• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.160.4-160
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• 2001

Many physical systems today are modeled by interacting continuous and discrete states that influence the dynamic behavior. Hybrid system models, suitable for describing the essential dynamics of a fairly large class of physical systems in control engineering applications, contain both continuous dynamics and discrete dynamics. We discuss the design of efficient hybrid controllers for the platoon maneuvers on an AHS. For the modeling of a hybrid system including the merge and split operations, we introduce the safety distance policy for the merge and split operations. Then, the platoon system will be modeled by a hybrid system. In addition, the hybrid controller for the proposed merge and split operation models will be presented. Finally, we will demonstrate our scenarios ...

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.561-564
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• 2002

For the reduction of fuel consumption of high speed, the aerodynamic drag must be reduced. In early vehicle design process, it is very important to have information about aerodynamic characteristics of design models. In this phase CFD methods are usually used to predict the aerodynamic forces. But commercial programs using turbulence models cannot give a good agreement with experimental result and have also problems with convergence. PowerFLOW employs a new technology called DIGITAL PHYSICS, which provides a different approach to simulating fluids. DIGITAL PHYSICS uses a lattice-based approach (extended from lattice-gas and lattice-Boltzmann methods) where time, space and velocity are discrete. This discrete system represents the Wavier-Stokes continuum behavior without the numerical instability Issues of traditional CFD solvers, such as convergence. In this paper, aerodynamic performance of vehicles are simulated using PowerFLOW by Exa and results are compared with experimental wind tunnel data.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.12
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• pp.1183-1187
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• 2011

In this paper, an optimal FIR (Finite-Impulse-Response) filter is proposed for discrete time-varying state-space models. The proposed filter estimates the current state using measured output samples on the recent time horizon so that the variance of the estimation error is minimized. It is designed to be linear, unbiased, with an FIR structure, and is independent of any state information. Due to its FIR structure, the proposed filter is believed to be robust for modeling uncertainty or numerical errors than other IIR filters, such as the Kalman filter. For a general system with system and measurement noise, the proposed filter is derived without any artificial assumptions such as the nonsingular assumption of the system matrix A and any infinite covariance of the initial state. A numerical example show that the proposed FIR filter has better performance than the Kalman filter based on the IIR (Infinite- Impulse-Response) structure when modeling uncertainties exist.

• International Journal of Control, Automation, and Systems
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• v.4 no.5
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• pp.645-652
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• 2006

In this paper a new type of filter, called the $H_2/H_{\infty}$ FIR filter, is proposed for discrete-time state space signal models. The proposed filter requires linearity, unbiased property, FIR structure, and independence of the initial state information in addition to the performance criteria in both $H_2$ and $H_{infty}$ sense. It is shown that $H_2,\;H_{\infty}$, and $H_2/H_{\infty}$ FIR filter design problems can be converted into convex programming problems via linear matrix inequalities (LMIs) with a linear equality constraint. Simulation studies illustrate that the proposed FIR filter is more robust against temporary uncertainties and has faster convergence than the conventional IIR filters.

• Proceedings of the Korea Society for Simulation Conference
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• 1996.05a
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• pp.15-15
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• 1996

A shop floor control system (SFCS) is the central part of a CIM system used to control the activities of several pieces of manufacturing equipment (e.g., NC machines, robots, conveyors, AGVs, AS/RS). The SFCS receives orders and related process plans, and then performs selecting a specific process routing, allocating resources, scheduling the workpieces, downloading the processing instructions (e.g., RS-274 instructions for NC machines, VAL II programs for robot), monitoring the progress of activities, detecting and recovering from errors, and preparing reports on the status of the manufacturing system. Simulation has been utilized in discovering control policies used for resolving shop floor be control problems such as resource contentions, part dispatching, deadlock. The simulation model must be designed to respond to real-time data coming from a shop floor. However, to rapidly build a realtime simulation model of SFCS cannot be easily accomplished. This talk is to address an automatic program generator of discrete event simulation model for shop floor control from process plans and resource models. The program generator is capable of constructing complete discrete simulation models for multi-product and multi-stage flexible manufacturing systems.

• The Journal of Engineering Geology
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• v.5 no.2
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• pp.155-165
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• 1995

Fluid flow studies of fractured rocks require three-dimensional modeling of the fracture system. The stochastic discrete fracture models constructed by Monte Carlo simulation technique were applied to the analysis of groundwater flow and mass transport in fractured rock for the assessment of tightness criteria of underground LPG storage cavern. The parameters that most affect the conceptual discrete fracture modeling proved either fracture orientation or size and on the fract'lre flow interpretation proved conductive fracture intensity. The fracture transmissivity played important role in solute transport in fractured rock simulated by particle tracking approach. It was partly recognized that the calibrated stochastic discrete fracture model can be used for the tightness criteria of underground LPG storage cavern.

