• Title/Summary/Keyword: boundary friction.

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Simulation of Compression Molding Considering Slip at Interface for Polymeric Composite Sheet (섬유강화 고분자 복합판의 압축성형에 있어서 금형-재료계면의 미끄름을 고려한 유동해석)

  • 장수학;김석호;백남주;김이곤
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.163-168
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    • 1991
  • During Compression molding of polymeric composite materials, the flow characteristics should be obtained. Understanding the flow states may be useful for determination of optimum molding conditions, charge pattern etc. So far, for obtaining the flow analysis, no-slip boundary condition was applied on the mold surface. However, The study under consideration of the slip was conducted by Barone and Caulk. They have introduced the nondimensional parameter which is the ratio of viscous to friction resistance and governs the frictional condition. But the method for determining the parameter could not be proposed. In our work, the parameter which explains the interfacial friction is measured under a variety of molding conditions. Two-dimensional rectangular part and circular hollow disk are simulated with the measured parameter using the finite element method. Effects of the parameter on shapes of flow fronts are also presented.

Analysis of a Journal and Thrust FDB and a Conical FDB in the Spindle Motor of a Computer Hard Disk Drive (HDD 스핀들 모터용 저널-스러스트 유체동압 베어링과 코니컬 유체동압 베어링의 특성해석비교)

  • Kim, Bum-Cho;Jang, Gun-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.478-483
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    • 2005
  • This paper presents the comparison analysis of a Journal and thrust FDB (fluid dynamic bearing) and a conical FDB in a HDD spindle motor. The Reynolds equation is appropriately transformed to describe journal, thrust and conical bearing. Finite element method is applied to analyze the FDB by satisfying the continuity of mass and pressure at the interface between the hearings. The pressure field of the bearings is numerically approximated by applying the Reynolds boundary condition. The load and friction torque are obtained by integrating the pressure and the velocity gradient along the fluid film. The flying height of the spindle motor is measured to verify the proposed analytical result. This research shows that the conical bearing generates bigger load capacity and less friction torque than the journal and thrust bearing in a HDD spindle motor.

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Pin-Boss Stress Analysis Coupled with Oil Film Pressure of a Diesel Engine Piston Receiving 200 bar Combustion Pressure (200 bar 연소압을 받는 디젤엔진 피스톤 핀-보스의 유막 압력을 고려한 응력해석)

  • Chun, Sang-Myung;Lee, J.S.;Joo, D.H.;Park, S.J.
    • Tribology and Lubricants
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    • v.24 no.4
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    • pp.196-204
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    • 2008
  • In this study, the pressure distributions on the oil film of piston pin bearings are found by two-dimensional lubrication analysis in order to help the optimum design of the bearings of piston pin. The lubrication analysis is carried out together with an equation related with the oil pressure-viscosity index. The oil film pressure distribution is used as an input data for pressure boundary conditions at the piston pin-boss surface. Finally, the piston pin-boss stress distribution coupled with the thermal stress is calculated, and then compared with the results of the stress analysis which is not counted with the oil film pressure boundary condition.

Effects of radiation on wall-friction and heat-transfer in a convergent- divergent nozzle (복사가 수축 확대 노즐의 벽면에서 열전달과 벽마찰에 미치는 효과)

  • 강신형;이준식;김성훈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1639-1644
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    • 1990
  • Effects of radiation on the wall-friction and heat transfer in the convergent and divergent nozzle of a rocket motor are investigated in the present paper. Radiative heat transfer cools down the core gas, and the decrease in the gas temperature reduces the convective heat transfer on the wall. Radiation heat transfer is estimated by using mean-beam-length approach and core flow is assumed to be one-dimensional isentropic. The compressible thermal boundary layer is solved by a finite difference method. The Cebeci-Smith eddy viscosity model is adopted for the present study. Convective heat transfer is reduced at the throat of the nozzle and is almost compensated with an increase in radiative transfer. In the sequel total heat transfer rate is slightly reduced. However, radiation heat transfer is dominant in the converging part of the nozzle.

Horizontal Earth Pressure of the Backfill in the Narrowly Excavated Ground Considering Various Boundary Conditions (좁게 굴착된 뒤채움 지반의 경계조건에 따른 수평응력 변화에 관한 연구)

  • Kim, Hee Su;Ban, Hoki;Moon, Chang-Yeul
    • Journal of the Korean GEO-environmental Society
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    • v.18 no.11
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    • pp.19-26
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    • 2017
  • When narrowly excavated in the urban area, the wall of backfill space is not only symmetrical but also asymmetrical. In this case, the horizontal stress induced by backfilling depends mostly on the wall asymmetry and the wall friction angle. Therefore, in this study, the model test in the laboratory was conducted to investigate horizontal earth pressure with depth considering various boundary conditions such as base width, wall friction, relative density of backfill, and wall angle. As the wall is smoother and wall angle is lower from the bottom, the results showed higher the horizontal stresses due to the increase of vertical stresses.

