• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.1
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• pp.8-16
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• 1986

For digital process control, a low order discrete time modeling method is suggested and a direct digital control algorithm has been developed. The modeling method maintains process order of 3, while the sampling rate is doubled for fast response. With easy calculation it is possible to compute the model parameters and the controller gains. Controller tuning is possible on the spot. Simulation results show that this method has better performance than the deadbeat control agorithm.

• Structural Engineering and Mechanics
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• v.55 no.2
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• pp.315-334
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• 2015

This study's primary aim is to check the existence of a representative volume element for granular materials and determine the link between the properties (responses) of macro structures and the size of the discrete particle assembly used to represent a constitutive relation in a two-scale model. In our two-scale method the boundary value problem on the macro level was solved using finite element method, based on the Cosserat continuum; the macro stresses and modulus were obtained using a solution of discrete particle assemblies at certain element integration points. Meanwhile, discrete particle assemblies were solved using discrete element method under boundary conditions provided by the macro deformation. Our investigations focused largely on the size effects of the discrete particle assembly and the radius of the particle on macro properties, such as deformation stiffness, bearing capacity and the residual strength of the granular structure. According to the numerical results, we suggest fitting formulas linking the values of different macro properties (responses) and size of discrete particle assemblies. In addition, this study also concerns the configuration and displacement fluctuation of discrete particle assemblies on the micro level, accompanied with the evolution of bearing capacity and deformation on the macro level.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.4
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• pp.487-492
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• 2004

This paper deals with modeling method and application of Fuzzy Discrete Event System(FDES). FDES have characteristics which Crisp Discrete Event System(CDES) can't deals with and is constituted with the events that is determined by vague and uncertain judgement like biomedical or traffic control. In general, the modeling method of CDES has been studied many times, but that of FDES hasn't been nearly studied by qualitative character and scarcity of applicated system. This paper models traffic system with FDES's character in FTTPN and designs a traffic signal controller.

• Journal of the Korea Society for Simulation
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• v.10 no.3
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• pp.1-14
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• 2001

A hybrid system is defined as a mixture of continuous systems and discrete event systems. This paper first proposes a framework for hybrid systems modeling, called Hybrid Discrete Event System Specification (HDEVS) formalism. It then presents a method for simulators interoperation in which a continuous system simulator and a discrete event simulator are executed together in a cooperative manner. The formalism can specify a hybrid system in a way that a continuos system and a discrete event system are separately modeled by their own specification formalisms with a support of well-defined interface. We call such interface an A/E converter for analog-to- event conversion and an E/A converter for event-to-analog conversion. Simulators interoperation is based on the concept of pre-simulation in which simulation time for a continuous simulator is advanced in accordance with a discrete event simulator.

• Geomechanics and Engineering
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• v.33 no.4
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• pp.353-367
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• 2023

The construction of a protective embankment is a suitable strategy to stop and control high-energy rock blocks' impacts during the rockfall phenomenon. In this paper, based on the discrete element numerical method, by modeling an existing embankment reinforced with geogrid, its stability status under the impact of a rock block with two types of low and high kinetic energy, namely 2402 and 4180 kJ, respectively, has been investigated. The modeling results show that the use of geogrid has caused the displacement in the front and back of the embankment to decrease by more than 30%. In this case, the reinforced embankment has stopped the rock block earlier. The displacements obtained from the DEM modeling are compared with the displacements measured from an actual practical experiment to evaluate the results' validity. Comparison between the results shows that the displacement values are close together, while the maximum percentage error in previous studies by an analytical method and the finite element method was 76.4% and 36.6%, respectively. Therefore, the obtained results indicate the discrete numerical method's high ability compared to other numerical and analytical methods to simulate and design the geogrid-reinforced soil embankment under natural disasters such as rockfall with a minor error.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.4
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• pp.352-357
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• 2007

This paper deals with modeling method and application of Fuzzy Discrete Event System(FDES). FDES have characteristics which Crisp Discrete Event System(CDES) can't deals with and is constituted with the events that is determined by vague and uncertain judgement like biomedical or traffic control. We proposed Real-time Fuzzy Temporal Logic Framework(RFTLF) to model Fuzzy Discrete Event System. It combines Temporal Logic Framework with Fuzzy Theory. We represented the model of traffic signal systems for intersection to have the property of Fuzzy Discrete Event System with Real-time Fuzzy Temporal Logic Framework and designed a traffic signal controller for smooth traffic flow. Moreover, we proposed the method to find the minimum-time route to reach the desired destination with information obtained in each intersection. In order to evaluate the performance of Real-time Fuzzy Temporal Logic Framework model proposed in this paper, we simulated unit-time extension traffic signal controller model of the latest signal control method on the same condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.156-164
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• 2000

In this study, a discrete time model for a simplified front wheel suspension system which has nonlinear dampling and stiffness property is introduced. The model is estimated from the discrete data which are generated based on the real car parameter. The performance of the proposed method is evaluated through numerical simulation, and the simulation results show that the proposed method can estimate the nonlinear behavior of the suspension system very well.

• Korean Journal of Computational Design and Engineering
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• v.18 no.3
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• pp.224-233
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• 2013

For the scheduling and the job assignment of the ship hull production design which is a process-based work, we suggest the simulation-based scheduling using the discrete-event-based business process simulation. First, we analyze the ship hull production design process from the perspective of a job assignment to make it into the simulation model using DEVS (Discrete Event System Specification) which is the representative modeling method for a discrete-event simulation. Based on the APIs of the open-source discrete-event simulation engine, we implement the simulation using the Groovy script. We develop the scenario generator in which the user defines detail information of the construction drawing and its member blocks, and design engineers information, and the various setting for the simulation including the job assignment strategy. We use the XML files from this scenario generator as inputs of simulation so that we can get simulation result in forms of Gantt chart without changes of the simulation model.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1876-1885
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• 2003

The artificial potential field (APF) methods provide simple and efficient motion planners for practical purposes. However, these methods have a local minimum problem, which can trap an object before reaching its goal. The local minimum problem is sometimes inevitable when an object moves in unknown environments, because the object cannot predict local minima before it detects obstacles forming the local minima. The avoidance of local minima has been an active research topic in the potential field based path planing. In this study, we propose a new concept using a virtual obstacle to escape local minima that occur in local path planning. A virtual obstacle is located around local minima to repel an object from local minima. We also propose the discrete modeling method for the modeling of arbitrary shaped objects used in this approach. This modeling method is adaptable for real-time path planning because it is reliable and provides lower complexity.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1331-1336
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• 2008

This paper suggests a method using Bayesian inference to estimate the parameters of Weibull distribution and acceleration parameters under the condition that the stresses are time-dependent functions. A Bayesian model based on the discrete time approximation is formulated to infer the parameters of interest from the failure data of the virtual tests and a statistical analysis is considered to decide the most probable mean values of the parameters for reasoning of the failure data.