• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.04a
• /
• pp.208-213
• /
• 2002

Near field ground motions contain distinct, large amplitude pulses in both velocity and displacement. This paper presents an investigation on the characteristics of near filed earthquakes and their effects on seismic demands. For this purpose 20 sets of near field ground motion and 20 sets of far filed ground motion are compared with respect to Linear Elastic Response Spectrum(LERS), Response Modification Factor(R), Inelastic Response Spectrum(IRS), and performance point of Capacity Spectum Method(CSM).

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.05a
• /
• pp.461-464
• /
• 2003

A new control volume finite element method is proposed for three dimensional analysis of polymer flow. Tetrahedral finite element is employed and co-located interpolation procedure for pressure and velocity is implemented. Inclusion of pressure gradient term in the velocity shape functions prevents the checkerboard pressure field from being developed. Vectorial nature of pressure gradient is considered in the velocity shape function so that velocity profile in the limit of very small Reynolds number becomes physically meaningful. The proposed method was verified through three dimensional simulation of pipe flow problem for Newtonian and power-law fluid. Calculated pressure and velocity field showed an excellent agreement with analytic solutions for pressure and velocity. Driven-cavity problem, which is reported to yield checkerboard pressure filed when conventional finite element method is applied, could be solved without yielding checkerboard pressure field when the proposed control volume finite element method was applied. The proposed method could be successfully applied to the three dimensional mold filling problem.

• Computers and Concrete
• /
• v.20 no.6
• /
• pp.711-718
• /
• 2017

Nanotechnology is a new filed in concrete structures which can improve the mechanical properties of them in confronting to impact and blast. However, in this paper, a mathematical model is introduced for the concrete models subjected to impact load for wave propagation analysis. The structure is simulated by the sinusoidal shear deformation theory (SSDT) and the governing equations of the concrete model are derived by energy method and Hamilton's principle. The silicon dioxide ($SiO_2$) nanoparticles are used as reinforcement for the concrete model where the characteristics of the equivalent composite are determined using Mori-Tanaka approach. An exact solution is applied for obtaining the maximum velocity of the model. In order to validate the theoretical results, three square models with different impact point and Geophone situations are tested experimentally. The effect of different parameters such as $SiO_2$ nanoparticles volume percent, situation of the impact, length, width and thickness of the model as well as velocity, diameter and height of impactor are shown on the maximum velocity of the model. Results indicate that the theoretical and experimental dates are in a close agreement with each other. In addition, using from $SiO_2$ nanoparticles leads to increase in the stiffness and consequently maximum velocity of the model.

• 한국가시화정보학회:학술대회논문집
• /
• 2003.11a
• /
• pp.99-102
• /
• 2003

PIV(Particle Image Velocimetry)was used to visualize the interaction of reed valve of the reciprocating compressor. The valve is the key part which governs the efficiency, noise and reliability of the compressor, so the development of analytical model about valve performance is necessary. As the valve reed is opened and closed by pressure pulsation, the flow characteristic of the refrigerant passing the valve is very important. In the present study, a circular disk with inclination is assumed to be the valve reed of a reciprocating compressor, The mean velocity shows the vortical characteristic of this flow. It is found that the back flow is affected by the height of reed valve of reciprocating compressor.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.442-451
• /
• 2008

The evaluation of field degree of consolidation on soft clays has been an important problem in geotechnical areas. Monitoring either settlements or pore water pressures has been widely applied in the filed, but occasionally they have some problems. This study addresses the suggestion and application of another method for evaluating the degree of consolidation using shear wave velocities. A research site where soft clay layers were consolidated by surcharging loads was chosen. Laboratory tests were performed to determine the relation between shear wave velocity and effective stress. Field seismic tests were conducted several times during the consolidation of the clay layers. The tests results show that the shear wave velocity increased significantly as clays consolidated. The shear wave velocities at each field stress states were derived from the laboratory results and the degree of consolidation was evaluated by comparing the shear wave velocities obtained by laboratory and field seismic methods. In most stress states, the degree of consolidation evaluated using the shear wave velocity matched well with that obtained from field settlement record, showing the potential of applying the method using shear waves in the evaluation of field degree of consolidation on soft clay deposits.

