• International Journal of Fluid Machinery and Systems
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• 제4권2호
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• pp.289-306
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• 2011

In the development of very high head pumped storage projects, one of the critical problems is the strength of pumpturbine runners. Data obtained by stress measurements of high head pump-turbine runners indicated that dynamic stress due to the vibration of runner might be detrimental, possibly to cause fatigue failure, if the runner were designed without proper consideration on its dynamic behaviour. Numerous field stress measurements of runners and model tests conducted with hydrodynamic similarity revealed that the hydraulic excitation force developed by the interference of rotating runner blades with guide vane wakes sometimes would induce such heavy vibration of runner. Theoretical and experimental investigations on both the hydraulic excitation force and the natural frequencies of runner have been conducted to explore this forced vibration problem.

• International Journal of Fluid Machinery and Systems
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• 제2권3호
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• pp.260-268
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• 2009

The effects of acoustic modes in the penstock on the self-excited oscillation in hydraulic power system were studied by assuming a finite sound velocity in the penstock. The flow in the draft tube is considered to be incompressible assuming that the length of the draft tube is smaller than the wavelength of the oscillation. It was found that various acoustic modes in the penstock can become unstable (amplified) by the diffuser effect of the draft tube or the effect of swirl flow from the runner. Their effects on each mode are discussed.

• 유공압시스템학회논문집
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• 제7권1호
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• pp.11-19
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• 2010

A gas-assisted hydraulic breaker uses both hydraulic and pneumatic energies and the appropriate balance between them mostly effects its performance. Mathematical modeling of the breaker is established and verified by experiment. Through sensitivity analysis using AMESim, the key design parameters are selected, which mostly affect the performance of the breaker. Taguchi method is used to optimize the key design parameters to maximize the output power for long and short strokes through simulation. As the result, the output power as well as the impact energy are increased significantly compared with the existing design. The pressure pulsation in the supply line is reduced to a tolerable level and the dynamic characteristics of the piston displacement is also improved by the optimization.

• 유공압시스템학회논문집
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• 제7권3호
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• pp.13-19
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• 2010

Hydraulic systems are widely used as a power transfer and/or power control system due to its flexibility, controllability, accuracy and high power density. Valve controlled and/or pump capacity controlled systems are normally adopted as a control device, but nowadays pump speed controlled systems are emerging as a new energy-efficient hydraulic control system. In this paper the pump speed controlled system for the cylinder position control of a counter balance circuit is investigated by simulation study and position control experiments were carried out. As a result, the possibility and efficiency of the pump speed controlled system were verified.

• 유공압시스템학회논문집
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• 제5권2호
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• pp.20-26
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• 2008

The most vehicle active suspension system is activated by a hydraulic source and transmission system which has nonlinear characteristics. Even though we have designed a proper controller for this system, it sometimes cannot show remarkable performance characteristics because of many factors that undercut the performance of the hydraulic system, such as nonlinearity, modelling errors, parameter variations etc. So, the robust controller that prevents a system from lowering its performance is needed. In this study, the sliding mode control which is the representative one of robust controllers is adopted to investigate system parameter sensibility. As a result, the sliding mode controller shows robustness to the system parameters variations relative to the other controllers.

• 유공압시스템학회논문집
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• 제1권1호
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• pp.23-30
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• 2004

This paper deals with the issue of trajectory tracking control of a hydraulic excavator using disturbance observer in order to compensate external disturbances occuring from coupling between attachment, asymmetry of a single rod cylinder, and deadzone of main control valve. Disturbance compensation control system with disturbance observer has been constructed for the boom and arm respectively. Simulation results were compared with experimental results to validate the computer simulation system of hydraulic excavator itself. Computer simulation shows that disturbance compensation control is effective for compensating system nonlinearity and thus improves positioning accuracy and trajectory tracking performance. Steady state error has been decreased by adding PI controller to this control scheme.

• 유공압시스템학회논문집
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• 제1권1호
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• pp.1-9
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• 2004

This paper addresses an approximation and tracking control of recurrent neural networks(RNN) using two-dimensional iterative learning algorithm for an electro-hydraulic servo system. And two dimensional learning rule is driven in the discrete system which consists of nonlinear output function and linear input. In order to control the trajectory of position, two RNN's with the same network architecture were used. Simulation results show that two RNN's using 2-D learning algorithm are able to approximate the plant output and desired trajectory to a very high degree of a accuracy respectively and the control algorithm using two same RNN was very effective to control trajectory tracking of electro-hydraulic servo system.

• 유공압시스템학회논문집
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• 제1권3호
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• pp.14-19
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• 2004

The Direct Drive Valve used in this study contains a pressure-feedback-loop in itself, then it can eliminate nonlinearity such as the square-root-term in flow rate calculation and the change of bulk modulus of hydraulic oil. In this study, assuming that the dynamic characteristic of the DDV is modelled as a first order lag system, an parameter identification method using the input data and the output data is applied to obtain DDV's mathematical model. Then, a state feedback controller was designed to implement the force control of hydraulic system, and the control performance was evaluated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.267-272
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• 1995

The paper describes an approach for measuring flow ripple generated by oil hydraulic axial piston pumps. Flow ripple has periodic waveforms due to the cyclic nature of a pump's operation, and interacts with the connected hydraulic systems such as pipes and components to produce a pressure ripple, also known as fluid-borne noise. It is indispensable to measure a flow ripple because increasing of vibration and noise caused by a flow ripple has become a point to be considered and has need of solving these problems. The measurement of flow ripple with high frequencies from oil hydraulic axial piston pumps is msde by using the remote instantaneous flow rate measurement method. As a result, the reverse flow through the relief groove in valve plate has an important effect upon a flow ripple generated by a pumps.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.829-834
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• 2000

This paper is primarily directed toward analyzing the transient response characteristics in hydraulic pipe lines. The exact solution to the transient response characteristics was obtained by using the complicated transfer function derived by Iberall. The discrepancy with the exact and approximate is small, so the approximate solution is adopted to the theoretical one. An equation was derived which describes the pressure times relationship Hat occurs at the end of volume terminated transmission line following a sudden pressure change at its inputs. As a result, It is found that the density has relationship about the Wave Propagation is very useful in analyzing the transient response characteristics of hydraulic pipe lines. The velocity of Pressure wave Propagation decreases as the density of fluid increased.