• Title/Summary/Keyword: variable design parameter

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Concept of Seasonality Analysis of Hydrologic Extreme Variables and Design Rainfall Estimation Using Nonstationary Frequency Analysis (극치수문자료의 계절성 분석 개념 및 비정상성 빈도해석을 이용한 확률강수량 해석)

  • Lee, Jeong-Ju;Kwon, Hyun-Han;Hwang, Kyu-Nam
    • Journal of Korea Water Resources Association
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    • v.43 no.8
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    • pp.733-745
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    • 2010
  • Seasonality of hydrologic extreme variable is a significant element from a water resources managemental point of view. It is closely related with various fields such as dam operation, flood control, irrigation water management, and so on. Hydrological frequency analysis conjunction with partial duration series rather than block maxima, offers benefits that include data expansion, analysis of seasonality and occurrence. In this study, nonstationary frequency analysis based on the Bayesian model has been suggested which effectively linked with advantage of POT (peaks over threshold) analysis that contains seasonality information. A selected threshold that the value of upper 98% among the 24 hours duration rainfall was applied to extract POT series at Seoul station, and goodness-fit-test of selected GEV distribution has been examined through graphical representation. Seasonal variation of location and scale parameter ($\mu$ and $\sigma$) of GEV distribution were represented by Fourier series, and the posterior distributions were estimated by Bayesian Markov Chain Monte Carlo simulation. The design rainfall estimated by GEV quantile function and derived posterior distribution for the Fourier coefficients, were illustrated with a wide range of return periods. The nonstationary frequency analysis considering seasonality can reasonably reproduce underlying extreme distribution and simultaneously provide a full annual cycle of the design rainfall as well.

Application of Adaptive Control Theory to Nuclear Reactor Power Control (적응제어 기법을 이용한 원자로 출력제어)

  • Ha, Man-Gyun
    • Nuclear Engineering and Technology
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    • v.27 no.3
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    • pp.336-343
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    • 1995
  • The Self Tuning Regulator(STR) method which is an approach of adaptive control theory, is ap-plied to design the fully automatic power controller of the nonlinear reactor model. The adaptive control represent a proper approach to design the suboptimal controller for nonlinear, time-varying stochastic systems. The control system is based on a third­order linear model with unknown, time-varying parameters. The updating of the parameter estimates is achieved by the recursive extended least square method with a variable forgetting factor. Based on the estimated parameters, the output (average coolant temperature) is predicted one-step ahead. And then, a weighted one-step ahead controller is designed so that the difference between the output and the desired output is minimized and the variation of the control rod position is small. Also, an integral action is added in order to remove the steady­state error. A nonlinear M plant model was used to simulate the proposed controller of reactor power which covers a wide operating range. From the simulation result, the performances of this controller for ramp input (increase or decrease) are proved to be successful. However, for step input this controller leaves something to be desired.

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A Design of 2 DOF PID Controller Using Performance Index (평가지표를 이용한 2자유도 PID제어기 설계)

  • 유항열;이정국;이금원;이준모
    • Journal of the Institute of Convergence Signal Processing
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    • v.5 no.1
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    • pp.66-72
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    • 2004
  • PID control has been well used for several decades. For PID algorithms, some tuning methods are used for selecting PID parameters and with these selected parameters, PID control system is designed. But in some cases various kinds of performance indices are used instead of well-known tuning rules, and so variable type of performance index must be tested so that the designed control system meets the some specifications. For 2 DOF PID controller design this paper presents a linear combinational type of performance indices constituting of index for robust performance, which is obtained by h infinity norm of a weighted complementary sensitivity function, including other time domain indices such as error, energy and changing rate of control input. By numerical methods, the optimal 2 DOF PID parameters are obtained. Therefore various types of 2 degree of freedom PID controllers such as I-PD controller are used so that this two degree of freedom PID controllers may give more desirable output characteristics. Simulations are done with MATLAB m file and mdl files.

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A Study on the LCC Type High Frequency DC/DC Converter for Contactless Power Supply System (비접촉 전원장치에 적용한 LCC형 고주파 공진 DC/DC 컨버터에 관한 연구)

  • Kim, Dong-Hee;Hwang, Gye-Ho
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.21 no.6
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    • pp.55-64
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    • 2007
  • This paper represents characteristics and design example of series loaded LCC type high frequency resonant DC-DC converter with variable parallel capacitor in the secondary side of inductive power transformer. In this converter, ZVS(zero voltage switching) technique is applied to reduce turn-off switching losses, and the applied converter used the PFM switching pattern to control output voltage. The operating characteristics of the proposed converter is analyzed using nomalized parameter such as switching frequency and load factor with varing the secondary parallel resonant capacitor. The results of analysis show the operating characteristics and design method of the proposed converter using characteristic values. And the proposed converter can be applied for the contactless power supply with linear transfer system such as dean room facilities of semiconductor and Flat Panel Display.

