• Structural Engineering and Mechanics
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• 제45권6호
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• pp.837-851
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• 2013

In construction industry, strength is a primary criterion in selecting a concrete for a particular application. The concrete used for construction gains strength over a long period of time after pouring the concrete. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting for 28 days for such a test would serve the rapidity of construction, nor would neglecting it serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction of the strength of concrete would be of great significance. On this backdrop, the method is proposed to establish a predictive relationship between properties and proportions of ingredients of concrete, compaction factor, weight of concrete cubes and strength of concrete whereby the strength of concrete can be predicted at early age. Multiple regression analysis was carried out for predicting the compressive strength of concrete containing Portland Pozolana cement using statistical analysis for the concrete data obtained from the experimental work done in this study. The multiple linear regression models yielded fairly good correlation coefficient for the prediction of compressive strength for 7, 28 and 40 days curing. The results indicate that the proposed regression models are effectively capable of evaluating the compressive strength of the concrete containing Portaland Pozolana Cement. The derived formulas are very simple, straightforward and provide an effective analysis tool accessible to practicing engineers.

• 대한안전경영과학회지
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• 제13권3호
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• pp.1-8
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• 2011

The overall goal of a safety based railroad system is either to eliminate hazards in designing or to minimize the possibility of it. In order to indicate system safety or low risk although it may not be possible to achieve zero risk conditions, first, it shall ensure that any disasters would occur due to system operation because the prescribed specifications are properly fulfilled and there are no failures of any kind. Second, the risk of faults or failures leading to a mishap must be eliminated or minimized by using fault-tolerance or fail-safe procedures. This paper will attempt to summarize the personal and social risk criterion at widely scattered points, presently used as a safety approach in all over EU, in order to establish the step by step procedures of the detailed standard for railway facilities. In addition, we present the new safety analysis method using the SIL-based evaluation standard and the Reachability Graph of the Petri Net.

• 한국통신학회논문지
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• 제27권6C호
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• pp.571-580
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• 2002

본 논문은 DiffServ 방식의 Assured Service에 대한 서비스 제공 방안으로서 Assured Service 서브 클래스별로 할당하는 대역폭의 양을 차별화하여 요구되는 버퍼 크기에 따라 서브 클래스별로 보장하는 최대 지연시간을 상대적으로 차등화 하였다. 또한 In-profile 트래픽에 대한 수율과 링크 이용률을 극대화 시킬 수 있도록 네트워크 토폴로지와 Assured Service 서브 클래스별로 할당되는 대역폭의 비율에 따라 결정되는 버퍼 크기를 기준으로 RIO 변수 값을 설정하고 접속제어의 기준이 되는 출력링크 대역폭의 크기를 설정하는 방안을 제안하였다. 시물레이션 결과는 제안하는 방식을 통해 Assured Service에 대한 서비스 수용 용량을 도출할 수 있고, 제안된 RIO 변수 값을 적용하여 In-profile 트래픽의 수율 및 링크 이용률을 극대화시킬 수 있음을 보인다.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권6호
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• pp.376-382
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• 2005

In this paper, practical biped humanoid robot is presented, designed, and modeled by fuzzy system. The humanoid robot is a popular research area in robotics because of the high adaptability of a walking robot in an unstructured environment. But owing to the lots of circumstances which have to be taken into account it is difficult to generate stable and natural walking motion in various environments. As a significant criterion for the stability of the walk, ZMP (zero moment point) has been used. If the ZMP during walking can be measured, it is possible for a biped humanoid robot to realize stable walking by a control method that makes use of the measured ZMP. In this study, measuring the ZMP trajectories in real time situations throughout the whole walking phase on the flat floor and slope are conducted. And the obtained ZMP data are modeled by fuzzy system to explain empirical laws of the humanoid robot. By the simulation results, the fuzzy system can be effectively used to model practical humanoid robot and the acquired trajectories will be applied to the humanoid robot for the human-like walking motions.

• 전력전자학회논문지
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• 제4권3호
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• pp.223-230
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• 1999

일반적인 슬라이딩 모드 제어기 동조 방법은 동조 피라미터의 수가 플랜트의 차수에 비례하기 때문에 고차의 프로세스에서는 어렵고, 실용적이지 못하다. Camacho(1996)은 고차의 프로세스를 시간 지연 항이 포함된 1차 프로세스로 모델링한 고정 구조 슬라이딩 모드 제어기 설계 방법을 제안하였다. 그러나 Camacho가 제안한 방법은 시간 지연 항을 1차 Taylor 급수로 근사화하는 과정에서 발생되는 근사 오차에 의해 오버슈트, 정착시간, 명령추종 등에 문제점이 있다. 본 논문에서는 이를 개선하기 위해 가중치를 고려한 새로운 형태의 Taylor 근사 기법과 이를 토대로 새로운 슬라이딩 모드 제어기 설계 방법을 제안하고자 한다.

