Wave Propagation Distance Research Articles

Scavenging waves and influence distances of gas absorption around single liquid aerosols in clouds

Scavenging wave propagation and influence distances for various gases absorbed by single liquid aerosols in the atmosphere are predicted to evaluate the effect of droplet–droplet interaction on transient mass transfer processes in clouds. Three greenhouse gases, CH 4, N 2O, and CO 2, as well as five air pollutants, H 2S, SO 2, HCl, NH 3, and HNO 3, are taken into account. Considering the three greenhouse gases and the air pollutant H 2S, because the driving forces of mass diffusion in the gas phase are by far smaller than those of the liquid phase, the gaseous scavenging behaviors in the vicinity of the droplets are absent. It thus reveals that the effect of mutual interaction of droplets on the absorption processes of these solutes is fairly slight. In regard to the other four air pollutants SO 2, HCl, NH 3, and HNO 3, their mass diffusion numbers are relatively high, rendering that the scavenging waves in the gas phase are clearly observed in the initial uptake period. Increasing mass diffusion number makes the influence distance of the scavenging wave farther and the curvature effect along the droplet surface more pronounced. Consequently, it is recognized that the droplet–droplet interaction in clouds tends to decrease the absorption rate and elongate the uptake period as gases with large mass diffusion numbers are absorbed by droplets. In other words, the distance between cloud droplets will become an important parameter in determining the droplet absorption rate.

A numerical model for wave propagation in curvilinear coordinates

Using the perturbation method, a time dependent parabolic equation is developed based on the elliptic mild slope equation with dissipation term. With the time dependent parabolic equation employed as the governing equation, a numerical model for wave propagation including dissipation term in water of slowly varying topography is presented in curvilinear coordinates. In the model, the self-adaptive grid generation method is employed to generate a boundary-fitted and varying spacing mesh. The numerical tests show that the effects of dissipation term should be taken into account if the distance of wave propagation is large, and that the outgoing boundary conditions can be treated more effectively by introduction of the dissipation term into the numerical model. The numerical model is able to give good results of simulating wave propagation for waters of complicatedly boundaries and effectively predict physical processes of wave propagation. Moreover, the errors of the analytical solution deduced by Kirby et al. (1994) [Kirby, J.T., Dalrymple, R.A., Kabu, H., 1994. Parabolic approximation for water waves in conformal coordinate systems. Coastal Engineering 23, 185–213.] from the small-angle parabolic approximation of the mild-slope equation for the case of waves between diverging breakwaters in a polar coordinate system are corrected.

High-Frequency Earthquake Ground-Motion Scaling in Utah and Yellowstone

Velocity seismograms from the University of Utah Seismograph stations are used to quantify high-frequency ground motion scaling for the Yellowstone region and the Wasatch front in Utah. This study uses a data set consisting of over 3000 waveforms from 93 stations and 506 regional earthquakes and mining-associated seismic events that occurred in the years 1995-2001. All events lie within the upper crust with magnitudes less than 5.5. The signals were processed to examine the peak ground velocity and Fourier velocity spectra in the frequency range of 1.0-16.0 Hz. Regression results for Utah are characterized by rapid decreases of amplitude at short distances, which requires low Q and a rapid geometrical spreading g ( r ) for the forward modeling. Q ( f ) = 160 f 0.75, κeff = 0.05 sec and Δσ = 300 bars are selected to predict the excitation terms when combined with the derived geometrical spreading. The frequency-dependent excitation of mining-associated events differs significantly from that of earthquakes because of either an additional attenuation due to shallow source depth or apparent low stress drops associated with the slow collapse of long tunnels. A Q ( f ) = 140 f 0.70 and geometrical spreading less rapid than r -1.0 at short distance ranges are used to describe the wave propagation distance dependence in the Yellowstone region. The Yellowstone attenuation functional D ( r, f ) is very different from that of Utah, perhaps because a shallow wave guide in the caldera traps more energy. The Yellowstone excitation spectra were modeled using Δσ = 30 bars and κeff = 0.04 sec. Manuscript received 24 October 2003.

