Fluid Dynamics advances in Gunshot Backspatter: Characterization, - PowerPoint PPT Presentation

Fluid Dynamics advances in Gunshot Backspatter: Characterization, Modeling and Reconstruction D. Attinger (1) , P. M. Comiskey (2) , A. L. Yarin (2) (1) , Iowa State University (2) University of Illinois in Chicago d

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Characterization: Backspatters are complex pattern 37,000 stains 3

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Proportion Stain diameter [mm] 6

Data of Celestina Rossi, L. Harold et al., “ Cranial Backspattter Pattern Production Utilizing Human Cadavers ”, being finalized for JFS 3193 spots found 926 stains Elapsed time is 17.49 seconds. 7

Characterization of backspatter atomization: the MFRC database by Laber, Epstein and Taylor • Over 150 high-speed videos of common bloodletting mechanisms • Used for BPA training • Described qualitatively in literature • Not yet described quantitatively https://www.ameslab.gov/mfrc/bpa-videos 8

9 7Aa1 .22 cal bullet impacting bloodied sponge

Atomization cone measured from MFRC movies Forward spatter backspatter   out   out bullet   out   out 10

bullet Forward spatter Backward spatter  out 11 P. M. Comiskey, A. L. Yarin, and D. Attinger, "High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets," Forensic Science International, vol. 276, pp. 134-141, 2017.

Measuring velocities with Particle Image Velocimetry (PIV) W. Thielicke, E.J. Stamhuis, PIVlab-Time Resolved Digital Particle Image Velocimetry Tool for MATLAB (v 1.41), (2014), doi:http://dx.doi.org/10.6084/ m9.figshare.1092508. 12 http://faculty.mccormick.northwestern.edu/richard-lueptow/images/fire-sprinkler.jpg

Characterization: Velocities measured on MFRC movies with PIV Forward spatter 7Aa1: 7Ab1: Backward spatter 13 P. M. Comiskey, A. L. Yarin, and D. Attinger, "High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets," Forensic Science International, vol. 276, pp. 134-141, 2017.

Modeling backspatter atomization V acceleration 2 2R V  accelerati on R Rayleigh – Taylor instability breaks accelerated blood into drops when a heavier fluid (blood) is accelerated towards Explosion supernova a lighter fluid (air). 15 https://en.wikipedia.org/wiki/Rayleigh–Taylor_instability

Modeling backspatter atomization (2) • the Rayleigh-Taylor instability determines distribution of droplet diameter d and velocities ������� ������� � ≅ ������� ∙ ����� ������������ • by conservation of linear momentum, the average angle of ejection is estimated 16

Comparison of experiments and modeling (1) Impact angle Modeling (experiments) R + Radial location 17 P. M. Comiskey, A. L. Yarin, and D. Attinger, "High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets," Forensic Science International, vol. 276, pp. 134-141, 2017.

Comparison of experiments and modeling (2) Modeling (experiments) Number of stains r + radial location r, cm 18 P. M. Comiskey, A. L. Yarin, and D. Attinger, "High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets," Forensic Science International, vol. 276, pp. 134-141, 2017.

Relevance to Crime Scene Reconstruction? d=20cm Number of stains d=50cm r + R= function (d) Radial location r, cm d   out R 19

Conclusions • A characterization software for spatters can save days of work in evaluating blood spatter • Cone angle and initial velocities of drops in gunshot backspatter were measured • Theoretical model was produced for gunshot backspatter • Theoretical model results are in very good agreement for distribution of impact angles and stain numbers from experiments • Relevance for BPA reconstruction is discussed – I am eager to see more realistic backspatter data P. M. Comiskey, A. L. Yarin, and D. Attinger, "Prediction and Experimental Comparison of a Blunt Bullet Gunshot in Bloodstain Pattern Analysis," Phys Rev Fluids, 2017. 20

Acknowledgements and bibliography: •Iowa State University •US Department of Justice, National Institute of Standards (CSAFE) •Yu Liu, Kris de Brabanter, Ying Xing, Basant Sikarwar, John Polansky, Prashant Agrawal [1] D. Attinger, C. Moore, A. Donaldson, A. Jafari, and H. A. Stone, "Fluid dynamics topics in bloodstain pattern analysis: comparative review and research opportunities," Forensic Sci Int, vol. 231, pp. 375-96, 2013. [2] P. M. Comiskey, A. L. Yarin, and D. Attinger, "Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis," Physical Review Fluids, vol. 2, p. 073906, 2017. [3] T. L. Laber, B. P. Epstein, and M. C. Taylor, "High speed digital video analysis of bloodstain pattern formation from common bloodletting mechanisms," IABPA News, pp. 4-12, 2008. [4] P. Agrawal, L. Barnet, and D. Attinger, "Bloodstains on woven fabric: Simulations and experiments for quantifying the uncertainty on the impact and directional angles," accepted 2017 in Forensic Science International. [5] P. M. Comiskey, A. L. Yarin, and D. Attinger, "High-Speed Video Analysis of Forward and Backward Spattered Blood Droplets," Forensic Science International, vol. 276, pp. 134-141, 2017. [6] Celestina Rossi, L. Harold et al., “Cranial Backspattter Pattern Production Utilizing Human Cadavers”, being finalized for Journal Forensic Sciences [7] P. M. Comiskey, A. L. Yarin, S. Kim, and D. Attinger, "Prediction of blood back spatter from a gunshot in bloodstain pattern analysis," Physical Review Fluids, vol. 1, p. 043201, 2016. 21