Pulsed Rayleigh Research Articles

Transient scattering of a Rayleigh wave by a cluster of subwavelength resonators—Towards asymptotic modeling of seismic surface metabarriers

A seismic metabarrier (intended for surface waves mitigation effect) is modeled as a cluster of single-degree-of-freedom resonator units deposited on the surface of an isotropic homogeneous elastic half-space. It is assumed that each resonator has a frictionless flat rigid base of diameter much smaller than the wavelength of an incoming surface wave. The slow-motions asymptotic method is applied for constructing the first-order asymptotic model of multiple time-dependent scattering of a pulsed Rayleigh wave with respect to the vertical displacements of the resonators (including their rigid bases and inertial elements) and the normal contact forces (time-dependent integral characteristics of the contact reactions beneath the resonator bases). Both the stationary and transient multiple scattering scenarios are considered. The variation of the amplitude reduction factor due to the model parameters variation is studied in detail.

Implications of polarized pupil degradation due to focal shifts in dynamically ranged Rayleigh beacons

A dynamically ranged pulsed Rayleigh beacon using sensed wavefronts across a system's pupil plane is proposed for tomographic quantification of the atmospheric turbulence strength. This method relies on relaying light from a telescope system's pupil plane to a wavefront sensor and having precise control of the light-blocking mechanisms to filter out scattered light from the unwanted scattering regions along the propagation path. To accomplish this, we tested and incorporated design features into the sensing system that we believe, to the best of our knowledge, are unique. Dynamically changing the range of the beacon source created focal shifts along the optical axis in the telescope sensing system. This effect induced polarization degradation in the optical pupil. As a result, polarization nonuniformity within the Pockels cell resulted in light leakages that corrupted the sensed data signals. To mitigate this unwanted effect, an analysis of the polarization pupil had to be completed for the range of possible Rayleigh beacon source distances, relating the change in polarization to the ability of a Pockels cell to function as an optical shutter. Based on the resultant polarization pupil analysis, careful design of the light relay architecture of the sensing system was necessary to properly capture sensed wavefront data from a series of intended ranges. Results are presented for the engineering design of the Turbulence and Aerosol Research Dynamic Interrogation System sensing system showing the choices made within the trade space and how those choices were made based on an analysis of the polarization pupil. Based on what we learned, recommendations are made to effectively implement a polarization-based Pockels cell shutter system as part of a dynamically ranged Rayleigh beacon system.

脉冲预泵浦瑞利BOTDA系统的解析模型与仿真

脉冲预泵浦瑞利BOTDA系统的解析模型与仿真

A model for pulsed Rayleigh wave and optimal EMAT design

A model has been developed for the prediction of the transient displacement of a Rayleigh wave generated by an electromagnetic acoustic transducer (EMAT), operating on the Lorentz principle. This model can be used to calculate Rayleigh waves of arbitrary forces. A linear coil and a spiral coil are considered as two examples. Out-of-plane displacement of the Rayleigh wave is measured experimentally using a Michelson laser interferometer. Good agreement is observed between the calculated and the measured results, demonstrating the value of this method. This paper explains how the Lorentz forces due to the static and dynamic magnetic fields work constructively and destructively, indicating that the orientation of the external magnetic field must be correct to achieve an efficient generation of the Rayleigh wave.

A numerical model for pulsed Rayleigh wave scattering from general surface features : Blake, R.J.; Bond, L.J. Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 914–919. Butterworth and Co. (Publishers) Ltd., Guilford, Surrey (1987)

A numerical model for pulsed Rayleigh wave scattering from general surface features : Blake, R.J.; Bond, L.J. Ultrasonics International 87, Conference Proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 914–919. Butterworth and Co. (Publishers) Ltd., Guilford, Surrey (1987)

A Turbulent Reacting Flow Model that Incorporates Detailed Chemical Kinetics

ABSTRACT A turbulent reacting flow model has been developed, based upon a stochastic modeling approach that is applicable over a wide range of Reynolds and Schmidt numbers. All relevant length scales are resolved in one dimension which allows for direct implementation of detailed chemical kinetic calculations and molecular transport. Experiments were performed in a turbulent plug flow reactor for validation and application of the model to investigate the combined effects of turbulent mixing and chlorine chemistry on the formation of products of incomplete combustion. Methyl chloride was injected into the plug flow reactor whose baseline flow was the hot-product stream of a Toroidal Jet-Stirred Combustor. The micromixing and chemical reaction of the injected material with the baseline flow was monitored as a function of distance from the point of injection. Measurements of pulsed laser Rayleigh scattering were used to determine the extent of mixing while species concentrations were measured via extractive ...

Inhibition of a Fuel Lean Ethylene/Air Flame in a Jet Stirred Combustor by Methyl Chloride: Experimental and Mechanistic Analyses

Abstract Probability density functions (PDFs) of instantaneous temperature have been obtained for fuel lean C2 H4 /air burning in a toroidal jet stirred combustor (TJSC) using pulsed laser Rayleigh scattering. The PDFs provide a very sensitive measure of departures from perfectly stirred reactor (PSR) behavior, Narrow PDFs were obtained under stable operating conditions. As the mean combustion temperature was reduced or the reaction kinetics decelerated by the addition of CH3,C1, the PDFs exhibited a bimodal distribution indicative of localized blowout. Modeling of the reactions indicates that chlorine primarily destabilizes this hydrocarbon oxidation system by inhibiting the burnout of CO. This inhibition is affected through significant depletion of OH in the presence of relatively high levels of HC1 by the reaction OH + HC1 = H2O + CI. Inhibition is further affected by the termination reaction CI + HO2 + HCI + O2 because HO2 is a source of OH.

A numerical model for pulsed Rayleigh wave scattering from general surface features

A numerical model for pulsed Rayleigh wave scattering from general surface features

Scattering of a pulsed Rayleigh wave by a spherical cavity in an elastic half space

The time-dependent scattering by a spherical cavity in an elastic half space is considered. The incoming wave is a pulsed Rayleigh wave. The stationary part of the problem is solved by the T-matrix method, and an integration in frequency is performed with a modified gaussian weight function. The displacement components at some points on the surface of the half space are computed and shown in a number of plots.

Scattering of pulsed Rayleigh surface waves by a cylindrical cavity

A pulsed Rayleigh surface wave of prescribed shape is incident on a cylindrical cavity which is parallel to both the plane free surface and the plane wave front. Multiple reflections at the cylindrical and plane free surface are considered and the resulting displacements and stress components are calculated in the surrounding of the cavity by approximately summing infinite double sums. Use is made of the stationary loading case simulated by a periodic train of wave pulses and its time Fourier series representation and of expansions of all incident and reflected waves in terms of cylindrical wave functions. For reflection, the free surface of the half-space is approximated by a fictitious convex (or concave) cylindrical surface of “large” radius. The wave pattern due to a single pulse loading is constructed from the stationary solution by enforcing homogeneous initial conditions in the half-space ahead of the single loading pulse and by prescribing a wide spacing in the periodically set-forth train of pulses. The numerical results for stresses and dynamic stress magnification factors are especially useful for the interpretation of recent measurements in dynamic photoelasticity.