• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2181-2190
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• 1993

An electro-hydraulic controlled rig type CVT(Continuously Variable Transmission) system was developed and its performance tests were carried out for the optimal operation. A CVT map was suggested based on the speed ration-axial force-torque relationship which was derived from the metal belt CVT mechanics. Also, a real time control and operation software was developed for the electro-hydraulic CVT system. By using the software and the CVT map, the control system was designed for the CVT speed ratio control with various drive modes. The electro-hydraulic CVT system developed in this study showed that the optimal operation algorithm could be obtained for the best fuel economy or the maximum power mode.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.729-735
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• 2012

A LQG/LTR(linear quadratic Gaussian/loop transfer recovery) controller with an integrator is designed to control the electro-hydraulic positioning system. Without considering the nonlinearity in the dead-zone, computer simulations are performed and show good performances and tracking abilities with the feedback controller based on the linear system model. However, the performance of the closed loop hydraulic positioning system shows big steady-state error in real system because of the dead-zone. In this paper, the feedback controller with a nonlinear compensator is introduced to overcome the dead-zone phenomenon in hydraulic systems. The inverse dead-zone as a nonlinear compensator is used to cancel out the dead-zone phenomenon. Experimental tests are performed to verify the performance of the controller.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.614-619
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• 2012

A LQG/LTR(Linear Quadratic Gaussian/Loop Transfer Recovery) controller with an integrator is designed to control the electro-hydraulic positioning system. Without considering the nonlinearity in the dead-zone, computer simulations are performed and show good performances and tracking abilities with the feedback controller based on the linear system model. However, the performance of the closed loop hydraulic positioning system shows big steady-state error in real system because of the dead-zone. In this paper, the feedback controller with a nonlinear compensator is introduced to overcome the dead-zone phenomenon in hydraulic systems. The inverse dead-zone as a nonlinear compensator is used to cancel out the dead-zone phenomenon. Experimental tests are performed to verify the performance of the controller.

• Proceedings of the Korean Geotechical Society Conference
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• 1994.03b
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• pp.3-12
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• 1994

Based on the shear failure mechanism, hydraulic fracturing criteria are extended to three dimensional stress state. According to the situation of the directions of borehole and major principal stress axes, three equations can be derived for three dimensional hydraulic fracturing problems. By comparing these equations, a single criterion is selected for hydraulic fracturing pressure in cohesive soils. The criterion is a function of maximum principal stress, minimum principal stress and soil parameters in UU conditions. The equation indicates that with any increase in maximim principal stress, hydraulic fracturing pressure decreases. In order to prove the integrity of the criteria, laboratory tests are performed on compacted cubical specimens using true a triaxial apparatus. The shape and direction of fractures are determined by injecting colored water after fracture initiation. It is found that the direction of fractures are perpendicular to the o1 plane.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.54-60
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• 2009

Qualification test items and those certification procedures of aircraft hydraulic pump are investigated in this report. Weight minimization through optimal design of aircraft hydraulic pump and its certification process investigation are very important. In this report, some fundamental performance data was presumed for the normal aircraft hydraulic pump, and then basic procedures for qualification tests are presented.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.9-17
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• 2018

Brazilian splitting tests, uniaxial compression tests and triaxial compression tests are carried out on the coal samples cored from Shanxi group $II_1$ coal seam of Jiaozuo coal mine, Henan province, China, to obtain their property parameters. Considering the bedding has notable effect on the property parameter of coal, the samples with different bedding angles are prepared. The effects of bedding on the anisotropic characteristics of the coal seam are investigated. A geological geomechanical model is built based on the geology characteristics of the Jiaozuo coal mine target reservoir to study the effects of bedding on the fracture propagations during hydraulic fracturing. The effects of injection pressure, well completion method, in-situ stress difference coefficient, and fracturing fluid displacement on the fracture propagations are investigated. Results show bedding has notable effects on the property parameters of coal, which is the key factor affecting the anisotropy of coal. The hydraulic cracks trends to bifurcate and swerve at the bedding due to its low strength. Induced fractures are produced easily at the locations around the bedding. The bedding is beneficial to form a complicated fracture network. Experimental and numerical simulations can help to understand the effects of bedding on hydraulic fracturing in coalbed methane reservoirs.

• Journal of Navigation and Port Research
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• v.36 no.8
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• pp.659-664
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• 2012

Coastal vegetaion consists of rooted flowering marine plants that provide a variety of ecosystem services to the coastal areas they colonize. The attenuation of waves and sediments stabilization are often listed among these services. From this point of view, artificial vegetation model is an effective method of controlling sea bed and stabilization without damaging the landscape or the stability of the coastaline. In this study, numerical and hydraulic physical test for predicting deposition proces of a navigation channel caused by wave action is proposed. In the numerical model, we develop a numerical model for describing the wave attenuation and sediment transport in a navigation channel with a vegetation area. In addition, hydraulic model tests is performed in a navigation channel with irregular waves to examine the effect of vegetation in relation to deposition reduction in navigation channel. A comparison between the results of hydraulic and numerical tests shows resonable agreement.

