Showing papers on "Wave propagation published in 1968"
TL;DR: In this article, a criterion for judging the relative effeciency of excitation of piezoelectric surface waves as a function of crystal plate orientation and propagation direction is developed based on a velocity change upon application of a thin conducting sheet to the surface.
Abstract: A criterion for judging the relative effeciency of excitation of piezoelectric surface waves as a function of crystal plate orientation and propagation direction is developed. This criterion is based on a velocity change upon application of a thin conducting sheet to the surface. Plots of surface wave velocity for various orientations of the crystal surface are presented as a function of propagation direction for the conducting sheet in contact with and infinitely far removed from the crystal surface. A plot of a typical velocity variation as a function of height of the conducting sheet is also presented. Evidence in support of the criterion of using velocity changes as an indicator of efficiency is presented in the form of mechanical displacement and electric potential plots for several orientations and propagation directions. All velocity displacements and potential calculations were carried out under the assumption that the crystal medium was lithium niobate.
641 citations
TL;DR: In toroidal systems with geodesic curvature, an electrostatic acoustic mode occurs with plasma motion in the magnetic surfaces, perpendicular to the field as discussed by the authors, and this mode should dominate ordinary sound waves associated with motion along the field.
Abstract: In toroidal systems with geodesic curvature an electrostatic acoustic mode occurs with plasma motion in the magnetic surfaces, perpendicular to the field. In typical stellarators this mode should dominate ordinary sound waves associated with motion along the field.
624 citations
TL;DR: In this article, the role of horizontal wind shears in the vertical propagation of planetary Rossby waves is investigated using an adiabatic linear model and the authors discuss wave guides formed by regions of weak westerly wind.
Abstract: The role of horizontal wind shears in the vertical propagation of planetary Rossby waves is investigated using an adiabatic linear model. We discuss wave guides formed by regions of weak westerly wind. If the wave guide is formed by trapping of waves between strong westerlies and/or the geometric poles, the ducting occurs as a wave propagation in discrete normal modes of the internal wave guide. On the other hand, for wave guides formed by one or more lines of zero wind, waves are absorbed rather than reflected at the zero wind line so that there are no normal modes of the wave guide. Disturbances excited in the lower stratosphere in the equatorial zero wind wave guide will terminate somewhere in the equatorial stratosphere, but eddy motions may be maintained in the tropics at higher levels by leakage from the Aleutian high planetary wave propagating vertically in a polar wave guide. The Aleutian high should he significantly attenuated by such leakage. The theory of zero wind line absorption sugg...
295 citations
TL;DR: Linear wave interaction with oblique shock waves, noting dependence of transmission, reflection and generation coefficients on Mach number was studied in this paper, where linear wave interaction was shown to have a strong dependence on the Mach number.
Abstract: Linear wave interaction with oblique shock waves, noting dependence of transmission, reflection and generation coefficients on Mach number
289 citations
01 Aug 1968
TL;DR: A review of the recent developments in the field of random fluctuations of an electromagnetic wave propagated over a line-of-sight path is presented in this paper, where the major interest is in the optical to millimeter wavelength range where fluctuations in amplitude, phase, and angle of arrival are important system considerations.
Abstract: A review of the recent developments in the field of random fluctuations of an electromagnetic wave propagated over a line-of-sight path is presented. The major interest is in the optical to millimeter wavelength range where fluctuations in amplitude, phase, and angle-of-arrival are important system considerations. It is assumed that the fluctuations are the result of variations in the refractive index caused by turbulence in the atmosphere. The review concentrates on the major approximations involved in the theoretical developments, and in particular, attempts to put in perspective the arguments over Rytov's method. The paper includes a number of previously untranslated results from the Russian literature, and some previously unpublished results of the author's. A brief assessment of new theoretical approaches and a discussion of some extremely important experimental work are given.
233 citations
TL;DR: In this paper, the general theory of the parametric excitation of coupled waves developed in the preceding paper is applied to the parameterized interaction of the electrostatic waves in a plasma with radiation whose frequency is close to the electron plasma frequency.
Abstract: The general theory of the parametric excitation of coupled waves developed in the preceding paper is applied to the parametric interaction of the electrostatic waves in a plasma with radiation whose frequency is close to the electron plasma frequency. On the basis of the hydrodynamic equations, the coupled equations for the electron plasma wave and ion acoustic wave are derived. The effect of the Landau damping is also considered phenomenologically. Using the coupled wave equations, the expressions for the threshold radiation intensity, the frequency shift at the threshold and the growth rate above threshold are obtained. In particular, the dependence of these quantities on the wave-length of the electrostatic waves is discussed in detail. The results are compared with experiment of Stern and Tzoar.
