While the traditional trajectory planning methods are used in robotic belt grinding of blades with an uneven machining allowance distribution, it is hard to obtain the preferable profile accuracy and surface quality t...While the traditional trajectory planning methods are used in robotic belt grinding of blades with an uneven machining allowance distribution, it is hard to obtain the preferable profile accuracy and surface quality to meet the high-performance requirements of aero-engine. To solve this problem, a novel trajectory planning method is proposed in this paper by considering the developed interpolation algorithm and the machining allowance threshold. The residual height error obtained from grinding experiments of titanium alloy sample was compensated to modify the calculation model of row spacing, and a new geometric algorithm was presented to dynamically calculate the cutter contact points based on this revised calculation model and the dichotomy method. Subsequently, the off-line machining program is generated based on a double-vector controlling method to obtain an optimal contact posture. On this basis, three sets of robotic grinding tests of titanium alloy blades were conducted to investigate the advantages of the proposed method.The comparative experimental results revealed that the presented algorithm had improved the surface profile accuracy of blade by 34.2% and 55.1%, respectively. Moreover, the average machined surface roughness was achieved to 0.3 μm and the machining efficiency was obviously promoted. It is concluded that this research work is beneficial to comprehensively improve the machined quality of blades in robotic belt grinding.展开更多
在林业研究中,胸径-树高二元联合分布多由相同边缘分布构造,而林分的胸径与树高的实际分布状况可能有所差异。为降低这种差异带来的影响,依据佳木斯市孟家岗林场的115块长白落叶松人工林数据,选择适用条件低、适应范围广的Copula函数方...在林业研究中,胸径-树高二元联合分布多由相同边缘分布构造,而林分的胸径与树高的实际分布状况可能有所差异。为降低这种差异带来的影响,依据佳木斯市孟家岗林场的115块长白落叶松人工林数据,选择适用条件低、适应范围广的Copula函数方法拟合落叶松胸径-树高二元联合分布模型。首先选择威布尔(Weibull)、广义威布尔(G-Weibull)、逻辑斯蒂(Logistic)、轻量逻辑斯蒂(Logit-Logistic)、伽马(Gamma)、对数正态(Log-Normal)6个分布函数作为备选基础模型,根据K-S(kolmogorov smirnov test)检验与半参数估计结果筛选并构建Copula胸径-树高二元联合分布模型,再通过负对数似然(negative log-likelihood,NLL)、Sn拟合优度统计量和似然比检验(likelihood ratio test,LRT)与二元对数logistic分布函数和二元Weibull分布函数进行比较,最后使用雷诺误差指数(error index of Reynolds,EI)对模型预测能力进行评估。结果表明,基于Copula函数的二元分拟合结果与模型(EI=0.3184)预估能力皆优于二元Weibull分布(EI=0.6381)和二元对数Logistic分布(EI=0.9490),说明此方法构建胸径-树高二元联合Copula分布模型能够很好地描述落叶松人工林胸径树高联合分布,以Copula方法构建树高-胸径联合分布是可行的。展开更多
This paper deals with the issue of preparation of the aiming angles with the use of tabular firing tables and needed determination of the ballistic elements μ_B(ballistic wind w_B,w_(xB),w_(ZB),ballistic(virtual) tem...This paper deals with the issue of preparation of the aiming angles with the use of tabular firing tables and needed determination of the ballistic elements μ_B(ballistic wind w_B,w_(xB),w_(ZB),ballistic(virtual) temperature τ_B.ballistic density p_B) from the standardized met messages.The weighting factors are used for the calculation of ballistic elements μ_B that are incorporated into the trajectory calculations characteristics of weapon and ammunition.Two different methodologies practically used in the praxis are analysed and compared.For the comparison of the two methodologies the reference height of trajectory determined from the weighting factor functions is employed.On the basis of the analyses conducted,the potential for further increase in accuracy of these aiming angles preparation methods is pointed out.展开更多
As a new remote sensing technology, the global navigation satellite system（GNSS） reflection signals can be used to collect the information of ocean surface wind, surface roughness and sea surface height. Ocean altim...As a new remote sensing technology, the global navigation satellite system（GNSS） reflection signals can be used to collect the information of ocean surface wind, surface roughness and sea surface height. Ocean altimetry based on GNSS reflection technique is of low cost and it is easy to obtain large amounts of data thanks to the global navigation satellite constellation. We can estimate the sea surface height as