• Steel and Composite Structures
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• 제46권6호
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• pp.805-821
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• 2023

This study developed an evaluation system to explore the effect of the environmental temperature on the stress redistribution produced by cable stress relaxation of structural members in a steel cable-stayed bridge. The generalized Maxwell model is used to estimate stress relaxation at different temperatures. The environmental temperature is represented using the thermal coefficients and temperature loads. The fmincon optimization function is used to determine the set of stress relaxation parameters at different temperatures for all cables. The ABAQUS software is employed to investigate the stress redistribution of the steel cable-stayed bridge caused by the cable stress relaxation and the environmental temperature. All of these steps are set up as an evaluation system to save time and ensure the accuracy of the study results. The developed evaluation system is then employed to investigate the effect of environmental temperature and cable type on stress redistribution. These studies' findings show that as environmental temperatures increased up to 40 ℃, the redistribution rate increased by up to 34.9% in some girders. The results also show that the cable type with low relaxation rates should be used in high environmental temperature areas to minimize the effect of cable stress relaxation.

• International journal of advanced smart convergence
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• 제4권1호
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• pp.45-53
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• 2015

This paper is proposed mathematical load modelling based on system identification approach of energy consumption of residential air conditioning. Due to air conditioning is one of the significant equipment which consumes high energy and cause the peak load of power system especially in the summer time. The demand response is one of the solutions to decrease the load consumption and cutting peak load to avoid the reservation of power supply from power plant. In order to operate this solution, mathematical modelling of air conditioning which explains the behaviour is essential tool. The four type of linear model is selected for explanation the behaviour of this system. In order to obtain model, the experimental setup are performed by collecting input and output data every minute of 9,385 BTU/h air-conditioning split type with $25^{\circ}C$ thermostat setting of one sample house. The input data are composed of solar radiation ($W/m^2$) and ambient temperature ($^{\circ}C$). The output data are power and energy consumption of air conditioning. Both data are divided into two groups follow as training data and validation data for getting the exact model. The model is also verified with the other similar type of air condition by feed solar radiation and ambient temperature input data and compare the output energy consumption data. The best model in term of accuracy and model order is output error model with 70.78% accuracy and $17^{th}$ order. The model order reduction technique is used to reduce order of model to seven order for less complexity, then Kalman filtering technique is applied for remove white Gaussian noise for improve accuracy of model to be 72.66%. The obtained model can be also used for electrical load forecasting and designs the optimal size of renewable energy such photovoltaic system for supply the air conditioning.

• 설비공학논문집
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• 제24권1호
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• pp.1-8
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• 2012

Recently, the needs of system performances such as working speed and processing accuracy in machine tools have been increased. Especially, the speed increment generates harmful heat at both moving part of the machine tools and handicrafts. The heat is a main drawback to progress accuracy of the processing. Hence, a cooler system to control temperature is inevitable for the machine tools. In general, two representative control schemes, hot-gas bypass and variable speed control of a compressor, have been adopted in the water cooler system. In this paper, comparisons of system performances according to the control schemes in a cooler for machine tools were conducted in detail. Each proportional-integral feedback controller for the two different control systems is designed. The system performances, especially the temperature control accuracy and coefficient of performance which is a criterion of energy saving, were mainly analyzed through various experiments using 1RT water cooler system with different two types of control scheme. These evaluations will provide useful information to choose suitable water cooler system for the engineers who design controllers of the cooler system for machine tools.

• 한국수소및신에너지학회논문집
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• 제34권2호
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• pp.162-168
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• 2023

The fast refueling process of compressed hydrogen has an important impact on the filling efficiency and safety. With the development and use of hydrogen energy, the demand for precision measurement of filling hydrogen thermodynamic parameters is also increasing. In this paper, the compressibility factor calculation model of high-pressure hydrogen gas was studied, and the basic equation of state and thermo-physical parameters were calculated. The hydrogen density data provided by the National Institute of Standards and Technology was compared with the calculation results of each model. Results show that at a pressure of 0.1-100 MPa and a temperature of 233-363 K, the calculation accuracy of the Zheng-Li equation of state was less than 0.5%. In the range of 0.1-70 MPa, the accuracy of Redich-Kwong equation is less than 3%. The hydrogen pressure more influences on the compressibility factor than the hydrogen temperature does. Using the Zheng-Li equation of state to calculate the compressibility factor of on-board high pressure hydrogen can obtain high accuracy.

