• 한국정보과학회논문지:시스템및이론
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• 제29권6호
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• pp.354-360
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• 2002

지연시간 계산은 지연시간을 고려한 배치 단계에서 백만 번 이상도 수행되므로 효과적이면서 간단해야 한다. 본 논문에서는 계산은 매우 빠르고 간단하지만 수 백%의 오차를 가질 수 있는 Elmore delay를 개선하기 위해 Elmore delay와 SPICE 결과의 비율을 보상값으로 이용하는 방법을 제안한다. 제안한 새로운 방법은 resistance shielding effects를 고려하여 실험적으로 지연시간을 보상하여 그 오차를 크게 줄이며, 계산 복잡도는 Elmore delay와 같은 정도로 간단하다. Elmore delay가 31.6 ~ 145.2% 오차를 갖는 RC 트리에 대하여 실험한 결과, 보상된 delay의 오차는 2.5 ~ 22.7%로 크게 줄었다.

• 한국정밀공학회지
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• 제19권8호
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• pp.63-70
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• 2002

In end milling process, the undeformed chip section area and cutting forces vary periodically with phase change of the tool. However the real undeformed chip section area deviates from the geometrically ideal one owing to cutter runout and tool shape error. In this study, a method of estimating the real undeformed chip section area which reflects cutter runout and tool shape error was presented in up end milling process using measured cutting forces. The average specific cutting resistance, Ka is defined as the main cutting force component divided by the modified chip section area. Ka value becomes smaller as the helix angle increases from $30^circC \;to\;40\circC$. But it becomes larger as the helix angle increases from $40^\circ$to 50 . On one hand, the Ka value shows a tendency to decrease with increase of the modified chip section area and this tendency becomes distinct with smaller helix angle.

• Journal of information and communication convergence engineering
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• 제20권4호
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• pp.303-308
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• 2022

Simulating the heat transfer in a composite material is an important topic in material science. Difficulties arise from the fact that adjacent materials cannot match perfectly, resulting in discontinuity in the temperature variables. Although there have been several numerical methods for solving the heat-transfer problem in imperfect contact conditions, the methods known so far are complicated to implement, and the computational times are non-negligible. In this study, we developed a ResNet-type deep neural network for simulating a heat transfer model in a composite material. To train the neural network, we generated datasets by numerically solving the heat-transfer equations with Kapitza thermal resistance conditions. Because datasets involve various configurations of composite materials, our neural networks are robust to the shapes of material-material interfaces. Our algorithm can predict the thermal behavior in real time once the networks are trained. The performance of the proposed neural networks is documented, where the root mean square error (RMSE) and mean absolute error (MAE) are below 2.47E-6, and 7.00E-4, respectively.

• Korean Journal of Acupuncture
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• 제38권4호
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• pp.282-289
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• 2021

Objectives : The purpose of this study is to construct a model of the possible thermal runaway of electronic moxibustion and to implement an appropriate risk management method. Methods : To reproduce the system error situation of the electronic moxibustion circuit equipped with microcontroller unit, temperature sensor and heater, a code was set to disable the signal input to temperature sensor and maintain "high" heating signal to heater. The temperature change of electronic moxibustion was compared between 3 types of heater module; module 1 consisting of a combination of heater+0 ohm+0 ohm resistance, module 2 consisting of a combination of heater+Polymeric Positive Temperature Coefficient (PPTC)+0 ohm resistance, and module 3 consisting of a combination of heater+PPTC+10 ohm resistance. The temperature change was measured using a polydimethylsiloxane (PDMS) silicone phantom. After maintaining surface temperature of the phantom at 31~32℃ for 20 seconds, electronic moxibustion was applied. After operating electronic moxibustion, the temperature change was measured for 660 seconds on the surface and 900 seconds at 2 mm depth. Results : Regardless of the module type, the time-dependent change in temperature showed a rapid rise followed by a gentle curve, and a sharp drop in temperature after reaching the maximum temperature about 10 minutes after the switching the moxibustion on. Temperature measured at the depth of 2 mm below the surface increased slower and to a lesser extent. Module 1 reached highest peak temperature with largest change of temperature at both depths followed by module 2, and 3. Conclusions : Through the combination of PPTC+resistance with the heater of electronic moxibustion, it is possible to limit the rise in temperature even with the software error. Thus, this setting can be used as an independent safety measure for the electronic moxibustion control unit.

