• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.1
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• pp.35-42
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• 2021

This paper presents an on-line finite element model updating method for in-service structures using measured data. Conventional updating methods, which are based on numerical optimization, are not efficient for on-line updating because they generally require repeated eigenvalue analyses until convergence criteria are met. The proposed method enables fully automated on-line finite element model updating, almost simultaneously with vibration measurement, without any user intervention or off-line procedures. The automated covariance-driven stochastic subspace identification (Cov-SSI) method is utilized to identify modal frequencies and vectors, and the identified modal data is fed to the neural network of the inverse eigenvalue function to produce the updated finite element model parameters. Numerical examples for a wind excited 20-story building structure shows that the proposed method can update the series of finite element model parameters automatically. It is also shown that sudden changes in the structural parameters can be detected and traced successfully.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.2
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• pp.121-128
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• 2021

In this paper, we propose a path generation and tracking algorithm of an unmanned air vehicle in a two-dimensional plane given the initial and final points. The path generation algorithm using the Dubins curve proposed in this work has the advantage that it can be applied in real time to an unmanned air vehicle. The path tracking algorithm is an algorithm similar to the line-of-sight induction algorithm. In order to efficiently control the direction angle, a gain related to the look ahead distance concept is introduced. Most of UAVs have the limited maximum curvature due to the structural constraints. A numerical simulation is conducted to follow the path generated by the sliding mode controller considering the angular velocity limit. The path generation and tracking performance is verified by comparing the suggested controller with conventional control techniques.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.171-174
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• 2010

적절한 근사화 과정을 통하여 구축된 축소 시스템은 전체 시스템의 거동을 적은 수의 정보를 통하여 효과적으로 표현할 수 있다. 효과적인 시스템 축소를 위하여 본 연구에서는 주파수 영역 Karhunen-Loeve (Frequency-domain Karhunen-Loeve, FDKL) 기법과 시스템 등가 확장 축소 과정(System equivalent expansion reduction process, SEREP)을 연동한 축소 기법을 제안한다. 적합직교분해(Proper orthogonal decomposition)의 한 방법인 FDKL기법을 통하여 최적모드(Optimal mode)를 구하고 이에 SEREP을 적용하여 자유도 변환 행렬을 구한다. 이때 주자유도 선정은 2단계 축소기법을 적용한다. 최종적으로 제안된 기법은 수치예제를 통하여 검증한다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1732-1739
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• 2017

This paper presents a sensorless vector control algorithm of closed loop Gopinath flux observer to enhance the robustness at low speed by switching P/PI mode. Closed loop Gopinath flux observer has the problem in sensorless vector control of induction motor at low speed. This paper solves the problem using the characteristic function of closed loop Gopinath flux observer. P mode shows better performance than PI mode under the cut-off frequency of observer. But P mode always has a flux error due to DC offset, so this paper combines P mode and PI mode. This algorithm shows good performance over wide speed range. The performance has been confirmed through computer simulations using MATLAB SIMULINK and experiments.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.729-738
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• 2021

Feedback flow control using an artificial neural network was numerically investigated for NACA0015 Airfoil to suppress flow separation on an airfoil. In order to achieve goal of flow control which is aimed to reduce the size of separation on the airfoil, Blowing&Suction actuator was implemented near the separation point. In the system modeling step, the proper orthogonal decomposition was applied to the pressure field. Then, some POD modes that are necessary for flow control are extracted to analyze the unsteady characteristics. NARX neural network based on decomposed modes are trained to represent the flow dynamics and finally operated in the feedback control loop. Predicted control signal was numerically applied on CFD simulation so that control effect was analyzed through comparing the characteristic of aerodynamic force and spatial modes depending on the presence of the control. The feedback control showed effectiveness in pressure drag reduction up to 29%. Numerical results confirm that the effect is due to dramatic pressure recovery around the trailing edge of the airfoil.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.69-78
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• 2002

This paper describes the analysis results for tensile behavior of tubular column to H-beam connection with T stiffeners. Using the elasto-plastic finite element method, analysis results are compare with experimental results. Parametric analyses with different size of T-stiffener have conducted to understand the stress distribution at the connections. Stress concentration in elastic region and PEEQ distribution in plastic region are plotted for different shape. The results of analysis were applied to design equations and were checked for the applicability of design equations.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.637-647
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• 1997

As stated in Part(I), the use of the isolator is meant to protect a structure from seismic risk, by concentrating the inelastic deformations to relatively cheap and replaceable devices while the rest of the structures remains elastic. This research has been carried out to investigate the effects of various structural parameters and isolator characteristics on the seismic response of Base Isolated Bridges. Simplified analysis method for practical design is developed by using the results. The Proposed Code-Type approach method can be used to estimate the inertial forces accurately, not only at the isolator but throughout the height of the Base-Isolated Bridges. The proposed method is recommended to use in preliminary design tool or even a final design tool for Base Isolated Bridges. For the validation of simplified design method, examples with artificial earthquake time history and design response spectrum for P.C Box Bridge with bilinear hysteretic steel damper are evaluated.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.67-71
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• 1990

This study is concerned with the optimum design of stiffened cylindrical members frequently found in floating offshore platforms with constraints on reliability. Minimised is the expected total cost which is composed of the structural cost and the expected failure cost. Some design requirements drawn from variotus design codes are also considered as constraints. Reliability of critical component in a structure only is considered in this paper and the system failure is discarded since the probability of system failure is in general much smaller than the probability of component failure and it is very difficult to evaluate the cost due to system failure. Ultimate strength only is considered and not the fatigue strength. Several parametric studies are illustrated and the optimum solutions for different strength models which are now in use for the design of stiffened cylinders are derived to show the optimum designs against different strength models for the same type of structural component. The present results lead to the important conclusions relating to the posibility of more cost saving in the design of such structure through the reliability-based optimisation process.

• The Journal of the Korea Contents Association
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• v.19 no.6
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• pp.481-490
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• 2019

The purpose of this paper is to recognize and embody the implications of the concept of interactivity. Among the many types of interactivity already proposed, this paper sheds light especially on the so-called contingent interactivity. The contingency means a condition in which a particular performance or selection of a subject is considered neither necessary nor conclusive, and also the potential for various activities of this subject. The contingent interaction comes into being when the involvements of users in dealing with a message or content are experimental or creative. The interaction does not orient toward the completion of content or the immersion to a particular reality. Rather, the results of a user's contingent performance are not the finalized content and have characteristics that lead to the continuous modification. In order to embody this meaning of contingent interactivity, the paper examined the two example, the film re-cut and game modding. In both cases, it is comprehensive that the user of these two new media activities lies in the contingent situation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.5
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• pp.518-527
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• 2016

The present study considers the usage of concentrated forces to simulate real panel flutter. The concept of using concentrated forces have been validated for studying the flutter of wing structure in subsonic flow, yet its application in the supersonic region remained to be explored. Hence, a simply supported panel subjected to forces, equivalent to aerodynamic force is considered for studying supersonic panel flutter. The distributed aerodynamic forces are approximated to few concentrated forces by taking numerical integration. The aeroelastic equation is formulated using the classical small-deflection theory and the piston theory for linear panel flutter whereas for emulated panel flutter the flutter equation is derived by replacing the pressure due to aerodynamic loading with pressure from concentrated loading. Finally, flutter frequency, flutter dynamic pressure, and corresponding mode shape are found for emulated panel flutter and compared with linear panel flutter. Two important parameters, the number of concentrated forces and their location are discussed through numerical examples and optimization process respectively. So far, the flutter results acquired in this study are reasonable to suggest the feasibility of reproducing panel flutter using concentrated forces.