• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.755-760
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• 2016

The demand for independent generators using renewable energy has been increasing. Among those independent generators, small wind turbine generators have been actively developed. Permanent magnets are generally used for small wind turbine generators to realize a simple structure and small volume. On the other hand, cogging torque is included due to the structure of the permanent magnet synchronous machine, which can be the source of noise and vibration. The cogging torque can be varied by the shape of the permanent magnet and core, and it can be reduced using the appropriate design techniques. This paper proposes a design technique that can reduce the cogging torque by changing the shape of the permanent magnets for SPMSM (Surface Permanent Magnet Synchronous Motor), which is used widely for small wind turbine generators. Evolution Strategy, which is one of non-deterministic optimization techniques, was adopted to find the optimal shape of the permanent magnets that can reduce the cogging torque. The angle and outer diameter of permanent magnet were set as the design variable. A 300W class wind turbine generator, whose pole/slot combination was 8 poles/18 slots, was designed with the proposed design technique. The properties of the generator, including the cogging torque and output voltage, were calculated. The calculation results showed that the cogging torque of the optimized model was reduced compared to that of the initial model. The design technique proposed by this paper can be an effective measure to reduce the cogging torque.

• International Journal of Highway Engineering
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• v.3 no.4 s.10
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• pp.127-136
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• 2001

To increase the structural integrity of concrete box culvert good compaction by the dynamic compaction roller with bi9 capacity is as effective as good backfill materials. It is needed for effective compaction that a compaction roller closes to concrete structure with high frequency. However structural distress of the culvert could be occur due to the excessive earth pressure by great dynamic compaction load. To investigate the characteristics of Induced stress by compaction, a box culvert was constructed with changing cushion materials and compaction methods. Two types of cushion material such as tire rubber chip and EPS(Expanded Polystyrene) were used as cushion panels and they are set on the culverts before backfill construction. Laboratory test result of cushion material says that the value of dynamic elastic modulus of rubber is lesser than that of EPS. On the other hand, material damping of rubber material is greater than that of EPS. In most case, dynamic compaction rollers with 10.5 ton weights were used and vibration frequency was applied 30Hz for the great compaction energy. This paper presents the main results on the characteristics of dynamic earth pressures during compaction. The amounts of induced dynamic pressures$(\Delta\sigma\;h)$ by compaction are affected with construction condition such as compaction frequency, depth of pressure cell, distance between roller and the wall of culvert and roller direction. Based on the measured values dynamic lateral pressure on the culverts, it could be said that orthogonal direction of roller to the length of culvert is more effective to compaction efficiency than parallel direction.

• Tribology and Lubricants
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• v.34 no.3
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• pp.84-92
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• 2018

Bearings are essential for reducing vibration and wear, in order to achieve high durability and increase longevity. White metal treatment of tilting pads via centrifugal casting method has the possibility of increasing durability. However, this manufacturing method has drawbacks such as long processing time, high defect rate, and harmful health effects. Laser cladding deposition technique is a powerful method that can address these issues by decreasing the processing time and providing good adhesion. In this study, we suggest optimum conditions for laser cladding deposition that can be used in industrial applications. We deposited a soft white metal layer on SCM440 that is primarily used in shafts to minimize wear of bearing pads. During the laser deposition process, we controlled factors such as laser power, powder feed rate, and laser head speed to determine the optimum conditions. In addition, we measured the hardness using micro Vickers, and performed field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and friction tests to investigate the mechanical properties and surface characteristics for different parameters. Based on the experimental results, we suggest that laser power, powder feed rate, and laser head speed of 1.3 kW, 2.5 rpm, and 10 mm/s, respectively, constitute the optimum conditions for producing white metals using laser cladding.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.141-151
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• 2015

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.170-174
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• 2007

