Spherical Propagation Research Articles

Acoustically invisible feeding blue whales in Northern Icelandic waters.

Fixed passive acoustic monitoring can be used for long-term recording of vocalizing cetaceans. Both presence monitoring and animal density estimation requires the call rates and sound source levels of vocalizations produced by single animals. In this study, blue whale calls were recorded using acoustic bio-logging systems in Skjálfandi Bay off Húsavík, Northeast Iceland, in June 2012. An accelerometer was attached to individual whales to monitor diving behavior. During 21 h recording two individuals, 8 h 45 min and 13 h 2 min, respectively, 105 and 104 lunge feeding events and four calls were recorded. All recorded calls were down-sweep calls ranging from 105 to 48 Hz. The sound duration was 1-2 s. The source level was estimated to be between 158 and 169 dB re 1μPa rms, assuming spherical sound propagation from the possible sound source location to the tag. The observed sound production rates and source levels of individual blue whales during feeding were extremely small compared with those observed previously in breeding grounds. The feeding whales were nearly acoustically invisible. The function of calls during feeding remains unknown.

Laminar burning velocities of premixed nitromethane/air flames: An experimental and kinetic modeling study

Due to its high lubricity, nitromethane is a fuel regularly used in model engine or more generally in race engine. The objective of this study is to improve our knowledge and understanding of the combustion of nitromethane for better evaluating its potential as fuel for automotive spark-ignition engines. To achieve this goal, unstretched laminar burning velocities of nitromethane–air mixtures were measured using spherical propagation methodology at 423K over a pressure range from 0.5 to 3bar and equivalence ratios from 0.5 to 1.3. The data indicated a typical adverse effect of pressure on laminar burning velocities. Based on the work done by Zhang et al. (2011) [7], a modified detailed kinetic model including 88 species and 701 reactions was proposed. Comparisons between experimental and simulated un-stretched laminar flame speed were made and showed good agreement. The new kinetic mechanism was also used to successfully simulate published experiments and rationalize the unusual occurrence of maximum flame speed in the fuel-lean region.

Corrigendum

James, R.R. (2012). Wind Turbine Infra and Low-Frequency Sound: Warning Signs That Were Not Heard. Bulletin of Science, Technology & Society, 32(2): 108-127. (Original doi: 10.1177/0270467611421845 ) In this article, on page 118, text is missing the quotes and the reference to the page of book is incomplete and not in the correct location. Please see the revised paragraph with the changes: “Multiple wind turbines complicate matters further. From relatively long distances, an assembly of machines appears as a point source . . .” “Closer to the turbines, they begin to act as a line source. The decay rate for line sources is 3-dB, not 6 dB for true spherical propagation.” (p.379, Wind Energy Coming of Age) The standard wind turbine computer model used to estimate sound levels for wind Project assumes “Spherical Propagation” not “Line Propagation” even though turbines are arranged in rows. This error means that the tables of sound levels and the contour maps grossly underestimate the true impact of the sounds on adjacent properties located along the rows.

Experimental and Numerical Study of Laminar Burning Velocity of Ethane–Air Mixtures of Variable Initial Composition, Temperature and Pressure

Pressure–time records of ethane–air centrally ignited explosions in a spherical closed vessel have been used to study the flame propagation in mixtures with various initial concentrations, pressures and temperatures ([C2H6] = 3.40–7.60 vol %, p0 = 30–130 kPa, T0 = 298–433 K). The normal burning velocities have been calculated from pressure–time records for an extended duration of spherical propagation by means of an improved equation for the burnt mass fraction, recently discussed. For the stoichiometric ethane–air mixture, Su,st = (43.5 ± 1.0) cm/s was obtained, within the range of reported literature data from the spherical bomb technique. The normal burning velocities were examined in correlation with the temperature and pressure reached during flame propagation, in single experiments. A power law has been used to describe the dependency of burning velocities on pressure and temperature. The thermal exponents of burning velocities range between 1.40 and 2.20, revealing the influence of the initial pres...

