In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.F...In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups.This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries.The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields.The phase difference between the two second-harmonic components after reflection from the boundary—that is,the reflected and the newly generated second harmonic—is emphasized.The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.展开更多
为研究插入道岔施工(Turnout Inserting Construction,TIC)对既有高速道岔锁定轨温(StressFree Rail Temperature of Existing high-speed Turnout,SFRTET)的影响,提出基于双向应变法的锁定轨温变化测试方案,推导不同因素影响下的锁定...为研究插入道岔施工(Turnout Inserting Construction,TIC)对既有高速道岔锁定轨温(StressFree Rail Temperature of Existing high-speed Turnout,SFRTET)的影响,提出基于双向应变法的锁定轨温变化测试方案,推导不同因素影响下的锁定轨温变化测量原理,确定监测数据的处理方法,并开展道岔锁定轨温变化现场试验研究.研究结果表明:基于锁定轨温变化监测方法确定的传感器安装时轨温与实测数据差异仅1.4%,验证了测试方案的合理性和数据处理方法的正确性;高速道岔的锁定轨温会受插入道岔各工序施工的影响,其在轨道结构拆除、轨道结构施工、道岔形位精调和工电联调3个工序中表现出显著的动态变化特征,即锁定轨温经历多次循环变化才达到稳定状态;既有高速道岔锁定轨温受侧股钢轨重新焊接施工影响最为显著,尤其是靠近焊接位置的侧股钢轨,其锁定轨温变化达12.87℃,建议侧股钢轨重新焊接工序尽可能选择在轨温接近既有道岔原锁定轨温时开展.展开更多
基金supported by the National Research Foundation of Korea(Grant No.2016M2A2A9A03913683)the National Natural Science Foundation of China(Grant No.51575541).
文摘In nonlinear acoustic harmonic generation in solids with stress-free boundaries,such a boundary is known to destructively change the second harmonic generation,and the pulse-echo method is not practically applicable.Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups.This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries.The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields.The phase difference between the two second-harmonic components after reflection from the boundary—that is,the reflected and the newly generated second harmonic—is emphasized.The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.
文摘为研究插入道岔施工(Turnout Inserting Construction,TIC)对既有高速道岔锁定轨温(StressFree Rail Temperature of Existing high-speed Turnout,SFRTET)的影响,提出基于双向应变法的锁定轨温变化测试方案,推导不同因素影响下的锁定轨温变化测量原理,确定监测数据的处理方法,并开展道岔锁定轨温变化现场试验研究.研究结果表明:基于锁定轨温变化监测方法确定的传感器安装时轨温与实测数据差异仅1.4%,验证了测试方案的合理性和数据处理方法的正确性;高速道岔的锁定轨温会受插入道岔各工序施工的影响,其在轨道结构拆除、轨道结构施工、道岔形位精调和工电联调3个工序中表现出显著的动态变化特征,即锁定轨温经历多次循环变化才达到稳定状态;既有高速道岔锁定轨温受侧股钢轨重新焊接施工影响最为显著,尤其是靠近焊接位置的侧股钢轨,其锁定轨温变化达12.87℃,建议侧股钢轨重新焊接工序尽可能选择在轨温接近既有道岔原锁定轨温时开展.