Plastic wave front propagation in cylindrical bars

Making use of the dynamic, elastic-plastic finite element program, the elastic-plastic wave propagation in a cylindrical bar with a circular cross section is analysed for linear strain hardeningt Special attention is given to the influence of strain rate on. the axial stress distribution for variou. impact loading conditions. Comparison is made between numerical two-dimensional and analytical one-dimensional results for structural low alloy steel (C-Mo-Cr) having strain rate dependens dynamic mechanical properties. The implications of practical importance for experimental dynamic plasticity studies by means of Hopkinson Split Pressure Bar (HSPB) technique are discussed in detail.     

Secondary streaming accompanying the wave propagation in narrow pipes

A theory describing the secondary streaming that accompanies the acoustic wave propagation in a narrow cylindrical pipe of infinite length is presented.     

Theory of wave propagation in one-dimensional random media containing two-scale inhomogeneities

Pacific Oceanographic Institute, Far-Eastern Branch of the Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 3, pp. 274–279, March, 1991.     

A mathematical model for wave propagation in elastic tubes with inhomogeneities: Application to blood waves propagation

We study the propagation of waves in an elastic tube filled with an inviscid fluid. We consider the case of inhomogeneity whose mechanical and geometrical properties vary in space. We deduce a system of equations of the Boussinesq type as describing the wave propagation in the tube. Numerical simulations of these equations show that inhomogeneities prevent separation of right-going from left-going waves.Then reflected and transmitted coefficients are obtained in the case of localized constriction and localized rigidity. Next we focus on wavetrains incident on various types of anomalous regions. We show that the existence of anomalous regions modifies the wavetrain patterns.     

低温柱状等离子体传播特性的研究

分析了轴对称柱状等离子中波的传播特性,研究了表面波模式下的电磁波传播的色散关系,给出了波矢随等离子体参数、介电常数、结构尺寸、工作频率的变化曲线。结果表明,可以通过选择适当的等离子体参数、介电常数以及结构尺寸来控制波的传播特性。     

Physical peculiarities of wave propagation in coupled cylindrical slot lines

Wave characteristics in coupled cylindrical slot lines (CSL’s) of circular cross section are studied for the first time in the context of a rigorous electromagnetic theory. The wave spectrum splitting in symmetrical coupled CSLs for slot waves is discussed. Dispersion characteristics of waves in modifications of coupled CSL’s for different geometric parameters are analyzed. It is shown that one of the fast slot waves behaves as a wave in a quasiclosed waveguide, having very small losses in some frequency region. The mutual transformation effect of surface waves has been shown. Institute of Radiophysics and Electronics, Ukrainian National Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 9, pp. 1172–1181, September, 1997.     

Vibration characteristic analysis of buried pipes using the wave propagation approach

A theoretical analysis for the free vibration of simply supported buried pipes has been investigated using the wave propagation approach. The pipe modeled as a thin cylindrical shell of linear homogeneous isotropic elastic material buried in a linear isotropic homogeneous elastic medium of infinite extent. The vibrations of the pipe are examined by using Flüggle shell equation. The natural frequencies are obtained for the pipes surrounded by vacuo or elastic medium. The results are compared with those available in the literature and agreement is found with them. It is found that the free vibration frequency of the pipe does not appear for some of the axial or circular vibration modes and the real natural frequencies of the pipe are significantly dependent on the rigidity of the surrounding medium.     

Experimental and numerical investigations of axisymmetric wave propagation in cylindrical pipe filled with fluid

Acoustic wave propagation in fluid-filled cylindrical pipe with arbitrary thickness is investigated numerically and experimentally. The vibrational properties of the coupled fluid-pipe system are evaluated by a layerwise approach, which is similar to the finite-strip method. In this approach, the thick cylindrical wall is divided into a number of thin cylindrical layers in the thickness direction. The displacements in the thickness direction for each layer are approximated by linear-shape functions. The governing equation is obtained by using an energy minimization principle. The dispersion curves, distribution of vibrational energy between pipe wall and contained fluid, and displacement fields are examined. The dependence of the dispersion curves on wall thickness is discussed. Two PZT ring transducers adhered to the outer surface of pipe are used as source and receiver, respectively. The propagating waves generated by burst signals are measured. To localize transient signal both in time and frequency domains, the discrete wavelet transform is applied to decomposing the receiving signal into several components. Each component is limited to a narrower bandwidth. Therefore the frequency-dependent group velocity is estimated. The experimental and numerical results are compared.     

Characteristics of wave propagation and energy distributions in cylindrical elastic shells filled with fluid

The dispersion behaviour and energy distributions of free waves in thin walled cylindrical elastic shells filled with fluid are investigated. Dispersion curves are presented for a range of parameters and the behaviour of individual branches is explained. A non-dimensional equation which determines the distribution of vibrational energy between the shell wall and the contained fluid is derived and its variation with frequency and material parameters is studied.     

Stress wave propagation from electrical discharge on cylindrical aluminum rod

Electrical sparking on a cylindrical metallic rod generates a pulse of stress waves which propagate through the rod. The results of the theory of continuous harmonic waves in solid cylinders are used to explain the form of the signal coming from a piezoelectric transducer which is rigidly attached to the rod at different distances from the discharge location.     

