• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.29-36
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• 2003

A cylindrical constant volume combustion chamber was used to investigate the flow characteristics at spark plug and the combustion characteristics of inhomogeneous charge methane-air mixture under several parameters. The flow characteristics such as mean velocity and turbulence intensity was analyzed by hot wire anemometer. Combustion pressure development measured by piezoelectric pressure transducer was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. Mean velocity and turbulence intensity had the maximum value at 200 or 300ms and then decreased to beneath 0.05m/s gradually at 3 seconds. Second mixture is accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the burn rate.

• Structural Engineering and Mechanics
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• v.10 no.4
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• pp.299-312
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• 2000

The response of an embedded body to dynamic loads is greatly influenced by the reactions of the soil to the motion of the body. The properties of the soil surrounding embedded bodies (e.g., piles) may be different than those of the far-field for a variety of reasons. It may be weakened or strengthened according to the method of installation of piles, or altered due to applying one of the soil strengthening technique (e.g., electrokinetic treatment of soil, El Naggar et al. 1998). In all these cases, the shear strength of the soils and its shear modulus vary gradually in the radial direction, resulting in a radially inhomogeneous soil layer. This paper describes an analysis to compute vertical and torsional dynamic soil reactions of a radially inhomogeneous soil layer with a circular hole. These soil reactions could then be used to model the soil resistance in the analysis of the pile vibration under dynamic loads. The soil layer is considered to have a piecewise, radial variation for the complex shear modulus. The model is developed for soil layers improved using the electrokinetic technique but can be used for other situations where the soil properties vary gradually in the radial direction (strengthened or weakened). The soil reactions (impedance functions) are evaluated over a wide range of parameters and compared with those obtained from other solutions. A parametric study was performed to examine the effect of different soil improvement parameters on vertical and torsional impedance functions of the soil. The effect of the increase in the shear modulus and the width of the improved zone is investigated.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3390-3397
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• 2022

Among the different techniques available, nuclear methods, including gamma-gamma logging tools, are of special importance. Though the real environment which surrounds the drilled borehole is a complex fractured medium which the fluid can flow through the porosities, simulation studies generally use the traditional model of a homogeneous mixture of formation and the liquid. Considering a previously published study, which shows that modeling of fluid flow in fractured reservoirs and simulating the formation as an inhomogeneous fractured medium leads to different results compared with those of homogeneous mixture, here we study the effect of the presence of drilling fluid (mudcake) on the response of the detectors in both the models. To study this effect, a typical gamma-gamma logging tool was modeled by using the MCNPX Monte Carlo code. The results show that the responses of the detectors in the mixture model in the presence of various thicknesses of mudcake are sensitive to the density of the formation material. However, this effect is not notable in the inhomogeneous fractured medium. These results emphasize the importance of the model employed for simulation of the medium in gamma-gamma well-logging.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.39-49
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• 1994

In this paper, An inversion technique to reconstruct permittivity profiles of 2-D inhomogeneous dielectric objects by iterativeprocess using the moment-methodand improved newton's algoritham is presented. In order to reduce the noise effect in the scattered fieldon the reconstructed permittivity profiles, the cell size of inversescattering is made be larger than that of forward scattering. Performing numerical calculations of dielectric scatterer it is demonstrated that this inversion is able to reconstruct dielectric objectshaving large size and inhomogeneous characteristics, which is insentive tothe noise effect in the scattered field on the reconstructed result.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.617-624
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• 2000

Abnormal grain growth in alumina was investigated during sinter-HIP process for better understanding of pressure effect on microstructural development. Abnormal grain growth of monolithic alumina was observed near surface region rather than interior region of specimen. Finite element analysis was used to estimate the pressure distribution developed in the specimen. Pressure distribution analysis was in good agreement with grain size distributjion in the specimen. The results of finite element analysis provided that abnormal grain growth monolithic alumina was resulted from the inhomogeneous pressure distribution in the specimen. MgO addition in alumina was effective for the suppression of abnormal grain growth in alumina under inhomogeneous pressure distribution during sinter-HIP process.

• Current Optics and Photonics
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• v.5 no.1
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• pp.45-51
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• 2021

The effect of the out-of-plane retardation (Rth) of a substrate film on the viewing-angle dependence of transmittance (TR) in a display device was investigated. When the polarization state of input light deviates from the transmission axis of the polarizer, Rth of the substrate film induces inhomogeneous viewing-angle dependence of TR. The inhomogeneity of TR gets worse for greater values of of Rth. The inhomogeneous TR profile can be eliminated by inserting compensation films, which convert the input polarization state to the linear polarization state parallel to the transmission axis of the polarizer.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.24-31
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• 2004

A cylindrical constant volume combustion bomb is used to investigate the combustion characteristics and to analyzer the heat quantity of inhomogeneous charge methane-air mixture. To analyze the heat quantity, some definitions including the CHR ratio, the UHC ratio and the HL ratio are needed and are calculated. It is shown that the effect of stratification is not significant in case of the overall excess air ratio of 1.1, mainly due to the higher heat loss and lower thermal efficiency compared to those of homogeneous condition. In the case of the overall excess air ratio of 1.4, as the initial charge pressure decreases, the CHR ratio has been decreased while the HL ratio has been increased, Generally, as the initial charge pressure increases, the amount of injection mixture has been decreased and has resulted in lower mean velocity and turbulence intensity for injection mixture. Also, the injected mixture is too rich to result in mixing deficiency in combustion chamber. From these results, it could be possible to acquire the improvement of thermal efficiency and the reduction of heat loss simultaneously through the 2-stage injection in CNG direct injection engine.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.61-67
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• 2018

The effects of subsurface inhomogeneities on the detection of buried metal pipes in ground-penetrating radar(GPR) signals are investigated numerically. To model the electrical properties of the subsurface inhomogeneities, the continuous random media(CRM) generation technique is introduced. For the electromagnetic simulation of GPR signals, the finite-difference time-domain(FDTD) method is implemented. As a function of the standard deviation and the correlation length of the relative permittivity distribution for a randomly inhomogeneous ground, the GPR signals of the buried metal pipes are compared using numerical simulations. As the subsurface inhomogeneities increase, the GPR signals of the buried pipes are distorted because of the effect of the subsurface clutter.

• International Journal of Automotive Technology
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• v.5 no.3
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• pp.181-188
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• 2004

A cylindrical constant-volume combustion chamber was used to investigate the flow characteristics at the spark electrode gap and the combustion characteristics of an inhomogeneous charge methane-air mixture under several parameters such as stratified pattern, initial charge pressure, ignition time and the excess air ratio of the initial charge mixture. Flow characteristics including mean velocity and turbulence intensity were analyzed by a hot-wire anemometer. The combustion pressure development, measured by a piezo-electric pressure transducer, was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. It was found that the mean velocity and turbulence intensity had the maximum value around 200-300 ms and then decreased gradually to near-zero value at 3000 ms. For the stratified patterns, the combustion rate under the rich injection (RI) condition was the fastest. Under the initial charge conditions, the second mixture was accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the combustion rate.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.1
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• pp.30-37
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• 1999

Transmissivity and the signal loss in soil are computed. An electric field expression for the inhomogeneous complex media modelled by two layers is shown as an integral form. Volume scattering occurs in inhomogeneous media, and iterative Born approximation is used to analyze this scattering effect. The degree of randomness is controlled by specifying the variance and correlation length. Expression for the transmissivity and the signal loss is presented as the parameter of soil moisture contents, soil particle radius, temperature and frequency. The analysis shows that big deviation in signal loss depends on the temperature variation remarkably and the physical reason of unusual level is explained.