An analysis of the particle trajectories in spherical blast waves reflected from real and ideal surfaces

1981 ◽  
Vol 59 (10) ◽  
pp. 1380-1390 ◽  
Author(s):  
J. M. Dewey ◽  
D. J. McMillin
Keyword(s):  
High Speed ◽  
Ground Surface ◽  
Blast Waves ◽  
Particle Trajectories ◽  
Shock Interactions ◽  
Pressure Time ◽  
Time Histories ◽  
Particle Velocities ◽  
Spherical Shock ◽  
Fixed Times

High speed photogrammetry has been used to measure the particle trajectories in the flows resulting from the interaction of two identical explosively produced spherical shock waves. It is postulated that the interaction simulated the reflection of a spherical shock from an ideal nonenergy-absorbing surface. The "ideal" reflections were compared with reflections from two types of ground surface. From the observed particle trajectories the particle velocities, gas densities, and hydrostatic, dynamic, and total pressures in the complex air flows behind the shock interactions have been computed. These flows are described as two dimensional fields at fixed times and as time histories at fixed locations. The Mach stem shocks at the ground surfaces were weaker than those at corresponding positions near the interaction planes, but the magnitudes of the flow properties in these waves decreased more slowly and, at later times, became greater than those in the waves at the interaction planes. Computed pressure–time histories were compared to measurements made using electronic transducers and good agreement was found.

Gaseous Deflagration in Piping: Part 1 — Experimental Observations

2017 ◽  
Author(s):  
Thomas C. Ligon ◽  
David J. Gross ◽  
John C. Minichiello
Keyword(s):  
High Speed ◽  
Structural Response ◽  
Analysis And Design ◽  
Flame Acceleration ◽  
Pressure Time ◽  
Piping Systems ◽  
Time Histories ◽  
Short Test ◽  
Semi Empirical ◽  
Measured Pressure

The focus of this paper is on gaseous deflagration in piping systems and the corresponding implications on piping analysis and design. Unlike stable detonations that propagate at a constant speed and whose pressure-time histories can in some cases be predicted analytically, deflagration flame speeds and pressure-time histories are transient and depend on both the gas mixture and geometry of the pipe. This paper presents pressure and pipe strain data from gaseous deflagration experiments in long and short test apparatuses fabricated from either 2-inch or 4-inch diameter pipes. These data are used to demonstrate a spectrum of measured pressure-time histories and corresponding pipe response. It is concluded that deflagrations can be categorized as either “high” or “slow” speed with respect to pipe response. Slow deflagrations can be treated as quasi-static pressurizations, but high speed deflagrations can generate shock waves that dynamically excite the pipe. The existence of a transition from quasi-static to dynamic response has ramifications in regards to piping structural analysis and design, and a method for predicting the expected deflagration structural response using a semi-empirical flame acceleration model is proposed.

scholarly journals Numerical investigation into the influence of cubicle positioning in large-scale explosive arena trials

2016 ◽  
Vol 7 (4) ◽  
pp. 547-560 ◽  
Author(s):  
Thomas Payne ◽  
Andrew Williams ◽  
Thomas Worfolk ◽  
Samuel Rigby
Keyword(s):  
Large Scale ◽  
Central Charge ◽  
Free Field ◽  
Separation Distance ◽  
Blast Waves ◽  
Positive Phase ◽  
Pressure Time ◽  
Field Peak ◽  
Time Histories ◽  
Different Levels

In arena blast testing, a common and economical practice employed is to distribute several targets radially around a central charge. However, if these targets are positioned too proximally, reflections and diffractions of blast waves off neighbouring cubicles can affect the nature of expected blast loading. Computational fluid dynamics software has been used through an extensive series of simulations to identify the levels of interference in incident pressure–time histories with and without an obstructing target present. The data were post-processed to identify the Cartesian co-ordinates in which different levels of interference in peak incident overpressure and incident positive phase impulse were achieved. The results indicated that in all cases, there was a greater interference in peak incident overpressure than incident positive phase impulse values directly proximal to the target but, at greater separations, significant differences in incident positive phase impulse existed where peak incident overpressure had returned to free-field equivalent magnitudes. When compared with the established ‘rules of thumb’ for cubicle placement, for targets at different stand-off ranges, an angle of 45° to the rear cubicle still holds some practical relevance, although it is too acute to cover all interference effects. For targets positioned at the same stand-off range, a separation distance of two cubicle widths is generally too conservative and, in many cases, more cubicles can be positioned around the charge. A bespoke recommendation table has been presented for targets at stand-off ranges between 15 and 50 m to allow users to identify the minimum distance from a target at which obstructed-field peak incident overpressure and incident positive phase impulse values differ negligibly from free-field equivalents.