• 한국멀티미디어학회논문지
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• 제24권1호
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• pp.30-39
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• 2021

Research in the field of health lighting has continued to advance to reproduce the color temperature of natural light which periodically changes. However, most of this research could only reproduce a uniform circadian color temperature of natural light, therefore failing to realize the characteristics of the circadian cycle of color temperature difference by latitude and longitude. To reproduce the color temperature of natural light on which the characteristics of a region are reflected, the collection technology of real-time characteristics of natural light is needed. If the color temperatures which are not within a periodical pattern due to climate changes, etc., are measured, it will be difficult to judge the occurrence (presence) of the anomalies and to reproduce the circadian cycle of the color temperature of natural light. Therefore, this study proposes an algorithm for judging the anomalies in real time based on the sliding window to reproduce the color temperature of natural light. First, the natural light characteristics DB collected through the on-site measurement were analyzed, the differential values at a one-minute interval were calculated and examined, and then representative color temperature circadian patterns by solar terms were drawn. The anomalies were then detected by the application of the sliding window that calculated the deviation of the color temperature for the measured color temperature data set, which was collected through RGB sensors, while moving along the time sequence. In addition, the presence of anomalies was verified through the comparison study between the detection results and the representative circadian cycle of the color temperature by solar term. The judgment method for the anomalies from the measured color temperature of natural light was proposed for the first time, confirming that the proposed method was capable of detecting the anomalies with an average accuracy of 94.6%.

• 한국작물학회지
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• 제62권2호
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• pp.105-112
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• 2017

본 연구는 쌀과 현미의 연산 또는 신 구곡 판별법을 개발하기 위하여 쌀의 저장기간 동안 변화되는 지방의 일종인 인지질 성분을 지표물질로 이용하여 쌀과 현미의 신 구곡 판별식을 작성하였고 미지의 시료를 이용하여 판별식 검증을 수행하였다. 또한 벼의 저장 온도와 시기에 따른 인지질 지표의 판별정확도를 분석함으로써 인지질 지표의 실용적인 활용 가능성을 연구한 결과를 요약하면 다음과 같다. 1. 인지질 지표를 이용하여 쌀에 대한 판별식을 작성한 결과 쌀의 연산별 분류적중률은 90%, 신 구곡의 분류적중률은 97%로 나타나 연산 판별식보다 신 구곡 판별식의 적중률이 높게 나타났다. 따라서 신 구곡 판별식을 쌀의 판별식으로 확립하였고 연산을 알고 있는 미지의 시료를 이용하여 개발된 판별식의 정확도를 분석한 결과 판별식 정확도는 1차 분석에서는 82%, 2차 분석에서는 80%로 나타났다. 2. 현미에 대한 인지질 지표의 신 구곡 분류적중률은 96%로 나타나 95%이상의 적중률을 보여주었으므로 현미의 신 구곡 판별식을 확립하였다. 미지의 시료를 이용하여 개발된 판별식의 정확도를 분석한 결과 93%로 나타나 판별 정확도가 쌀에 비해 높게 나타났다. 현미는 백미에 비해 지방 함량이 많기 때문에 신곡과 구곡 간의 인지질 함량의 차이가 크게 나타나는 경향이었다. 3. 저장온도와 시기에 따른 쌀의 판별 정확도를 분석하기 위하여 벼 보관창고에서 동일한 시료를 수집하여 기확립된 쌀의 신 구곡 판별식에 대입하였을 때 상온 보관된 쌀의 정확도는 57.9~92.1%로 나타났고, 저온 보관된 쌀의 정확도는 86.8~94.7%의 범위로 나타났다. 쌀의 경우 저장 온도와 시기에 따라 판별되는 정확도가 달라졌고 저온 보관된 시료가 상온 보관된 시료에 비해 시기별 판별 정확도의 차이가 적은 것으로 나타났다. 4. 현미의 저장온도 및 시기에 따른 판별 정확도를 분석하기 위하여 벼 보관창고에서 동일한 시료를 수집하여 기 확립된 현미의 신 구곡 판별식에 대입하였을 때 상온 보관된 현미의 정확도는 94.7~100%로 나타났고, 저온 보관된 현미의 정확도는 92.1~100%의 범위로 나타났다. 현미의 경우 쌀에 비해 지방함량이 많고 강층의 존재로 산패가 더디게 진행되기 때문에 저장온도 및 시기에 상관없이 92%이상의 판별 정확도를 나타내었다.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.896-905
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• 2003

