• 한국건설관리학회논문집
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• 제17권3호
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• pp.71-80
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• 2016

대규모 복합 프로젝트(complex project) 또는 메가 프로젝트(mega project)들에서 확률적으로 공정계획을 수립하는 대표적인 방법이 PERT (Project Evaluation and Review Technique)기법이다. PERT기법은 작업공기의 불확실성에만 중점을 두고 작업간 연결관계는 Finish-to-Start(FS)관계로 제한되기 때문에 작업간 중복관계가 존재할 경우 작업간 연결관계의 불확실성에 대한 확률적인 추정이 불가능하다. PERT기법의 이러한 한계를 극복하기 위해, 작업간 다양한 중복관계들의 불확실성을 고려하여 사업전체 공기를 추정하는 방법으로 PLET (Probabilistic Linkage Evaluation Technique)기법을 제안되었다. 그러나 PLET 기법에 의한 사업공기 추정은 작업간 연결관계의 불확실성만을 고려할 뿐, PERT기법에서의 작업공기에 대한 불확실성은 고려하지 않으므로, 완전한 사업공기 추정방법이라 할 수 없다. 본 논문은 작업공기의 불확실성을 고려하는 PERT기법과 작업간 연결관계의 불확실성을 고려하는 PLET기법을 결합시켜 사업공기를 추정하는 통합 모델을 제안하고 확률적 타당성을 검증한다. 그리고 통합 모델의 일정계산방법을 제시하고 이를 실제사례에 적용하여 검증함으로써, 고위험 건설사업의 공정계획을 수립할 때 보다 폭넓고 다양한 위험요인들을 통합적으로 고려하는 확률적 사업공기 추정 방법을 제안하는 것이다.

• 한국농공학회논문집
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• 제48권6호
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• pp.45-56
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• 2006

The finite element method is a practical tool to compute the response of the irregularly layered soil deposit to the base-rock motions. The method is useful not only in estimating the interaction between the structure and the surrounding soil as a whole and the local behavior of the contacting area in detail, but also in predicting the resulting behavior of the superstructure affected by such soil-structure interactions. However, the computation of finite element analysis is marched in the time domain (TD), while the site response analysis has been carried out mostly in the frequency domain (FD) with equivalent linear analysis. This study is intended to compare the results of the TD and FD analysis with focus on the peak response accelerations and the predominant frequencies, and thus to evaluate the applicability and the validity of the finite element analysis in the site response analysis. The comparison shows that one can obtain the results very close to that of FD analysis, from the finite element analysis by including sufficiently large width of foundation in the model and further by applying partial mode superposition. The finite element analysis turned out to be well agreeing with FD analysis in their computed results of the peak acceleration and the acceleration response spectra, especially at the surface layer.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권1호
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• pp.37-46
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• 2004

A novel rotor speed estimation method using model reference adaptive control(MRAC) is proposed to improve the performance of a sensorless vector controller. In the proposed method, the stator current is used as the model variable for estimating the speed. In conventional MRAC methods, the relation between the two model errors and the speed estimation error is unclear. In the proposed method, the stator current error is represented as a function of the first degree for the error value in the speed estimation. Therefore, the proposed method can produce a fast speed estimation. The robustness of the rotor flux-based MRAC, back EMF-based MRAC, and proposed MRAC is compared based on a sensitivity function about each error of stator resistance, rotor time constant, mutual inductance. Consequently, the proposed method is much more robust than the conventional methods as regards errors in the mutual inductance, stator resistance. Therefore, the proposed method offers a considerable improvement in the performance of a sensorless vector controller at a low speed. In addition, the superiority of the proposed method and the validity of sensitivity functions were verified by simulation and experiment.

• 대한기계학회논문집B
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• 제23권5호
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• pp.593-602
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• 1999

This paper presents combustion characteristics of LPG-air mixture ignited by the plasma jet in a cylindrical vessel with constant volume, in which our focus is placed on the multi-hole plug configuration. Four types of the plug configuration depending on the number of orifice and the arranged angle are considered, along with two cases of conventional spark ignition for comparison. Not only the flame propagation is photographed at intervals, but the pressure in the combustion chamber is also recorded through the entire combustion process. The results show that the plasma jet ignition enhances the overall combustion rate remarkably in comparison to the spark ignition by generating irregular flame front and penetrating through the unburned mixture. The combustion enhancement rate agrees favorably with the available data, which supports the validity of our experiment. Synthetically estimating, the two-hole sixty-degree plug appears to be the most desirable, in that the maximum pressure as well as the combustion duration is less affected by the sub-energy level than the others. It is also deduced that there may exist an optimal plug configuration capable of rapid combustion for a specific combustion chamber.

