为应对自然风随机性与波动性带来的风速预测精度低的问题,提出一种基于频-时转换与Informer的强风等级预测方法(a strong-wind level prediction method with frequency-time transformation and Informer,FT-Informer)。该方法通过预...为应对自然风随机性与波动性带来的风速预测精度低的问题,提出一种基于频-时转换与Informer的强风等级预测方法(a strong-wind level prediction method with frequency-time transformation and Informer,FT-Informer)。该方法通过预测强风等级并输出包含多级强风信息的风速等级概率分布表,提升高铁系统在强风环境下的调度能力。首先,将Informer作为主要预测器,基于编码器-解码器架构和自注意力机制,预测实时风速。然后,引入频-时转换(frequency-time trans-formation,FT)方法对预测风速的随机脉动特性进行数值分析,进而实现风速波动范围的遍历模拟,降低风速波动性对预测结果的干扰。最后,为提供更具决策支持性的大风预警信息,构建预测风速的概率密度函数(probability density function,PDF)样本矢量集,模拟随机脉动风场的全概率尺度,从而生成未来一段时间内风速等级的概率分布表。实验结果表明,所提出的预测方法在风速等级预测精度上明显优于其他5种模型。其中预测准确率提高0.64%~10.36%,预测等级偏差为1的误差率降低0.36%~6.78%。值得注意的是,所提方法预测等级偏差为2的概率为0,与其他模型相比预测效果提升0.19%~3.68%。此外,在不同时间间隔及不同数据集的泛化实验中,该方法均展现出较强的鲁棒性和泛化性,在功率谱拟合度实验(power spectrum fitting experiment)以及风速概率精度对比实验中,验证了各强风等级概率计算结果的有效性。研究方法不仅降低了随机脉动风对预测结果的干扰,还为铁路调度人员提供未来一段时间内铁路沿线3个强风等级的发生概率,助力铁路部门制定更加精准且细致的调度决策,从而为列车在强风环境下的安全运营提供有力保障。展开更多
Comparing and analyzing the difference between automatic-observed and manual-observed wind speed based on the wind speed parallel observations in two methods, we find that many elements can influence the difference be...Comparing and analyzing the difference between automatic-observed and manual-observed wind speed based on the wind speed parallel observations in two methods, we find that many elements can influence the difference between automatic-observed and manual-observed wind speed, including the levels of speed wind, observation instruments and different regions. According to these elements, correction has been conducted, and find that the correction according to the level of wind speed has the best correction effect.展开更多
热带气旋(Tropical Cyclone,TC)作为一种强烈的天气系统,其破坏力不仅受强度影响,也与其尺度密切相关.TC的移动速度如何影响其尺度仍缺乏系统研究.基于1988-2021年北大西洋的最佳路径(Extended Best Track,EBT)资料和ERA5再分析资料,分...热带气旋(Tropical Cyclone,TC)作为一种强烈的天气系统,其破坏力不仅受强度影响,也与其尺度密切相关.TC的移动速度如何影响其尺度仍缺乏系统研究.基于1988-2021年北大西洋的最佳路径(Extended Best Track,EBT)资料和ERA5再分析资料,分析了TC移动速度与最大风速半径(Radius of Maximum Wind,RMW)、17 m·s^(-1)风圈半径(R17)之间的统计关系及其影响物理机制.结果表明,R17随移动速度增强呈显著增大趋势,且高分位R17对移速变化更敏感;RMW随移动速度增加而略有扩大,其变化主要由R17的变化造成.在影响物理机制上,发现快速移动TC显著削弱海温冷却,从而维持或增强表面焓通量,提升了大气的不稳定性;同时,显著增强前方低层辐合.热力和动力途径的协同作用驱动更强的上升运动,并促进螺旋雨带的发展,而雨带产生的非绝热加热增强角动量的向内输送,最终导致外围风场扩张、R17增大,RMW也随之增大.展开更多
针对CTCS-3级列控系统在无线消息超时降级至CTCS-2级运行时速度差异较大的问题,提出在后备模式下将CTCS-2顶棚速度由300 k m/h调整为350 k m/h,并将国内高铁线路坡度情况分为3类,经过分析线路坡度、制动距离等因素,提出将轨道电路信息...针对CTCS-3级列控系统在无线消息超时降级至CTCS-2级运行时速度差异较大的问题,提出在后备模式下将CTCS-2顶棚速度由300 k m/h调整为350 k m/h,并将国内高铁线路坡度情况分为3类,经过分析线路坡度、制动距离等因素,提出将轨道电路信息码最高扩展至L9码。相关设备需按此方案进行修改。该技术可实现CTCS-3级列控系统在350 km/h等速降级为CTCS-2级的冗余切换,覆盖国内所有既有350 k m/h等级高铁。通过以上技术改进,能够最大限度降低对运行时分的影响,充分发挥CTCS-2级后备系统的作用。展开更多
Mean sea level rise and climatological wind speed changes occur as part of the ongoing climate change and future projections of both variables are still highly uncertain. Here the Baltic Sea’s response in extreme sea...Mean sea level rise and climatological wind speed changes occur as part of the ongoing climate change and future projections of both variables are still highly uncertain. Here the Baltic Sea’s response in extreme sea levels to perturbations in mean sea level and wind speeds is investigated in a series of simulations with a newly developed storm surge model based on the nucleus for European modeling of the ocean(NEMO)-Nordic. A simple linear model with only two tunable parameters is found to capture the changes in the return levels extremely well. The response to mean sea level rise is linear and nearly spatially uniform, meaning that a mean sea level rise of 1 m increases the return levels by a equal amount everywhere. The response to wind speed perturbations is more complicated and return levels are found to increase more where they are already high. This behaviour is alarming as it suggests that already flooding prone regions like the Gulf of Finland will be disproportionally adversely affected in a future windier climate.展开更多