A Study of ADS Slip Ratio Control using Solenoid Valve (전자밸브를 이용한 ABS 슬립율 제어에 관한 연구)

  • Choi, Jong-Hwan;Kim, Sung-Su;Yang, Soon-Yong;Park, Sung-Tae;Lee, Jin-Kul
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.676-681
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    • 2001
  • ABS is a safety device, which adds hydraulic system to the existing brake system to prevent wheel from locking, so we can obtain maximum braking force on driving. The hydraulic system to control braking pressure consists of sol-flow type using solenoid valve, flow control valve or consists of sol-sol type using two solenoid valve. In this paper, the hydraulic system in ABS is composed of sol type using a 3port-2position solenoid valve, and vehicle system is composed of 1/4 vehicle model. And slip ratio is controlled using PWM (Pulse-Width-Modulation) control algorithm. Braking friction coefficient and tracking friction coefficient which are described by slip ratio's function have maximum value when slip ratio has its value from 0.1 to 0.3. And slip ratio is controlled constantly in this boundary value even in the variation of road's condition in some boundary.

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Flow and Heat Transfer Analysis of Copper-water Nanofluid with Temperature Dependent Viscosity Past a Riga Plate

  • Ahmad, A.;Ahmed, S.;Abbasi, F.M.
    • Journal of Magnetics
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    • v.22 no.2
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    • pp.181-187
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    • 2017
  • Flow of electrically conducting nanofluids is of pivotal importance in countless industrial and medical appliances. Fluctuations in thermophysical properties of such fluids due to variations in temperature have not received due attention in the available literature. Present investigation aims to fill this void by analyzing the flow of copper-water nanofluid with temperature dependent viscosity past a Riga plate. Strong wall suction and viscous dissipation have also been taken into account. Numerical solutions for the resulting nonlinear system have been obtained. Results are presented in the graphical and tabular format in order to facilitate the physical analysis. An estimated expression for skin friction coefficient and Nusselt number are obtained by performing linear regression on numerical data for embedded parameters. Results indicate that the temperature dependent viscosity alters the velocity as well as the temperature of the nanofluid and is of considerable importance in the processes where high accuracy is desired. Addition of copper nanoparticles makes the momentum boundary layer thinner whereas viscosity parameter does not affect the boundary layer thickness. Moreover, the regression expressions indicate that magnitude of rate of change in effective skin friction coefficient and Nusselt number with respect to nanoparticles volume fraction is prominent when compared with the rate of change with variable viscosity parameter and modified Hartmann number.

Numerical Analysis of High-Reynolds-Number Flow around Axisymmetric Body (축대칭체 주위 고 레이놀즈수 유동에 대한 수치해석)

  • Choi, Jung-Kyu;Kim, Hyoung-Tae
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.6
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    • pp.631-636
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    • 2008
  • In this paper, numerical analysis based on the RANS equation and the Realizable ${\kappa}-{\varepsilon}$ turbulence model is carried out for flows around an axisymmetric body at three Reynolds numbers($1.22{\times}10^7$, $1.0{\times}10^8$, $1.5{\times}10^8$) and the numerical results are compared with experiments data. Computed velocity distributions agree well with experiments as the Reynolds number increases. Pressure distributions agree well with the results of the potential flow except the tail region but differ from experiments for the parallel middle body as well as tail region. Pressure gradients show a good agreement with those of potential flow and experiment except the tail region. Friction coefficients show that the numerical results generally are lower than the experimental results estimated from the measured velocity. The difference of friction coefficients between the calculation and the experiment increases with growing of a boundary layer.

A Harbour Oscillation Model by Galerkin Finite Element Method (Galerkin 유한요소법에 의한 항내 정온도 모형)

  • 서승남;연영진
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.6 no.4
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    • pp.439-451
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    • 1994
  • A numerical model for harbour oscillation is presented by use of Galerkin finite element method. The governing equation is used by the modified mild slope equation derived from Chen (1986) in which bottom friction is incorporated. Since the existing absorbing boundary condition. however. is shown to be incorrect correct boundary condition and forcing term due to an incident plane wave are rederived. Computation results for a rectangular harbour are shown in comparison with both laboratory data and existing numerical results. After the values of friction factor (f) and reflection coefficient (K$_{r}$) are discussed, the set (K$_{r}$=0, 94, f=0) is found to be best fitted to the laboratory data of the rectangular harbour.

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Turbulent boundary layer control via electro-magnetic forces (전자기력을 이용한 난류경계층 제어)

  • Lee J.-H.;Sung H, J.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.03a
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    • pp.166-171
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    • 2004
  • Direct numerical simulations are peformed to investigate the physics of a spatially developing turbulent boundary layer flow suddenly subjected to spanwise oscillating electro-magnetic forces in the near-wall region. The Reynolds number based on the inlet momentum thickness and free-stream velocity is $Re_\theta=300$. A fully-implicit fractional step method is employed to simulate the flow. The mean flow properties and the Reynolds stresses are obtained to analyze the near-wall turbulent structure. It is found that skin-friction and turbulent kinetic energy can be reduced by the electro-magnetic forces. Instantaneous flow visualization techniques are used to observe the response of streamwise vortices to spanwise oscillating forces. The near-wall vortical structures are clearly affected by spanwise oscillating electro-magnetic forces.

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