• 대한의용생체공학회:의공학회지
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• 제8권1호
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• pp.41-48
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• 1987

In estimating the freguency-dependent attenuation coefficient, we analyzed the range-dependent ultrasonic beam and proposed the method of calculating the experimental equation of beam pattern in order to reduce the error on the influence of beam pattern. These experimental equations are divided into the spectral centroid and the spec ural standard deviation slope according to axial propagation length. These are repnesented by the first-order equation in the near field of the beam and the second- order eqLlatlon In the far field. In order to prove the validity of this method, the attenuation coefficients of the non-corrected ease and the corrected case are compared. Using the reflected signal from acryle plate, the attenuation coefficients were estimated by the spectral shift method ann the spectral difference method. The result shows attenuation coeffi talents after correction are better than attenuation coefficients before correction. And this method can be applied In vivo measurement.

• 대한조선학회지
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• 제24권1호
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• pp.51-66
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• 1987

In this paper, the authors investigate theoretically the motion and longitudinal strength of ships among waves talking account of the effects of nonlinearities such as the hull shape, bottom emergence, and hydrodynamic impact. Incidentally the ship is treated as an elastic beam in heading wave condition regarding characteristics of slamming and whipping-according to the variation in the range of a quarter length of the ship forward and the increase of the elastic modes up to 4-th vibration mode were investigated by the present theory. Calculations are performed for 97m container ship and its validity is confirmed by a series of model tests. Conclusions obtained are as follows; 1) Acceleration and pressure estimated by the present theory are in good accordance with experiments. 2) The present non-linear theory may be applied for estimating longitudinal bending moment of ships in slamming and whipping conditions. 3) In investigation of the characteristic in response according to shape variation for parts under draft and vow-flare in the range of a quarter length of the ship forward, dynamic responses due to the former were much more conspicuous than those due to the later. 4) In the maximum bending moment, the considering case up to 2-the mode are larger, about $10{\sim}15%$, than that up to 4-th mode.

• 센서학회지
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• 제27권4호
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• pp.209-215
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• 2018

Recent research in animal behavior has shown that gradient information plays an important role in finding food and home. It is also important in optimization of performance because it indicates how the inputs should be adjusted for maximization/minimization of a performance index. We introduce perturbation as an additional input to obtain gradient information. Unlike the typical approach of calculating the gradient from the derivative, the proposed processing is very robust to noise since it is performed as a summation. Experimental results prove the validity of the process of spatial gradient acquisition. Quantitative indices for measuring the effect of the amplitude and the frequency are developed based on linear regression analysis. Drones are very useful for environmental monitoring and an autonomous path planning is required for unstructured environment. Guiding the drone for finding the origin of the interested physical property is done by estimating the gradient of the sensed value and generating the drone trajectories in the direction which maximizes the sensed value. Simulation results show that the proposed method can be successfully applied to identify the source of the physical quantity of interest by utilizing it for path planning of an autonomous drone in 3D environment.

• Structural Engineering and Mechanics
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• 제26권5호
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• pp.499-516
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• 2007

An experimental method denoted as Impulse Method is proposed as a cost-effective non-destructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz's quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.

• 한국군사과학기술학회지
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• 제13권2호
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• pp.196-203
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• 2010

The bistatic sonar operations using a spatially-separated source and receiver are classified into cooperative and non-cooperative operations. In the cooperative operation, an active signal of a friendly ship is used and the source information is known previously. In the non-cooperative operation, an active signal of the enemy is used and it is difficult to find out the source information. The source information consists of the range, speed, course and frequency of the source. It gives advantage to operating bistatic sonar. This paper suggests a method of estimating the source information with geographic information in the sea and the single-ping of the enemy. The source range is given using one geographic point. And the source speed, course and the frequency of the enemy's source signal are given using two geographic points. Finally, the validity of the scheme is confirmed through a simulation study.

• 전기학회논문지
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• 제66권9호
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• pp.1325-1333
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• 2017

The sensorless control of blushless DC motor(BLDCM) is based on the $120^{\circ}$ control in which the back electromotive force(Back EMF) for estimating the position of the rotor can be detected. However, the $120^{\circ}$ control has a disadvantage that the torque constant is small as compared with $180^{\circ}$ control which can not detect the back EMF. The $150^{\circ}$ control which complements these problems makes it possible to detect the back EMF and improve the torque constant by 12.5% compared to the $120^{\circ}$ control. Therefore, this paper compares the output characteristics of BLDCM through finite element method analysis (FEA) by the conventional and proposed control methods of BLDCM for water circulation system and proposes design for downsizing and weight reduction of BLDCM according to secured torque constant. The validity of the proposed control and design proposal is proved through simulation and experimental results by comparing the output characteristics of $120^{\circ}$ control and $150^{\circ}$ control.