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《物理学报》2017,(5)
多孔材料内部含有大量孔隙,孔隙一旦塌陷就回归为密实物质.但孔隙塌陷沉积的能量将提升基体材料的温度,导致热力学状态量发生变化.尤其是在冲击波压缩下,多孔材料的温升很高,温度变化对其他热力学状态量的变化影响很大,因此解决多孔材料的温度计算是不可回避的问题.本文在研究Grneisen通用函数γ_v(v)的基础上,将密实材料的德拜温度函数通过数学的方法,延拓到多孔材料的密度范围,建立了多孔材料的等效德拜温度函数θ(v);并据此推导出了多孔材料的等熵温度函数T_s(v).再借鉴多孔材料0 k等熵功相等的假设,建立了多孔材料与密实材料在相等压强下等熵功相等的计算模型,给出了多孔材料的等熵压强函数于是,齐备了冲击波压缩下多孔材料温度和压强计算的参考方程,即温度方程T_s(v)和压强方程p_s(v).为了检验本文方法的有效性,以Cu为例计算了孔隙度m=1.13,1.22,1.41,1.56,1.98等5种多孔材料的冲击压强和冲击温度,计算结果与实验数据相符较好.同时,用其他方法做了计算,两种方法计算结果的比较,显示出本文计算方法的可靠性. 相似文献
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介绍电致变色薄材料最佳掺杂含量的定量理论。该理论建立了电子薄膜材料的某一物理性能与晶体结构、制备方法和掺杂剂含量之间的联系,给出了一个能够拟合实验曲线的具有确定物理意义的抛物线方程。该方程的极值点确定了最佳掺杂含量与晶体结构和制备方法之间的定量关系,进而得到了一个最佳掺杂含量的表达式。分析三氧化钨电致变色薄膜材料的掺杂改性的实验结果,应用最佳掺杂含量表达式定量计算了三氧化钨以及三氧化钼电致变色薄膜材料的最佳掺杂含量,定量计算的结果与实验数据相符合。该理论方法也适用于其他材料最佳掺杂粒子数分数的理论计算。 相似文献
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基于表面阻抗边界条件时域有限差分(FDTD)方法研究了一维斜入射情况下非磁化等离子体薄涂层涂敷金属材料的电磁散射特性, 该方法忽略对薄层背景材料进行网格剖分, 大大减少了计算量. 首先推导了理想导体涂敷等离子体薄涂层的表面阻抗频域表达式, 然后代入边界条件并变换到时域, 再用分段线性递推卷积方法将时域表达式离散得到FDTD迭代式. 编程计算了垂直及斜入射情形下的平行极化和垂直极化反射系数, 通过验证算例与解析解对比, 结果表明该方法的准确性和有效性. 最后利用该方法分析了不同入射角对反射系数的影响. 相似文献
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The use of finite difference schemes to compute the scattering of acoustic waves by surfaces made up of different materials with sharp surface discontinuities at the joints would, invariably, result in the generations of spurious reflected waves of numerical origin. Spurious scattered waves are produced even if a high-order scheme capable of resolving and supporting the propagation of the incident wave is used. This problem is of practical importance in jet engine duct acoustic computation. In this work, the basic reason for the generation of spurious numerical waves is first examined. It is known that when the governing partial differential equations of acoustics are discretized, one should only use the long waves of the computational scheme to represent or simulate the physical waves. The short waves of the computational scheme have entirely different propagation characteristics. They are the spurious numerical waves. A method by which high wave number components (short waves) in the wave scattering process is intentionally removed so as to minimize the scattering of spurious numerical waves is proposed. This method is implemented in several examples from computational aeroacoustics to illustrate its effectiveness, accuracy and efficiency. This method is also employed to compute the scattering of acoustic waves by scatterers, such as rigid wall acoustic liner splices, with width smaller than the computational mesh size. Good results are obtained when comparing with computed results using much smaller mesh size. The method is further extended for applications to computations of acoustic wave reflection and scattering by very small surface inhomogeneities with simple geometries. 相似文献
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This paper investigates the dispersion relations of axisymmetric wave propagation in initially twisted bi-material compound cylinders, within the scope of the piecewise homogeneous body model, utilizing 3D linearized wave propagation theory in an initially stressed body. It is assumed that the constituents of the compound cylinder are isotropic and homogeneous. The corresponding eigen-value problem is formulated and the solution method for this problem as well as the algorithm for obtaining the numerical results is developed. The numerical results illustrate the influence of the initial twisting of the compound cylinder on the dispersion of the axisymmetric wave propagation as presented and discussed in the present paper. In particular, it is established that as a result of the existence of the initial twisting, at least in one constituent of the considered compound cylinder, the axisymmetric longitudinal and torsional waves cannot propagate separately, i.e. the new type axisymmetric waves, which differ from the axisymmetric torsional and longitudinal waves, must appear. 相似文献
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Nelson AM Hoffman JJ Anderson CC Holland MR Nagatani Y Mizuno K Matsukawa M Miller JG 《The Journal of the Acoustical Society of America》2011,130(4):2233-2240
Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone. 相似文献
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Young-June Kang Sung-Hoon Baik Weon-Jae Ryu Koung-Suk Kim 《Optics & Laser Technology》2003,35(5):323-329
A phase shifting pulsed holographic interferometer was applied to the experimental study of the propagation of laser-induced shock waves over metal plates. A double-pulsed ruby laser was used to generate the shock waves and to make a holographic interferogram of the wave fields. The phase shifting method with a dual-reference beam solved the sign ambiguity problem in holographic fringe patterns and allowed a quantitative evaluation of the phase of the interference patterns. The transient surface profile and propagation behavior of the shock wave over plates were investigated from the holographic fringe patterns. 相似文献
