Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2016 Numerical modeling and characterization of blast waves for application in blast-induced mild traumatic brain injury research Michael Phillips Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Aerospace Engineering Commons Recommended Citation Phillips, Michael, "Numerical modeling and characterization of blast waves for application in blast-induced mild traumatic brain injury research" (2016). Graduate Theses and Dissertations. 15789. https://lib.dr.iastate.edu/etd/15789 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Numerical modeling and characterization of blast waves for application in blast-induced mild traumatic brain injury research by Michael G. Phillips A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Aerospace Engineering Program of Study Committee: Jonathan D. Regele, Major Professor Alric P. Rothmayer Thomas Ward Iowa State University Ames, Iowa 2016 Copyright © Michael G. Phillips, 2016. All rights reserved. ii TABLE OF CONTENTS LIST OF TABLES . iv LIST OF FIGURES . v ACKNOWLEDGEMENTS . vii ABSTRACT . viii CHAPTER 1. MOTIVATION AND BACKGROUND . 1 1.1 Energy Distribution of Blast Waves in 1D and 3D . .1 1.2 Shock Tube as an Alternative Blast Wave Source . .2 1.3 Shock Tube Blast Wave Important Design Parameters . .3 1.3.1 Internal Versus External Specimen Placement . .3 1.3.2 Changing Driver Section Gas and Explosives for Different Blast Profiles .4 1.3.3 Simple Wave vs Complex Wave . .4 1.3.4 Shock Tube Geometric Influence . .4 1.3.5 Temperature Difference Between Explosive and Driven Gas . .5 1.4 Application of Shock Tube Produced Blast Waves in Medical Research . .5 1.5 Mitigate Blast Wave Obstruction, Experimental Mounts, Restraints, and Instru- mentation . .6 CHAPTER 2. ELUCIDATING THE ROLE OF COMPRESSION WAVESAND IMPACT DURATION FOR GENERATING MILD TRAUMATIC BRAIN INJURY IN RATS . 8 2.1 Introduction . .9 2.2 Numerical Approach . 10 iii 2.3 Results . 12 2.3.1 Compression Wave Formation . 12 2.3.2 Analyzing Blast Wave Behavior Along the Centerline . 12 2.3.3 Comparing Numerical and Experimental Results . 14 2.4 Conclusion . 17 CHAPTER 3. BLAST WAVE CHARACTERIZATION USING NUMERICAL MODEL- ING FOR APPLICATION IN TRAUMATIC BRAIN INJURY RESEARCH . 18 3.1 Introduction . 18 3.2 Problem Statement . 21 3.2.1 Nomenclature . 21 3.2.2 Governing Equations . 23 3.2.3 Computational Geometry . 25 3.2.4 Numerical Methods . 26 3.3 Results . 26 3.3.1 General Behavior . 26 3.3.2 Centerline Gauge Static Pressure Attenuation . 29 3.3.3 Centerline Blast Wave Gauge Static and Dynamic Pressure . 29 3.3.4 Off-Axis Blast Wave Static and Dynamic Pressure Behavior . 33 3.4 Conclusion . 40 CHAPTER 4. SUMMARY OF CONTRIBUTIONS . 41 4.1 General Conclusions . 41 4.2 Future Work . 42 APPENDIX A. TRACKING BLAST WAVE FRONT . 43 A.1 Curvature of the Blast Wave . 43 A.2 Planarity Normal-Curved Transition . 45 BIBLIOGRAPHY . 48 iv LIST OF TABLES Table 3.1 Non-dimensional variable declarations (prime quantities indicate di- mensional quantities) . 24 v LIST OF FIGURES Figure 2.1 A two dimensional representation shows the geometric configuration of the problem. 10 Figure 2.2 Domain pressure profile shown at different times provides initial con- ditions and follows the shock and expansion wave development and propagation. 13 Figure 2.3 A log-log plot shows converging simulation results with increasing grid resolution. 14 Figure 2.4 An x-t pressure contour plot shows the evolution of the shock and ex- pansion waves after the diaphragm bursts. 15 Figure 2.5 A line plot provides a comparison between experiment and simulation. 16 Figure 3.1 Simple Blast Wave Static Pressure Profile . 19 Figure 3.2 2D Shock Tube Experimental Model . 21 Figure 3.3 Non-Dimensional Simplified Domain, Distances Relative to Tube Inner Radius, R0 .................................... 25 Figure 3.4 2D Axisymmetric Pressure Contour Through Time for PR = 3 . 27 Figure 3.5 Shock Wave Growth and Development Downstream of Tube Exit for Pressure Ratios 3(a) and 20(b) . 28 Figure 3.6 Centerline Shock Wave Pressure Attenuation . 29 Figure 3.7 Eulerian Static and Dynamic Pressure Along Centerline for Multiple Pressure Ratios, PR = 3, 5, 10, 20 . 30 Figure 3.8 Centerline Ratio between Peak Dynamic Over Pressure and Peak Static Over Pressure for PR = 3,5,10,20 . 32 vi Figure 3.9 Centerline Blast Wave Parameters, Pressure Ratio is 3 . 33 Figure 3.10 Blast wave tracked at 6 locations downstream of tube exit, Red dots represent Eulerian pressure probes of shock locations . 34 Figure 3.11 Off-axis (2D axisymmetric) Eulerian gauge static and dynamic pressure histories, pressure ratio is 3 . 35 Figure 3.12 Static Over Pressure Wave Parameters for PR = 3 . 