Structure of weak shock waves in 2-D layered material systems

Shock waves in homogeneous materials in the absence of phase transitions are understood to have a one-wave structure. However, upon loading of a layered heterogeneous material system a two-wave structure is obtained––a leading shock front followed by a complex pattern that varies with time. This dual shock-wave pattern can be attributed to material architecture through which the shock wave propagates, i.e. the impedance (and geometric) mismatch present at various length scales, and nonlinearities arising from material inelasticity and failure. The objective of the present paper is to provide a better understanding of the role of material architecture in determining the structure of weak shock waves in 2-D layered material systems. Normal plate-impact experiments are conducted on 2-D layered material targets to obtain both the precursor decay and the late-time dispersion. The particle velocity at the free surface of the target plate is measured by using a multi-beam VALYN VISAR. In order to understand the effects of layer thickness and the distance of wave propagation on elastic precursor decay and late-time dispersion several different targets with various layer and target thicknesses are employed. Moreover, in order to understand the effects of material inelasticity both elastic–elastic and elastic–viscoelastic bilaminates are utilized. The results of these experiments are interpreted by using asymptotic techniques to analyze propagation of acceleration waves in 2-D layered material systems. The analysis makes use of the Laplace transform and Floquet theory for ODE’s with periodic coefficients [Asymptotic solutions for wave propagation in elastic and viscoelastic bilaminates. In: Developments in Mechanics, Proceedings of the 14th Mid-Eastern Mechanics Conference, vol. 26, no. 8, pp. 399–417]. Both wave-front and late-time solutions for step-pulse loading on layered half-space are compared with the experimental observations. The results of the study indicate that the structure of acceleration waves is strongly influenced by impedance mismatch of the layers constituting the laminates, density of interfaces, distance of wave propagation, and the material inelasticity.

Shock wave compression behavior of aluminum foam

The shock wave compression behavior of the open cell aluminum foam with relative density of 0.396 was studied through planar impact experiments. Using polyvinylidene fluoride (PVDF) piezoelectric gauge technique, the stress histories and propagation velocities of shock wave in the aluminum foam were measured and analyzed. The results show that the amplitude of shock wave attenuates rapidly with increasing the propagation distance in the aluminum foam, and an exponential equation of the normalized peak stress vs propagation distance of shock wave is established, the attenuation factor in the equation is 0.286. Furthermore, the Hugoniot relation, v 5=516.85 + 1.27v p, for the aluminum foam is determined by empirical fit to the experimental Hugoniot data.

OS02W0287 Ultrasonic characterization of interface of metals

A laser ultrasonic method has been developed for inspection of hot-clad aluminum/steel interface. Because of high temperature, the conventional contact or immersion ultrasonic testing is not applicable for this purpose, therefore, non-contact nondestructive testing is required. Among non-contact ultrasonic methods, the laser ultrasonic method has relatively high S/N ratio and spatial resolution. Line-focused YAG pulse laser excites many ultrasonic waves on the plate surface. Beyond a certain distance from the irradiated area, only the Lamb waves of various modes prevail than other modes of waves. A broadband laser interferometer detects the out-of-plane displacement of many kinds of the Lamb waves. The received time-domain signals are superposition of the waveform of the individual Lamb wave, therefore, identification of interface delamination of aluminum/steel clad pate is difficult. We propose a new laser ultrasonic method for detecting interface delamination of hot-clad aluminum/steel plates with the group velocity dispersion of the Lamb waves. By apply the wavelet transformation on the received time-domain signals, we calculate the group velocity dispersion curves of several Lamb wave's modes. The dispersion curves agree well with theoretical dispersion curve of the defect-free clad plate. If some delamination appears within Lamb wave propagation distance, a noticeable distortion of the dispersion curve appears. By taking the differential of the dispersion maps of the intact and delaminated plate, we identify the delamination of the hot-clad plates.

Real-time nondestructive evaluation of fiber composite laminates using low-frequency Lamb waves.