A Study on the Optimal Welding Condition for Root-Pass in Horizontal Butt-Joint TIG Welding (수평자세 맞대기 TIG 초층용접에서 최적용접조건의 선정에 관한 연구)

  • Jung, Sung Hun;Kim, Jae-Woong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.4
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    • pp.321-327
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    • 2017
  • In this study, to investigate the shape of the back bead as a weld quality parameter and to select the optimal condition of the root-pass TIG welding of a horizontal butt-joint, an experimental design and the response surface method (RSM) have been employed. Three parameters are used as input variables, which include the base current, peak current, and welding speed. The back bead width is selected as an output variable representing the weld quality, the target value of the width is 5.4 mm. Conducting the experiments according to the Box-Behnken experimental design, a $2^{nd}$ regression model for the back bead width was made, and the validation of the model was confirmed by using the F-test. The desirability function was designed through the nominal-the-best formula for the appropriate back bead width. Finally, the following optimal condition for welding was selected using the RSM: base current of 0.9204, peak current of 0.8676, and welding speed of 0.3776 in coded values. For verification, a test welding process under the optimal condition was executed and the result showed the back bead width of 5.38 mm that matched the target value well.

Study on the Optimization of Parameters for Burring Process Using 980MPa Hot-rolled Thick Sheet Metal (980MPa급 열연 후판재 버링 공정의 변수 최적화 연구)

  • Kim, S.H.;Do, D.T.;Park, J.K.;Kim, Y.S.
    • Transactions of Materials Processing
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    • v.30 no.6
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    • pp.291-300
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    • 2021
  • Currently, starting with electric vehicles, the application of ultra-high-strength steel sheets and light metals has expanded to improve mileage by reducing vehicle weight. At a time when internal combustion engine vehicles are rapidly changing to electric vehicles, the application of ultra-high-strength steel is expanding to satisfy both weight reductions and the performance safety of the chassis parts. There is an urgent need to improve the quality of parts without defects. It is particularly difficult to estimate the part formability through the finite element method (FEM) in the burring operation, so product design has been based on the hole expansion ratio (HER) and experience. In this study, design of experiment (DOE), analysis of variance (ANOVA), and regression analysis were combined to optimize the formability by adjusting the process variables affecting the burring formability of ultra-high-strength steel parts. The optimal variables were derived by analyzing the influence of variables and the correlation between the variables through FE analysis. Finally, the optimized process parameters were verified by comparing experiment with simulation. As for the main influence of each process variable, the initial hole diameter of the piercing process and the shape height of the preforming process had the greatest effects on burring formability, while the effect of a lower round of punching in the burring process was the least. Moreover, as the diameter of the initial hole increased, the thickness reduction rate in the burring part decreased, and the final burring height increased as the shape height during preforming increased.

A study to improve the accuracy of the naive propensity score adjusted estimator using double post-stratification method (나이브 성향점수보정 추정량의 정확성 향상을 위한 이중 사후층화 방법 연구)

  • Leesu Yeo;Key-Il Shin
    • The Korean Journal of Applied Statistics
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    • v.36 no.6
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    • pp.547-559
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    • 2023
  • Proper handling of nonresponse in sample survey improves the accuracy of the parameter estimation. Various studies have been conducted to properly handle MAR (missing at random) nonresponse or MCAR (missing completely at random) nonresponse. When nonresponse occurs, the PSA (propensity score adjusted) estimator is commonly used as a mean estimator. The PSA estimator is known to be unbiased when known sample weights and properly estimated response probabilities are used. However, for MNAR (missing not at random) nonresponse, which is affected by the value of the study variable, since it is very difficult to obtain accurate response probabilities, bias may occur in the PSA estimator. Chung and Shin (2017, 2022) proposed a post-stratification method to improve the accuracy of mean estimation when MNAR nonresponse occurs under a non-informative sample design. In this study, we propose a double post-stratification method to improve the accuracy of the naive PSA estimator for MNAR nonresponse under an informative sample design. In addition, we perform simulation studies to confirm the superiority of the proposed method.