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Based on the complex Snell's law of lossy media, a ray tracing method is proposed to study the propagation attenuation characteristics of electromagnetic (EM) waves in plasma sheaths. The plasma sheath is modelled as layered media. This method considers the complex ray characteristics of inhomogeneous plane EM waves, tracks the propagation rays of EM waves in each layer of media, and calculates the propagation attenuation of EM waves in each layer of media according to the propagation direction of the complex rays. The attenuation during numerical cumulative propagation is the total attenuation of EM waves through the plasma sheath. By comparing the results with that obtained from the WKB method, the accuracy of the ray tracing algorithm is proved. The results of the propagation attenuation of a blunt cone model are calculated by the proposed method, and the effects of different parameters on the EM wave propagation attenuation in the plasma sheath are analysed at different heights, velocities, incident angles, and incident positions. Studying the propagation characteristics of EM waves in the plasma sheath is of importance in application for radar target tracking, blackout communication, and other issues. 相似文献
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Coupled perturbed mode theory combines conventional coupled modes and perturbation theory. The theory is used to directly calculate mode coupling in a range-dependent shallow water problem involving propagation through continental shelf internal solitary waves. The solitary waves considered are thermocline depressions, separating well-mixed upper and lower layers. The method is fast and accurate. Results highlight mode coupling associated with internal solitary waves, and mode capture or loss to and from the discrete mode spectrum. 相似文献
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The modified Ambartsumyan method of addition of layers is used for solving the problem of oblique light propagation through a layer of gyrotropic metamaterial in the field of two counterpropagating ultrasonic waves. It is shown that the studied system can operate as a tunable optical diode. The possibility of controlling the system parameters by changing the parameters of ultrasonic waves is studied. 相似文献
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A new method, which combines the edge-element method with the mode-matching procedure, is developed for the reflection and
radiation analysis of the dielectric rod antenna excited by the HE11 hybrid mode. Unlike the conventional method to treat the radiation as a “source-field” problem, in the present approach,
the eigenvalue problem of the dielectric guided-wave structure is calculated first, and then the radiation problem is transferred
to the propagation problem of a series of surface waves and space waves from the viewpoint of scattering. As a result, the
analysis procedure is tremendously simplified. Numerical results calculated with the present method agree well with those
given in the literature; thus the effectiveness of the present approach is verified. 相似文献
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Chen Ciang Chia Jung-Ryul Lee Chan-Yik Park Hyo-Mi Jeong 《Optics & Laser Technology》2012,44(2):428-440
Laser ultrasonic wave propagation imaging methods have great potential for integrated structural health management and non-destructive evaluation. However, application of these techniques to complex structures in the field is difficult because they give rise to complicated wave propagation patterns. We developed an anomalous wave propagation imaging method with adjacent wave subtraction using laser ultrasonic scanning to solve this problem. The proposed method is suitable for non-destructive evaluation of complex structures because it highlights the propagation of anomalous waves related to structural discontinuities, and suppresses complex incident waves without the need of pre-stored reference data. In this study, the method was applied to a real composite wing subjected to bending and impact tests. The method enhanced the visibility of the anomalous waves related to damages such as stringer tip debonding, skin-spar debonding, and invisible impact damage. Based on these anomalous waves, variable time window amplitude mapping was performed to show the damage location, size, and shape resemble to the actual damage. Comparisons showed that the methods performed better than the ultrasonic A-scan in terms of damage detection and sizing accuracy. The presence of structural elements such as spars, stringers, ribs, and surface-mounted PZT elements did not adversely affect the inspection. The proposed wing test setup with a built-in ultrasonic propagation imaging system for automatic NDE could be easily expanded throughout a hanger for maintenance inspection. 相似文献
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In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae in the propagation path. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. Since the fast wave mainly propagates in trabeculae, this wave is considered to reflect the structure of trabeculae. For a new diagnosis method using the information of this fast wave, therefore, it is necessary to understand the generation mechanism and propagation behavior precisely. In this study, the generation process of fast wave was examined by numerical simulations using elastic finite-difference time-domain (FDTD) method and experimental measurements. As simulation models, three-dimensional X-ray computer tomography (CT) data of actual bone samples were used. Simulation and experimental results showed that the attenuation of fast wave was always higher in the early state of propagation, and they gradually decreased as the wave propagated in bone. This phenomenon is supposed to come from the complicated propagating paths of fast waves in cancellous bone. 相似文献