• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.12
• /
• pp.1330-1337
• /
• 2004

In this study, the equations of motion of a rigid rotor supported by magnetic bearings are derived via Hamilton's principle, and transformed to a state-space form for control purpose. The optimal motion control of rotor magnetic bearing system based on the LQR(linear quadratic regulator) theory is addressed. New schemes related to the selection of the state weighting matrix Q and the control weighting matrix R involved in the quadratic functional to be minimized are proposed. And the robust control of the system with an LMI(linear matrix inequality) based H$_{\infty}$ theory is dealt with in this paper. Loop shapings of TFM (transfer function matrix) are used to increase the performance of control capability of the system. The control abilities of LQR and H$_{\infty}$ controller are compared by simulation and experimental tests and show that the capability of H$_{\infty}$ controller is superior to that of LQR.

• Membrane Journal
• /
• v.26 no.1
• /
• pp.38-42
• /
• 2016

Polyvinylpyrrolidone (PVP), which is glassy polymer to have amide functional group, was induced to fabricate the facilitated olefin transport membranes for olefin/paraffin separation. Separation performance for the mixed gas consisting of propylene and propane (50 : 50 vol%) was measured by gas chromatography and bubble flow meter. The properties of membranes were confirmed by scanning electron microscope and FT-IR. The results of long-term separation tests showed the selectivity of 15 and permeance of 1.3 GPU. The membranes was compared with poly(2-ethyl-2-oxazoline) $(POZ)/AgBF_4/Al(NO_3)_3$ membranes and the characteristics were confirmed as polymer matrix for facilitated transport membranes.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.725-733
• /
• 2008

A thixotropic grout has been developed for the use of filling a tail void in the shield TBM and as well as various ground voids. The grout developed in this study is a mixture of inorganic substance, cement and some functional additives. Its engineering characteristics was investigated by measuring a viscosity and unconfined compressive strengths. The optimum mix proportion for an effective thixotropic grout was proposed through several repeated laboratory tests. The various physical properties such as thixotropy, unconfined compressive strengths, and durability of the thixotropic grout and the gels produced from the grout were compared with those of the well-known waterglass-type grout such as L.W.. The thixotropic grout developed in the study exhibited an excellent performance for back-filling of tail voids in the shield TBM based on experimental results compared to the existing waterglass grout.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.03a
• /
• pp.338-350
• /
• 2010

As existing materials for ground reinforcement, chemical grout material using cementitous materials and waterglass was used. But many problems in terms of ground reinforcement effects were implicated. In this study, for development and applicability verification of new materials, viscosity, fluidity, permeability, Self-Leveling, keeping of drilled hole, antiwashout underwater, resistance of water (groundwater dilution and minimize material eluting) and the early strength and long-term strength characteristics of developed materials was confirmed, and material standards, and establishing construction standards for the various model tests were conducted. As a result, high viscosity, flowability, permeability and keeping of drilled hole characteristics are excellent, in addition to the early strength properties, dilution does nat occur to groundwater, including groundwater is available for dealing with environmental issues. Application of basic and reinforcement method by Filler function in addition to structure can also or development of a new concept can be expected. In addition, middle and large-diameter drilled shaft, micropile, ground anchors, soil-nailing, steel pipes multi-grouting reinforcement for cement injection process could be used enough to even be considered.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.1283-1290
• /
• 2005

A thixotropic grout has been newly developed for the use of back-filling a tail void in the shield tunnel and filling up ground voids. The grout developed in the study is a mixture of colloidal silica, cement and some functional additives. Its engineering characteristics was investigated by measuring a viscosity and unconfined compressive strengths. The optimum mixing proportion for an effective thixotropic grout was proposed through several repeated laboratory tests. The various physical properties such as thixotropy, unconfined compressive strengths, and durability of the thixotropic grout and the gels produced from the grout were compared with those of the well-known waterglass grout such as L.W.. The thixotropic grout developed in the study exhibited an excellent performance for back-filling of tail voids, based on experimental results compared to the existing waterglass grout.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.11
• /
• pp.1221-1227
• /
• 2012

As demands on micro-products increase significantly with raising functional integration and increasing complexity, microfoming attracts a lot of attention in the manufacture of micro-products. Since the conventional big forming systems are not adequate to achieve sufficient tolerances of micro-scale parts, it is necessary to reduce the scale of the forming equipment and devices. In addition, understandings on the size effects, which exist in the material behavior and process characterization of microforming processes, need to be expanded. In this study, a miniaturized forming system based on the ball screw and servo motor actuator was developed for the efficient micro-parts production. In addition, tensile tests and cylindrical upsetting experiments were performed to evaluate the performance of the microforming system and to investigate the flow stress and friction size effects in microforming processes.