Assessment of elliptic flame front propagation characteristics of iso-octane, gasoline, M85 and E85 in an optical engine

Premixed fuel–air flame propagation is investigated in a single-cylinder, spark-ignited, four-stroke optical test engine using high-speed imaging. Circles and ellipses are fitted onto image projections of visible light emitted by the flames. The images are subsequently analysed to statistically evaluate: flame area; flame speed; centroid; perimeter; and various flame-shape descriptors. Results are presented for gasoline, isooctane, E85 and M85. The experiments were conducted at stoichiometric conditions for each fuel, at two engine speeds of 1200rpm (rpm) and 1500rpm, which are at 40% and 50% of rated engine speed. Furthermore, different fuel and speed sets were investigated under two compression ratios (CR: 5.00 and 8.14). Statistical tools were used to analyse the large number of data obtained, and it was found that flame speed distribution showed agreement with the normal distribution. Comparison of results assuming spherical and non-isotropic propagation of flames indicate non-isotropic flame propagation should be considered for the description of in-cylinder processes with higher accuracy. The high temporal resolution of the sequence of images allowed observation of the spark-ignition delay process. The results indicate that gasoline and isooctane have somewhat similar flame propagation behaviour. Additional differences between these fuels and E85 and M85 were also recorded and identified.

Thermodynamic model for prediction of performance and emission characteristics of SI engine fuelled by gasoline and natural gas with experimental verification

In this study, a thermodynamic cycle simulation of a conventional four-stroke SI engine has been carried out to predict the engine performance and emissions. The first law of thermodynamics has been applied to determine in-cylinder temperature and pressure as a function of crank angle. The Newton-Raphson method was used for the numerical solution of the equations. The non-differential form of equations resulted in the simplicity and ease of the solution to predict the engine performance. Two-zone model for the combustion process simulation has been used and the mass burning rate was predicted by simulating spherical propagation of the flame front. Also, temperature dependence of specific heat capacity has been considered. The performance characteristics including power, indicated specific fuel consumption, and emissions concentration of SI engine using gasoline and CNG fuels have been determined by the model. The results of the present work have been evaluated using corresponding available experimental data of an existing SI engine running on both gasoline and CNG. It has been found that the simulated results show reasonable agreement with the experimental data. Finally, parametric studies have been carried out to evaluate the effects of equivalence ratio, compression ratio and spark timing on the engine performance characteristics in order to show the capability of the model to predict of engine operation.

Burning Velocity of Propane–Air Mixtures from Pressure–Time Records during Explosions in a Closed Spherical Vessel

The flame propagation during the deflagration of the propane–air mixtures with variable initial concentration, pressure, and temperature ([C3H8] = 2.60–6.20 vol %, p0 = 30–200 kPa, and T0 = 298–433 K) in a spherical closed vessel with central ignition was monitored by means of pressure measurements. Using an improved relationship for the burnt mass fraction, the burning velocities were calculated from pressure–time records over an extended duration of spherical propagation. A very good agreement was found between the burning velocities of atmospheric laminar C3H8/air flames and literature data. Computed burning velocities, obtained from numerical modeling of one-dimensional laminar flames using two detailed chemical kinetic schemes (Warnatz mechanism and GRI Mech 3.0, respectively) are discussed in comparison to experimental burning velocities. The measured burning velocities are correlated with pressure and temperature using a power law; the baric and thermal exponents, ν and μ, lie within the usual range characteristic to alkane–air laminar flames.

Wavefront propagation in turbulence: an unified approach to the derivation of angular correlation functions

A general expression of the spatial correlation functions of quantities related to the phase fluctuations of a wave that have propagated through the atmospheric turbulence are derived. A generalization of the method to integrand containing the product of an arbitrary number of hypergeometric functions is presented. The formalism is able to give the coefficients of phase-expansion functions orthogonal over an arbitrary circularly symmetric weighting function for an isotropic turbulence spectrum, as well as to describe the effect of the finite outer and inner scales of the turbulence and to describe the spherical propagation or to derive the effects of the analytical operators acting on the phase such as the derivatives of any order. The derivation of the generalized integrals with multiparameters is based on the Mellin transforms integration method.