Amid the nondestructive evaluation techniques available for the inspection of composite materials, only a few are suitable for implementation while the component is in service. The investigation examines the application of Lamb waves at low-frequency-thickness products for the detection of delaminations in thick composite laminates. Surface-mounted piezoelectric devices were excited with a tone burst to generate elastic waves in the structure. Experiments were carried out on composite beam specimens where wave propagation distances over 2 m were achieved and artificially induced delaminations as small as 1 cm2 were successfully identified. The feasibility of employing piezoelectric devices for the development of smart structures, where a small and lightweight transducer system design is required, has been demonstrated. The resonance spectrum method, which is based on the study of spectra obtained by forced mechanical resonance of samples using sine-sweep excitation, has been proposed as a technique for measuring the A0 Lamb mode phase velocity. The finite-element method was also used to investigate qualitatively the dynamic response of laminates to wave propagation. Several locations and spatial distribution of the actuators were examined showing the advantages of using transducers arrays for the inspection of large structures.

PLANE HORIZONTAL TRANSVERSE WAVES IN ELASTIC PIEZOPOWDERS

A procedure and results of computer simulation of plane horizontal transverse waves are described. Three materials — gallium arsenide, bismuth germanate, and lead zirconate–titanate ceramics — are selected as the piezoelectric phase. The second phase of the powder is always lead. To describe waves in the powder, the microstructural theory of two-phase mixtures is used. Therefore, the computer simulation was intended to study the influence of the lead content by volume on the wave velocities and the microstructural wave-propagation pattern — decomposition of a wave into two modes, simultaneous propagation of both modes in each phase of the powder, etc. First, sets of physical constants (elastic, piezoelectric, and dielectric) of mixture theory were evaluated for three types of powders (with the piezoelectric phase as one of the above-mentioned materials) with the volume piezoelectric-phase content varying from 0.01 to 0.5 with step 0.005. Further, dispersion curves for both modes and 3D-graphs of amplitudes as functions of the wave propagation time and distance were plotted for 300 compositions of powders (three types, each of 100 modifications). Of the phenomena described, we should first of all point out that all the phase velocities increase twice upon changing the content of the powder in the piezoelectric phase from a very small amount to the maximum possible

Health monitoring of composites using Lamb waves generated by piezoelectric devices

The present paper examines the application of low frequency Lamb waves for the detection of delaminations in composite laminates. Surface mounted piezoelectric devices were excited with a tone burst of few cycles generating a propagating stress wave along the structure. Experiments were carried out on composite beam specimens, for which wave propagation distances over 2 m were achieved and artificially induced delaminations as small as 1 cm2 were successfully identified. The feasibility of employing piezoelectric devices for the development of smart structures, for which a small and lightweight transducer system design is required, has been demonstrated. Finite element results of wave propagation in wide plates are also presented.

Laser-induced shock waves in PMMA confined foils

Confined ablation experiments were performed to measure pulsed laser-induced shock wave profiles in aluminum and copper foils by using polyvinylidene fluoride (PVDF) gauges. The aluminum and copper targets of 40–200 μm thickness were irradiated by neodymium laser at 1.06 μm wavelength and at a pulse width of 33 ns (FWHM, full-width at half-maximum) at a power density around 0.45 G W/cm 2. A 3 mm thick polymethyl methacrylate (PMMA) overlay was used to confine the target. Experimental measurements revealed the dependence of the laser-induced shock pressure on the thickness and material properties of the target. It was found that attenuation of peak pressure of the laser-induced shock waves could be well fitted by a power-form function P M=P 0X −n . Here, n is a parameter relevant to material properties, P 0 is the pressure when X=1 and P M is the maximum pressure at X, the propagation distance of the shock wave from the front surface of the target. A simplified analytical description is presented to illustrate the features of the shock profiles obtained from experiments. The space–time diagram of wave propagation and the successive pressure states were determined from which theoretical pressure time profiles were constructed. Both the experiment and theoretical analysis inferred a shock pressure of 4.5–5.5 kbar in the target. Some direct ablation experiments were also conducted to evaluate the enhancement of pressure for PMMA confinement. By comparison with direct ablation, confined ablation can increase the pressure by 7.5–11.8 times. The study provides the data for the PMMA-confined targets.