• Journal of Environmental Science International
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• v.18 no.3
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• pp.315-323
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• 2009

Hydraulic gradient of the landfill soils is estimated by Devlin (2003) method, and its variation characteristics from rainfall and permeability of the aquifer material are analyzed. The study site of 18 m $\times$ 12 m is located in front of the Environment Research Center at the Pukyong National University, and core logging, slug/bail test and groundwater monitoring was performed. The sluglbail tests were performed in 9 wells (except BH9 well), and drawdown data with elapsed time for bail tests were analyzed using Bouwer-Rice and Hvorslev methods. The average hydraulic conductivity estimated in each of the test wells was ranged $1.991{\times}10^{-7}{\sim}4.714{\times}10^{-6}m/sec$, and the average hydraulic conductivity in the study site was estimated $2.376{\times}10^{-6}m/sec$ for arithmetic average, $1.655{\times}10^{-6}m/sec$ for geometric average and $9.366{\times}10^{-7}m/sec$ for harmonic average. The permeability of landfill soils was higher at the east side of the study site than at the west side. Groundwater level in 10 wells was monitored 44 times from October 2 to November 7, 2007. The groundwater level was ranged 1.187$\sim$1.610 m, and the average groundwater level range in each of the well showed 1.256$\sim$1.407 m. The groundwater level was higher at the east side than at the west side of the study site, and this distribution is identify to it of hydraulic conductivity. The hydraulie gradient and the major flow direction for 10 wells were estimated 0.0072$\sim$0.0093 and $81.7618{\sim}88.0836^{\circ}$, respectively. Also, the hydraulic gradient and the major flow direction for 9 wells were estimated 0.0102$\sim$0.0124 and $84.6822{\sim}89.1174^{\circ}$, respectively. The hydraulic gradient of the study site increased from rainfall (83.5 mm) on October 7, causing by that the groundwater level of the site with high permeability was higher. The hydraulic gradient estimated on and after October 16 was stable, due to almost no rainfall. Thus, it was confirmed that the variation of the hydraulic gradient in the landfill soils was controlled by the rainfall.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.223-235
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• 2020

In this study, pulse tests were undertaken at an underground research facility, as part of in-situ hydraulic tests, to derive the hydrogeological characteristics of crystalline rock. The applicability of pulse tests for estimating the transmissivity of a fractured rock mass was evaluated by comparing the results to those from a slug test. Results from the pulse and slug tests were very similar for the test section, with both tests indicating low transmissivity. A slight difference between the results of pulse and slug tests, however, was observed in the section with the transmissivity larger than 1 × 10^-8 ㎡/s, which is likely due to the difference in the radii of influence of the tests. Furthermore, when the pulse test was conducted in permeable zones where transmissivity was larger than 1 × 10^-7 ㎡/s, it was difficult to produce accurate results. This lack of accuracy was due to the rapid recovery of the hydraulic head in these permeable test zones. When performing pulse tests, it was important to accurately measure the pressure when valves were opened and closed in order to apply the head change in the test section. Although it is difficult to derive the hydrogeological characteristics from pulse tests in areas with high permeability, these tests can be used as an economical test method for identifying hydrogeological characteristics in a relatively short time, especially when deriving the transmissivity of rocks with low permeability.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.15-22
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• 2016

Hydraulic falling head and slug tests were carried out in an alluvium aquifer using a borehole stability device. The hydraulic testing had proved difficult in alluvial formations of sands and gravels due to borehole collapse and unstable borehole walls within the test section. This study aims to improve the hydraulic test results by using a borehole stability device. The device can minimize the collapse of borehole walls, and the use of a filter with a constant opening ratio improves the calculations per unit area of the test section. Permeability obtained from the falling head test without a borehole stability device was 8.82 × 10⁻⁵m/sec. When the borehole stability device was installed in the same test section the measured permeability increased to 4.00 × 10⁻⁴m/sec, which is 4.5 times that obtained without the borehole device. The relatively low permeability obtained using the conventional test method is attributed to the presence of a fine-grained slime generated during drilling and a reduction of the test area in the test interval due to a gradual collapse of the borehole walls. This study considers how the use of a borehole stability device to prevent borehole collapse can influence the results of hydraulic tests in alluvial formations. It is expected that the results can be used as a basis for improving the reliability and applicability of hydraulic tests performed in alluvial aquifers.