• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.302-307
• /
• 2005

The discharge coefficient in segmental wedge having ninety degrees vertex angle for the five kinds of opening ratio with differential pressure taps located at both upstream and downstream of one diameter of pipe was measured main purpose of this work is placed on developing the proper form of an equation for the discharge coefficient of a segmental wedge used as a primary element of flow metering devices, and from thata six-term equation which can express the variability of opening ratios was developed. The same assumption and hypotheses were used and tested for all procedures as conventional differential producers; however, the range of the opening ratio over this work is more expanded than previous studies. The opening ratios of segmental wedge, namely 0.3, 0.4, 0.5, 0.6 and 0.7 were investigated the Reynolds number based on the spool inside diameter ranges from 12,000 to 380,000, the resulting equation for the discharge coefficient is relatively simple; it contains only one variable-opening ratio because the characteristic of discharge coefficient of segmental wedge has little connection with the Reynolds number as shown by previous studies.

• Journal of the Society of Naval Architects of Korea
• /
• v.44 no.6
• /
• pp.666-674
• /
• 2007

It is very important to estimate static squeezing pressure distributions for lining material of sterntube after bearing at dry dock stage since the maximum squeezing pressure value can be one of the significant characteristics representing coming navigation performances of the propulsion system. Moderate oil film pressure between lining material and propulsion shaft is also essential for safe ship service. In this paper, Hertz contact theory is explained to derive static squeezing pressure. Reynolds equation simplified from Navier-Stokes equation is centrally differentiated to numerically obtain dynamic oil film pressures. New shaft alignment technology of nonlinear elastic multi-support bearing elements is also used in order to obtain external forces acting on lining material of bearing. For 300K DWT class VLCC with synthetic bush of sterntube after bearing, static squeezing pressures are calculated using derived external forces and Hertz contact theory. Optimum partial slope of the after bush is presented by parametric shaft alignment analyses. Dynamic oil film pressures are comparatively evaluated for partially bored and unbored after bush. Finally it is proved that the partial slope can drastically reduce oil film pressure during engine running.

• Journal of Advanced Marine Engineering and Technology
• /
• v.23 no.5
• /
• pp.687-694
• /
• 1999

This study was conducted to develop new drying process for automatic control and marine engi-neering system. Air-water tests were carried out to investigate dryer performance. The dispersed flow in he dryer test apparatuses was also simulated by using a numerical code which solves the Dittus-Boelter equation for continuous liquid phase and the Reynolds equation of droplet motion for continuous liquid phase and the Reynolds equation of droplet motion for dispersed phase to predict droplet removal efficiency. Proper conditions for dehumidification were optimized by response ambient conditions. When the selected indexes were constrained in the range of 85-98% moisture content above $15^{\circ}$ and more than mass flow rates of moist air 750kg/h. The numerical results were compared with the experimental data pertaining to the removal effi-ciency at chamber stage and overall pressure drop along concentric tubes Good agreement was obtained as for the efficiency while relatively poor agreement was obtained for the relative humidity. The results also showed that the efficiency depended strongly on the relative humidity at the inlet condition which indicated the importance of estimating the heat exchanger length. Effects of some design parameters in both removal efficiency and breakthrough onset condition are discussed.

• Water Engineering Research
• /
• v.3 no.3
• /
• pp.163-176
• /
• 2002

In this study, laboratory experiments have been performed to investigate characteristics of the velocity fields and turbulence for non-buoyant plane jet in the vicinity of the jet nozzle using PIV system. The experimental results show that, in the transition region, the lateral velocity profile is in good agreement with Gaussian distribution. However, the coefficient of Gaussian distribution, $\K_{u,}$, decreases with longitudinal distance in the transition region. The existing theoretical equation for the centerline velocity tends to overestimate the measured data in the transition region. A new equation for the centerline velocity derived by incorporating varying $k_{u}$ gives better agreement with the measured data than the previous equation. The results of the turbulence characteristics show peak values are concentrated on the shear layers. The Reynolds shear stress profile shows the positive peak in the upper layer and negative peak in the lower layer. The turbulent kinetic energy also provides double peaks at the shear layers. The peak of the Reynolds shear stress and the turbulent kinetic energy increases until x/B=8, and then it decreases afterwards.s.

