• Journal of Electrical Engineering and Technology
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• v.1 no.2
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• pp.161-169
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• 2006

Load representation has a significant impact on power system analysis and control results. In this paper, composite load models are developed based on on-line measurement data from a practical power system. Three types of static-dynamic load models are derived: general ZIP-induction motor model, Exponential-induction motor model and Z-induction motor model. For the dynamic induction motor model, two different third-order induction motor models are studied. The performances in modeling real and reactive power behaviors by composite load models are compared with other dynamic load models in terms of relative mismatch error. In addition, numerical consideration of ill-conditioned parameters is addressed based on trajectory sensitivity. Numerical studies indicate that the developed composite load models can accurately capture the dynamic behaviors of loads during disturbance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.932-937
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• 2008

The transformer inrush current can cause a voltage drop by source impedance. This current can impact sensitive loads by the voltage drop. Therefore, it is necessary to take measures to limit this inrush current. This study, described in this paper, analyzes the power quality affected by transformer inrush current using the X power system in Korea. The Electromagnetic Transients Program(EMTP) is used to analyze the transient phenomenon. We discuss a method to model the hysteresis curve of the transformer in EMTP. We carried out various simulations to analyze the power quality during transformer energization. The analysis results of voltage drop by the inrush current occurrence when certain requirements are met are presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.218-225
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• 2000

This paper presents intermediate results of an on-going research for identification of the modal and the stiffness parameters of a bridge based on the ambient vibration data caused by the traffic loadings. The main algorithms consist of the random decrement method incorporating band-pass filters for estimation of the free vibration signals the cross spectral density method for identification of the modal parameters and the neural networks technique for estimation of the element-level stiffness changes. An experimental study is carried out on a scaled bridge model with a composite section subjected to various moving vehicle loadings. Vertical accelerations are measured at several locations on the girder. The estimated frequencies and mode shapes are found to be well-compared with those obtained from the impact tests. The estimated stiffness changes using the neural networks are found to be very good for the case with the simulated data. However the accuracy is found to be not quite satisfactory for the case with the experimental data particularly for the small value of the stiffness changes.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.55-60
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• 2011

For the bolster type bogie, bolster anchor body connections are proviede to transmit the longitudinal loads for traction or braking between the carbody and the truck. The bolster anchor body connection is generally composed of anchor rod bracket, anchor rod and its fastening devices. The bolster anchor body connection shall be basically capable of withstanding a longitudinal load resulting from excessive braking case or impact. Additionally the north America standard requires that the anchor rod bracket shall be frangible, I.e. the anchor rod bracket shall fail and fall away under load before the carbody structure is damaged since to protect the cabody structure in the event of unexpected accident. This paper describes the shear connection design using the optimized mechanical fasteners in the bolster anchor body connection to satisfy these Northe America requirements.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.439-445
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• 2017

Plunging breaker slamming pressures on vertical or sloping sea dikes are one of the most severe and dangerous loads that sea dike structures can suffer. Many studies have investigated the impact forces caused by breaking waves for maritime structures including sea dikes and most predictions of the breaker forces are based on empirical or semi-empirical formulae calibrated from laboratory experiments. However, the wave breaking mechanism is complex and more research efforts are still needed to improve the accuracy in predicting breaker forces. This study proposes a semi-empirical formula, which is based on impulse-momentum relation, to calculate the slamming pressure due to plunging wave breaking on a sloping sea dike. Compared with some measured slamming pressure data in two literature, the calculation results by the new formula show reasonable agreements. Also, by analysing probability distribution function of wave heights, the proposed formula can be converted into a probabilistic expression form for convenience only.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.04a
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• pp.1-8
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• 1994

An automated procedure which allows adaptation of spatial and time discretization simultaneously in finite element analysis of linear elastodynamic problems is presented. For dynamic problems having responses dominated by high frequency modes, such as those with impact, explosive, traveling and earthquake loads high gradient stress regions change their locations from time to time. And the time step size may need to vary in order to deal with whole process ranging from transient phase to steady state phase. As the sizes of elements in space vary in different regions, the procedure also permits different time stepping. In such a way, the best performance attainable by the finite element method can be achieved. In this study, we estimate both of the kinetic energy error and stran energy error induced by spatial and time discretization in a consistent manner. Numerical examples are used to demonstrate the performance of the procedure.

• Fibers and Polymers
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• v.3 no.1
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• pp.31-37
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• 2002

Most fibers are irregular, and they are often subjected to combined loading conditions during processing and enduse. In this paper polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.

• IE interfaces
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• v.17 no.2
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• pp.142-148
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• 2004

The objective of bridge construction cost allocation is to distribute in a fair and rational manner the bridge construction costs among those vehicles using the bridge. In most bridge construction cost allocation studies, bridge construction costs are mainly distributed according to traffic load(gross vehicle weight), without any consideration of bridge capacity requirements(the number of lanes). In this paper, a bridge cost allocation method for considering both traffic capacity and traffic loads is developed. The proposed method is based on cooperative game theory, particularly two concepts known as the Aumann-Shapley (A-S) value and Shapley value. This method can help to analyze the impact of traffic capacity costs. By applying the proposed method to an example, traffic capacity cost is found to be high so that traffic capacity should be considered to allocate the bridge construction costs to vehicle classes in a more equitable manner.

• Journal of the Korean Operations Research and Management Science Society
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• v.34 no.3
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• pp.137-153
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• 2009

In this paper, we present an analytic model that evaluates the performance of B-MAC protocol under contention transmission conditions of two senders in a single-hop wireless sensor network. Our model considers the impact of several important factors such as sleep cycle, the backoff mechanism and incoming traffic loads. After obtaining the service delay distribution of a sending node and expected delay of a receiving node, an iterative algorithm is presented for calculating the performance measures such as expected energy consumption usage per packet and latency. Simulation results show that the proposed analytic model can accurately estimate the performance measures under different traffic conditions.

• Structural Monitoring and Maintenance
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• v.4 no.2
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• pp.175-194
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• 2017

Research to date has mainly focused on structural analysis and design of wind turbines considering turbulent aerodynamic loading. The combined effects of wind and seismic loading have not been studied by many researchers. With the recent expansion of wind turbines into seismically active regions research is now needed into the implications of seismic loading coupled with turbulent aerodynamic loading. This paper proposes a monitoring procedure for onshore horizontal axis wind turbines (HAWTs) subjected to this combined loading regime. The paper examines the impact of seismic loading on the 5-MW baseline HAWT developed by the National Renewable Energy Laboratory (NREL). A modified version of FAST, an open-source program developed by NREL, is used to perform the dynamic analysis.