Pohang, South Korea
Pohang, South Korea
Time filter
Source Type

Cho S.-J.,Pohang University of Science and Technology | Jin M.,RIST | Kuc T.-Y.,SKKU | Lee J.S.,Pohang University of Science and Technology
Nonlinear Dynamics | Year: 2014

In this paper, we present a new technique, developed using time-delay estimation (TDE) and supervising switching control (SSC), for the control and synchronization of chaos systems. The proposed technique consists of three units: a time-delay estimation unit that cancels system dynamics, a pole placement control unit that shapes error dynamics, and an SSC unit that is activated when the system dynamics are rapidly changing. We prove the stability of the closed-loop system using the Lyapunov analysis method. To verify the control and synchronization performance of the proposed technique (TDE-SSC), we compare it with TDC using numerical simulation. Our results indicate that the proposed scheme is an easily understood, numerically efficient, robust, and accurate solution for the control and synchronization of chaos systems. © 2013 Springer Science+Business Media Dordrecht.

Seok S.-H.,RIST | Seok S.-H.,Tohoku University | Miki T.,Tohoku University | Hino M.,Tohoku University | Hino M.,Hokkaido Polytechnic College
ISIJ International | Year: 2011

The Ti deoxidation equilibrium of Fe-Ni, Fe-Cr and Fe-Cr-Ni alloys saturated with 'Ti3O5' and Ti2O3 phase was clarified in previous researches. Solubility of Fe, Cr and/or Ni oxides in 'Ti3O5' phase equilibrated with liquid Fe-Ni, Fe-Cr and Fe-Cr-Ni alloys at 1823 K to 1923 K were measured by SEM-EDS. It was confirmed that the solubility of Fe, Cr and/or Ni oxide in 'Ti3O 5' phase at low Ti content increase with decrease of Ti content in alloys. Titanium content that dissolution of Fe, Cr and/or Ni oxide into 'Ti3O5' phase becomes apparent increases with increase of Cr and/or Ni content of the alloys. The activity of Ti deoxidation product, 'Ti3O5' phase, equilibrated with Fe-Ni, Fe-Cr and Fe-Cr-Ni alloys was also evaluated by Redlich-Kister type polynomial. Equilibrium between Ti and O at low Ti content of those alloys was analyzed using the activity of 'Ti3O5' phase. © 2011 ISIJ.

Ham G.-S.,Andong National University | Kim H.-J.,RIST | Ji D.-H.,New Energy And Industrial Technology Development Organization | Lee K.-A.,Andong National University
Key Engineering Materials | Year: 2016

A Cu-36at.%In-15at.%Ga coating layer is manufactured using a warm spray process and ternary alloy powders. The powder used had a particle-size distribution of 5∼22μ with a spherical shape and average particle size of 11.6μ. Pure aluminum plate was used as a substrate. As a result, a CIG coating layer with 120μ thickness was successfully obtained. In order to improve the density of the coating layer, post heat treatment was applied for 1 hour in each condition of 200, 300 and 400°C. Phase analysis of the powder initially used identified Cu9In4, Cu9Ga4 phases, and Cu9In4, Cu9Ga4, Cu3Ga phases were identified after warm spraying. As heat treatment was applied, porosity decreased from 0.98% (as sprayed) to 0.8% (400°C), showing an increase in density, and hardness also decreased from 304Hv (as sprayed) to 258Hv (400°C). © 2016 Trans Tech Publications, Switzerland.

Lee K.-A.,Andong National University | Jin Y.-M.,Andong National University | Sohn Y.-H.,Advanced Materials Processing and Analysis Center | Namkung J.,RIST | Kim M.-C.,RIST
Metals and Materials International | Year: 2011

This study tried to examine the suitability of strip casting processes such as PFC for soldering Au-Sn strips and to investigate changes in the microstructure and mechanical properties of the manufactured strips, following heat-treatment. Optimal production conditions were established for Au-20 %Sn strips and implemented to actually produce them. The inhomogeneous microstructure with indistinct phases that was present prior to heating was transformed into a homogeneous microstructure in which the continuous Au 5Sn phase surrounded the ìm-sized AuSn phases. Tensile results showed that the as-cast strip exhibited zero plasticity and a tensile strength of 338.3 MPa. After heating, the figure dropped somewhat while the plastic strain improved to 1.6%. As for the enhanced plasticity in the heat-treated strip, the continuous pattern of the ductile Au5Sn that surrounds the brittle AuSn was assumed to have caused plastic strain to take place on the boundaries of two phases, therefore resulting in the initiation and propagation of cracks. © KIM and Springer.

Lee J.,Italian Institute of Technology | Dallali H.,Italian Institute of Technology | Jin M.,RIST | Caldwell D.,Italian Institute of Technology | Tsagarakis N.,Italian Institute of Technology
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2016

This paper focuses on the development of a dynamic model-free whole-body controller for a humanoid robot with high kinematic redundancy. The proposed controller is based on force-level operational-space control framework, which computes joint torques for the required forces of prioritized multiple tasks. While typical approaches based on this framework require to obtain an accurate robot dynamics model, which has been generally recognized as a major hurdle to overcome for implementation in real humanoid robots, the proposed controller incorporates adaptive sliding-mode and online dynamics estimation schemes; thus, it can be easily realized on a humanoid without identifying complex robot dynamic parameters. As a result, the gains of the proposed controller are adaptively adjusted to assure the control accuracy, when the humanoid robot changes its posture and undergoes uncertain disturbances. Experiments with a 23-DoFs humanoid under uncertain disturbances verify that the proposed controller can robustly perform multiple tasks with high accuracy. © 2016 IEEE.

