Velocities In Different Directions Research Articles

Free vibrations of drill strings in hyper deep vertical bore-wells

This paper considers the problems on investigation of the dynamic bending of elongated drill string tubes studied with allowance made for destabilizing effects of the longitudinal non-uniform preloading, action of torque, inertia forces of rotation and internal flows of washing liquid (mud). As a result of the completed analysis, natural wave and vibration modes are constructed, their frequencies are calculated. It is shown through the study of appropriate dispersion equations that free bending vibrations of unbounded rods can be realized only in the modes of regular dextral and sinistral spiral waves propagating with different velocities in different directions. The modes of free vibrations of the bounded drill strings possess more complicated irregular spiral shapes.

A Quantitative Damage Identification Method for CF/EP Composite Laminates Based on Lamb Waves

This paper describes a quantitative damage identification method for CF/EP composite laminates based on Lamb waves excited by distributed PZT wafers. The fundamental symmetric mode S0 is considered to detect defects (hole) in the plate. The Morlet wavelet and the cross-correlation analysis are introduced as signal processing tools for determining the time-of-flight (ToF) of Lamb wave. Considering the difference of Lamb wave velocities in different directions in a composite plate, the relationship of Lamb wave velocity in a unidirectional fibre reinforced laminate is studied and validated experimentally and numerically. In addition, a defect identification approach is revealed based on a regular arrangement of PZT wafers. Then, on the basis of the relationship of the wave velocity and the ToF, the location of a hole is identified by proposed method. Results demonstrate that the method is feasible in quantitative diagnosis of composite structures.

How do albatrosses fly around the world without flapping their wings?

Albatrosses fly long distances over the Southern Ocean, even around the world, almost without flapping their wings; this has raised interest in how they perform such a feat. On a cruise to the South Atlantic I observed albatrosses soaring in a characteristic swooping zigzag flight that appears to combine two soaring techniques to gain energy—wind–shear soaring (dynamic soaring) using the vertical gradient of wind velocity and wave-slope soaring using updrafts over waves. The observed characteristic swooping flight is shown in a new illustration and interpreted in terms of the two soaring techniques. The energy gain estimated for “typical conditions” in the Southern Ocean suggests that wind–shear soaring provides around 80–90% of the total energy required for sustained soaring. A much smaller percentage is provided by wind shear in light winds and significant swell when wave-slope soaring dominates. A simple dynamical model of wind–shear soaring is proposed based on the concept of a bird flying across a sharp wind–shear layer as first described by Lord Rayleigh in 1883 and later developed with Pennycuick’s (2002) description of albatrosses “gust soaring.” In gust soaring a bird exploits structures in the wind field, such as separated boundary layers and eddies in the lee of wave crests, to obtain energy by climbing headed upwind and descending headed downwind across a thin wind–shear layer. Benefits of the model are that it is simple to understand, it captures the essential dynamics of wind–shear soaring, and it provides reasonable estimates of the minimum wind shear required for travel velocity in different directions with respect to the wind. Travel velocities, given in a travel velocity polar diagram, can be combined with tacking to fly in an upwind direction faster than the wind speed located at the top of the wind–shear layer.

First-Principles Study of Structural, Elastic and Electronic Properties of OsSi

First-principles study of structural, elastic, and electronic properties of the B20 structure OsSi has been reported using the plane-wave pseudopotential density functional theory method. The calculated equilibrium lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The dependence of the elastic constants, the aggregate elastic modulus, the deviation from the Cauchy relation, the elastic wave velocities in different directions and the elastic anisotropy on pressure have been obtained and discussed. This could be the first quantitative theoretical prediction of the elastic properties under high pressure of OsSi compound. Moreover, the electronic structure calculations show that OsSi is a degenerate semiconductor with the gap value of 0.68 eV, which is higher than the experimental value of 0.26 eV. The analysis of the PDOS reveals that hybridization between Os d and Si p states indicates a certain covalency of the Os-Si bonds.

