Sawfishes stealth revealed using computational fluid dynamics.

Detailed computational fluid dynamics simulations for the rostrum of three species of sawfish (Pristidae) revealed that negligible turbulent flow is generated from all rostra during lateral swipe prey manipulation and swimming. These results suggest that sawfishes are effective stealth hunters that may not be detected by their teleost prey's lateral line sensory system during pursuits. Moreover, during lateral swipes, the rostra were found to induce little velocity into the surrounding fluid. Consistent with previous data of sawfish feeding behaviour, these data indicate that the rostrum is therefore unlikely to be used to stir up the bottom to uncover benthic prey. Whilst swimming with the rostrum inclined at a small angle to the horizontal, the coefficient of drag of the rostrum is relatively low and the coefficient of lift is zero.

Finite element analysis of a micromechanical model of bone and a new 3D approach to validation.

Finite Element Analysis (FEA) is now widely used to analyse the mechanical behaviour of bone structures. Ideally, simulations are validated against experimental data. To date, validation of Finite Element Models (FEMs) has been 2 Dimensional (2D) only, being based on comparison with surface-mounted strain gauge readings. In this study we present a novel 3-Dimensional (3D) approach to validation that allows comparison of modelled with experimental results between any two points in 3D space throughout the structure, providing magnitude and direction data for comparison, internally and externally. Specifically, we validate a FEM of a rat tibia, including trabecular network geometry, using a material testing stage housed within a microCT scanner. We further apply novel landmark based morphometric approaches to more effectively compare modelled and experimental results. 542 landmark points on the cortical and trabecular bone surfaces of the model were selected and validated in 3D against experimental data. This approach may hold considerable potential in fields wherein a better understanding of the mechanical behaviour of trabecular networks is important, e.g., the studies of osteoporosis and trabecular loss after orthopaedic implant insertion.

Toward integration of geometric morphometrics and computational biomechanics: new methods for 3D virtual reconstruction and quantitative analysis of Finite Element Models.

The ability to warp three-dimensional (3D) meshes from known biological morphology to fit other known, predicted or hypothetical morphologies has a range of potential applications in functional morphology and biomechanics. One of the most challenging of these applications is Finite Element Analysis (FEA), a potentially powerful non-destructive tool in the prediction of mechanical behaviour. Geometric morphometrics is another typically computer-based approach commonly applied in morphological studies that allows for shape differences between specimens to be quantified and analysed. There has been some integration of these two fields in recent years. Although a number of shape warping approaches have been developed previously, none are easily accessible. Here we present an easily accessed method for warping meshes based on freely available software and test the effectiveness of the approach in FEA using the varanoid lizard mandible as a model. We further present new statistical approaches, strain frequency plots and landmark point strains, to analyse FEA results quantitatively and further integrate FEA with geometric morphometrics. Using strain frequency plots, strain field, bending displacements and landmark point strain data we demonstrate that the mechanical behaviour of warped specimens reproduces that of targets without significant error. The influence of including internal cavity morphology in FEA models was also examined and shown to increase bending displacements and strain magnitudes in FE models. The warping approaches presented here will be useful in a range of applications including the generation and analysis of virtual reconstructions, generic models that approximate species means, hypothetical morphologies and evolutionary intermediaries.