• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.1-10
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• 2020

This paper investigates the influence of the Circulating Water Channel (CWC) side wall and support struts on the hydrodynamic coefficient prediction for Autonomous Underwater Vehicles (AUVs) experiments. Computational Fluid Dynamics (CFD) method has been used to model the CWC tests. The hydrodynamic coefficients estimated by CFD are compared with the prediction of experiments to verify the accuracy of simulations. In order to study the effect of side wall on the hydrodynamic characteristics of the AUV in full scale captive model tests, this paper uses the CWC non-dimensional width parameters to quantify the correlation between the CWC width and hydrodynamic coefficients of the chosen model. The result shows that the hydrodynamic coefficients tend to be constant with the CWC width parameters increasing. Moreover, the side wall has a greater effect than the struts.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.2
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• pp.41-46
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• 2007

Butterfly valves are commonly used as control valves in applications where the pressure drops required of the valves relatively low. As the shutoff valve (on/off service) or throttling valves (for flow or pressure control), the higher order and the better precision of butterfly valves are required. The it's more and more essential to know the flow characteristic around the valve. Due to the fast progress of the flow visualization and numerical technique, it becomes possible to observe the flows around a valve and to estimate the performance of a valve. Researching these results did not gave only access to understand the process of the valve flows at different valve opening angles, but also was made to determine the accuracy of the employed method. Furthermore, the results of the three-dimensional analysis can be used in the design of butterfly valve in the industry.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.2
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• pp.188-193
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• 2005

Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

• Bulletin of the Society of Naval Architects of Korea
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• v.11 no.2
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• pp.7-14
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• 1974

Hydrodynamic moments produced by the rolling oscillation on the free surface and the associated swaying force were exactly calculated by Ursell-Tasai method for the cylinders with Kim's chine form sections($a_1,\;a_7$). The coefficient of the added moment of inertia $K_{\varphi^{\tau}}$, the progressive wave height ratio $\bar{A}$, the coefficient of swaying forces $K_{RS}$, ${\alpha}_{RS}$ of rolling oscillations are shown in the several figures. The results of the computation were compared with those of lewis form sections. It is concluded that the effect of the section form on the added moment of inertia is significant for the cylinder with the section of same beam-draft ratio and sectional area coefficient, on the other hand, a little effect appears on the wave damping.

• Environmental Engineering Research
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• v.19 no.4
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• pp.345-354
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• 2014

In this paper, effects of physical configurations and operating conditions on bubble column performance were analyzed in terms of bubble hydrodynamic and mass transfer parameters. Bubble column with 3 different dimensions and 7 gas diffusers (single / multiple orifice and rigid / flexible orifice) were applied. High speed camera and image analysis program were used for analyzing the bubble hydrodynamic parameters. The local liquid-side mass transfer coefficient ($k_L$) was estimated from the volumetric mass transfer coefficient ($k_La$) and the interfacial area (a), which was deduced from the bubble diameter ($D_B$) and the terminal bubble rising velocity ($U_B$). The result showed that the values of kLa and a increased with the superficial gas velocity (Vg) and the size of bubble column. Influences of gas diffuser physical property (orifice size, thickness and orifice number) can be proven on the generated bubble size and the mass transfer performance in bubble column. Concerning the variation of $k_L$ coefficients with bubble size, 3 zones (Zone A, B and C) can be observed. For Zone A and Zone C, a good agreement between the experimental and the predicted $K_L$ coefficients was obtained (average difference of ${\pm}15%$), whereas the inaccuracy result (of ${\pm}40%$) was found in Zone B. To enhance the high $k_La$ coefficient and absorption efficiency in bubble column, it was unnecessary to generate numerous fine bubbles at high superficial gas velocity since it causes high power consumption with the great decrease of $k_L$ coefficients.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.81-87
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• 2015

