• Proceedings of the KSME Conference
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• 2001.06d
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• pp.382-389
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• 2001

In the present study, local heat transfer rates for co-rotating disks with two modified hubs having ventilation holes are investigated for Rossby number of 0.04, 0.1 and 0.35 to evaluate the influence of incoming flows through hub holes. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using Laser Doppler Anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by the disk rotation. The basic flow structure in a cavity between co-rotating disks consists of three regions; the solid-body rotating inner region, the outer region with turbulence vortices and the shroud boundary layer region. The heat/mass transfer. rates on the co-rotating disks are very low near the hub due to the solid-body rotation and those increase rapidly in the outer region due to turbulence mixing. The modified hubs with ventilation holes enhances significantly the heat/mass transfer rates on the region near the hub. The results also show that the heat transfer of Hub-2 is superior to that of Hub-1, but Hub-1 is more profitable for destructing the solid-body rotating inner region.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.41-48
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• 2010

Non-contacting, laser-based resonant ultrasound spectroscopy (L-RUS) was applied to characterize the microstructure of a material. L-RUS is widely used by virtue of its many features. Firstly, L-RUS can be used to measure mechanical damping which related to the microstructural variations (grain boundary, grain size, precipitation, defects, dislocations etc). Secondly, L-RUS technology can be applied to various areas, such as the noncontact and nondestructive quality test for precision components as well as noncontact and nondestructive materials characterization. In addition, L-RUS technology can measure the whole field resonant frequency at once. In this paper, we evaluated material characteristics such as resonant frequency, nonlinear propagation characteristic through the development of Laser-Based Resonant Ultrasound spectroscopy (Laser-RUS) System for the detection of Micro Crack in Materials.

• Advanced Composite Materials
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• v.18 no.4
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• pp.297-314
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• 2009

A design method is proposed to optimize the stacking sequence of laminated composite plates for desired vibration characteristics. The objective functions are the natural frequencies of the laminated plates, and three types of optimization problems are studied where the fundamental frequency and the difference of two adjacent frequencies are maximized, and the difference between the target and actual frequencies is minimized. The design variables are a set of discrete values of fiber orientation angles with prescribed increment in the layers of the plates. The four lamination parameters are used to describe the bending property of a symmetrically laminated plate, and are optimized by a gradient method in the first stage. A new technique is introduced in the second stage to convert from the optimum four lamination parameters into the stacking sequence that is composed of the optimum fiber orientation angles of all the layers. Plates are divided into sub-domains composed of the small number of layers and designed sequentially from outer domains. For each domain, the optimum angles are determined by minimizing the errors between the optimum lamination parameters obtained in the first step and the parameters for all possible discrete stacking sequence designs. It is shown in numerical examples that this design method can provide with accurate optimum solutions for the stacking sequence of vibrating composite plates with various boundary conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1201-1207
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• 2008

Numerical analysis information will be very useful to improve fluid system. General information about an internal gas flow is presented by numerical analysis approach. Relating with hydrogen compressing system, which have an important role in hydrogen energy utilization, this should be a useful tool to observe the flow quickly and clearly. Flow characteristic analysis, including pressure and turbulence kinetic energy distribution of hydrogen gas coming to the cylinder of a reciprocating compressor are presented in this paper. Suction-passage model is designed based on real model of hydrogen compressor. Pressure boundary conditions are applied considering the real condition of operating system. The result shows pressure and turbulence kinetic energy are not distributed uniformly along the passage of the Hydrogen system. Path line or particles tracks help to demonstrate flow characteristics inside the passage. The existence of vortices and flow direction can be precisely predicted. Based on this result, the design improvement, such as reducing the varying flow parameters and flow reorientation should be done. Consequently, development of the better hydrogen compressing system will be achieved.

• Journal of Environmental Science International
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• v.12 no.4
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• pp.419-426
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• 2003

This study was performed to research ozone concentration related to airmass thunderstorm using 12 years meteorological data(1990~2001) at Busan. The occurrence frequency of thunderstorm during 12 years was 156 days(annual mean 13days). The airmass thunderstorm frequency was 14 days, most of those occurrence at summertime(59%). In case August 4, 1996, increase of ozone concentration was simultaneous with the decrease of temperature and increase of relative humidity, In case July 23, 1997, ozone concentration of western site at Busan increased, while its of eastern site decreased as airmass thunderstorm occurred(about 1500LST). It is supposed that these ozone increases are the effect of ozone rich air that is brought down by cumulus downdrafts from height levels where the ozone mixing ratio is larger. Thunderstorms can cause downward transport of ozone from the reservoir layer in the upper troposphere into planeta교 boundary layer(PBL). This complex interaction of source and sink processes can result in large variability fer vertical and horizontal ozone distributions. Thus a variety of meteorological precesses can act to enhance vertical mixing between the earth's surface and the atmospheric in the manner described fer thunderstorm.