Characteristics of Dynamic Parameter of Sandy Soil According to Grout Injection Ratio (그라우트 주입율 변화에 따른 사질토의 동적계수 특성)

  • Ahn, Kwangkuk;Park, Junyoung;Oh, Jonggeun;Lee, Jundae;Han, Kihwan
    • Journal of the Korean GEO-environmental Society
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    • v.12 no.5
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    • pp.59-63
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    • 2011
  • Ground dynamic parameter such as shear elastic modulus and damping ratio is a very important variable in design of ground-structure with repeated load and dynamic load. Shear elastic modulus and damping ratio on small strain below linear limit strain is constant regardless of strain. Shear elastic modulus as the maximum shear elastic modulus and damping ratio as the minimum damping ratio were considered. As a lot of experiment related to the maximum shear elastic modulus, which is in dynamic deformation characteristics, have been conducted, many factors including voiding ratio, over consolidation ratio(OCR), confining pressure, geology time, PI, and the number of load cycle affect to dynamic soil characteristic. However, the research of ground dynamic characteristic improved with grout is absent such as underground continuous wall construction, deep mixing method, umbrella arch method. In order to investigate the dynamic soil characteristics improved with grout, in this study, resonant column tests were performed with changing water content(20%, 25%, 30%) and injection ratio of grout(5%, 10%, 15%), cure time(7th day, 28th day) As a result, shear elastic modulus and damping ratio, which are ground dynamic parameter, are affected by the injection ratio of milk grout, cure time and water content.

A Study on the Effects of Perceived Value on Customer Satisfaction, and Repurchase Intention among Traditional Markets Users in KOREA (지각된 가치가 고객만족과 재구매 의도에 미치는 영향에 관한 연구 : 전통시장 이용 고객을 중심으로)

  • Cho, Joon-Sang
    • Journal of Distribution Science
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    • v.11 no.10
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    • pp.93-105
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    • 2013
  • Purpose - This empirical analysis determines the structured causal relations between perceived value, customer satisfaction, and repurchase intention among users of traditional markets. The results of this analysis would help merchants and market operators indevisingan appropriate strategy to successfully manage traditional markets. Research design, data, methodology - The perceived value model of traditional markets includes functional value (price), functional value (quality), emotional value, and social value. In this study, the perceived value of traditional markets is considered as an independent variable, while customer satisfaction and repurchase intention are shown as the dependent variables, where customer satisfaction is also considered as the mediating variable. The study aims to ascertain the extent of influence of the perceived value of traditional markets on customer satisfaction and repurchase intention. We use regression analysis to verify the effects. The measurement items were already deemed as reliable and valid in the previous study, but for this purpose, we made some modifications. We distributed questionnaires to 300 consumers on a national scale, and finally used 241 consumer responses among these as a sample. We analyzed the data using the SPSS 21.0 statistical program. Results - We obtained the following results. First, the order of perceived value dimensions of traditional markets that positively impact customer satisfaction is functional value (price), social value, emotional value, and functional value (quality). Second, the perceived value sometimes directly affects repurchase intention; its effect is typically strong with customer satisfaction as a parameter. The order of perceived value dimensions that positively impact repurchase intention is social value, functional value (price), emotional value, and functional value (quality). Third, the perceived value significantly influences repurchase intention, with customer satisfaction as the mediating variable. Conclusions - We should recognize the importance of perceived value in retail distribution markets, such as traditional markets. Moreover, we need to develop strategies to improve the perceived value. The practical implications of the study are as follows. First, with regards to functional value (quality; price) dimensions, we should have an appropriate assortment of high quality products that are reasonably priced. In addition, customers are satisfied with the friendly service, discounts, and other benefits provided by the merchants. Second, in terms of emotional value dimension, we need to develop differentiated events that provide fun and emotional experience to the customers. Third, in the context of social values dimension, we should strive to positively influence society to enhance social image through activities such as social services and contribution to community development. On the basis of these results, we present the implications, limitations, and future directions for the research. One of the policy implications of the study is that merchants of traditional markets must actively select customers and develop customer value. However, this study is limited in the fact that the population used for data collection is not fully representative, as the survey only covered some specific areas. Moreover, future studies could also benefit with additional research using moderating variables.

Performance Analysis of a Bit Mapper of the Dual-Polarized MIMO DVB-T2 System (이중 편파 MIMO를 쓰는 DVB-T2 시스템의 비트 매퍼 성능 분석)

  • Kang, In-Woong;Kim, Youngmin;Seo, Jae Hyun;Kim, Heung Mook;Kim, Hyoung-Nam
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38A no.9
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    • pp.817-825
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    • 2013
  • The UHDTV system, which provides realistic service with ultra-high definite video and multi-channel audio, has been studied as a next generation broadcasting service. Since the conventional digital terrestrial transmission system is not capable to cover the increased transmission data rate of the UHDTV service, there are great necessity of researches about increase of data rate. Accordingly, the researches has been studied to increase the transmission data rate of the DVB-T2 system using dual-polarized MIMO technique and high order modulation. In order to optimize the MIMO DVB-T2 system where irregular LDPC codes are used, it is necessary to study the design of the bit mapper that matches the LDPC code and QAM symbols in MIMO channel. However, the research related to the design of the bit mapper has been limited to the SISO system. Therefore, this paper defines a new parameter that indicates the VND distribution of MIMO DVB-T2 system and performs the performance analysis according to the parameter which will be helpful for designing a MIMO bit mapper.