• 한국산학기술학회논문지
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• 제21권1호
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• pp.1-7
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• 2020

일반라멘가교의 거동에 영향을 미치는 여러 하중들 중에서 온도하중은 중요한 하중임에도 불구하고 이에 대한 충분한 검토가 부족한 실정이다. 일반라멘가교의 온도하중에 의한 응력을 감소시키기 위해서는 열변형으로 인한 거더의 수평변위는 자유롭고, 발생내력은 최소가 되도록 하여야 한다. 슬라이딩가교는 일반라멘가교와 달리 온도하중으로 인한 축방향 변형을 허용하여 축응력을 감소시키고 휨응력은 전달시키는 구조이다. 본 연구는 슬라이딩거더를 가진 라멘가교의 온도거동과 구조효율성을 일반라멘가교와 비교하여 분석하였다. 분석을 위하여 경간장 10, 20, 30, 40m, 교각높이 2, 4, 6m의 경우에 대하여 일반라멘가교와 슬라이딩가교의 구조해석을 수행하였다. 하중은 연직 고정하중과 축방향 온도하중을 재하하고, 마찰계수는 매끄러운 상태와 윤활상태의 중간인 0.4를 적용하였다. 구조해석결과 슬라이딩가교는 온도하중 증가에 관계없이 경간장 증가에 따라 응력이 증가하며 일반라멘가교는 온도가 증가하거나 경간장이 증가할수록 응력이 증가하였다. 일반라멘가교에 비해 슬라이딩가교의 거더 중앙부 응력은 20에서 50%, 교각 하단부 응력은 50에서 90% 감소하였다. 따라서 온도하중이 작용하는 슬라이딩가교는 축응력이 감소하며 동일 제원의 일반라멘가교와 비교하여 구조효율성을 확보할 수 있다.

• 경영과학
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• 제26권1호
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• pp.77-91
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• 2009

It is the most important sucess factor for the electricity generation industry to minimize operations cost of surplus electricity generation through accurate demand forecasts. Temperature forecast is a significant input variable, because power demand is mainly linked to the air temperature. This study estimates the information value of the temperature forecast by analyzing the relationship between electricity load and daily air temperature in Korea. Firstly, several characteristics was analyzed by using a population-weighted temperature index, which was transformed from the daily data of the maximum, minimum and mean temperature for the year of 2005 to 2007. A neural network-based load forecaster was derived on the basis of the temperature index. The neural network then was used to evaluate the performance of load forecasts for various types of temperature forecasts (i.e., persistence forecast and perfect forecast) as well as the actual forecast provided by KMA(Korea Meteorological Administration). Finally, the result of the sensitivity analysis indicates that a $0.1^{\circ}C$ improvement in forecast accuracy is worth about $11 million per year.

• 설비공학논문집
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• 제19권5호
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• pp.394-402
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• 2007

To estimate the cooling load for the following day, outdoor temperature and humidity are needed in hourly base. But the meteorological administration forecasts only maximum and minimum temperature. New methodology is proposed for predicting hourly outdoor temperature and humidity by using the forecasted maximum and minimum temperature. The correlations for normalized outdoor temperature and specific humidity has been derived from the weather data for five years from 2001 to 2005 at Seoul, Daejeon and Pusan. The correlations for normalized temperature are independent of date, while the correlations for specific humidity are linearly dependent on date. The predicted results show fairly good agreement with the measured data. The prediction program is also developed for hourly outdoor dry bulb temperature, specific humidity, dew point, relative humidity, enthalpy and specific volume.

• 설비공학논문집
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• 제27권1호
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• pp.50-56
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• 2015

Korea district heating systems have mainly used setting temperature control and outdoor reset control. Different from such conventional normal methods, a thermal-load control proposed in Sweden can decrease the return temperature and reduce pump power consumptions because the control is able to provide the appropriate amount of required heat. In this study, further improved predictive optimal control in addition to the conventional controls were simulated in order to verify its effect in district heating system using TRNSYS 17. $200m^2$ apartment housing which accounts for 25% in Korea and is used as a calculation model;. the number of households in the simulation was 9. As a result, a higher temperature difference and decreasing flow rate at primary loop were shown when using thermal-load control.