Pressure effects on elastic and thermodynamic properties of ZrB2

A theoretical formalism to calculate the single crystal elastic constants for hexagonal crystals from first principle calculations is described. The calculated values compare favorably with recent experimental results. An expression to calculate the bulk modulus along crystallographic axes of single crystals, using elastic constants, has been derived. The calculated linear bulk moduli are found to be in good agreement with the experiments. The shear modulus, Young’s modulus, and Poisson’s ratio for ideal polycrystalline ZrB2 are also calculated and compared with corresponding experimental values. The shear anisotropic factors and anisotropy in the linear bulk modulus are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. The calculated elastic properties are found to be in good agreement with experimental values when the generalized gradient approximation is used for the exchange and correlation potential. It is found that the elastic constants and the Debye temperature of ZrB2 increase monotonically and the anisotropies weaken with pressure. The thermal properties including the equation of state, linear compressibility, ductility, and the heat capacity at various pressures and temperatures are estimated.

Elastic, electronic and optical properties of the filled tetrahedral semiconductor α-LiCdAs

We have investigated the elastic, electronic and optical properties of the Nowotny–Juza filled tetrahedral semiconductor α-LiCdAs using the pseudo-potential plane-wave within the density functional theory. A numerical first-principles calculation of the elastic constants was used to calculate C 11, C 12 and C 44. The values of the sound velocities in different directions have been calculated. The isotropic elastic moduli, namely bulk modulus, shear modulus, Young's modulus, Poisson's ratio and Lamé's constants are calculated in framework of the Voigt–Reuss–Hill approximation for ideal polycrystalline α-LiCdAs aggregate. We estimated the Debye temperature of α-LiCdAs from the average sound velocity. The analysis of the site and momentum projected densities and charge density reveals strongly covalent Cd–As and strongly ionic Li–As bonds. Band structures show that α-LiCdAs is a narrow direct band gap. The variation of the fundamental band gap versus pressure is well fitted to a quadratic function and a direct to an indirect band gap transition occurs at 15.30 GPa. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient and electron energy loss are calculated for radiation up to 20 eV. The results are compared with the available experimental and theoretical results.

Anisotropic structure beneath central Java from local earthquake tomography

In this study we present the new tomographic code ANITA which provides 3‐D anisotropic P and isotropic S velocity distribution based on P and S traveltimes from local seismicity. For the P anisotropic model, we determine four parameters for each parameterization cell. This represents an orthorhombic anisotropy with one predefined direction oriented vertically. Three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0°, 60°, and 120°, and one is a perturbation along the vertical axis. The nonlinear iterative inversion procedure is similar to that used in the LOTOS code. We have implemented this algorithm for the updated data set of central Java, part of which was previously used for the isotropic inversion. It was obtained that the crustal and uppermost mantle velocity structure beneath central Java is strongly anisotropic with 7–10% of maximal difference between slow and fast velocity in different directions. In the forearc (area between southern coast and volcanoes), the structure of both isotropic and anisotropic structure is strongly heterogeneous. Variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust. Beneath volcanoes we observe faster velocities in vertical direction, which is probably an indicator for vertically oriented structures (channels, dykes). In the crust beneath the middle part of central Java, north to Merapi and Lawu volcanoes, we observe a large and very intense anomaly with a velocity decrease of up to 30% and 35% for P and S models, respectively. Inside this anomaly E‐W orientation of fast velocity takes place, probably caused by regional extension stress regime. In a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and/or penetration of quasi‐horizontal lenses with molten magma. In the mantle, trench parallel anisotropy is observed throughout the study area. Such anisotropy in the slab entrained corner flow may be due to presence of B‐type olivine having predominant axis parallel to the shear direction, which appears in conditions of high water or/and melting content.

Elastic, electronic and optical properties of the filled tetrahedral semiconductor LiCdP

The elastic, electronic and optical properties of the filled tetrahedral semiconductor LiCdP have been investigated using the pseudo-potential plane wave method within the local density functional theory. A numerical first-principles calculation of the elastic constants was used to calculate C11, C12 and C44. The values of the sound velocities in different directions have been calculated. We derived the bulk and shear moduli, Young modulus and Poisson's ratio for ideal polycrystalline LiCdP. We estimated the Debye temperature of LiCdP from the average sound velocity. Band structures show that LiCdP is a direct band gap. The density of states and Mulliken charge populations analysis show that the Cd–P bond is typically covalent with a strong hybridization as well as that the Li–P bond has a significant ionic character. The variation of the gap versus pressure is well fitted to a quadratic function and a direct to an indirect band gap transition occurs at 6.80 GPa. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient and electron energy loss are calculated for radiation up to 20 eV. The results are compared with the available theoretical and experimental data.

