Adaptive Mesh Generation for Planar Problems for Dynamic Finite Element Analysis

Jung, Yochan,Hong, Seungpyo,Yoon, Chongyul Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The finite element method(FEM) is an approximate method that is used in various analyses. In order to use the finite element method in a structural analysis, users choose both element type and mesh. Adaptive mesh generation is a technique that improves the accuracy of FEM results through refinements of mesh using the results from the previous analysis step. In this study, the concept of representative strain value is introduced to analyze structures subjected to dynamic loadings using adaptive mesh generation. Representative strain is a sign of error in an element based on the standard deviation of strains. The scheme uses both the h-method and the r-method for adaptive mesh generation. The study presents criteria for regenerations of meshes that apply both the r-method and the h-method. This study examines the validity of the strategy to obtain an effective mesh through a cantilever example under a concentrated load with varying values. The proposed strategy reduces calculation time and a good accuracy is obtained.

The Simulation of Reactor Physics Test for the Research Reactor HANARO

Noh, Taewan Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The paper describes the development of a reactor power control algorithm using the program simulator for the simulation of dynamic behavior of a nuclear reactor. Before the full development of the algorithm for the commercial nuclear power plant, the Korean research reactor HANARO was chosen as a sample reactor for the simulation and for the reactor physics test. All the dynamic characteristics of HANARO were mathematically modeled into a computer program and the parameters of the plant components and the algorithm of reactor control system are adjusted to improve the transient performances as well as to satisfy the constraints imposed on the plant. Several physics parameters such as control rod worth, isothermal temperature defect, and power defec are correlated. These parameters were measured in serial order at the same core condition. The transient response of the plant shows satisfactory behavior and are well corresponding to the result of reactor physics test.

Synthesis and photophysical study of heteroleptic iridium(III) complex

Kim, Jun Ho,Kim, Young Sik Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (CˆN) ligands are reported. In order to improve the luminescence efficiency by avoiding triplettriplet (T-T) annihilation, the iridium complex, Ir(ppy)_(2)(dpq), is designed and prepared where ppy and dpq represent 2-phenylpyridine and 2,4-diphenylquinoline, respectively. Two ppy ligands and a dpq ligand act as a source of energy supply. Since Ir(ppy)_(3) and Ir(dpq)_(3)can be placed in the metal-to-ligand charge transfer (MLCT) excited state, they absorb light effectively. When Ir(ppy)_(2)(dpq) is placed in excited state, the excitation energy is not quenched or deactivated but quickly intramolecular transferred from two ppy ligands to one luminescent dpq ligand. This is because the triplet energy level of ppy is higher than that of dpq and light is emitted from dpq ligand in the end. Thus, Ir(ppy)_(2)(dpq) shows strong photoluminescence from dpq ligand. To analyze luminescent mechanism, we calculated these complexes having two different ligand sets theoretically by using computational method.

Development of Rainfall Runoff Forecasting Model for Water Resources Management in a Catchment Scale

Song, Jaiwoo,Jeong, Woochang Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The purpose of this study is to acquire how to construct a real-time rainfall-runoff forecasting system (RRFS) to analyze the streamflow states of the major points at up and downstream of adam in order to simulate the low flow in the dry season as well as to improve the uncertainty of flood prediction in the flood season.The RRFS includes the following functions; 1) integrated management of water quantity and water quality, 2) identification of characteristics of water use for municipal, industrial and agricultural purposes, 3) derivation of hydrologic rainfall-runoff relationship, and 4) estimation of streamflow by sub-basins and major points. In this paper, it will be introduced the RRFS developed by the web-based interface technology and also its application to the Geum river basin.

