• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.135-142
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• 2008

Hydraulic power steering system has been adopted in seniority passenger and commercial vehicle system for an easy maneuverability and a smoother ride. In this study, hydraulic power steering system analysis model which includes hydraulics and mechanical sub-systems was developed using commercial software, AMESim in order to predict characteristics for various steering components. Each component which constructs system was modeled and verified by experimentally obtained characteristics curves of each components. The parameter sensitivity analysis such as valve opening area, torsional stiffness of torsion bar for system design are carried out by the analysis and experimental method. The predicted results by the development model were a good agreement with experimentally obtained results. The sensitivity investigation results rotary torque when changing an input shaft edge width, was most sensitive, to change in angle and slot width and supply flow of input shaft edge is not a lot sensitively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.2
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• pp.104-110
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• 1984

An electro-hydraulic copying system is developed and its performance is experimentally investigated. As compared with a mechanical hydraulic coping system, this system has a basic difference in that; (1) the stylus movement is converted into an electrical signal via a position transducer. (2)the actuator displacement is also measured by a position sensing element, which serves as a feedback signal. Since the system parameters affect the control performance, the response characteristics such as percentage overshoot, rise time, settling time and steady state error are experimentally obtained under variation of these variables. The system parameter include supply pressure, servo amplifier gain and feedback gain. The experimental result shows that the cutting tool follows a stylus input motion to a desirable accuracy. The implication of this result indicates that the developed system can enhance the copying accuracy of the conventionally used mechanical type of hydraulic copying system.

• Journal of Drive and Control
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• v.15 no.1
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• pp.16-27
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• 2018

Hydraulic torque load simulator is essential to test and qualify the performance of various angle control systems. Typically a flapper-type second stage servovalve is applied to the load simulator, but here the direct drive servovalve, which is a kind of one-stage valve and affected by the large flow force, is applied. Since the torque load is applied not to the stationary shaft but to the rotating shaft of the angle control system, the controlled torque of load simulator is not accurate due to the rotating speed of the angle control system. A feedforward compensator is designed and applied to minimize the disturbance-like effect. A mathematical model is derived and linearized to analyze the stability, accuracy and responsiveness of the torque load simulator. The parameter effects of a controller, servovalve, hydraulic motor, rotating spring shaft are analyzed and summarized. The goodness of the linear analysis is verified by the digital computer simulations using both the linear and nonlinear mathematical models.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.412-420
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• 2003

This study describes the merits of PWM control of hydraulic system using high speed on-off valves. Generally, Electro-hydraulic valves can be classified into two classification: valves which are controlled by analog signal and which are controlled by digital. The former includes hydraulic servo valves and proportional valves which require A/D converters as interface to digital computer and too costly and sensitive to oil contamination because of complexity in structures. The latter includes high speed on-off valves which do not require A/D converters because they are normally operated in a pulse width modulation(PWM) method, and are low in price and robust to oil contamination because of their simple structures. The objectives of this study is to analyze the limit cycle which regularly appear in the position control system using 2/2way high speed on-off valves and to give a criterion for the stability of this system. The nonlinear characteristics of PWM and cylinder friction of this system are described by harmonic linearization and the effects of parameter variations to the system stability are simulated.

• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.562-567
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• 2010

A One-Dimensional Water Flow and Contaminant Transport in Unsaturated Zone (FTUNS) code has been developed in order to interpret radionuclide migration in an unsaturated zone. The pore-size distribution index (n) and the inverse of the air-entry value ($\alpha$) for an unsaturated zone were measured by KS M ISO 11275 method. The hydraulic parameters of the unsaturated soil are investigated by using soil from around a nuclear facility in Korea. The effect of hydraulic parameters on radionuclide migration in an unsaturated zone has been analyzed. The higher the value of the n-factor, the more the cobalt concentration was condensed. The larger the value of $\alpha$-factor, the faster the migration of cobalt was and the more aggregative the cobalt concentration was. Also, it was found that an effect on contaminant migration due to the pore-size distribution index (n) and the inverse of the air-entry value ($\alpha$) was minute. Meanwhile, migrations of cobalt and cesium are in inverse proportion to the Freundich isotherm coefficient. That is to say, the migration velocity of cobalt was about 8.35 times that of cesium. It was conclusively demonstrated that the Freundich isotherm coefficient was the most important factor for contaminant migration.