The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of...The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM(CRECM)is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.展开更多
Many research results show that ocean ambient noise and wind speed are highly relevant, and the surface wind speed can be effectively inverted using ocean noise data. In most deep-sea cases, the ambient noise of mediu...Many research results show that ocean ambient noise and wind speed are highly relevant, and the surface wind speed can be effectively inverted using ocean noise data. In most deep-sea cases, the ambient noise of medium frequency is mainly determined by the surface wind, and there is a conventional relationship between them. This paper gives an equation which shows this relationship firstly, and then a surface-wind inversion method is proposed. An efficient particle filter is used to estimate the speed distribution, and the results exhibit more focused close to the actual wind speed. The method is verified by the measured noise data, and analysis results showed that this approach can accurately give the trend of sea surface wind speed.展开更多
Objective To present a novel modified level set algorithm for medical image segmentation. Methods The algorithm is developed by substituting the speed function of level set algorithm with the region and gradient infor...Objective To present a novel modified level set algorithm for medical image segmentation. Methods The algorithm is developed by substituting the speed function of level set algorithm with the region and gradient information of the image instead of the conventional gradient information. This new algorithm has been tested by a series of different modality medical images. Results We present various examples and also evaluate and compare the performance of our method with the classical level set method on weak boundaries and noisy images. Conclusion Experimental results show the proposed algorithm is effective and robust.展开更多
Daily observations of wind speed at 12 stations in the Greater Beijing Area during 1960–2008 were homogenized using the Multiple Analysis of Series for Homogenization method. The linear trends in the regional mean an...Daily observations of wind speed at 12 stations in the Greater Beijing Area during 1960–2008 were homogenized using the Multiple Analysis of Series for Homogenization method. The linear trends in the regional mean annual and seasonal （winter, spring, summer and autumn） wind speed series were-0.26,-0.39,-0.30,-0.12 and-0.22 m s-1 （10 yr）-1 , respectively. Winter showed the greatest magnitude in declining wind speed, followed by spring, autumn and summer. The annual and seasonal frequencies of wind speed extremes （days） also decreased, more prominently for winter than for the other seasons. The declining trends in wind speed and extremes were formed mainly by some rapid declines during the 1970s and 1980s. The maximum declining trend in wind speed occurred at Chaoyang （CY）, a station within the central business district （CBD） of Beijing with the highest level of urbanization. The declining trends were in general smaller in magnitude away from the city center, except for the winter case in which the maximum declining trend shifted northeastward to rural Miyun （MY）. The influence of urbanization on the annual wind speed was estimated to be about-0.05 m s-1 （10 yr）-1 during 1960–2008, accounting for around one fifth of the regional mean declining trend. The annual and seasonal geostrophic wind speeds around Beijing, based on daily mean sea level pressure （MSLP） from the ERA-40 reanalysis dataset, also exhibited decreasing trends, coincident with the results from site observations. A comparative analysis of the MSLP fields between 1966–1975 and 1992–2001 suggested that the influences of both the winter and summer monsoons on Beijing were weaker in the more recent of the two decades. It is suggested that the bulk of wind in Beijing is influenced considerably by urbanization, while changes in strong winds or wind speed extremes are prone to large-scale climate change in the region.展开更多
Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different ...Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach–Based on large eddy simulation(LES)method and Kirchhoff–Ffowcs Williams and Hawkings(K-FWH)equations,the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings–The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train.The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train,the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car,and the quadrupole sources are mainly distributed in the wake area.When the train runs at three speed levels of 400,500 and 600 km$h1,respectively,the radiated energy of quadrupole source is 62.4%,63.3%and 71.7%,respectively,which exceeds that of dipole sources.Originality/value–This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.展开更多
This paper presents an efficient liver-segmentation system developed by combining three ideas under the operations of a level-set method and consequent processes. First, an effective initial process creates mask and s...This paper presents an efficient liver-segmentation system developed by combining three ideas under the operations of a level-set method and consequent processes. First, an effective initial process creates mask and seed regions. The mask regions assist in prevention of leakage regions due to an overlap of gray-intensities between liver and another soft-tissue around ribs and verte-brae. The seed regions are allocated inside the liver to measure statistical values of its gray-intensities. Second, we introduce liver-corrective images to represent statistical regions of the liver and preserve edge information. These images help a geodesic active contour (GAC) to move without obstruction from high level of image noises. Lastly, the computation time in a level-set based on reaction-diffusion evolution and the GAC method is reduced by using a concept of multi-resolution. We applied the proposed system to 40 sets of 3D CT-liver data, which were acquired from four patients (10 different sets per patient) by a 4D-CT imaging system. The segmentation results showed 86.38% ± 4.26% (DSC: 91.38% ± 2.99%) of similarities to outlines of manual delineation provided by a radiologist. Meanwhile, the results of liver segmentation only using edge images presented 79.17% ± 5.15% or statistical regions showed 74.04% ± 9.77% of similarities.展开更多
A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flot...A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.展开更多
基金Supported by Meteorological Data Sharing Center Project (2005DKA31700-01,GX07-01-01)2009 Specific Research in Non-profit Sector (200906041-053)
文摘Comparing and analyzing the difference between automatic-observed and manual-observed wind speed based on the wind speed parallel observations in two methods, we find that many elements can influence the difference between automatic-observed and manual-observed wind speed, including the levels of speed wind, observation instruments and different regions. According to these elements, correction has been conducted, and find that the correction according to the level of wind speed has the best correction effect.
文摘热带气旋(Tropical Cyclone,TC)作为一种强烈的天气系统,其破坏力不仅受强度影响,也与其尺度密切相关.TC的移动速度如何影响其尺度仍缺乏系统研究.基于1988-2021年北大西洋的最佳路径(Extended Best Track,EBT)资料和ERA5再分析资料,分析了TC移动速度与最大风速半径(Radius of Maximum Wind,RMW)、17 m·s^(-1)风圈半径(R17)之间的统计关系及其影响物理机制.结果表明,R17随移动速度增强呈显著增大趋势,且高分位R17对移速变化更敏感;RMW随移动速度增加而略有扩大,其变化主要由R17的变化造成.在影响物理机制上,发现快速移动TC显著削弱海温冷却,从而维持或增强表面焓通量,提升了大气的不稳定性;同时,显著增强前方低层辐合.热力和动力途径的协同作用驱动更强的上升运动,并促进螺旋雨带的发展,而雨带产生的非绝热加热增强角动量的向内输送,最终导致外围风场扩张、R17增大,RMW也随之增大.
