• Transactions of The Korea Fluid Power Systems Society
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• v.8 no.4
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• pp.9-16
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• 2011

Because of the increasing demand on the high precision and high response of a machinery, proportional control valves are widely adopted at various application fields. This paper studies on the static and dynamic characteristics of a pilot proportional pressure control valve. An experimental apparatus including hydraulic pump, variable speed inverter, pressure and flow sensors and data aquisition system was set up. And various experiments such as P-Q-V curves, step responses due to input voltage and flow rate, hysteresis, frequency response of the proportional valve was carried out and the results are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.8
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• pp.1164-1172
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• 1998

The three dimensional numerical method using actuator disk blade row model is applied for calculating the flowfield interaction between an outlet guide vane (OGV) and a pylon in a typical civil turbofan engine. The static pressure distortion produced by the pylon is decaying upstream but is still felt at the turbofan exit, and hence can significantly affect the fan performance. The OGV amplifies the static pressure perturbation decaying upstream. The calculation results show that cyclic OGV which consists of three types of blades with different exit angles can reduce more than half of the asymmetries of total pressure and static pressure propagated through the OGV with uniform exit blade angle.

• The KSFM Journal of Fluid Machinery
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• v.8 no.1 s.28
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• pp.16-22
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• 2005

This paper presents the method of ROL(Rate Of Loading) improvement for the Motor Operated Gate Valve operated in high differential pressure condition. ROL is one of the most important evaluation parameters for the valve ability. It is close to correlation in stem factor (SF) and appears different value by the differential pressure of fluid. ROL and SF are analyzed by the static test and dynamic test. The obtained result show that the modification of stem factor is very important factor for the ROL improvement. In order to obtain the same value of SF between static and dynamic test, stem and stem nut should be combined appropriately by the repetition test.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.51-57
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• 2015

The purpose of this study is to verify the performance of a static mixer for mixing of biogas and town gas by numerical analysis and demonstration test. The reason for designing a static mixer is that there is a need to mix town gas with biogas when there is less production of biogas in biogas sites. Non-uniformity in the outlet section was calculated for investigating the performance of a static mixer. Non-uniformity was based on the mole fraction of methane in a mixture of biogas and town gas. Low non-uniformity means that biogas and town gas are mixed well through this static mixer. Also, pressure drop at the outlet section of a static mixer was calculated. The pressure drop is less than 0.2% in this static mixer. This static mixer is suitable for applying to a 5MW bio-gas turbine through the demonstration test in the field.

• Journal of the Korean Society of Physical Medicine
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• v.13 no.3
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• pp.27-37
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• 2018

PURPOSE: The purpose of this study was to investigate and evaluate muscle activity and foot pressure during gait, and isokinetic strength and balance in persons with functional ankle instability (FAI). METHODS: Nine healthy subjects (CON, n=9) without FAI and 11 patients (FAI, n=11) with FAI participated in the study after having been screened with an ankle instability instrument and a balance error scoring system. In addition, FAI was classified as non-involved (FAI-N) or involved (FAI-I), and CON was classified as dominant or non-dominant. All subjects were evaluated for isokinetic strength (plantar flexion, dorsiflexion, inversion and eversion of $30^{\circ}/sec$ and $60^{\circ}/sec$), balance (static and dynamic), muscle activity (tibialis anterior, peroneus longus and gastrocnemius) and foot pressure (static and dynamic) during gait. RESULTS: Results showed that plantar flexion (p<.05), dorsiflexion (p<.05), inversion (p<.01) and eversion (p<.00) of $60^{\circ}/sec$ were significantly decreased in FAI-I compared to those in FAI-N and CON. C 90 of static balance with eyes open (p<.01) and closed (p<.00) were significantly increased in FAI compared to those in CON. Forward position of dynamic balance (p<.01) was significantly decreased in FAI compared to that in CON. Gastrocnemius and peroneus longus of dynamic muscle activity (p<.01), left and right weight distribution of static foot pressure (p<.00) and pressure distribution of dynamic foot pressure (p<.00) were significantly decreased in FAI-I compared to those in FAI-N. CONCLUSION: We demonstrated that ankle strength, balance, muscle activity and foot pressure were significantly correlated with FAI.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.19 no.1
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• pp.49-54
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• 2013