well as the position of the specular reflection point. This paper focuses on the study of the algorithm to determine the specular reflection point and altimetry equations to estimate the sea surface height over the reflection region. We derive the error equation of sea surface height based on the error propagation theory. Effects of the Doppler shift and the size of the glistening zone on the altimetry are discussed and analyzed at the same time. Finally, we calculate the sea surface height based on the simulated GNSS data within the whole day and verify the sea surface height errors according to the satellite elevation angles. The results show that the sea surface height can reach the precision of 6 cm for elevation angles of 55° to 90°, and the theoretical error and the calculated error are in good agreement.展开更多
Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are kno...Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are knowledge gaps on the accuracy variations in rugged and complex landscapes,and previous studies have often not relied on robust internal and external validation measures.Thus,there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications.In this study,we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution,readily available,free-access and global coverage 1 arc-second(30 m)DEMs:NASADEM,ASTER GDEM,Copernicus GLO-30,and ALOS World 3D(AW3D).The assessment is carried out at landscapes spread across Cape Town,Southern Africa(urban/industrial,agricultural,mountain,peninsula and grassland/shrubland)and forested national parks in Gabon,Central Africa(low-relief tropical rainforest and high-relief tropical rainforest).The statistical analysis is based on robust accuracy metrics that cater for normal and non-normal elevation error distribution,and error ranking.In Cape Town,Copernicus DEM generally had the least vertical error with an overall Mean Error(ME)of 0.82 m and Root Mean Square Error(RMSE)of 2.34 m while ASTER DEM had the poorest performance.However,ASTER GDEM and NASADEM performed better in the low-relief and high-relief tropical forests of Gabon.Generally,the DEM errors have a moderate to high positive correlation in forests,and a low to moderate positive correlation in mountains and urban areas.Copernicus DEM showed superior vertical accuracy in forests with less than 40%tree cover,while ASTER and NASADEM performed better in denser forests with tree cover greater than 70%.This study is a robust regional assessment of these global DEMs.展开更多
基金supported by the National Natural Science Foundation of China(No.52075059)the Natural Science Foundation of Chongqing(No.cstc2020jcyj-msxm X0266)。
文摘While the traditional trajectory planning methods are used in robotic belt grinding of blades with an uneven machining allowance distribution, it is hard to obtain the preferable profile accuracy and surface quality to meet the high-performance requirements of aero-engine. To solve this problem, a novel trajectory planning method is proposed in this paper by considering the developed interpolation algorithm and the machining allowance threshold. The residual height error obtained from grinding experiments of titanium alloy sample was compensated to modify the calculation model of row spacing, and a new geometric algorithm was presented to dynamically calculate the cutter contact points based on this revised calculation model and the dichotomy method. Subsequently, the off-line machining program is generated based on a double-vector controlling method to obtain an optimal contact posture. On this basis, three sets of robotic grinding tests of titanium alloy blades were conducted to investigate the advantages of the proposed method.The comparative experimental results revealed that the presented algorithm had improved the surface profile accuracy of blade by 34.2% and 55.1%, respectively. Moreover, the average machined surface roughness was achieved to 0.3 μm and the machining efficiency was obviously promoted. It is concluded that this research work is beneficial to comprehensively improve the machined quality of blades in robotic belt grinding.
