Bloodstain Pattern Analysis: implementation of a fluid dynamic model for position determination of victims

Laan, Nick; Bruin, Karla G. de; Slenter, Denise; Wilhelm, Julie; Jermy, Mark; Bonn, Daniel

doi:10.1038/srep11461

Cited by 64 publications

(48 citation statements)

References 25 publications

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“…[16]. The authors of [17] reconstructed drop trajectories using ballistic calculations, considering gravity and drag forces, and determined the region of origin with about four times higher accuracy than under the assumption of straight trajectories.…”

Section: Introductionmentioning

confidence: 99%

Prediction of blood back spatter from a gunshot in bloodstain pattern analysis

et al. 2016

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A theoretical model for predicting and interpreting blood-spatter patterns resulting from a gunshot wound is proposed. The physical process generating a backward spatter of blood is linked to the Rayleigh-Taylor instability of blood accelerated toward the surrounding air, allowing the determination of the initial distribution of drop sizes and velocities. Then the motion of many drops in air is considered with governing equations accounting for gravity and air drag. Based on these equations, a numerical solution is obtained. It predicts the atomization process, the trajectories of the back-spatter drops of blood from the wound to the ground, the impact angle, and the impact Weber number on the ground, as well as the distribution and location of bloodstains and their shape and sizes. A parametric study is undertaken to predict patterns of backward blood spatter under realistic conditions corresponding to the experiments conducted in the present work. The results of the model are compared to the experimental data on back spatter generated by a gunshot impacting a blood-impregnated sponge. A theoretical model for predicting and interpreting blood-spatter patterns resulting from a gunshot wound is proposed. The physical process generating a backward spatter of blood is linked to the Rayleigh-Taylor instability of blood accelerated toward the surrounding air, allowing the determination of the initial distribution of drop sizes and velocities. Then the motion of many drops in air is considered with governing equations accounting for gravity and air drag. Based on these equations, a numerical solution is obtained. It predicts the atomization process, the trajectories of the back-spatter drops of blood from the wound to the ground, the impact angle, and the impact Weber number on the ground, as well as the distribution and location of bloodstains and their shape and sizes. A parametric study is undertaken to predict patterns of backward blood spatter under realistic conditions corresponding to the experiments conducted in the present work. The results of the model are compared to the experimental data on back spatter generated by a gunshot impacting a blood-impregnated sponge.

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Section: Introductionmentioning

confidence: 99%

Prediction of blood back spatter from a gunshot in bloodstain pattern analysis

et al. 2016

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“…Then, the prediction of drop trajectories in such jets makes use of the initial drop sizes and initial velocities resulting from the Rayleigh-Taylor instability and proceeds, accounting for gravity and air drag forces, with the latter being diminished by the drop-drop interaction through air mentioned above [7]. It should be emphasized that few other studies account for gravity and air drag (albeit without accounting for the drop-drop interaction) to predict blood spatter patterns [10][11][12], however, they do not consider the physical mechanism of drop formation.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

2017

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A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the target (and perforated by the bullet) is predicted and compared with experimental data. The experimental data were acquired with a porous polyurethane foam sheet target impregnated with swine blood, and the blood drops were collected on a vertical cardstock sheet which was perforated by the blunt bullet. The highly porous target possesses a low hydraulic resistance and therefore resembles a pool of blood shot by a blunt bullet normally to its free surface. The back spatter pattern was predicted numerically and compared to the experimental data for the number of drops, their area, the total stain area, and the final impact angle as functions of radial location from the bullet hole in the cardstock sheet (the collection screen). Comparisons of the predicted results with the experimental data revealed satisfactory agreement. The predictions also allow one to find the impact Weber number on the collection screen, which is necessary to predict stain shapes and sizes. A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the t...

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“…Thus wetting of porous materials depends on the impact speed and angle, although little work has yet investigated the proper characterization of this wetting-drying behavior and its dependence on WDR parameters. The contact area of droplets impacting with an impact angle is elongated along the projected direction of the impact velocity and the length of contact area is traditionally estimated using the cosine of the impact angle (Laan et al 2015). This approach is used for water droplet impingement on a brick in Abuku et al (2009c).…”

Section: Question 7: How Do Rain Droplets Interact With Porous Materimentioning

confidence: 99%

Ten questions concerning modeling of wind-driven rain in the built environment

Derome

Kubilay

Defraeye

et al. 2017

Building and Environment

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Wind-driven rain (WDR) in the built environment is a complex multiscale phenomenon. Wind flows in complex urban environment and rain events of various intensities may lead to very different rain deposition distributions within the city. Proper modelling of WDR is required as moisture is a main cause of material degradation in the built environment but also as understanding the water cycle in the urban environment is essential to provide solutions for the urban heat island, amongst others. What are the main aspects to be taken into account to predict wind-driven rain? How should such aspects be considered and modeled? Is it possible and relevant to predict in detail the moisture loads due to rain in complex systems as cities? This paper answers these questions from a multiscale perspective combining modeling and experimental work. The different scales relevant for accurate estimation of wind-driven rain in the built environment are presented. Rain deposition on complex geometries can be modeled by CFD, taking into account turbulent dispersion. Such modeling provides the impact velocity and angle of attack for each droplet size at any location on the urban surfaces. Using this information and the structure of the surface, the fate of the rain droplets can be predicted, namely whether it splashes, bounces or simple spreads. KeywordsWind-driven rain, built environment, droplet trajectory, computational fluid dynamics (CFD), WDR catch ratio, droplet fate, porous materials Introduction Rain in the built environment is a complex phenomenon which has impact on, amongst others, durability of the materials, vitality of urban vegetation, management of storm water and comfort, safety and health of the population. Not only does rain induce an environmental load on the surfaces it impacts, but, contrary to the other environmental loads of solar radiation and wind flow, a large part of the rain water remains present after the rain event and such presence must be accounted for despite the fleeting and stochastic nature of liquid flow. To properly capture rain, the different time scales of the phenomenon need to be considered. The first time scale is the few minutes rain droplets spend in the air before deposition. Air flow is drastically affected by the presence of buildings, influencing the distribution of rain load in the built environment. Then, the few milliseconds when droplets impact surfaces explain the different outcomes of spreading, splashing and/or rebound. The settlement of droplets on surfaces takes minutes, and the wetting of the surface and absorption in the porous media take several hours. In addition, as more and more droplets rest on a surface, they may coalesce and form a water film, resulting in rivulets and film run-off on the different surfaces. After a rain event, evaporation of the droplets and drying of the materials can take hours to days. As such rain deposition and the ensuing fate, i.e. the succession of subjected phenomena, of water is a multifaceted phenomenon which can be appropriately mo...

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Bloodstain Pattern Analysis: implementation of a fluid dynamic model for position determination of victims

Cited by 64 publications

References 25 publications

Prediction of blood back spatter from a gunshot in bloodstain pattern analysis

Prediction of blood back spatter from a gunshot in bloodstain pattern analysis

Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

Ten questions concerning modeling of wind-driven rain in the built environment

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