• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1383-1392
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• 2009

A disadvantage in the design of a hypotrochoidal gear pump as in a gerotor pump is a lack of parts that can be adjusted to compensate for wear in the rotor set, and as a consequence, it causes a sharp reduction of volumetric efficiency. In this paper, an attempt has been made to reduce the wear rate between the rotors of a hypotrochoidal gear pump. Using the knowledge of shape design on the rotors, the contact stresses without hydrodynamic effect between the rotors' teeth are evaluated through the calculation of the Hertzian contact stress. Based on the above result and the sliding velocity between the rotors, a genetic algorithm (GA) is used as an optimization technique for minimizing the wear rate proportional factor (WRPF). The result shows that the wear rate or the WRPF can be reduced considerably, e.g. approximately 12.8% in this paper, throughout the optimization using GA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.681-687
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• 2001

Two-phase cross-flow exists in many shell-tube heat exchangers such as steam generators, condensers and reboilers. An understanding of flow-induced vibration excitation mechanism is necessary to avoid problems due to excessive tube vibration. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross-flow simulated by air-water mixtures. Normal(30$^{\circ}$) and rotated (60$^{\circ}$)triangular, and normal(90$^{\circ}$) and rotated (45$^{\circ}$) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1,000kg/$m^2$ㆍ s and void fraction from 0 to 100%. The effects of tube bundle geometry on vibration excitation mechanism such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed. A lower pitch-to-diameter results in a higher hydrodynamic mass. The effect of tube bundle configurations on damping and random turbulence excitation is minor. The effect of pitch-to-diameter on the fluidelastic instability, however, is significant.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.109-112
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• 1997

The Hydrodynamic performance of the trileaflet polymer prosthetic valves depends on the design of the leaflet and the physical properties of the leaflet membrane. In order to study the effect of leaflet membrane elasticity on the hemodynamic performance of trileaflet prosthetic valve, leaflet membranes are manufactured using two different polymers - Biospan and Tecoflex SG-93A. The hemodynamic performance parameters are measured under steady and physiological pulsatile flow, and compared with monoleaflet polymer valve(floating valve) and bileaflet mechanical valve(St. Jude Medical valve). Well designed trileaflet valve shows the lowest mean pressure drop among the tested valves. The trileaflet valves with Biospan membrane show lower pressure drop and back low comparing to those with Tecoflex membrane. More elastic membrane may provide wide opening area during systole and close membrane ree edge contact during diastole. Durability of trileaflet valves are also tested in vitro. Trileaflet valves with non-uniform membrane thickness ail within 17 days because of stress concentration. Trileaflet polymer valves with uniform membrane thickness perform well over 55 days without failure.

• Corrosion Science and Technology
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• v.16 no.1
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• pp.23-30
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• 2017

The inhibition effect of thioureido imidazoline inhibitor (TAI) for flow accelerated corrosion (FAC) at different locations for an X65 carbon steel elbow was studied by array electrode and computational fluid dynamics (CFD) simulations. The distribution of the inhibition efficiency measured by electrochemical impedance spectroscopy (EIS) is in good accordance with the distribution of the hydrodynamic parameters at the elbow. The inhibition efficiencies at the outer wall are higher than those at the inner wall meaning that the lower inhibition efficiency is associated with a higher flow velocity, shear stress, and turbulent kinetic energy at the inner wall of the elbow, as well as secondary flow at the elbow rather than the mass transport of inhibitor molecules. Compared to the static condition, the inhibition efficiency of TAI for FAC was relatively low. It is also due to a drastic turbulence flow and high wall shear stress during the FAC test, which prevents the adsorption of inhibitor and/or damages the adsorbed inhibitor film.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.488-503
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• 2012

The stern boat deployment system was investigated to evaluate the capability of launching and recovering rigid hull inflatable boat (RHIB) via the stern ramp. The main parameters to launch and recover RHIB were tested at the design stage. The combined hydrodynamic effect of the stern wake and the water jet flow made it difficult to maintain the maneuvering and sea-keeping ability of RHIB approaching to the stern ramp. The safe recovery course was proposed to maintain the directional control of RHIB and to reduce the combined hydrodynamic effect in the transom zone. To evaluate the feasibility of RHIB recovery, the stern sill depth was measured in various conditions and the ramp availability time was obtained. Also, the experimental percent time operability (PTO) test was performed by the number of successive launching and recovering operations.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.447-459
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• 2012