• Computers and Concrete
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• v.21 no.2
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• pp.189-197
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• 2018

A discrete element approach is used to investigate the effects of confining stress on the shear behaviour of joint's bridge area. A punch-through shear test is used to model the concrete cracks under different shear and confining stresses. Assuming a plane strain condition, special rectangular models are prepared with dimension of $75mm{\times}100mm$. Within the specimen model and near its four corners, four equally spaced vertical notches of the same depths are provided so that the central portion of the model remains intact. The lengths of notches are 35 mm. and these models are sequentially subjected to different confining pressures ranging from 2.5 to 15 MPa. The axial load is applied to the punch through the central portion of the model. This testing and models show that the failure process is mostly governed by the confining pressure. The shear strengths of the specimens are related to the fracture pattern and failure mechanism of the discontinuities. The shear behaviour of discontinuities is related to the number of induced shear bands which are increased by increasing the confining pressure while the cracks propagation lengths are decreased. The failure stress and the crack initiation stress both are increased due to confining pressure increase. As a whole, the mechanisms of brittle shear failure changes to that of the progressive failure by increasing the confining pressure.

• Proceedings of the Korean Society of Computational and Applied Mathematics Conference
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• 2003.09a
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• pp.1-1
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• 2003

In this talk, a reduced-order modeling methodology based on centroidal Voronoi tessellations (CVT's)is introduced. CVT's are special Voronoi tessellations for which the generators of the Voronoi diagram are also the centers of mass (means) of the corresponding Voronoi cells. The discrete data sets, CVT's are closely related to the h-means clustering techniques. Even with the use of good mesh generators, discretization schemes, and solution algorithms, the computational simulation of complex, turbulent, or chaotic systems still remains a formidable endeavor. For example, typical finite element codes may require many thousands of degrees of freedom for the accurate simulation of fluid flows. The situation is even worse for optimization problems for which multiple solutions of the complex state system are usually required or in feedback control problems for which real-time solutions of the complex state system are needed. There hava been many studies devoted to the development, testing, and use of reduced-order models for complex systems such as unsteady fluid flows. The types of reduced-ordered models that we study are those attempt to determine accurate approximate solutions of a complex system using very few degrees of freedom. To do so, such models have to use basis functions that are in some way intimately connected to the problem being approximated. Once a very low-dimensional reduced basis has been determined, one can employ it to solve the complex system by applying, e.g., a Galerkin method. In general, reduced bases are globally supported so that the discrete systems are dense; however, if the reduced basis is of very low dimension, one does not care about the lack of sparsity in the discrete system. A discussion of reduced-ordering modeling for complex systems such as fluid flows is given to provide a context for the application of reduced-order bases. Then, detailed descriptions of CVT-based reduced-order bases and how they can be constructed of complex systems are given. Subsequently, some concrete incompressible flow examples are used to illustrate the construction and use of CVT-based reduced-order bases. The CVT-based reduced-order modeling methodology is shown to be effective for these examples and is also shown to be inexpensive to apply compared to other reduced-order methods.

• Journal of Power Electronics
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• v.17 no.2
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• pp.442-452
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• 2017

This paper deals with the input-output modeling of a vector controlled PMSM drive system and design of a simple multiple model adaptive control (MMAC) scheme with desired transient responses. We present a discrete-time modeling technique using closed-loop identification that can experimentally identify the equivalent models in the d-q coordinates. A bank of linear models for the equivalent plant of the current loop is first obtained by identifying them at several operating points of the current to account for nonlinearity. Based on these models, we suggest a simple q-axis MMAC combined with a fixed d-axis controller. After the current controller is designed, another equivalent model including the current controller in the speed control loop shall be similarly obtained, and then a fixed speed controller is synthesized. The proposed approach is demonstrated by experiments. The experimental set up consists of a surface mounted PMSM (5 KW, 220V, 8 poles) equipped with a flywheel load of 220kg and a digital controller using DSP (TMS320F28335).

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.5
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• pp.2186-2203
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• 2020

Security administrators of companies and organizations need to come up with proper countermeasures against cyber-attacks considering infrastructures and security policies in their possession. In order to develop and verify such countermeasures, the administrators should be able to reenact both cyber-attacks and defenses. Simulations can be useful for the reenactment by overcoming its limitations including high risk and cost. If the administrators are able to design various scenarios of cyber-attacks and to develop simulation models from their viewpoints, they can simulate desired situations and observe the results more easily. It is challenging to simulate cyber-security issues, because there is lack of theoretical basis for modeling a wide range of the security field as well as pre-defined basic components used to model cyber-attacks. In this paper, we propose a modeling method for cyber-security simulations by developing a basic component and a composite model, called Abstracted Cyber-Security Unit Model (ACSUM) and Abstracted Cyber-security SIMulation model (ACSIM), respectively. The proposed models are based on DEVS(Discrete Event systems Specification) formalism, a modeling theory for discrete event simulations. We develop attack scenarios by sequencing attack behaviors using ACSUMs and then model ACSIMs by combining and abstracting the ACSUMs from a security perspective. The concepts of ACSUM and ACSIM enable the security administrators to simulate numerous cyber-security issues from their viewpoints. As a case study, we model a worm scenario using ACSUM and simulate three types of simulation models based on ACSIM from a different security perspective.