• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.109.1-109
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• 2001

This paper deals with the path following problem of car-like intelligent mobile robot. A robust sliding mode control law based on time-varying state feedback is performed via Lyapunov method for path tracking of nonholonomic mobile robot with uncertainties. At first, A sliding control law is designed by combing the natural algebraic structure of the chained form system with ideas from sliding mode theory. Then, a robust control law is proposed to impose robustness against bounded uncertainties in path tracking. The problem of estimating the asymptotic stability region and the sliding domain of uncertain sliding mode system with bounded control input is also discussed. The proposed sliding mode control law can ensure the global reaching condition of the uncertain control system.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.1
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• pp.54-64
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• 2006

To augment weakly damped lag mode stability of a hingeless helicopter rotor blade in hover, piezoelectric shunt with a resistor and an inductor circuits for passive damping has been studied. A shunted piezoceramics bonded to a flexure of rotor blade converts mechanical strain energy to electrical charge energy which is dissipated through the resistor in the R-L series shunt circuit. Because the fundamental lag mode frequency of a soft-in-plane hingeless helicopter rotor blade is generally about 0.7/rev, the design frequency of the blade system with flexure sets to be so. Experimentally, the measured lag mode frequency is 0.7227/rev under the short circuit condition. Therefore the suppression mode of this passive damping vibration absorber is adjusted to 0.7227/rev. As a result of damping enhancement using passive control, the passive damper which consists of a piezoelectric material and shunt circuits has a stabilizing effect on inherently weakly damped lag mode of the rotor blades, at the optimum tuning and resistor condition.

• Journal of Korean Society for Atmospheric Environment
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• v.10 no.2
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• pp.124-129
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• 1994

Aerosol size distribution was determined using Anderson sampler for the anions( sulfate nitrate and chloride ) and TSP. Ionic species concentration and size distribution have been investigated in the daytime and nightime individually. Size classified samples were extracted with distilled water and analyzed for C $l^{[-10]}$ , N $O_3$$^{[-10]}$ and S $O_4$$^{2-}$, by ion chromatography. The size distribution of these ions and TSP was analyzed to investigate the seasonal and diurnal variation of concentrations as follows: (1)Size distribution of TSP showed bi- modal type in the daytime, but indicated tri-mode distribution in the nightime without any seasonal variation. (2)Sulfate concentrations were higher in fine- mode both in the daytime and nightime but fraction of sulfate was higher in coarse-mode during the Yellow Sand Period. (3)Nitrate and Chloride ions are dominant in fine-mode in winter while dominant in coarse-mode in the summer.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.5
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• pp.388-392
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• 2012

In this paper, a sampler model for the P-type current mode control employing low pass filter is proposed. Even though the frequency response of the compensator used in a P-type current mode control employing low pass filter is similar to that of P-type compensator, the sampler model has to be obtained from the method used in PI-type current mode control. In order to show the usefulness of the proposed method, prediction results of the proposed model are compared to those from the circuit level simulator, PSIM.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.1-9
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• 2000

This study shows the defect detection and sizing capability of ultrasonic guided waves in the nondestructive inspection of heat exchanger and steam generator tubing. Phase and group velocity dispersion curves for the longitudinal and flexural modes of a sample Inconel tube were presented for the theoretical analysis. EDM(Electric Discharge Machining) wears in tubing under a tube support plate and circumferential laser notches in tubing were detected by an axisymmetric and a non-axisymmetric transducer set up, respectively. EDM wears were detected with L(0, 2), L(0, 3) and L(0, 4) modes and among them L(0, 4) mode was found to be the most sensitive. It was also found that the flexural modes around L(0, 1) mode could be used for the detection and sizing of laser notches in the tubing.

• KSBB Journal
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• v.25 no.5
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• pp.471-477
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• 2010

In order to improve bio-ethanol productivity by various cultivation methods in this paper, the culture modes using food wastes, such as batch culture, high-cell-density fermentation, SSF (simultaneous saccharification and fermentation) by fill & draw, continuous culture by fill & draw were performed and their productivities were compared. SSFs by fill & draw were performed by continuous decompression using 1 L evaporator system, and by 10 L bioreactor without decompression. In addition, the continuous cultures by fill & draw mode using SFW (saccharafied food wastes) medium were performed by changes of 40% culture broth with intervals of 12 h (0.03 $h^{-1}$), 6 h (0.07 $h^{-1}$), 3 h (0.13 $h^{-1}$). Consequently, productivities of bio-ethanol were 2.52 g/L-h and 1.30 g/L-h in batch culture and high- cell-density fermentation, respectively. The productivities of SSF by fill & draw showed 2.24 g/L-h and 2.03 g/L-h in continuous decompression with 1 L evaporator and 10 L bioreactor without decompression, respectively. Also, the productivities in continuous culture by fill & draw modes showed 2.02 g/L-h, 4.07 g/L-h and 6.25 g/L-h by medium change with intervals of 12 h, 6 h, and 3 h, respectively. In conclusion, the highest ethanol productivity was obtained in the continuous culture mode by fill & draw with dilution rate of 0.13 $h^{-1}$.

