• Korea-Australia Rheology Journal
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• v.15 no.3
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• pp.131-150
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• 2003

A new numerical algorithm of finite element methods is presented to solve high Deborah number flow problems with geometric singularities. The steady inertialess planar 4 : 1 contraction flow is chosen for its test. As a viscoelastic constitutive equation, we have applied the globally stable (dissipative and Hadamard stable) Leonov model that can also properly accommodate important nonlinear viscoelastic phenomena. The streamline upwinding method with discrete elastic-viscous stress splitting is incorporated. New interpolation functions classified as rational interpolation, an alternative formalism to enhance numerical convergence at high Deborah number, are implemented not for the whole set of finite elements but for a few elements attached to the entrance comer, where stress singularity seems to exist. The rational interpolation scheme contains one arbitrary parameter b that controls the singular behavior of the rational functions, and its value is specified to yield the best stabilization effect. The new interpolation method raises the limit of Deborah number by 2∼5 times. Therefore on average, we can obtain convergent solution up to the Deborah number of 200 for which the comer vortex size reaches 1.6 times of the half width of the upstream reservoir. Examining spatial violation of the positive definiteness of the elastic strain tensor, we conjecture that the stabilization effect results from the peculiar behavior of rational functions identified as steep gradient on one domain boundary and linear slope on the other. Whereas the rational interpolation of both elastic strain and velocity distorts solutions significantly, it is shown that the variation of solutions incurred by rational interpolation only of the elastic strain is almost negligible. It is also verified that the rational interpolation deteriorates speed of convergence with respect to mesh refinement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1689-1699
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• 1996

A study on the transitional boundary layer with arbitrary pressure gradient under various upstream conditions is very important for engineering applications like the performance predictions of the turbomachineries under various and strong disturbances. Experimental data on the transitional boundary layer for real cascades of the turbomachinery are rare because of difficulties in boundary layer experiments. Flow on NACA0012 airfoil is more similar to the real case than that on the flat plate with which many researches are done. The data of the transitional flow on the airfoil could be used to verify or to develop a turbulence model for numerical simulations. The experiment was performed with two cases of Reynolds number at a=0$^{0}$ and one case of Reynolds number at a=5$^{0}$ . The measured data are the transition length and the wall shear stresses. These two characteristic values are measured within 25%~90% of the airfoil chord by Computation Preston tube Method(CPM) proposed by Nitsche et al.(1983). At a=0$^{0}$ , transition occured at 70% and 55% of chord length when R $e_{c}$=6*10$^{5}$ and 8* 10$^{5}$ , respectively. It started when R {\theta}=500 regardless of R $e_{c}$, and ended when R {\theta}=750, and 850 respectively. The transition length was 15~20% of the chord length. At a=5$^{0}$ (R $e_{c}$=6*10$^{5}$ ), boundary layer on the pressure side does not undergo transition, but on the suction side transition occured at .chi.$_{c}$/c=0.16 and ended at .chi.$_{c}$/c=0.22.c//c=0.22./c=0.22.c//c=0.22.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.21-30
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• 2005

In this paper, we propose lane detection and trackinB algerian using B-Snake as robust algorithm. One of chief virtues of Lane detection algorithm using B-Snake is that it is possible to specify a wider range of lane structure because B-Spline conform an arbitrary shape by control point set and that it doesn't use any camera parameter. Using a robust algorithm called CHVEP, we find the vanishing point, width of lane and mid-line of lane because of the perspective parallel line and then we can detect the both side of lane mark using B-snake. To demonstrate that this algorithm is robust against noise, shadow and illumination variations in road image, we tested this algorithm about various image divided by weather-fine, rainy and cloudy day. The percentage of correct lane detection is over 95$\%$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.16 no.1
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• pp.3263-3291
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• 1974