Although research efforts for brain waves have prospered in medicine and engineering, acupuncture still has a long way to go regarding researches on brain waves analysis. Thus this study set out to analyze brain waves stimulated by indirect mugwort moxibustion, which was part of acupuncture techniques, and to investigate their correlations with the automatic nervous system. For the experiments, stimulation was given to Jungwan, Shingwol and Gwanwon, which were some of the spots on the body suitable for acupuncture, through indirect mugwort moxibustion. The subjects' brain waves were measured before the stimulation, during the stimulation, and one hour and two hours after the stimulation. The measurements were analyzed with Matlab 7.0 for FFT and frequency power spectrum. Then the ${\alpha}$, ${\beta}$, ${\delta}$, and ${\theta}$ waves were analyzed and examined for changes to the percentage of each frequency and to the amplitude of vibration according to the stages of stimulation. The EEG data of the entire brain were translated into FFT to analyze the percentage of the ${\alpha}$, ${\beta}$, ${\delta}$, and ${\theta}$ waves. As a result, the ${\alpha}$ waves recorded a double increase after the stimulation. The power spectrum analysis results of the entire brain decreased the ${\alpha}$ and ${\beta}$ waves dropping in the energy level, which suggested that the parasympathetic nerves were activated. When the results of the study were compared with those of the previous study, it's confirmed that indirect moxibustion stimulation could cause changes to the automatic nervous system and bring stability to those who were nervous or under stress due to the proportionate increase of the ${\alpha}$ waves.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.4
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• pp.763-770
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• 1997

The air abrasive technique is a non-mechanical method by which teeth are treated before restoration and stains and calculi are removed from tooth surfaces using the kinetic energy of small particles. The air abrasive technique in dentistry was first introduced in the 1950's with as instrument called 'Airdent'. But, as the main restorative materials of the period were amalgam and gold, and the instrument's inability to control the flow of particles caused the particles to be spread throughout the clinics, widespread use was not possible. In the 1990's, as these techincal problems were solved and more interest in new restorative materials rose in an effort to preserve sound tooth structure, new developements took place in instruments related to the air abrasive technique. The air abrasive technique produces less pressure, vibration and heat that might cause patient discomfort and facilitates the preservation of sound tooth structure. It also reduces the need for anesthesia and is less harmful to the pulp. Other advantages include increase in dentin bonding strength of composite resin, lower possibility of saliva contamination and maintenance of a dry field. But there is not direct contact between the nozzle and the tooth, the operator cannot use his or her tactile sense and must rely solely upon visual input. Other disadvantages are: the tooth preparation depends on the operator's ability; alpha-alumina particles, after bouncing off the tooth surface, cause damage to dental mirrors; the equipment is expensive and takes up a certain amount of space in the clinic. The author conducted case report using the air abrasive technique on patient visiting the Department of Pediatric Dentistry at Seoul National University Dental Hospital and arrived at the following conclusions. 1. The tooth preparation capability of different air abrasive devices varied widely among manufacturers. 2. It was more effective in treating early caries lesions and stains compared to lesions where caries had already progressed to produce soft dentin. 3. The cold stream and noise caused by the evacuation system was a major cause of discomfort to pediatric patients. 4. As there is no direct contact with tooth surface when using the air abrasive technique for tooth preparation, considerable experience and skill is required for proper tooth preparation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.447-453
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• 1999

Congruent $LiNbO_3$ crystals with doped Mg and codoped with Mn or Fe were grown by the Czochralski method. It is known that the physical properties of $LiNbO_3$ depend strongly on the addition of Mg and transition metals. This is established by studying the following properties; XRD patterns, the phase transition temperature, energy of the fundamental absorption edge, the shape of the absorption band of the $OH^-$ vibration and lines of the ESR of $Fe^{3+},\; Mn^{2+}$. The position of the UV absorption edge and the shape and peak point of the absorption band of the $OH^-$ vibrational band changed monotonously up to a critical concentration of $Mg^{2+}$ ions. The mechanism of the incorporation of Mg ions changes at this concentration. The transition temperature was estimated by measuring the dielectric temperature behavior up to $1230^{\circ}C$ in a frequency range of 100Hz to 10MHz. EPR of $Mn^{2+}\;and\; Fe^{3+}$ ions were employed to investigated the Mg doping effects in the $LiNbO_3$ crystal. The increase of linewidths and the asymmetry of signals were observed in all crystals. New signals of $Fe^{3+}$ arising from the new centers were observed I the heavily Mg-doped crystals.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.249-255
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• 2010

