• Tribology and Lubricants
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• v.18 no.1
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• pp.55-60
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• 2002

In many dynamic systems, there are unwanted oscillation which may arise the reduction of performance. Especially in low sliding speed condition, the stick-slip is an important issue because it because unstable motion as well as inaccurate position control in the system. Most previous works on the stick-slip are, however, only concerned with simple modeling under the condition of constant normal force. The normal force and the amount of hydraulic oil are variable with a cylinder stroke in the telescopic boom. This paper presents the pressure variations during stick-slip with the cylinder of telescope boom. Pressure variations by stick-slip has a similar pattern to that of single mass-spring model. The stick-slip is gradually decreased by means of increased flow rate.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.1060-1067
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• 2009

Previous research on the slope failure has mainly reported that most of the slope failures occur due to surface rainfall infiltration in the rainy season. A slope of which surface is protected by shotcrete or plants, can also fail due to increase in pore water pressure from the ground water flow beneath the surface, rather than from the surface. In this study such case of slope behavior is investigated using the model test and numerical method including strength reduction method. Hydraulic boundary conditions of the slopes is considered using coupled numerical scheme. The failure mechanism of the slope is investigated and the effect of pore water pressure on slope safety is identified. Increase in pore water pressure due to lateral infiltration has significantly reduced the stability of slope.

• Transactions of Materials Processing
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• v.19 no.2
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• pp.113-119
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• 2010

Hydroforming is the technology that utilizes hydraulic pressure to form tube or sheet materials into desired shapes inside die cavities. Tube hydroforming provides a number of advantages over the conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength. In many case, hydroformed parts have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. In this study for the numerical process design FE analysis was performed with DYNAFORM 5.5. Die parting angle and circumferential expansion ratio was optimized. With optimized condition, bulge and hydroforming experiments to form flange were performed. Forming characteristic at various pressure conditions was analyzed and optimized internal pressure condition was evaluated. The results show that flanged parts can be successfully produced by tube hydroforming process.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.89-95
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• 2016

This study investigated the design factors of the opening area in order to consider the kinematic stability of a valve plate, conducting an analysis of the reduction effects of pressure pulsation and flow ripple depending on the design factors, using the $SimulationX^{(R)}$ (Germany) hydraulic analysis program. Further, we performed a structure analysis to confirm the kinematic stability of the valve plate in a swash plate type piston pump, and analyzed the effects of pulsation on a 1-step V-type notch, 2-step V-type notch, and 2-step U-type notch to determine the effects of pulsation reduction. Finally, we show the effectiveness of our proposed design of the pre-compression sections on a valve plate in terms of low pulsation by using the hydraulic analysis program, $SimulationX^{(R)}$.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.162-169
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• 2000

This study was carried out to develop a continuously variable-speed transmission(CVT) for agricultural tractor. A full-toroidal CVT mechanism with four discs and six rollers was selected as a device for changing speed ratio continuously. In the step of system layout design, the sizes of roller cylinders and end-load cylinder, which were critical factors for controlling the variator, were designed. Also the control pressure range was designed to limit the contact pressure of variator. In order to make the maximum speed of vehicle as 30km/h, the planetary gear and the six pairs of gears were designed. Also the hydraulic clutch, silent chain, hydraulic manifold and electronic controller were designed. After the design, a prototype with CVT controller was developed and tested. The speed of vehicle was changed continuously to the speed set by driver and the settling time was about 0.52 second at the step-response test (reduction ratio of variator 2.0 to 1.0), which was acceptable as a response time for working with tractor.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.165-170
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• 2009

Pressure ripple, vibration and noise level are measured in each parts of the power steering system. MD(Mahalanobis Distance) is calculated by using MTS(Mahalanobis Taguchi System) with measured data, and noise sensitive components are selected. The components applied detail design parameters are made and data is measured. After that MD is calculated also. Mean value and SN ratio can be obtained from the MD. Effective noise reduction technique and dominant design parameters in hydraulic power steering system are introduced.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.296-303
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• 2002

Tribology, in other words, interacting surfaces in relative motion, is essential in life. The relative motion on surfaces may cause some problems with heat, vibration, noise, and so on. Unwanted vibrations by friction, which may arise during the operation of machines, are costly in terms of reduction of performance and service life. All these phenomena inolve stick-slip. The telescopic boom operations involves stick-slip oscillations like slideways. Unwanted stick-slip oscillations on telescopic boom operations cannot achieve smooth sliding and many developers of that machine makes a lot of effort to remove or reduce it. So this paper presents stick-slip oscillation with pressure of the hydraulic cylinder which drives booms, and attempts a theoretical approach for the numerical analysis for its stick-slip condition.

