• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.173-181
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• 2000

The stability of a structural plate is a crucial problem which causes wrinkling and buckling. In this paper, the effect of the pattern of spot-welding points in the two rectangular plate on the shear buckling load is studied with respect to the thickness, the aspect ratio of plates, the number of welding spots. Buckling coefficient of the simple plate was compared with that of two plates with various conditions to extract the effect of buckling strength. The effect of the number of welding spots are studied in two directions, longitudinal and transverse directions. The concluded that the reinforcement effect was maximized when the aspect ratio was close to 1.5 and that the effect of number of welding spots in longitudinal direction was larger than that in transverse direction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.4
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• pp.285-294
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• 1993

An oscillatory motion of natural convection in a two-dimensional square enclosure fitted with a horizontal partition is investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was positioned perpendicularly at the mid-height of one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were carried out with the variations of the partition length and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). As the results, an oscillatory motion of natural convection has perfectly shown the periodicity with the decrease of Rayleigh number, and the stability was reduced to a chaotic state with the increase of Rayleigh number. The period of oscillation gets shorten with the decrease of the partition length and the increase of Rayleigh number. The frequency of oscillation obtained by the variations of stream function is more similar to the experimental results than that of the average Nusselt number. The stability of oscillation grows worse with the increase of Rayleigh number. The transition Rayleigh number for the chaos is gradually decreased with the increase of the partition length.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.181-190
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• 2013

In this study, a total of 51 cases of hydraulic model tests has been conducted for various wave conditions and slope angles of breakwater to develop a stability formula for Rakuna-IV armoring a rubble-mound breakwater. The stability number of the formula is expressed as a function of relative damage, number of waves, structural slope, and surf similarity parameter. The stability formula is derived separately for plunging and surging waves, the greater of which is used. The transitional surf similarity parameter from plunging waves to surging waves is also presented. Lastly, to explain the stability of Rakuna-IV to the engineers who are familiar with the stability coefficient in the Hudson formula, the required weight of Rakuna-IV is calculated for varying significant wave height for typical plunging and surging wave conditions, which is then compared with those of the Hudson formula using several different stability coefficients.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1055-1065
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• 2009

In this study, stability analysis of boundary layers on airfoils is performed by using parabolized stability equations(PSE). Boundary layer edge conditions are obtained by compressible inviscid flow calculations. Mean velocity and temperature profiles of the laminar boundary layer are obtained by solving compressible boundary layer equations in generalized curvilinear coordinates with fourth order accuracy in the wall normal direction. Laminar mean flow profiles are used as input data for PSE to investigate growth rates of disturbances and stability characteristics. For the cases of boundary layer on NACA0012 and HSNLF(1)-0213 airfoils at Mach number 0.5, growth rates with respect to disturbance frequencies and profiles of disturbance amplitude are investigated. The effect of angle of attack on stability characteristics are examined at both upper and lower surfaces. The neutral stability curves, effect of Mach number and effect of airfoil section shapes are also analyzed.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.52 no.4
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• pp.469-473
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• 2007

With the aim to analyze stability performance of six promising barley genotypes, eleven yield related characters were evaluated employing varied irrigation treatments under the tropical climate of Northern part in Bangladesh. Analysis of variance(ANOVA), phenotypic index, regression co-efficient(bi) and deviation from regression($s^2_d$) of the individual genotypes were estimated to evaluate the stable performance of the genotypes. A significant interaction was observed between the genotypes and irrigation period($G{\times}T$). Among all the genotypes, BSH-2 showed stable performance for plant height under different irrigation period, where $P>\bar{X},\;bi{\sim}1\;and\;s^2_d{\sim}0$. High phenotypic index, lower bi value and low deviations from regression were observed in case of spikelet number per spike and grain number per spike for genotype BSH-2 and plant height, spike length and harvest index per plant for BB-2 which suggest that those parameters were not usually affected by irrigation. On the other hand the genotype BSH-2 for tiller number and BB-1 for the fertile tiller number were not suitable for favorable moisture content, where $P<\bar{X},\;bi>1.0\;and\;low\;s^2_d$. Thus we suggest that genotype BSH-2 might have transmit high mean and increased phenotypic stability to the next progenies, which may consider as an ideal genotype for developing improved barely cultivars.

• Journal of Mechanical Science and Technology
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• v.14 no.3
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• pp.358-368
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• 2000

The hydrodynamic stability of the Karman boundary-layer flow due to a rotating disk has been numerically investigated for moving disturbance waves. The disturbed flow over a rotating disk can lead to transition at much lower Re than that of the well-known Type I instability mode. This early transition is due to the excitation of the Type II instability mode of moving disturbances. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The reformulated stability equations are slightly different with the previous ones. However, the present neutral stability results are considerably different with the previously known ones. It is found that the flow is always stable for a disturbance whose dimensionless wave number k is greater than 0.75.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3033-3038
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• 2007

In this research, Rayleigh instability of gas-liquid flow in annular pipe is studied in film boiling using viscous potential flow. Viscous potential flow is a kind of approximation of gas-liquid interface considering velocity field as potential including viscosity. A dispersion relation is obtained including the effect of heat and mass transfer and viscosity. New expression for dispersion relation in film boiling and critical wave number is obtained. Viscosity and heat and mass transfer have a stabilizing effect on instability and its effect appears in maximum growth rate and critical wave number. And the existence of marginal stability region is shown.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.156-161
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• 1999

new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under a13 bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number)0.01, we can not ignore the effect of slip for journal bearing.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.2
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• pp.189-199
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• 1999

This paper presents an optimization algorithm for a stable Self Dynamic Neural Network(SDNN) using genetic algorithm. Optimized SDNN is applied to a problem of controlling nonlinear dynamical systems. SDNN is dynamic mapping and is better suited for dynamical systems than static forward neural network. The real-time implementation is very important, and thus the neuro controller also needs to be designed such that it converges with a relatively small number of training cycles. SDW has considerably fewer weights than DNN. Since there is no interlink among the hidden layer. The object of proposed algorithm is that the number of self dynamic neuron node and the gradient of activation functions are simultaneously optimized by genetic algorithms. To guarantee convergence, an analytic method based on the Lyapunov function is used to find a stable learning for the SDNN. The ability and effectiveness of identifying and controlling a nonlinear dynamic system using the proposed optimized SDNN considering stability is demonstrated by case studies.

• Tribology and Lubricants
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• v.17 no.1
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• pp.28-32
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• 2001

A new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under all bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number＞0.01, we can not ignore the effect of slip for Journal bearing.