The present study numerically investigates the effect of the wavy leading edge on hydrodynamic characteristics for the flow of rectangular wings with the low aspect ratio of 1.5. Five different wave lengths at fixed wavy amplitude have been considered. Numerical simulations are performed at a wide range of the angle of attack ($0^{\circ}{\leq}{\alpha}{\leq}40^{\circ}$) at one Reynolds number of $10^6$. The wavy wings considered in this study did not experience enough lift drop to be defined as the stall, comparing with the smooth wing. However, in the pre-stall region, the wavy wings reveal the considerable loss of the lift, compared to the smooth wing. In the post-stall, the lift coefficients of the smooth wing and the wavy wings are not much different. The pressure coefficient, limiting streamlines and the iso-surface of the spanwise vorticity are also highlighted to examine the effect of the wave length on the flow structures.

• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.4
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• pp.10-20
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• 1984

When the hydrodynamic coefficients of the ship maneuvering equation are estimated by captive model test, it is difficult to take account of the scale effect between model and full scale ship. This scale effect problem can be overcome by processing the sea trial data with system identification. Extended Kalman filter is used as a system identification technique for the modification of the simulation equation as well as the estimation of hydrodynamic coefficients The phenomena of simultaneous drifting of linear coefficients occur. It is confirmed that two coefficients in each pair-$(Y_v',\;Y_r'-m'u'),\;(N_v',\;N_r')$-are simultaneously drifting and all 4 coefficients are drifting together. Particularly simultaneous drifting and 2 coefficients in each pair is more significant. It is also shown that the simultaneous drifting of 4 coefficients can be reduced by choosing the input data which have the random v'/r' curve and 4 coefficients are estimated within $2{\sim}4%$ error, which may be noise level. So, it is recommended to operate the rudder randomly in sea trial or model test for the application of system identification technique.

• Journal of the Korea Society for Simulation
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• v.21 no.1
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• pp.35-43
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• 2012

In this study, underwater behaviors of negative buoyant body and positive buoyant body, which are ejected from a platform, are compared through eject test and simulation. CFD(Computational Fluid Dynamics) method is used to calculate the hydrodynamic derivatives of negative buoyant body with varied hull. Hydrodynamic derivatives that cannot be calculated with CFD are used with the same values of base shape. The pitch angles of test data are much bigger than those of simulated data, and the reason is supposed to be the trailing air effect. A more accurate simulation is possible via modified force modeling which reflects this phenomenon. The underwater behaviors of positive buoyant body and negative buoyant body are somewhat different with each other at the same eject condition, but it may not be a problem in the view of operation.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1203-1212
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• 2004

The purpose of this study is to predict and understand the hydrodynamic forces and their nonlinear behaviors of fluid motion around the submerged plate oscillating near a free surface. To achieve this objective, we have developed a composite grid method for the solution of a radiation problem. The domain is divided into two different grids; one is a moving grid system and the other is a fixed grid system. The moving grid is employed for the body fitted coordinate system and moves with the body. This numerical method is applied to calculation of radiation forces generated by the submerged plate oscillating near a free surface. In order to investigate the characteristics of the radiation forces, the forced heaving tests have been performed with several amplitudes and different submergences near a free surface. These experimental results are compared with the numerical ones obtained by the present method and a linear potential theory. As a result, we can confirm the accuracy of the present method. Finally, the effect of nonlinear and viscous damping has been evaluated on the hydrodynamic forces acting on the submerged plate.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.184-198
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• 2020

Decisions of the design speed, MCR, and engine capacity have been empirically made by assuming the value termed the sea margin. Due to ambiguity regarding the effect of some factors on the sea margin, the value has been commonly decided based on experience. To evaluate the value from a new viewpoint, it is necessary to construct an approach to estimate the sea margin through an objective procedure based on a physical and mathematical model. In this paper, a framework to estimate the actual sea margin of an LNGC based on the maneuvering equations of motion is suggested by considering the hull, propeller, rudder, and given sea route under wind and waves. The fouling effect is additionally quantified as the increase of total resistance by considering the re-docking period. The operation data is reviewed to amend the increase of the total resistance considering the speed loss of a ship. Finally, the factor of how much the resistance increases due to fouling is newly obtained for the vessel. Based on the comparison of the estimated sea margin with the empirical range of the sea margin, the constructed framework is regarded as feasible.