• 한국정밀공학회지
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• 제30권10호
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• pp.1031-1039
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• 2013

This paper presents gain optimization of a 6-DOF underwater robotic platform with 4 rotatable thrusters. To stabilize the 6-DOF motion of the underwater robotic platform, a back-stepping controller is designed with 6 proportional gains and 6 derivative gains. The 12 gains of the backstepping controller are optimized to decrease settling time in step response in 6-DOF motion independently. Stability criterion and overshoots are used as a constraint of the optimization problem. Trust-region algorithm and hybrid Taguchi-Random order Coordinate search algorithm are used to determine the optimal parameters, and the results by two methods are analyzed. Additionally, the resulting controller shows improved performance under disturbances.

• 대한기계학회논문집B
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• 제25권3호
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• pp.422-432
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• 2001

An analytical characterization is presented on the transient heat transfer by an oscillating flow through a porous slab. Based on a two-equation model, analytic solutions are obtained for both the fluid and solid temperature variations. Two parameters are identified as the Stanton number for the internal heat exchange and the ratio of the thermal capacities between the solid and fluid phases. The heat transfer characteristics are shown to be classified into four regimes according to the two parameters and physical interpretation is presented on the particular heat transfer processes within each regime. In addition, the condition for the local thermal equilibrium between the phases is examined and the relevant criterion is suggested.

• 대한조선학회논문집
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• 제43권1호
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• pp.96-102
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• 2006

In this study, an optimization routine with genetic algorithms is coupled for the selection of free variables for the production of a control signal for the motion of wave board in the numerical wave tank. An excitation function for the controlling of the wave board is formulated on basis of amplitude modulation for the generation of nonlinear wave packets. The found variables by the optimization serve for the determination of wave board motion both with the computation and with the experiment. The breaking criterion of the water waves is implemented as boundary condition for the optimization procedure. With the analysis of the time registration on the local position in the wave tank the optimization routine is accomplished until the given design wave with defined surface elevation is found. Water surface elevation and associated fields of velocity and pressure are numerically computed.

• 임상간호연구
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• 제25권2호
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• pp.142-150
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• 2019

Purpose: The aim of this study was to evaluate the efficiency of the Humpty Dumpty Falls Scale as one of the falls risk assessment tools, and also to evaluate risk factors as predictors of falls in pediatric patient populations. Methods: In a retrospective, case-control design with data from the electronic medical records of 13 pediatric patients who fell and 1,941 who did not fall before matching and 429 who did not fall after matching by gender, age, diagnosis, and length of stay. Results: All the variables showed no significant differences after matching. At the cutoff score of 13, sensitivity, specificity, negative and positive predictive values were 92.3%, 37.1%, 99.9%, and 0.01%, respectively. The area under the Receiver Operating Characteristics was 0.597. The results from the logistic regression showed that the pediatric inpatient population who had higher risk scores was significantly associated with falls. The odds ratios ranged from 1.31 to 4.71 with 90% confidence interval. Conclusion: The saturation impairments criterion as one of the diagnostic parameter was negatively associated with falls, but the relative risk score was higher than the other criteria. Therefore, it seems that the diagnostic parameter seems to be required to verify results through large sample studies.

• 한국전기전자재료학회논문지
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• 제32권4호
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• pp.313-319
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• 2019

Induction motors connected with a three-phase AC system may malfunction due to reverse phase or open phase faults. Conventional overcurrent relays and overheating relays are used to prevent such accidents; however, their drawbacks include a low response speed and false operation. Therefore, in this study, a digital relay for the reverse-open phase was designed and fabricated. This relay can detect the reverse phase and open phase faults and send a trigger signal to the control circuit. The proposed relay was developed based on a microcontroller. The detection times of the reverse phase and open phase were verified as 320ms and 80ms, respectively. Compared with conventional relays that only protect the motor from one type of fault, the proposed relay can detect both, reverse phase and open phase faults. In addition, the fault detection, identification criterion, and trigger signal patterns can be modified by programming according to the requirements of users.