中文摘要：

当变截面闭管（CTVCS）的固有一阶反共振频率设计在接近共振基频的倍频处，共振基频激励下的二次谐波将受到极大抑制，以致在闭管末端可获得高声压、低谐波畸变的波形。相比等截面闭管，CTVCS内的二次谐波特性较为复杂，且在研究范围内，谐波随基波声压级的增长未出现明显的饱和趋势。

英文摘要：

For a closed tube with varying cross-sections（CTVCS）, when the frequency of the first natural anti-resonance is designed to be near twice of that of the fundamental resonance, the second harmonic driven under the fundamental resonance frequency will be largely suppressed. Thus a high sound pressure waveform with low harmonic distortion at the end of the tube can be obtained. Compared with the closed tube of a constant cross-section, the properties of the second harmonic in CTVCS are rather complicated. This research shows the trend of the acoustic pressure level of harmonics growing with the fundamental component, but no discernible saturation.