• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2393-2399
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• 2011

In the case where the bottom of railroad is penetrated by non-excavation construction method, the design is performed based on the assumption that there is no displacement and no change of stress However, measurement data showed that reduction of earth pressure and relaxation of stress take place by the displacement. In this study, we investigated the earth pressure on the structure under the railroad constructed by a non-excavation method and the stress relaxation region. The design based on earth pressure is non-economical because it is an over design. Relaxation of stress may lead to road base settlement and rail irregularly due to the reduced railroad supporting stiffness, to ballast crack in the case of concrete roadbed. The result showed that it is reasonable to set the stress on the structures as active earth pressure not as earth pressure at rest. Additionally, the study on the stress relaxation region identified the regions that should be supported in future construction by a non-excavation method.

• Geomechanics and Engineering
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• v.9 no.4
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• pp.513-530
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• 2015

Commonly, the base stability of sheeted excavation pits against seepage failure by heave is evaluated by using two-dimensional groundwater flow models and Terzaghi's failure criterion. The objective of the present study is to investigate the effect of three-dimensional groundwater flow on the heave for sheeted excavation pits with various dimensions. For this purpose, the steady-state groundwater flow analyses are performed by using the finite element program ABAQUS 6.12. It has been shown that, in homogeneous soils depending on the ratio of half of excavation width to embedment depth b/D, the ratio of safety factor obtained from 3D analyses to that obtained from 2D analyses $FS_{(3D)}/FS_{(2D)}$ can reach up to 1.56 and 1.34 for square and circular shaped excavations, respectively. As failure body, both an infinitesimal soil column adjacent to the wall (Baumgart & Davidenkoff's criterion) and a three-dimensional failure body with the width suggested by Terzaghi for two-dimensional cases are used. It has been shown that the ratio of $FS_{(Terzaghi)}/FS_{(Davidenkoff)}$ varies between 0.75 and 0.94 depending on the ratio of b/D. Additionally, the effects of model size, the shape of excavation pit and anisotropic permeability on the heave are studied. Finally, the problem is investigated for excavation pits in stratified soils, and important points are emphasized.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.2
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• pp.153-161
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• 2009

A domain/boundary decomposition method is applied for efficient analyses of thermo-elasto-viscoplastic damage and contact problems under the assumption of infinitesimal deformation. For the decomposition of a whole domain and contact boundaries, all the equality constraints on the interface and contact interfaces are restated with simple penalty functional. Therefore, the non-linearity of the problem is localized within finite element matrices in a few subdomains and on contact interfaces. By setting up suitable solution algorithms, the computational efficiency can be improved considerably. The general tendency of the computational efficiency is illustrated with some numerical experiments.

• Structural Engineering and Mechanics
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• v.24 no.5
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• pp.621-639
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• 2006

Stability of a cylindrical shell subject to a uniform axial compression, which is a power function of time, is examined within the framework of small strain elasto-plasticity. The material of the shell is incompressible and the effect of the elastic unloading is considered. Initially, employing the infinitesimal elastic-plastic deformation theory, the fundamental relations and Donnell type stability equations for a cylindrical shell have been obtained. Then, employing Galerkin's method, those equations have been reduced to a time dependent differential equation with variable coefficient. Finally, for two initial conditions applying a Ritz type variational method, the critical static and dynamic axial loads, the corresponding wave numbers and dynamic factor have been found. Using those results, the effects of the variations of loading parameters and the variations of power of time in the axial load expression as well as the variations of the radius to thickness ratio on the critical parameters of the shells for two initial conditions are also elucidated. Comparing results with those in the literature validates the present analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.4
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• pp.304-311
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• 2001

An experimental study on the countercurrent two-phase flow in narrow rectangular channels has been performed. The void fraction and the pressure gradient were investigated using air and water in 760 mm long, 100 mm wide. vertical test sections with 2, 3 and 5 mm channel gaps. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.08 and 0 to 2.5 m/s ranges. respectively. the experimental results were compared with the previous correlations, which were mainly for round tubes, and the qualitative trends were found to be in good agreements. However the quantitative discrepancies were hardly neglected. as the superficial gas velocities increased, the void fraction increased and the pressure gradient decreased, where the effects of the liquid superficial velocities were infinitesimal. as the gap width of the rectangular channel increased the void fraction and the 2-phase frictional pressure gradient approached those values for the round tubes. Equi-periphery diameter, rather than the hydraulic diameter, seemed to be more effective in the analysis of two-phase flow behavior.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.79-82
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• 1997

