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Modeling of Ultrasonic and Terahertz Radiations in Defective Tiles for Condition Monitoring of Thermal Protection Systems

机译：缺陷瓷砖中超声波和太赫兹辐射的建模，用于热保护系统的状态监测

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Condition based monitoring of Thermal Protection Systems (TPS) is necessary for safe operations of space shuttles. In the current research Terahertz radiation (T-ray) has been used to detect mechanical and heat induced damages in TPS tiles. Voids and cracks inside the foam tile are denoted as mechanical damage while property changes due to long and short term exposures of tiles to high heat are denoted as heat induced damage.Ultrasonic waves cannot detect cracks and voids inside the tile because the tile material (silica foam) has high attenuation for ultrasonic energy. Instead, electromagnetic terahertz radiation can easily penetrate into the foam material and detect the internal voids although this electromagnetic radiation finds it difficult to detect delaminations between the foam tile and the substrate plate. Thus these two technologies are complementary to each other for TPS inspection.Ultrasonic and T-ray field modeling in free and mounted tiles with different types of mechanical and thermal damages has been the focus of this research. Shortcomings and limitations of FEM method in modeling 3D problems especially at high-frequencies has been discussed and a newly developed semi-analytical technique called Distributed Point Source Method (DPSM) has been used for this purpose.A FORTRAN code called DPSM3D has been developed to model both ultrasonic and electromagnetic problems using the conventional DPSM method. DPSM has been extended from ultrasonic applications to electromagnetic to model THz Gaussian beams, multilayered dielectrics and Gaussian beam-scatterer interaction problems. Since the conventional DPSM has some drawbacks, to overcome it two modification methods called G-DPSM and ESM have been proposed.The conventional DPSM in the past was only capable of solving time harmonic (frequency domain) problems. In this research DPSM has been extended to model DPSM transient problems. This modified technique has been denoted as t-DPSM.Using DPSM, scattering of focused ultrasonic fields by single and multiple cavities in fluid&solid media is studied. A comparison between the radiation forces generated by the ultrasonic energies reflected from two small cavities versus a single big cavity is also carried out.
机译：对热保护系统（TPS）进行基于状态的监视对于航天飞机的安全运行是必要的。在当前的研究中，太赫兹辐射（T射线）已用于检测TPS瓷砖中机械和热引起的损伤。泡沫瓷砖内部的空隙和裂缝表示为机械损伤，而瓷砖长期和短期暴露于高温导致的性能变化则表示为热引起的损伤。超声波无法检测到瓷砖内部的裂缝和空隙，因为瓷砖材料（二氧化硅泡沫）对超声波能量具有很高的衰减。取而代之的是，电磁太赫兹辐射可以很容易地渗透到泡沫材料中并检测内部空隙，尽管这种电磁辐射发现很难检测到泡沫砖与基板之间的分层。因此，这两种技术在TPS检查中是互为补充的。在具有不同类型的机械和热损伤的自由砖和已安装砖中的超声和T射线场建模一直是这项研究的重点。讨论了有限元方法在3D问题建模中的缺点和局限性，特别是在高频情况下，并且为此目的使用了一种新开发的半分析技术，称为分布式点源方法（DPSM）。使用常规DPSM方法对超声和电磁问题进行建模。 DPSM已从超声应用扩展到电磁，以模拟THz高斯光束，多层电介质和高斯光束与散射体的相互作用问题。由于传统的DPSM有一些缺点，因此，为了克服这一缺点，提出了两种修改方法，分别称为G-DPSM和ESM。过去的传统DPSM仅能够解决时谐波（频域）问题。在本研究中，DPSM已扩展为模型化DPSM瞬态问题。这项改进的技术被称为t-DPSM。利用DPSM，研究了聚焦和超声场在流体和固体介质中单腔和多腔的散射。还比较了两个小腔体相对于单个大腔体反射的超声能量所产生的辐射力。

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    Kabiri Rahani Ehsan;

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  • 年度 2011
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