• Journal of Drive and Control
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• v.11 no.4
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• pp.53-60
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• 2014

This paper proposes a control scheme to reduce the power consumption of a variable displacement swash-plate type piston pump supplying oil to a valve-controlled hydraulic cylinder at constant pressure. Whenever flow rate demand was absent, the swash plate angle and the pump speed were changed to the minimum values required to compensate for the internal leakage flow. In response to command signals, the pump speed was changed in proportion to the absolute mean value of the speed component for position commands. At the same time, a pressure regulator was activated to maintain constant system pressure by precisely adjusting the pump speed with the swash plate angle fixed at the maximum. The conventional system consisting of a pressure-compensated variable displacement type pump is driven at a constant speed of 1,800rpm. By comparison, computer simulation and experimental results showed that idling power at stand-by status could be reduced by up to 70% by reducing the pump speed from 1,800rpm to 300rpm and the swash plate angle to the minimum.

• Membrane and Water Treatment
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• v.8 no.2
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• pp.185-199
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• 2017

Low-pressure membrane filtration is increasingly used for tertiary treatment of wastewater effluent organic matter (EfOM), mainly comprising organic base/neutral compounds. In-line coagulation with underdosing, charge neutralization, and sweep floc conditions prior to ultrafiltration (UF) was studied to determine removals of the EfOM components and consequent reduction of fouling using polyethersulfone membranes. Coagulation and UF substantially reduced fouling for all coagulation conditions while removing from 7 to 38% of EfOM organic acids. From 7 to 16% of EfOM organic base/neutrals were removed at neutral pH but there was no significant removal for slightly acid coagulation conditions even though fouling was substantially reduced. Sweep floc produced the lowest resistance to filtration but may be inappropriate for in-line use due to the large added volume of solids. Charge-neutralization resulted in poor recovery of the initial flux with hydraulic cleaning. Under-dosing paralleled sweep floc in reducing hydraulic resistance to filtration (for sub-critical flux) and the initial flux was also easily recovered with hydraulic cleaning. Hydrophobic and hydrophilic base/neutrals were identified on the fouled membranes but as previously reported the extent of fouling was not correlated with accumulation of organic base/neutrals.

• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.37-47
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• 2014

Unsaturated hydraulic conductivity (HC) is integrated theoretically from soil water retention curves (SWRC) by Mualem capillary model, but the prediction of HC is extremely sensitive to small variation of matric suction near saturation. Near saturation, the Mualem HC based on smooth SWRC decreases abruptly and has problems in the reliability of hydraulic behavior and the stability of numerical solutions. To improve van Genuchten-Mualem (VGM) HC, the van Genuchten SWRC model is modified within range of low matric suction (arbitrary air entry pressure). At an arbitrary air entry pressure, the VG SWRC is linearized in log scale until full saturation. The modified VG SWRC does not affect the fit of actual retention behavior and either the parameters of original VG SWRC fit. Using the modified VG SWRC, the VGM HC is modified to integrate for each interval decomposed by arbitrary air entry pressure. An analytical solution on modified VGM HC is proposed each interval, to protect the rapid change in HC near saturation. For silty soils, VGM models of HC function underestimate the unsaturated permeability characteristics and especially show rapid reduction near saturation. The modified VGM model predicts more accurate HC functions for Korean weathered soils. Furthermore, near saturation, the saturated HC is conserved by the modified VGM model. After 2-D infiltration analysis of an actual slope, the hydraulic behaviors are compared for VGM and the modified models. The prediction by the proposed model conserved the convergence of solutions on various rainfall conditions. However, the solution by VGM model did not converge since the conductivity near saturation reduced abruptly for heavy rainfall condition. Using VGM model, the factor of safety is overestimated in both initial and final stage during heavy rainfall. Stability analysis based on infiltration analysis could simulate the actual slope failure by the proposed model on HC.