Unsteady Radial Flow of Gas Through Porous Media—Variable Viscosity and Compressibility

1956 ◽  
Vol 23 (1) ◽  
pp. 128-132
Author(s):  
J. S. Aronofsky ◽  
J. D. Porter
Keyword(s):  
Porous Media ◽  
High Speed ◽  
Gas Flow ◽  
Variable Viscosity ◽  
Substantial Effect ◽  
Massachusetts Institute Of Technology ◽  
Computer Laboratory ◽  
Pressure Time ◽  
Time Histories ◽  
Institute Of Technology

Abstract Calculations of pressure-time histories and flow rates are presented for radial unsteady flow of gases through porous media. Some nonideal gas properties are considered by expressing gas viscosity and gas compressibility (z-factor) as simple functions of pressure. These calculations were obtained by using the high-speed, electronic computer called “Whirlwind” which is located at the Digital Computer Laboratory of the Massachusetts Institute of Technology. The results demonstrate that variable viscosity and compressibility can exert a substantial effect on transient gas-flow systems. A simple means is suggested for estimating the velocity of gas flowing across an inner radial boundary into a hole when the gas pressure is held constant at that boundary.

The properties of a blast wave obtained from an analysis of the particle trajectories

1971 ◽  
Vol 324 (1558) ◽  
pp. 275-299 ◽  
Keyword(s):  
Blast Wave ◽  
High Speed ◽  
Time Derivative ◽  
Blast Waves ◽  
High Speed Photography ◽  
Flow Properties ◽  
Particle Trajectories ◽  
Adiabatic Flow ◽  
First Time ◽  
Shock Fronts

It is shown that all of the flow properties within an unsteady shock wave of intermediate strength can be determined by an analysis of the experimentally observed particle trajec­tories. The analysis has been applied to the blast waves from two large trinitrotoluene (t. n. t.) explosions. The particle trajectories were observed by high-speed photography of smoke tracers formed close to the charges immediately before detonation. The density throughout the flow was determined by application of the Lagrangian conservation of mass equation. This was then used to calculate the pressure, assuming adiabatic flow for each air element between shock fronts. The temperature and sound speed throughout the flow were found from the pressure and density, assuming a perfect gas equation of state. The particle velocity within the flow was obtained from the time derivative of the observed particle trajectories. The results have been compared with other blast measurements and with theoretical calcula­tions. It is estimated that the technique gives the flow properties to an accuracy comparable with that for other forms of measurement, namely, 5 to 10%. This is the first time that it has been possible to describe all the properties of a blast wave based on experimental measurements, only.

Study on Edge Contact Area and Surface Integrity of Workpiece in Point Grinding Process

2009 ◽  
Vol 407-408 ◽  
pp. 577-581
Author(s):  
Shi Chao Xiu ◽  
Zhi Jie Geng ◽  
Guang Qi Cai
Keyword(s):  
Surface Integrity ◽  
Contact Area ◽  
High Speed ◽  
Ground Surface ◽  
Depth Of Cut ◽  
Grinding Wheel ◽  
Grinding Process ◽  
Edge Contact ◽  
Cylindrical Grinding ◽  
Theoretic Foundations

During cylindrical grinding process, the geometric configuration and size of the edge contact area between the grinding wheel and workpiece have the heavy effects on the workpiece surface integrity. In consideration of the differences between the point grinding and the conventional high speed cylindrical grinding, the geometric and mathematic models of the edge contact area in point grinding were established. Based on the models, the numerical simulation for the edge contact area was performed. By means of the point grinding experiment, the effect mechanism of the edge contact area on the ground surface integrity was investigated. These will offer the applied theoretic foundations for optimizing the point grinding angles, depth of cut, wheel and workpiece speed, geometrical configuration and size of CBN wheel and some other grinding parameters in point grinding process.

An Experimental Investigation of the Auto-Ignition Properties of Two C5 Esters: Methyl Butanoate and Butyl Methanoate

2007 ◽  
Author(s):  
Stephen M. Walton ◽  
Carlos Perez ◽  
Margaret S. Wooldridge
Keyword(s):  
Low Temperature ◽  
High Speed ◽  
Combustion Engine ◽  
Low Temperature Combustion ◽  
Moderate Pressure ◽  
Molecular Weights ◽  
Auto Ignition ◽  
Methyl Butanoate ◽  
Temperature Combustion ◽  
Time Histories

Ignition studies of two small esters were performed using a rapid compression facility (RCF). The esters (methyl butanoate and butyl methanoate) were chosen to have matching molecular weights, and C:H:O ratios, while varying the lengths of the constituent alkyl chains. The effect of functional group size on ignition delay time was investigated using pressure time-histories and high speed digital imaging. The mixtures studied covered a range of conditions relevant to oxygenated fuels and fuel additives, including bio-derived fuels. Low temperature and moderate pressure conditions were selected for study due to their relevance to advanced low temperature combustion strategies, and internal combustion engine conditions. The results are discussed in terms of the reaction pathways affecting the ignition properties.

