• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.1
• /
• pp.246-253
• /
• 2013

This paper addresses the technology of active flow control for stabilizing a flow field. In order for flow field modeling from the control point of view, the huge-data set from CFD(computational fluid dynamics) are reduced by using a POD(Proper Orthogonal Decomposition) method. And then the flow field is expressed with dynamic equation by low-order modelling approach based on the time and frequency domain analysis. A neural network flow estimator from the pressure information measured on the surface is designed for the estimation of the flow state in the space. The closed-loop system is constructed with feedback flow controller for stabilizing the vortices on the flow field.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.9
• /
• pp.1617-1624
• /
• 2006

This paper presents system modeling, modified space vector PWM implementation and design of a closed loop controller of the Z-source inverter which consists of L and C components and shoot-through zero vectors for DGS. Zero vector periods of SVPWM utilized to boost DC-link voltage instead of conventional DC/DC converter and transformer. Only two shoot-through vut(nn are used for DC link voltage control during one switching period without loss of non-zero vectors. Discrete time sliding mode controller, robust servomechanism controller are designed to realize fast and no-overshoot current response and a steady state voltage error. Simulation results are shows the effectiveness of the proposed algorithm.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.5
• /
• pp.155-160
• /
• 2018

In this paper, we found that buffer cache in general systems does not perform well in rendering software, and presented a new buffer cache management scheme that resolves this problem. To do so, we collected various file I/O traces of rending software and analyzed their characteristics. From this analysis, we observed that file I/Os in rendering consist of long loops, short loops, random accesses, and write-once accesses. Based on this observation, we presented a buffer cache management scheme that allocates cache space to each access types and manages them appropriately, thereby improving the buffer cache performances by 19% on average and up to 55%.

• Proceedings of the KIEE Conference
• /
• 2005.10b
• /
• pp.158-160
• /
• 2005

This paper presents a new approach to the problem of designing a cascaded three-parameters controller for a given linear time invariant (LTD plant in unity feedback system. We consider a proportional-integral-derivative (PID) and a first-order controller with specified overshoot and settling time. This problem is difficult to solve because there may be no analytical solution due to the use of low-order controller and furthermore. the zeros of controller just appear in the zeros of feedback system. The key idea of our method is to impose a constraint on the controller parameters so that the zeros of resulting controller are distant from the dominant pole of closed-loop system to the left as far as the given interval. Two methods realizing the idea are suggested. We have employed the characteristic ratio assignment (CRA) in order to deal with the time response specifications. It is noted that the proposed methods are accomplished only in parameter space. Several illustrative examples are given.

• Journal of Ocean Engineering and Technology
• /
• v.21 no.5
• /
• pp.47-54
• /
• 2007

Ship structures are subject to severe environmental loads causing appreciable hull girder deflection which in turn affects the piping system attached to the main hull in the form of displacement load. While this load may cause failure in the pipes, loops have been widely adopted as a measure of preventing this failure with the idea that they may lower the stress level in a pipe by absorbing some portion of the displacement load. But as the loops also have some negative effects such as causing extra manufacture cost, deteriorating the function of the pipe and occupying extra space, the number and the dimensions of the loops adopted need to be minimized. This research develops a design formula for pipe loops. The accuracy of the proposed design formula was verified by comparing two results respectively obtained by the proposed formula and MSC/NASTRAN. The paper ends with the sample example showing the efficiency of the proposed formula.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.8 no.5
• /
• pp.416-424
• /
• 1984

A numerical and experimental investigation was carried out on the single-phase natural circulation system. This study is concerned with the multiloop system which is relevant to the primary system of the pressurized water reactor. For numerical analysis, five time-dependent governing equations were derived using the one-dimensional lumped parameter model. These equations were discretized by the space-time integration technique, and a simplified computer program, SIMFARS, was developed to solve those discretized equations. Experiments were performed for two purposes-one is to validate the developed code, and the other is to understand the qualitative behavior of the natural circulation loop. Comparison of the computational results with experiments, and several experimental and numerical results are presented in this article.

• Journal of Mechanical Science and Technology
• /
• v.16 no.1
• /
• pp.75-82
• /
• 2002

A simultaneous optimal design problem of structural and control systems is discussed by taking a 3-D truss structure as an object. We use descriptor forms for a controlled object and a generalized plant because the structural parameters appear naturally in these forms. We consider a minimum weight design problem for structural system and disturbance suppression problem for the control system. The structural objective function is the structural weight and the control objective function is $H_{\infty}$ norm from the disturbance input to the controlled output in the closed-loop system. The design variables are cross sectional areas of the truss members. The conditions for the existence of controller are expressed in terms of linear matrix inequalities (LMI) By minimizing the linear sum of the normalized structural objective function and control objective function, it is possible to make optimal design by which the balance of the structural weight and the control performance is taken. We showed in this paper the validity of simultaneous optimal design of structural and control systems.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.1
• /
• pp.126-132
• /
• 2012

This paper suggests a design method of the model-following H${\infty}$ control system having robust performance. This H${\infty}$ control system is designed by applying genetic algorithm(GA) with reference model to the optimal determination of weighting functions and design parameter ${\gamma}$ that are given by Glover-Doyle algorithm which can design H${\infty}$ controller in the state space. These weighting functions and design parameter ${\gamma}$ are optimized simultaneously in the search domain guaranteeing the robust performance of closed-loop system. The effectiveness of this H${\infty}$ control system is verified by applying to the boiler-turbine control system.

• Journal of Ocean Engineering and Technology
• /
• v.23 no.1
• /
• pp.158-163
• /
• 2009

Many longitudinal pipes in ships are subject to considerable loads, caused by hull girder bending in the ships and/or thermal loads in some special pipes through which fluids with highly abnormal temperatures are conveyed. As these loads may cause failure in the pipes or their supporting structures, loops have been widely adopted to prevent such failure, based on the idea that they can lower the stress level in a pipe byabsorbing some portion of these loads. But as the loops also have some negative effects, such as causing extra manufacturing cost, deteriorating the function of the pipe, and occupying extra space, the number and dimensions of these loops need to be minimized. This research developed design formulas for pipe loops, modeling them as a spring element, for which the axial stiffness is calculated based on the beam theory, incorporating the flexibility effect of the straight portion of the pipe. The accuracy of the proposed design formulas was verified by comparing two results obtained from the proposed formulas and MSC/NASTRAN. This paper concludes with a sample application of the proposed formulas, showing their efficiency.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.64 no.7
• /
• pp.1005-1011
• /
• 2015

This paper proposes the DC offset compensation algorithm with fast response to the sensed grid voltage in the single-phase grid connected inverter. If the sensor of the grid voltage has problems, the DC offset of the grid voltage can be generated. This error must be resolved because the DC offset can generate the estimated grid frequency error of the phase-locked loop (PLL). In conventional algorithm to compensate the DC offset, the DC offset is estimated by integrating the synchronous reference frame d-axis voltage during one period of the grid voltage. The conventional algorithm has a drawback that is a slow dynamic response because monitoring the one period of the grid voltage is required. the proposed algorithm has fast dynamic response because the DC offset is consecutively estimated by transforming the d-axis voltage to synchronous reference frame without monitoring one cycle time of the grid voltage. The proposed algorithm is verified from PSIM simulation and the experiment.