• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1700-1709
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• 1993

The stepped specimen which is subjected to step loading is modeled to study the initiation and growth of adiabatic shear band using explicit time integration finite element method. Three different clearance sizes are tested. The material model for the stepped specimen includes effects of strain hardening, strain rate hardening and thermal softening. It is found that the material inside the fully grown adiabatic shear band experiences three phase of deformation, (1) homogeneous deformation phase, (2) initiation/incubation phase, and (3) fast growth phase. The second phase of deformation is initiated after sudden shear stress drop which occurs at the same time regardless of the clearance size. The incubation time prior to fast growth phase increases, as the clearance size of the stepped specimen increases. Whereas, after incubation period, the growth rate of the adiabatic shear band decreases, as the clearance size decreases. It is also found that two adiabatic shear band may develop instead of one for the smaller clearance size.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.19-27
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• 2018

It follows from the basic principles of mechanics of deformable solids relating to the strength, stability and propagation of elastic waves that the Earth's inner core cannot exist in the form of a spherical structure in the assumed thermobaric conditions and calculation values of physico-mechanical parameters. Pressure level reaches a value that is significantly greater than the theoretical limit of medium strength in the model approximations at the surface of the sphere of the inner core. On the other hand, equilibrium state of the sphere is unstable on the geometric forming at much lower loads under the influence of the "dead" surface loads. In case of the action of "follower" loads, the assumed pressure value on the surface of the sphere is comparable with the value of the critical load of "internal" instability. In these cases, due to the instability of the equilibrium state, propagation of homogeneous deformations becomes uneven in the sphere. Moreover, the elastic waves with actual velocity cannot propagate in such conditions in solid medium. Violation of these fundamental conditions of mechanics required in determining the physical and mechanical properties of the medium should be taken into account in the integrated interpretations of seismic and laboratory (experimental) data. In this case, application of the linear theory of elasticity and elastic waves does not ensure the reliability of results on the structure and composition of the Earth's core despite compliance with the required integral conditions on the mass, moment of inertia and natural oscillations of the Earth.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.3
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• pp.405-412
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• 2017

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the platform. Qualitative analysis was conducted for the time history of vapor volume fraction distributions. Uncorking pressure around the projectile and platform was analyzed to predict impact force acting on the surfaces. The results of 6DOF analysis presented similar tendency with the surficial pressure distributions.

• Journal of ILASS-Korea
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• v.21 no.1
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• pp.29-36
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• 2016

The effect of high ambient temperature and pressure conditions on the combustion performance of n-butanol, n-heptane and its mixing fuel (BH 20) were studied in this work. To reveal this, the closed homogeneous reactor model applied and 1000-1200 K of the initial temperature, 20-30 atm of initial pressure and 1.0 of equivalence ratio were set to numerical analysis. It was found that the results of combustion temperature was increased and the ignition delay was decreased when the ambient conditions were elevated since the combustion reactivity increased at the high ambient conditions. On the contrary, under the low combustion temperature condition, the combustion pressure was more influenced by the ambient temperature in the same ambient conditions. In addition, the total mass and the mass density of tested fuels were influenced by the ambient pressure and temperature. Also, soot generation of mixing fuel was decreased than n-heptane fuel due to the oxygen content of n-butanol fuel.

• Smart Media Journal
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• v.1 no.3
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• pp.22-28
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• 2012

As the smart media becomes more popular, the demand for high-quality 3D images and depth maps is increasing. However, performance of the current technologies to acquire depth maps is not sufficient. The depth maps from stereo matching methods have low accuracy in homogeneous regions. The depth maps from depth cameras are noisy and have low-resolution due to technical limitations. In this paper, we introduce the state-of-the-art algorithms for depth map enhancement and up-sampling from conventional methods using only depth maps to the latest algorithms referring to both depth maps and their corresponding color images. We also present depth map enhancement algorithms for hybrid camera systems in detail.

