共查询到20条相似文献,搜索用时 49 毫秒
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提出一种通过声管测量粘弹性覆盖层反射系数,识别粘弹性动态力学参数的方法。分别设计实心覆盖层和圆柱空腔覆盖层,测量实心覆盖层的反射系数可以计算得到粘弹性介质的复纵波声速,测量圆柱空腔覆盖层的反射系数、并结合求解粘弹性圆柱管的特征方程可以获得粘弹性介质的复剪切波声速,进而计算复杨氏模量和复泊松比。最后,对某种橡胶材料进行了声管测试,并对粘弹性动态力学参数的识别结果进行了分析和讨论。 相似文献
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海底作为海洋波导的重要边界,其反射系数对声传播起着至关重要的作用。为了快速而准确地获取海底反射系数,提出了一种基于脉冲压缩技术的测量方法,对接收信号进行压缩来提取反射波。该方法不仅可以克服实验过程中经常遇到的多途干扰,而且测量过程简单,可以同时获得测量频带内所有频点的反射系数,即实现了对反射系数的宽带测量。在实验室环境条件下,针对广泛覆盖于大陆架及沿海地区的沙质沉积物反射系数进行了测量,通过20~60 kHz频率范围内窄带和宽带测量结果的比较发现,宽带测量结果在频带边缘存在一定的偏差和起伏,但可以采用增大发射信号带宽提高压缩效果或用适当的窗函数压低旁瓣的方法来得到频率范围更宽、精度更高的测量结果。 相似文献
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用改进的Prony方法在自由场中测量材料的反射系数 总被引:2,自引:1,他引:1
本文介绍了Prony方法在自由场中测量材料反射系数方面的应用,研究了其改进的方法,编制了程序,并进行了计算机模拟,对其中的时间窗、展开阶次、既定极点、步长等因素进行了全面讨论。结论说明:Prony方法用于分析短时瞬态信号,对自由空间的声学材料小样品的低频测试来说,具有相当满意的效果。 相似文献
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B. Boroomand A. A. Tabatabaei E. Oate 《International journal for numerical methods in engineering》2005,63(3):351-379
A stabilized version of the finite point method (FPM) is presented. A source of instability due to the evaluation of the base function using a least square procedure is discussed. A suitable mapping is proposed and employed to eliminate the ill‐conditioning effect due to directional arrangement of the points. A step by step algorithm is given for finding the local rotated axes and the dimensions of the cloud using local average spacing and inertia moments of the points distribution. It is shown that the conventional version of FPM may lead to wrong results when the proposed mapping algorithm is not used. It is shown that another source for instability and non‐monotonic convergence rate in collocation methods lies in the treatment of Neumann boundary conditions. Unlike the conventional FPM, in this work the Neumann boundary conditions and the equilibrium equations appear simultaneously in a weight equation similar to that of weighted residual methods. The stabilization procedure may be considered as an interpretation of the finite calculus (FIC) method. The main difference between the two stabilization procedures lies in choosing the characteristic length in FIC and the weight of the boundary residual in the proposed method. The new approach also provides a unique definition for the sign of the stabilization terms. The reasons for using stabilization terms only at the boundaries is discussed and the two methods are compared. Several numerical examples are presented to demonstrate the performance and convergence of the proposed methods. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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阐述了磁性法测定钢中残余奥氏体含量的原理和方法,并研制了一种基于磁性法的钢中残余奥氏体含量测定装置。该测定装置可以实现换向法、甩脱法和动态法等3种残余奥氏体含量测定方法,其中换向法和甩脱法以不同方式静态测定残余奥氏体含量,动态法能够在试件拉伸过程中连续、快速地动态测定残余奥氏体含量与应变的对应关系。该测定装置以LabVIEW为平台,构成了虚拟仪器系统,对数据进行采集、分析和处理,实现了可视化操作、自动测量、曲线显示和数据保存等功能。使用该装置采用3种方法分别对M50NiL轴承钢中的残余奥氏体含量进行了测定,试验结果表明该测定装置能够精确地测定钢中的残余奥氏体含量。 相似文献
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Marc S. Ingber Andrea A. Mammoli Mary J. Brown 《International journal for numerical methods in engineering》2001,52(4):417-432
In many cases, boundary integral equations contain a domain integral. This can be evaluated by discretization of the domain into domain elements. Historically, this was seen as going against the spirit of boundary element methods, and several methods were developed to avoid this discretization, notably dual and multiple reciprocity methods and particular solution methods. These involved the representation of the interior function with a set of basis functions, generally of the radial type. In this study, meshless methods (dual reciprocity and particular solution) are compared to the direct domain integration methods. The domain integrals are evaluated using traditional methods and also with multipole acceleration. It is found that the direct integration always results in better accuracy, as well as smaller computation times. In addition, the multipole method further improves on the computation times, in particular where multiple evaluations of the integral are required, as when iterative solvers are used. The additional error produced by the multipole acceleration is negligible. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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在聚合物共混体系中,界面张力对聚合物相容性有着重要影响,决定着相与相之间的粘接性,成为控制其最终相态结构的一个重要因素,是研究多相聚合物相态结构的基础。文中综述了聚合物熔体界面张力的测定方法,这些测定方法主要有热力学方法、流变学方法以及动力学方法三大类;介绍了每种方法的基本原理,并对其优缺点及适用范围进行了简单说明。其中,动力学方法是使用最多、相对准确的,对该方法进行了重点介绍,并且讨论了动力学方法中熔体粘弹性对界面张力测定的影响。 相似文献
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Based on a combination of Hellinger–Reissner principle with its dual, a mixed/hybrid method of non‐saddle point type has been presented in the previous papers. In the paper, an application of the method to two‐dimensional elasticity problems is considered in a manner of combination of mathematical analysis with numerical investigation. How to construct a combined hybrid scheme of high performance is discussed, and several four‐node quadrilateral CH‐elements are systematically verified. In brief, this paper shows that for the hybrid element scheme, the energy compatibility condition, introduced in Zhou (Combined hybrid finite element method without requirement for Babuska‐Brezzi condition, to appear) is the ultimate key to the achievement of high performance. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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纳米氧化锌材料的制备方法及结构表征 总被引:3,自引:0,他引:3
文章介绍了纳米ZnO材料的常用制备方法,如应用较多的气-固-液法、气相法、水热法和有着较好应用前景的电化学法,以及各类纳米ZnO材料的结构表征,并展望了纳米ZnO材料的发展前景。 相似文献