This comparative review highlights the relationships between the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) in the physical sciences. In both the BPA and FD communities, scientists study the motion and phase change of a liquid in contact with air, or with other liquids or solids. Five aspects of BPA related to FD are discussed: the physical forces driving the motion of blood as a fluid; the generation of the drops; their flight in the air; their impact on solid or liquid surfaces; and the production of stains. For each of these topics, the relevant literature from the BPA community and from the FD community is reviewed. Comments are provided on opportunities for joint BPA and FD research, and on the development of novel FD-based tools and methods for BPA. Also, the use of dimensionless numbers is proposed to inform BPA analyses. Keywordsbloodstain pattern analysis, review, dimensionless number, drop generation, trajectory, impact, stain Disciplines Laboratory and Basic Science Research | Other Mechanical EngineeringComments NOTICE: this is the author's version of a work that was accepted for publication in Forensic Science International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Forensic Science International, [231, 1-3, (2013) Abstract: This comparative review highlights the relationships between the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) in the physical sciences. In both the BPA and FD communities, scientists study the motion and phase change of a liquid in contact with air, or with other liquids or solids. Five aspects of BPA related to FD are discussed: the physical forces driving the motion of blood as a fluid; the generation of the drops; their flight in the air; their impact on solid or liquid surfaces; and the production of stains. For each of these topics, the relevant literature from the BPA community and from the FD community is reviewed. Comments are provided on opportunities for joint BPA and FD research, and on the development of novel FD-based tools and methods for BPA. Also, the use of dimensionless numbers is proposed to inform BPA analyses.
High energy gas fracturing is a simple approach of applying high pressure gas to stimulate wells by generating several radial cracks without creating any other damages to the wells. In this paper, a numerical algorithm is proposed to quantitatively simulate propagation of these fractures around a pressurized hole as a quasi-static phenomenon. The gas flow through the cracks is assumed as a one-dimensional transient flow, governed by equations of conservation of mass and momentum. The fractured medium is modeled with the extended finite element method, and the stress intensity factor is calculated by the simple, though sufficiently accurate, displacement extrapolation method. To evaluate the proposed algorithm, two field tests are simulated and the unknown parameters are determined through calibration. Sensitivity analyses are performed on the main effective parameters. Considering that the level of uncertainty is very high in these types of engineering problems, the results show a good agreement with the experimental data. They are also consistent with the theory that the final crack length is mainly determined by the gas pressure rather than the initial crack length produced by the stress waves.
Three-dimensional discontinuous deformation analysis (3-D DDA) with high-order displacement functions has been derived for the requirement of highly accurate stress and strain calculations. The high-order displacement function allows nonlinear distributions of stresses and strains within a discrete block, which significantly enhances 3-D DDA as an analysis technique. Formulations of stiffness and force matrices in second-and third-order 3-D DDA due to elastic stress, initial stress, body force, point load, fixed point, inertial force, normal and shear contact forces and friction force are presented. The VC++ codes for the second-and third-order cases have been developed, and they have been applied to examples of 3-D beams, bending under various loading conditions applied at the end and to an example of discontinuous problem. Results of modeling, are well in agreement with theoretical solutions. In contrast, the results calculated for the same model, using original first-order 3-D DDA are far from the theoretical solutions.blocks [13,14]. The NMM, still retaining most of the DDA's attractive features, can be considered a generalized finite element and DDA method. Additionally, Chen et al. developed the high-order version of the manifold method [15] and Cheng et al. [16] showed that the use of more advanced Wilson non-conforming element in NMM can be useful in obtaining more accurate results for simple covers. Cheng and Zhang [17] presented three-dimensional NMM based on tetrahedron and hexahedron elements.An alternative approach is to include more polynomial terms in the displacement function. Unlike the sub-blocking method, it is possible to obtain good results using high-order displacement functions without discretizing the blocks. In the sub-blocking method, constraints between subblocks may not be satisfied accurately, which may lead to some errors in results, but this source of error is avoided in higher-order methods. The number of unknowns of analysis for one block using third-order displacement function is equal to the unknowns of analysis for a block divided into five sub-blocks. Using the sub-blocking method, to obtain good results comparable those from using a third-order displacement function, it is usually necessary to divide a block to many sub-blocks; however, the accuracy is problem dependent. Chern et al. [18] and Koo et al. [19] implemented a second-order displacement function in 2-D DDA. Ma et al. [20] and Koo and Chern [21] implemented a third-order displacement function in 2-D DDA method. Hsuing [22] developed a more general formulation for 2-D DDA. These studies showed that complicated stress and strain fields can be modeled using high-order displacement functions. MacLaughlin and Doolin [23] provided a review of more than 100 published and unpublished validation studies on the DDA approach. Previous DDA studies focused on solving problems in two dimensions, but in many engineering problems, three-dimensional effects have to be considered. Up to now, relatively little work on DDA development ...
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