• Journal of the Korean Society of Combustion
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• v.21 no.1
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• pp.1-7
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• 2016

This study was performed to provide the basic information of the combustion, CO and $NO_X$ characteristics of biodiesel in accordance with equivalence ratio. The closed homogeneous reactor model used for the analysis. The analysis conditions were set to 900 K of the initial temperature, 20 atm of initial pressure and equivalence ratio was changes from 0.6 to 1.4. The results of analysis were predicted and compared in terms of combustion temperature, combustion pressure, CO and $NO_X$ emissions. The results of combustion characteristics showed that ignition delay was decreased and the combustion temperature and combustion pressure was increased in accordance with equivalence ratio. CO emission was decreased in lean condition(${\Phi}$ < 1.0), however, CO emission was increased in rich condition(${\Phi}$ > 1.0) because oxygen supply insufficient. $NO_X$ emission showed the largest amount in condition 0.8 of equivalence ratio because the oxygen concentration was sufficient.

• Journal of Korean Society for Atmospheric Environment
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• v.6 no.1
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• pp.11-21
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• 1990

To quantitatively estimate the effect of yellow sand(loess) fromt he Northern China, various soil sources having similar chemical compositions to yellow sands should be separated and identified. After that, mass contribution for yellow sand can be calculated. The study showed that it was impossible to solve this problem by the traditional bulk analyses. However, particle-by-particle analysis by a CCSEM (computer controlled scanning electron microscope) gave enormous potentials to solve it. To perform this study, seven soil source data analyzed by CCSEM were obtained from Texas, U.S.A. Initially, each soil date was classified into two groups, coarse and fine particle groups since the particle number distribution showed a minimum occurring at 5.2$\mu$m of aerodynamic diameter. Particles in each group were then classified into one of the 283 homogeneous particle classes by the universal classification rule which had been built by an expert system in the early study. Further, mass fractions and their uncertainties for each class in each source were calculated by the Jackknife method, and then source profile matrix for the 7 soil sources was created. To use the profile matrix in the study of source contribution, it is necessary to test the degree of collinearity among sources. The profiles were tested by the singular value decomposition method. As a result, each soil source characterized by artificially created variables was totally independent each other and is ready to use in source contribution studies as a receptor model.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.6
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• pp.681-687
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• 2008

It is well known that the water infiltration rate depends on soil properties such as soil water content, water head, capillary suction, density, hydraulic conductivity, and porosity. However, most of proposed infiltration models assume that the air phase is continuous and in equilibrium with the atmosphere or air compression and air entrapment on infiltration was not considered. This study presents experimental results on unsaturated water infiltration to relate air entrapment and hydraulic conductivity function based on soil air properties. The objectives of this study were to measure change of soil air pressure ahead of wetting front under air drain and air confined condition to find the confined air effect on infiltration rate, to reduce the entrapped air volume related with soil air pressure to increase the soil permeability, and to make a basis of infiltration process model for the purpose of improvement of infiltration rate in the homogeneous soil column. The results of the work show that soil air pressure increases according to increasement of the saturated soil depth rather than the wetting front depth during infiltration process.

• Economic and Environmental Geology
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• v.25 no.1
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• pp.73-77
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• 1992

This paper compares numerical quadrature techniques for computing an inverse Fourier transform integral in two-dimensional resistivity modeling. The quadrature techniques using exponential and cubic spline interpolations are examined for the case of a homogeneous earth model. In both methods the integral over the interval from 0 to ${\lambda}_{min}$, where ${\lambda}_{min}$, is the minimum sampling spatial wavenumber, is calculated by approximating Fourier transformed potentials to a logarithmic function. This scheme greatly reduces the inverse Fourier transform error associated with the logarithmic discontinuity at ${\lambda}=0$. Numrical results show that, if the sampling intervals are adequate, the cubic spline interpolation method is more accurate than the exponential interpolation method.

• Communications of the Korean Institute of Information Scientists and Engineers
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• v.5 no.1
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• pp.04-10
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• 1987

We consider a time sharing computer system with a single processor where tasks ofK different types arrive at the system according to independent time homogeneous Poisson processes from outside. A task, after given a quantum for processing, leaves the system, or changes the type and rejoins the system according to specified probabilitycs. While many existing priority time sharing models determine the priorities of tasks strictly by their service time requirements, this paper develops a new scheduling rule wherein the importances or urgencies in addition to the service time requirements of tasks are counted, by inposing an appropriate reward structure on the system. Also presented is the algorithm through which to determine the rankings of K types according to this new scheduling rule.