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

2

d

3

Characterization: Backspatters are complex pattern

37,000 stains

4

5

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Stain diameter [mm] Proportion

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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.

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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

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7Aa1 .22 cal bullet impacting bloodied sponge

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backspatter Forward spatter

Atomization cone measured from MFRC movies

out  out  out  out 

bullet

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• 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.

• ut



Forward spatter Backward spatter bullet

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Measuring velocities with Particle Image Velocimetry (PIV)

http://faculty.mccormick.northwestern.edu/richard-lueptow/images/fire-sprinkler.jpg

• 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.

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• 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. 7Aa1: 7Ab1:

Characterization: Velocities measured on MFRC movies with PIV

Forward spatter Backward spatter

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https://en.wikipedia.org/wiki/Rayleigh–Taylor_instability

Rayleigh–Taylor instability breaks accelerated blood into drops when a heavier fluid (blood) is accelerated towards a lighter fluid (air).

Modeling backspatter atomization

R V

• n

accelerati

2



V 2R

Explosion supernova

acceleration

• the Rayleigh-Taylor instability determines distribution of droplet

diameter d and velocities

• by conservation of linear momentum, the average angle of ejection

is estimated

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≅ ∙

Modeling backspatter atomization (2)

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• 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.

R +

Impact angle

Comparison of experiments and modeling (1)

Modeling (experiments) Radial location

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• 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.

r +

Number of stains

Comparison of experiments and modeling (2)

Modeling (experiments) radial location r, cm

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d=20cm d=50cm d

Number of stains

r +

Radial location r, cm

R

Relevance to Crime Scene Reconstruction?

out 

R= function (d)

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

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• 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.

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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.