37 Figure 3.13 Dynamic Pressure, Wave Parameters for PR = 3 . 38 Figure 3.14 Ratio of Dynamic Over Pressure Impulse and Static Peak Over Pressure Impulse for PR = 3 . 39 Figure A.1 Original Shock Location vs Parabola Correction at T ime = 5:25 . 44 Figure A.2 Parabola and Fitted Function Corrected Shock Curvature and Location at T ime = 5:25 ................................. 45 Figure A.3 Tracking Curved-Normal Transition Region of Shock Wave (Allocating Locations Experiencing Wave Planarity) . 46 Figure A.4 2D Axisymmetric Blast Wave Front Curvature for Pressure Ratio of 3 . 46 vii ACKNOWLEDGEMENTS The culmination of the research I have performed over the previous years was influenced by many people. I would like to thank Dr. Jonathan Regele for the guidance and expertise while navigating an interesting research project. He provided structure while encouraging the investigation of new approaches to solve problems. His encouragement played a vital role in my decision to pursue graduate school. I would like to thank my committee members, Dr. Alric Rothmayer and Dr. Thomas Ward, for their contribution and investigative ideas for my research project. I owe a large debt to my family for all the support, advice, and encouragement throughout the extent of my research. I can’t count the number of phone calls and text messages. I’d like to thank the members of my research team: Mohamad Aslani, Wyatt Hagen, Dan Garrick, Zahra Hosseinzadeh-Nik, Fynn Reinbacher, and Ryan Goetsch for their ideas, sup- port, and friendship throughout graduate school. Lastly, I’d like to thank all of my friends and acquaintances I have had the pleasure of meeting in my time at Iowa State. I enjoyed my years in Ames and will remember these experiences largely due to these friendships. viii ABSTRACT Human exposure to blast waves, including blast-induced traumatic brain injury, is a de- veloping field in medical research. Experiments with explosives have many disadvantages including safety, cost, and required area for trials. Shock tubes provide an alternative method to produce free field blast wave profiles. A compressed nitrogen shock tube experiment in- strumented with static and reflective pressure taps is modeled using a numerical simulation. The geometry of the numerical model is simplified and blast wave characteristics are derived based upon static and pressure profiles. The pressure profiles are analyzed along the shock tube centerline and radially away from the tube axis. The blast wave parameters found from the pressure profiles provide guidelines for spatial location of a specimen. The location could be based on multiple parameters and provides a distribution of anticipated pressure profiles experience by the specimen. 1 CHAPTER 1. MOTIVATION AND BACKGROUND Blast waves are created any time an explosive is detonated. An open field, simple blast wave is represented by a shock wave followed directly by an expansion wave. The combina- tion of these two waves create a relative static over pressure followed by a duration of negative relative static pressure which pulls mass back toward the center of the explosion. Explosives have a variety of applications from recreation, to tools used for demolition, to their use as propellants. Unfortunately, improvised explosive devices have seen an increase in usage in terrorist attacks [25]. The blast waves created by these devices primarily cause injury with the static over pressure wave which emanates spherically from the explosive source [44]. The parts of the human body which are influenced greatly by the over pressure are the regions filled by air including the lungs, digestive system, and middle ear [15], [41]. Air is a highly compressible gas while other materials in the body, like muscle, bone, and water, are much less compressible. The brain remains a highly sensitive organ and suffers injury from even small variations of pressure inside the skull and research on mild traumatic brain injury has developed increasing motivation [42]. A shock tube is utilized for recreating an open field blast wave. The first document shock tube was created in the late 1800’s [53] and was explo- sive driven. A compressed nitrogen experimental shock tube is numerically modeled. The numerical model is extended to a compressed air shock tube which is used to characterize the development of the blast wave upon expulsion from the shock tube exit. 1.1 Energy Distribution of Blast Waves in 1D and 3D The strength and affected radius of the blast wave produced in an explosion is dependent on the amount of chemical energy which is converted to internal and kinetic energy by the 2 explosion. The energy of the explosion is distributed by the blast wave to the surrounding air.