• Journal of Environmental Science International
• /
• v.20 no.1
• /
• pp.107-118
• /
• 2011

While the assessment of mean flow field is very important to characterize the hydrodynamic aspect of the flow regime in river, the conventional methodologies have required very time-consuming efforts and cost to obtain the mean flow field. The paper provides an efficient technique to quickly assess mean flow field by developing and applying spatial averaging method utilizing repeatedly surveyed acoustic Doppler current profiler(ADCP)'s cross-sectional measurements. ADCP has been widely used in measuring the detailed velocity and discharge in the last two decades. In order to validate the proposed spatial averaging method, the averaged velocity filed using the spatial averaging was compared with the bench-mark data computed by the time-averaging of the consistent fix-point ADCP measurement, which has been known as a valid but a bit inefficient way to obtain mean velocity field. The comparison showed a good agreement between two methods, which indicates that the spatial averaging method is able to be used as a surrogate way to assess the mean flow field. Bed shear stress distribution, which is a derived hydrodynamic quantity from the mean velocity field, was additionally computed by using both spatial and time-averaging methods, and they were compared each other so as to validate the spatial averaging method. This comparison also gave a good agreement. Therefore, such comparisons proved the validity of the spatial averaging to quickly assess mean flow field. The mean velocity field and its derived riverine quantities can be actively used for characterizing the flow dynamics as well as potentially applicable for validating numerical simulations.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.58.2-58.2
• /
• 2015

We investigate the decaying incompressible MHD turbulence by including the effect of the expansion and contraction of background medium. In such an environment, incompressible MHD turbulence has two kinds of time scale. One is the eddy turn-over time (teddy), the other is the expansion/contraction time (texp-cntr). The turbulence is expected to behave differently according to the relationship between the two time scales. For instance, for teddy < texp-cntr, the turbulence would be decay more or less as in a static medium. On the other hand, for teddy > texp-cntr, the effects of expansion and contraction would be dominant. We examine the properties of turbulence in these two regime cases. Based on it, we derive a scaling for the time evolution of flow velocity and magnetic field. (i) In the decay effect dominant case, the velocity and magnetic field scale as $\sqrt{{\rho}v}{\sim}a^{-3}$, $b{\sim}a^{-2.5}$(expanding media) and $\sqrt{{\rho}v}{\sim}a^{-2}$, $b{\sim}a^{-1.5}$(contracting media). The total energy and residual spectra follow the $E^T_k{\sim}k^{-5/3}$, $E^R_k{\sim}k^{-7.3}$ in the inertial range. (ii) In the expanding and contracting dominant case, the velocity and magnetic field scale as $\sqrt{{\rho}v}{\sim}a^{-2.5}$, $b{\sim}a^{-2}$ (expanding/contracting media). The Kinetic and magnetic energy spectra follow the $E^K_k{\sim}a^{-5}$, $E^M_k{\sim}a^{-4}$. We have confirmed that scaling of velocity and magnetic filed is almost the same from the analytic estimates and computational models

• 한국초전도학회:학술대회논문집
• /
• v.9
• /
• pp.369-372
• /
• 1999

Using Ag sheathed multi filamentary Bi-2223 tape, stability against heat pulse has been investigated. The measured normal zone propagation(NZP) velocity of the tape was found to be faster due to increase of operating current and magnetic field, and agree well with calculated data from one dimensional heat balance equation. Minimum quench energy(MQE) was found to be larger than 17 J at 30 K zero magnetic filed at operating current of 96.5 with respect to I$_c$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.11 no.4
• /
• pp.160-165
• /
• 2001

The effects of various metals on Field Aided Lateral Crystallization (FALC) behaviors of amorphous silicon (a-Si) were investigated. Under an influence of electric field, metals such s Cu, Ni and Co were found to fasten the lateral crystallization toward a metal-free region, exhibiting a typical FALC behavior while the lateral crystallization of a-Si was not obvious for Pd. However, Au, Al and Cr did not induce the lateral crystallization of a-Si in metal-free region. Such phenomenological differences in various metals were studied in terms of dominant diffusing species (DDS) in the reaction between metal and Si. It was judged that the applied electric field enhanced the crystallization velocity by accelerating the diffusion of metal atoms since the occurrence of lateral crystallization would be strongly dependent on the diffusion of metal atoms than that of Si atoms. Therefore, it was concluded that he only metal-dominant diffusing species in the reaction between metal and Si results in the crystallization of a-Si in metal-free region.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.5
• /
• pp.67-75
• /
• 2013

This study is flow analysis on the smoke collector in smoking room. The smoke collector for improving impure air at smoking area is analyzed and the inner flow filed in smoke collector is confirmed on the study result. The velocity with pressure distribution according to suction flow rate at filter entrance is also compared. Pressure characteristic and pressure resistance coefficient are analyzed according to flow analysis result for each other filter. The pressure drop of about 15 Pa occurs at the normal driving mode to strainer inlet from HEPA filter outlet. On the other hand, the pressure drop about 44% increases at turbo mode.