Stall inception and warning in a single-stage transonic axial compressor with axial skewed slot casing treatment

Characteristic changes in the stall inception in a single-stage transonic axial compressor with an axial skewed slot casing treatment were investigated experimentally. A rotating stall occurred intermittently in a compressor with an axial skewed slot, whereas spike-type rotating stalls occurred in the case of smooth casing. The axial skewed slot suppressed stall cell growth and increased the operating range. A mild surge, the frequency of which is the Helmholtz frequency of the compressor system, occurred with the rotating stall. The irregularity in the pressure signals at the slot bottom increased decreasing flow rate. An autocorrelation-based stall warning method was applied to the measured pressure signals. Results estimate and warn against the stall margin in a compressor with an axial skewed slot.     

Five New Oxylipins from Chaenomeles sinensis

In the course of our continuing search for bioactive constituents of Korean medicinal plants, we isolated five new oxylipins, chaenomic acid A–E ( 1 – 5 ), and six known ones ( 6 – 11 ) from the twigs of Chaenomeles sinensis. The structures of the new compounds ( 1 – 5 ) were determined by spectroscopic methods, including 1D and 2D NMR (¹H and ¹³C NMR, ¹H–¹H COSY, HMQC, HMBC, and NOESY), olefin cross‐metathesis, and LC/MS analysis. The known compounds ( 6 – 11 ) were identified by comparison of their spectroscopic data and specific optical rotation with the reported data. The isolated compounds ( 1 – 11 ) were tested for their inhibitory effects on nitric oxide production in lipopolysaccharide‐activated murine microglial cells and for their cytotoxic activities against four human cancer cell lines (A549, SK‐OV‐3, A498, and HCT‐15).     

Effect of nafion membrane thickness on performance of vanadium redox flow battery

The performance of vanadium redox ow batteries (VRFBs) using different membrane thicknesses was evaluated and compared. The associated experiments were conducted with Nafion® 117 and 212 membranes that have 175 and 50 μm of thickness, respectively. The charge efficiency (CE) and energy efficiency (EE) of VRFB using Nafion® 117 were higher than those of VRFB using Nafion® 212, while power efficiency was vice versa. In terms of amounts of charge and discharge that are measured in different charging current densities, the amounts in VRFB using Nafion® 212 are more than that in VRFB using Nafion® 117. To further characterize the effect of membrane thickness on VRFB performance, electrochemical impedance spectroscopy (EIS) and UV-vis. spectrophotometer (UV-vis) were used. In EIS measurements, VRFB using Nafion® 117 was more stable than that using Nafion® 212, while in UV-vis measurements, vanadium crossover rate of VRFB usingNafion® 212 (0.0125M/hr) was higher than that of VRFB using Nafion® 117 (0.0054 M/hr). These results are attributed to high crossover rate of vanadium ion in VRFB using Nafion® 212. With these results, vanadium crossover plays more dominant role than electrochemical reaction resistance in deciding performance of VRFB in condition of different membranes.     

Divergent vibration of a test cylinder with a control cylinder at the rear

The objective of this study was to experimentally investigate flow-induced vibration occurring in a test cylinder capable of free vibration when there was a control cylinder with a diameter half of that of the test cylinder behind the test cylinder. This paper intensively investigated divergent vibration among flow-induced vibration characteristics of the test cylinder. The mechanism for generating divergent vibration was also determined. To clarify the mechanism, flow-induced vibration characteristics of the test cylinder and wakes were investigated when the control cylinder was located closely to the rear of the test cylinder. Among tests for investigating wakes, a visualization test was also conducted using hydrogen bubble as a dye in a water channel. As a result, it was found that when the control cylinder was in close proximity to the rear of the test cylinder, the divergent vibration that appeared in the test cylinder was divided into three patterns based on vibration amplitude characteristics. Results of wake investigation revealed that the presence of the control cylinder affected the emission frequency, shape, and intensity of the vortex discharged from the test cylinder, which in turn affected vibration characteristics of the test cylinder. As a result of investigating flow-induced vibration characteristics of the test cylinder using different methods by changing the flow velocity, vibration inertia was found to one cause for the divergent vibration of the cylinder.

     

Improving tracking performance of industrial SCARA robots using a new sliding mode control algorithm

This paper addresses the implementation of a new sliding mode control algorithm for high speed and high precision tasks, which is robust against variations in the robot parameters and load. The effects of nonlinear dynamics, which are difficult to model accurately, become prominent in high speed operations. This paper attempts to treat the nonlinear dynamics of a SCARA robot as a disturbance. Based upon this approach, a new sliding mode control algorithm is proposed, in which a switching control input can be obtained easily and is determined to satisfy the existence condition for sliding mode control. A graphic simulator is used to evaluate the proposed algorithm for a SCARA robot. Simulation results show that the proposed algorithm is robust against disturbances and can reduce the magnitude of chattering, which is an unavoidable problem in sliding mode control. Experiments are carried out to validate the simulated results with an industrial SCARA robot using DSPs.     

