• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1849-1854
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• 2009

This paper describes the design, evaluation and implementation of a compensating algorithm for an iron-cored measurement current transformer (CT) that removes the effects of the hysteresis characteristics of the iron-core. The exciting current resulting from the hysteresis characteristics of the core causes an error of the CT. The proposed algorithm decomposes the exciting current into the core loss current and the magnetizing current and each of them is estimated. The core loss current is calculated from the secondary voltage and the voltage-core loss current curve. The core flux linkage is calculated and then inserted into the flux-magnetizing current curve to estimate the magnetizing current. The exciting current at every sampling interval is obtained by summing the core loss and magnetizing currents and then added to the measured current to obtain the correct secondary current. The voltage-core loss current curve and flux-magnetizing current curves, which are different from the conventional curves, are derived in this paper. The performance of the proposed algorithm is validated under various conditions using EMTP generated data. The experimental test results of an iron-core type electronic CT, which consists of the iron-core and the compensation board, are also included. The results indicate that the proposed algorithm can improve the accuracy of the measurement CT significantly, and thus reduce the size and the cost of the CT.

• Advances in concrete construction
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• v.8 no.3
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Smart Structures and Systems
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• v.24 no.3
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• pp.303-317
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• 2019

Magneto-rheological fluid (MRF) rotatory dampers are normally used for controlling the constant rotation of machines and engines. In this research, such a device is proposed to act as variable stiffness device to alleviate the rotational oscillation existing in the many engineering applications, such as motor. Under such thought, the main purpose of this work is to characterize the nonlinear torque-angular displacement/angular velocity responses of an MRF based variable stiffness device in oscillatory motion. A rotational hysteresis model, consisting of a rotatory spring, a rotatory viscous damping element and an error function-based hysteresis element, is proposed, which is capable of describing the unique dynamical characteristics of this smart device. To estimate the optimal model parameters, a modified whale optimization algorithm (MWOA) is employed on the captured experimental data of torque, angular displacement and angular velocity under various excitation conditions. In MWOA, a nonlinear algorithm parameter updating mechanism is adopted to replace the traditional linear one, enhancing the global search ability initially and the local search ability at the later stage of the algorithm evolution. Additionally, the immune operation is introduced in the whale individual selection, improving the identification accuracy of solution. Finally, the dynamic testing results are used to validate the performance of the proposed model and the effectiveness of the proposed optimization algorithm.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1111-1123
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• 2016

To study seismic performance of steel frame-bent structure, one specimen with one-tenth scale, three-bay, and five-story was tested under reversed cyclic lateral load. The entire loading process and failure mode were observed, and the seismic performance indexes including hysteretic loops, skeleton curve, ductility, load bearing capacity, drift ratio, energy dissipation capacity and stiffness degradation were analyzed. The results show that the steel frame-bent structure has good seismic performance. And the ductility and the energy dissipation capacity were good, the hysteresis loops were in spindle shape, which shape were full and had larger area. The ultimate elastic-plastic drift ratio is larger than the limit value specified by seismic code, showing the high capacity of collapse resistance. It can be helpful to design this kind of structure in high-risk seismic zone.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.455-458
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• 2002

In recent years, precision positioning stage is demanded fur some industrial fields such as semi conductor lithography, ultra precision machining and fabricating of nano structure. In this research, precision multi-axis positioning stage, which consists of pzt actuator, flexure, and capacitance gauge, is designed and developed. The performance of it such as 3-axis positioning, characteristic of motion and resolution is verified.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1388-1390
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• 1994

A polyimide-based capacitive humidity sensor has been designed and fabricated using silicon integrated-circuit technology, and its performance measured. The sensor showed excellent linearity, low temperature coefficient, and low hysteresis over a wide range of relative humidity and temperature. The signal conditioning circuits for detecting relative humidity and converting it to voltage have been developed based on a charge redistribution between capacitors using switched -capacitors.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.214-218
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• 2002

In recent years, precision positioning stage is demanded for some industrial fields such as semi-conductor lithography, ultra precision machining, and fabricating of nano structure. In this research, precision multi-axis positioning stage, which consists of pzt actuator, flexure, and capacitance gauge, is designed and developed. The performance of 3-axis positioning, characteristics of motion and resolution are verified.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.162-164
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• 1994

This paper proposes a servo control system of brushless motor at a low and high speed range. The control system is composed of the PI controller for high-speed control and the modified PI controller for low-speed control and the current controller using the hysteresis current control PWM method. The speed control performance is shown by the computer simulation.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1379-1394
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• 2002

In case of a single input single output (SISO) system with a nonlinear term, a signal compression method is useful to identify a system because the equivalent impulse response of linear part from the system can be extracted by the method. However even though the signal compression method is useful to estimate uncertain parameters of the system, the method cannot be directly applied to a unique system with hysteresis characteristics because it cannot estimate all of the two different dynamic properties according to its motion direction. This paper proposes a signal compression method with a pre-processor to identify a unique system with two different dynamics according to its motion direction. The pre-processor plays a role of separating expansion and retraction properties from the system with hysteresis characteristics. For evaluating performance of the proposed approach, a simulation to estimate the assumed unknown parameters for an arbitrary known model is carried out. A motion platform with several single-rod cylinders is a representative unique system with two different dynamics, because each single-rod cylinder has expansion and retraction dynamic properties according to its motion direction. The nominal constant parameters of the motion platform are experimentally identified by using the proposed method. As its application, the identified parameters are applied to a design of a sliding mode controller for the simulator.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.157.2-157.2
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• 2016

Water repellent surfaces may enhance the condensation by efficiently removing the condensed droplets. However, such surfaces may lose their original performance as they are exposed to external mechanical stresses. In this work, we fabricated spray-coated mechanically robust superhydrophobic surfaces using treated titanium dioxide (Type 1) or silica particles (Type 2). Then we compared the mechanical robustness of such surfaces with the silane-coated superhydrophobic surface and PEEK coated surface using a controlled-sand blasting method. The results show that the spray-coated samples can maintain the same level of the contact angle hysteresis than silane-coated superhydorphobic surface after sand blasting at 2 bar. The spray-coating method was applied to the tube type condenser and the condensation behaviors were observed within the environmental chamber with controlled pressure, humidity and non-condensable gas. Previously-reported droplet jumping was observed in the early stage of the condensation event, but soon the droplet jumping stopped and only dropwise condensation was observed since the condensed droplets were pinned on the cracks at spray-coated surfaces. The static contact angle decreases from $158.0^{\circ}$ to $133.2^{\circ}$, and hysteresis increases from $3.0^{\circ}$ to $23.5^{\circ}$ when active condensation occurs on such surfaces. This work suggests the benefits and limitation of spray-coated superhydrophobic condensers and help develop advanced condensers for practical use.