• Journal of the Society of Naval Architects of Korea
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• v.36 no.1
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• pp.47-52
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• 1999

The influence of propeller revolution on measurement of fluctuating pressure is almost minimized in the KRISO cavitation tunnel and the measurement accuracy of fluctuating pressure acting on a flat plate due to a cavitating propeller is improved. The measurement data for Sydney Excess propeller is compared with the measurement results of other research institutes loading to the conclusion that KRISO data is so stable and reasonable. The fluctuating pressure data measured on a model ship and the prototype ship is compared with the data measured on the flat plate. The solid boundary factor, derived from a calculation based on a lifting surface theory, is applied to predict full scale pressure level from the experimental data on the flat plate, showing quite reasonable agreement with full scale data.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.33-42
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• 1998

In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1445-1451
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• 1994

To calculate the wave pressure acting on coastal structures under the design wave condition, it is often necessary to numerically reproduce the big standing wave profiles close to wave breaking condition. For this, the governing equation and all nonlinear terms occurring in boundary conditions should be effectively considered in the numerical wave profile. In particular, the velocity square term in the free surface boundary condition is very important. A boundary element method is applied here to calculate the standing wave profile with the velocity square term fully treated by Newton iterative method. In order to check the validity of the method, the numerical wave profiles are compared to ones calculated by the perturbation method, the Fourier approximation method and the hydraulic experiment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.997-1001
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• 2000

In this paper, the case studies of reducing rotational errors is theoretically done for a grinding spindle with an active magnetic bearing system. The rotational errors acting on the magnetic bearing spindle are due to mass unbalance of rotor, runout, grinding excitation and unmodeled nonlinear dynamics of electromagnets. For the most case, the electrical runout of sensor target is big even in well finished surface, this runout can cause a rotation error amplified by feedback control system. The adaptiveed forward method based on LMS algorithm is discussed to compensate this kind of runout effects, and investigated its effectiveness by numerical simulation and experimental analysis. The electrical runout form the rear sensor target of grind spindle is about 70$\mu\textrm{m}$ with harmonic frequencies. The rotor orbit size in rear bearing is reduced about to 5$\mu\textrm{m}$ due to 1X and 2X rejection by feedforward control.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1487-1494
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• 1990

In this paper the dynamic characteristics of self acting air lubricated slider bearing of hard disk/head system are investigated. The dynamic equations of magnetic head mechanism considering both parallel and pitch motion and the time dependent modified Reynolds equation are analyzed and the dynamic pressure distribution of air film is numerically calculated in frequency domain by small perturbation method and finite difference scheme with variable grid. The dynamic response of the slider spacing is obtained accordingly as the moving recording surface vibrates in parallel mode.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.69-75
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• 2016

Polydimethylsiloxane (PDMS) is used as a scaffold for cell culture. Because both the stress and strain acting on the substrate and the hemodynamic environment are important for studying mechano-transduction of cellular function, the traction force of the surface of a substrate has been measured using fluorescence images of particle distribution. In this study, deformation of the cross-sectional plane of a PDMS block was measured by correlating particle image distributions to validate the particle image strain measurement technique. Deformation was induced by a cone indentor and a shearing parallel plate. Measured deformations from particle image distributions were in agreement with the results of a computational structure analysis using the finite-element method. This study demonstrates that the particle image correlation method facilitates measurement of deformation of a polymer scaffold in the cross-sectional plane.

• Journal of KSNVE
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• v.8 no.5
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• pp.974-980
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• 1998

The analysis of dynamic responses are carried out on several orthotropic systems due to transient line source. These include infinite and semi-infinite spaces. The media possess orthotropic or higher symmetry. The lode is in the form of a normal stress acting with parallel to symmetry axis on the plane of symmetry within the materials. The results are first derived for responses of infinite media due to a harmonic line source. Subsequently the results for semi-infinite are derived by using superposition of the solution in the infinite medium together with a scattered solution from the boundaries. The sum of both solutions has to satisfy stress free boundary conditions thereby leading to the complete solutions. Explicit splutions for the displacements due to transient line loads are then obtaind by using Cargniard-DeHoop contour.

• Ocean Systems Engineering
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• v.8 no.2
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• pp.223-246
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• 2018

In this paper the results of CFD simulations, that were carried out to study the impact pressures acting on a symmetric wedge during water entry under the influence of gravity, are presented. The simulations were done using a solver implementing finite volume discretization and using the VOF scheme to keep track of the free surface during water entry. The parameters such as pressure on impact, displacement, velocity, acceleration and net hydrodynamic forces, etc., which govern the water entry process are monitored during the initial stage of water entry. In addition, the results of the complete water entry process of wedges covering the initial stage where the impact pressure reaches its maximum as well as the late stage that covers the rebound process of the buoyant wedge are presented. The study was conducted for a few touchdown velocities to understand its influence on the water entry phenomenon. The simulation results are compared with the experimental measurements available in the literature with good accuracy. The various computational parameters (e.g., mesh size, time step, solver, etc.) that are necessary for accurate prediction of impact pressures, as well as the entry-exit trajectory, are discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.5
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• pp.424-432
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• 2002

Numerical analysis has been conducted to characterize deposition rates of aerosol particles onto a heated, rotating disk with electrostatic effect under the laminar flow field. The particle transport mechanisms considered were convection, Brownian diffusion, gravitational settling, thermophoresis and electrophoresis. The aerosol particles were assumed to have a Boltzmann charge distribution. The electric potential distribution needed to calculate local electric fields around the disk was calculated from the Laplace equation. The Coulomb, the image, the dielectrophoretic and the dipole-dipole forces acting on a charged particle near the conducting rotating disk were included in the analysis. The averaged particle deposition vetocities and their radial distributions on the upper surface of the disk were calculated from the particle concentration equation in a Eulerian frame of reference, along with a rotation speed of 0∼1,000rpm, a temperature difference of 0∼5K and a charged disk voltage of 0∼1000V.Finally, an approximate deposition velocity model for the rotating disk was suggested. The present numerical results showed relatively good agreement with the results of the present approximate model and the available experimental data.

• Journal of Ocean Engineering and Technology
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• v.29 no.4
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• pp.309-316
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• 2015

Lifting lugs are frequently used in shipyards to transport and turn over the blocks of ships and offshore structures. With the development of shipbuilding technology, blocks have increased in size, and block management technology has assumed a more important role in shipbuilding to enhance the productivity. For the sake of economics, as well as the safe design of a lug structure, a more rational design procedure based on a rigorous structural analysis is needed. This study investigated the strength characteristics of T-type lugs, considering the influence of blocks on which lugs are attached, by varying the in-plane and out-of-plane load direction. In this paper, the ultimate strength is also addressed for cases that include or do not include blocks in the strength analysis. In the present results, when there was a load acting in the normal direction to the block surface, the strength characteristics became poor, and the ultimate strength decreased. This paper ends by describing the need for further study to develop a more rational design for a lug structure.