文摘针对CTCS-3级列控系统在无线消息超时降级至CTCS-2级运行时速度差异较大的问题,提出在后备模式下将CTCS-2顶棚速度由300 k m/h调整为350 k m/h,并将国内高铁线路坡度情况分为3类,经过分析线路坡度、制动距离等因素,提出将轨道电路信息码最高扩展至L9码。相关设备需按此方案进行修改。该技术可实现CTCS-3级列控系统在350 km/h等速降级为CTCS-2级的冗余切换,覆盖国内所有既有350 k m/h等级高铁。通过以上技术改进,能够最大限度降低对运行时分的影响,充分发挥CTCS-2级后备系统的作用。
基金funding from the project “Future flooding risks at the Swedish Coast: Extreme situations in present and future climat”, Ref. No. P02/12 by Lansforsakringsbolagens Forskningsfondthrough the Swedish Civil Contingencies Agency (MSB) through the project “Hazard Support: Risk-based decision support for adaptation to future natural hazards”
文摘Mean sea level rise and climatological wind speed changes occur as part of the ongoing climate change and future projections of both variables are still highly uncertain. Here the Baltic Sea’s response in extreme sea levels to perturbations in mean sea level and wind speeds is investigated in a series of simulations with a newly developed storm surge model based on the nucleus for European modeling of the ocean(NEMO)-Nordic. A simple linear model with only two tunable parameters is found to capture the changes in the return levels extremely well. The response to mean sea level rise is linear and nearly spatially uniform, meaning that a mean sea level rise of 1 m increases the return levels by a equal amount everywhere. The response to wind speed perturbations is more complicated and return levels are found to increase more where they are already high. This behaviour is alarming as it suggests that already flooding prone regions like the Gulf of Finland will be disproportionally adversely affected in a future windier climate.
基金supported by the National Natural Science Foundation of China (51535006, 51805259)Natural Science Foundation of Jiangsu Province of China (BK20180431)+2 种基金Fundamental Research Funds for the Central Universities of China (3082018NP2018406)Young Elite Scientists Sponsorship Program by CAST of ChinaJiangsu Key Laboratory of Precision and Micro-Manufacturing Technology of China
文摘The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM(CRECM)is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.11174235 and 61101192)
文摘Many research results show that ocean ambient noise and wind speed are highly relevant, and the surface wind speed can be effectively inverted using ocean noise data. In most deep-sea cases, the ambient noise of medium frequency is mainly determined by the surface wind, and there is a conventional relationship between them. This paper gives an equation which shows this relationship firstly, and then a surface-wind inversion method is proposed. An efficient particle filter is used to estimate the speed distribution, and the results exhibit more focused close to the actual wind speed. The method is verified by the measured noise data, and analysis results showed that this approach can accurately give the trend of sea surface wind speed.
文摘Objective To present a novel modified level set algorithm for medical image segmentation. Methods The algorithm is developed by substituting the speed function of level set algorithm with the region and gradient information of the image instead of the conventional gradient information. This new algorithm has been tested by a series of different modality medical images. Results We present various examples and also evaluate and compare the performance of our method with the classical level set method on weak boundaries and noisy images. Conclusion Experimental results show the proposed algorithm is effective and robust.
