• Computational Structural Engineering
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• v.7 no.3
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• pp.143-152
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• 1994

Superelement technique for structural analysis of large scale objects such as airplanes or vessels is effective especially in the harsh hardware environments. In this paper, a crane vessel of OHI 5000 which is capable of lifting 5000 tons in tie-backs and capable of revolving with 3000 tons is investigated in the view point of structural safety using superelements through the substructure scheme. Also an effective substructure procedure, a unique load extraction method and finite element modeling technique are demonstrated. Comprehensive reinforcement blueprints are derived based on the analysis results. Successful application of substructure technique is achieved through the structural analysis of the crane vessel. The analysis technique developed in this paper can be a guideline for similar large scale structures' relevant safety identification.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.409-420
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• 2002

This paper proposed a technique of structural re-analysis for the evaluation of dynamic responses of bridge structure under moving loads using experimental modal results. For successful structural re-analysis, it is required to have accurate estimation techniques of the modal characteristics of bridge structures. The natural frequencies and mode shapes were identified by direct fourier analysis techniques and damping ratios by the random decrement method, respectively. An interpolation method was also proposed for the extension of mode shape measured on limited DOFs. Second, the structural reanalysis was performed using moving mass model and identified modal parameters. The results from the reanalysis show that the proposed technique is very reasonable to evaluate the actual behavior of bridge structures under moving loads.

• Earthquakes and Structures
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• v.13 no.5
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• pp.473-484
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• 2017

The objective of this paper is to report on a study of the use of unstiffened thin steel plate shear walls (SPSWs) for the seismic performance improvement of reinforced concrete frames with deficient lateral rigidity. The behaviour of reinforced concrete frames during seismic activities was rehabilitated with an alternative and occupant-friendly retrofitting scheme. The study involved tests of eight 1/3 scale, one bay, two storey test specimens under cyclic quasi-static lateral loadings. The first specimen, tested in previous test program, was a reference specimen, and in seven other specimens, steel infill plates were used to replace the conventional infill brick or the concrete panels. The identification of the load-deformation characteristics, the determination of the level of improvement in the overall strength, and the elastic post-buckling stiffness were the main issues investigated during the quasi-static test program. With the introduction of the SPSWs, it was observed that the strength, stiffness and energy absorption capacities were significantly improved. It was also observed that the experimental hysteresis curves were stable, and the composite systems showed excellent energy dissipation capacities due to the formation of a diagonal tension field action along with a diagonal compression buckling of the infill plates.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.4
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• pp.35-44
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• 1989

In this paper, a precisely speed-controlled DC servo motor system utilizing direct adaptive control (DAC) algorithm which require that neither satisfaction of the perfect model following conditions (PMFC) nor explicit parameter identification is proposed. Computer simulation as well as experiments using MC-68000 are implemened with the above input trajectory fairly well in spite of load disturbances and parameter variations. Presented algorithm is simple and effective both in software and hardware applications.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.1
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• pp.60-68
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• 1999

This paper deals with the tracking control problem of industrial robotic manipulators with unknown or changing dynamics. The proposed method makes use of multiple moodels and switching mechanism by fuzzy inference of the manipulator in an indirect adaptive controller architecture. The models used for the indmtification of the manipliator are identical, except for the initial estimates of the unknown inertial pararmeters of the manipulator and its load. The torque input that is applied to the joint actuators is determined at every instant by the identification model that best approximates the robot dynamics. Simulation results are also included to dermnstrate the improvement in the tracking perfermance when the proposed method is used.s used.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.106-113
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• 2004

Most of mechanical structures are composed of many substructures connected to one another by various types of mechanical joints. In automotive engineering, it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. In this study, the dynamic response of vehicle structure to external forces is classified an inverse problem involving strains from the experiment and the analysis. The practical dynamic forces are determined by the combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit force and with measured strain by a strain gage under driving load, respectively. In a stressed body, inter-molecular chemical bonds are failed beyond the certain magnitude. The failure of molecular structure in material is considered as a time process of which rate is determined by mechanical stress. That is, the failure of inter-molecular chemical bonds is the fatigue lift of material. This kinetic concept is expressed as lethargy coefficient. And S-N curve is obtained with the lethargy coefficient from quasi-static tensile test. Equivalent practical dynamic force is obtained from the identification of practical dynamic force for one loading point. Using the practical dynamic force and S-N curve, fatigue life of a window pillar is analyzed with FEM under the identified force by the procedure of above mentioned.

