• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.8-18
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• 2002

Formulation of the far-field method for the prediction of time-mean hydrodynamic force and moment acting on a 3-D surface-piercing body in waves is reviewed. It is found that the inequality between the weight of the floating body and its buoyancy force permits the replacement of the fluid particles inside the control surface by the fluid particles outside the control surface. Under such circumstances, momentum exchanges across the control surface make the time-mean value of the time rate of the momentum of the fluid inside the control surface non-vanishing. It is a second-order quantity which is hard to calculate by the far-field method. The drift forces and moments on half-immersed ellipsoids are calculated by both the far-field method and the near-field method. The discrepancy between two numerical results is presented and discussed.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1650-1658
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• 2011

The quality control of compaction fills has been commonly performed via the field density measurement and plate load tests. However, the engineer frequently encounters difficulties in actually controling the quality due to the uncertainty in the field density measurement as well as the plate load tests. To overcome these difficulties, Park et al. (2009) proposed an alternative quality control method based on the measurement of the compressive wave velocities. In this study, the compressive wave velocities measured in the full-scale model test site were analyzed. Direct arrive seismic tests were performed after the completion of each trackbed layer. To identify a relationship between elastic wave velocities and degree of compaction, laboratory compaction tests were conducted.

• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.569-585
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• 2013

The use of the rigid polyurethane foam (RPF) to strengthen sandwich structures against blast terror has great interests from engineering experts in structural retrofitting. The aim of this study is to use the RPF to strengthen sandwich steel structure under blast load. The sandwich steel structure is assembled to study the RPF as structural retrofitting. The filed blast test is conducted. The finite element analysis (FEA) is also used to model the sandwich steel structure under shock wave. The sandwich steel structure performance is studied based on detonating different TNT explosive charges. There is a good agreement between the results obtained by both the field blast test and the numerical model. The RPF improves the sandwich steel structure performance under the blast wave propagation.

• Journal of electromagnetic engineering and science
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• v.18 no.3
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• pp.212-214
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• 2018

The finite-difference time-domain (FDTD) model was developed to analyze electromagnetic (EM) wave propagation in an inhomogeneous ionosphere. The EM analysis of ionosphere is complicated, owing to various propagation environments that are significantly influenced by plasma frequency, cyclotron frequency, and collision frequency. Based on the simple auxiliary differential equation (ADE) technique, we present an accurate FDTD algorithm suitable for the EM analysis of complex phenomena in the ionosphere under arbitrary-direction geomagnetic field. Numerical examples are used to validate our FDTD model in terms of the reflection coefficient of a single magnetized plasma slab. Based on the FDTD formulation developed here, we investigate EM wave propagation characteristics in the ionosphere using realistic ionospheric data for South Korea.

• Journal of computational fluids engineering
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• v.5 no.3
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• pp.23-31
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• 2000

The three-dimensional unsteady compressible Full Navier-Stokes equation solver with sliding multi-block method has been applied to analyze three dimensional characteristics of the viscous flow field and compression wave around the high speed train which is entering into a tunnel. The numerical scheme of AF + ADI was used to efficiently solve Navier-Stokes equations in the curvilinear coordinate system. The vortex formation owing to the viscous interaction around the train was found and the generation of compression wave due to the blockage effects was observed ahead of the train in the form of plane wave. The three dimensional characteristics of the flow field compared to the analytic results were discussed in detail. The variation of pressure of tunnel wall surface and velocity profile of the train are identified as the train enters into a tunnel. The changes in aerodynamic forces and streamlines of each specific sections are also discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.773-777
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• 1995

This thesis attempt to explore the shape of stress wave propagation of 3-dimensional stress field which is made in the process of time increment. A finite element code about 3-dimensional stress wave propagation is developed for investigating the changing shape of the fracture by the impact load. The Finite Element Code, which is the solution for the 3-dimensional stress wave analysis, based on Galerkins and Newmark- .betha. method at time increment step. The tensile stress and compressive stress become larger with the order of the middle, the upper and the opposite layers when the impact load is applied. In a while the shear stress become larger according to the order of the upper, the middle and the opposite layers when impact load applied.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1608-1613
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• 2003

In the semiconductor and the optical industry, a new transport system which can replace the conventional sliding system is required. These systems are driven by the magnetic field and the conveyer belt. The magnetic field damages semiconductor and contact force scratches the optical lens. The ultrasonic wave driven system can solve these problems. In this paper, the object transport system using the excitation of ultrasonic wave is proposed. The experiments for finding the optimal excitation frequency, finding phasedifference between two ultrasonic wave generators are performed. The relationship of transporting speed according to the change of flexural beam shape is verified. In addition, the system performance for practical use is evaluated.

• 전기의세계
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• v.22 no.3
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• pp.35-48
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• 1973

This paper deals with wave propagations in solid state electron plasmas from the view point of treating the plasma as a conducting fluid, and especially consideration is extended to the effect of diffusion on the permittivities and dispersion relations. The analysis is based on the conception of the self-consistent field approximation. It is shown for the cases of the specific physical configurations that the positions of the null elements in the permittivity tensors are not affected by the diffusion terms, and the diffusion effect appears only in the case of the space-charge wave. It is also shown that the magnitude of the real part of wave vector is in proportion to the 3/2nds power of the field in some regions.

• Journal of the Korean institute of surface engineering
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• v.27 no.6
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• pp.327-334
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• 1994

This work concerns a research for helicon wave plasma generators with applications to materials pro-cessing. For this end, helicon wave plasma source has been designed, constructed and tested. High density plasma was successfully produced and diagnosed with Langmuir probe. The measured maximum plasma de-nsity in this work was $10^{11}cm{-3}$ with 295 gauss of magnetic field and electron temperature was about 3.5eV. The uniformity of plasma densities in the radial direction was excellent with 160 gauss of magnetic field on the cross section which is 10cm apart from the edge of the exciting coil.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.141-144
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• 2004

Nowadays, there has been substantial interest in whether there is an association between electromagnetic field exposure and living environment. It is increased the demand that electromagnetic wave environment and its countermeasure. In the present study, we has applied the electromagnetic absorbent inorganic paint of 'I' corporations, and measured electromagnetic waves generated in new apartment before occupancy using the standard field electromagnetic wave generating device we developed. The measurement before occupancy was $100\~131V/m$, but the measurement after occupancy was $6.9\~8.0V/m$ less than 10V/m, the comprehensive electromagnetic wave limit allowed by TCO in Sweden. The implication is that domestic apartment are exposed to extremely poor electromagnetic wave environment. Nevertheless, there have been neither serious efforts to overcome this problem, nor its alternatives and related standards. Therefore, it is necessary to continue research of related fields to establish standards and plans to improve the situation.