• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• Journal of Power System Engineering
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• v.4 no.4
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• pp.70-77
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• 2000

On the dynamic behavior of a simple beam the influences of the velocities and distance of two moving masses have been studied by numerical method. The instant amplitude of a simple beam is calculated and analyzed for each position of the moving masses represented by the time functions. As increasing the velocties of two moving masses on the simple beam, the amplitude of the transverse vibration of the simple beam is decreased and the frequency of the transverse vibration of the simple beam is increased. As the distance between two moving masses increase, the transverse displacement of the simple beam is decrease. The simple beam is very stable in second mode at $\bar{a}=0.5$ and in third mode at $\bar{a}=0.3$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1269-1275
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• 2006

The purpose of this study is to investigate the effect of bend angle on the collapse behavior of locally wall thinned pipe bends. For this purpose, the present study performed three-dimensional finite element analysis on the 30-, 60-, and 90-degree pipe bends with local wall thinning at the center of intrados, extrados, and crown, and evaluated the collapse moment for different thinning dimensions under closing- and opening-mode bending with a constant internal pressure. The results showed that, for intrados and extrados wall thinning, the reduction in the collapse moment due to local wall thinning became significant with decreasing bend angle of pipe bends. This effect of bend angle was enhanced with increasing thinning dimensions, and it was clearer fur opening-mode bending than for closing-mode bending. For crown wall thinning, however, the effect of bend angle was unclear and was less sensitive to the change of wall thinning shapes.

• Structural Engineering and Mechanics
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• v.84 no.4
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• pp.479-488
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• 2022

Aiming to examine different failure patterns in multistory URM walls, two 1/3 scaled three-story and three-bay URM models were designed for the quasi-static loading tests to contrastively investigate the failure processes and characteristics of the multistory URM walls. Two different failure responses were observed with special attention paid to the behavior of spandrel-failure mode. By evaluating the seismic performance and deformation behavior of two test walls, it is demonstrated that spandrels, that haven't been properly designed in some codes, are of great significance in the failure of entire URM walls. Additionally, compared with pier-failure mode, spandrel-failure for multistory URM building is more reasonable and advisable as its effectively participation in energy dissipation and its efficiently improvement on seismic capacity and deformation in the overall structure. Furthermore, the experimental results are beneficial to improve seismic design and optimize reinforcement method of URM buildings.

• Journal of Korean Society of Transportation
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• v.13 no.4
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• pp.31-45
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• 1995

In recent year, especially in the mode choice analysis, it has been perceived that the importance of individual performance data using stated preference(SP) experiments as well as revealed preference data . Since SP experiments present respondent with various hypothetical alternatives, which are produced by a combination of a number of different attribute levels, and ask them to indicate a preference, it is possible to analyze travel behavior under a situation of potential environment change such as proposed alternative mode of transportation. The basic problems, however, remains that SP are not consistent with the actual travel behaviors and the research reports for stability of mode choice model using SP data has not been sufficient. Under this background, this study is to examine the characteristics of mode choice model using the SP data by the following items. $\circled1$ Analysis of factors affecting the mode choice behavior by the variance analysis of orthogonal-arrays-table $\circled2$ The reliability of SP data by transfer intention data $\circled3$ The stability of SP responses obtained from repetitive question by the comparison of model coefficient specified by each repetitive data. $\circled4$ The stability of ranking data in mode choice model For the analysis, we assumed subway operations in the Gwang-Ju , and set up a choice-set of hypothetical options based on Experimental Design Method.

• Geomechanics and Engineering
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• v.18 no.3
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• pp.315-328
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• 2019

