• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1487-1490
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• 2002

In this paper, a design methodology of fuzzy sliding mode control scheme for a hydraulic elevator controlled by inverter is presented. The proposed scheme uses a fuzzy sliding mode controller(FSMC), which is designed based on the similarity between the fuzzy logic control(FLC) and the sliding mode control(SMC). The proposed method has advantages that the stability and the robustness of the FLC are proved and ensured by the sliding mode control law, and the computation burden could be reduced greatly. The validity and the effectiveness of the proposed control method have been shown through the real world industrial application results.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.64-69
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• 2002

A numerical study has been peformed for evaluation of convection schemes for thermal hydraulic analysis in a liquid metal reactor Four convection schemes, HYBRID, QUICK, SMART and HLPA included in the CFX-4 code are considered. The performances of convection schemes are evaluated by applying them to the five test problems. The accuracy, stability and convergence are tested. It is shown that the HYBRID scheme is too diffusive, and the QUICK scheme exhibits overshoots and undershoots, and the SMART scheme shows convergence oscillations, and the HLPA scheme preserves the boundedness without causing convergence oscillations. The accuracies of SMART, QUICK and HLPA schemes are comparable. Thus, the use of HLPA scheme is highly recommended for thermal hydraulic analysis in a liquid metal reactor.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.226-233
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• 1999

A transmitting antenna mounted on the naval vessels can be easily exited by exogenous disturbances such as wave and impact. Gimbal system need for the controller to maintain the robust performance against various modeling uncertainties and disturbances. PI controller, however, cannot supply good robust performance under situation. Thus a robust $H_{\infty}$ control scheme is used to ensure a specified dynamic response under above conditions. Gimbal system controlled simplified as 2 DOF system that ignored coordinate co-relations of each direction and hydraulic system is linearly modelled. In this paper, we compared those of simulation to the results of experiment and H$_{\infty}$ controller, proposed, showed the good response and stability than PI controller.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.44-52
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• 1994

Load simulator is essential to test and quality the performance of various control systems. It is good time to introduce a method to design and analyze the load simulator or since many research centers and industrial companies are trying to buy or design the load simulator. The stability, accuracy and response speed of the simulator are represented by the system parameters such as the hydraulic motor characteristics, the servovalve characteristics, supply pressure, rotational inertia, rotational spring constant, sensor and controller gains. Two design examples are shown here. A load simulator for a position control system and that for a velocity control system are designed. The goodness of the proposed method is verified by the digital computer simulations.

• Journal of Drive and Control
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• v.15 no.4
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• pp.61-66
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• 2018

Almost every hydraulic system is equipped with a pressure relief valve, to maintain working pressure of the system at a pre-determined level. Thus, dynamic characteristics of such a relief valve, in conjunction with other hydraulic components, are important in designing the hydraulic control system. The single stage pressure relief valve is dynamically undesirable, due to relatively low viscous damping, that causes high frequency oscillations. This problem is overcome by introducing orifices in the inner pilot line, and drain line. In this study, for the single stage spool type pressure relief valve, the system equations were derived through an adequate linearisation and several simplifications were made, to use the transfer function formulation technique. All coefficients were evaluated and used, to make some results by using Matlab software. Results of analysis are compared with experimental results. In this study, parameters affecting stability of valve design are determined and suggested relative to the design.

• Structural Monitoring and Maintenance
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• v.6 no.1
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• pp.1-17
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• 2019

Preserving reservoir safety has recognized to be important for the public where a vast majority of dams are located upstream of greatly populated cities and industrialized areas. Buckling, floatation and cavitation have caused failure in the spillway gates and conveyance features during past catastrophic events; showed their vulnerability and need for regular inspection along with reviewing design calculations to ensure the spillway meet current design standards. This paper investigates the hydraulic and structural consideration of dam's spillway by evaluating the data of Karkheh Dam's. Discharge capacity, flood routings and cavitation damage risk were main features for hydraulic considerations where hydrostatic and hydrodynamic forces and stability conditions were considered in structural considerations.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.54-59
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• 2019

The main objective of nuclear reactor safety is to maintain the nuclear fuel in a thermally safe condition with enough safety margins during normal operation and anticipated operational occurrences. In this research, core flow bypass is studied under the conditions of the unavailability of safety systems. As core bypass occurs, the core flow rate is assumed to decrease exponentially with a time constant of 25 s to new steady state values of 20, 40, 60, and 80% of the nominal core flow rate. The thermal hydraulic code PARET is used through these calculations. Reactor thermal hydraulic stability is reported for all cases of core flow bypass.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10a
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• pp.747-752
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• 1987

The dynamic characteristics of a load-sensing hydraulic servo system are complex and highly unstable. Another property of the system is that the setting value of pump compensator is closely related to energy efficiency as well as control performance of the system. This necessitates the development of an effective control algorithm which guarantees good control performance, stability and energy efficiency. This paper considers a suboptimal PID control for the velocity control problem of the load-sensing hydraulic servo system. The results of simulations studies and experiments show that the proposed suboptimal controller can produce much better control performance than nonoptimal controllers and give effective energy efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.4
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• pp.31-40
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• 1986

With the tendency toward high speed and high pressure in centrifugal pumps, the problem of sub-synchronous vibration has arisen, caused by the hydraulic forces of the working fluid, such as wearring, balance piston, impeller, etc.. These forces can drastically alter the rotor critical speeds and stability characteristics, and can be acted significant destabilizing forces. For preventing such self-excited vibration, the desing of the rotor system needs, which would secure the stability of the machine. In this paper, a procedure is presented for dynamic modeling of rotor-bearing-seal-impeller systems which consist of rigid disks, distributed parameter finite rotor elements and discrete bearings, seals and impellers. A finite element model including the effects of rotatory inertia and gyroscopic moments is developed using the consistent matrix approach. The technique of dynamic matrix reduction is applied to the shaft matrices to reduce them to a set of matrices of dynamic of significantly fewer degrees of freedom. The representation of bearing, seal and impeller elements is in term of linearized stiffness and damping matrices by reasonably small perturbations from equilibrium. The stability behavior of a typical double suction centrifugal pump is presented. Results show the influence of clearance and flow conditions on running speeds and stability characteristics.

• Journal of the Korean Society of Safety
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• v.19 no.2
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• pp.88-92
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• 2004

The paper decribes a procedure for the evaluation of the effect of seepage force on stability of slopes. The stability of an embankment impounding a water reservoir is highly depend upon the location of seepage line with the embankment. To evaluate the accurate safety factor of an embankment, it is important to illustrate the seepage phenomenon. Of particular interest is the stability following a rapid change of reservoir level. Seepage forces in embankments are easily determined interest is the stability following a rapid change of resrvoir level. Seepage forces in embankments are easily detemined if frictional forces are expressed in relation to hydraulic gradient I. If a piezometer is inserted into a body of embankment, the level to which fee water rises is a measure of the energy at that point.