Spiral waves in rotating twisted elastic pipes

The problem of propagation of bending waves in rotating pipes prestressed by longitudinal force and torque is stated and solved. Such waves are shown to be spiral ones. It is established that four waves exist for every wavelength, two of which are right-handed spirals and the other two are left-handed. These waves propagate with different velocities in different directions

Sound velocities and single-crystal elasticity of orthoenstatite to 1073 K at ambient pressure

Single-crystal Brillouin spectroscopy measurements have been carried out to 1073 K and ambient pressure to determine the elastic modulus tensor of a natural orthopyroxene, nearly pure Mg end-member (Mg 0.994Fe 0.002Al 0.004) 2(Si 0.996Al 0.004) 2O 6 orthoenstatite. Three single-crystal specimens with orthogonal crystallographic orientations were prepared for Brillouin measurements to determine all the single-crystal elastic moduli ( C ij ). The single-crystal elastic moduli were calculated using the measured velocities of sound and our independent measurement of the volume thermal expansion. These are, to our knowledge, the highest temperatures at which the complete single-crystal elastic modulus tensor of orthoenstatite has been measured. The elastic moduli at ambient conditions obtained in this study are in excellent agreement with previous measurements on Mg 2Si 2O 6 orthoenstatite (OEN). The elastic anisotropy of OEN is approximately the same at all measured temperatures. The velocities in different directions change at different rates, with C 33 showing the largest temperature dependence (decreasing with temperature almost twice as fast as C 11 or C 22). The variation of elastic moduli with temperature is linear up to approximately 673 K, above which some of the moduli decrease with a quadratic dependence on temperature. The non-linear behavior is in accord with recent elastic mode softening observations in orthoenstatite at higher temperatures and could add support to account for a thermally induced solid-state mechanism for the low velocity zone in Earth's upper mantle.

Anisotropy of elastic, magnetic and microstructural properties of the Callovo-Oxfordian argillite

We investigated the anisotropic behaviour of the Callovo-Oxfordian argillite in laboratory experiments, and analysed the rock microstructure using different imaging techniques. The starting material was a core retrieved at 460 m depth in well EST204 at the site of the French Underground Research Laboratory in the Meuse/Haute-Marne region, from which 17 small subcores were prepared in three orthogonal directions. The anisotropy of magnetic susceptibility (AMS) was studied using a KLY3S kappabridge. The technique allows one to determine the susceptibility tensor which can be represented by an ellipsoid with principal axes K max, K int and K min in decreasing order. We found that the AMS ellipsoid is consistent with an oblate fabric. We have also investigated the elastic anisotropy through the measurement of P-wave velocity in different directions, following the procedure described in our previous works [Louis, L., David, C., Robion, P., 2003. Comparison of the anisotropic behaviour of undeformed sandstones under dry and saturated conditions. Tectonophysics 370, 193–212; Louis, L., Robion, P., David, C., 2004. A single method for the inversion of anisotropic data sets with application to structural studies. Journal of Structural Geology 26, 2065–2072]. The anisotropy of P-wave velocity is significantly larger than the anisotropy of magnetic susceptibility. Interestingly, we found an excellent correlation between AMS and the anisotropy of P-wave velocity, with a minimum velocity V min and susceptibility K min fairly well constrained in the direction perpendicular to bedding. Both from the elastic and magnetic viewpoint, the argillite behave as a transverse isotropic medium, which is typical of a sedimentary fabric with no clear sign of tectonic fabric. Our data set on P- and S-wave velocity measurements allowed for the full determination of the transverse isotropy stiffness tensor as well as the Thomsen’s parameters within the framework of weak anisotropy. We also present some results of a study of the rock microstructure and its structural anisotropy using stereological techniques and X-ray microtomography. The microtomography technique revealed the existence of tubular structures made of dense material (pyrite), the origin of which is not clearly defined but has probably to do with bioturbation during the formation of the sediment.