• Smart Structures and Systems
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• v.29 no.4
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• pp.599-616
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• 2022

Bridge displacement contains vital information for bridge condition and performance. Due to the limits of direct displacement measurement methods, the indirect displacement reconstruction methods based on the strain or acceleration data are also developed in engineering applications. There are still some deficiencies of the displacement reconstruction methods based on strain or acceleration in practice. This paper proposed a novel method based on long short-term memory (LSTM) networks to reconstruct the bridge dynamic displacements with the strain and acceleration data source. The LSTM networks with three hidden layers are utilized to map the relationships between the measured responses and the bridge displacement. To achieve the data fusion, the input strain and acceleration data need to be preprocessed by normalization and then the corresponding dynamic displacement responses can be reconstructed by the LSTM networks. In the numerical simulation, the errors of the displacement reconstruction are below 9% for different load cases, and the proposed method is robust when the input strain and acceleration data contains additive noise. The hyper-parameter effect is analyzed and the displacement reconstruction accuracies of different machine learning methods are compared. For experimental verification, the errors are below 6% for the simply supported beam and continuous beam cases. Both the numerical and experimental results indicate that the proposed data fusion method can accurately reconstruct the displacement.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.35-35
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• 2023

The main reason for its instability is sediment scouring downstream of hydraulic structures. Both physical and numerical models have been used to investigate the influence of soil properties on scour hole geometry. Nevertheless, no research has been conducted on resistance parameters that affect sedimentation and erosion. In addition, auxiliary structures like wing walls, which are prevalent in many real-world applications, have rarely been studied for their impact on morphology. The hydraulic characteristics of steady flow through a boxed culvert are calibrated using a 3D Computational Fluid Dynamics model compared with experimental data in this study, which shows a good agreement between water depth, velocity, and pressure profiles. Test cases showed that 0.015 m grid cells had the lowest NRMSE and MAE values. It is also possible to quantify sediment scour numerically by testing roughness/d₅₀ ratios (c_s) and diversion walls at a meander flume outlet. According to the findings, c_s = 2.5 indicates a close agreement between numerical and analytical results of maximum scour depth after the culvert; four types of wing walls influence geometrical deformation of the meander flume outlet, resulting in erosion at the concave bank and deposition at the convex bank; two short headwalls are the most appropriate solution for accounting for small changes in morphology. A numerical model can be used to estimate sediment scour at the meander exit channel of hydraulic structures based on the roughness parameter of soil material and headwall type.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.1
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• pp.39-47
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• 2014

In this study, 2 degree of freedom PID controller is added to the conventional feed-forward controller for the purpose of improving its limitations such as set-point of tracking performance and disturbance suppression performance in the conventional PID controller. And the controller parameters optimization as a Real Coded Genetic Algorithm (RCGA) is used. Simulation and experiments verify the performance of the controller.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1613-1626
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• 2002

This paper presents hybrid control of an active suspension system with a full-car model by using H$\sub$$\infty$/ and nonlinear adaptive control methods. The full-car model has seven degrees of freedom including heaving, pitching and rolling motions. In the active suspension system, the controller shows good performance: small gains from the road disturbances to the heaving, pitching and rolling accelerations of the car body. Also the controlled system must be robust to system parameter variations. As the control method, H$\sub$$\infty$/ controller is designed so as to guarantee the robustness of a closed-loop system in the presence of uncertainties and disturbances. The system parameter variations are taken into account by multiplicative uncertainty model and the system robustness is guaranteed by small gain theorem. The active system with H$\sub$$\infty$/ controller can reduce the accelerations of the car body in the heaving, pitching and rolling directions. The nonlinearity of a hydraulic actuator is handled by nonlinear adaptive control based on the back-stepping method. The effectiveness of the controllers is verified through simulation results in both frequency and time domains.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.1
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• pp.120-125
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• 2005

In this paper, We propose the fuzzy controller for the gain tuning of PID controller The proposed controller doesn't use the crisp output error and rule tables though with a fuzzy inference process in forward fuzzifier, New Fuzzy PID Controller assigns relations and ranges of two variables of PID gain parameters. These new gain parameters are calculated by the fuzzy inference with max-min ranges of Kp and Kd. The Ki parameter is computed automatically between Kp and Kd parameter Is calculated by Ziegler-Nickels tuning rules. Finally we experimented the propose controller by the hydraulic servo motor control system. We can obtained desired results through the good control characteristics.