• Journal of Advanced Marine Engineering and Technology
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• v.11 no.3
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• pp.61-69
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• 1987

The PID controller is one of the most popular devices for control systems and the adjustment of its parameters has been generally accomplished by semi-empirical rules and has been considered only in the view of improvement of the control performance. But in modern control theory, a quadratic form is introduced as a criterion function which considers not only to improve quality of control but also to save energy required for the control. In this paper, authors propose a method of the parameter adjustment of the PID controller by means of maximum principle minimizing the quadratic criterion function and establish a link between the conventional parameter adjustment method and the technique of the modern optimal control theory in the design of a PID controller.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.1
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• pp.38-44
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• 1998

The modified maximum likelihood estimation method is used to estimate the nondimensional aerodynamic derivatives of a single turbo-prop aircraft at a specified flight condition for the best deduction of the dynamic characteristics. In wind axes the six degree of freedom equations are algebraically linearized so that the linear state equation contains aerodynamic derivatives in a state-space form and is used in the maximum likelihood method. The simulated data added with the measurement noise is used as a flight test data which is necessary to the estimation of nondimensional aerodynamic derivatives. It is obtained by implementing the 6-DOF nonlinear flight simulation. In the flight simulation, the effects of several control input types, control deflection amplitudes, and the turbulence intensities on the statistical convergence criteria are also examined and quantitative analysis of the results is discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.53-63
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• 1997

In this paper, we present a new macroblock-based bit allocation scheme in multiple MPEG-1 video encoders system and a single multiplexer over a single channel. The proposed scheme models the relations between fate(Bits/MB) and distortion(MSE/MB), rate and quantizer parameter(QP), distortion and quantizer parameter, respectively, in the same form. By using these relations, we minimize the Larangian cost function to obtain a bit allocation scheme based on macroblock unit. Experimental results show that the proposed scheme can reduce MSE compared to other conventional buffer-based rate control methods, i.e. independent buffer control method and shared common buffer control one. And we confirmed, through computer simulation, that the proposed scheme can be effectively modified to maintain the objective quality of a specific video service at a constant level.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.3
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• pp.55-61
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• 2003

The form accuracy of parts has become an important parameter. Therefore, not only dimensional tolerance but also geometric tolerances are used in the design stage to satisfy the required quality and functions of parts. But the information on the machining conditions, which can satisfy the assigned geometric tolerance in do sign, is insufficient. The objectives of this research are to study the effects of the grinding parameters such as traverse speed, work speed, depth of cut, and dwell time on the after-ground workpiece shape, and to find out the major parameters among them The results are as follows; The effects of work speed and depth of cut on the workpiece shape are negligible compared with the effect of traverse speed. These is an optimal dwell time depending on the traverse speed. The optimal dwell time is decreasing as the traverse speed is increasing.

• Transactions of Materials Processing
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• v.19 no.4
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• pp.203-209
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• 2010

In the hot press forming process (HPF), a martensitic structure is obtained by controlling the cooling rate when cooling a boron sheet that is heated up to over $900^{\circ}C$. The HPF process has various advantages such as the improvement in formability and material properties and minimal spring back of the deformed materials. The factors related to the cooling rate depend on the heat transfer characteristics between heated materials and dies. Therefore, in this study, the cooling rate is controlled by adjusting the heat transfer coefficient of the material at the pressing process. And, the mechanical properties and microstructure of the deformed material is demonstrated during the HPF process where cold dies are used to form the heated steel plate. This is achieved by varying the major forming conditions that control the cooling rate regarded as the most important process parameter.

• Journal of the Korean Ceramic Society
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• v.20 no.3
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• pp.217-226
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• 1983

Adquate amount of calcia was added to the regent-grade Zirconia body. Here the amount and the form of calcia were 7-21 mol% and regent-grade calcium cabonate respectively. The specimens were fired at 175$0^{\circ}C$ for 0, 3, 5 and 7 hours respectively. The phase Strength X-ray diffraction analysis and Scaning electron microscopy. The results were as follows (1) As the additive amount of calcia was increased the firing linear shrinkage apparent density compressive strength and modulus of rupture decreased but the apparent porosity increased. (2) The specimens soaked and containing calcia displayed the grain growth. (3) Monoclinic and cubic zirconia were seen in the sepcimens containing 7 mol% calcia. When without soaking the specimens containing 7-10 mol% calcia had the volume change by monoclinic$\rightleftharpoons$tetragonal transformation. (4) The lattice parameter increased according as the calcia additive was increased. The specimens containing above 19mol% calcia had the costant lattice parameter. The value of that was from 5.1264 to 5.1396 $\AA$ in the case of 7 hours soaking.

• Proceedings of the KIEE Conference
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• 2001.07e
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• pp.108-112
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• 2001

Vector control schemes are used in inverter-fed induction motor drives to obtain high performance. Crucial to the success of the vector control scheme is the knowledge of the instantaneous position of the rotor flux. However, the position of the rotor flux change with temperature and magnetic saturation of the motor. This variation cause deterioration of both steady state and dynamic operation of the motor drives. Performance degradation is in the form of input-output torque nonlinearity and saturation of the motor. Analytic expressions are derived to evaluate the effects due to parameter sensitivity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.7-11
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• 2003

for many years already, testing laboratories, research institutes and manufactures try to find a reliable water tree accelerated ageing test that is able to show whether a polymer Medium Voltage cable os susceptible to water treeing or not. Test on laboratory samples, model cable designs, and fell size cable are presented. Apart form aging, another important aspect of any accelerated aging test is the right choice of th preconditioning method. THTS paper is the analysis of weibull distribution method after an accelerated aging test of MV(Medium Cable) cable.

• Nuclear Engineering and Technology
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• v.49 no.8
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• pp.1645-1653
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• 2017

This investigation explores the thermally stratified stretchable flow of an Oldroyd-B material bounded by a linear stretched surface. Heat transfer characteristics are addressed through thermal stratification and heat generation/absorption. Formulation is arranged for mixed convection. Application of suitable transformations provides ordinary differential systems through partial differential systems. The homotopy concept is adopted for the solution of nonlinear differential systems. The influence of several arising variables on velocity and temperature is addressed. Besides this, the rate of heat transfer is calculated and presented in tabular form. It is noticed that velocity and Nusselt number increase when the thermal buoyancy parameter is enhanced. Moreover, temperature is found to decrease for larger values of Prandtl number and heat absorption parameter. Comparative analysis for limiting study is performed and excellent agreement is found.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.11
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• pp.1031-1037
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• 2000

Isothermal vapor-liquid equilibrium(VLE) data have been obtained for the systems of propane(R290)+1,1,1,2-tetrafluoroethane(R134a) and 1,1,1,2-tetrafluoroethane(R134a)+isobutane(R60A) in the temperature range of 253.15 to 323.15K. Experiments were performed in a circulation type apparatus by injecting vapor through liquid pool using a magnetic pump. Both systems form azeotropes in the temperature range of this study. The experimental results were estimated with the Peng-Robinson equation of state. When the temperature-dependent binary interaction parameter was used in the Peng-Robinson equation of state, the absolute average deviation of the measured bubble point pressures from the values correlated by the Peng-Robinson equation was 0.65% and 0.78% for R290+R134a and R134a+600a, respectively. Azeotropic compositions for both systems were presented.