental frequency of the water in the tank. Similarly, the hydrodynamic pressure increases with the increase of width of the block for all exciting frequencies when the block is at the centre of tank. The left and right walls of tank have experienced different hydrodynamic pressure when the block is placed at off-centre. However, the increase in hydrodynamic pressure on nearest tank wall becomes insignificant after a certain value of the distance between the wall and the rigid block.

Hydrodynamic Pressure and Shear Stress in Chemical Mechanical Polishing (화학기계적연마 공정의 윤활역학적 압력 및 전단응력 분포 해석)

  • 조철호;박상신;안유민
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.1
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    • pp.179-184
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    • 2000
  • Chemical Mechanical Polishing (CMP) refers to a material removal process done by rubbing a work piece against a polishing pad under load in the presence of chemically active and abrasive containing slurry. CMP process is a combination of chemical dissolution and mechanical action. The mechanical action of CMP involves hydrodynamic behavior. The liquid slurry is trapped between the work piece and pad forming a hydrodynamic film. For the first step to understand material removal mechanism of the CMP process, the hydrodynamic analysis is done with semiconductor wafer. Three-dimensional Reynolds equation is applied to get pressure distribution of the slurry film. Shear stress distributions on the wafer surface are also analyzed

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Hydrodynamic Behavior Analysis of Vertical-Cylindrical Liquid-Storge Tanks by Mathematically Analytic Method (수학적 해석 방법에 의한 액체저장탱크의 액동압 거동 해석)

  • Park, Jong-Ryul;Oh, Taek-Yul
    • Proceedings of the KSME Conference
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    • pp.628-635
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    • 2001
  • Hydrodynamic behavior and response of vertical-cylindrical liquid-storage tank is considered. The equation of the liquid motion is shown by Laplace's differential equation with the fluid velocity potential. The solution of the Laplace's differential equation of the liquid motion is expressed with the modified Bessel functions. Only rigid tank is studied. The effective masses and heights for the tank contents are presented for engineering design model.

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An Experimental Study on Oil Pressure Distribution in the Piston-Cylinder Mechanism (피스톤-실린더 기구에서 오일압력 분포에 관한 실험적 연구)

  • Kim, Yeong-Hwan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.10 no.6
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    • pp.77-82
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    • 2011
  • The piston-cylinder mechanism is widely adopted in the hydraulic machine components. In these cases, the hydrodynamic pressures are generated in the clearance gap between the piston and cylinder under lubrication action of the piston. Under the eccentric and tilted condition of the piston in the cylinder bore, the non-symmetric pressure distributions in the circumferential direction result in lateral forces. When the lateral forces act as increasing the eccentricity and tilting ratios, excessive wear can be result in cylinder and piston which are well known 'hydraulic locking' phenomena. In this paper, the hydrodynamic pressures generated in the clearance are measured using a stationary piston and moving cylinder apparatus. The experimental results showed that the hydrodynamic pressure distributions are highly affected by the speed and eccentricity of the cylinder and the oil viscosity.

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.

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.