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根据频率特性对圈养宽吻海豚(Tursiops truncatus)在自由游动和训练两种实验条件下的声通讯信号进行分类,并利用双尾t检验统计分析方法对两种条件下的信号声谱参数进行统计比较。结果显示,宽吻海豚在自由状态下通讯信号的种类多并以正弦型为主,而训练期间的通讯信号则大多数为上扫频类。此外,统计分析表明起始频率不能反映这两种状态的不同(p=0.22)。结束频率、最小频率、最大频率、频率变化量、拐点数、环形数、阶数、波形数和周期等则显示了两种状态显著的差异性(p0.05)。结果为今后海豚声行为研究提供一定的科学参考和基础。 相似文献
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Mechanism of the excitation of single pure mode L(0, 2) and its interaction with the defect in a hollow cylinder 下载免费PDF全文
Guided elastic waves have a great potential in pipe inspection as an efficient and low-cost nondestructive evaluation (NDE) technique, among which the wave of mode L(0, 2) receives a lot of attention because this mode is the fastest mode in a weakly dispersive region of frequency to minimize dispersion effects over a long distance and sensitive to the defects distributed circumferentially. Though many experimental and numerical researches have already been carried out about the excitation of L(0, 2) and its interaction with the defect in a hollow cylinder, its excitation mechanism has not been clarified yet. In this paper based on the transient response solution of the hollow cylinder, derived by the method of eigenfunction expansion, the theory about the exciting mechanism of mode L(0, 2) is advanced and the effects of the spatial distribution, vibration frequency and direction of the external force on the excitation are discussed. And the pure mode L(0, 2) is excited successfully under the parameters obtained through theoretical analysis. Furthermore, its interactions with some kinds of defects in hollow cylinders are simulated with the method of finite element analysis (FEA) and the results agree well with those obtained by other researchers. 相似文献
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无限液体介质内管道轴对称纵向导波激发与传播特性研究 总被引:1,自引:0,他引:1
利用声-结构耦合有限元法,分别对轴对称分布径的向及轴向外力作用在无限液体介质内未充液及充液管道内壁所激发导波进行了模拟,并进一步利用短时傅里叶变换技术对瞬态波形作时频分析,在此基础上,结合色散及衰减曲线,探讨了外力分布特征对导波激发的影响.研究表明,无限液体介质内未充液管中L(0,2)模式及充液管中L(0,3)~L(0,4)模式皆具有高群速度、弱色散且弱衰减频带,适宜用于缺陷探测,而通过控制轴对称分布外力的频率,并令其沿轴向作用于管内壁或外壁,可实现上述导波模式的高效激发. 相似文献
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针对水下目标逆合成孔径声呐(Inverse Synthetic Aperture Sonar,ISAS)图像识别问题中观测角度随机多变,目标结构相互遮挡问题,提出一种基于多亮点拓扑矢量特征的ISAS水下目标识别方法。通过分析ISAS成像过程中散射点位置由三维空间向二维成像平面的投影关系,表明了横向定标后的声呐图像中强亮点之间的距离仅由目标散射结构之间的物理距离决定,据此基于强亮点之间的相互距离,构造能稳定描述不同观测角度下目标的拓扑矢量特征。然后通过K-means聚类获取多聚类中心以克服目标结构互相遮挡造成的亮点缺失问题。最终采用最近邻分类器实现目标识别。水池缩比模型实验表明,该方法对于水下目标的识别率达到84.0%。 相似文献
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