scholarly journals On the formation of Friedlander waves in a compressed-gas-driven shock tube

2016 ◽  
Vol 472 (2186) ◽  
pp. 20150611 ◽  
Author(s):  
Abiy F. Tasissa ◽  
Martin Hautefeuille ◽  
John H. Fitek ◽  
Raúl A. Radovitzky
Keyword(s):  
Shock Tube ◽  
Analytical Model ◽  
Blast Waves ◽  
Rational Approach ◽  
Initial Structure ◽  
Shock Tubes ◽  
Rarefaction Waves ◽  
Wave Interactions ◽  
Compressed Gas ◽  
Volume Method

Compressed-gas-driven shock tubes have become popular as a laboratory-scale replacement for field blast tests. The well-known initial structure of the Riemann problem eventually evolves into a shock structure thought to resemble a Friedlander wave, although this remains to be demonstrated theoretically. In this paper, we develop a semi-analytical model to predict the key characteristics of pseudo blast waves forming in a shock tube: location where the wave first forms, peak over-pressure, decay time and impulse. The approach is based on combining the solutions of the two different types of wave interactions that arise in the shock tube after the family of rarefaction waves in the Riemann solution interacts with the closed end of the tube. The results of the analytical model are verified against numerical simulations obtained with a finite volume method. The model furnishes a rational approach to relate shock tube parameters to desired blast wave characteristics, and thus constitutes a useful tool for the design of shock tubes for blast testing.

Understanding the Mechanics of Blast Pressure Waves Inside a Shock-Tube: Effects of Geometry Optimization on the Blast Profile

2017 ◽  
Author(s):  
Ashkan Eslaminejad ◽  
Hesam Sarvghad-Moghaddam ◽  
Mariusz Ziejewski ◽  
Ghodrat Karami
Keyword(s):  
Shock Tube ◽  
Cross Section ◽  
Blast Waves ◽  
Head Model ◽  
Maximum Pressure ◽  
Pressure Waves ◽  
Cfd Analysis ◽  
Shock Tubes ◽  
Ansys Cfx ◽  
Negative Impulse

While many theoretical and numerical studies have been carried out to study blast induced traumatic brain injury (bTBI), validation of simulation results is still a concern due to moral issues and experimental constraints. Shock-tubes are one of the major means for replicating blast waves in a controlled medium. North Dakota State University Shock-tube (NDSUST) has been designed to simulate the blast shockwaves in an attempt to study and investigate bTBI. However, accurate replication of a blast profile in terms of the impulse and overpressure is highly dependent on the geometrical features of the shock-tube. To this end, numerical methods such as computational fluid dynamic (CFD) analysis can help to evaluate and increase the efficiency of the current shock-tubes. The NDSUST contains three major parts, namely, driver (the high pressure container), driven cone, and the chamber to setup the head model. The driver and driven cone are separated by layers of Mylar membrane. Shockwaves are defined by three pressure-time characteristics; positive phase (positive impulse), negative phase (negative impulse), and maximum pressure (overpressure). While the current NDSUST simulated most shockwave characteristics accurately, the negative impulse was observed to be considerably long. The diameter of Mylar membrane interface, the volume of the deriver, and the chamber room cross-section connected to the driven cone, were considered as possible parameters affecting the efficiency of the shock-tube. Accordingly, NDSUST was modeled in ANSYS CFX using its actual dimensions. A transient CFD analysis was carried out using ANSYS CFX to simulate the turbulent, supersonic, and compressible flow upon rupture of the Mylar membrane in order to study the pressure wave propagation inside the shock-tube. No-slip boundary conditions were chosen for the shock-tube walls. Driver and driven sections were considered as two separate domains connected using an interface. The shockwave was generated by setting the driver and driven sections at high and low pressures, respectively and running the simulation for a total time of 1 second. The primary results revealed that the current cross-section at the interface of the driven cone and the square chamber caused the pressure disruption (pressure oscillation) upon entrance of the pressure waves into the chamber room. In addition, it was concluded that the driver volume would affect the negative impulse’s duration and the negative peak pressure.

Simulation of blast waves with tailored explosive charges

1985 ◽  
Vol 158 ◽  
pp. 137-152
Author(s):  
M. Sanai ◽  
H. E. Lindberg ◽  
J. D. Colton
Keyword(s):  
Shock Tube ◽  
Charge Density ◽  
Cost Effective ◽  
Development Programme ◽  
Blast Waves ◽  
Charge Density Distribution ◽  
Test Conditions ◽  
Order Of Magnitude ◽  
Explosive Charges ◽  
Simulation Time

We have developed a compact and cost-effective shock tube to simulate the static and dynamic pressures of blast waves. The shock tube is open at both ends and is driven by high explosives distributed over a finite length of the tube near one end. The overall charge length is determined by the simulation time of interest, and the charge-density distribution is tailored to produce the pressure-waveform shape desired. For the shock tube to simulate a typical blast wave, the charge density must be highest at the charge front (closest to the test section) and gradually reduced towards the back. The resulting shock tube is an order of magnitude shorter than a conventional dynamic airblast simulator (DABS) in which concentrated explosives are used to drive the shock.Tailored charges designed using this method were built and tested in a simulation development programme sponsored by the U.S. Defense Nuclear Agency (DNA). The pressures measured for several charge distributions agreed very well with SRI's PUFF hydrocode computations and demonstrated the feasibility of the compact simulator under realistic test conditions.