For Underwater vehicles, Unwanted roll excursions are inevitable as they are caused by induced propeller torque, disturbances, and banking motion during turns. To estimate the manoeuvring performance of underwater vehicle, it is necessary to obtain the roll coefficient of body. This paper was covered estimation of roll coefficient of underwater vehicle using STAR-CCM+, commercial CFD(Computational Fluid Dynamics) code. The RANS equations for incompressible fluid flows was solved numerically by using a finite volume method. An MRF(Moving Reference Frame) Method was Also adopted for rotations of body. For the validation, the flow around a DARPA SUBOFF bare hull model was simulated and good agreement with experiments was obtained. And Pure roll coefficients were calculated and campared with the experimental data which were presented by Seoul National University. Finally, an underwater vehicle model with propeller was simulated and analyzed for estimation of roll coefficient variation caused by induced propeller torque.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.2
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• pp.121-126
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• 1996

The hydrodynamic coefficients estimation (HCE) is important to design the autopilot and to predict the maneuverability of an underwater vehicle. In this paper, a system identification is proposed for an HCE of an underwater vehicle. First, we attempt to design the HCE algorithm which is insensitive to initial conditions and has good convergence, and which enables the estimation of the coefficents by using measured displacements only. Second, the sensor and measurement system which gauges the data from the full scale trials is constructed and the data smoothing algorithm is also designed to filter the noise due to irregular fluid flow without changing the data characteristics itself. Lastly the hydrodynamic coefficients are estimated by applying the measured data of full scale trials to the developed algorithm, and the estimated coefficients are verified by full scale trials.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.57-59
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• 2002

The dissolution process of NAPLs is significantly important in predicting the transport and/or fate of the contaminants and designing remedial systems. In this research, experimental observations on dissolution of TCE pool under various hydrodynamic conditions are done using an aquifer model. Hydrodynamic parameters such as linear pore velocity and dispersion coefficient are estimated from the results of preliminary tracer tests using bromide as conservative tracer before doing the TCE dissolution experiments. It is found that hydrodynamic parameters are distinctly affected by the clay lens imbeded in the aquifer model. Nonequilibrium and transient dissolution rates are observed from the results of TCE dissolution experiments.

• Journal of the Institute of Convergence Signal Processing
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• v.24 no.2
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• pp.97-102
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• 2023

Numerical simulations have been performed to investigate the hydrodynamic characteristics of the rudder since they play an important role in naval architecture fields. Although some values such as hydrodynamics forces can be measured easily in the towing tanks, it is difficult to obtain the detailed information of the flow fields such as pressure distribution, velocity distribution, vortex generation from experiments. In the present study, the effects of hydrodynamic coefficients and Reynolds number acting on the rudder were studied by using Computational Fluid Dynamics(CFD). Ansys fluent, one of commercial CFD solvers, solves the Navier-Stokes equations and the k-epsilon turbulence model is selected for the viscous model to solve RANS equations. At first, drag coefficients and lift coefficient for different angle of attack are obtained by using a CFD commercial code for KCS rudder. Secondly, the 2-D lift coefficients and drag coefficients are compared with 3-D coefficients at the same conditions. Thirdly, the effects of Reynolds number on the hydrodynamic forces are investigated.

• Membrane Journal
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• v.12 no.2
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• pp.90-96
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• 2002

A novel methodology on the calculations of osmotic pressure and gradient diffusion coefficient has been provided ill the present study, by applying a succinct numerical analysis on the experimental results. Although both the osmotic pressure and the gradient diffusion coefficient represent a fundamental characteristic in related membrane filtrations such as microfiltration and ultrafiltration, neither theoretical analysis nor experiments can readily determine them. The osmotic pressure of colloidal suspension has been successfully determined from a relationship between the data of the time-dependent permeate flux, their numerical accumulations, and their numerical derivatives. It is obvious that the osmotic pressure is gradually increased, as the particle concentration increases. The thermodynamic coefficient was calculated from the numerical differentiation of the correlation equation of osmotic pressure, and the hydrodynamic coefficient was evaluated from the previously developed relation for an ordered system. Finally, the estimated gradient diffusion coefficient, which entirely depends on the particle concentration, was compared to the previous results obtained from the statistical mechanical simulations.