Methods of the characteristics evaluation of turbo-molecular pumps (TMP) are well-defined in the international measurement standards such as ISO, PNEUROP, DIN, JIS, and AVS. The Vacuum Center in the Korea Research Institute of Standards and Science (KRISS) has recently designed, constructed, and established the integrated characteristics evaluation system of TMPs based on the international documents by continuously pursuing and acquiring the reliable international credibility through measurement perfection. The measurement of TMP pumping speed is normally performed with the throughput and orifice methods dependent on the mass flow regions. However, in the UHV range of the molecular flow region, the high uncertainties of the gauges, mass flow rates, and conductance are too critical to precisely accumulate reliable data. In order to solve the uncertainty problems of pumping speeds in the UHV range, we introduced a SRG with 1% accuracy and a constant volume flow meter (CVFM) to measure the finite mass flow rates down to $10^{-1}$ Pa-L/s with 3% uncertainty for the throughput method. In this way we have performed the measurement of pumping speed down to $10^{-4}$ Pa with an uncertainty of less than 6% for a 1000 L/s TMP. In this article we suggest that the CVFM has an ability to measure the conductance of the orifice experimentally with flowing the known mass through the orifice chambers, so that we may overcome the discontinuity problem encountering during introducing two measurement methods in one pumping speed evaluation sequence.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.181-188
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• 2015

The non-contact permanent magnet gear has advantages of high efficiency and improved reliability. It has other advantages of no mechanical friction loss, very little noise and vibration, and no need for lubricant. With these advantages, the non-contact permanent magnet gear that solves the physical contact problem of the mechanical gear has drawn attention. Due to this unique non-contact characteristic, the non-contact permanent magnet gear which is capable of non-contact torque transmission has replaced mechanical gear. The mechanical gears which is in many fields of the modern industry, is used mostly for power transmitting mechanical devices. However, it also has the problem of a low torque density, which requires improvement. In this paper, a novel pole piece shape is proposed in order to improve the problem of low torque density of the non-contact permanent magnet gear. The experiment data required for predicting the relationships among them are obtained using finiteelement Operating method based on two-dimensional (2-D) numerical analysis. Therefore, this paper derived an optimal model for thenon-contact permanent magnet gear with the novel pole piece using the Box-Behnken design, and the validity of the optimal design of the proposed pole piece shape through variance analysis and regression analysis demonstrated. In this paper, we performed the thransfer torque analysis in order to improve the torque density and power density, we have performed on optimal design of proposed pole piece shape using box-behnken.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.49-55
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• 2009

Our domestic economy has been developed very rapidly after 1960's. Also, it is dramatically increasing traffic on road and surround environmental issues. Especially, rapid economic growth has been induced large construction of pavement, and bigger and higher traffic for transportation. These are making air pollution, traffic noise and vibration. The social requirement against the revealed road environment and traffic sound reduction is being demanded. Traffic noise of city zone is showed over the environmental specification more than 57%. In order to overcome these situations, the social attention is being increased. The quiet pavement is the same format of permeable pavement, but is not same for functional performance. In this research, it has been carried out to evaluate the fundamental-mechanical properties of hot mix asphalt for quiet pavement. Especially, couple of laboratory tests are conducted like marshall stability, resilient modulus, indirect tensile test, and compaction energy analysis with gyratory compaction curve. Also, two-layer pavement system has been adopted for developing of quiet pavement. The basic performance of hot mix asphalt of quiet pavement show a satisfaction of specification of hot mix asphalt.