• 동력기계공학회지
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• 제17권1호
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• pp.77-84
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• 2013

The proportional pressure control valve that was used to relief valve has different dynamic characteristics on each case. Because this valve has different assembling or processing error and environmental condition. However, a customer who used the relief valve wants to have a steadily performance even if the dynamic characteristics of valve was changed. For this reason, the manufacturer try to make the robust controller that has simple structure. This paper concerns about the design of robust controller that didn't affected by plant parameter's changing. The control strategy is a model reference control that conducted by on line identification problem, gradient method and Lyapunov equation. This adaptvie control law's validity that this paper deal with was confirmed by an results of step response test or hysteresis test.

• 한국데이터정보과학회:학술대회논문집
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• 한국데이터정보과학회 2004년도 춘계학술대회
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• pp.39-50
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• 2004

The decision tree approach is most useful in classification problems and to divide the search space into rectangular regions. Decision tree algorithms are used extensively for data mining in many domains such as retail target marketing, fraud dection, data reduction and variable screening, category merging, etc. CHAID(Chi-square Automatic Interaction Detector) uses the chi-squired statistic to determine splitting and is an exploratory method used to study the relationship between a dependent variable and a series of predictor variables. In this paper we propose CHAID algorithm by cube-based proportional sampling and explore CHAID algorithm in view of accuracy and speed by the number of variables.

• Journal of the Korean Data and Information Science Society
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• 제15권4호
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• pp.803-816
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• 2004

The decision tree approach is most useful in classification problems and to divide the search space into rectangular regions. Decision tree algorithms are used extensively for data mining in many domains such as retail target marketing, fraud dection, data reduction and variable screening, category merging, etc. CHAID uses the chi-squired statistic to determine splitting and is an exploratory method used to study the relationship between a dependent variable and a series of predictor variables. In this paper we propose CHAID algorithm by cube-based proportional sampling and explore CHAID algorithm in view of accuracy and speed by the number of variables.

• 터널과지하공간
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• 제8권2호
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• pp.79-86
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• 1998

This study was performed to suggest to suggest suitable design conditions of water curtain system through analysis on pressure down in boreholes by hydraulic tests carried out I construction fields for underground oil storages. The influence by hydraulic conductivities of rock mass around boreholes on pressure down in boreholes was analysed. The relationship between array of boreholes and their pressure down was also analysed. Groundwater flow analysis on crude oil and LPG storages was carried out to evaluate results of field tests and to investigate distribution of hydraulic gradient in rock mass around cavern using finite difference method. As the results, hydraulic tests showed that pressure down in boreholes was inverse proportional to the hydraulic conductivity of surrounding rock mass. The rate of pressure down of boreholes was not influenced by water curtain system more than 20m over cavern and was proportional to installation interval of boreholes. The hydraulic gradient in rock mass around cavern was proportional to distance and interval of boreholes and its value was not satisfactory to oil tightness condition in case of no water curtain system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5328-5346
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• 2016

An optimal power control algorithm based on convex optimization is proposed for base stations in long term evolution networks. An objective function was formulated to maximize the proportional fairness of the networks. The optimal value of the objective function was obtained using convex optimization and distributed methods based on the path loss model between the base station and users. Field tests on live networks were conducted to evaluate the performance of the proposed algorithm. The experimental results verified that, in a multi-cell multi-user scenario, the proposed algorithm increases system throughputs, proportional fairness, and energy efficiency by 9, 1.31 and 20.2 %, respectively, compared to the conventional fixed power allocation method.

• Journal of Communications and Networks
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• 제13권6호
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• pp.633-638
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• 2011

In this paper, we consider resource allocation with proportional fairness in the downlink orthogonal frequency division multiple access relay networks, in which relay nodes operate in decode-and-forward mode. A joint optimization problem is formulated for relay selection, subcarrier assignment and power allocation. Since the formulated primal problem is nondeterministic polynomial time-complete, we make continuous relaxation and solve the dual problem by Lagrangian dual decomposition method. A near-optimal solution is obtained using Karush-Kuhn-Tucker conditions. Simulation results show that the proposed algorithm provides superior system throughput and much better fairness among users comparing with a heuristic algorithm.

• Journal of Communications and Networks
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• 제12권1호
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• pp.30-42
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• 2010

In this work we consider the problem of downlink resource allocation for proportional fairness of long term received rates of data users and quality of service for real time sessions in an OFDMA-based wireless system. The base station allocates available power and subchannels to individual users based on long term average received rates, quality of service (QoS) based rate constraints and channel conditions. We formulate and solve a joint bandwidth and power optimization problem, solving which provides a performance improvement with respect to existing resource allocation algorithms. We propose schemes for flat as well as frequency selective fading cases. Numerical evaluation results show that the proposed method provides better QoS to voice and video sessions while providing more and fair rates to data users in comparison with existing schemes.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 추계학술대회 논문집
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• pp.143-144
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• 2016

The circulating current control within the phase legs is one of the main control objectives in a modular multilevel converter (MMC) under different operating conditions. This paper proposes a control strategy of circulating currents in the MMC under unbalanced voltage by using a proportional-resonant (PR) controller. Under the unbalanced voltage, the circulating currents in the MMC consists of three components such as positive-sequence, negative-sequence, and zero-sequence circulating currents. With the PR controller, all components of the circulating current will be directly controlled in the stationary reference frame without decomposing into positive- and negative-sequence components. Thus, the ripples in the circulating currents and the DC current are suppressed under the unbalanced voltage. The effectiveness of the proposed method is verified by simulation results based on PSCAD/EMTDC simulation program.

• 드라이브 ㆍ 컨트롤
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• 제17권4호
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• pp.54-71
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• 2020

In light of the environmental challenges, energy-saving strategies are currently under investigation in the construction industry. This paper focuses on the energy-saving method used in the hydraulic system based on independent metering (IM) technologies, which can overcome the lost energy at the main control valve of the conventional electrohydraulic servo system. By scientifically arranging the proportional valves, the IM system can individually control the flow rate of the inlet and the outlet ports of the actuators. In addition, the IMV system can be used to effectively regenerate energy under different operating modes, thereby saving more energy than conventional hydraulic systems. Therefore, the IMV system has a great potential to improve the energy efficiency of hydraulic machinery. The overall IMV system, including the configuration, proportional valve, operation mode, and the control strategy is introduced via state-of-the-art hydraulic technologies. Finally, the challenges of IM systems are discussed to provide researchers with directions for future development.

• 품질경영학회지
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• 제17권2호
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• pp.17-26
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• 1989

This paper is concerned with forecasting the existing number of errors in the computer software and optimizing the stopping time of the software test based upon the forecasted number of errors. The most commonly used models have assessed software reliability under the assumption that the software failure late is proportional to the current fault content of the software but invariant to time since software faults are independents of others and equally likely to cause a failure during testing. In practice, it has been observed that in many situations, the failure rate decrease. Hence, this paper proposes a mathematical model to describe testing situations where the failure rate of software limearly decreases proportional to testing time. The least square method is used to estimate parameters of the mathematical model. A cost model to optimize the software testing time is also proposed. In this cost mode two cost factors are considered. The first cost is to test execution cost directly proportional to test time and the second cost is the failure cost incurred after delivery of the software to user. The failure cost is assumed to be proportional to the number of errors remained in the software at the test stopping time. The optimal stopping time is determined to minimize the total cost, which is the sum of test execution cast and the failure cost. A numerical example is solved to illustrate the proposed procedure.