Spherical shock-wave propagation in three-dimensional granular packings

We investigate numerically the spherical shock-wave propagation in an open dense granular packing perturbed by the sudden expansion of a spherical intruder in the interior of the pack, focusing on the correlation between geometrical fabrics and propagating properties. The measurements of the temporal and spatial variations in a variety of propagating properties define a consistent serrated wave substructure with characteristic length on the orders of particle diameters. Further inspection of particle packing reveals a well-defined particle layering that persists several particle diameters away from the intruder, although its dominant effects are only within one to two diameters. This interface-induced layering not only exactly coincides with the serrated wave profile, but also highlights the competition between two energy transmission mechanisms involving distinct transport speeds. The alternating dominances between these two mechanisms contribute to the nonlinear wave propagation on the particle scale. Moreover, the proliferation of intricate three-dimensional contact force networks suggests the anisotropic stress transmission, which is found to also arise from the localized packing structure in the vicinity of the intruder.

A Two-Dimensional Wave Prediction Model Along the Best Track of Typhoon Linda 1997

Problem statement: A two-dimensional wave prediction model along the best track of Typhoon Linda 1997 was interested to study the impact of typhoon wind-wave characteristics. The dynamical wave model with deep water condition was used to predict the wave height (Hs) of Typhoon Linda before and after entering into the Gulf of Thailand (GoT). Approach: The standard one-way nested grid for a regional scale of the third generation WAve Model Cycle 4 (WAMC4) is scrutinized in the present study. This model is enabled to solve the spectral energy balance equation on a coarse resolution grid in order to produce boundary conditions for a small area by the nested grid technique along the best track of typhoon. The model takes full advantage of the fine resolution wind fields in space and time produced by the available US Navy Operational Global Atmospheric Prediction System (NOGAPS) model with 1° resolution. The nested grid application was developed in order to gradually increase the resolution from the open ocean towards the South China Sea (SCS) and the Gulf of Thailand (GoT) respectively. Results: The model results were predicted at five stations which were before and during the typhoon entering into the GoT. The wind speeds of the stations 1-5 were in ranges of 5.14-29.81, 4.11-28.27, 0.51-24.67, 0.51-31.35 and 0.51-33.41 m sec-1, respectively. While the Hs of these stations were found in ranges of 0.54-2.99, 0.68-2.85, 0.11-1.57, 0.12-2.92 and 0.09-2.76 m, respectively. The model results were compared with buoy observations at Ko-Chang and Rayong locations in the GoT which were obtained from the Seawatch project. The comparison of those results at Ko-Chang and Rayong showed the percentage errors of 11.20 and 15.12% respectively. Conclusion: The model results presented the relationship of typhoon wind-induced ocean wave at five stations along the best track. The tendency of the Hs from the model in the spherical coordinate propagation with deep water condition in the fine grid domain was in good agreement with the Hs from the observations.

2.5D modelling of elastic waves in transversely isotropic media using the spectral element method

The spectral-element method provides an accurate alternative to the finite-element method for modelling elastic waves in anisotropic media. With the aim of reducing the high computational overheads of 3D modelling, we have implemented 2.5D spectral-element modelling of elastic waves, initially for vertically transversely isotropic media, and then extended to a tilted transversely isotropic medium with a dipping symmetry-axis. We have investigated different categories of absorbing boundaries to minimise artificial boundary reflections, including viscous boundary conditions and two distinct 2.5D formulations of perfectly matched layers (PMLs). Both PML methods use complex coordinate stretching, but the first method is only applicable in the frequency-domain. The other method uses the decomposed gradient operator and can be applied in both the time-domain and frequency-domain. Traditional 2D modelling exhibits cylindrical wave propagation characteristics from a line source. Our 2.5D modelling results, presented as images of seismic wavefields, illustrate the more realistic spherical propagation from a point source.

