Shock Tube Design for High Fidelity Blast Wave Simulation

Author(s):  
Christopher Ostoich ◽  
Mark Rapo ◽  
Brian Powell ◽  
Humberto Sainz ◽  
Philemon Chan

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.

Author(s):  
Aravind Sundaramurthy ◽  
Raj K. Gupta ◽  
Namas Chandra

Detonation of a high explosive (HE) produces shock-blast wave, noise, shrapnel, and gaseous product; while direct exposure to blast is a concern near the epicenter; shock-blast can affect subjects even at farther distances. The latter is characterized as the primary blast with blast overpressure, time duration, and impulse as shock-blast wave parameters (SWPs). These parameters in turn are a function of the strength of the HE and the distance from the epicenter. It is extremely important to carefully design and operate the shock tube to produce a field relevant SWPs. In this work, we examine the relationship between shock tube adjustable parameters (SAPs) and SWPs to deduce relationship that can be used to control the blast profile and emulate the field conditions. In order to determine these relationships, 30 experiments by varying the membrane thickness, breech length (66.68 to 1209.68 mm) and measurement location was performed. Finally, ConWep was utilized for the comparison of TNT shock-blast profiles with the profiles obtained from shock tube. From these experiments, we observed the following: (a) burst pressure increases with increase in the number of membrane used (membrane thickness) and does not vary significantly with increase in the breech length; (b) within the test section, overpressure and Mach number increases linearly with increase in the burst pressure; however, positive time duration increases with increase in the breech length; (c) near the exit of the shock tube, there is a significant reduction in the positive time duration (PTD) regardless of the breech length.


2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Jacques Massoni ◽  
Laurent Biamino ◽  
Georges Jourdan ◽  
Ozer Igra ◽  
Lazhar Houas

The present work shows that weak blast waves that are considered as being harmless can turn to become fatal upon their reflections from walls and corners inside a building. In the experimental part, weak blast waves were generated by using an open-end shock tube. A three level building model was placed in vicinity to the open-end of the used shock tube. The evolved wave pattern inside the building rooms was recorded by a sequence of schlieren photographs; also pressure histories were recorded on the rooms' walls. In addition, numerical simulations of the evolved flow field inside the building were conducted. The good agreement obtained between numerical and experimental results shows the potential of the used code for identifying safe and dangerous places inside the building rooms penetrated by the weak blast wave.


Author(s):  
Mark Rapo ◽  
Chong Whang ◽  
Philemon Chan

Due to the great concern that blast overpressure can cause mild traumatic brain injury (mTBI), there is strong interest in putting sensors on warfighters to collect theater data for correlation with medical outcomes. One approach is to mount multiple pressure sensors on the warfighter to measure the blast overpressure environment. An event recognition algorithm that is based on the sensor data recordings is needed to reconstruct the incident blast wave that impacts the warfighter. Blast impingement pressure on an object is highly dependent on the angle of incidence at the point of impact; shadowing and recirculating flow effects can complicate the sensor data pattern. Using computational fluid dynamics (CFD) simulation, the present work demonstrates that for a warfighter in an upright posture in an open blast environment, a three-sensor event recognition algorithm can be developed to reconstruct the incident blast wave (generally characterized as a Friedlander wave). Three-dimensional Navier-Stokes’ based CFD simulations were performed to predict pressure recordings at the three sensor locations for a range of horizontal blast waves impacting the warfighter at all angles of incidence. The predicted peak pressures and durations were recorded and stored in a lookup table. Using an inverse problem approach, it was found that based on the three-sensor data recorded for each event, an algorithm exists for reconstructing the blast incident wave. The established event recognition algorithm is limited to warfighters with upright posture in open blast. Work is being continued to generalize and extend the method to include complex blasts involving multiple reflections and other posture orientations.


2021 ◽  
Author(s):  
Suthee Wiri ◽  
Charles Needham ◽  
David Ortley ◽  
Josh Duckworth ◽  
Andrea Gonzales ◽  
...  

