• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.99-106
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• 2014

In order to study the reasonable design thermal loads, the steel box girder bridge specimen which have no concrete slab was manufactured with the real size dimension. The temperature data were measured for 5 month at the 18 thermo gauges which were attached according to height. The temperature differences between the top and bottom flange in steel box girder specimen were calculated and the temperature gradient models were proposed by the probabilistic method. This proposed model showed a correlation of approximately 97% when compared with the similar model of Euro Code. Thus, the temperature gradient models which were suggested in this study may be used as the basis data in calculating the design load temperature.

• Journal of the Korean Society of Visualization
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• v.12 no.1
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• pp.13-17
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• 2014

The growth of micro bubble has been simulated under the variation of ambient pressure. The Rayleigh-Plesset equation governs the dynamic growth and collapse of a bubble according to pressure and temperature conditions. The Rayleigh-Plesset equation was solved by 4th-order Runge-Kutta method for wide range of pressure variations. As numerical parameters, the pressure difference between initial and final pressures, and the temporal pressure gradient are changed. The results show that the pressure difference has little effect on the growth rate of the micro bubble in the inertia controlled growth region. On the other hand, the growth rate increases linearly with the increase of the pressure gradient.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.12
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• pp.7350-7356
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• 2014

To study the reasonable design thermal loads, a steel box girder bridge specimen, which has no concrete slab, was manufactured with real size dimensions. The temperature data was obtained at the web and diaphragm using thermo gauges that were attached according to height. In the hottest day, the temperature differences between the top and bottom of the bridge model were calculated. The temperatures in the actual bridge were measured and the temperature of the bridge specimen was compared. The temperature gradient models were proposed in both the web and the diaphragm. The proposed models showed a correlation of approximately 95.8% compared to the Euro code. This study can provide basis data for temperature-load design in the nation.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.61-68
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• 2001

In this paper, an analytical method and a difference approximation method to calculate the gradient of an objective function have been applied to the directivity optimization in an adaptive ultrasonic transducer which is combined with a point source array and an optimization algorithm (DFP method). To compare these two methods, quasi-ideal .beam with a beam width and direction specified are chosen as the desired directivity. As the numerical results, the difference approximation method shows better suppressive capacity of side lobe level, good stability in the convergence processing, faster convergence speed and excellent adaptability compared with the analytical method.

• Journal of the Korean Wood Science and Technology
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• v.19 no.4
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• pp.52-61
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• 1991

In this paper, the difference of the property of absorption and desorption for five species in semi-steady state are studied. The species used are listed in Table 1 and the dimension of specimen was $8\times8{\times}T$(Tangential direction)cm and tested in various conditions. A change of average moisture content with time were measured in each cycles. The results obtained are summarized as follows. When the relative humidity in air was maximum or minimum, the distribution of moisture In wood of all specimens were illustrated by exponential curves of decrease or increased from lace 10 center of wood. From the consideration of coefficient of decrease(C), the amount of moisture change of spruce was larger than the others. The pheonomenon was considered no relation to the specific gravity in air dry, but the wood structures. The velocity of the absorption and desorption for species decreased in the order spruce(Picea sitchensis) neodobam(Fagus crenata), solsong(Tsuga heterophylla), meranti(Shorea sp.) and kaesoo(Cercidiphyllum japoicum). In case of constant temperature and water vapor pressure is changed. the amount of absorbed moisture was larger than that of constant water vapor pressure and temperature vaned. In this fact, it is considered that the property of sorption of wood is strongly influenced by vapor pressure gradient than temperature gradient.

• The Transactions of the Korea Information Processing Society
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• v.3 no.6
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• pp.1553-1567
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• 1996

The numerous applications surface interpolation include the modeling and visualization phenomena. A tetrahedrization is one of pre-processing steps for 4-D space interpolation. The quality of a piecewise linear interpolation 4-D space depends not only on the distribution of the data points in $R^2$, but also on the data values. We show that the quality of approximation can be improved by data dependent tetraheadrization through visualization of 4-D space. This paper discusses Delaunary tetrahedrization method(sphere criterion) and one of the data dependent tetrahedrization methods(least squares fitting criterion). This paper also discusses new data dependent criteria:1) gradient difference, and 2) jump in normal direction derivative.

• Coupled systems mechanics
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• v.8 no.2
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• pp.129-146
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• 2019

The main goal of this work is to develop a numerical simulator to study an isothermal single-phase two-component flow in a naturally fractured oil reservoir, taking into account advection and diffusion effects. We use the Peng-Robinson equation of state with a volume translation to evaluate the properties of the components, and the discretization of the governing partial differential equations is carried out using the Finite Difference Method, along with implicit and first-order upwind schemes. This process leads to a coupled non-linear algebraic system for the unknowns pressure and molar fractions. After a linearization and the use of an operator splitting, the Conjugate Gradient and Bi-conjugated Gradient Stabilized methods are then used to solve two algebraic subsystems, one for the pressure and another for the molar fraction. We studied the effects of fractures in both the flow field and mass transport, as well as in computing time, and the results show that the fractures affect, as expected, the flow creating a thin preferential path for the mass transport.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.380-388
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• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation of condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new numerical scheme to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the cupid code.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1354-1357
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• 2003

Mold Analysis is crucial factors in the design of injection molding process. Since the qualify of products depends on filing, shrinkage and etc, the procedure of prediction through analysis in the design of injection molding process is needed. In many cases, this kind of analysis makes it possible to predict pressure pattern which determines the condition of injection molding process. Crystallinity is the factor that determines the shrinkage of products. The studies showed the factors that had been related to the degree of crystallinity, which were mostly Weight Reduction, mold temperature and melt temperature. Therefore, the objective of this study is to see the differences of the degree of crystallinity depending on the positions of foamed plastics. The procedure of this study is as the following. First, Simulate the pressure gradient in mold cavity that can produces specimen by using Moldflow. Secondly, produce specimen and measure the degree or crystallinity of each part of specimen by using XRD. Lastly, identify the sensitivity of conventional plastic and foamed plastic on pressure gradient by comparing the simulation and the results of measurement.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.2
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• pp.205-212
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• 2011

In this paper, we have proposed a method for quantization of the stratification strength in the sea water and analysing the distributions of the maximum stratification depths calculated by the method at the seas near the Korean peninsular. For calculating the stratification strength, modified and applied the potential energy anomaly formular which was suggested by Simpson in 1977. The data had been collected by NFRDI from 1971 to 2008 were used to determine the maximum vertical density gradient depth and the relative potential energy anomaly at that depth. In the East Sea, the stratification depth has become deepened about 20m in February and April since 1971. In Yellow-South Sea, the maximum density gradient depth has been deepened about 10m only in December during the same period and the difference of the stratification depth between summer and winter has been enlarged. These trends of variation of stratification strength and depth near the Korean peninsular should be investigated more carefully and continuously. And the results of these studies could be adopted for the more efficient operation of underwater weapon and detection systems.