218 citations
TL;DR: In this article, it was shown that the basic system of equations belongs to the exceptional case defined in that paper and in the lowest order of perturbation it can be reduced to the Kortweg-de Vries equation for all angles of propagation.
Abstract: The Reductive Perturbation Method established in a previous paper is applied to the analysis of hydromagnetic wave of small but finite amplitude propagating in a cold plasma. It is shown that the basic system of equations belongs to the exceptional case defined in that paper and in the lowest order of perturbation it can be reduced to the Kortweg-de Vries equation for all angles of propagation.
215 citations
TL;DR: In this paper, the existence of surface waves with a longitudinal character is deduced theoretically and the properties of these waves are predicted, in contrast to capillary waves, the longitudinal waves are governed by the surface elastic modulus rather than by surface tension.
Abstract: The existence of hitherto unobserved surface waves with a longitudinal character is deduced theoretically and the properties of these waves are predicted. In contrast to capillary waves, the longitudinal waves are governed by the surface elastic modulus rather than by surface tension; they are accompanied by a horizontal rather than by a vertical surface movement and they are connected with a liquid flow of a highly dissipative character causing a rapid damping. Under normal experimental conditions capillary waves and longitudinal waves are superimposed, but the longitudinal wave is usually damped out much more rapidly, except at high elastic modulus.
202 citations
TL;DR: In this paper, an expansion technique analogous to that of Stokes in the study of surface waves was used to investigate the effects of finite amplitude on a progressive train of internal gravity waves.
Abstract: An expansion technique, analogous to that of Stokes in the study of surface waves, is used to investigate the effects of finite amplitude on a progressive train of internal gravity waves. The paper is divided into two main parts, a study of interfacial waves in a two-fluid system and an examination of internal waves in a continuously stratified fluid. Experimental evidence is presented which confirms some of the theoretical predictions. The validity of the Boussinesq approximation is examined and particular examples are taken to illustrate the general results.
182 citations
TL;DR: In this paper, the authors derived a simple theory of free shelf waves, which, however, is more general than previous theories in that shorter as well as longer waves are taken into account.
Abstract: Taking the case of a continental shelf of exponential slope, and assuming zero horizontal divergence, the authors derive a simple theory of free shelf waves, which, however, is more general than previous theories in that shorter as well as longer waves (in comparison with previous work) are taken into account. The properties of the waves are discussed, and the dispersion curves for each mode are obtained. Although the phase velocities of shelf waves are always in the same sense as those of Kelvin waves, there is a negative group velocity for a range of wavelengths, indicating that energy can propagate in the opposite sense. A similar approach is used to derive a theory for free waves propagating on a shelf between two regions of constant depth. The limiting case of a shelf of zero width is also considered, and is compared with a limiting case of the ‘double-Kelvin’ waves discovered by Longuet-Higgins (1967).
161 citations
TL;DR: In this paper, a self-consistent model was proposed to represent the Ohmic conduction process in the bulk of the fluids, with surface shears induced by the free interfacial charges placed in dynamic equilibrium by viscous stresses.
Abstract: It is well known that electromechanical polarization surface waves propagate along the lines of electric field intensity imposed tangential to the interface between perfectly insulating fluids. These waves have a stiffening effect on electrohydrodynamic equilibria that is analogous to that of the Alfven surface waves on hydromagnetic equilibria. An investigation is presented of the dynamical effects of charge relaxation on these waves. A self‐consistent model represents the relaxation in terms of an Ohmic conduction process in the bulk of the fluids, with surface shears induced by the free interfacial charges placed in dynamic equilibrium by viscous stresses. The dominant effect of the charge relaxation is to produce overstability. Experiments are described where this instability appears as a spontaneous oscillation of the interface with wavenumbers directed along the lines of electric field intensity. Detailed analytical results are given for liquid‐gas and liquid‐liquid interfaces. The field required to produce incipient instability and the propagation direction of the observed instability are satisfactorily predicted. It is found that in this liquid‐vapor case, relatively simple explicit expressions can be given for the incipient instability conditions. A discussion is given of the significance of this work for the dielectrophoretic orientation of liquids in the zero‐gravity environments of space.