Quantifying the insertion loss of hearing protection using a compressed gas shock tube

2018 ◽  
Vol 143 (3) ◽  
pp. 1934-1934
Author(s):  
Theodore F. Argo ◽  
Nate Greene ◽  
James Easter ◽  
Daniel J. Tollin ◽  
Timothy J. Walilko
Keyword(s):  
Shock Tube ◽  
Insertion Loss ◽  
Hearing Protection ◽  
Compressed Gas ◽  
Loss Of Hearing

Use of Shock Tubes for Blast Testing

2013 ◽  
Author(s):  
Chong Whang ◽  
Warren Chilton ◽  
Philemon Chan
Keyword(s):  
Shock Wave ◽  
Shock Tube ◽  
Laboratory Method ◽  
Physical Models ◽  
Test Model ◽  
Shock Tubes ◽  
Cfd Simulations ◽  
Data Comparison ◽  
Blast Overpressure ◽  
Blast Testing

A computational fluid dynamics (CFD) study was carried out with data comparison to provide guidance for the control of open shock tube wave expansion to simulate field blast loadings for the conduct of biomechanical blast overpressure tests against surrogate test models. The technique involves the addition of a diffuser to the shock tube to prevent overexpansion before the shock wave impacts the test model. Mild traumatic brain injury (mTBI) has been identified as the signature injury for the conflicts in Iraq and Afghanistan, and blast overpressure from improvised explosive devices (IEDs) has been hypothesized as a significant mTBI risk factor. Research in the understanding of the mechanism of blast induced mTBI has been very active, which requires blast testing using animal and physical models. Full scale field blast testing is expensive. The use of shock tubes is clearly a viable cost effective laboratory method with many advantages. CFD simulations with data comparison show that without a diffuser, the shock wave exiting the tube tends to over expand producing an incident waveform with a short positive duration followed by a significant negative phase that is different from a Friedlander wave. However, the overexpansion effects can be mitigated by a diffuser. Shock tube tests also support the simulation results in which a diffuser improves the waveform from the shock tube. CFD simulations were validated by shock tube tests.

Comparative Study of the Dynamic Response of Different Materials Subjected to Compressed Gas Blast Loading

2011 ◽  
Author(s):  
Brandon J. Hinz ◽  
Matthew V. Grimm ◽  
Karim H. Muci-Ku¨chler ◽  
Shawn M. Walsh
Keyword(s):  
Dynamic Response ◽  
High Speed ◽  
Mechanical Response ◽  
Blast Loading ◽  
Test Sample ◽  
Blast Waves ◽  
Small Scale ◽  
Acceleration Time Histories ◽  
Compressed Gas ◽  
Brain Tissue Damage

Understanding the dynamic response of materials under blast and impact loading is of interest for both military and civilian applications. In the case of blast loading, the mitigation characteristics of materials employed in personal protective equipment (PPE) is of particular importance. Without adequate protection, exposure of the head to blast waves may result in or contribute to brain tissue damage leading to traumatic brain injury (TBI). The development of simple but representative laboratory experiments that can be used to study the mechanical response of different materials and/or material combinations to blast loading could be very useful for the design of PPE such as helmets. This paper presents a basic experimental setup that can be conveniently used to perform such studies using small scale compressed gas blasts. An open end shock tube is employed to generate the blasts used to load flat plate samples placed in a special rigid holder. Acceleration time histories at selected locations in the sample are used to generate data to compare the dynamic response and blast mitigation effectiveness of different specimens. High speed schlieren video is used to correlate the arrival of the shock wave and air flow that follows with the motion of the test sample.

Shock Tube Design for High Fidelity Blast Wave Simulation

2015 ◽  
Author(s):  
Christopher Ostoich ◽  
Mark Rapo ◽  
Brian Powell ◽  
Humberto Sainz ◽  
Philemon Chan
Keyword(s):  
Shock Tube ◽  
Blast Wave ◽  
Laboratory Data ◽  
Blast Waves ◽  
High Fidelity ◽  
Ongoing Research ◽  
Wave Simulation ◽  
Blast Overpressure ◽  
Blast Exposure ◽  
Significant Pathway

Traumatic brain injury (TBI) has been recognized as the signature wound of the current conflicts and it has been hypothesized that blast overpressure can contribute a significant pathway to TBI. As such, there are many ongoing research efforts to understand the mechanism to blast induced TBI, which all require blast testing using physical and biological surrogates either in the field or in the laboratory. The use of shock tubes to generate blast-like pressure waves in a laboratory can effectively produce the large amounts of data needed for research into blast induced TBI. A combined analytical, computational, and experimental approach was developed to design an advanced shock tube capable of generating high quality out-of-tube blast waves. The selected tube design was fabricated and laboratory tests at various blast wave levels were conducted. Comparisons of tube-generated laboratory data with explosive-generated field data indicated that the shock tube could accurately reproduce blast wave loading on test surrogates. High fidelity blast wave simulation in the laboratory presents an avenue to rapidly and inexpensively generate the large volumes of data necessary to validate and develop theories linking blast exposure to TBI.

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