Determination of full set material constants of piezoceramics from phase velocities

The determination of elastic and piezoelectric constants by means of the resonance method is described in detail in the Institute of Electrical and Electronics Engineers Standards. However, in practice, it is not easy to obtain a self-consistent complete set of elastic and piezoelectric coefficients using the resonance method alone, since the geometric requirements are often too difficult to meet in some materials and property variation from sample to sample could be substantial. In this article, we report on a characterization scheme by regression of ultrasonic velocities in different directions. The method using the Levenberg-Marquardt algorithm is very stable. Only two samples are needed to determine the whole set of the material constants. The method has been applied to doped piezoceramic lead zirconate titanate and material constants obtained at the same frequency show excellent self-consistency.

Density functional theory for calculation of elastic properties of orthorhombic crystals: Application to TiSi2

A theoretical formalism to calculate the single crystal elastic constants for orthorhombic crystals from first principle calculations is described. This is applied for TiSi2 and we calculate the elastic constants using a full potential linear muffin-tin orbital method using the local density approximation (LDA) and generalized gradient approximation (GGA). The calculated values compare favorably with recent experimental results. An expression to calculate the bulk modulus along crystallographic axes of single crystals, using elastic constants, has been derived. From this the calculated linear bulk moduli are found to be in good agreement with the experiments. The shear modulus, Young’s modulus, and Poisson’s ratio for ideal polycrystalline TiSi2 are also calculated and compared with corresponding experimental values. The directional bulk modulus and the Young’s modulus for single crystal TiSi2 are estimated from the elastic constants obtained from LDA as well as GGA calculations and are compared with the experimental results. The shear anisotropic factors and anisotropy in the linear bulk modulus are obtained from the single crystal elastic constants. From the site and angular momentum decomposed density of states combined with a charge density analysis and the elastic anisotropies, the chemical bonding nature between the constituents in TiSi2 is analyzed. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. The calculated elastic properties are found to be in good agreement with experimental values when the generalized gradient approximation is used for the exchange and correlation potential.

Right atrial free wall conduction velocity and degree of anisotropy in patients with stable sinus rhythm studied during open heart surgery.

Although the perpetuation of several supraventricular arrhythmias is critically dependent upon intra-atrial conduction, the literature lacks detailed information on normal values of conduction velocity and degree of anisotropy. In order to explore these factors further, we have measured conduction velocities at the right atrial free wall during sinus rhythm and during atrial pacing in four directions parallel and perpendicular to the atrioventricular groove in patients with normal atria and stable sinus rhythm. Using a Bard Cardiac Mapping System, atrial ECGs were recorded using a 3 x 4 cm electrode array with 56 equally spaced bipolar electrodes in 12 patients undergoing open heart surgery due to ischaemic heart disease or Wolf-Parkinson-White syndrome. A bipolar pen probe connected to a Medtronic 5328 stimulator was used for pacing at a 10% higher rate than sinus rhythm. The local activation times were manually set and isochronal activation maps were created for each recording. The conduction velocities were calculated from the activation maps over a distance ranging from 2.2 to 4.2 cm. The majority of the activation maps showed no signs of anisotropy; the others had less than 15% spatial inhomogeneity of conduction. Mean conduction velocity, calculated from five consecutive beats, was 88 +/- 9 cm.s-1 (mean +/- SD), ranging between 68 +/- 4 and 103 +/- 3 cm.s-1 during sinus rhythm. Mean conduction velocity during atrial pacing was 81 +/- 16 cm.s-1 at a propagation direction of 0 degree, 74 +/- 14 cm.s-1 at a 90 degrees direction, 79 +/- 12 cm.s-1 at 180 degrees and 78 +/- 20 cm.s-1 at 270 degrees, where 0 degree was parallel to the atrioventricular groove in the cranial direction and the angle increased counter-clockwise. Mean conduction velocity during sinus rhythm was significantly higher (P < 0.05) than during atrial pacing at the 90 degrees and 180 degrees directions but not compared to atrial pacing at 0 degree or 270 degrees. There was no significant difference in mean conduction velocity in different directions during atrial pacing. Although anisotropy was documented during conduction velocity in individual cases, conduction velocity was not dependent on propagation direction at the epicardial right atrial free wall in patients with stable sinus rhythm. These findings do not exclude the presence of internodal preferential pathways as these are located sub-epicardially and a marked transmural discordance in activation has previously been documented in the vicinity of such pathways.

Multi-Frequency Electromagnetic Stirring of Liquid Metals.