A study on conformational changes by electron charges in viologen single molecules by using STM

The topography of self-assembled viologen derivatives (VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH) molecules on an octanethiol (C(8)) self-assembled monolayer (SAM) modified gold surface was measured using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). We demonstrate here a novel matrix SAM appropriate for isolation of the viologen molecules. The C(8) was used for a matrix SAM, in which the VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH were inserted at molecular lattice defects. The isolated single molecules of viologen derivatives inserted in the matrix SAM were observed as protrusions in STM topography using a constant current mode. We measured the topographic heights (VC(8)SH: 1.53nm, VC(10)SH: 2.01nm, HSC(8)VC(8)SH: 2.71nm, and HSC(10)VC(10)SH: 3.3nm) of the molecular protrusions using STM. Also, changes in the central axis of viologen molecules were observed as VC(8)SH (0.5-0.73nm), VC(10)SH (0.4-0.74nm), HSC(8)VC(8)SH (0.67-0.84nm), and HSC(10)VC(10)SH (0.67-0.99nm), respectively.     

Adaptive control and stability analysis of nonlinear crane systems with perturbation

This paper presents an adaptive control approach using a model matching technique for 3-DOF nonlinear crane systems. The proposed control is linearly composed of two control frameworks: nominal PD control and corrective control. A nonlinear crane model is approximated by means of feedback linearization to design nominal PD control avoiding perturbation. We propose corrective control to compensate system error feasibly occurring due to perturbation, which is derived by using Lyapunov stability theory with bound of perturbation. Additionally, we achieve stability analysis for the proposed crane control system and analytically derive sufficient stability condition with respect to its perturbation. Numerical simulation is accomplished to evaluate our proposed control and demonstrate its reliability and superiority compared to traditional control method.     

Continuous measurement of interaction forces between wheel and rail

Oscillatory wheel load fluctuation of considerable amplitude is always observed in railway cars traveling at high speed. This paper describes a continuous method for measuring the derailment coefficient and the forces between the wheel and rail. The acceleration measured on the axle box indicates that the frequency of this fluctuation can be as high as 70 Hz. Continuous measurement of wheel load using conventional methods is not possible due to this high frequency phenomenon. We have developed a new method for continuous measurement of these forces and the derailment coefficient using two pairs of strain gauge bridges with output phases shifted by 90°, and summing their outputs with a weighting function. This method works for measuring the forces between wheel and rail at high frequencies.     

Experimental study on heat transfer characteristics of internal heat exchangers for CO2 system under cooling condition

This paper presents the heat transfer characteristics of the internal heat exchanger (IHX) for CO₂ heat pump system. The influence on the IHX length, the mass flow rate, the shape of IHX, the operating condition, and the oil concentration was investigated under a cooling condition. Four kinds of IHX with a coaxial type and a micro-channel type, a mass flow meter, a pump, and a measurement system. With increasing of the IHX length, the capacity, the effectiveness, and the pressure drop increased. For the mass flow rate, the capacity of micro-channel IHX are higher about 2 times than those of coaxial IHX. The pressure drop was larger at cold-side than at hot-side. In the transcritical CO₂ cycle, system performance is very sensitive to the IHX design. Design parameters are closely related with the capacity and the pressure drop of CO₂ heat pump system. Along the operating condition, the performance of CO₂ IHXs is different remarkably. For oil concentration 1, 3, 5%, the capacity decreases and the pressure drop increased, as compared with oil concentration 0%. This paper was recommended for publication in revised form by Associate Editor Yong Tae Kang Prof. Young-Chul Kwon received his B.S. degree in Precision Mechanical Engineering from Pusan National University, Korea, in 1989. He then received his M.S. and Ph.D. degrees from POSTECH, in 1991 and 1996, respectively. Dr. Kwon is currently a Professor at the Division of Mechanical Engineering at Sunmoon University in Chungnam, Korea. He serves as a chief of the Institute of Automation and Energy Technology. Dr. Kwon’s research interests include heat exchanger, CO₂ cycle, heat pump, and energy recovery ventilator for HVAC&R. Mr. Dae-Hoon Kim is currently Doctoral student at the Mechanical Engineering from Hanyang University in Seoul, Korea. His research topics include experimental and numerical of CO₂ heatpump system. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Prof. Jae-Heon Lee received his B.S. degree in Mechanical Engineering from Seoul National University, Korea, in 1971. He then received his M.S. and Ph. D. degree from Seoul National University in 1977 and 1980, respectively. Dr. Lee is currently a Professor at the school of Mechanical Engineering at Hanyang University in Seoul, Korea. Dr. Lee is currently a president at the Korea Institute research interests include simulation of thermal fluid and Plant engineering and construction. Dr. Jun-Young Choi received his B.S. degree in Mechanical Engineering from Yonsei University, Republic of Korea, in 1989. He then received his M.S. and Ph. D. degrees from Yonsei University in 1991 and 1999, respectively. Dr. Choi is currently a chief researcher with the 18 years experience on the energy performance testing of HVAC/R product. He is now assigned to the Energy Technology Center at Basic Industry Division at Korea Testing Laboratory. He has been involved in the development of Design and Manufacturing Technology for Air-Conditioner E.E.R. and Performance Testing Equipment for Cooling and Heating System with Non-CFCs, and natural refrigerants. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Dr. Sang Jae Lee received his Ph.D. degree in Mechanical Engineering from Hanyang University, KOREA, in 2008. Dr. Lee is currently a Researcher at the Korea Institute of Industrial Technology in Cheonan, Korea. Dr. Lee’s research interests CO₂ heatpump system, liquid desiccant air conditioning system and Micro heat exchanger.