ABSTRACT Introduction The Office of Naval Research sponsored the Blast Load Assessment-Sense and Test program to develop a rapid, in-field solution that could be used by team leaders, commanders, and medical personnel to make science-based stand-down decisions for service members exposed to blast overpressure. However, a critical challenge to this goal was the reliable interpretation of surface pressure data collected by body-worn blast sensors in both combat and combat training scenarios. Without an appropriate standardized metric, exposures from different blast events cannot be compared and accumulated in a service member’s unique blast exposure profile. In response to these challenges, we developed the Fast Automated Signal Transformation, or FAST, algorithm to automate the processing of large amounts of pressure–time data collected by blast sensors and provide a rapid, reliable approximation of the incident blast parameters without user intervention. This paper describes the performance of the FAST algorithms developed to approximate incident blast metrics from high-explosive sources using only data from body-mounted blast sensors. Methods and Materials Incident pressure was chosen as the standardized output metric because it provides a physiologically relevant estimate of the exposure to blast that can be compared across multiple events. In addition, incident pressure serves as an ideal metric because it is not directionally dependent or affected by the orientation of the operator. The FAST algorithms also preprocess data and automatically flag “not real” traces that might not be from blasts events (false positives). Elimination of any “not real” blast waveforms is essential to avoid skewing the results of subsequent analyses. To evaluate the performance of the FAST algorithms, the FAST results were compared to (1) experimentally measured pressures and (2) results from high-fidelity numerical simulations for three representative real-world events. Results The FAST results were in good agreement with both experimental data and high-fidelity simulations for the three case studies analyzed. The first case study evaluated the performance of FAST with respect to body shielding. The predicted incident pressure by FAST for a surrogate facing the charge, side on to charge, and facing away from the charge was examined. The second case study evaluated the performance of FAST with respect to an irregular charge compared to both pressure probes and results from high-fidelity simulations. The third case study demonstrated the utility of FAST for detonations inside structures where reflections from nearby surfaces can significantly alter the incident pressure. Overall, FAST predictions accounted for the reflections, providing a pressure estimate typically within 20% of the anticipated value. Conclusions This paper presents a standardized approach—the FAST algorithms—to analyze body-mounted blast sensor data. FAST algorithms account for the effects of shock interactions with the body to produce an estimate of incident blast conditions, allowing for direct comparison of individual exposure from different blast events. The continuing development of FAST algorithms will include heavy weapons, providing a singular capability to rapidly interpret body-worn sensor data, and provide standard output for analysis of an individual’s unique blast exposure profile.


Author(s):  
Jihui Geng ◽  
J. Kelly Thomas

A key component of explosion hazard evaluations is the determination of standoffs to given blast overpressure values. Many such evaluations use a simplified methodology that assumes that the blast wave propagates from the explosion source to the target location without interacting with intervening buildings or structures (i.e., without blast wave shielding). This is obviously a perfectly acceptable approach for a screening study, but blast wave shielding effects can be significant in certain circumstances (e.g., within a building group). A methodology was proposed by the UK Health & Safety Laboratory (HSL) in 2001 to account for blast shielding due to buildings/structures between the explosion source and target location. The HSL methodology is based on the blast waves generated by high explosives (HE). This paper extends the blast shielding evaluation to blast waves generated from pressure vessel bursts (PVB) and vapor cloud explosions (VCE). The influences of blast wave shape parameters (overpressure, duration and rise time) on blast wave shielding are examined. The results indicate that the degree of blast shielding is strongly dependent on the source of the blast wave (i.e., on the blast wave shape parameters) and that the shielding factors obtained with HE blast waves are not always directly applicable for PVB and VCE blast waves.


Author(s):  
X. Gary Tan ◽  
Amit Bagchi

Current understanding of blast wave transmission and mechanism of primary traumatic brain injury (TBI) and the role of helmet is incomplete thus limiting the development of protection and therapeutic measures. Combat helmets are usually designed based on costly and time consuming laboratory tests, firing range, and forensic data. Until now advanced medical imaging and computational modeling tools have not been adequately utilized in the design and optimization of combat helmets. The goal of this work is to develop high fidelity computational tools, representative virtual human head and combat helmet models that could help in the design of next generation helmets with improved blast and ballistic protection. We explore different helmet configurations to investigate blast induced brain biomechanics and understand the protection role of helmet by utilizing an integrated experimental and computational method. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we solved the dynamic problem of helmet and head under the blast exposure. Experimental shock tube tests of the head surrogate provide benchmark quality data and were used for the validation of computational models. The full-scale computational NRL head-neck model with a combat helmet provides physical quantities such as acceleration, pressure, strain, and energy to blast loads thus provides a more complete understanding of the conditions that may contribute to TBI. This paper discusses possible pathways of blast energy transmission to the brain and the effectiveness of helmet systems at blast loads. The existing high-fidelity image-based finite element (FE) head model was applied to investigate the influence of helmet configuration, suspension pads, and shell material stiffness. The two-phase flow model was developed to simulate the helium-air shock wave interaction with the helmeted head in the shock tube. The main contribution was the elucidation of blast wave brain injury pathways, including wave focusing in ocular cavities and the back of head under the helmet, the effect of neck, and the frequency spectrum entering the brain through the helmet and head. The suspension material was seen to significantly affect the ICP results and energy transmission. These findings can be used to design next generation helmets including helmet shape, suspension system, and eye protection.


