共查询到10条相似文献,搜索用时 31 毫秒
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对粘接结构进行超声导波无损检测与评估是一个有挑战性的前沿性课题.针对此问题,研究了SH0导波在界面为理想连接的三层板状粘接结构中传播时的相位变化情况.首先基于波传播的控制方程,建立了粘接结构中反射和透射SH0导波相对于入射SH0导波的相位差解析模型.然后利用数值模拟计算了铝/环氧树脂/铝粘接结构中反射和透射SH0导波的相位差曲线.最后分析了入射角度和频厚积的变化对反射和透射SH0导波相位差的影响.结果表明,对于具体的粘接结构,反射和透射SH0导波在其中传播时的相位差变化主要依赖于入射角度、频率等参数.在特定的频厚积下,当声波水平入射时,反射和入射SH0导波同相位.无论入射角度为多大,随着频厚积的增大,反射SH0导波的相位差曲线均会产生周期性谐振.对于透射SH0导波,当声波垂直入射时,其相位差曲线的改变无规律可循;但是随着入射角度逐渐增大,透射SH0导波的相位差曲线逐渐变规则.所得结果可为实验时研究板状粘接结构中SH0导波的传播特性以及提取SH0导波回波中的有用信息和定位提供一定的理论指导. 相似文献
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用模态法识别结构弹性碰撞载荷的可行性 总被引:16,自引:5,他引:16
本文在探讨杆的纵向和横向碰撞问题基础上,论证了用模态叠加法求解结构弹性撞击载荷的可行性。发展了识别撞击载荷的数值方法。用波传播理论、弹性接触理论和模态理论等有关知识对载荷历程进行了分析和解释,并验证了所给方法的精度和实用性。 相似文献
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弹性波在色散关系经过设计的梯度结构中传播时会产生空间分频现象和波场能量增强现象,即不同频率的弹性波会在结构的不同位置停止向前传播并发生能量聚集,这就是弹性波彩虹捕获效应.其相关研究成果可以促进结构健康监测、振动控制以及能量俘获等领域的发展.本文通过所设计的梯度结构梁,系统地研究了弯曲波彩虹捕获效应及其在压电能量俘获中的应用.首先,利用传递矩阵法获得了梯度结构梁元胞能带结构的解析解,进而分析了弯曲波彩虹捕获效应的产生机理:不同频率的弯曲波会在不同元胞附近群速度减小到零,从而停止向前传播并发生反射;入射波和反射波的叠加,以及群速度减小带来的能量聚集,会显著增强反射处的波场能量.其次,通过有限元仿真和实验验证了弯曲波彩虹捕获效应的空间分频现象和波场能量增强现象.最后,通过有限元多物理场耦合仿真和实验,研究了粘贴PVDF压电薄膜的梯度结构梁相对于均匀梁的弯曲波能量俘获效果及其随入射波频率的变化规律.结果表明,在弯曲波彩虹捕获效应发生频带内,粘贴在梯度结构梁上的PVDF压电薄膜的输出电压约为粘贴在均匀梁相应位置处的PVDF压电薄膜的输出电压的2倍. 相似文献
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《Journal of Fluids and Structures》1999,13(1):143-152
The flow in the wake of a finite-length cylinder has been studied experimentally both before and after the transition to turbulence. This instability occurs at Reynolds numbers around 180–190. One end of the cylinder was fixed to the bottom of the test-section of a wind tunnel, whilst the other terminated in the open flow (free end). For these boundary conditions four main frequency modes within the wake can be identified. These are a centre-cell mode at the Strouhal frequency, end-cell modes with a frequency below the Strouhal frequency, a mode exhibiting the difference frequency between the centre-cell and end-cell modes, and a low-frequency mode (appearing only after transition to turbulence). In this work the energy content of these four modes has been determined throughout the wake, both before and after transition to turbulence. For three of the modes, the energy content is the same before and after transition, whereas the low-frequency mode exhibits energy two to four orders of magnitude greater after transition than before. Hence it is clear that the additional turbulence energy appearing in the wake after transition is located predominantly in this low-frequency mode. The appearance of this low-frequency mode is characterized by the simultaneous appearance of a peak in the power spectra of the velocity fluctuations centred about zero frequency (but with finite width). Consequently, the appearance of this zero frequency peak can be taken as the signature of the onset of turbulence. By considering the downstream growth rates of this low-frequency mode, evidence is presented which suggests that transition to turbulence may occur as a result of wake transition in the downstream central plane of the cylinder. 相似文献
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林拜松 《应用数学和力学(英文版)》1984,5(5):1693-1699
According to Iliushin's small elastic-plastic deformation theory, in this paper, we derive the basic equations of planestrain problems in a power hardening and incompressible material. In addition, this paper presents two methods to solve these basic equations, i.e. the displacement function stress method and the stress function strain method. Two examples have been calculated to illustrate the application of these two methods. 相似文献
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双材料界面中存在材料黏性效应, 对界面裂纹尖端场的分布和界面本身性能
的变化起着重要的影响. 考虑裂纹尖端的奇异性, 建立了双材料界面扩展裂纹尖端的弹黏塑
性控制方程. 引入界面裂纹尖端的位移势函数和边界条件, 对刚性-弹黏塑性界面I型界面
裂纹进行了数值分析, 求得了界面裂纹尖端应力应变场, 并讨论了界面裂纹尖端场随各影响
参数的变化规律. 计算结果表明, 黏性效应是研究界面扩展裂纹尖端场时的一个主要因素,
界面裂纹尖端为弹黏塑性场, 其场受材料的黏性系数、马赫数和奇异性指数控制. 相似文献
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两自由度耦合van der Pol振子的拟主振动解 总被引:1,自引:0,他引:1
本文运用非线性系统的模态方法研究了两自由度耦合van der Pol振子。从退化系统稳定的主振动解出发,得到了原系统的拟主振动解,并给出了系统周期运动的条件,讨论了系统周期解、概周期解的分叉。 相似文献