文摘在林业研究中,胸径-树高二元联合分布多由相同边缘分布构造,而林分的胸径与树高的实际分布状况可能有所差异。为降低这种差异带来的影响,依据佳木斯市孟家岗林场的115块长白落叶松人工林数据,选择适用条件低、适应范围广的Copula函数方法拟合落叶松胸径-树高二元联合分布模型。首先选择威布尔(Weibull)、广义威布尔(G-Weibull)、逻辑斯蒂(Logistic)、轻量逻辑斯蒂(Logit-Logistic)、伽马(Gamma)、对数正态(Log-Normal)6个分布函数作为备选基础模型,根据K-S(kolmogorov smirnov test)检验与半参数估计结果筛选并构建Copula胸径-树高二元联合分布模型,再通过负对数似然(negative log-likelihood,NLL)、Sn拟合优度统计量和似然比检验(likelihood ratio test,LRT)与二元对数logistic分布函数和二元Weibull分布函数进行比较,最后使用雷诺误差指数(error index of Reynolds,EI)对模型预测能力进行评估。结果表明,基于Copula函数的二元分拟合结果与模型(EI=0.3184)预估能力皆优于二元Weibull分布(EI=0.6381)和二元对数Logistic分布(EI=0.9490),说明此方法构建胸径-树高二元联合Copula分布模型能够很好地描述落叶松人工林胸径树高联合分布,以Copula方法构建树高-胸径联合分布是可行的。
基金support of financial means from the industrial research project of the Ministry of the Interior of the Czech Republic-project code VG20122015076:"Two survey points range-finding system utilization for perimeter security(screen)"the Research project for the development of the Department of Weapons and Ammunition,Faculty of Military Technology, University of Defence,Brno,PRO K-201
文摘This paper deals with the issue of preparation of the aiming angles with the use of tabular firing tables and needed determination of the ballistic elements μ_B(ballistic wind w_B,w_(xB),w_(ZB),ballistic(virtual) temperature τ_B.ballistic density p_B) from the standardized met messages.The weighting factors are used for the calculation of ballistic elements μ_B that are incorporated into the trajectory calculations characteristics of weapon and ammunition.Two different methodologies practically used in the praxis are analysed and compared.For the comparison of the two methodologies the reference height of trajectory determined from the weighting factor functions is employed.On the basis of the analyses conducted,the potential for further increase in accuracy of these aiming angles preparation methods is pointed out.
基金financially supported by the National Natural Science Foundation of China(Grant No.41374009)the Shandong Natural Science Foundation of China(Grant No.ZR2013DM009)+3 种基金the National Basic Research Program of China(973 ProgramGrant No.2013CB733302)the Public Benefit Scientific Research Project of China(Grant No.201412001)the SDUST Research Fund(Grant No.2014TDJH101)
文摘As a new remote sensing technology, the global navigation satellite system（GNSS） reflection signals can be used to collect the information of ocean surface wind, surface roughness and sea surface height. Ocean altimetry based on GNSS reflection technique is of low cost and it is easy to obtain large amounts of data thanks to the global navigation satellite constellation. We can estimate the sea surface height as well as the position of the specular reflection point. This paper focuses on the study of the algorithm to determine the specular reflection point and altimetry equations to estimate the sea surface height over the reflection region. We derive the error equation of sea surface height based on the error propagation theory. Effects of the Doppler shift and the size of the glistening zone on the altimetry are discussed and analyzed at the same time. Finally, we calculate the sea surface height based on the simulated GNSS data within the whole day and verify the sea surface height errors according to the satellite elevation angles. The results show that the sea surface height can reach the precision of 6 cm for elevation angles of 55° to 90°, and the theoretical error and the calculated error are in good agreement.
基金supported by the(i)Commonwealth Scholarship Commission and the Foreign,Commonwealth and Development Office in the UK[Grant number NGCN-2021-239](ii)University of Cape Town Postgraduate Funding Office.
文摘Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are knowledge gaps on the accuracy variations in rugged and complex landscapes,and previous studies have often not relied on robust internal and external validation measures.Thus,there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications.In this study,we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution,readily available,free-access and global coverage 1 arc-second(30 m)DEMs:NASADEM,ASTER GDEM,Copernicus GLO-30,and ALOS World 3D(AW3D).The assessment is carried out at landscapes spread across Cape Town,Southern Africa(urban/industrial,agricultural,mountain,peninsula and grassland/shrubland)and forested national parks in Gabon,Central Africa(low-relief tropical rainforest and high-relief tropical rainforest).The statistical analysis is based on robust accuracy metrics that cater for normal and non-normal elevation error distribution,and error ranking.In Cape Town,Copernicus DEM generally had the least vertical error with an overall Mean Error(ME)of 0.82 m and Root Mean Square Error(RMSE)of 2.34 m while ASTER DEM had the poorest performance.However,ASTER GDEM and NASADEM performed better in the low-relief and high-relief tropical forests of Gabon.Generally,the DEM errors have a moderate to high positive correlation in forests,and a low to moderate positive correlation in mountains and urban areas.Copernicus DEM showed superior vertical accuracy in forests with less than 40%tree cover,while ASTER and NASADEM performed better in denser forests with tree cover greater than 70%.This study is a robust regional assessment of these global DEMs.