Analysis of ryanodine receptor clusters in rat and human cardiac myocytes

Single rat ventricular myocytes and human ventricle tissue sections were labeled with antibodies against the ryanodine receptor (RyR) and alpha-actinin to examine the 3D distribution of RyRs with confocal microscopy. Image contrast was maximized by refractive index matching and deconvolution. The RyR label formed discrete puncta representing clusters of RyRs or "couplons" around the edges of the myofilaments with a nearest-neighbor spacing of 0.66 +/- 0.06 microm in rat and 0.78 +/- 0.07 microm in human. Each bundle of myofibrils was served by approximately six couplons, which supplied a cross-sectional area of approximately 0.6 microm(2) in rat and approximately 0.8 microm(2) in human. Although the couplons were in reasonable registration with z-lines, there were discontinuities in the longitudinal position of sarcomeres so that dislocations in the order of RyR clusters occurred. There was approximately 53% longitudinal registration of RyR clusters, suggesting a nonrandom placement of couplons around the sarcomere. These data can explain the spherical propagation of Ca(2+) waves and provide quantitative 3D data sets needed for accurate modeling of cardiac Ca(2+)-induced Ca(2+) release. By quantifying labeling intensity in rat ventricular myocytes, a lower limit of 78 RyRs per cluster (on average) was obtained. By modeling the couplon as a disk wrapping around a t-tubule and fitting cluster images, 95% of couplons contained between 120 and 260 RyRs (assuming that RyRs are tight packed with a spacing of 29 nm). Assuming similar labeling efficiency in human, from the fluorescence intensity alone we estimate that human ventricular myocytes contain approximately 30% fewer RyRs per couplon than rat.

Large eddy simulation of the backdraft phenomenon

A sub-grid scale model for partially premixed combustion has been adapted and applied to simulate the backdraft phenomena. A fast deflagration or backdraft is produced when into a hot, fuel-rich compartment an inflow of fresh air is suddenly allowed through an opening. It is essentially a violent combustion process involving both premixed and non-premixed regimes. The present model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion. The ‘flame index’ concept was used to separate the two different combustion regimes. This index describes the structure of the flame based on fuel and oxygen gradients. Due to the lack of detailed experimental measurements, the results were largely analysed qualitatively. The predictions have provided valuable insight into the backdraft phenomenon suggesting that the development of backdraft can be divided into five phases, i.e. initial condition, free “spherical propagation, “plane” front propagation, stretching of the flame front through the opening and fireball outside the container. Quantitatively, the experimentally measured and predicted lapse of time between the maximum over- and under-pressure at the opening of the container is found to be in reasonably good agreement.

Parametric spherical wave multiple‐input and multiple‐output model for ray‐based simulations

In this paper, a three‐dimensional parametric spherical wave model is presented that constructs the multiple‐input and multiple‐output (MIMO) channel from a single single‐input and single‐output realization of a ray‐based simulator. This model assumes that rays do not change in the vicinity of the arrays. It uses spherical propagation and image theory to construct the MIMO channel for any array configuration. The main novelty of this model is that it takes into account multiple reflections, diffraction, variations in the reflection coefficient for single‐bounce rays, and variations in the diffraction coefficient. Reflection is shown to be sensitive for hard polarization at the Brewster angle, though these rays have very low energy. Diffraction must be considered at the shadow boundaries of the diffraction wedge and assuming a constant diffraction coefficient, leads to inaccurate results at these regions. It is shown that in outdoor environments and for long distances, this model and the planar wave model provide similar results. However, at short distances, the parametric spherical wave model yields more accurate MIMO channels. Finally, the model is compared to some measurements in an outdoor environment.

Finite-rate evaporation and droplet drag effects in spherical flame front propagation through a liquid fuel mist

An evolution equation for a laminar flame front propagating into an air and liquid fuel mist cloud is derived for the first time, accounting for both the finite-rate evaporation of the fuel droplets and the slip velocity between them and their host environment. The asymptotic analysis employed in developing the equation exploits the usual inverse large activation energy parameter associated with chemical reaction in the flame and a small drag parameter. It is demonstrated that, in the no-slip velocity case, increasing the vaporization Damköhler number can produce flame extinction, presumably due to the more intense heat loss incurred due to droplet heat absorption necessary for vaporization. Droplet drag can also induce extinction due to the longer residence time of the droplets in any locale (than if there was no slip), leading to more vaporization with greater attendant heat loss. The predicted results for droplet velocity are compared to independent experimental data from the literature with good qualitative agreement.