Abnormal Inflow Wave Propagation in Patients with Doppler Characteristics of Impaired Left Ventricular Relaxation

With application of the range ambiguity, a delay between the flow onset at both the mitral valve and the apex has been shown to be present in patients with a severely dilated and poorly contracting left ventricle and those with acute myocardial infarction with abnormal apical wall motion, but the delay has been absent in normal subjects. Nevertheless, whether there is a delay between the flow onset at both regions in the presence of impaired left ventricular relaxation remains unknown. This study was undertaken to evaluate the left ventricular inflow wave propagation in control subjects and patients with impaired left ventricular relaxation. Eighteen patients with normal systolic function and Doppler characteristics of impaired relaxation of the left ventricle and 17 age- and sex-matched healthy control subjects were included. Range ambiguity was used to simultaneously record the phantom Doppler signals from the mitral valve region and the true ones from the apex. The inflow wave propagation velocity was derived from the inflow wave propagation distance divided by the time between the mitral valve and the apex. There was always some delay between the flow onset at both the mitral valve and the apex in both the controls and the patients (47 +/- 13 msec vs 85 +/- 19 msec, P < 0.001). The inflow wave propagation velocity was 160 +/- 50 cm/sec and 90 +/- 20 cm/sec in the control subjects and the patients, respectively (P < 0.001). Multiple linear regression analyses of the significantly correlated variables stepwisely selected the deceleration time of the E wave (R(2) = 0.53, P < 0.001) and age (R(2) = 0.06, P = 0.039) as the significant determinants of the left ventricular inflow wave propagation velocity. In conclusion, the application of the range ambiguity offers a new method of determining the left ventricular inflow wave propagation velocity, and Doppler characteristics of impaired left ventricular relaxation are associated with a slower inflow wave propagation from the mitral valve to the apex.

Micro particle trapping by opposite phases ultrasonic travelling waves

When two ultrasonic transducers are placed side by side and are driven by continuous signals with opposite phases, an acoustic black spot with zero acoustic power is produced just in front of the boundary of the two ultrasonic transducers, regardless of the wave propagation distance. By this effect, the acoustic radiation field can be modulated spatially. The modulated acoustic field applies the acoustic radiation force to small objects, such as micro particles, in the direction perpendicular to the ultrasonic wave propagation direction. If the small objects flow into the acoustic field by the surrounding fluid flow, they are trapped inside the acoustic black spot. In this paper, a micro particle trapping system, which is based on the opposite phases ultrasonic traveling waves, is proposed. Some characteristics of the method, such as size of the micro particles trapped inside the flow and phase error between two ultrasonic waves, are discussed. The basic experiment is carried out by polystyrene spheres.

The use of a parallel virtual machine (PVM) for finite-difference wave simulations

Computer modelling is now applied routinely throughout the geosciences in an attempt to create synthetic data for comparison with real data. At present, in seismology, there is no analytical solution to the wave equation which allows wave simulations in “geologically realistic” (complex) media. Consequently, computationally expensive numerical solutions are required. Using a finite-difference solution to the wave equation provides a suitable means of modelling seismic waves in a heterogeneous medium. However, when applying this method the grid sizes and the number of time steps required (to ensure numerical stability and sufficiently long wave propagation distances) are limited because of their demand on computer time and memory. Supercomputers represent an obvious solution to these limitations. This paper presents an alternative which is inexpensive, convenient and portable. By clustering a set of processors, for example PCs or workstations, a parallel configuration can be obtained by using the processors available on each machine to perform sections of the calculations simultaneously. By using Parallel Virtual Machine (PVM) — a public domain software package which allows a programmer to create and access a concurrent computing system made from networks of loosely coupled processing elements (Geist and others, 1994) — we have reduced wall-clock times and increased array sizes for a finite-difference solution to the acoustic, elastic and viscoelastic wave equations. In this paper we present methods of parallelizing a serial code and load-balancing this parallelized code. A comparison of serial and parallel wall-clock times, a comparison of wall-clock times on a variety of clusters of machines and the role of communication in this application are presented for a finite-difference solution to the acoustic wave equation.

