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首页> 外文会议>IUTAM Symposium on Diffraction and Scattering in Fluid Mechanics and Elasticity Jul 16-20, 2000 Manchester, United Kingdom >ULTRASONIC BACKSCATTERING ENHANCEMENTS FOR TRUNCATED OBJECTS IN WATER: QUANTITATIVE MODELS, TESTS AND SPECIAL CASES
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ULTRASONIC BACKSCATTERING ENHANCEMENTS FOR TRUNCATED OBJECTS IN WATER: QUANTITATIVE MODELS, TESTS AND SPECIAL CASES

机译：水中截断物的超声反散射增强：定量模型，测试和特殊情况

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This survey is concerned with the scattering of sound in water by objects whose size significantly exceeds the acoustic wavelength. Diffraction from the edges of the object can be important for regions where reflected contributions are weak. Elastic contributions to the scattering, however, can be much larger in magnitude for certain viewing angles than simple edge diffraction. Such elastic contributions can greatly enhance the visibility of truncated cylinders imaged with a sonar. For situations where the dominant elastic contributions are the result of leaky waves excited on truncated objects, an approximation method has been developed. Leaky waves have phase velocities that exceed the speed of sound in water. Examples include Rayleigh waves on metallic objects, the symmetric generalization of Lamb waves on plates and shells, and (at sufficiently high frequencies) the lowest antisymmet- ric generalization of a Lamb wave. This type of scattering enhancement has been measured by us for metallic tilted bluntly truncated cylinders and cubes and glass disks. For most of these examples, the leaky wave is significantly attenuated upon traveling the length of the scatterer. As a consequence of that damping, the quality factor Q is small for the global modes associated with the reverberations of the leaky waves between truncations on the object. Consequently resonances associated with the global modes of the scatterer can be unimportant. In the case of shells, the leaky Lamb waves are sufficiently dispersive that frequency-dependent synchronization conditions must be met to facilitate strong coupling between the leaky waves and the incident acoustic field. largets fabricated from materials where either the shear wave velocity or both the shear and the longitudinal wave velocities are less than the speed of sound in water involve special considerations. Examples of such materials include rubbers and plastics in contrast to the metallic targets noted earlier. Significant backscattering enhancements associated with refracted waves and caustics have been .verified and modeled for tilted truncated plastic and rubber cylinders. Rayleigh waves on plastics have subsonic velocities relative to water and must be modeled differently than for the corresponding metallic target.
机译：该调查与尺寸大大超过声波波长的物体在水中的声音散射有关。对于反射贡献较弱的区域，对象边缘的衍射可能很重要。但是，对于某些视角，对散射的弹性贡献可能会比简单的边缘衍射大得多。这种弹性作用可以极大地提高声纳成像的截断圆柱的可见性。对于主要的弹性贡献是由在截短的物体上激发的泄漏波引起的情况，已经开发了一种近似方法。泄漏波的相位速度超过水中的声速。例子包括金属物体上的瑞利波，板和壳上的兰姆波的对称泛化，以及（在足够高的频率下）兰姆波的最低反对称泛化。我们已经针对金属倾斜的钝截圆柱体，立方体和玻璃圆盘测量了这种类型的散射增强。对于大多数这些示例，泄漏波在散射体的长度上传播时会大大衰减。由于该阻尼，对于与对象上的截断之间的泄漏波的混响相关联的全局模式，品质因数Q小。因此，与散射体的整体模式相关的共振可能不重要。在壳的情况下，泄漏的兰姆波足够分散，必须满足与频率相关的同步条件，以促进泄漏波与入射声场之间的强耦合。由剪切波速度或剪切波与纵向波的速度均小于水中声速的材料制成的大型物体需要特别考虑。与先前提到的金属靶材相比，这种材料的实例包括橡胶和塑料。对于倾斜的截断的塑料和橡胶圆柱体，已经验证和建模了与折射波和焦散有关的显着反向散射增强。塑料上的瑞利波具有相对于水的亚音速，因此必须采用与相应金属目标不同的模型进行建模。

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