• Journal of Environmental Science International
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• v.22 no.4
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• pp.397-406
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• 2013

With the methodology of AHP, this paper focuses on communication activities and their constituents in city parks, selecting 11 constituents, natural or artificial, and establishes an evaluation model on the basis of the analysis of the characteristics of tourists' communication activities in order to obtain the weight and order of importance of the constituents of communication activities space. First-grade indicators influence weight and the order of the constituents of communication activities space are: artificial constituents (0.6614) > natural constituents (0.3386). The weight and order of five secondary indicators attached to natural constituents: private space (0.1538) > shade tree (0.0955) > gentle slope mound (0.0474) > beautiful waterscape (0.0270) > sunshine lawn (0.0149); the weight and order of six secondary indicators attached to artificial constituents: field boundary (0.2865) > Leisure chairs (0.1843) > resting areas (0.0795) > appropriate square (0.0533) > tree-lined road (0.0352) > landscape sketch (0.0227).Using modern decision analysis methodology to research the relationship of environment constituent elements has great theoretical and practical significance for the scientific design and construction of suitable environment for human needs.

• The KSFM Journal of Fluid Machinery
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• v.12 no.1
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• pp.22-27
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• 2009

The important problems that arise in the design and performance of the axial flow turbine are the prediction and control of secondary flows. Some progresses have been made on understanding flow conditions that occur when the inlet endwall boundary layer separates at the point in the endwall and rolls up into the horseshoe vortex. And the flows though an axial turbine tend to be extremely complex due to its inherent unsteady and viscous phenomena. The passing wakes generated from the trailing edge of the stator make an interaction with the rotor. Unsteady flow should be considered rotor/stator interactions. The main purpose of this research is control of secondary flow and improvement efficiency in turbine by leading edge modification in unsteady state. When the wake from the stator ran into the modified leading edge of the rotor, the leading edge generated the weak pressure fluctuation by complex passage flows. In conclusion, leading edge modification(bulb2) results in the reduced total pressure loss in the flow field.

• Journal of Korean Association for Spatial Structures
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• v.13 no.1
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• pp.87-96
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• 2013

This study investigated characteristics of buckling load and effective buckling length by member rigidity of dome-typed space frame which was sensitive to initial conditions. A critical point and a buckling load were computed by analyzing the eigenvalues and determinants of the tangential stiffness matrix. The hexagonal pyramid model and star dome were selected for the case study in order to examine the nodal buckling and member buckling in accordance with member rigidity. From the numerical results, an effective buckling length factor of adopted models was bigger than that of Euler buckling for the case of fixed boundary. These numerical models indicated that the influence of nodal buckling was greater than that of member buckling as member rigidity was higher. Besides, there was a tendency that the bifurcation appeared on the equilibrium path before limit point in the member buckling model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.47-54
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• 1993

For the numerical analysis of free oscillation characteristics in a harbor with general boundary and bottom topography, finite element method is applied. The governing Helmholtz equation is transformed into a generalized matrix eigenvalue problem using the standard finite element procedure. A computer code is developed for the numerical evaluation of natural frequencies and free oscillation modes. In the eigensolution process, a shifting strategy is devised for the treatment of numerical singularity. Scaling of coefficient matrix is also found to be effective for the alleviation of numerical ill-conditioning. For the test problems, firstly, analytical and numerical solutions are compared and validity of the code is obtained. Hence the method is successfully applicable for the real-world problems with general geometric boundaries and bottom topography.

• Composites Research
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• v.15 no.2
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• pp.1-10
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• 2002

The strength of glass/epoxy fabric joints under pin-loading is estimated based on the characteristics length method and experiment. To investigate the effect of finite element idealization for the contact between pin and laminate, three modeling cases are analyzed; assuming the cosine load distribution around the contact area, constraining the radial displacement at the hole boundary, and using the contact element. To study the effect of failure criteria, Tsai-Wu and Yamada-Sun methods are applied on the characteristic curve. The results of the nonlinear analysis using the contact element showed good agrements with experimental data in both laminates made of uni-directional prepreg tapes and fabrics. In terms of failure criteria, Tsai-Wu method showed better agreement with experimental results than the one by Yamada-Sun laminate.