TL;DR: To give a realistic representation of the pulse propagation in arteries a theoretical analysis of the wave propagation through a viscous incompressible fluid contained in an initially stressed elastic tube is considered.
TL;DR: In this paper, the basic relations of the acoustoelasticity are deduced by means of the infinitesimal wave propagation in a deformed isotropic elastic material.
01 Oct 1968
TL;DR: In this article, it was shown that the axial wave fields in a paraboloidal reflector can be represented by a spectrum of near-spherical hybrid waves propagating along the axis.
Abstract: The fields scattered by circular symmetric reflector illuminated by a linearly polarised wave incident normally on the aperture are calculated from the induced surface currents. It is shown that the fields in the axial region can be represented by a spectrum of near-spherical hybrid waves propagating along the axis. For large microwave focusing reflectors, the wavefronts are effectively plane in the significant part of the image space. The axial wave fields are linear combinations of the TEln and TMln fields appropriate for circular metal pipes, but can be bounded only by anisotropic-reactance surfaces. Axial-wave theory is used to investigate the characteristics of the fields in the focal region of a paraboloidal reflector, when the incident wave is uniform and plane. For radiotelescope focal ratios, the image structure differs significantly from the classical Airy pattern, deduced by scalar analysis, of optical focusing systems. Energy vortexes circulating about the dark rings influence the efficiency obtainable from aperture-type feeds in the focal plane. Application of axial-wave analysis to spherical reflectors, and the synthesis of high-efficiency low-noise feeds, using hybrid-waves in corrugated guides, are described briefly.
TL;DR: In this paper, the authors studied the effect of electromagnetic waves in metals in a magnetic field and found that the electromagnetic wave in metals can be modelled as a magnetic wave wave.
Abstract: (1968). Electromagnetic waves in metals in a magnetic field. Advances in Physics: Vol. 17, No. 69, pp. 605-747.
TL;DR: The seismic velocities of many granites at shallow depths in the earth's crust may be significantly larger than was previously believed and other properties are affected; correction for the effect of cracks on thermal conductivity raises the average heat flow in shield areas by as much as 20 percent.
Abstract: Granite compressional wave velocity and electrical resistivity variations with depth, explaining discrepancy between in situ and laboratory measurements on dry samples
TL;DR: In this paper, a set of displacement equations of motion is proposed for the dynamic analysis of fiber-reinforced composites, where representative elastic moduli are used for the binder, and the elastic and geometric properties of the fibers are combined into effective stiffnesses.
Abstract: : A set of displacement equations of motion is proposed that is suitable for the dynamic analysis of fiber-reinforced composites. In deriving the equations, representative elastic moduli are used for the binder, and the elastic and geometric properties of the fibers are combined into effective stiffnesses. With the aid of certain assumptions regarding the deformation of the fibers, and by employing a smoothing operation, approximate kinetic and strain energy densities for the fiber-reinforced composite are obtained. Application of Hamilton's principle yields the displacement equations of motion. The proposed set of equations is employed to study the propagation of plane harmonic waves propagating in the direction of the fibers and normal to the fiber direction. Plane transverse waves propagating in the direction of the fibers are dispersive, and dispersion curves are shown. By proper choice of the representative elastic moduli of the binder, the phase velocity at infinite wave length for transverse waves propagating in the direction of the fibers, and the constant phase velocities for longitudinal waves and waves propagating in the other directions, agree with the values predicted by the effective modulus theory. (Author)
TL;DR: In this paper, the authors considered the propagation of harmonic pressure waves through a Newtonian fluid contained within a thick-walled, viscoelastic tube, and the results indicated that the fluid impedance is smaller than predicted by the rigid tube model or by Womersley's constrained elastic tube model.
TL;DR: A method has been developed to determine the phase velocities and damping of sinusoidal axial waves in the carotid artery of anesthetized dogs with the aid of an electro-optical tracking system and appears to be more elastic in the axial than in the circumferential direction.
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01 Aug 1968
TL;DR: In this paper, three models were examined to study the transmission of ocean waves through an ice field, where the effect of ice thickness, water depth, and the wavelength and angle of incidence of the incoming ocean wave was considered.