Experimental work of grain bin was carried out to develop the methods of natural air in-bin drying and storage. The method is considered to be more economical, labour saving, and an effective countermeasure to grain loss. To examine the possibility of farm use of the grain bin and to analyze the related factors concerned with in-bin grain drying and storage, ambient air conditions (especially the change of air temperature and relative humidity) and grain quality during drying and storage periods were investigated. A laboratory model bin was constructed to investigate the effect of different forced air conditions on the drying characteristics of rice. In addition, a grain bin with 2.2m diameter and 1.8m height, considered to be the optimum size for the average Korean farm, was constructed and tested to examine the drying and storing characteristics of rice. The weather data analyzed in this study was the nine-year (from 1964 to 1972) record of air temperature and relative humidity in the Suweon area, and the thirty-year (from 1931 to 1960) record of pentad normal relative humidity and air temperature in the Seoul area. From the results of the weather data analyses, the adequate air delivery hours (which was arbitrary defined as the condition to give less than 75% relative humidity) to dry the rice during October were about nine hours (from approximately 10 A.M. to 7 P.M, ) a day, in which the average air temperature was about 15.9$^{\circ}C$ and average relative humidity was 66%. The occurence of days having three hours of such conditions was 1, 2, and 1-day within the 1st, 2nd add last 10-day periods for the month of October, respectively. Therefore, it may be considered that the weather condition in October was satisfactory for the forced natural air drying. The results of the laboratory model bin test were analyzed to obtain the drying curve and drying rate for different drying stages and grain layers in the bin corresponding to various conditions of forced natural air. A drying experiment with a prototype grain bin showed that an approximate 5 percent grain moisture gradient through a 1.6 meter grain deposit was observed after 80 hours of intermittent drying, giving an over dried zone in the lower grain layers and an extremely high grain moisture zone in the upper layers. This indicates that an effective measure should be taken to reduce this high moisture gradient. In order to investigate the drying characteristics of bulk grain in a layerturning operation a grain bin test was performed. This showed a significant improvement of uniform drying. In this test, approximate 107 hours were required to dry a depth of 1.6 meter of grain from an initial moisture content of 22.2 percent to a moisture content of 16.7 percent using an air delivery rate of 2.8 cubic meter per a minute per every cubic meter of grain. This resulted in a 2 percent moisture gradient from the top to the bottom of the bin. During storage period, till the end of June the average temperature of grain was 2~3$^{\circ}C$ higher than ambient air temperature. But during July when the grain moisture content went up slightly (less than 1 percent), the average temperature of the grain also increased to 3~5$^{\circ}C$ higher than ambient air temperature. It is therefore recommended that for safe grain storage, grain should not be stored in sheet metal bins after mid May. From the above results, in-bin rice drying and storage can be used effectively on Korean farms. It is strongly recommended that the use of grain-bin system should be implemented for farm use to improve farm drying and storage of rice.

• Progress in Medical Physics
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• v.11 no.1
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• pp.49-57
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• 2000

New method about the dose optimization problem in radiation treatment was researched. Since all conditions are more complex and there are more relevant variables, the solution of three-dimensional treatment planning is much more complicate than that of current two-dimensional one. There(ore, in this study, as a method to solve three-dimensional dose optimization problem, the considered variables was minized and researched by reducing the domain that solutions can exist and pre-determining the important beam parameters. First, the dangerous beam range that passes critical organ was found by coordinate transformation between linear accelerator coordinate and patient coordinate. And the beam size and rotation angle for rectangular collimator that conform tumor at arbitrary beam position was also determined. As a result, the available beam position could be reduced and the dependency on beam size and rotation angle, that is very important parameter in treatment planning, totally removed. Therefore, the resultant combinations of relevant variables could be greatly reduced and the dose optimization by objective function can be done with minimum variables. From the above results, the dose optimization problem was solved for the two-dimensional radiation treatment planning useful in clinic. The objective function was made by combination of dose gradient, critical organ dose and dose homogeniety. And the optimum variables were determined by applying step search method to objective function. From the dose distributions by optimum variables, the merit of new dose optimization method was verified and it can be implemented on commercial radiation treatment planning system with further research.

• Journal of the Korean Geographical Society
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• v.42 no.4
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• pp.469-487
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• 2007

Grain-Size Trend Analysis is the methodology to identify net sediment transport pathways, based on the assumption that the movement of sediment from the source to deposit leaves the identifiable spatial pattern of mean, sorting, and skewness of grain size. It can easily be implemented with low cost, so it has great potentials to contribute to geomorphological research, whereas it can also be used inadequately without recognition of its limitations. This research aims to compare three established methods of grain-size trend analysis to search for the adequate way of application, and also suggest the research tasks needed in improving this methodology 1D pathway method can corporate the field experience into analyzing the pathway, provide the useful information of depositional environments through X-distribution, and identify the long-term trend effectively. However, it has disadvantage of the dependence on subjective interpretation, and a relatively coarse temporal scale. Gao-Collins's 2D transport vector method has the objective procedure, has the capability to visualize the transport pattern in 2D format, and to identify the pattern at a finer temporal scale, whereas characteristic distance and semiquantitative filtering are controversial. Le Roux's alternative 2D transport vector method has two improvement of Gao-Collins's in that it expands the empirical rules, considers the gradient of each parameters as well as the order, and has the ability to identify the pattern at a finer temporal scale, while the basic concepts are arbitrary and complicated. The application of grain sire trend analysis requires the selection of adequate method and the design of proper sampling scheme, based on the field knowledge of researcher, the temporal scale of sediment transport pattern targeted, and information needed. Besides, the relationship between the depth of sample and representative temporal scale should be systematically investigated in improving this methodology.