Active Audit and Topology Adaptation in Unstructured P2P Overlay Networks

Park, Jun-Cheol Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

To make a peer-to-peer(P2P) network free from selfish or malicious peers is a challenging task because of the flat, fully distributed, autonomous, and anonymous nature of such networks. In this paper, we focus on a peer's intentional act of dropping a relaying message, which is hard to be traced to its doer. We propose an audit and topology adaptation scheme to confine and weaken the ill effect from peers dropping messages on other peers in an unstructured P2P network. Using active network technologies, the scheme makes some routers with augmented capability assist the peers in adjusting their overlay connections. It uses a small set of basic primitives only and thus applies to all kinds of unstructured P2P networks. In fact, any legacy peer can execute the algorithm used in the scheme for its own gain by issuing a single query as if it were searching for a file. The scheme encourages the peers to comply with the protocol of the network, which leads to the improvement of service quality and peer satisfaction level. As preliminary results, a restricted usage pattern of the scheme is experimented using various metrics, which demonstrates the practicality of the approach.

Object Tracking and Elimination using Level-of-Detail Canny Edge Maps

Park, Jihun Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

We propose a simple method for tracking a nonparameterized subject contour in a single video stream with a moving camera. Then we eliminate the tracked contour object by replacing the background scene we get from other frame that is not occluded by the tracked object. Our method consists of two parts: first we track the object using LOD (Level-of-Detail) canny edge maps, then we generate background of each image frame and replace the tracked object in a scene by a background image from other frame. In order to track a contour object, LOD Canny edge maps are generated by changing scale parameters for a given image. A simple (strong) Canny edge map has the smallest number of edge pixels while the most detailed Canny edge map, Wcanny_(N) , has the largest number of edge pixels. To reduce side-effects because of irrelevant edges, we start our basic tracking by using simple (strong) Canny edges generated from large image intensity gradients of an input image, called Scanny edges. Starting from Scanny edges, we get more edge pixels ranging from simple Canny edge maps until the most detailed (weaker) Canny edge maps, called Wcanny maps along LOD hierarchy. LOD Canny edge pixels become nodes in routing, and LOD values of adjacent edge pixels determine routing costs between the nodes. We find the best route to follow Canny edge pixels favoring stronger Canny edge pixels. The first frame background scene is determined by camera motion, and other background scenes are computed from the previous background scenes.

Eigenvalue Analysis of Overhang Structures by Pseudospectral Method

Lee, Jinhee Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The pseudospectral method is applied to the free vibration analysis of overhang structures which consist of Timoshenko beams. The analysis is based on the Chebyshev polynomials. Each section of the overhang structure has its own basis functions, and the continuity conditions at the intermediate support as well as the boundary conditions are treated separately as the constraints of the basis functions. Natural frequencies of overhang structures with pinned-pinned-free support conditions are provided for different thickness-to-length ratios and for different span ratios. The computed natural frequencies agree with those of Euler-Bernoulli beams when the thickness-to-length ratio is small but deviate considerably as the thickness-to-length ratio grows larger.

The Effect of Train Acceleration on the Pantograph Dynamics

Kim, Jung Soo Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

The dynamic characteristics of the pantograph are evaluated by conducting a test run in which signals from accelerometers and load cells attached to the various parts of the pantograph assembly are evaluated. By analyzing these signals, it has been found that the dynamic characteristics of the pantograph are strongly influenced by the train speed, with the major frequency components arising from the train traversing the span spacing and the 8.5 Hz component originating from the panhead resonance. The train acceleration is found to have significant influence on the span passing frequency but negligible effect on the resonant response.

A study on various phase-shifted fiber grating realization methods

Park, Dongwook Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

We analyze the spectral characteristics of the various types of phase-shifted fiber Bragg gratings that can be realized by controlling the UV exposure during the grating formation process. In particular, their reflection spectra are computed and compared against those of the ideal discrete phase-shift version.

Neural Network Based Trajectory Tracking Control for Intelligent Pneumatic Servo Systems

Cho, Seung Ho Research Institute of Science and Technology HONGI 2005 Hongik Journal of Science and Technology Vol.9 No.-

This paper proposes a neural network based trajectory tracking control scheme for intelligent pneumatic servo systems. The PID controllers are currently widely used in industrial applications because they are simple, cheap and show good performance. However, it is limited in some applications where the nonlinear effect is dominant. Pneumatic systems have inherent nonlinearities such as compressibility of air and nonlinear frictions present in cylinders. A neural network is combined with PID control to compensate for these nonlinearities. A trajectory tracking control experiment using the proposed control scheme has been performed and a significant reduction in tracking error is achieved.