• 전자공학회논문지B
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• 제31B권4호
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• pp.145-154
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• 1994

This paper proposes an efficient method for improving the training performance of the neural network by using a hybrid of a stochastic approximation and a backpropagation algorithm. The proposed method improves the performance of the training by appliying a global optimization method which is a hybrid of a stochastic approximation and a backpropagation algorithm. The approximate initial point for a stochastic approximation and a backpropagation algorihtm. The approximate initial point for fast global optimization is estimated first by applying the stochastic approximation, and then the backpropagation algorithm, which is the fast gradient descent method, is applied for a high speed global optimization. And further speed-up of training is made possible by adjusting the training parameters of each of the output and the hidden layer adaptively to the standard deviation of the neuron output of each layer. The proposed method has been applied to the parity checking and the pattern classification, and the simulation results show that the performance of the proposed method is superior to that of the backpropagation, the Baba's MROM, and the Sun's method with randomized initial point settings. The results of adaptive adjusting of the training parameters show that the proposed method further improves the convergence speed about 20% in training.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.608-613
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• 2019

The purpose of the present study is to analyze and evaluate the performance of a small Darrieus wind turbine installed at the Urumsil region of Deokjeok-do Island in the west of South Korea 50 km away from Incheon. This place has no government electricity so alternate resources of energy needed to be installed there. For this purpose a small Darrieus wind turbine with the capacity of 1.5 kW was developed and installed at the site. The experimental power output of the wind turbine is less than the designed power at the same values of wind speed. This power loss is mainly due to the highly unsteady nature wind of sudden changes in magnitude of wind speed and wind angle. The results of current study can be used to make a future power generation plan for Deokjeok-do and other nearby small islands.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.869-873
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• 2008

Optimization method for the open loop commutation time intervals in HDD spindle start-up control is presented in this paper. A hard disk drive(HDD) uses a sensorless brushless DC motor(BLDC) for the platter rotation. Because there is no direct sensor for the rotor position, open loop commutations after sensing the rotor position at a standstill using inductive sensing method are performed to speed up the rotor up to a certain speed where the zero crossings of the back electromotive force(EMF) are measurable. Therefore successful open loop commutations are necessary for the stable start-up control of the spindle motors. Random neighborhood search(RNS) algorithm is introduced as a optimization technic in this paper. Rotor speed and its standard deviation are used as a cost function and commutation intervals obtained from the spindle motion equation are used as initial parameter values for the RNS. With the help of the proposed method optimized open loop commutation time intervals for the very low start-up current are acquired and tested. The experimental results shows that the proposed method can decrease the start-up failure rate of a HDD spindle motor.

• 대한전자공학회논문지SP
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• 제49권3호
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• pp.98-105
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• 2012

본 논문은 고품질을 갖는 음성재생 속도제어를 위한 새로운 방법을 다루었다. 제안 방법은 재생 속도에 따른 음성 신호의 활성화 영역을 검출하는 가변적 임계필터링 솔루션을 제공하였다. 임계필터링을 위한 임계값은 주어진 배속에 따라 재생되는 음성 신호 내의 각 프레임의 통계(평균과 표준편차)에 의해 가변적으로 결정되며 프레임 내의 활성화 블록구간 만을 축출하는데 사용된다. 또한 높은 재생 속도에 따른 피치 손상과 같은 품질 저하를 최소화하기 위하여, 임계필터링은 유, 무성음 구분 없이 상대적은 낮은 활성도를 갖는 블록들을 우선적으로 제거한다. 실험 결과, 제안 방식은 기존의 피치 축출을 사용하는 SOLA(Synchonized OverLap Add) 방식보다 높은 품질 갖는 재생속도 제어 솔루션을 제공함을 알 수가 있었다.

• 한국지리정보학회지
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• 제19권4호
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• pp.146-156
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• 2016

본 연구에서는 과거 대형산불 지역의 사례분석을 통해 대형산불 발생 전의 건조현상과 강풍 등 악기상 정보와 임상조건을 활용하여 대형산불이 일어날 위험성이 있는 지역을 미리 예보할 수 있는 체계를 개발하였다. 사례분석은 과거 20년간 발생한 100ha 이상의 대형산불 37건을 대상으로 하였다. 대형산불 위험지역은 소나무림 30ha 이상 지역 중 주변 소나무림간 최대 이격거리가 2km 범위 내에 있는 지역을 대상으로 선정하였다. 평균풍속은 평균 5.3m/s, 최대 11.6m/s, 표준편차는 2.5m/s 범위에서 대형산불이 발생하는 특성을 보였다. 실효습도는 평균 30%, 최소 13%, 표준편차 14.5%로 나타났다. 이러한 분석결과를 통해 대형산불 발생 위험이 높은 소나무림 추출 지역을 대상으로 '대형산불 주의보'는 실효습도 30~45% 범위에서 2일 이상 지속되고 풍속이 7m/s 이상일 때 발효하고, '대형산불 경보'는 실효습도 30% 미만이 2일 이상 지속되고 풍속이 11m/s 이상이 예상될 때 발효하는 것이 타당한 것으로 나타났다. 따라서 향후 '대형산불 위험예보'로 인해 악기상 변화에 따른 대형산불 위험지역에 대한 선택과 집중의 산불방지 활동이 가능할 것으로 판단된다.