In some applications of electromgnetic stirring of metals a characteristic flow pattern is requested in the melt which requires a certain volume force distribution. The possibilities to achieve such a volume force distribution by a suitable geometry and position of the stirrer are limited. More flexibility is obtained when the stirring is performed with two or more magnetic fields traveling with different velocities in different directions. It is shown in the present paper that such a stirring can be realized with a conventional stirrer by feeding its three-phase winding with a current made up by superposition of two or more currents with different frequencies and traveling directions.

Assessment of Fracture-Induced Anisotropy in the Austin Chalk Formation (Upper Cretaceous), Central Texas: ABSTRACT

This study relates geophysical and geological data to the detection of fractures and their influence on the movement of fluid in the Atco Member of the Austin Chalk in central Texas. In areas of production, the Austin Chalk has very low matrix permeabilities, with hydrocarbons confined to zones of near-vertical, stress-aligned fractures. Horizontal drilling has been estimated to increase per well reserves in the Austin Chalk from 75,000 bbl and 82 mmcf to 500,000 bbl and 500 mmcf. The objective of deviated wells in the Austin Chalk is to intersect at right angles as many of the hydrocarbon-prone fracture zones as possible. Therefore, the detection and description of these fracture zones prior to drilling is critical. Fractures have been proven to influence the velocities of shear waves. To assess shear wave velocities in different directions, several shear wave refraction and three-component vertical seismic profiles have been acquired. These data provided a measure of the fracture-induced shear wave anisotropy and an indication of the dominant fracture trend. Other data, including azimuthal resistivity surveys, cores, and aerial photographs, provided additional control for evaluating the fractures. The final phase of the study compares the geophysical and geological interpretations to the result of shallowmore » groundwater pumping tests. The pumping tests have been conducted in vertical boreholes and were designed to evaluate the influence of the fracturing on fluid movement.« less

Wave propagation in transversely impacted composite laminates

An experimental investigation was conducted to determine wave-propagation characteristics, transient-strain distributions and residual properties for unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 ms−1 (820 ft/s). Tests were conducted at normal and 45-deg oblique impact. Strain signals obtained from surface and embedded strain gages were recorded and analyzed to determine the types of waves, propagation velocities, peak strains, strain rates and attenuation characteristics. The predominant wave is a flexural on propagating at different velocities in different directions. The flexural wave velocity is higher in the higher-modulus direction. In general, measured wave velocities were higher than theoretically predicted. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. Strain rates up to 640 s−1 were measured. Under oblique 45-deg impact, the flexural wave is still the predominant one. Peak strains under this oblique impact range between 36 and 56 percent of those under normal impact of the same velocity. Residual elastic properties and strength were measured around the point of impact. The most significant result was a reduction in the transverse strength of the unidirectional laminates. The dynamics of impact were also studied with high-speed photography. The projectile is completely flattened within 50–70 μs and the total contact time is of the order of 300 μs.

Pressure and temperature derivatives of the isotropic polycrystalline shear modulus for 65 elements

The first-principles calculations based on density-functional theory were performed to investigate the structural properties, phase stability, and elastic properties of several selected Hf–Al intermetallics. The calculated formation enthalpies show that HfAl2 is the most stable in these intermetallics. The predicted elastic moduli results indicate that the order in the degree of elastic anisotropy is HfAl > Hf2Al > D022-HfAl3 > Hf3Al2 > Hf5Al3 > Hf2Al3 > D023-HfAl3 > L12-HfAl3 > Hf4Al3 > HfAl2. By using the procedure of Brugger, the calculated sound velocities in different directions for the Hf–Al intermetallics are anisotropic. The Debye temperatures were also estimated from the elastic constant evaluations of Hf–Al intermetallics.

Wave Surfaces Due to Impact on Anisotropic Plates

The stress waves induced in anisotropic plates by transverse, short- duration impact forces are examined in this report The anisotropy is related to the layup angles of the fibers of a fiber composite laminated plate. Using a modification of Mindlin's approximate theory of plates, it is shown that both extensional and bending waves are generated by transverse impact. The magnitudes of the wave velocities in different directions are calculated for graphite fiber-epoxy matrix plates for various layup angles. Finally, the shapes of the wave fronts or wave surfaces due to point impact are also presented for the cases mentioned.