• Ocean Systems Engineering
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• v.12 no.2
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• pp.143-157
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• 2022

In this study, the nominal wake field of a semi-displacement type high-speed vessel was computed at full scale by using CFD (Computational Fluid Dynamics) and GEOSIM-based approaches. A scale effect investigation on nominal wake field of benchmark Athena vessel was performed with two models which have different model lengths. The members of the model family have the same Fr number but different Re numbers. The spatial components of nominal wake field have been analyzed by considering the axial, radial and tangential velocities for models at different scales. A linear feature has been found for radial and tangential components while a nonlinear change has been obtained for axial velocity. Taylor wake fraction formulation was also computed by using the axial wake velocities and an extrapolation technique was carried out to get the nonlinear fit of nominal wake fraction. This provides not only to observe the change of nominal wake fraction versus scale ratios but also to estimate accurately the wake fraction at full-scale. Extrapolated full-scale nominal wake fractions by GEOSIM-based approach were compared with the full-scale CFD result, and a very good agreement was achieved. It can be noted that the GEOSIM-based extrapolation method can be applied for estimation of the nominal wake fraction of semi-displacement type high-speed vessels.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.5 s.122
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• pp.456-463
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• 2007

It is important to improve the initial launch conditions of golf ball at impact between golf club and ball to get a long flight distance. The flight distance is greatly influenced by the initial launch conditions such as ball speed, launch angle and back spin rate. It is also important to analyze the mechanism of ball spin to improve the initial conditions of golf ball. Back spin rate is created by the contact time and force. Previous studies showed that the contact force is determined as the resultant force of the reaction forces normal and tangential to the club face at the contact point. The normal force causes the compression and restitution of ball, and the tangential force creates the spin. Especially, the tangential force is known to take either positive or negative values as the ball rolls and slides along the club face during impact. Although the positive and negative tangential forces are known to create and reduce the back spin rate, respectively, the mechanism of ball spin creation has not yet been discussed in detail in the literature. In this paper, the influence of the contact force between golf club and ball is investigated to analyze the mechanism of impact. For this purpose, the contact force and time at impact between golf club head and ball are computed using FEM and compared with previous results. In addition, we investigate the impact phenomenon between golf club head and ball by FEM and clarify the mechanism of ball spin creation accurately, particularly focusing on the effect of negative tangential force on ball spin rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1017-1022
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• 2007

It is important to improve the initial launch conditions of golf ball at impact between golf club and ball to get a long flight distance. The flight distance is greatly influenced by the initial launch conditions such as ball speed, launch angle and back spin rate. It is also important to analyze the mechanism of ball spin to improve the initial conditions of golf ball. Back spin rate is created by the contact time and force. Previous studies showed that the contact force is determined as the resultant force of the reaction forces normal and tangential to the club face at the contact point. The normal force causes the compression and restitution of ball, and the tangential force creates the spin. Especially, the tangential force is known to take either positive or negative values as the ball rolls and slides along the club face during impact. Although the positive and negative tangential forces are known to create and reduce the back spin rate, respectively, the mechanism of ball spin creation has not yet been discussed in detail in the literature. In this paper, the influence of the contact force between golf club and ball is investigated to analyze the mechanism of impact. For this purpose, the contact force and time at impact between golf club head and ball are computed using FEM and compared with previous results. In addition, we investigate the impact phenomenon between golf club head and ball by FEM and clarify the mechanism of ball spin creation accurately, particularly focusing on the effect of negative tangential force on ball spin rate.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.1
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• pp.84-90
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• 1996

A theoretical analysis is presented on the mechanics of diamond blade sawing. The normal and tangential components of cutting force are calculated. Experimental results are also presented, which show the effects of cutting variables such as cutting speed, feed speed, cutting area, and concentration of diamond blade on the cutting forces. The experimental results are found to be in good agreement with those predicted by the analytical calculation.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.334-340
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• 2002

This paper proposes a new anti-slip re-adhesion control system fur electric railway vehicle driven by inverter-fed induction motors. This paper introduces an instantaneous tangential farce coefficient estimator between driving wheel and rail, which is based on disturbance observer. The torque command of proposed system regulates to exceed this estimated tangential farce coefficient in order to avoid undesirable slip phenomenon of driving wheels. We have already proposed the anti-slip re-adhesion control system based on disturbance observer for simplified one wheel equivalent model successfully. This paper extend to this system to the actual bogie system, which has four driving wheels driven by two induction motors fed by one inverter. In order to apply anti-slip re-adhesion control to the actual bogie system a new anti-slip re-adhesion control based on both disturbance observer and speed sensor-less vector control of induction motor with quick response are combined. The experimental results and the numerical simulation results prove the validity of the proposed control system.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.177-186
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• 2006

Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensionaldirect numerical simulations (DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

• Journal of the Korean Society of Combustion
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• v.12 no.2
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• pp.10-19
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• 2007

Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensional direct numerical simulations(DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.787-792
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• 2000

Ultra-abrasives such as diamond and CBN have used to maintain accuracy and form deviation for superalloy etc. This study contains the dry cylindrical grinding of metals with Vitrified-bond CBN wheel. For various conditions of grinding speed, workpiece speed, grinding depth and feed speed of table, the grinding resistance, the surface roughness, and the material removal are measured and discussed. The results are as follows.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.11
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• pp.1088-1094
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• 2006

In this paper, an auto path generation and an active compliance grinding control using 3-axis farce sensor are presented. These control algorithms enable the grinding robot to follow unknown path of various workpiece shape pattern. The robot is able to go grinding along unknown paths by position controller managing tangential direction angle and cutting speed, with only information about the start position and the end position. Magnitude and direction of normal force are calculated using force data that go through low pass filter. Moreover, normal and tangential directions are separated for force control and velocity control, respectively.

• Journal of Electrochemical Science and Technology
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• v.5 no.3
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• pp.82-86
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• 2014

This work presents the variation of formic acid oxidation on Pt depending on hydrodynamic condition using a rotating disk electrode. As the rotating speed increases, the oxidation rate of formic acid decreases under voltammetric and chronoamperometric measurements. The coverages of poison formed from formic acid during the chronoamperomertric investigations decrease when the rotating speed increases. As the roughness factor of Pt electrode surface increases, on the other hand, the current density of formic acid oxidation increases. These observations are discussed in terms of the tangential flow along Pt electrode surfaces generated by the rotating disk electrode, which reduces a contact time between formic acid and a Pt site, thus the formic acid adsorption.