航空发动机主轴中滚动轴承为了降低系统振动经常与弹性环式挤压油膜阻尼器(elastic ring squeeze film damper, ERSFD)联合使用。基于滚动轴承动力学理论和流体力学控制方程,采用变步长积分算法建立圆柱滚子轴承与ERSFD耦合的动力学分...航空发动机主轴中滚动轴承为了降低系统振动经常与弹性环式挤压油膜阻尼器(elastic ring squeeze film damper, ERSFD)联合使用。基于滚动轴承动力学理论和流体力学控制方程,采用变步长积分算法建立圆柱滚子轴承与ERSFD耦合的动力学分析模型,对外圈带ERSFD的圆柱滚子轴承保持架振动特性和打滑率进行研究。研究结果表明:与未装配ERSFD的圆柱滚子轴承相比,ERSFD可以提高圆柱滚子轴承保持架的稳定性。过大或过小的弹性环凸台数量与宽度都不利于圆柱滚子轴承保持架的稳定性,需要选择合适的凸台数量和宽度。径向载荷与转速对带弹性环的圆柱滚子轴承保持架稳定性影响显著,保持架涡动频率的谐波次数随着径向载荷的增加而减少,其对应的幅值也减小;保持架涡动频率的谐波次数随着转速的增加而增加,其对应幅值也增加。展开更多
A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed.The deformation characteristics of the bridge foundation piles and ...A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed.The deformation characteristics of the bridge foundation piles and anti-slide piles were analyzed in different loading conditions.The dynamic response law of a silty clay landslide with an inclined interlayer was summarized.The spacing between the rear anti-slide piles and bridge foundation should be reasonably controlled according to the seismic fortification requirements,to avoid the two peaks in the forced deformation of the bridge foundation piles.The“blocking effect”of the bridge foundation piles reduced the deformation of the forward anti-slide piles.The stress-strain response of silty clay was intensified as the vibration wave field appeared on the slope.Since the vibration intensified,the thrust distribution of the landslide underwent a process of shifting from triangle to inverted trapezoid,the difference in the acceleration response between the bearing platform and silty clay landslide tended to decrease,and the spectrum amplitude near the natural vibration frequency increased.The rear anti-slide piles were able to slow down the shear deformation of the soil in front of the piles and avoid excessive acceleration response of the bridge foundation piles.展开更多
目的探讨3.0T磁共振弥散加权成像(DWI)结合液体衰减翻转恢复(FLAIR)序列、三维动脉自旋标记成像(3D ASL)双不匹配技术对不明发病时间急性脑梗死(ACI)患者的应用价值。方法选取我院进行3.0T磁共振DWI、FLAIR、3D ASL、磁共振血管成像(MRA...目的探讨3.0T磁共振弥散加权成像(DWI)结合液体衰减翻转恢复(FLAIR)序列、三维动脉自旋标记成像(3D ASL)双不匹配技术对不明发病时间急性脑梗死(ACI)患者的应用价值。方法选取我院进行3.0T磁共振DWI、FLAIR、3D ASL、磁共振血管成像(MRA)扫描的不明时间窗的急性脑梗死患者35例,并同时满足DWI高信号且FLAIR在相应的DWI高信号区未显影及DWI高信号、3D ASL存在灌注减低区且灌注减低区/DWI高信号区>1.2双不匹配,并存在大血管闭塞患者。同时选取明确发病时间窗内(<4.5 h)急性脑梗死患者35例,进行再灌注治疗。比较两组患者治疗前及治疗后24 h NIHSS评分、两组90 d mRS评分及颅内出血的发生率。结果双不匹配组与明确时间窗组治疗前后24 h NIHSS评分比较有显著性差异(P<0.05)。90 d mRS比较无显著性差异(P>0.05)。结论DWI-FLAIR、DWI-3D ASL双不匹配可作为不明发病时间急性脑梗死患者发病时间、缺血半暗带及再灌注情况的有效评估手段,为静脉溶栓、桥接治疗以及保守治疗提供依据。展开更多
文摘航空发动机主轴中滚动轴承为了降低系统振动经常与弹性环式挤压油膜阻尼器(elastic ring squeeze film damper, ERSFD)联合使用。基于滚动轴承动力学理论和流体力学控制方程,采用变步长积分算法建立圆柱滚子轴承与ERSFD耦合的动力学分析模型,对外圈带ERSFD的圆柱滚子轴承保持架振动特性和打滑率进行研究。研究结果表明:与未装配ERSFD的圆柱滚子轴承相比,ERSFD可以提高圆柱滚子轴承保持架的稳定性。过大或过小的弹性环凸台数量与宽度都不利于圆柱滚子轴承保持架的稳定性,需要选择合适的凸台数量和宽度。径向载荷与转速对带弹性环的圆柱滚子轴承保持架稳定性影响显著,保持架涡动频率的谐波次数随着径向载荷的增加而减少,其对应的幅值也减小;保持架涡动频率的谐波次数随着转速的增加而增加,其对应幅值也增加。
基金Sichuan Science and Technology Program under Grant No.2023NSFSC0894Major Project of the Science and Technology Research and Development Program of the Ministry of Railways of China under Grant No.Z2012-061。
文摘A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed.The deformation characteristics of the bridge foundation piles and anti-slide piles were analyzed in different loading conditions.The dynamic response law of a silty clay landslide with an inclined interlayer was summarized.The spacing between the rear anti-slide piles and bridge foundation should be reasonably controlled according to the seismic fortification requirements,to avoid the two peaks in the forced deformation of the bridge foundation piles.The“blocking effect”of the bridge foundation piles reduced the deformation of the forward anti-slide piles.The stress-strain response of silty clay was intensified as the vibration wave field appeared on the slope.Since the vibration intensified,the thrust distribution of the landslide underwent a process of shifting from triangle to inverted trapezoid,the difference in the acceleration response between the bearing platform and silty clay landslide tended to decrease,and the spectrum amplitude near the natural vibration frequency increased.The rear anti-slide piles were able to slow down the shear deformation of the soil in front of the piles and avoid excessive acceleration response of the bridge foundation piles.
文摘目的探讨3.0T磁共振弥散加权成像(DWI)结合液体衰减翻转恢复(FLAIR)序列、三维动脉自旋标记成像(3D ASL)双不匹配技术对不明发病时间急性脑梗死(ACI)患者的应用价值。方法选取我院进行3.0T磁共振DWI、FLAIR、3D ASL、磁共振血管成像(MRA)扫描的不明时间窗的急性脑梗死患者35例,并同时满足DWI高信号且FLAIR在相应的DWI高信号区未显影及DWI高信号、3D ASL存在灌注减低区且灌注减低区/DWI高信号区>1.2双不匹配,并存在大血管闭塞患者。同时选取明确发病时间窗内(<4.5 h)急性脑梗死患者35例,进行再灌注治疗。比较两组患者治疗前及治疗后24 h NIHSS评分、两组90 d mRS评分及颅内出血的发生率。结果双不匹配组与明确时间窗组治疗前后24 h NIHSS评分比较有显著性差异(P<0.05)。90 d mRS比较无显著性差异(P>0.05)。结论DWI-FLAIR、DWI-3D ASL双不匹配可作为不明发病时间急性脑梗死患者发病时间、缺血半暗带及再灌注情况的有效评估手段,为静脉溶栓、桥接治疗以及保守治疗提供依据。
