Philip Clausen

Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation

The American sabercat Smilodon fatalis is among the most charismatic of fossil carnivores. Despite broad agreement that its extraordinary anatomy reflects unique hunting techniques, after >150 years of study, many questions remain concerning its predatory behavior. Were the “sabers” used to take down large prey? Were prey killed with an eviscerating bite to the abdomen? Was its bite powerful or weak compared with that of modern big cats? Here we quantitatively assess the sabercats biomechanical performance using the most detailed computer reconstructions yet developed for the vertebrate skull. Our results demonstrate that bite force driven by jaw muscles was relatively weak in S. fatalis, one-third that of a lion (Panthera leo) of comparable size, and its skull was poorly optimized to resist the extrinsic loadings generated by struggling prey. Its skull is better optimized for bites on restrained prey where the bite is augmented by force from the cervical musculature. We conclude that prey were brought to ground and restrained before a killing bite, driven in large part by powerful cervical musculature. Because large prey is easier to restrain if its head is secured, the killing bite was most likely directed to the neck. We suggest that the more powerful jaw muscles of P. leo may be required for extended, asphyxiating bites and that the relatively low bite forces in S. fatalis might reflect its ability to kill large prey more quickly, avoiding the need for prolonged bites.

An empirical model for fatigue behavior prediction of glass fibre-reinforced plastic composites for various stress ratios and test frequencies

Current models used to predict the fatigue life of glass fibre-reinforced plastic composites do not accurately consider the effects of load stress ratios and load frequencies. These models usually require significant amount of experimental data to establish a set of characteristic fatigue curves for a given composite. This paper proposes a fatigue model for glass fibre-reinforced plastic composites that includes the non-linear effect of stress ratio and load frequency on the fatigue life. The model can be used to predict the fatigue behavior of a composite material using a well-defined minimum number of tests. Fatigue data from the literature and selected research laboratories were used to test the model. Predictions were found to be in good agreement with all experimental data adequately accounting for the influence of test frequency and stress ratio on the fatigue life of composites.

Computer simulation of feeding behaviour in the thylacine and dingo as a novel test for convergence and niche overlap

The extinct marsupial thylacine (Thylacinus cynocephalus) and placental grey wolf (Canis lupus) are commonly presented as an iconic example of convergence. However, various analyses suggest distinctly different behaviours and specialization towards either relatively small or large prey in the thylacine, bringing the degree of apparent convergence into question. Here we apply a powerful engineering tool, three-dimensional finite element analysis incorporating multiple material properties for bone, to examine mechanical similarity and niche overlap in the thylacine and the wolf subspecies implicated in its extinction from mainland Australia, Canis lupus dingo. Comparisons of stress distributions not only reveal considerable similarity, but also informative differences. The thylacines mandible performs relatively poorly where only the actions of the jaw muscles are considered, although this must be considered in the light of relatively high bite forces. Stresses are high in the posterior of the thylacines cranium under loads that simulate struggling prey. We conclude that relative prey size may have been comparable where both species acted as solitary predators, but that the dingo is better adapted to withstand the high extrinsic loads likely to accompany social hunting of relatively large prey. It is probable that there was considerable ecological overlap. As a large mammalian hypercarnivore adapted to taking small-medium sized prey, the thylacine may have been particularly vulnerable to disturbance.

Structural design of a composite wind turbine blade using finite element analysis

Abstract This paper describes preliminary work to optimise the use of material in a 2.5 m long fibreglass composite wind turbine blade. A program was written to create a detailed finite element mesh of the blade, using design data from blade element theory and panel code predictions, in a format suitable for direct input into a commercially available finite element software package. Finite element predictions compared well with static bending and twisting deflections of the blade and with the first two natural frequencies of vibration. The simulation of a rotating aerodynamically-loaded blade required a nonlinear analysis; the techniques for this analysis and the subsequent predictions are discussed. Different stacking arrangements of the elements from blade element theory to form the final blade shape were considered to minimise both tip deflection and the maximum value of stress for a blade operating at design conditions. The best arrangement aligned elements using a previously developed translation scheme and rotated the elements about their centre of area to the twist angle determined by blade element theory.

