• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.3
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• pp.289-296
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• 2002

New discrete-time modeling and simulation techniques are proposed which take advantages of the special features of PWM converter power stages and their compensation circuits. These techniques provide reduction of system order, and allow for the faster simulation without any numerical convergence problem. A buck converter with two-stage output filter Is employed to confirm the usefulness of the proposed techniques. The simulation results show these techniques can simulate the responoes of PWM converter system up to high frequencies.

• Geomechanics and Engineering
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• v.9 no.2
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• pp.145-167
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• 2015

Digital simulation has recently become the preferred method for designing complex and dynamic systems. Simulation packages provide interactive, block-diagram environment for modeling and simulating dynamic models. The block diagrams in simulation models are flowcharts which describe the components of dynamic systems and their interaction. This paper is the first part of the study for determining the seismic behavior of soil systems. The aim of this part is to present the constructed block diagrams for discrete-time analysis of seismic site amplification in layered media for vertically propagating shear waves. Detailed block diagrams are constructed for single and multiple soil layers by considering wave propagation with and without damping, respectively. The block diagrams for recursive filter to model attenuation in discrete-time form are also constructed. Finite difference method is used for strain calculation. The block diagrams are developed by utilizing Simulink which is a software add-on to Matlab.

• Proceedings of the Korea Society for Simulation Conference
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• 1992.10a
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• pp.7-7
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• 1992

Extending discrete event modelling formalisms to facilitate greater symbol manipulation capabilities is important to further their use in intelligent control and design of high autonomy systems. This paper defines an extension to the DEVS formalism that facilitates symbolic expression of discrete event times by extending the time base from the real numbers to the field of linear polynomials over the reals. A simulation algorithm is developed to generate the branching trajectories resulting from the underlying non-determinism. To efficiently manage linear polynomial constraints based on feasibility checking algorithm borrowed from linear programming. The extended formalism offers a convenient means to conduct multiple, simultaneous explorations of model behaviors. Examples of application are given with consideration on fault model analysis.

• Journal of Construction Engineering and Project Management
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• v.4 no.2
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• pp.31-40
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• 2014

The management of vehicular supply of "perishable" construction material, such as concrete mixes, faces a series of uncertainties such as weather, daily traffic patterns and accidents. Presented in this paper is a logistics control model for managing a hauling fleet with interrelated processes at both ends and queue capacities. Discrete event simulation is used to model the complex interactions of production units and the randomness of the real world. Two alternative strategies for ready mix concrete delivery, with and without an off-site waiting queue, are studied to compare supply performance. Secondly, the paper discusses the effect of an agent-based GPS tracking system providing real-time travel data that lessens the uncertainty of trucking time. The results show that the combination of GPS information with off-site queuing reduces productivity loss and process wastes of concrete placement as well as the idleness of supply trucks when crew or pump experience an unexpected stoppage.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.4
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• pp.93-98
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• 2020

Washboarding is a phenomenon in which a wavy shape occurs periodically and naturally on an unpaved road made of soil or gravel. This phenomenon causes high-frequency vibration of the traffic traveling on the road because of the height difference of the wave pattern, which may lead to vehicle failure. Consequently, associated research is needed concerning vehicle safety. Therefore, in this study, a numerical simulation was conducted using the discrete element method, which is often used for powder simulation. In contrast to previous studies, the results of this study demonstrate that washboarding can occur even in an environment of 1.5 m/s or less. However, the amount of washboarding is minimal. The study revealed that washboarding develops over time, such that sufficient development time is required before measurements are taken.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.136-146
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• 2021

This paper aims to numerically estimate the dynamic ice load on a conical structure. The Discrete Element Method (DEM) is employed to model the level ice as the assembly of numerous spherical particles. To mimic the realistic fracture mechanism of ice, the parallel bonding method is introduced. Cases with four different ice drifting velocities are considered in time domain. For validation, the statistics of time-varying ice forces and their frequencies obtained by numerical simulations are extensively compared against the physical model-test results. Ice properties are directly adopted from the targeted experimental test set up. The additional parameters for DEM simulations are systematically determined by a numerical three-point bending test. The findings reveal that the numerical simulation estimates the dynamic ice force in a reasonably acceptable range and its results agree well with experimental data.

• Journal of the Korea Society for Simulation
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• v.10 no.3
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• pp.15-30
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• 2001

Hybrid simulation may employ different types of simulation based on which models in different system types are developed. The simulation requires simulation time synchronization and data exchange between such simulators, which is called simulators interoperation. This paper develops such interoperable simulation environments for modeling and simulation of hybrid systems whose components consist of continuous and discrete event systems. The environments, one for centerized and the other for distribute, support interoperation between a discrete event simulator of DEVSim++ and a continuous simulator of MATLAB. The centerized environment, HDEVSim++, is developed by extending the sxisting DEVSim++ environment; the distributed environment, HDEVSimHLA, is developed using the HLA/RTl library. Verification of both environments is made and performance comparison between the two using a simple example is presented. .

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1089-1098
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• 1992

This paper concerns a discrete time control of noncolocated flexible mechanical systems by using time delay relation. A stability criterion of closed-loop system is derived in discrete time domain and a graphic method is developed for designing controllers. Based on this method, a derivative controller is designed for a simply supported uniform beam in the cases of colocation without time delay and of noncolocation with time delay. Some simulation results show the effectiveness of the suggested control.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.05a
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• pp.169-169
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• 2001

With the aid of fast computing power, resampling techniques are being introduced for simulation output analysis (SOA). Autocorrelation among the output from discrete-event simulation prohibit the direct application of resampling schemes (Threshold bootstrap, Binary bootstrap, Stationary bootstrap, etc) extend its usage to time-series data such as simulation output. We present a new method for inference from a regenerative process, regenerative bootstrap, that equals or exceeds the performance of classical regenerative method and approximation regeneration techniques. Regenerative bootstrap saves computation time and overcomes the problem of scarce regeneration cycles. Computational results are provided using M/M/1 model.

• Journal of KSNVE
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• v.10 no.3
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• pp.451-456
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• 2000

In this paper a discrete time model for the identification of nonlinear vibration system with stick-slip friction is proposed. The proposed model can handle the highly nonlinear behavior of the friction such as stick-slip phenomenon and Stribeck effect. The basic idea of the proposed model is as follows : If the nonlinearity of the system can be predicted as a simple function then this nonlinear function term cab be directly used in the discrete time model. By doing this the number of nonlinear terms in the model can be much less than those of NARMAX model which is widely used nonlinear discrete model. The simulation result shows that the proposed model can estimate the response of the nonlinear vibration system with stick-slip friction very well with less computational effort.