The current from the feed motor of a machine tool contains substantial information about the machining state. There have been many researches that investigated the current as a measure for the cutting forces. However it has not been reported that indirect measurement of the cutting forces from the current of the feed motor at rest is possible. The cutting force normal to the machined surface influences the machined surface of the workpiece, which makes it necessary to estimate this force to control the roughness of the machined surface. But the unpredictable behavior of the current prevents applying the current to prediction of the cutting state. In this paper, empirical approach was conducted to resolve the problem. Also parametric adaptive and fuzzy logic control strategies are applied to the force regulation problem. As a result, the current is shown to be related to the accumulation of the infinitesimal rotation of the motor, and besides the unpredictable behavior of the current is shown to be caused by the relationship. Subsequently the relationship between the current and the cutting force is identified, and it is presented that control of machined surface using the current of the feed motor at rest is possible.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.67-68
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• 2006

This study suggests a precision flow control system that enables fluid injection of a few grams at a time in a few ms time duration. The fluid injection system suggested here consists of a high pressure fluid pump, a 3 way 3 position directional control valve, an injector and an orifice. The orifice is located between the directional control valve and the injector. By supplying current signal to the directional control valve, the prescribed small amount of fluid can be supplied to a plant through the injector. The control robustness of the suggested system against the disturbances like the pressure change in a plant and the viscosity variation of the injected fluid is secured easily by using an orifice with very small inside diameter and setting the supply pressure with comparatively high value. The control performances of the suggested system are verified by numerical simulations and experiments. The outcomes of this research could be applied to the common rail injection control of lubrication oil for large size marine diesel engines, and other industrial plants.

• Structural Engineering and Mechanics
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• v.75 no.1
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• pp.59-69
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• 2020

The purpose of this study is to develop practical tools for the mechanical design of cylindrical porous media subjected to a broad gap in a hygrothermal environment. The planar axisymmetrical and transient hygrothermoelastic field in a porous hollow cylinder that is exposed to a broad gap of temperature and dissolved moisture content and is free from mechanical constraint on all surfaces is investigated considering the nonlinear coupling between heat and binary moisture and the diffusive properties of both phases of moisture. The system of hygrothermal governing equations is derived for the cylindrical case and solved to illustrate the distributions of hygrothermal-field quantities and the effect of diffusive properties on the distributions. The distribution of the resulting stress is theoretically analyzed based on the fundamental equations for hygrothermoelasticity. The safety hazard because of the analysis disregarding the nonlinear coupling underestimating the stress is illustrated. By comparing the cylinder with an infinitesimal curvature with the straight strip, the significance to consider the existence of curvature, even if it is infinitesimally small, is demonstrated qualitatively and quantitatively. Moreover, by investigating the bending moment, the necessities to consider an actual finite curvature and to perform the transient analysis are illustrated.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.105-106
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• 2008

As a carrier of malaria and sneak of blood, mosquitoes are an unpleasant insect. However, there are several unknown natural secretes related with mosquitoes. Among them, we focused on the blood sucking process of a female mosquito. The main objective of this study is to understand the mosquito's blood sucking mechanism that can be used to resolve the problem encountered in the injection or transport of infinitesimal biological fluids in a micro-chip. At first, the velocity fields of blood-sucking flow in a proboscis were measured using a micro-particle image velocimetry (PIV) technique. The velocity signals of flow in the proboscis show periodic variation. This seems to be resulted from the beating of the pharyngeal pump which works as driving power. To analyze the pumping mechanism, the temporal variation of the pharyngeal pump was visualized using the synchrotron X-ray micro-imaging technique. The volume variation was estimated by the help of digital image processing techniques. Once the main mechanism of blood sucking process was found, a effective micro-pumping system with high efficiency would be developed in near future.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.111-117
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• 1997

The sudden-stop apparatus is made to measure the residual stress of the infinitesimal area at the turning work surface by using the X-ray stress apparatus. This study is trued to make the cutting work the instantaneous stopping state in the normal working state. The behaviour of work material near the tool is estimated. The estimation method is that the distribution of residual stress can be also measured. The object is to clarify and control the mechanism to leave the adequate stress of the finishing surface. It's beginning is due to observe the occurrence state of the residual stress at the cutting work. The result obtained by this study is as follows. The chips are not separated from the work materials at all the cutting experiments of built-up edges or the shearing areas etc. which can be precisely observed by using the sudden-stop apparatus. The strain of movable system which can be seen at the part of working layer means the size of strain. This experiment proves that the working strain should be lessened to make the size of strain control the residual stress happened at the cutting surface.