Signal propagation in two-layer medium with random large-scale inhomogeneities

A formula is derived for the average intensity of a signal propagated in a medium with a semitransparent layer and random large-scale inhomogeneities. A solution is obtained by the interference-integral method and the resulting formula is represented as an integral with respect to the sines of the partial-wave exit angles. The case in which the emitted pulse has a Gaussian form is examined as an example. Results of numerical modeling of the average signal intensity and the width of the semitransparency frequency band are given.Institute of Applied Physics at Irkutsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 6, pp. 475–483, June, 1993.     

Surface acoustic wave propagation and inhomogeneities in low-density two-dimensional electron systems near the metal-insulator transition

We have measured the surface acoustic wave velocity shift in a GaAs/AlGaAs heterostructure containing a two-dimensional electron system (2DES) in a low-density regime (<10¹⁰ cm⁻²) at zero magnetic field. The interaction of the surface acoustic wave with the 2DES is not well described by a simple model using low-frequency conductivity measurements. We speculate that this conflict is a result of inhomogeneities in the 2DES, which become very important at low density. This has implications for the putative metal-insulator transition in two dimensions.     

Path-integral analysis of propagation in a waveguide with random inhomogeneities

The method of path integration is applied to the analysis of wave propagation in both a graded-index optical waveguide and in an otherwise homogeneous infinite medium whose refractive indices have random statistical inhomogeneities superposed upon a regular variation of refractive index with suitable averaged properties. The authors use techniques originally employed in the context of electron propagation in a set of random scatterers to calculate the averaged Green function describing paraxial wave propagation in a medium whose refractive index has statistical inhomogeneities. The concept of an averaged density of modes is introduced, and the paper presents detailed calculations of this quality for two limiting case. In the first, the correlation length associated with the distribution of inhomogeneities is zero along the direction of propagation. In the second, the Feynman variational technique is used to describe the propagator in a medium whose statistical inhomogeneities have an infinite correlation length along the direction of propagation. Comments are made about the intermediate case which is of greater relevance to real waveguides.     

Features of sound propagation in the ocean with fine-structure inhomogeneities

We analyze the results of an experiment using an explosive sound source in the tropical part of the Indian Ocean. We consider the time structure of sound signals in geometric shadow zones to a distance of 270 km and the scheme of how the sound field in the shadow zone is formed by rays reflected from horizontally extended fine-structured sound velocity layers. From the results of calculation using a wave program that realizes the method of psuedodifferential parabolic equations, we analyze the influence of signal scattering by fine-structure sound velocity inhomogeneities on the sound field distribution in a waveguide. We show that the field formed by spots of light in each of the shadow zones is generated by a regular field and propagates in parallel to it, taking energy from the regular zone in the near field and in each subsequent convergence zone. This mechanism causes an additional decrease in the field in illuminated zones, which can be interpreted as additional attenuation of the regular sound field.     

Harmonic wave propagation in an infinite viscoelastic medium with a periodic array of cylindrical elastic fibers

The work involves the propagation of plane harmonic waves in an infinite isotropic medium in which a doubly periodic array of cylindrical fibers is embedded. The direction of propagation is perpendicular to the fibers and the matrix material is taken to be viscoelastic in shear, modeled through hereditary integrals. A finite element method based on Galerkin's technique is employed, which leads to a non-linear eigenvalue problem. An iterative scheme is used to obtain two modes of dispersion, for both real and imaginary wave numbers, for a specific composite.     

无限长粘弹性圆柱管中轴对称波的传播模式和衰减

在Kelvin-Voigt线性粘弹性模型框架内研究了无限长粘弹性圆柱管中轴对称波的传播和衰减。通过一个复根搜索程序对频散方程的求解得到无量纲化相速度频散曲线和衰减曲线。比较了引入损耗因子后粘弹性圆柱管与弹性圆柱管中轴对称波传播的特性。给出了圆柱管的外内径之比、损耗因子和材料参数对相速度和衰减的影响。分析结果表明与弹性圆柱管相比粘弹性圆柱管中轴对称波的各阶传播模式均存在衰减,高阶传播模式并无严格意义的截止频率。损耗因子对第一阶传播模式的相速度影响很小,而对衰减的影响则比较大,穿孔率对波传播的相速度和衰减有相当大的影响。     

Simulation of elastic wave propagation in cylindrical structures including excitation by piezoelectric transducers

The development and optimization of non-destructive testing procedures usually needs experimental data. As experiments are time-consuming and expensive to conduct, we would like to use numerical data instead. This is admissible, if the simulation describes the physical experiments accurately. A three-dimensional displacement-stress finite-difference model is presented for a piezoelectric transducer coupled to an anisotropic tube. The allocation of the displacement and stress components on a staggered grid leads to a stable scheme. A full piezoelectric model of the transducer is used, including transverse isotropy in the elastic, dielectric, and piezoelectric constants. Similar to an experiment, elastic waves are excited in the corresponding simulation by applying a voltage signal to the electrodes of the piezoelectric transducer. Predictions of the simulation model for a piezoelectric ring transducer coupled to a carbon-fibre-reinforced shell are compared to experimental results to test the validity of the numerical data.