Dynamic failure mechanisms of ceramic bars : Experiments and numerical simulations

Failure mechanisms in ceramics are investigated by means of bar impact experiments and numerical simulations of the wave propagation event. Stress histories are measured by embedding manganin stress gauges in the ceramic bars. The fracture event is examined by high speed photography. A violent radial expansion, in a region close to the impact surface, followed by a cloud of debris is observed. Numerical simulations of the inelastic wave propagation event are performed with a multiple-plane microcracking model. The simulations show that when the impact stress exceeds a material threshold, the stress wave in the bar has a relatively short duration which is controlled by the rate of unconfined compressive damage. A nonzero inelastic strain rate at the wave front is required in the simulations to properly capture the measured stress attenuation with propagation distance. This feature is related to a heterogeneous material microstructure which is a common occurrence in ceramics. Furthermore, the simulations predict a radial expansion of the bar as a result of not only compressive but also tensile damage. The radial velocity histories on the bar surface are functions of wave propagation distance and damage rate. Tensile damage is induced by stress release from the rod surface and is restricted to the bar core, due to wave focusing, and to the bar free end. In the latest case, reflection of the compressive pulse produces bar spallation. The two dimensional distribution of tensile and compressive damage is assessed by means of contour plots of volumetric strain and the second invariant of the inelastic strain tensor.

Monostatic seismoacoustic scattering from 45° oblique cylindrical hole in thick floating ice plate

Laboratory ultrasonic modeling results are presented characterizing monostatic scattering of broadband pulsed seismoacoustic waves (2&amp;lt;ka&amp;lt;8) from a 45° oblique cylindrical hole in a thick floating ice plate. A vertical compressional disk transducer placed on the free surface of a floating plate is used to generate and detect diagonally propagating shear waves created by the vertical displacement of the disk [G. F. Miller and H. Pursey, Proc. R. Soc. London Ser. A 233, 55–69 (1955)]. Compressional, shear, and Rayleigh wave velocities are simultaneously obtained from the oblique hole reflections. Backscattering results from oblique empty and water filled holes in Plexiglas and ice models are compared. Data from a layered plate model shows the effect of velocity variation with depth on ray bending and monostatic scattering. In other experiments, the compressional transducer is located in the water below the floating plate. The described oblique hole monostatic reflection seismology method may be used to determine sea ice shear velocity using a compressional transducer on the free surface of the ice and a 45° hole made by a coring machine such as the PICO 45° ice coring rig currently used in sea ice electromagnetic and optical oceanography. One-sided accurate velocity measurements may be achieved because the wave propagation distance between transducer and reflection point deep inside the ice can be determined from the surface. The findings are applicable to NDE and geophysics. [Work supported by ONR.]

Attenuation of sound waves in drill strings

During drilling of deep wells, digital data are often transmitted from sensors located near the drill bit to the surface. Development of a new communication system with increased data capacity is of paramount importance to the drilling industry. Since steel drill strings are used, transmission of these data by elastic carrier waves traveling within the drill pipe is possible, but the potential communication range is uncertain. The problem is complicated by the presence of heavy-threaded tool joints every 10 m, which form a periodic structure and produce classical patterns of passbands and stop bands in the wave spectra. In this article, field measurements of the attenuation characteristics of a drill string in the Long Valley Scientific Well in Mammoth Lakes, California are presented. Wave propagation distances approach 2 km. A theoretical model is discussed which predicts the location, width, and attenuation of the passbands. Mode conversion between extensional and bending waves, and spurious reflections due to deviations in the periodic spacings of the tool joints are believed to be the sources of this attenuation. It is estimated that attenuation levels can be dramatically reduced by rearranging the individual pipes in the drill string according to length.

