• Journal of Power Electronics
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• v.11 no.2
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• Clean Technology
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• v.19 no.3
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• pp.295-299
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• 2013

This study was purposed and performed to evaluate removal efficiency of non-point source pollution in the process and system based on bio-retention design criteria regulated by EPA. Basic Column Reactors (BCR) were prepared for optimal determinations of inflow rate of first rainfall runoff and composition and ratio of soil layers. Removal efficiencies of non-point source pollution from synthetic runoff and real first rainfall runoff, directly sampled from motor way and parking lot, were analyzed, respectively. Removal efficiency of SS, BOD, COD, T-N, and T-P were all shown to be more than 80%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.351-358
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• 2016

An Electrical Point Machine (NS:New-type Switch), which is equipped and operated at railways in Korea, has been used since the 1960s after being imported from Japan. On the other hand, although the mechanical configuration has improved the position motor control circuit, the electrical connection has not been improved, so NS may have a problem, such as the interlocking system of automatic train operation. In addition, NS is the most vulnerable part in the railway system and a huge train accident may occur due to minor defects. The existing NS wiring set of the circuit controller should be checked only if fixed. Therefore, an excessive inspection time only by a Railroad Signal expert is required. In this paper, the improvement of electrical connection in a NS wiring set, such as the position motor control circuit, was developed and the prototype was installed at Seoul Metro in the distance to go section. The results can be used to help make appropriate adjustments. The improvement of the NS wiring set enhance the maintenance efficiency, passenger service and the stability of the signal system as well as reducing the maintenance cost.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.367-368
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• 2009

BSCCO HTS(High Temperature Superconductor) could be applied to superconducting cable, magnet and motor, using its hight critical properties. Especially, superconducting cable has a hight possibility of practical use due to the possibility of low voltage and high capacity transmission caused by its lower power loss than copper cable. In this paper, the transport characteristics of BSCCO superconducting cable, according to the change of BSCCO superconducting cable's accident point at phase $0^{\circ}$ and $45^{\circ}C$, were analyzed and compared each other. Consequently, when the accident was occur the resistance of the HTS was higher at the point phase $0^{\circ}$ than $45^{\circ}$ which means it will cause much higher load on the HTS.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.519-527
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• 1997

AISI 316 steel has been used extensively for heater and boiler tube of the structural plants such as power, chemical and petroleum plants under severe operating conditions. Usually, material degradation due to microcrack or precipitation of carbides and segregation of impurity elements, is occured by damage accumulated for long-term service at high temperature in this material. In this study, the effect of aging time on fracture toughness was investigated to evaluate the measurement of material degradation. The elastic-plastic fracture toughness behaviour of AISI 316 steel pipe aged at $550^{\circ}C$for 1h-10000h (the aged material) was characterized using the single specimen J-R curve technique and eletric potential drop method at normal loading rate(load-line displacement speed of 0.2mm/min) in room temperature and air environment. The fracture toughness data from above experiments is compared with the $J_{in}$ obtained from predicted values of crack initiation point using potential drop method.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.139-145
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• 1996

The machining accuracy and performance is largely influenced by the static, dynamic and thermal characteristics of spindle systems in machine tools, because the spindle system is a intermedium for cutting force from tool and machine powef from motor. Large cutting force and power are transmitted by bearing with a point or line contact. So, the spindle system is the static and dynamic weakest point in machine structure. For improvement of static stiffness of spindle system can be changed design parameters, such as diameter of spindle, stiffness of bearing and bearing span. But for dynamic stiffness, the change of the design parameters are not useful. In this paper, the combined bearing arrangement is suggested for high damping spindle system. The combined bearing arrangement is composed of tandem double back to back arrangement type ball bearins and a high damping hydrostatic bearing. The variation of static deflection and amplitude in first natural frequency is evaluated with the location of hydrostatic bearing between front and rear ball bearing. The optimized location of hydrostatic bearing for high static and dynamic stiffness is determined rapidly and exactly using the mode shape and transfer function of spindle. The calculation of damping effect on vibration by unbalance of grinding wheel and pulley in optimized spindle system is carried out to verify the validity of the combined bearing arrangement. Finally, the simulation of grinding process show that the surface roughness of workpiece with high damping spindle system is 60% better than with ball bearing spindle system.

• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.242-247
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• 2018

The automotive industry is making various efforts to cope with ever-increasing exhaust emissions and fuel economy regulations. However, this often results in degraded NVH (Noise, Vibration, and Harshness) performance. For example, we proposed the causes and improvements for the noise generated by the high-pressure pump noise of a gasoline engine, the change of acceleration noise due to dual injection of MPI (Multi-Point Injection) and GDI (Gasoline Direct Injection), the noise of a gasoline turbocharger, and the combustion noise deteriorated due to the injection parameters calibration in a diesel engine. Since these noises are caused by the high frequency noise, and the driver feels the rough sound quality, efforts to reduce them with proper NVH measures are indispensable.

• Journal of Drive and Control
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• v.11 no.1
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• pp.1-7
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• 2014

This paper presents a novel concept of wave energy converter for electric generation from the ocean wave energy. In this paper, a Multi-Point Absorbing Wave Energy Converter, shortened as MPAWEC by using Secondary Control Hydrostatic Transmission (SCHST) was proposed. The power take-off (PTO) system in the proposed MPAWEC includes multi heaving buoys to drive hydraulic pumps placed at different points. The application of SCHST in MPAWEC gives some advantages, such as longevity of hydraulic components; more energy is harvested; the variation of the pressure in the accumulator limited; therefore the accumulator volume is reduced and the output speed is more stable, etc. A PID controller was designed for speed control of the hydraulic motor. The simulation results indicated that the speed of the generator was ensured with the relative error as 0.67%; the efficiency of the proposed system was 71.4%.

• The Journal of Korean Physical Therapy
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• v.22 no.2
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• pp.47-53
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• 2010

Purpose: This study investigated the effect of electroacupuncture stimulation on changes in blood biochemistry in spinal cord injury (SCI) rats whose cords were damaged by 6-hydroxydopamine (6-OHDA). Methods: Twenty-one Sprague-Dawley adult male rats were assigned to one of three groups: normal (n=7), control (n=7) and experimental group (n=7). The experimental group received electroacupuncture (Es-160, ITO, Japan) for 15 minutes in the form of low frequency (2 Hz) stimulation to the zusanli point. After treatment, we observed motor behavior recovery using the inclined plane test. We also measured serum and CNS concentrations and activities of enzymes including creatine kinase (CK), alkaline phosphatase (ALP), and Immunoglobulin G (IgG). Statistical analysis was done using one-way analysis of variance (ANOVA). Results: Concentrations of CK, ALP and IgG were lower in the experimental group than in the control group. Functional recovery was evaluated by the maximal angle of the inclined board on which rats could maintain their initial position. This allowed us to monitor progressive locomotor recovery. The maximal angles of the inclined plane test were higher in the experimental group than in the control group (p<0.05). Conclusion: The results of this study showed that electroacupuncture to the zusanli point has a therapeutic effect on functional recovery after SCI.

• The Journal of Korean Physical Therapy
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• v.21 no.2
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• pp.9-14
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• 2009

Purpose: This study examined the effect of constraint-induced movement therapy (CIMT) on improving the hand function in hemiplegic side. Methods: Ten subjects without a control group were given CIMT to the hemiplegic side for 3 weeks. The effects of their hand function and sensibility were examined using a MAL and two point discrimination test. Repeated ANOVA was carried out for an analysis of the effects of the application of CIMT before and after treatment. Results: The participants showed significant improvement in their functional aspect with CIMT while there were no significant changes in the time domain variables. There was significant improvement in the quantitative and qualitative aspect of MAL, as well as significant improvement in the two-point discrimination function in all fingers. Conclusion: CIMT can enhance the motor function and sensory function of the hand in hemiplegic patients.