电离层F2层的临界频率(f_(o)F_(2))的平方与峰值电子密度(N_(m)F2)成正比,是影响GNSS性能的关键参数之一,提升电离层f_(o)F_(2)的预测精度对于优化GNSS广播电离层模型性能并提升GNSS的定位精度具有重要意义.本文基于中国及周边区域的18...电离层F2层的临界频率(f_(o)F_(2))的平方与峰值电子密度(N_(m)F2)成正比,是影响GNSS性能的关键参数之一,提升电离层f_(o)F_(2)的预测精度对于优化GNSS广播电离层模型性能并提升GNSS的定位精度具有重要意义.本文基于中国及周边区域的18个测高仪台站和COSMIC(constellation observing system for meteorology,ionosphere,and climate)掩星观测数据,综合考虑世界时、年积日、地理位置、太阳和地磁活动等多维特征,利用随机森林(random forest,RF)算法构建了电离层f_(o)F_(2)预测模型.通过与国际参考电离层(international reference ionosphere,IRI)-2020模型对比分析,验证了该模型的预测精度.研究结果表明,与IRI国际无线电咨询委员会(International Radio Consultative Committee,CCIR)和IRI国际无线电科学联盟(International Union of Radio Science,URSI)模型相比,RF模型的平均绝对误差(mean absolute error,MAE)分别降低了14.81%和17.11%,均方根误差(root mean squared error,RMSE)分别降低了11.21%和13.14%.此外,该模型在不同纬度、地方时、太阳活动和地磁活动条件下,均展现出优于IRI-2020的预测精度.本研究不仅有效提升了中国及周边区域电离层f_(o)F_(2)的预测精度,还为提高GNSS的准确性和可靠性奠定了重要基础.展开更多
The supercritical CO_(2) Brayton cycle is considered a promising energy conversion system for Generation IV reactors for its simple layout,compact structure,and high cycle efficiency.Mathematical models of four Brayto...The supercritical CO_(2) Brayton cycle is considered a promising energy conversion system for Generation IV reactors for its simple layout,compact structure,and high cycle efficiency.Mathematical models of four Brayton cycle layouts are developed in this study for different reactors to reduce the cost and increase the thermohydraulic performance of nuclear power generation to promote the commercialization of nuclear energy.Parametric analysis,multi-objective optimizations,and four decision-making methods are applied to obtain each Brayton scheme’s optimal thermohydraulic and economic indexes.Results show that for the same design thermal power scale of reactors,the higher the core’s exit temperature,the better the Brayton cycle’s thermo-economic performance.Among the four-cycle layouts,the recompression cycle(RC)has the best overall performance,followed by the simple recuperation cycle(SR)and the intercooling cycle(IC),and the worst is the reheating cycle(RH).However,RH has the lowest total cost of investment(C_(tot))of$1619.85 million,and IC has the lowest levelized cost of energy(LCOE)of 0.012$/(kWh).The nuclear Brayton cycle system’s overall performance has been improved due to optimization.The performance of the molten salt reactor combined with the intercooling cycle(MSR-IC)scheme has the greatest improvement,with the net output power(W_(net)),thermal efficiencyη_(t),and exergy efficiency(η_(e))improved by 8.58%,8.58%,and 11.21%,respectively.The performance of the lead-cooled fast reactor combined with the simple recuperation cycle scheme was optimized to increase C_(tot) by 27.78%.In comparison,the internal rate of return(IRR)increased by only 7.8%,which is not friendly to investors with limited funds.For the nuclear Brayton cycle,the molten salt reactor combined with the recompression cycle scheme should receive priority,and the gas-cooled fast reactor combined with the reheating cycle scheme should be considered carefully.展开更多
文摘电离层F2层的临界频率(f_(o)F_(2))的平方与峰值电子密度(N_(m)F2)成正比,是影响GNSS性能的关键参数之一,提升电离层f_(o)F_(2)的预测精度对于优化GNSS广播电离层模型性能并提升GNSS的定位精度具有重要意义.本文基于中国及周边区域的18个测高仪台站和COSMIC(constellation observing system for meteorology,ionosphere,and climate)掩星观测数据,综合考虑世界时、年积日、地理位置、太阳和地磁活动等多维特征,利用随机森林(random forest,RF)算法构建了电离层f_(o)F_(2)预测模型.通过与国际参考电离层(international reference ionosphere,IRI)-2020模型对比分析,验证了该模型的预测精度.研究结果表明,与IRI国际无线电咨询委员会(International Radio Consultative Committee,CCIR)和IRI国际无线电科学联盟(International Union of Radio Science,URSI)模型相比,RF模型的平均绝对误差(mean absolute error,MAE)分别降低了14.81%和17.11%,均方根误差(root mean squared error,RMSE)分别降低了11.21%和13.14%.此外,该模型在不同纬度、地方时、太阳活动和地磁活动条件下,均展现出优于IRI-2020的预测精度.本研究不仅有效提升了中国及周边区域电离层f_(o)F_(2)的预测精度,还为提高GNSS的准确性和可靠性奠定了重要基础.
基金This work was supported of National Natural Science Foundation of China Fund(No.52306033)State Key Laboratory of Engines Fund(No.SKLE-K2022-07)the Jiangxi Provincial Postgraduate Innovation Special Fund(No.YC2022-s513).
文摘The supercritical CO_(2) Brayton cycle is considered a promising energy conversion system for Generation IV reactors for its simple layout,compact structure,and high cycle efficiency.Mathematical models of four Brayton cycle layouts are developed in this study for different reactors to reduce the cost and increase the thermohydraulic performance of nuclear power generation to promote the commercialization of nuclear energy.Parametric analysis,multi-objective optimizations,and four decision-making methods are applied to obtain each Brayton scheme’s optimal thermohydraulic and economic indexes.Results show that for the same design thermal power scale of reactors,the higher the core’s exit temperature,the better the Brayton cycle’s thermo-economic performance.Among the four-cycle layouts,the recompression cycle(RC)has the best overall performance,followed by the simple recuperation cycle(SR)and the intercooling cycle(IC),and the worst is the reheating cycle(RH).However,RH has the lowest total cost of investment(C_(tot))of$1619.85 million,and IC has the lowest levelized cost of energy(LCOE)of 0.012$/(kWh).The nuclear Brayton cycle system’s overall performance has been improved due to optimization.The performance of the molten salt reactor combined with the intercooling cycle(MSR-IC)scheme has the greatest improvement,with the net output power(W_(net)),thermal efficiencyη_(t),and exergy efficiency(η_(e))improved by 8.58%,8.58%,and 11.21%,respectively.The performance of the lead-cooled fast reactor combined with the simple recuperation cycle scheme was optimized to increase C_(tot) by 27.78%.In comparison,the internal rate of return(IRR)increased by only 7.8%,which is not friendly to investors with limited funds.For the nuclear Brayton cycle,the molten salt reactor combined with the recompression cycle scheme should receive priority,and the gas-cooled fast reactor combined with the reheating cycle scheme should be considered carefully.
