Charts based on millions of fluid dynamics simulations provide a simple tool to estimate how far from its source a specific blood stain can be found

Abstract

The bloodstain pattern analyst sometimes has to judge if a given stain could originate from a specific location. A wide range of values of the maximum distance that a blood drop can travel have been reported from experiments, ranging from less than one meter to more than 10 meter. Here we formulate the problem in a fluid dynamics and data mining framework. The fluid dynamics is solved with Newton's classical equation of motion coupled with well-established models for the gravity and drag forces that bend the trajectories of drops. The parameters screened are the drop size, initial velocity and launch angle, as well as the height of a blood source and the ceiling height. Combining a wide range of values of those five parameter commended the performance of more than 5 million fluid dynamic simulations. Results of those simulations have been searched and mined for parameters directly measurable on a crime scene, such as the stain size and stain ellipticity. The results are presented in simple charts. Those charts are easy to use, and do not require any knowledge of fluid dynamics from the analyst. Disciplines Aerodynamics and Fluid Mechanics | Forensic Science and Technology | Mechanical Engineering Comments This is a manuscript of an article published as Attinger, Daniel. "Charts based on millions of fluid dynamics simulations provide a simple tool to estimate how far from its source a specific blood stain can be found."

Experimental study of how far blood spatter stains on fabrics can be found from the blood source, and relevance to crime scene reconstruction

“…Each trajectory is calculated by numerical integration of Newton's second law for a drop moving through the air, proceeding forward in time until the drop either contacts the ceiling or floor, or breaks up in flight due to drag force. The trajectories and drag force are simulated with the method described in (Attinger 2019), with the main equations provided in the supplementary documentation. The drag force model considers the deformation of drops in flight and the corresponding increase of drag.…”

“…Following criticisms in a 2009 report on the scientific basis of forensics disciplines by the US National Research Council (NRC 2009) , governmental agencies such as the US National Institute of Justice have encouraged physics-based research in forensics. Over the last decade, several peer-reviewed studies (Buck and Kneubuehl 2012, Adam 2013, Attinger, Moore et al 2013, Camana 2013, Kabaliuk, Jermy et al 2014, Cho, Springer et al 2015, Laan, de Bruin et al 2015, Comiskey, Yarin et al 2016, Kim, Ma et al 2016, Kolbasov, Comiskey et al 2016, Kröll, Kettner et al 2017, Siu, Pender et al 2017, Arthur, Hoogenboom et al 2018, Feng, Michielsen et al 2018, Shiri, Martin et al 2018, Attinger 2019 have addressed specific challenges in the forensic discipline of bloodstain pattern analysis (BPA). These studies focused on providing quantitative, physics-based understanding of the properties of blood, the physical formation of blood drops, the flight of drops, and their impact and drying on a variety of target materials.…”

“…Regarding the above problem on how far a stain on fabric can be found from its source, (Attinger 2019) has recently proposed charts to evaluate how far a stain can be found from its source on a nonabsorbing surface. This manuscript investigates a related problem, albeit for the case of an absorbing fabric target.…”

Using the likelihood ratio in bloodstain pattern analysis

“…It describes how a bullet atomizes blood; how the impact of a fist on a moving face squeezes and splashes blood; how airborne droplets move along trajectories curved by gravity and slowed by drag; and how drops spread, wick, and dry onto materials as complex as fabrics. Only recently, peer-reviewed fluid dynamic studies have started to uncover the complex physics underlying BPA [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. The governing equations of fluid dynamics are called the Navier-Stokes equations; they are the expression of Newton's second law for fluids.…”

Observations and 3D Analysis of Controlled Cast‐Off Stains

“…New methods involving laser scanners and software , such as HemoSpat , HemoVision , and FARO Zone 3D , allow for accurate documentation of bloodstain patterns and for the calculation of area of origin using 3D. More recently, studies have been performed which are incorporating the effects of gravity and other physical effects to more accurately represent the path of the bloodstains in flight . With respect to cast‐off stains, there is currently a lack of techniques or methods which can provide an analysis for cast‐off stains that is similar to the area of origin calculations for bloodstain impacts.…”