• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.9
• /
• pp.731-737
• /
• 2014

A vortex chamber is a simple device that separates compressed gas into a high-temperature stream and a low-temperature stream. It is increasing in popularity as a next-generation heat exchanger, but the flow physics associated with it is not yet well understood. In the present study, both experimental and numerical analyses were performed to investigate the temperature separation phenomenon inside the vortex chamber. Static pressures and temperatures were measured using high-sensitivity pressure transducers and thermocouples, respectively. Computational fluid dynamics was applied to simulate 3D unsteady compressible flows. The simulation results showed that the temperature separation is strongly dependent on the diameter of the vortex chamber and the supply pressure at the inlet ports, where the latter is closely related to the viscous work. The previous concept of a pressure gradient wave may not be a reasoning for temperature separation phenomenon inside the vortex chamber.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.36 no.6
• /
• pp.474-482
• /
• 2016

A Kelvin foam plate - widely used in the energy and transport industries as a lightweight structural material - was examined to estimate its Young's modulus using ultrasound. An isotropic tetrakaidecahedron foam structure was designed in SolidWorks and printed using 3D printer with an ABS plastic material. The 3D printed foam structure was used to build a foam plate with a 14 mm thickness ($50mm{\times}100mm$ in size) for the ultrasonic test. The Kelvin foam plate, a significantly porous medium, was completely filled with paraffin wax to enable the ultrasound to penetrate through the porous medium. The acoustic wave velocity of the wax-filled Kelvin foam was measured using the time of flight (TOF) method. Furthermore, the elastic modulus of the Kelvin foam was estimated based on an elastic structural model developed in this study. The Young's modulus of the produced Kelvin foam was observed to be approximately 3.4% of the bulk value of the constituent material (ABS plastic). This finding is consistent with experimental and theoretical results reported by previous studies.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.30 no.4
• /
• pp.373-379
• /
• 2010

EMAT has been applied in various fields for flaw detection and material characterization because it has noncontact property in wave generation and a good mode selectivity. Unfortunately, however, EMAT shows low signal to noise ratio relative to commercial contact transducer because of low energy conversion efficiency. If the phase matching through the control of time delay between each coil consisting of the array EMAT is accomplished, it is expected that it will be a solution for the improvement of low signal to noise ratio. In this experiment, the phased array EMATs which consists of 3 or 4 meander coils and one big magnet were fabricated for surface and vertical shear wave generation. Effect of phased delay control on signal directivity and amplitude enhancement was verified. A slit with the depth of 0.5 mm and a side-drill hole of 0.5 mm diameter were clearly detected by fabricated phased array EMATs, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.25 no.6
• /
• pp.405-411
• /
• 2013

A sediment transport calculation considering cohesive force is proposed to deal with the transport phenomena of cohesive sediment. In the proposed calculation, each sand particle is assumed to be surrounded by a thin layer of mud. The critical Shields parameter and bed-load sediment transport rate are modified to include the cohesive force acting on the sand particle. The proposed calculation is incorporated into a two-way coupled fluid-structure-sediment interaction model, and applied to wave-induced topographic change of artificial shallows. Numerical results show that an increase in the content ratio of the mud, cohesive resistance force per unit surface area and water content cause increases in the critical Shields parameter and decreases in the bed-load sediment transport rate, reducing the topographic change of the shallow without changing its trend. This suggests that mixing mud in the pores of the sand particles can reduce the topographic change of shallows.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.31 no.5
• /
• pp.609-621
• /
• 1998

Sand ridges in the South Sea of Korea have been investigated to reveal the surface morphology and vortical variation in sediment physical property. Both field and laboratory methods such as high resolution subbottom profiling, side scan sonar, and physical property and sediment textural study on cored sediments were employed. Asymmetric sand waves are found on the ridge, No prominent difference in the sediment was recorded throughout the ridge area. Sediment sorting is generally poor due to interbedded mud. Average compressional wave velocity is 1753 m/sec for the sand dominated core section, Most of cores show two prominent facies: facies A and B. Facies A is defined as modern mud sediment and B is dominated by relict sand. Facies B is characterized by gravel, sand, and shell fragment, It is suggested that the facies B was developed in transgressive environment by tide and sporadic high energy events.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.1 s.47
• /
• pp.33-39
• /
• 2006

Parameters including the seismic sources and the elastic wave propagation characteristics were analysed using the observed ground motions from 3 Kyoungju region earthquakes. The Levenberg-Marquardt algorithm was applied to invert all the variables non-linearly and simultaneously with S wave energy In frequency domain. Average stress drop of 3 events and local attenuation parameter ${\kappa}$ were estimated to about 48-bar and 0.0312 respectively. Regional attenuation parameter, Qo and ${\eta}$, were also estimated to be about 417 and 0.83. ${\kappa}$ values are much higher than that of EUS, even though smaller than that of WUS. All these values resultant from this study show that there are differences in some parameters of other studios due to differences in the governing equation. of acceleration motions