Nonlinear Wave Crest Distribution on a Vertical Breakwater

2018 ◽  
Author(s):  
Valentina Laface ◽  
Giovanni Malara ◽  
Felice Arena ◽  
Ioannis A. Kougioumtzoglou ◽  
Alessandra Romolo
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Vertical Wall ◽  
Surface Elevation ◽  
Wave Crest ◽  
Height Distribution ◽  
Free Surface Elevation ◽  
Pressure Transducers ◽  
Pressure Time ◽  
Time Histories

The paper addresses the problem of deriving the nonlinear, up to the second order, crest wave height probability distribution in front of a vertical wall under the assumption of finite spectral bandwidth, finite water depth and long-crested waves. The distribution is derived by relying on the Quasi-Deterministic representation of the free surface elevation in front of the vertical wall. The theoretical results are compared against experimental data obtained by utilizing a compressive sensing algorithm for reconstructing the free surface elevation in front of the wall. The reconstruction is pursued by starting from recorded wave pressure time histories obtained by utilizing a row of pressure transducers located at various levels. The comparison shows that there is an excellent agreement between the proposed distribution and the experimental data and confirm the deviation of the crest height distribution from the Rayleigh one.

Ultra-High Speed Grinding Using a CBN Wheel for a Mirror-Like Surface Finish

2005 ◽  
Vol 291-292 ◽  
pp. 67-72 ◽  
Author(s):  
M. Ota ◽  
T. Nakayama ◽  
K. Takashima ◽  
H. Watanabe
Keyword(s):  
Surface Finish ◽  
High Speed ◽  
High Efficiency ◽  
Ground Surface ◽  
Machining Process ◽  
Grinding Wheel ◽  
Cbn Wheel ◽  
Ultra High Speed ◽  
High Speed Grinding ◽  
Grinding Conditions

There are strong demands for a machining process capable of reducing the surface roughness of sliding parts, such as auto parts and other components, with high efficiency. In this work, we attempted to grind hardened steel to a mirror-like surface finish with high efficiency using an ultra-high speed grinding process. In the present study, we examined the effects of the work speed and the grinding wheel grain size in an effort to optimize the grinding conditions for accomplishing mirror-like surface grinding with high efficiency. The results showed that increasing the work speed, while keeping grinding efficiency constant, was effective in reducing the work affected layer and that the grinding force of a #200 CBN wheel was lower than that of a #80 CBN wheel. Based on these results, a high-efficiency grinding step with optimized grinding conditions was selected that achieved excellent ground surface quality with a mirror-like finish.

Shock waves in microchannels

2013 ◽  
Vol 724 ◽  
pp. 259-283 ◽  
Author(s):  
G. Mirshekari ◽  
M. Brouillette ◽  
J. Giordano ◽  
C. Hébert ◽  
J.-D. Parisse ◽  
...  
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Large Scale ◽  
Numerical Models ◽  
Incident Shock ◽  
Incident Shock Wave ◽  
Navier Stokes ◽  
Shock Attenuation ◽  
Pressure Time ◽  
Time Histories

AbstractA fully instrumented microscale shock tube, believed to be the smallest to date, has been fabricated and tested. This facility is used to study the transmission of a shock wave, produced in a large (37 mm) shock tube, into a 34 $\mathrm{\mu} \mathrm{m} $ hydraulic diameter and 2 mm long microchannel. Pressure microsensors of a novel design, with gigahertz bandwidth, are used to obtain pressure–time histories of the microchannel shock wave at five axial stations. In all cases the transmitted shock wave is found to be weaker than the incident shock wave, and is observed to decay both in pressure and velocity as it propagates down the microchannel. These results are compared with various analytical and numerical models, and the best agreement is obtained with a Navier–Stokes computational fluid dynamics computation, which assumes a no-slip isothermal wall boundary condition; good agreement is also obtained with a simple shock tube laminar boundary layer model. It is also found that the flow developing within the microchannel is highly dependent on conditions at the microchannel entrance, which control the mass flux entering into the device. Regardless of the micrometre dimensions of the present facility, shock wave propagation in a microchannel of that scale exhibits a behaviour similar to that observed in large-scale facilities operated at low pressures, and the shock attenuation can be explained in terms of accepted laminar boundary models.

Modification of seismograph records for effects of local soil conditions

1972 ◽  
Vol 62 (6) ◽  
pp. 1649-1664 ◽  
Author(s):  
P. Schnabel ◽  
H. Bolton Seed ◽  
J. Lysmer
Keyword(s):  
San Francisco ◽  
Ground Surface ◽  
Soil Conditions ◽  
Local Soil ◽  
Geological Conditions ◽  
Soil Deposits ◽  
Time Histories ◽  
Seismic Records ◽  
Local Soil Conditions ◽  
Good Agreement

abstract A procedure for modifying the time histories of seismic records for the effect of local soil conditions is presented. The method is based on a conventional one-dimensional wave-propagation approach with equivalent linear soil properties, extended to practical use for transient motions through the Fast Fourier technique. The validity of the approach is tested against the motions recorded at four soil sites and one rock site during the 1957 San Francisco earthquake. The good agreement between the computed and recorded values indicates that rock motions can be computed from motions recorded on soil deposits, and that the computed rock motions in turn can be used to predict the motion that would have been recorded under different soil and geological conditions. The method is also used to evaluate the probable rock motions in the vicinity of El Centro in the earthquake of 1940 and the ground surface motions that could have been developed on various soil conditions in the same general area.

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