Accurate and efficient seismic modeling in random media

The optimum method for seismic modeling in random media must (1) be highly accurate to be sensitive to subtle effects of wave propagation, (2) allow coarse sampling to model media that are large compared to the scale lengths and wave propagation distances which are long compared to the wavelengths. This is necessary to obtain statistically meaningful overall attributes of wavefields. High order staggered grid finite‐difference algorithms and the pseudospectral method combine high accuracy in time and space with coarse sampling. Investigations for random media reveal that both methods lead to nearly identical wavefields. The small differences can be attributed mainly to differences in the numerical dispersion. This result is important because it shows that errors of the numerical differentiation which are caused by poor polynomial interpolation near discontinuities do not accumulate but cancel in a random medium where discontinuities are numerous. The differentiator can be longer than the medium scale length. High order staggered grid finite‐difference schemes are more efficient than pseudospectral methods in two‐dimensional (2-D) elastic random media.

Methodological approaches to an assessment of the impact of power facilities on the landscape

1. The examined method permits obtaining as a first approximation in monetary terms the loss of the aesthetic value of a landscape from an analysis of variants of power stations based on an analysis of various unrelated factors of an ecological and technical character. 2. The results of calculating the annual siting losses of power facilities showed that the most advantageous is a power complex WPS+HES+TPS and the least a TPS. This is evidently explained by the considerably greater ecological loss and specific land-use intensity of a TPS compared to other participants of power complexes. It is important to note that the values of the annual losses from power complexes can be reduced still more by reducing or completely eliminating a number of negative factors of WPSs. For example, the factor of visual perception of a WPS can be concealed by the appropriate color or state of the environment [1, 16–18], or the factor of the electromagnetic effect of a WPS can be removed by siting the repeaters along the periphery of the AG farm [17, 18]. On the other hand, with consideration of the distance of flood wave propagation in emergency situations at a HES, some increase of losses is possible. 3. The need for quantitative consideration of a decrease of the aesthetic value of the landscape and other ecological effects of various power facilities induces the authors to recommend it in a comparative assessment of the ecological and social impacts of these facilities.

Solution of the Fourth-moment Equation by an Adaptive Grid Method

Abstract The parabolic fourth moment equation for a plane wave is integrated numerically using an adaptive grid algorithm. Results are compared with those from an accurate, but far less efficient, operator splitting method, and agree very closely. The adaptive approach has several advantages over current fixed grid methods. The primary one is that significant reductions in computer memory usage can be obtained without a concomitant increase in run time. It is also ideally suited for accurate integration of the fourth-moment equation for an extremely large range of values of both the scattering parameter, Γ, and the wave propagation distance.

Revised finite sound ray integration method based on Kirchhoff's integral equation.

This thesis explains the calculation theory of a revised finite sound ray integration method and the algorithm based on the integration equation, which is obtained by the solution of Kirchhoff, from the wave equation. It also explains the calculation of small rectangular space pulse response by using the revised finite sound ray integration method, and correspondence of the values with model test values. The theoretical equation which is the basis of this calculation method is the transformed equation of Kirchhoff's integration equation, that is assuming a point source of sound without dimensions. In order to calculate this equation, the integral domain on the boundary surface, which changes in accordance with the lapse of time, and the sound wave propagation distance, etc. have to be obtained. We, therefore, simulated the spherical progressive wave by utilizing a multiple number of sound rays, which were radiated from the sound source at equal solid angle, and then obtained the various necessary information for the calculation. Up to this time, the said calculation method is programmed on the condition that the pursuing sound rays are only mirror reflecting sound rays, and a small computer can be used for the calculation. When we measured the pulse response by using a 1/4 scale rectangular room model, which was composed of complete reflecting surfaces and a complete sound absorbing surface, and the results were compared with the calculation values by the revised finite sound ray integration method, we were able to obtain very reasonable results.