Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various dam...Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various damages in twist drilling and chip removal clog in core drilling could happen,inevitably reducing hole quality and hole-manufacturing efficiency.This paper proposes the wave-motion milling(WMM)method for CFRP hole-manufacturing to improve hole quality.This paper presents a motion path model based on the kinematics of the WMM method.The wave-motion cutting mode in WMM was analyzed first.Then,comparison experiments on WMM and conventional helical milling(CHM)of CFRP were carried out under dry conditions.The results showed that the hole surface quality of the CFRP significantly improved with a decrease of 18.1%–36%of Ra value in WMM compared to CHM.WMM exerted a significantly weaker thrust force than that of CHM with a reduction of 12.0%–24.9%and 3%–7.7%for different axial feed per tooth and tangential feed per tooth,respectively.Meanwhile,the hole exit damages significantly decreased in WMM.The average tear length at the hole exit in WMM was reduced by 3.5%–29.5%and 35.5%–44.7%at different axial feed per tooth and tangential feed per tooth,respectively.Moreover,WMM significantly alleviated tool wear.The experimental results suggest that WMM is an effective and promising strategy for CFRP hole-manufacturing.展开更多
Precise vertical total electron contents (VTEC) and its time variation have been obtained by using GPS dual-frequency observations collected by the continuously operating GPS tracking stations distributed over China. ...Precise vertical total electron contents (VTEC) and its time variation have been obtained by using GPS dual-frequency observations collected by the continuously operating GPS tracking stations distributed over China. Us-ing VTEC data, the wave-motion appearing in the iono-sphere on November 3, 2003 is monitored and analyzed when a small solar flare happened. Detailed discussion with the VTEC and its change rate series, which are derived from the observations (data) from PRN23 satellite, indicates that the wave-motion mainly contains two dominant frequencies and propagates almost along the meridian line toward south. Additionally, the fluctuation of the mean VTEC has been calculated in a regional Single Layer Model (SLM) iono-spheric shell in the range of N28.0°―34.0° and E118.0°―123.0°. The spectral analysis and the multi-resolution analy-sis of mean VTEC time series show that the periods of these two components of the wave-motion at middle altitude are around 60 and 25 min separately, and the amplitudes can be up to 1.0―2.0 TECU and 0.4―0.7 TECU respectively. Mean- while, the relative motion between the wave-motion and the Ionosphere Pierce Points (IPPs), which are defined as the cross points between the line-of-sight of the GPS signals and the SLM thin shell, reveals that the traveling speeds of the two components are about 120―150 m/s and 30―40 m/s respectively.展开更多
目前基于毫米波雷达的人体动作识别方法存在人体动作特征利用不足导致识别精度低,与多维特征融合方式简单导致模型参数量增加的问题。针对以上问题,提出了一种基于毫米波雷达的三维特征自适应融合人体动作识别方法。首先,对雷达回波信...目前基于毫米波雷达的人体动作识别方法存在人体动作特征利用不足导致识别精度低,与多维特征融合方式简单导致模型参数量增加的问题。针对以上问题,提出了一种基于毫米波雷达的三维特征自适应融合人体动作识别方法。首先,对雷达回波信号进行时频分析以获取人体动作距离、多普勒与角度特征,并在时域上拼接构建三维特征数据集。然后,设计了一种带有特征自适应融合器的三分支卷积神经网络,实现对三维特征数据集的高维抽象特征提取与多维特征的自适应融合。最后,通过活动分类器得到人体动作检测结果。实验结果表明,所提方法的人体动作识别平均准确率可达到96.41%,受试者工作特征曲线下面积(Area Under the Curve,AUC)值可达到0.984,优于单维特征识别方法与多种三维特征融合方法。展开更多
基金supported by National Natural Science Foundation of China(Grant No.51905024,51905138,51975035 and 91960203).
文摘Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various damages in twist drilling and chip removal clog in core drilling could happen,inevitably reducing hole quality and hole-manufacturing efficiency.This paper proposes the wave-motion milling(WMM)method for CFRP hole-manufacturing to improve hole quality.This paper presents a motion path model based on the kinematics of the WMM method.The wave-motion cutting mode in WMM was analyzed first.Then,comparison experiments on WMM and conventional helical milling(CHM)of CFRP were carried out under dry conditions.The results showed that the hole surface quality of the CFRP significantly improved with a decrease of 18.1%–36%of Ra value in WMM compared to CHM.WMM exerted a significantly weaker thrust force than that of CHM with a reduction of 12.0%–24.9%and 3%–7.7%for different axial feed per tooth and tangential feed per tooth,respectively.Meanwhile,the hole exit damages significantly decreased in WMM.The average tear length at the hole exit in WMM was reduced by 3.5%–29.5%and 35.5%–44.7%at different axial feed per tooth and tangential feed per tooth,respectively.Moreover,WMM significantly alleviated tool wear.The experimental results suggest that WMM is an effective and promising strategy for CFRP hole-manufacturing.
基金supported by the 100-Talent Fund of the Chinese Academy of Sciences in Astro-geodynamic Center of Shanghai Astronomical Observatorythe National Natural Science Foundation of China(Grant No.40174009)+2 种基金the Knowledge Creative Project of the Chinese Academy of Sciences(Grant No.KJCX2-SW-T1)the Shanghai Scientific Technology Development Fund(Grant No.JC14012)the Guangxi Fund for Youth(Grant No.9912008).
文摘Precise vertical total electron contents (VTEC) and its time variation have been obtained by using GPS dual-frequency observations collected by the continuously operating GPS tracking stations distributed over China. Us-ing VTEC data, the wave-motion appearing in the iono-sphere on November 3, 2003 is monitored and analyzed when a small solar flare happened. Detailed discussion with the VTEC and its change rate series, which are derived from the observations (data) from PRN23 satellite, indicates that the wave-motion mainly contains two dominant frequencies and propagates almost along the meridian line toward south. Additionally, the fluctuation of the mean VTEC has been calculated in a regional Single Layer Model (SLM) iono-spheric shell in the range of N28.0°―34.0° and E118.0°―123.0°. The spectral analysis and the multi-resolution analy-sis of mean VTEC time series show that the periods of these two components of the wave-motion at middle altitude are around 60 and 25 min separately, and the amplitudes can be up to 1.0―2.0 TECU and 0.4―0.7 TECU respectively. Mean- while, the relative motion between the wave-motion and the Ionosphere Pierce Points (IPPs), which are defined as the cross points between the line-of-sight of the GPS signals and the SLM thin shell, reveals that the traveling speeds of the two components are about 120―150 m/s and 30―40 m/s respectively.
文摘目前基于毫米波雷达的人体动作识别方法存在人体动作特征利用不足导致识别精度低,与多维特征融合方式简单导致模型参数量增加的问题。针对以上问题,提出了一种基于毫米波雷达的三维特征自适应融合人体动作识别方法。首先,对雷达回波信号进行时频分析以获取人体动作距离、多普勒与角度特征,并在时域上拼接构建三维特征数据集。然后,设计了一种带有特征自适应融合器的三分支卷积神经网络,实现对三维特征数据集的高维抽象特征提取与多维特征的自适应融合。最后,通过活动分类器得到人体动作检测结果。实验结果表明,所提方法的人体动作识别平均准确率可达到96.41%,受试者工作特征曲线下面积(Area Under the Curve,AUC)值可达到0.984,优于单维特征识别方法与多种三维特征融合方法。