• 대한의용생체공학회:의공학회지
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• 제38권4호
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• pp.197-204
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• 2017

The aim of this study was to evaluate driving performance of normal subjects for controlling the steering wheel by using foot operated steering devices in the driving simulator. Many people with complete bilateral loss or loss of use of upper limbs but with normal lower limbs are frequently left without use and/ or control of their hands, arms, or the upper extremities of their bodies. As a result, persons disabled in this manner have problems in operation an automobile because they cannot grasp and manipulate a conventional steering wheel. Therefore, if foot operated steering devices are used for controlling the vehicle on in people with disabilities, the disabled people could improve their community mobility by driving a car safely. Ten normal subjects were involved in this research to evaluate steering performance by using three types of steering devices(conventional steering wheel, pedal type foot steering, circular type foot steering) in driving simulator. STISim Drive 3 program was used for testing the driving performance in two road scenarios: straight road and curved road at low and high speed of vehicle (40 km/h and 80 km/h). This study used two-way ANOVA to compare the influences of two factors(type of foot steering device and road scenario) in the three dependent variables of steering performance(standard deviation of lateral position, the lateral position of vehicle and the number of line crossing). The average values of the three dependent variables(standard deviation of lateral position, lateral position and the number of line crossing) of driving performance were significantly smaller for conventional steering wheel or pedal type foot steering than circular type foot steering.

• Journal of Welding and Joining
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• 제26권2호
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• pp.85-91
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• 2008

In general, the quality of a welding process tends to vary with depending on the work environment or external disturbances. Hence, in order to achieve the desirable quality of welding, we should have the optimal welding condition that is not significantly affected by these changes in the environment or external disturbances. In this study, we used a dual response surface method in consideration of both the mean output variables and the standard deviation in order to optimize the V-groove arc welding process. The input variables for GMA welding process with the dual response surface are welding voltage, welding current and welding speed. The output variables are the welding quality function using the shape factor of bead geometry. First, we performed welding experiment on the interested area according to the central composite design. From the results obtained, we derived the regression model on the mean and standard deviation between the input and output variables of the welding process and then obtained the dual response surface. Finally, using the grid search method, we obtained the input variables that minimize the object function which led to the optimal V-groove arc welding process.

• 방사성폐기물학회지
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• 제10권2호
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• pp.87-96
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• 2012

원자력시설 유지보수 및 해체시 다관절 매니퓰레이터 이상동작에 대한 작업자의 반응특성과 안전속도 수준을 다루고 있다. 매니퓰레이터 팔의 속도, 오류 가능성, 오류 형태와 같은 여러 가지 작업 조건에 따라 작업자의 반응시간, 고장 경보(false alarm), 실패(miss) 횟수 등에 대한 작업자의 반응 특성을 분석하였다. 매니퓰레이터 팔의 속도와 이상동작 형태는 반응시간에 영향을 주지만, 이상동작 가능성에 영향을 미치지 않았고, 두 요인 이상의 교호작용은 대체로 영향이 없었다. 매니퓰레이터 팔의 속도변화에 따른 반응시간 특성은 이상동작 형태에 따라 다르지만 대체로 약간 증가하는 추세를 보였다.

• International Journal of Korean Welding Society
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• 제5권1호
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• pp.15-28
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• 2005

The ball shear test was investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solder compositions were examined in this work: Sn-3.5Ag-0.75Cu and In-48Sn. The substrate was a common SMD type with solder bond pad openings of 460 $\mu$m in diameter. The microstructural investigations were carried out using SEM, and the IMCs were identified with EDS. Shear tests were conducted with the two varying test parameters. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force for both Sn-3.5Ag-0.75Cu and In-48Sn solder joints, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some undesirable effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces. The shear speed conditions were discussed with the stress analyses of the solder ball, and we cannot find any conspicuous finding which is related to optimum shear speed from the stress analyses.

• 한국철도학회논문집
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• 제17권3호
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• pp.157-164
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• 2014

판토그래프와 전차선간의 접촉력 특성은 차량에 대한 안정적 전원공급 특성인 집전성능을 평가하는 중요한 지표이다.본 연구에서는 HEMU-430x판토그래프의 동적 접촉력 특성을 속도에 따라 분석하였다. 그 결과 판토그래프의 접촉력 표준편차가 속도에 따라 증가함을 확인하였고, 주파수 분석을 통하여 전차선의 경간이 접촉력에 매우 큰 영향을 미치는 인자임을 확인하였다. 또한 400km/h 이상의 속도에서 안정적인 집전특성을 확보하려면 판토그래프와 가선간의 접촉력 표준편차가 작아져야 한다. 이를 위하여 전차선 장력증가, 판토그래프 집전판 경량화 등의 방안을 적용하였으며, 이에 대한 접촉력 측면에서의 효과를 정량적으로 분석하였다. 또한 개활지와 터널에서의 접촉력 특성의 차이에 대하여서도 주파수 분석을 통해서 분석하였다.