• Journal of Navigation and Port Research
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• v.31 no.2
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• pp.141-149
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• 2007

The competitiveness of container terminals hinges on minimizing the time vessels spend in port and on schedule services. Many previous researches on container terminals have tried to optimize the equipment allocation plan and to improve the activity of resources. Nevertheless, there have been few researches conducted on yard tractors, which move containers between the quay and the yard. The aim of this study is to propose the use of Real Time Location Systems (RTLS) based Dynamic Planning for yard tractors. Only RFID (Radio Frequency Identification) tags, which are attached to yard tractors, are able to support RTLS implementation. The system can provide real time job ordering in terms of load balancing using the information on location, in regards to the movement of yard tractors. This study will present the practical feasibility of RTLS, which can ultimately reduce the congestion of Hot Queues in container terminals. As a result, container terminals can be more productive and competitive. In order to accomplish the purpose of this study, we examined previous studies on the competitiveness of container terminals and summarized the potential of RTLS using RFID. In addition, we identified the role of yard tractors and proposed the two rules of Dynamic Planning for the yard tractors. We then fulfilled computational experiments on how yard tractors carrying containers by RTLS ordering Finally, the benefits and the implications of this study are discussed.

• Korean Journal of Metals and Materials
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• v.48 no.8
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• pp.780-789
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• 2010

The aim of this study is to evaluate the microstructure and tensile property of in-situ (TiB+TiC) particulate reinforced titanium matrix composites (TMCs) synthesized by the investment casting process. Boron carbide ($1,500{\mu}m$ and $150{\mu}m$) was added to the titanium matrix during vacuum induction melting, which can provide the in-situ reaction of $5Ti+B_4C{\rightarrow}4TiB+TiC$. 0.94, 1.88 and 3.76 wt% of $B_4C$ were added to the melt. The phases identification of the in-situ synthesized TMCs was examined using scanning electron microscopy, an X-ray diffractometer, an electron probe micro-analyzer and transmission electron microscopy. Tensile properties of TMCs were investigated in accordance with the reinforcement size and volume fraction. The improvement of tensile property of titanium matrix composites was caused by load transfer from the titanium matrix to the reinforcement and by grain refinement of titanium matrix and reinforcements.

• Smart Structures and Systems
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• v.24 no.2
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• pp.209-221
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• 2019

The classical Kalman filter (KF) provides a practical and efficient way for state estimation. It is, however, not applicable when the external excitations applied to the structures are unknown. Moreover, it is known the classical KF is only suitable for linear systems and can't handle the nonlinear cases. The aim of this paper is to extend the classical KF approach to circumvent the aforementioned limitations for the joint estimation of structural states and the unknown inputs. On the basis of the scheme of the classical KF, analytical recursive solution of an improved KF approach is derived and presented. A revised form of observation equation is obtained basing on a projection matrix. The structural states and the unknown inputs are then simultaneously estimated with limited measurements in linear or nonlinear systems. The efficiency and accuracy of the proposed approach is verified via a five-story shear building, a simply supported beam, and three sorts of nonlinear hysteretic structures. The shaking table tests of a five-story building structure are also employed for the validation of the robustness of the proposed approach. Numerical and experimental results show that the proposed approach can not only satisfactorily estimate structural states, but also identify unknown loadings with acceptable accuracy for both linear and nonlinear systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.6
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• pp.45-54
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• 2003

A public key certificate may be revoked before its validity period due to causes like the owner identification information change or the private key damage. Since a certificate has long valid time relatively, it is possible to become revoked during lifetime of certificate. The main technical issue in the public key infrastructure is how to handle the status of the certificate. We propose a simple mechanism for online certificate status validation that is suited to the financial network The characteristic of the proposed method is to broadcast certificate revocation information by using verifier list. The experimental results provide the same realtime as OCSP(Online Certificate Status Protocol). The proposed mechanism reduces the network load for certificate status validation in highly concentrated unbearable network.