• Journal of the Korean Society of Safety
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• v.25 no.3
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• pp.34-39
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• 2010

Unidirectional Carbon Fiber Reinforced Plastics (CFRP) are advanced materials which combine the characteristics of the light weight, high stiffness and strength. For those reasons, the use of the unidirectional CFRP has increased in jet fighters, aerospace structures. However, unidirectional CFRP composites have a lot of problems, especially delamination, compared with traditional materials such as steels and aluminums, and so forth. Therefore, the interlaminar fracture toughness for a laminate CFRP composite is very important. In this study, The mode II interlaminar fracture toughness was measured by using center notched flexure(CNF) test specimen. The CNF specimens using unidirectional carbon prepreg were fabricated by a hot-press with the gage pressure and temperature controller. And three kinds of a/L ratio was applied to these specimens. Here, we discuss the relations of the crack growth and the mode II interlaminar fracture under the four point bending CNF test. From the results, we shows that mode II interlaminar was occurred when the more $a_0$/L ratio, the less load. And $G_{IIC}$ also were obtained as 5.33, 2.9 and $0.58kJ/m^2$ according to $a_0$/L ratio=0.2, 0.3 and 0.4.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6446-6451
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• 2014

Pneumatic motors are quite attractive for many applications because of their competitive price, light-weight, easy assembly, safety in hazardous areas as well as other features, such as a good force/weight ratio and operation in exceptionally harsh environments. In contrast to these advantages, pneumatic motors have limited use in applications, particularly those requiring a fast and precise response. These undesirable characteristics are due to the high compressibility of air and from the nonlinearities in pneumatic systems. This paper presents the sliding mode controller based on 3-loop(SMCB3L), which increases the load stiffness to control the rotation angle of a pneumatic motor. The characteristics for the step responses and load disturbances of the proposed controller were compared with the conventional PID controller. The experimental results showed that a properly designed SMCB3L is capable of high positioning accuracy within ${\pm}0.05mm$. Furthermore, the load stiffness of the SMCB3L can be improved 3.5 fold compared to that of PID controllers.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.2
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• pp.259-265
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• 2008

Generally speaking, there are two widely used methods of Nitrogen removal from waste water: 1) nitrification using autotrophic microorganisms, and 2) denitrification using heterotrophic microorganisms. The C/N ratio is an important factor of the denitrification process. In this case, if methanol is added to increase the lacking organic matter, a high economic cost is incurred and methanol is left in the processed water. In an effort to fix these issues, autotrophic denitrification through the use of Hydrogen, Iron and Sulfur is being studied, and among those Sulfur is cheaper and carries out denitrification effectively, and therefore is being studied the most. In this study, after cultivating T. denitrificans, the presence of T. denitrificans was determined and the effectiveness of denitirification via T. denitrificans was studied. In order to find out about the inhibition of T. denitrificans from the loading of organic matter, this shows that the greater the loading of organic matter, the more the denitrification ability of T. denitrificans is hindered. In order to research the hindrance of T. denitrificans resulting from the loading of $NO_3{^-}-N$, these results show that concentrations less than 100mg/L per 100mL of gel volume do not hinder T. denitrificans. In order to research the optimization of denitrification resulting from T. denitrificans, three 500mL samples of Sulfur granules were prepared: 1) one with only T. denitrificans attached (Mode I), 2) one with both T. denitrificans and active sludge attached (Mode II), and 3) one with only active sludge attached (Mode III). The results showed that autotrophic denitrification using S from Mode I was the most active.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.329-335
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• 2014

This study aimed to understand the internal flow characteristics of a liquid droplet subject to periodic forced vibration. In order to predict the resonance frequency of a droplet, a high-speed camera and macro lens were used to capture internal flow characteristics of a droplet placed on a vibrating hydrophobic surface. Results showed that the droplet assumed a variety of shapes depending on the resonance mode of free droplet, particularly in modes 2, 4, 6, and 8. In addition, the induced internal vortex flow inside the droplet was also observed in each mode. Typically, the induced flow moved upwards along the axis of symmetry and downwards along the surface of the droplet, that is, from the apex to the contact line in modes 2 and 4, after which it broke into a smaller vortex. On the other hand, the large-scale vortex always remained steady in modes 6 and 8. The speed of the flow in mode 4 was always greater than that in mode 2, but those in modes 6 and 8 were similar.