• KIEAE Journal
• /
• v.6 no.4
• /
• pp.11-16
• /
• 2006

This work has carried out some preliminary studies for the utilization of a solar mini-dish system capable of concentrating solar rays to higher densities. A typical mini-dish system considered employs an array of solar mini-dishes where major components are light and compact. It consists of small mini-dishes, optical fiber bundles and diffusers at the end. Each mini-dish (typically has a 20 to 30 cm in diameter) is designed with a simple parabolic profile, concentrating sunlight (after the glass glazing cover to avoid dust deposition on the reflector and facilitate cleaning) onto a centrally-located small mirror which is placed on the bottom side of the transparent glass cover. The focused sunlight is reflected by the mirror surface onto a focal point where the receiving aperture of a homogenizer is located. Optical fibers are used to carry high-density solar rays to the other end where diffusers are mounted for indoor illumination. The proposed high density mini-dish system could make an efficient daylighting system as it excludes large moving parts and expandable if necessary. Each component of the system could be made from the off-the-shelf technology and thus, make the generic unit inexpensive to manufacture. Depending on spatial demand or characteristics, the amount of introducing daylight could be controlled. Preliminary tests have been carried out for a trial system to check any functional problems when in operation. Suggestions are also made to improve the design enhancing its performance and applicability.

• The Journal of Korean Physical Therapy
• /
• v.22 no.1
• /
• pp.53-60
• /
• 2010

Purpose: The purpose of our study was to evaluate the effects of an exercise program on activities of daily living (ADL), balance and cognition in elderly individuals with Alzheimer’s disease and vascular dementia. Methods: Thirty-two patients with mild to moderate cognitive impairment were assigned to one of two groups: an exercise group (n=16) and a control group (n=16). The exercise group carried on regular exercise for 60 minutes a day, 4-5 times per week for 8 weeks. The exercise group participated in an exercise program (treadmill training and physical training). ADL, balance and cognitive function were evaluated before and at the end of the program using the Korean modified Bathel Index (K-MBI), the Functional independence measure (FIM), the Berg balance scale (BBS), the Balance performance monitor (BPM), and the Mini mental state examination (MMSE) in both groups. Results: There were significant exercise-induced improvements in ADL and Balance from pre to post tests; but not in MMSE. Conclusion: Exercise programs can improve ADL and balance in elderly with Alzheimer’s disease and vascular dementia.

• The Journal of Korean Physical Therapy
• /
• v.24 no.1
• /
• pp.23-28
• /
• 2012

Purpose: The purpose of this study was to examine the difference between the faller and the non-faller in the test for balance and fear of falling. This was also done to determine whether the balance and the fear of falling are correlated in the elderly. Method: Forty eight subjects participated in this study, who attended the senior center in Daegu. Prior to the test, demographic data was collected. As for the balance test, Berg Balance Scale (BBS), Timed Up & Go (TUG), Short Physical Performance Battery (SPPB), Functional Reach Test (FRT), and One Leg Stance (OLS) were used. For measuring the fear of falling, Falls Efficacy Scale (FES) and Activities-specific Balance Confidence Scale (ABC) were used. Independent t-test and Pearson's correlation was performed using PASW 18.0 for windows. Result: All balance tests, except OLS, and fear of falling could discriminate between the faller and the non-faller. There existed a significant correlation between some balance test and fear of falling (r=0.64~0.86). Conclusion: The findings indicate that assessing the falling in the elderly, there needs to be a consideration of multiple aspects including the fear of falling and not only the balance test.

• Research in Community and Public Health Nursing
• /
• v.20 no.1
• /
• pp.59-66
• /
• 2009

Purpose: The purpose of study was to test the effect of lower extremity muscle strengthening exercise using elastic resistance on balance on elderly women. Methods: Twenty four women who were over 65 years old were randomly assigned to either the experimental group that received the exercise programme (n=12) or to the control group (n=12) that continued normal activities except programme. Exercises included the following 7 different activities; chair squat, knee flection, extension, hip flection, extension, calf muscle raise, ankle dorsiflection. All the participants were subject to 3 tests, including One-Leg Standing Test, Functional Reaching Test, and Up & Go Test. The measurements were made before the excercise, 4 and 8 weeks after the exercise. The data were analyzed by using the two way repeated ANOVA. Results: The results were as follows; As compared with change of balance capacity between groups, a significant difference was shown in the up and go test (p<.05), but not in balance performance clinical test of OLST (p>.05) and FRT (p>.05). Conclusion: The lower extremity muscle strengthening exercise using elastic resistance for the elderly women had some positive effects on the balance. Therefore this intervention can be broadly applied to other elders for preventing falls.