A linear motor has many advantages next to conventional feed mechanisms: high transitional speed and acceleration, high control performance, and good positioning accuracy at high speed. Through the omission of a power transfer element, the linear motor shows no wear and no backlash, has a long lifetime, and is easy to assemble. A disadvantage of the linear motor is low efficiency and resultant high-temperature rise in itself and neighboring structures during operation. This paper presents the thermal behavior of the linear motor as a feed mechanism in machine tools. To improve the thermal behavior, an insulation layer is used. By placing the insulation layer between the primary part and the machine table, both the temperature difference and the temperature fluctuation in the machine table due to a varying motor load are reduced.

• Structural Engineering and Mechanics
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• 제7권2호
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• pp.127-145
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• 1999

This paper deals with the development of an approach for evaluating the squash load and rigidity of unprotected concrete filled steel columns at elevated temperatures. The current approach of evaluating these properties is reviewed. It is shown that with a non-uniform temperature distribution, over the composite cross-section, the calculations for the squash load and rigidity are tedious in the current method. A simplified approach is proposed to evaluate the temperature distribution, squash load, and rigidity of composite columns. This approach is based on the model in Eurocode 4 and can conveniently be used to calculate the resistance to axial compression of a concrete filled steel column for any fire resistance time. The accuracy of the proposed approach is assessed by comparing the predicted strengths against the results of fire tests on concrete filled circular and square steel columns. The applicability of the proposed approach to a design situation is illustrated through a numerical example.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1469-1478
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• 2014

Use of acetonitrile in electrolytes promotes better operation of supercapacitors. Recent efforts show that electrolytes containing acetonitrile can also function in a wide range of operating temperatures. Therefore, this paper addresses the dielectric relaxation processes, structure and dynamic properties of the bulk acetonitrile at various temperatures. Systems of acetonitrile were modeled using canonical ensemble and simulated by employing Molecular Dynamics method. Results show that interactions among the molecules were correlated within a cut-off radius while parallel and anti-parallel arrangements are observed beyond this radius at relatively high and low temperatures respectively. Furthermore, effects of C-C-N and C-H bending modes were greatly appreciated on the power spectral density of time rate change of dipole-dipole correlations whereas frequency shifts were observed on all modes at the lowest temperature under consideration. Linear variations with temperature were depicted for reorientation times and self-diffusion coefficients. Shear viscosity was also computed with a good accuracy within a certain range of the temperature as well.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.1-8
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• 2009

This is a short review of how CFD contributed to hypersonic flights in the past 50 years. Two unexpected phenomena that occurred in the entry flights of the Apollo and Space Shuttle made us aware of the impact of the high temperature real-gas effects on hypersonic flights: pitching moment anomaly of up to 4 degrees, and radiation overshoot behind a shock wave. The so-called two-temperature nonequilibrium model was introduced to explain these phenomena. CFD techniques were developed to accommodate the two-temperature model. Presently, CFD can predict trim angle of attack to an accuracy of about 1 degree. A concerted effort was made to numerically reproduce the experimentally measured flow-field over a double-cone. As yet, perfect agreement between the experimental data and computation is not achieved. Scramjet technology development is disappointingly slow. The phenomenon of ablation during planetary entries is not yet predicted satisfactorily. In the future, one expects to see more research carried out on planetary entries and space tourism.