• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.38-42
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• 2003

In this paper, a radar scattering model for forest canopies has been developed based on an empirical rough surface scattering model and the radiative transfer theory. Leaves in the forest canopy are modeled by rectangular resistive sheets, brunches and trunks are modeled by cylinder, which sizes and orientations are randomly distributed. The scattering model has been verified with the measurement data of JPL/AirSAR system.

• Proceedings of the KIEE Conference
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• 1985.07a
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• pp.127-130
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• 1985

A stochastic model to predict radio interference field as caused by corona discharges on high voltage transmission lines has been developed. This model is based on corona discharge distributed randomly in time and space. A stochastic model for the corona current induced by corona discharges on power lines is proposed. On the basis of the proposed corona current model, a rigorous analysis is presented to evaluate the radio interference (RI) field caused by corona discharges on a single conductor using the stochastic method.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.73-78
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• 2003

In this research, we implement Realtime Air Diffusion Prediction System which is a parallel Fortran model running on distributed-memory parallel computers. The system is designed for air diffusion simulations with four-dimensional data assimilation. For regional air quality forecasting a series of dynamic downscaling technique is adopted using the NCAR/Penn. State MM5 model which is an atmospheric model. The realtime initial data have been provided daily from the KMA (Korean Meteorological Administration) global spectral model output. It takes huge resources of computation to get 24 hour air quality forecast with this four step dynamic downscaling (27km, 9km, 3km, and lkm). Parallel implementation of the realtime system is imperative to achieve increased throughput since the realtime system have to be performed which correct timing behavior and the sequential code requires a large amount of CPU time for typical simulations. The parallel system uses MPI (Message Passing Interface), a standard library to support high-level routines for message passing. We validate the parallel model by comparing it with the sequential model. For realtime running, we implement a cluster computer which is a distributed-memory parallel computer that links high-performance PCs with high-speed interconnection networks. We use 32 2-CPU nodes and a Myrinet network for the cluster. Since cluster computers more cost effective than conventional distributed parallel computers, we can build a dedicated realtime computer. The system also includes web based Gill (Graphic User Interface) for convenient system management and performance monitoring so that end-users can restart the system easily when the system faults. Performance of the parallel model is analyzed by comparing its execution time with the sequential model, and by calculating communication overhead and load imbalance, which are common problems in parallel processing. Performance analysis is carried out on our cluster which has 32 2-CPU nodes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.212-216
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• 2004

Bearingless motors are the rotational electric machine which utilize a common magnetic structure for rotation and magnetic suspension. Since the bearing function is combined with the motor, the shaft length can be shortened resulting in higher critical speeds. Relationship between suspension force and current of bearingless motor is clearly derived by prior research. However, relationship between displacement of rotor and suspension force is not precisely defined. In this paper, we present model of bearingless motor describing the radial force variation due to the movement of the rotor. Using a distributed magnetic circuit and maxwell stress tensor, we derived a mathematical expression for the radial force. For a slotless bearingless motor, we are able to find an analytical model presented in the form of stiffness. For a slotted motor, we can compute the stiffness by semi-analytical analysis. This model is validated by a finite-element-analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.414-417
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• 2001

In today's engineering world, any product development activity requires the expertise and the interaction of many different engineering. Therefore the various activities in a product development architecture are highly distributed and interdependent. The interdependence may be due to sharing of databases and transfer of information between various activities. This will require an integrated product model. That can support distributed design such that participants from different backgrounds collaborate towards one common goal. This paper presents the architecture of the product modeling system for the integration of CAD and CAE. It then reports on the study of STEP 10303 and UG open API focused on the integration of different technical environments.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.141-146
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• 2002

In the present design concept, the nonlinear behavior of bridges is allowed under large earthquake. Therefore, demands for nonlinear analyses of bridges are increased more and more especially in the area of seismic assessment. It is, however, difficult to solve the problem how the nonlinearity of columns should be modelled. In this study, the fiber element Is adopted for model ins pier column. The element is a kind of structural elements like frame element, and it can model the distributed plasticity of plastic hinge. A 3 span continuos bridge is taken for seismic analysis. First, the nonlinear static analysis the column at fixed support are performed so that the characteristics of column is investigated. Second, the nonlinear dynamic analyses of the full bridge model is performed, considering 3 directional earthquake excitations.

• Proceedings of the IEEK Conference
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• summer
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• pp.47-51
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• 2004

In this paper we propose a fair and secure e-commerce model for P2P network, in which communication entities can buy and sell products by P2P contract. In particular, we focus on a fair transaction protocol that is based on a collaboration with distributed communication entities. This feature makes our model very attractive in P2P networking environment which does not depend on any central trusted authority for managing communication entities.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.224-229
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• 1999

In distributed object oriented environment based upon wide heterogeneous network, effective cooperation policies between/among distributed objects are needed to resolve a complexity of management of distributed objects because of growing of a large stale of systems. Thus, in this paper, we propose three trading cooperation models between/among traders for supporting a high speed and a wide selection of trader service for clients, by considering three different cooperation models(light weight trader, simple negotiation and federation) depending upon their facilities, goals, and weights of goals.

• Proceedings of the KIEE Conference
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• 2001.05a
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• pp.42-45
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• 2001

The islanding protection for distributed resources (DR) becomes an important and emerging issue in power system protection since the distributed generator installations are rapidly increasing and most of the installed systems are interconnected with distribution network. In order to avoid the negative impacts on distributed network resulting from islanding operations of DR, it is necessary to detect the loss of mains (LOM) effectively. This paper presents a new LOM detection method using the rate of change in total harmonic distortion (THD) of current. The proposed method effectively detects LOM of the DR unit operating in parallel with the distribution network. We also verified the efficiency of the proposed method using the radial distribution network of IEEE 34 bus model.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.665-670
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• 2000

The paper presents the dynamic instability of a disc brake pad subjected to distributed friction forces. A brake pad can be modeled as a beam with two translational springs. The study of this prototypical model is intended to provide a fundamental understanding of disc brake pad instabilities. Governing equations of motion are derived form energy expressions and their corresponding solutions are obtained by employing the finite element method. The critical distributed friction force and the instability regions are demonstrated by changing two translational spring constants. Finally, the changes of eigen-frequencies of a beam determining instability types are investigated for various combinations of two spring constants.