• Journal of the Korean Chemical Society
• /
• v.37 no.1
• /
• pp.83-91
• /
• 1993

The eletrochemical behavior of light lanthanide complexes has been investigated by several electrochemical techniques in alkaline solutions. The composition of the complexes was determined by spectrophotometric method to be 1 : 1 and reduction mechanism was two steps 1 electron transfer reaction. The half wave potential of first peak depended on pH and cathodic current showed remarkably adsorptive properties. The results of DC and CV investigation demonstrated the quise-reversible nature of the electron transfer. The anion radical formed after first one electron reduction process, dimerizes to form dimer. The apparent irreversible behavior of the second wave is a result of the existence of a fast protonation following the second electron transfer. An exhaustive electrolysis was carried out at controlled potential of -1.80 V, deep blue color of the solution became progressively weaker, and then the solution became colorless solution. The final product of an exhaustive electrolysis is electro-inactive. The appearance of four steps may be explained by the fact the reduction of Ln-OCP elucidated ECEC mechanism.

• Journal of the Korean GEO-environmental Society
• /
• v.10 no.1
• /
• pp.35-41
• /
• 2009

It is necessary to consider the site amplification for estimating SSI (soil structure interaction) and seismic source with more confidence. The horizontal to vertical (H/V) ratio technique in spectral domain is one of several techniques to estimate empirical site transfer function. The technique, originally proposed by Nakamura (1989), is applied to analyze the surface waves in the microtremor records. However, the application of this technique has been widened to the shear wave energy of strong motions for estimating site amplification. The purpose of this paper is to estimate spectral ratio using observed data at the seismic stations distributed within Southern Korean Peninsula from the Fukuoka earthquake including 11 aftershocks. The results show that each station has the its own characteristics of the specific resonance, high-band, and low-band frequency. The characteristics of the resonance frequency is more important because the quality of the seismic records are dependent on the resonance frequency. The result can be used for the study of site classification and removal of the site amplification effects from observed records can give us more reliable seismic source parameters.

• Structural Engineering and Mechanics
• /
• v.66 no.3
• /
• pp.411-421
• /
• 2018

Although a rubber isolation cushion can reduce the dynamic response of a structure itself, it has little influence on the height of a sloshing wave and even may induce magnification action. Vertical baffles are set into a base-isolated Concrete Rectangular Liquid Storage Structure (CRLSS), and baffles are opened as holes to increase the energy dissipation of the damping. Problems of liquid nonlinear motion caused by baffles are described using the Navier-Stokes equation, and the space model of CRLSS is established considering the Fluid-Solid Interaction (FSI) based on the Finite Element Method (FEM). The dynamic response of an isolated CRLSS with various baffles under an earthquake is analyzed, and the results are compared. The results show that when the baffle number is certain, the greater the number of holes in baffles, the worse the damping effects; when a single baffle with holes is set in juxtaposition and double baffles with holes are formed, although some of the dynamic response will slightly increase, the wallboard strain and the height of the sloshing wave evidently decrease. A configuration with fewer holes in the baffles and a greater number of baffles is more helpful to prevent the occurrence of two failure modes: wallboard leakage and excessive sloshing height.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.12 no.2
• /
• pp.59-66
• /
• 1975

Recently, as the dimensions of energy carriers increase, especially in draft, a reliable prediction of the ship motions at finite depths of water becomes necessary. The purpose of this paper is to probe the effect of finite water depth on the hydrodynamic forces and ship motions, particularly heave and pitch, in longitudinal regular head waves, by comparing the experimental value of Freakes and Keay with the author's theoretical value obtained by applying the modified strip theory to the Mariner class ship. It is confirmed that generally the hydrodynamic coefficients in the equations of motion increase with decreasing water depth, and the wave exciting forces and moments decrease with decreasing water depth. Amplitudes of heave and pitch in longitudinal regular head waves decrease as the water depth in the range where the length of the incident wave is comparatively long. The effects of Froude Number on the hydrodynamic coefficients increase with decreasing water depth and is more noticeable in the case of heave than pitch. In heave, generally the discrepancy between the experimental value and the theoretical value is relatively small in the case of $F_n=O$, but it is very large in the case of $F_n=0.2$. It is considered that the trend stems from the ignorance of the three dimensional effect and the other effects due to shallowness of water on the hydrodynamic coefficients in the theoretical calculation. An extension of methods for calculating the two dimensional hydrodynamic forces to included the effect of forward speed should be recommended. It is required that more experimental works in finite water depths will be carried out for correlation studies between the theoretical calculation, according tp modified strip theory, and model experiments.