Lee D.,RIST | Lee T.,Seil Engineering
European Wind Energy Association Conference and Exhibition 2014, EWEA 2014 | Year: 2014

Four jacket substructures are designed for the four different offshore wind turbines (3.0MW, 5.0MW, 5.5MW, 7.0MW), which are under development in Korea. Transition pieces connecting towers and substructures are also designed in this basic design. In order to confirm safety of the substructures and transition pieces, dynamic characteristics, member stress level, maximum lateral displacement, geotechnical resistance, and pile driving is investigated in this project. Slop of the jacket leg is adjusted to avoid a resonance between the upper part and the lower part. Three different jacket brace layouts are considered in the structural designing part. Unfortunately, fatigue check has not been executed in this basic design. Usually, jacket substructures can be installed by either pre-piling method or post-piling method. Considering ocean environmental condition of the South-West Offshore Wind Farm project site and previous experience of the Korean construction engineers, post-piling method is selected for the offshore installation of the designed jacket substructures. Combination of installation vessel and equipment is also considered in this basic design.

An C.M.,Colorado School of Mines | Song J.-H.,RIST | Kang I.,Colorado School of Mines | Sammes N.,Colorado School of Mines
Journal of Power Sources | Year: 2010

In this paper, a graded Ni/YSZ cermet anode, an 8 mol.%YSZ electrolyte, and a lanthanum strontium manganite (LSM) cathode were used to fabricate a solid oxide fuel cell (SOFC) unit. An anode-supported cell was prepared using a tape casting technique followed by hot pressing lamination and a single step co-firing process, allowing for the creation of a thin layer of dense electrolyte on a porous anode support. To reduce activation and concentration overpotential in the unit cell, a porosity gradient was developed in the anode using different percentages of pore former to a number of different tape-slurries, followed by tape casting and lamination of the tapes. The unit cell demonstrated that a concentration distribution of porosity in the anode increases the power in the unit cell from 76 mW cm-2 to 101 mW cm-2 at 600 °C in humidified hydrogen. Although the results have not been optimized for good performance, the effect of the porosity gradient is quite apparent and has potential in developing superior anode systems. © 2009 Elsevier B.V. All rights reserved.

Kwon Y.B.,Yeungnam University | Kim G.D.,RIST | Kwon I.K.,Kangwon National University
Steel and Composite Structures | Year: 2014

This paper describes a series of compression tests performed on cold-formed steel channel sections with perforations in the web (thermal studs) fabricated from a galvanized steel plate whose thickness ranged from 1.0 mm to 1.6 mm and nominal yield stress was 295 MPa. The structural behavior and performance of thermal studs undergoing local, distortional, or flexural-torsional buckling were investigated experimentally and analytically. The compression tests indicate that the slits in the web had significant negative effects on the buckling and ultimate strength of thin-walled channel section columns. The compressive strength of perforated thermal studs was estimated using equivalent solid channel sections of reduced thickness instead of the studs. The direct strength method, a newly developed and adopted alternative to the effective width method for designing cold-formed steel sections in the AISI Standard S100 (2004) and AS/NZS 4600 (Standard Australia 2005), was calibrated to the test results for its application to cold-formed channel sections with slits in the web. The results verify that the DSM can predict the ultimate strength of channel section columns with slits in the web by substituting equivalent solid sections of reduced thickness for them. Copyright © 2014 Techno-Press, Ltd.

Park J.-Y.,Yonsei University | Chang W.-S.,RIST | Sohn I.,Yonsei University
Science and Technology of Welding and Joining | Year: 2012

The effect of MnO on the hydrogen solubility in the CaF 2-CaO-SiO 2 based welding flux system at 1823 K has been studied. At an acidic slag composition of CaO/SiO 2 molar ratio or basicity of 0·8 and below, MnO addition decreased the hydrogen solubility. At an intermediate slag composition of CaO/SiO 2 molar ratios of 1·1 and 1·3, the hydrogen solubility as a function of MnO additions resulted in a parabolic behaviour showing a minimum and then increasing with higher MnO content. MnO was found to behave as a basic oxide, which decreases the hydrogen solubility when the incorporation hydroxyl mechanism is dominant for an acidic slag and increases the hydrogen solubility when the free hydroxyl mechanism is dominant for a basic slag. This change in the dominant hydrogen dissolution mechanism was also apparent from the hydrogen solubility results at various CaO/SiO 2 molar ratios and fixed MnO contents. A higher hydrogen solubility in the slag is likely to lower the diffusible hydrogen content in the weld metal, and optimum MnO additions were suggested depending upon the basicity of the slag. Fourier transformed infrared analysis of as quenched slags showed that MnO depolymerised the slag network structure and correlated well with the effect on the hydrogen solubility in slags. © 2012 Institute of Materials, Minerals and Mining.

Rist | Date: 2012-11-14

Touch-free toilet-seat paper dispensing device comprising a case (13) containing toilet-seat papers (10), a mounting plate (5) fixed to the inside of the door of the case (13), and an electronic unit (9), a motor, a paper supply roller (3) mounted uniaxially with the motor, as well as a microswitch and a microswitch activating cam located on the mounting plate (5).The case (13) is wall-mountable and is equipped with an openable door and an opening on its lower part. A sensor (1) is installed in the door of the case (13), and the folded toilet-seat papers (10) are fixed in the case (13) on the side opposite to the door.

Loading RIST collaborators
Loading RIST collaborators