2021 ◽  
pp. bmjmilitary-2021-001796
Author(s):  
J W Denny ◽  
A S Dickinson ◽  
G S Langdon

‘Primary’ blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. With continued experimental focus on PBI mechanisms, recently on blast traumatic brain injury, meaningful test outcomes rely on appropriate simulated conditions. Selected PBI predictive criteria (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) are combined and plotted to provide rationale for generating clinically relevant loading conditions. Using blast engineering theory, explosion characteristics including blast wave parameters and fireball dimensions were calculated for a range of charge masses assuming hemispherical surface detonations and compared with PBI criteria. While many experimental loading conditions are achievable, this analysis demonstrated limits that should be observed to ensure loading is clinically relevant, realistic and practical. For PBI outcomes sensitive only to blast overpressure, blast scaled distance was demonstrated to be a useful parameter for guiding experimental design as it permits flexibility for different experimental set-ups. This analysis revealed that blast waves should correspond to blast scaled distances of 1.75<Z<6.0 to generate loading conditions found outside the fireball and of clinical relevance to a range of PBIs. Blast waves with positive phase durations (2–10 ms) are more practical to achieve through experimental approaches, while representing realistic threats such as improvised explosive devices (ie, 1–50 kg trinitrotoluene equivalent). These guidelines can be used by researchers to inform the design of appropriate blast loading conditions in PBI experimental investigations.


Author(s):  
Suguru Kushida ◽  
Kengo Asada ◽  
Kozo Fujii ◽  
Tomoaki Tatsukawa ◽  
Kazuyuki Sakamoto

Abstract Reduction methods of the jet flow associated with simulated blast waves by blast wave simulators are investigated by computational simulations. First, the cause of the jet flow is discussed. After that, the influence of the nozzle angle and the volume of the driver section on the jet flow are investigated. The obtained results show that the jet flow is caused by vortices which are generated at the edge of the nozzle and that the jet can be reduced by decreasing the driver section. Furthermore, the nozzle with the moderate angle reduces the jet flow near the nozzle exit and the nozzle with the widest angle reduces the jet flow far from the nozzle exit. These results indicate reducing the driver section and using the proper nozzle angle according to the distance from the nozzle exit are effective for reducing the jet flow.


2021 ◽  
Author(s):  
Ann Nakashima ◽  
Oshin Vartanian ◽  
Shawn G Rhind ◽  
Kristen King ◽  
Catherine Tenn ◽  
...  

ABSTRACT Introduction Recently, there has been increasing concern about the adverse health effects of long-term occupational exposure to low-level blast in military personnel. Occupational blast exposure occurs routinely in garrison through use of armaments and controlled blast detonations. In the current study, we focused on a population of breaching instructors and range staff. Breaching is a tactical technique that is used to gain entry into closed spaces, often through the use of explosives. Materials and Methods Initial measurements of blast overpressure collected during breaching courses found that up to 10% of the blasts for range staff and up to 32% of the blasts for instructors exceeded the recommended 3 psi exposure limit. Using a cross-sectional design, we used tests of balance, ataxia, and hearing to compare a sample of breachers (n = 19) to age-and sex-matched military controls (n = 19). Results There were no significant differences between the two groups on the balance and ataxia tests, although the average scores of both groups were lower than would be expected in a normative population. The prevalence of hearing loss was low in the breacher group (4 of 19), and hearing thresholds were not significantly different from the controls. However, the prevalence of self-reported tinnitus was significantly higher in the breacher group (12 of 19) compared with the controls (4 of 19), and all breachers who were identified as having hearing loss also reported tinnitus. Conclusions Our results suggest that basic tests of balance, ataxia, and hearing on their own were not sensitive to the effects of long-term occupational exposure to low-level blast. Some of the blast exposure levels exceeded limits, and there was a significant association of exposure with tinnitus. Future studies should supplement with additional information including exposure history and functional hearing assessments. These findings should be considered in the design of future acute and longitudinal studies of low-level blast exposure.


2020 ◽  
Vol 10 (20) ◽  
pp. 7193
Author(s):  
Maciej Skotak ◽  
Jonathan Salib ◽  
Anthony Misistia ◽  
Arturo Cardenas ◽  
Eren Alay ◽  
...  

This study demonstrates the orientation and the "shape factor" have pronounced effects on the development of the localized pressure fields inside of the helmet. We used anatomically accurate headform to evaluate four modern combat helmets under blast loading conditions in the shock tube. The Advanced Combat Helmet (ACH) is used to capture the effect of the orientation on pressure under the helmet. The three modern combat helmets: Enhanced Combat Helmet (ECH), Ops-Core, and Airframe, were tested in frontal orientation to determine the effect of helmet geometry. Using the unhelmeted headform data as a reference, we characterized pressure distribution inside each helmet and identified pressure focal points. The nature of these localized “hot spots” is different than the elevated pressure in the parietal region of the headform under the helmet widely recognized as the under-wash effect also observed in our tests. It is the first experimental study which indicates that the helmet presence increased the pressure experienced by the eyes and the forehead (glabella). Pressure fingerprinting using an array of sensors combined with the application of principle component analysis (PCA) helped elucidate the subtle differences between helmets.


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