• Tribology and Lubricants
• /
• v.22 no.6
• /
• pp.307-313
• /
• 2006

In this paper, a theoretical analysis is carried out to study the effect of viscosity variation with pressure in multiply grooved moving hydraulic spool valves. Analytical expressions for pressure distribution in the clearance and leakage flowrate are obtained solving one-dimensional Reynolds. For constant viscosity, an analytical expression for lateral force is also presented. The results showed that variation of viscosity with pressure affect highly on pressure distribution, leakage flowrate and lateral forces in hydraulic spool valves. Therefore additional intensive studies, including numerical analysis for two-dimensional Reynolds, should be required to investigate detailed lubrication characteristics of spool valves for high pressure.

• Journal of computational fluids engineering
• /
• v.16 no.2
• /
• pp.62-65
• /
• 2011

Characteristics of the pressure drop in an expanded bed have been compared to those in a packed bed for numerical study of the interphase drag in gas-particle flows. A numerical analysis of the pressure drop by the particle drag has been conducted according to the tube-to-particle diameter ratios and Reynolds numbers for comparison. As the tube-to-particle diameter ratios increase at the same Reynolds number, the pressure drop tends to converge. It has been confirmed that characteristics of the pressure drop in the expanded bed are similar to those in the packed bed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.12
• /
• pp.1681-1690
• /
• 2003

The effect of roughness is a change in the velocity and turbulence distributions near the surface. Turbulence models with surface roughness effect are applied to the fully developed flow in a two-dimensional, rough wall channel. Modified wall function model, low-Reynolds number k-$\varepsilon$ model, and k-$\omega$ model are selected for comparison. In order to make a fair comparison, the calculation results are compared with the experimental data. The modified wall function model and the low-Reynolds number k-$\varepsilon$ model require further refinement, while the k-$\omega$ model of Wilcox performs remarkably well over a wide range of roughness values.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.8
• /
• pp.1088-1094
• /
• 2002

A channel flow with a high Reynolds number but coarse grids is numerically studied to investigate the prediction possibility of its turbulence which is three-dimensional and time-dependent. In the present paper, a Reynolds-Averaged Navier-Stokes (RANS) model, a Large Eddy Simulation (LES) and a Navier-Stokes equation with no model are tested with a new approach of hybrid RANS/LES, which reduces to RANS model in the boundary layers and at separation, and to Smagorinsky-like LES downstream of separation, and then compared with each other. It is found that the simulations of hybrid RANS/LES method sustain turbulence like those of LES and with no model, and the results are stable and fairly accurate. This indicates strongly that gradual improvements could lead to a simple, stable, and accurate approach to predict turbulence phenomena of wall-bounded flow.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.5
• /
• pp.557-563
• /
• 1997

The unsteady flow in three-dimensional cubic cavity with narrow channel at upper region is investigated experimentally for three kinds of Reynolds number, 1*10/sup 4/, 3*10/sup 4/ and 5*10/sup 4/ based on the cavity width and cavity inlet mean flow velocity. Instant velocity vectors are obtained simultaneously at whole field by PIV(Particle Image Velocimetry). Wall pressure distributions are estimated using Poisson equation from the velocity data. Results of PIV reveal that severe unsteady flow fluctuation within the cavity are remarkable at all Reynolds numbers and sheared mixing layer phenomena are also found at the region where inlet driving flow is collided with the clock-wise rotating main primary vortex. Instant velocity profiles reveal that deformed forced vortex formation is observed throughout the entire region and spanwise kinetic energy migration is conspicuous.

• Journal of Navigation and Port Research
• /
• v.29 no.6 s.102
• /
• pp.523-528
• /
• 2005

The flow analysis is made to simulate the turbulent flow in the pipe with an obstacle. The models used are k-$\epsilon$, k-$\omega$, Spalart-Allmaras and Reynolds. The structured grid is used for the simulation The velocity vector, the pressure contour, the change of residual along the iteration number and the dynamic head are simulated for the comparison of four example cases. For the analysis, the commercial code is used.