• Journal of applied mathematics & informatics
• /
• v.40 no.3_4
• /
• pp.603-618
• /
• 2022

In this paper, a numerical solution of the generalized diffusion equation with a delay has been obtained by a numerical technique based on the Galerkin finite element method by applying the cubic B-spline basis functions. The time discretization process is carried out using the forward Euler method. The numerical scheme is required to preserve the delay-independent asymptotic stability with an additional restriction on time and spatial step sizes. Both the theoretical and computational rates of convergence of the numerical method have been examined and found to be in agreement. As it can be observed from the numerical results given in tables and graphs, the proposed method approximates the exact solution very well. The accuracy of the numerical scheme is confirmed by computing L₂ and L_∞ error norms.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.2
• /
• pp.104-110
• /
• 1997

Increase of marine transpotation in coastal area frequently yields oil spill accidents due to collision or grounding of oil tankers, which affects great deal of damages on ocean environments. Exact prediction of oil pollution area in time domain, which is called oil map, is very important for effective and efficient oil recovery and minimization of environmental damage. The prediction is carried out by considering the two distinct processes which are initial diffusion on the still water surface and advection due to tide, wind wave induced surface currents. In the present paper, only the initial diffusion is dealt with. Somewhat new simulation model and its numerical scheme are proposed to predict it. Simple diffusion experiment is also carried out to check the validity of the present method. Furthermore, some example simulations are performed for virtual oil spill accident. Quite realistic oil map including oil thickness distributions can be obtained by the present model.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.1
• /
• pp.128-138
• /
• 2015

Carbonation is one of the most critical deterioration phenomena to concrete structures exposed to high $CO_2$ concentration, sheltered from rain. Lots of researches have been performed on evaluation of carbonation depth and changes in hydrate compositions, however carbonation modeling is limitedly carried out due to complicated carbonic reaction and diffusion coefficient. This study presents a simplified carbonation model considering diffusion coefficient, solubility of $Ca(OH)_2$, porosity reduction, and carbonic reaction rate for low concentration. For verification, accelerated carbonation test with varying temperature and MIP (Mercury Intrusion Porosimetry) test are carried out, and carbonation depths are compared with those from the previous and the proposed model. Field data with low $CO_2$ concentration is compared with those from the proposed model. The proposed model shows very reasonable results like carbonation depth and consuming $Ca(OH)_2$ through reduced diffusion coefficient and porosity compared with the previous model.

• Current Photovoltaic Research
• /
• v.2 no.2
• /
• pp.59-62
• /
• 2014

Minority carrier diffusion length is one of the most important parameters of solar cells, especially for short circuit current density (Jsc). In this report, we proposed the calculating method of the minority carrier diffusion length ($L_n$) in CIGS solar cells through biased quantum efficiency (QE). To verify this method's reliability, we chose two CIGS samples which have different grain size and calculated $L_n$ for each sample. First of all, we calculated out that $L_n$ was 56nm and 97nm for small and large grain sized-cell through this method, respectively. Second, we found out the large grain sized-cell has about 7 times lower defect density than the small grain sized-cell using drive level capacitance profiling (DLCP) method. Consequently, we confirmed that $L_n$ was mainly affected by the micro-structure and defect density of CIGS layer, and could explain the cause of Jsc difference between two samples having same band gap.

• Journal of the Korean Geographical Society
• /
• v.28 no.2
• /
• pp.123-136
• /
• 1993

The growth of radidly improving computer and information technology has a profound impact upon economical, social and cultural sectors. With the progress of information technology, information-telecommunication services are produced. This service is used in sending the information to order service-users, and search the need information. This case study considers information-telecommunication service as a consumer-innovation. Information telecommunication services are provided by firms involved in collection. HiTEL(High-Telecommunication) service represents a subset of this group in that the collection, processing and transmission is primarily in an electronic from. The purpose of this paper is concerned with examining the spatial diffusion process, the issues, and behavior to used in HiTEL service one of the information-telecommunication services in Kwangju. HiTEL service is one of the typical information-telecommunication services, and is begun in Seoul and Kwangju area from October 1991, and diffusing several cities and regions now. Diffusion process of HiTEL services in Kwangju showed the irregular pattern in major residential areas, particularly Daewei-dong, Dongun-dong present higher adoption rate than other area, and where functioned as a diffusion center, the social and economic characteristics of residential area have a critical effect on diffusion process. The major adoption areas are recently built residential area, apartment districts, and diffusion direction shows two directions according to development of residental area; one is to south, another is from northeast to southwest. In order to understand the use-behavior of HiTEL service, questionary survey was carried out. Most adopters have a concern to actual life, as HiTEL, information of telephonenumber, and Daewoo Dial-Van compared with other information service. But the actual use-frequency of service is very low. In use of Kwangju regional information service, the use-frequency of operator is very low because of the lack of advertisement, the lack of providing information, and the low-concerns for regional information. But most of adopters need the providing of various regional information as regional news, education, medical and cultural events, housing, city-transportation, and job market. Thus, in order to increase and diffuse the HiTEL service, the establishment of diffusion strategies and the scheme for solution of related issues are very important. The direct diffusion strategies are the diffusion of information-mind, establishment of diffusion and education center, providing of regional information. The scheme for solution of related issues revealed in operating process are reduction of rental fee, development of the related technology and services.