La notion de spectre angulaire sphérique

The notion of a spherical angular spectrum leads to the representation of an electromagnetic wave as a superposition of spherical waves. It provides a direct way of interpreting the role of the pupil in the theory of image formation. The spherical angular spectrum propagation takes the same form as the field amplitude transfer from a spherical emitter to a spherical receiver. To cite this article: P. Pellat-Finet, P.-E. Durand, C. R. Physique 7 (2006).

Determination of vertical and horizontal permeabilities for vertical oil and gas wells with partial completion and partial penetration using pressure and pressure derivative plots without type-curve matching

it has been long recognized that in some reservoirs the flow does not follow the expected radial cylindrical pattern. Spherical flow may take place in systems with wells completed in thick reservoirs where a short completion interval is open to flow yielding a unique and more complex early-time pressure behavior. Some of the main reasons for partial penetration are to avoid coning of water and minimize sand production. A similar early-time pressure behavior may be due to the presence of plugged perforations. Such well completions are referred to as limited-entry, restricted-entry or partially penetrating wells. A typical case of spherical propagation of pressure transients occurs during the repeat formation tester measurements. Such a test measures spot formation pressures and recovers formation fluid samples for gaining an insight into the reservoir flow mechanics. The purpose of this study is to identify on the pressure and pressure derivative curves the unique characteristics for different flow regimes resulting from these type of completions and to determine various reservoir parameters, such as vertical, horizontal permeability, and various skin factors. The interpretation is performed using Tiab’s Direct Synthesis (TDS) Technique, introduced by Tiab (1993), which uses analytical equations obtained from characteristic lines and points found on the log-log plot of pressure and pressure derivative to determine permeability, skin and wellbore storage without using type-curve matching. The extension of this methodology for the case under study includes wellbore storage and skin effects. It is applied to both drawdown and buildup tests. We found that a spherical or hemispherical flow regime occurs prior to the radial flow regime whenever the penetration ratio of about 20%. A half-slope line on the pressure derivative is the unique characteristic identifying the presence of the spherical/hemispherical flow. The typical half-slope line of theses flow regimes is used to estimate spherical permeability and spherical skin values. These parameters are then used to estimate vertical permeability, anisotropy index and skin. Results of TDS technique where successufully compared to those of conventional technique for field and simulated examples.

The study of self-simulating properties of spherical shock front attenuation

In an isotropic medium the self-simulating theory is used in characterizing the spherical shock front attenuation. We first deduce the self-simulating equation of decaying spherical shock front propagation. Then the decaying propagation equation of the spherical shock front is shown in good agreement with experimental data.

Observation of Shock Wave Propagation by a Sonoluminescing Bubble

A simultaneous measurement system for a sonoluminescing bubble oscillation and radiated shock wave from the bubble is presented. It enables high-resolution and high-speed imaging. The nonlinear bubble oscillation and the shock wave generated at the moment of bubble collapse are observed by acoustical and optical measurements. In particular, a spherical propagation of the shock wave is optically observed by the schlieren method.

Numerical study of spherical blast-wave propagation and reflection

The objective of this study is to understand the flow structures of weak and strong spherical blast waves either propagating in a free field or interacting with a flat plate. A 5th-order weighted essentially non-oscillatory scheme with a 4th-order Runge-Kutta method is employed to solve the compressible Euler/Navier-Stokes equations in a finite volume approach. The real-gas effects are taken into account when high temperature occurs. A shock-tube problem with the real-gas effect is first tested in order to verify the solver accuracy. Moreover, unsteady shock waves moving over a stationary wedge with various wedge angles, resulting in different types of shock wave reflections, are also tested. It is found that the computed results agreed well with the existing data. Second, the propagation of a weak spherical blast wave, created by rupture of a high-pressure isothermal sphere, in a free field is studied. It is found that there are three minor shock waves moving behind the main shock. Third, the problem of a strong blast wave interacting with a flat plate is investigated. The flow structures associated with single and double Mach reflections are reported in detail. It is found that there are at least three local high-pressure regions near the flat plate.