• 설비공학논문집
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• 제5권3호
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• pp.198-206
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• 1993

Experimental results of two stage Gifford-McMahon cryorefrigerator are described. In-prototype experiments, drive mechanism is Scotch Yoke type driven by stepping motor, copper meshes and lead balls are used for regenerator's materials in the first stage and the second stage, respectively. To find optimal conditions of the cryopump, no load temperature and refrigeration capacity according to the variation of cycle frequency and operating pressure are measured, and the cool down and load characteristics at particular cycle frequencies are presented. In general, as the cycle frequency is lowered, no load temperature is dropped but refrigeration capacity is diminished. As the representative result, in a case that the cycle frequency is 70rpm and steady state pressure is 14 atm, no load temperature of second stage is lowered to 10.5K in 55 minuters, and in this situation the refrigeration capacity of the first stage is 42W at 80K, that of the second stage is 11 W at 20K.

• 설비공학논문집
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• 제12권6호
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• pp.609-615
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• 2000

The energy conservation is one of the most important issues in recent years. Especially, the energy conservation through improved control strategies is one of the most highly possible area to be implemented in the near future. The energy conservation of the ice storage system can be accomplished through the improved control strategies. A real time building load prediction algorithm was developed. The expected highest and the lowest outdoor temperature of the next day were used to estimate the next day outdoor temperature profile. The measured dry bulb temperature and the measured building load were used to estimate system parameters by using the on-line weighted recursive least square method. The estimated hourly outdoor temperatures and the estimated hourly system parameters were used to predict the next day hourly building loads. In order to see the effectiveness of the building load prediction algorithm, two different types of building models were selected and analysed. The simulation results show less than 1% in error for the prediction of the next day building loads. Therefore, this algorithm may successfully be used for the development of improved control algorithms of the ice storage system.

• 수산해양기술연구
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• 제58권4호
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• pp.359-366
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• 2022

In this study, the load fluctuation of the main engine is considered to be a disturbance for the jacket coolant temperature control system of the low-speed two-stroke main diesel engine on the ships. A nonlinear PID temperature control system with satisfactory disturbance rejection performance was designed by rapidly transmitting the load change value to the controller for following the reference set value. The feed-forwarded load fluctuation is considered the set points of the dual loop control system to be changed. Real-coded genetic algorithms were used as an optimization tool to tune the gains for the nonlinear PID controller. ITAE was used as an evaluation function for optimization. For the evaluation function, the engine jacket coolant outlet temperature was considered. As a result of simulating the proposed cascade nonlinear PID control system, it was confirmed that the disturbance caused by the load fluctuation was eliminated with satisfactory performance and that the changed set value was followed.

• Coupled systems mechanics
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• 제11권4호
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• pp.297-313
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• 2022

The objective of this paper is to study the effect of frequency in a two-dimensional orthotropic thermoelastic rotating solid with fractional order heat transfer in generalized thermoelasticity with two-temperature due to inclined load. As an application the bounding surface is subjected to uniformly and linearly distributed loads (mechanical and thermal source). The problem is solved with the help of Fourier transform. Assuming the disturbances to be harmonically time dependent, the expressions for displacement components, stress components, conductive temperature and temperature change are derived in frequency domain. Numerical inversion technique has been used to determine the results in physical domain. The results are depicted graphically to show the effect of frequency on various components. Some particular cases are also discussed in the present research.

• 대한임베디드공학회논문지
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• 제19권3호
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• pp.123-130
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• 2024

This paper proposes an EMPC (Explicit Model Predictive Controller) for temperature tracking control based on heat load prediction by an ESO (Extended State Observer) for a variable cooling circulation system with multiple indoor units connected to one outdoor unit. In this system, heat transfer and heat loss relative to the input temperature are modeled using system dynamics. Using this model, we design an EMPC based on an ESO that is robust to temperature changes and depends on airflow. To determine the stability of both the controller and the observer, asymptotic stability is verified through Lyapunov stability analysis. Finally, to validate the performance of the proposed controller, simulations are conducted under three scenarios with varying airflow, set temperature, and heat load.

• 한국전기전자재료학회논문지
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• 제28권1호
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• pp.46-50
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• 2015

The cable degradation process is largely divided into three steps; Step 1 : Thermal degradation, Step 2 : Weibull degradation, Step 3 : Partial discharge. it is progress in step order. This article aims to explain the process of cable degradation using the method of insulation resistance and accordingly to compose and manufacture a system of measuring the life of electrical cable. Before measuring the insulation resistance, a system of measuring the temperature and current of cables was made, and the established system was installed for test on the site of a power plant to collect the measured data. The current sensor was used TFC30P80A-CL420, and temperature sensor was used the DK-1270 PT100 sensor as RTD sensor. When measured the temperature and the load current at the same position, was confirmed that in case of the load current value was high, also temperature value high. Therefore, the correlation between load currents and temperature was verified, and the analysis of diagnostic data was evaluated, which could be utilized in identifying the fault condition of cable systems.