This paper presents an investigation on bearing capacity, load-settlement behavior and safety factor of rock-soil slopes reinforced using geogrid-box method (GBM). To this end, small-scale laboratory studies were carried out to study the load-settlement response of a circular footing resting on unreinforced and reinforced rock-soil slopes. Several parameters including unit weight of rock-soil materials (loose- and dense-packing modes), slope height, location of footing relative to the slope crest, and geogrid tensile strength were studied. A series of finite element analysis were conducted using ABAQUS software to predict the bearing capacity behavior of slopes. Limit equilibrium and finite element analysis were also performed using commercially available software SLIDE and ABAQUS, respectively to calculate the safety factor. It was found that stabilization of rock-soil slopes using GBM significantly improves the bearing capacity and settlement behavior of slopes. It was established that, the displacement contours in the dense-packing mode distribute in a broader and deeper area as compared with the loose-packing mode, which results in higher ultimate bearing load. Moreover, it was found that in the loose-packing mode an increase in the vertical pressure load is accompanied with an increase in the soil settlement, while in the dense-packing mode the load-settlement curves show a pronounced peak. Comparison of bearing capacity ratios for the dense- and loose-packing modes demonstrated that the maximum benefit of GBM is achieved for rock-soil slopes in loose-packing mode. It was also found that by increasing the slope height, both the initial stiffness and the bearing load decreases. The results indicated a significant increase in the ultimate bearing load as the distance of the footing to the slope crest increases. For all the cases, a good agreement between the laboratory and numerical results was observed.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1828-1829
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• 2006

In this paper, we propose sliding mode congestion controller for differentiated-services network. Two important issue in differentiated-services architecture are bandwidth guarantee and fair sharing of unsubscribed bandwidth among TCP flows with and without bandwidth reservation. We use tight upper and lower bounds for various settings of differentiated-services parameters using the loss-bounded model. The Sliding mode congestion controller scheme is designed using nonlinear control theory based on a nonlinear model of the network that is generated using fluid flow consideration. The methodology used is general and independent of technology, as for example TCP/IP or ATM. The sliding mode congestion controller methodology has been applied to an TCP network. We use NS-2 simulation to demonstrate that the proposed control methodology achieves the desired behavior of the network, and possesses important attributes. as e.g, stable and robust behavior, high utilization with bounded delay and loss, together with good steady-state and transient behavior.

• Coupled systems mechanics
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• v.7 no.1
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• pp.27-42
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• 2018

Behavior of soil is usually described with continuum type of failure models such as Mohr-Coulomb or Drucker-Prager model. The main advantage of these models is in a relatively simple and efficient way of predicting the main tendencies and overall behavior of soil in failure analysis of interest for engineering practice. However, the main shortcoming of these models is that they are not able to capture post-peak behavior of soil nor the corresponding failure modes under extreme loading. In this paper we will significantly improve on this state-of-the-art. In particular, we propose the use of a discrete beam lattice model to provide a sharp prediction of inelastic response and failure mechanisms in coupled soil-foundation systems. In the discrete beam lattice model used in this paper, soil is meshed with one-dimensional Timoshenko beam finite elements with embedded strong discontinuities in axial and transverse direction capable of representing crack propagation in mode I and mode II. Mode I relates to crack opening, and mode II relates to crack sliding. To take into account material heterogeneities, we determine fracture limits for each Timoshenko beam with Gaussian random distribution. We compare the results obtained using the discrete beam lattice model against those obtained using the modified three-surface elasto-plastic cap model.

• The Korean Journal of Applied Statistics
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• v.26 no.4
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• pp.661-674
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• 2013

We investigate the class registration behavior of college students with data collected from the spring semester of 2012. The network originally consists of a 2-mode network between a student and class subjects. We first transform the 2-mode network into 1-mode network of students. We also subdivide it into a smaller network such as components and communities to understand the detailed behavior of students in class registration. Finally, the relationship between GPA and the centrality measures, gender, and grade of students is analyzed using a multiple regression analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1458-1467
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• 1992

Recently, the composite materials have been researched actively by many researchers because of its useful properties. Especially, an interface crack on the dissimilar material exposes the behavior of the mixed mode crack even though under only the tension stress. In the previous papers, crack energy density(CED) was shown as the crack behavior evaluation parameter which can be expressed consistently from the onset until a final fracture. In a present paper, the basic properties of CED on the interface crack are examined because the results by CED at the homogeneous material above are also expected to be held at the dissimilar material. And we proposed that the contribution of each mode of CED can be separated and be evaluated. Furthermore, the total CED and contribution of each mode are evaluated by domain integral through a finite element analysis at the elastic crack model and the basic examination are carried out.