标题: | 轨道导波的特性研究的数值模拟 Characterization of Guided Wave Propagation in Rails and Numerical Simulation |
作者: | 郑冠明 Zheng, Guan-Ming 尹庆中 Ching-Chung Yin 机械工程系所 |
关键字: | 导波;铁轨;双维有限元素法;暂态分析;时频谱图;guided wave;rail;bi-dimensional finite-element method;transient analysis;time-frequency spectrogram |
公开日期: | 2015 |
摘要: | 铁轨是具有工字型断面的线性结构,铁轨导波被局限沿着轨道的传递,拥有多模态及频散的波传特性。本研究采用三维有限元素套装软体及双维有限元素法计算JIS 60铁轨导波的频散曲线。双维有限元素法又称为半解析有限元素法,采用复变指数函数描述导波波传,波导断面之有限元素位移则采用一般的内插函数,元素多寡会影响高频范围的频散曲线准确度。频散曲线是个别模态之波长与频率的函数,上述两种方法获得的轨道导波频散曲线非常吻合。 简支撑及周期支撑铁轨的暂态模拟响应,经小波转换映射成时频谱图,与波包延迟时间解析解比较,发现脉冲讯号可以激发特定的对称及反对称导波。LS-DYNA模拟音频脉冲激振铁轨导波都会出现低频暂态响应,采用套装软体ANSYS之直接积分法则不会出现低频响应。模拟铁轨道床基板的周期支撑会使导波响应在区间发生多次反射 Rail is a linear structure having I-shaped cross section. Guided waves in a rail are characterized by multimodal and frequency dispersive wave propagation since energy is confined within the waveguide. In this study, commercial three-dimensional finite-element (FE) code and bi-dimensional FE approach are used to determine the dispersion curves of guided waves in JIS 60 rails. The latter is also called the semi-analytic FE method. The formulation uses complex exponential functions to describe the wave propagation in the waveguide and conventional interpolation functions for displacement in finite elements across the cross-section. Accuracy of dispersion curves at high frequencies is influenced by the number of finite elements. The dispersion curve of individual guided wave mode is a function of wave length and frequency. Numerical results obtained from both methods are in very good agreement. Transient responses simulated for simply supported and periodically supported rails have been mapped into time-frequency spectrograms by wavelet transform. The spectrograms are compared with analytical delay times of wave packets. Several specific symmetric and anti-symmetric modes can be actuated in impulse excitement. Unexpected low-frequency signals accompanying the tone-burst induced transient responses are discovered in simulation by LS-DYNA. But they do not appear using ANSYS direct integration method. Multiple reflected guided wave responses occur between adjacent periodical supports, which emulate base plate supports for rails. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT070251076 http://hdl.handle.net/11536/127492 |
显示于类别: | Thesis |