• 조명전기설비학회논문지
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• 제14권6호
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• pp.69-77
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• 2000

본 논문에서는 찬우$\mid$강하법에 의한 접지저항 및 대지첸위 분표의 측캠시 전휴보조전극의 영향에 대하여 기술하였으며, 측정시 오치를 최소화하는 기법을 제안하였다. 전위강해법은 전위와 천류의 측정에 이론적인 비1깅을 두고 있으며, 측정오차는 주로 측정시 설치하는 보조전극의 위치와 자체저항에 기인한다. 피측정 접지전극의 접지저항은 전위강하법에서 전위보조전극을 피측정 접지전극과 전류보조전극이 이루는 일직선상에 위치시킬 때 61.8[%]법칙을 적용하여 측정한다. 하지만 건물이나 포장도로, 구조물 등이 산재해 있는 도심의 경우에는 현장에서 피측정 접지전극과 전류보조전극 사이에 적결한 이격거리 확보가 불가능하거냐 전류보조전극의 접지저행값이 피측정 챔 지전극에 비하여 큰 값을 가지는 경우가 있다. 파측정 접지천극과 전류보조전극을 충분히 이격시키지 않거나 전류류보조전극의 접지저항값이 피측청 접지전극의 접지저항보다 비정상척으로 큰 경우 접지저항의 측정은 오차를 수반하게 되며, 측정된 접지저항값은 오차즐 보정해 주어야 한다. 본 연구애서 측정대상 전극은 길이 2.4[m]의 봉형 접지전극으호 하였으며, 전류보조전극의 영향을 고려할 때 피측정 접지전극과 전류보조전극의 적정한 이격거리는 피측정 접치전극 길이의 5배 이상으로 하여야 전위보조전극을 사설하기가 용이하며 측정정확도의 확보에 유리하다. 또한 전류보존전극의 접지저항값이 피측정 접지전극의 접지저항값 약 36.5배 이하에서는 거의 오차를 발생시키지 않는다.

• 조명전기설비학회논문지
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• 제23권4호
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• pp.39-46
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• 2009

본 논문에서는 저항과 클록 주파수 변동에 의한 문제를 효과적으로 감소시킬 수 있는 풀 디지털 정전용량 방식의 터치키를 제안한다. 제안된 방식은 측정하고자 하는 정전용량 두 개와 두 정전용량 사이의 저항으로 구성되어 있으며, 각 정전용량과 저항의 지연을 각각 측정한 후 두 지연의 비를 구한다. 양자화 오차를 무시할 경우 두 지연의 비는 측정하고자 하는 두 정전용량의 비로 표시되어 저항 값과 클럭 주파수와 무관하다. 실험결과에서도 제안된 방법이 저항과 클록주파수에 의한 변동을 효과적으로 줄일 수 있음을 보였으며, 제안된 방법의 정전용량 해상도가 1.04[pF]여서 터치키로 사용될 수 있음을 보였다.

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.530-543
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• 2013

This paper describes a control scheme of speed sensorless fuzzy direct torque control (FDTC) of permanent magnet synchronous motor for electric vehicle (EV). Electric vehicle requires fast torque response and high efficiency of the drive. Speed sensorless FDTC In-wheel PMSM drives without mechanical speed sensors at the motor shaft have the attractions of low cost, quick response and high reliability in electric vehicle application. This paper presents a new approach to estimate the speed of in-wheel electrical vehicles based on Model Reference Adaptive System (MRAS). The direct torque control suffers in low speeds due to the effect of changes in stator resistance on the flux measurements. To improve the system performance at low speeds, a PI-fuzzy resistance estimator is proposed to eliminate the error due to changes in stator resistance. High performance sensorless drive of the in-wheel motor based on MRAS with on line stator resistance tuning is established for four motorized wheels electric vehicle and the whole system is simulated by matalb/simulink. The simulation results show the effectiveness of the new control strategy. This proposed control strategy is extensively used in electric vehicle application.

• 한국생산제조학회지
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• 제26권2호
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• pp.243-250
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• 2017

A numerical study was conducted to calculate the cooling capacity variation of a power plant ACC (air-cooled condenser) caused by changes in operating conditions. A numerical model was developed using the ${\varepsilon}-NTU$ and finite volume method, containing 100 elements for a single low fin tube. The model was validated through a comparison of cooling capacity between the simulated values and manufacturer's data. Even though simple assumptions and previously presented heat transfer correlations were applied to the model, the prediction error was 1.9%. The simulated variables of the operating conditions were air velocity, air temperature, and mass flux. The analysis on the variation of thermal resistance along the tube showed that the water side thermal resistance was higher than the air side thermal resistance at the downstream end of the tube, indicating that the ACC capacity could be increased by applying technology to enhance in-tube flow condensation heat transfer.

• 한국지열·수열에너지학회논문집
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• 제8권4호
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• pp.8-16
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• 2012

The use of energy pile foundation has been increased for economic utilization of geothermal energy. This paper describes an experimental and numerical study on thermal response tests (TRTs) using W and 3U-shaped ground heat exchangers (GHEs) in precast-high strength concrete (PHC) energy piles. Ground thermal conductivity and borehole thermal resistance were measured and compared with those numerical analysis. W-shpaed GHE showed higher heat transfer behavior than 3U-shaped one because of different conditions such as pile size and volume of grout. That is, ground thermal conductivity using W-shaped GHE was higher than that of 3U shaped GHE, and borehole thermal resistance vice versa. The relative error of borehole resistance values between numerical and analytical solution was less than 5%.

• Computers and Concrete
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• 제13권2호
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• pp.255-270
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• 2014

Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber ($V_f$ = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.