• Corrosion Science and Technology
• /
• v.5 no.4
• /
• pp.117-122
• /
• 2006

Hydrogen permeation measurements have been carried out on API X65 grade linepipe steel. In order to study the effect of steel microstructure on hydrogen diffusion behavior in linepipe steel, the accelerated cooling condition was applied and then three different kinds of microstructures were obtained. Hydrogen permeation measurement has been performed in reference to modified ISO17081 (2004) and ZIS Z3113 method. Hydrogen trapping parameters in these steels were evaluated in terms of the effective diffusivity ($D_{eff}$), permeability ($J_{ss}L$) and the amount of diffusible hydrogen. In this study, microstructures which affect both hydrogen trapping and diffusion were degenerated pearlite (DP), acicular ferrite (AF), bainite and martensite/austenite constituents (MA). The low $D_{eff}$ and $J_{ss}L$ mean that more hydrogen can be trapped reversibly or irreversibly and the corresponding steel microstructure is dominant hydrogen trapping site. The large amount of diffusible hydrogen means that corresponding steel microstructure is predominantly reversible. The results of this study suggest that the hydrogen trapping efficiency increases in the order of DP, bainite and AF, while AF is the most efficient reversible trap.

• Structural Engineering and Mechanics
• /
• v.60 no.3
• /
• pp.529-545
• /
• 2016

In this article, the generalized coupled non-Fickian diffusion-thermoelasticity analysis is carried out using an analytical method. The transient behaviors of field variables, including mass concentration, temperature and displacement are studied in a strip, which is subjected to shock loading. The governing equations are derived using generalized coupled non-Fickian diffusion-thermoelasticity theory, which is based on Lord-Shulman theory of coupled thermoelasticity. The governing equations are transferred to the frequency domain using Laplace transform technique and then the field variables are obtained in analytical forms using the presented method. The field variables are eventually determined in time domain by employing the Talbot technique. The dynamic behaviors of mass concentration, temperature and displacement are studied in details. It is concluded that the presented analytical method has a high capability for simulating the wave propagation with finite speed in mass concentration field as well as for tracking thermoelastic waves. Furthermore, the obtained results are more realistic than that of others.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.5
• /
• pp.1253-1263
• /
• 1994

The experimental study is carried out to identify the combustion generated noise mechanism in free turbulent jet diffusion flames. Axial mean fluctuating velocities in cold and reacting flow fields were measured using hot-wire anemometer and LDv.The overall sound pressure level and their spectral distribution in far field with and without combustion were also measured in an anechoic chamber. The axial mean velocity is 10-25% faster and turbulent intensities are about 10 to 15% smaller near active reacting zone than those in nonreacting flow fields. And sound pressure level is about 10-20% higher in reacting flow fields. It is also shown that the spectra of the combustion noise has lower frequency characteristics over a broadband spectrum. These results indicate that the combustion noise characteristics in jet diffusion flames are dominated by energy containing large scale eddies and the combusting flow field itself. Scaling laws correlating the gas velocity and heat of combustion show that the acoustic power of the combustion noise is linearly proportional to the 3.8th power of the mean axial velocity rather than 8th power in nonreacting flow fields, and the SPL increases linearly with logarithmic 1/2th power of the heat of combustion.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.910-915
• /
• 2005

In this study a series of tests(bench scale test) are carried out for increasing in strength of clayey soil by EK-Injection method. In addition, the effects of strength increase in the treated sample are measured by operating the vane shear test device during 25 days at 5 days intervals in order to estimate the effect of ground improvement caused by diffusion. The test results show that the strength increase was developed approximately double to 7 times in comparison to initial shear strength, and outstanding strength increase was created as much as 7 times while injecting the sodium silicate and phosphoric acid in anolyte and catholyte. In addition, the measured shear strength with the influence of diffusion and reduction of water-content had a tendency to converge in constant value in proportion to elapsed time. As a result of this study, strength increment developed by the influence of EK-Injection and diffusion rather than the reduction of water-content were high as 1000% on average

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.5
• /
• pp.1269-1279
• /
• 1995

An experimental study is carried out on turbulent diffusion flames stabilized by a circular cylinder in a divergent duct flow. A commercial grade gaseous propane is injected from two slits on the rod as fuel. Flame stability limits, as well as size and temperrature of recirculation zone, are measured by direct and schlieren photographs to clarify the characteristics and structure of diffusion flames and to assess the effect of various divergent angle of duct. The results of the present study are as follows. Temperature in the recirculation zone decreases with increasing divergent angle. The blow-off velocity in parallel duct is higher than that in divergent duct. Critical blow-off velocity is expected to be about 8-12 degree through blow-off velocity pattern. Regardless of divergent angles, the length of recirculation zone is nearly constant, and this length becomes longer with rod diameter. Pressure gradient has an effect on the eddy structure in shear layer behind the rod. With the increase of divergent angle, large scale eddies by dissipated energy in shear layer are split into small scale eddies, and the flame becomes a typical distributedreacting flame.