基金supported by grants from the MOST NBRPC(2009CB421401)CNNSF(41075063) and the CMA Institute of Urban Meteorology
文摘Daily observations of wind speed at 12 stations in the Greater Beijing Area during 1960–2008 were homogenized using the Multiple Analysis of Series for Homogenization method. The linear trends in the regional mean annual and seasonal （winter, spring, summer and autumn） wind speed series were-0.26,-0.39,-0.30,-0.12 and-0.22 m s-1 （10 yr）-1 , respectively. Winter showed the greatest magnitude in declining wind speed, followed by spring, autumn and summer. The annual and seasonal frequencies of wind speed extremes （days） also decreased, more prominently for winter than for the other seasons. The declining trends in wind speed and extremes were formed mainly by some rapid declines during the 1970s and 1980s. The maximum declining trend in wind speed occurred at Chaoyang （CY）, a station within the central business district （CBD） of Beijing with the highest level of urbanization. The declining trends were in general smaller in magnitude away from the city center, except for the winter case in which the maximum declining trend shifted northeastward to rural Miyun （MY）. The influence of urbanization on the annual wind speed was estimated to be about-0.05 m s-1 （10 yr）-1 during 1960–2008, accounting for around one fifth of the regional mean declining trend. The annual and seasonal geostrophic wind speeds around Beijing, based on daily mean sea level pressure （MSLP） from the ERA-40 reanalysis dataset, also exhibited decreasing trends, coincident with the results from site observations. A comparative analysis of the MSLP fields between 1966–1975 and 1992–2001 suggested that the influences of both the winter and summer monsoons on Beijing were weaker in the more recent of the two decades. It is suggested that the bulk of wind in Beijing is influenced considerably by urbanization, while changes in strong winds or wind speed extremes are prone to large-scale climate change in the region.
基金The research was supported by the National Key Research and Development Program(Grant No.2020YFA0710903)the Financial Funding Project for Central Colleges and Universities(Grant No.202045014)the Science and Technology Research and Development Program of China State Railway Group Co.,Ltd.(Grant No.P2019J008).
文摘Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach–Based on large eddy simulation(LES)method and Kirchhoff–Ffowcs Williams and Hawkings(K-FWH)equations,the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings–The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train.The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train,the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car,and the quadrupole sources are mainly distributed in the wake area.When the train runs at three speed levels of 400,500 and 600 km$h1,respectively,the radiated energy of quadrupole source is 62.4%,63.3%and 71.7%,respectively,which exceeds that of dipole sources.Originality/value–This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.
文摘This paper presents an efficient liver-segmentation system developed by combining three ideas under the operations of a level-set method and consequent processes. First, an effective initial process creates mask and seed regions. The mask regions assist in prevention of leakage regions due to an overlap of gray-intensities between liver and another soft-tissue around ribs and verte-brae. The seed regions are allocated inside the liver to measure statistical values of its gray-intensities. Second, we introduce liver-corrective images to represent statistical regions of the liver and preserve edge information. These images help a geodesic active contour (GAC) to move without obstruction from high level of image noises. Lastly, the computation time in a level-set based on reaction-diffusion evolution and the GAC method is reduced by using a concept of multi-resolution. We applied the proposed system to 40 sets of 3D CT-liver data, which were acquired from four patients (10 different sets per patient) by a 4D-CT imaging system. The segmentation results showed 86.38% ± 4.26% (DSC: 91.38% ± 2.99%) of similarities to outlines of manual delineation provided by a radiologist. Meanwhile, the results of liver segmentation only using edge images presented 79.17% ± 5.15% or statistical regions showed 74.04% ± 9.77% of similarities.
文摘A novel flotation froth image segmentation based on threshold level set method is put forward in view of the problem of over-segmentation and under-segmentation which occurs when the existing method segmented the flotation froth images. Firstly, the proposed method adopts histogram equalization to improve the contrast of the image, and then chooses the upper threshold and lower threshold from grey value of histogram of the image equalization, and complete image segmentation using the level set method. In this paper, the model which integrates edge with region level set model is utilized, and the speed energy term is introduced to segment the target. Experimental results show that the proposed method has better segmentation results and higher segmentation efficiency on the images with under-segmentation and incorrect segmentation, and it is meaningful for ore dressing industrial.