Background: The purposed of this study is to examine the static and dynamic plantar foot pressure in chronic low back pain patients and normal adults. Methods: The subjects were divided into a group of 30 patients with chronic low back pain and a control group of 30 healthy persons. While static posture and dynamic posture at comfortable walking speeds, the low back pain group and the control group measured their plantar foot pressure and the trajectory of their center of pressure (COP) using the Matscan(R) system. Independent t-tests were measured to compare differences in plantar foot pressure characteristics between the left side and right side of the low back pain group and the control group. Results: In the comparison of differences in plantar foot pressure characteristics between the left side and right side of the low back pain group and the control group, the anteroposterior (AP) displacement of COP showed significant differences (p<.05). Although the low back pain group and the control group did not show any significant differences in leg length, weight distribution, mediolateral (ML) displacement of COP, static contract area, dynamic contract areas (p>.05), increases in the contract area values were shown in the hind foot in general. Conclusion: In this study, it was shown that patients with chronic low back pain were walking with short AP displacement of the COP as a compensatory action to avoid pain.

• International Journal of Fluid Machinery and Systems
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• v.9 no.3
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• pp.237-244
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• 2016

An unsteady three-dimensional simulation based on Reynolds time-averaged governing equation and RNG $k-{\varepsilon}$ turbulence model, was presented for pump-as-turbine, the pressure fluctuation characteristic of hydraulic turbine with guide vane was obtained. The results show that the time domains of pressure fluctuation in volute change periodically and have identical cycles. In volute tongue and inlet pressure fluctuations are light, while in dynamic and static coupling interface pressure fluctuations are serious; In impeller blade region the pressure fluctuation of pressure surface are lighter than that of suction surface. The dominant frequencies of pressure fluctuation concentrate in low frequency region, and concentrate within 2 times of the blade passing frequency.

• Journal of Power System Engineering
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• v.17 no.3
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• pp.35-43
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• 2013

Generally, the chassis of an indoor RAC is composed of a rear-guider and a stabilizer. The aerodynamic performance of a cross-flow fan is strongly influenced by the various design factors of the chassis of an indoor RAC. The purpose of this paper is to select the optimum design factors through the aerodynamic performance of a cross-flow fan. The design factors are the leading angle of a rear-guider (${\theta}_1$), a stabilizer setup angle(${\theta}_2$), a rear-guider clearance(${\epsilon}_1$), and a stabilizer clearance(${\epsilon}_2$), respectively. As a result, the optimum design factors of an indoor RAC can be presented as a combination of ${\theta}_1=33^{\circ}$, ${\theta}_2=55^{\circ}$, ${\epsilon}_1=6{\sim}8mm$, and ${\epsilon}_2=7mm$ through the analysis of a static pressure coefficient and a static pressure efficiency.

• Geomechanics and Engineering
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• v.12 no.6
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• pp.935-948
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• 2017

An experimental program was conducted to investigate the effects of the static compaction pressure, cement content, water/cement ratio, and curing time on unconfined compressive strength (UCS) of the cement treated sand. UCS were conducted on samples prepared with 4 different cement/sand ratios and were compacted under the lowest and highest static pressures (8 MPa and 40 MPa). Each sample was cured for 7 and 28 days to observe the impact of curing time on UCS of cement treated samples. Results of the study showed the unconfined compressive strength of sand increased as the cement content (5% to 10%) of the cement-sand mixture and compaction pressure (8 MPa to 40 MPa) increased. UCS of sand soil increased 30% to 800% when cement content was increased from 2.5% to 10%. Impact of compaction pressure on UCS decreased with a reduction in cement contents. On the other hand, it was observed that as the water content the cement-sand mixture increased, the unconfined compressive strength showed tendency to decrease regardless of compaction pressure and cement content. When the curing time was extended from 7 days to 28 days, the unconfined compressive strengths of almost all the samples increased approximately by 2 or 3 times.

• Journal of Power System Engineering
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• v.19 no.6
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• pp.19-25
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• 2015

The unsteady-state, incompressible and three-dimensional large eddy simulation(LES) was carried out to analyze the aerodynamic performance of three-dimensional small-size axial fan(SSAF) with the different depth of bellmouth. The static pressure coefficients analyzed by LES predict a little bit larger than measurements except stall region regardless of the installation depth between SSAF and bellmouth. Moreover, static pressure efficiencies analyzed by LES show about maximum 30% at the actual operating point ranges, but measurements do not. Therefore, if the blades of conventional SSAF have some more rigidity and complete dynamic balance, the aerodynamic performance of SSAF will be some more improved. In consequence, LES shows the best prediction performance in comparison with any other Reynolds averaged Navier-Stokes(RANS) method.