Abstract: Three models are examined to study the transmission of ocean waves through an ice-field. In each case the effect of ice thickness, water depth, and the wavelength and angle of incidence of the incoming ocean wave is considered. In Model 1 the ice is assumed to consist of floating non-interacting mass elements of varying thickness and the shallow-water approximation is utilized to simplify the equations. A simple cosine distribution varying in one direction only is assumed. In Model 11 the mass elements, of constant thickness, interact through a bending stiffness force so that the ice acts as a thin elastic plate. The mass elements are connected through a surface tension force in Model 111 so that the ice is simulated by a stretched membrane. In both Models 11 and 111 the full linearized equations are solved. Because of the complexity of the resulting analysis, calculations of the reflection and transmission coefficients, and the pressure under the ice, are made in Model 11 on the basis of the shallow water approximation.
TL;DR: In this article, a special solution of the linearized equations for an equatorial β-plane is described, and it is shown that the solution is a vertically propagating gravity wave in the x-z plane which is in geostrophic balance in the meridional plane.
Abstract: A special solution of the linearized equations for an equatorial β-plane is described. The meridional velocity is set identically zero and it is shown that the solution is a vertically propagating gravity wave in the x-z plane which is in geostrophic balance in the meridional plane. These waves are shown to be similar to Kelvin waves in a bounded ocean. Some implications of the atmospheric “Kelvin” waves for equatorial dynamics are discussed.
TL;DR: In this paper, the frequency and velocity of disturbance waves in two phase annular flow have been measured and correlated as functions of the flow rates, and the velocities of individual waves were found to be normally distributed about the mean with a standard deviation that was independent of the mean velocity.
TL;DR: In this article, the authors extended the linear stability analysis of free-surface flows to include the erodibility of the bed and showed that erodability increases the stability of the free surface, in qualitative agreement with previous experiments.
Abstract: Wave propagation in one-dimensional erodible-bed channels is discussed by using the shallow-water approximation for the fluid and a continuity equation for the bed. In addition to gravity waves, a third wave, which gives the velocity of propagation of a bed disturbance, is found. An appropriate dimensional analysis yields the quasi-steady approximation for the complete shallow-water equations.The well-known linear stability analysis of free-surface flows is extended to include the erodibility of the bed. The critical Froude number Fc above which the free-surface of the fluid may become unstable is obtained. It is shown that erodibility increases the stability of the free surface, in qualitative agreement with previous experiments if qb > qs, qb and qs being respectively the contact-bed discharge and suspended-material discharge. The stability theory is also used to discuss coupled beds and surface waves. From it, five different configurations have been obtained: a sinusoidal wave pattern moving downstream, a transition zone and antidunes moving upstream, moving downstream and stationary. These bed forms are in agreement with experimental results; hence shallow-water theory seems to give a reasonable explanation of the boundary instability.It is shown that the quasi-steady approximation and Kennedy's (1963) stability analysis will be in agreement if (kh)2 [Lt ] 1, where k is the wave number, and h is the depth of the water. When the phase shift δ is introduced in the quasi-steady approximation, the five bed patterns derived from the full equations are found again.
TL;DR: In this paper, the self-similar one-dimensional propagation of a strong shock wave in a medium with exponentially varying density and ray-tube area is studied, using the Eulerian approach of Sedov.
Abstract: The self-similar one-dimensional propagation of a strong shock wave in a medium with exponentially varying density and ray-tube area is studied, using the Eulerian approach of Sedov. Conservation integrals analogous to Sedov's are obtained, with the expression for the Lagrangian variable. Calculated results are compared with the predictions of the CCW (Chisnell, Chester and Whitham) approximation. It was found that, in contrast to the implosion case, the propagation parameter from the CCW approximation is in error by 15% or more.
TL;DR: In this article, a family of source and receiver types and for geometry corresponding to plausible acoustic logging tools in oil wells are computed for the purely elastic case, which is necessary to cope with the singularities of the integrands in performing numerical integrations.
Abstract: Transient waveforms have been computed for a family of source and receiver types and for geometry corresponding to plausible acoustic logging tools in oil wells. The acoustic tool now in commercial use is one member of the family. The computations also treat flexural waves and torsional waves. All quantities are expressed in terms of appropriate vector and scalar potentials, and output waveforms are obtained by numerical evaluation of triple Fourier transforms. When loss parameters are included in the stress‐strain relations, the Fourier inversion formulas are free of singularities and numerical integration is straightforward. For the purely elastic case, it is necessary to cope with the singularities of the integrands in performing the numerical integrations. Dispersion curves and other features agree with earlier publications on wave propagation along concentric cylinders.