High‐Resolution Three‐Dimensional Computer Simulation of Hominid Cranial Mechanics

In vivo data demonstrates that strain is not distributed uniformly on the surface of the primate skull during feeding. However, in vivo studies are unable to identify or track changes in stress and strain throughout the whole structure. Finite element (FE) analysis, a powerful engineering tool long used to predict the performance of man‐made devices, has the capacity to track stress/strain in three dimensions (3‐D) and, despite the time‐consuming nature of model generation, FE has become an increasingly popular analytical device among biomechanists. Here, we apply the finite element method using sophisticated computer models to examine whether 3‐D stress and strain distributions are nonuniform throughout the primate skull, as has been strongly suggested by 2‐D in vivo strain analyses. Our simulations document steep internal stress/strain gradients, using models comprising up to three million tetrahedral finite elements and 3‐D reconstructions of jaw adducting musculature with both cranium and mandible in correct anatomical position. Results are in broad concurrence with the suggestion that few regions of the hominid cranium are clearly optimized for routine feeding and also show that external stress/strain does not necessarily reflect internal distributions. Findings further suggest that the complex heterogeneity of bone in the skull may act to dissipate stress, but that consequently higher strain must be offset by additional strain energy. We hypothesize that, despite energetic costs, this system may lend adaptive advantage through enhancing the organisms ability to modify its behavior before reaching catastrophic failure in bony or dental structures. Anat Rec, 290:1248–1255, 2007.

Cranial performance in the Komodo dragon (Varanus komodoensis) as revealed by high-resolution 3-D finite element analysis

The Komodo dragon (Varanus komodoensis) displays a unique hold and pull‐feeding technique. Its delicate ‘space‐frame’ skull morphology differs greatly from that apparent in most living large prey specialists and is suggestive of a high degree of optimization, wherein use of materials is minimized. Here, using high‐resolution finite element modelling based on dissection and in vivo bite and pull data, we present results detailing the mechanical performance of the giant lizards skull. Unlike most modern predators, V. komodoensis applies minimal input from the jaw muscles when butchering prey. Instead it uses series of actions controlled by postcranial muscles. A particularly interesting feature of the performance of the skull is that it reveals considerably lower overall stress when these additional extrinsic forces are added to those of the jaw adductors. This remarkable reduction in stress in response to additional force is facilitated by both internal and external bone anatomy. Functional correlations obtained from these analyses also provide a solid basis for the interpretation of feeding ecology in extinct species, including dinosaurs and sabre‐tooth cats, with which V. komodoensis shares various cranial and dental characteristics.

Effects of Gape and Tooth Position on Bite Force and Skull Stress in the Dingo (Canis lupus dingo) Using a 3-Dimensional Finite Element Approach

Models of the mammalian jaw have predicted that bite force is intimately linked to jaw gape and to tooth position. Despite widespread use, few empirical studies have provided evidence to validate these models in non-human mammals and none have considered the influence of gape angle on the distribution of stress. Here using a multi-property finite element (FE) model of Canis lupus dingo, we examined the influence of gape angle and bite point on both bite force and cranial stress. Bite force data in relation to jaw gape and along the tooth row, are in broad agreement with previously reported results. However stress data showed that the skull of C. l. dingo is mechanically suited to withstand stresses at wide gapes; a result that agreed well with previously held views regarding carnivoran evolution. Stress data, combined with bite force information, suggested that there is an optimal bite angle of between 25 degrees and 35 degrees in C. l. dingo. The function of these rather small bite angles remains unclear.

Measurements of a swirling turbulent boundary layer developing in a conical diffuser

Abstract Measurements were made of the swirling boundary layer developing in a conical diffuser with a 20° included angle and an area ratio of 2.84. The inlet swirl was close to solid-body rotation and was of sufficient magnitude to prevent boundary layer separation but just insufficient to cause recirculation in the core flow. A single hot-wire was traversed from the wall to the centerline to determine the mean velocities. All six Reynolds stresses were measured within the boundary layer using a rotatable X-probe. The discussion concentrates on the complex response of the turbulence to the numerous perturbations imposed by the swirl and the geometry, of which the dominant ones appear to be the axial pressure gradient and the streamline curvature.

Research and development issues for small wind turbines

This paper discusses some of the major research and development issues for small wind turbines whose upper power limit we take arbitrarily as 50 kW. The basis for the comparison is the mature technology available for large turbines which has yet to be fully diffused downwards. After defining and categorising the important features of small turbines, the paper considers the major issues of blade aerodynamics, especially starting performance and materials and manufacturing methods. We conclude with a brief discussion of current developments in technology, which should increase the level of small turbine technology towards that of large machines.

Some effects of swirl on turbulent mixing layer development

An experimental study has been conducted to investigate the effects of swirl on the streamwise development of an axisymmetric turbulent mixing layer. The initial boundary layer was tripped well upstream of the lip. All three mean velocities and the six independent components of the Reynolds stress tensor were measured using a rotatable cross‐wire probe for three swirl numbers (0, 0.2, and 0.4). The zero swirl case was found to develop as expected, with a linear growth rate and the peak Reynolds stresses approaching constant asymptotic levels. The results show that the swirling mixing layer is affected by the angular momentum instability over almost the whole layer. The effect of the instability is to increase all the peak Reynolds stresses within the mixing layer, with the peaks increasing monotonically with swirl number. The largest increases occurred in the spanwise normal stress and the two secondary shear stresses. A part of the increase in the turbulence stresses is attributed to ‘‘extra’’ production...