Retrieving reflection arrivals from passive seismic data using Radon correlation

<p>Since explosive and impulsive seismic sources such as dynamite, air guns, gas guns, or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body-waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body-waves are usually weak in comparison to surface waves which are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body-waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, three-layer model which includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions which are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged-horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.</p>

Retrieving reflection arrivals from passive seismic data using Radon correlation

Since explosive and impulsive seismic sources such as dynamite, air guns, gas guns or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body waves are usually weak in comparison to surface waves that are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, a three-layer model that includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions that are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.

A Rapid Throughput System for Shock and Impact Characterization: Design and Examples in Compaction, Spallation, and Impact Welding

Many important physical phenomena are governed by intense mechanical shock and impulse. These can be used in material processing and manufacturing. Examples include the compaction or shearing of materials in ballistic, meteor, or other impacts, spallation in armor and impact to induce phase and residual stress changes. The traditional methods for measuring very high strain rate behavior usually include gas-guns that accelerate flyers up to km/s speeds over a distance of meters. The throughput of such experiments is usually limited to a few experiments per day and the equipment is usually large, requiring specialized laboratories. Here, a much more compact method based on the Vaporizing Foil Actuator (VFA) is used that can accelerate flyers to over 1 km/s over a few mm of travel is proposed for high throughput testing in a compact system. A system with this primary driver coupled with Photonic Doppler Velocimetry (PDV) is demonstrated to give insightful data in powder compaction allowing measurements of shock speed, spall testing giving fast and reasonable estimates of spall strength, and impact welding providing interface microstructure as a function of impact angle and speed. The essential features of the system are outlined, and it is noted that this approach can be extended to other dynamic tests as well.

Performance and Modeling of a Two-Stage Light Gas Gun Driven by Gaseous Detonation

A two-stage light gas gun driven by gaseous detonation was newly constructed, which can make up for the disadvantages of the insufficient driving capability of high-pressure gas and the constraints of gunpowder. The performance of the gas gun was investigated through experiments and a quasi-one-dimensional modeling of it was also developed and described in detail. The model accounts for the friction and heat transfer to the tube wall for gases by adding a source term. An improved model has been established to consider the inertial loads in the piston or projectile and model the friction force with the tube wall. Besides, the effects of pump tube pressure on the performance of the gas gun are also investigated numerically. Simulations of the pressure histories in the pump tube and the piston and projectile velocities were conducted. A good agreement was observed between the computational predictions and experimental results. The results showed that the friction between the piston and wall had only small influence on the piston velocity. The proposed numerical approach is suitable for the development of two-stage light gas guns and tests of the operating conditions.

Forms of possible delamination of the liner in a metal composite high pressure vessel

The purpose of the paper was to study the effect of induced gas perturbations in the reservoir on the ballistic characteristics of single-stage gas guns. Two ways of waves generation at the initial moment are considered: by means of a non-uniform initial distribution of gas parameters and by creating a shock wave propagating from the bottom of the reservoir by external forces. The study is based on the numerical solution of one-dimensional gas-dynamic equations on a moving grid. Findings of research show that for relatively large (compared to the accelerating gas mass) mass of the projectiles, the wave processes induced by inhomogeneous filling lead to an increase in the muzzle velocity 1.4 times, and the shock waves generation by an external source — 1.8 times.

Laser-Driven High-Velocity Microparticle Launcher In Atmosphere And Under Vacuum

The study of high-velocity microparticles is important to a wide range of both space and terrestrial applications. In space, high- and hyper-velocity micro-debris and micrometeorites, while also a subject of study, pose a threat to equipment and personnel integrity [1–4]. On earth, high-velocity microparticle impact can be, for instance, utilized for therapeutic purposes in the field of biolistics [5] or to build metallic coatings via the cold spray method [6]. While macroscale projectile impacts have been studied using well established experimental tools, such as light-gas guns, optical methods are gaining interest in the field of micro-particle impacts.

X-ray diffraction diagnostic paired with gas gun driven compression of polyethylene

Understanding the kinetics of phase transitions, including decomposition from reactants to products under extreme condition events is challenging. Capturing these processes require: 1) diagnostics that probe on the timescales and at energies capable of interacting with the dynamically evolving products, penetrating the opaqueness of the changing system; and 2) detectors sensitive enough to observe these events. Synchrotrons and free electron lasers provide ke-V-energy x-ray beams capable of penetrating the optical-opaqueness of the temporally evolving products. At the Dynamic Compression Sector at the Advanced Photon Source, the x-ray beam is coupled to single and two-stage gas guns capable of producing planar shocks at a range of projectile velocities while capturing in situ x-ray diffraction/scattering of the evolving material under dynamic compression. In this work, we demonstrate the utility of this approach in measuring the evolution of crystalline domains in shocked high-density polyethylene to P = 7.45 GPa, and have observed the compression and orientation of the polymer chains in real time.

PECULIARITIES OF FIRE-FIGHTING CEREBRAL BRAIN WOUND IN PEACEFUL TIMES IN CHILDREN

Firearms craniocerebral wounds of peacetime are the one of urgent problems of modern neurosurgery. There are no clear statistics, the approved classification of gunshot wounds to the head, algorithm of the treatment and tactics of managing children patients. The greatest number of cases of injuries is caused by modern pneumatic and gas guns, which, by their capacity, are not inferior to firearms. The purpose of this study is to summarize the accumulated experience in countries where there is a legalization of weapons and there was registered a high percentage of its spread among the civilian population, as well as the use of prognostic scales for choosing the tactics of treating patients with gunshot wounds to the head.

Experimental complexes for investigation of behavior of materials at a strain rate of 5·102÷105 s-1

A description of experimental complexes, methodological and hardware means for determining the mechanical properties of materials under high-speed deformation and fracture is given in the report. Determination of mechanical properties in the strain rate range 5•102÷103 s-1 is the first direction of work in the laboratory of “Dynamic Materials Testing”. These tests are done using automated complexes based on the Kolsky method and its modifications for compression, tension and shearing. It is also possible to determine the fracture toughness, the characteristics of dynamic crack resistance, as well as to obtain stressstrain curves of low-density materials under uniaxial strain. Original gas guns with a caliber of 10, 20 and 57 mm are used for creation a dynamic load. The study of the behavior of materials at strain rates of 105 s-1 and higher is the second direction of work. In this case, the methods of a planewave shock experiment based on gas guns of 57 and 85 mm caliber are used. Manganine and dielectric pressure sensors, as well as laser interferometry are used for measuring the parameters of elastoplastic waves and for determining such important characteristics as impact compressibility, Hugoniot yield strength, spall strength.