Computational aerodynamic analysis of a Micro-CT based bio-realistic fruit fly wing

The aerodynamic features of a bio-realistic 3D fruit fly wing in steady state (snapshot) flight conditions were analyzed numerically. The wing geometry was created from high resolution micro-computed tomography (micro-CT) of the fruit fly Drosophila virilis. Computational fluid dynamics (CFD) analyses of the wing were conducted at ultra-low Reynolds numbers ranging from 71 to 200, and at angles of attack ranging from -10° to +30°. It was found that in the 3D bio-realistc model, the corrugations of the wing created localized circulation regions in the flow field, most notably at higher angles of attack near the wing tip. Analyses of a simplified flat wing geometry showed higher lift to drag performance values for any given angle of attack at these Reynolds numbers, though very similar performance is noted at -10°. Results have indicated that the simplified flat wing can successfully be used to approximate high-level properties such as aerodynamic coefficients and overall performance trends as well as large flow-field structures. However, local pressure peaks and near-wing flow features induced by the corrugations are unable to be replicated by the simple wing. We therefore recommend that accurate 3D bio-realistic geometries be used when modelling insect wings where such information is useful

Micromechanics of sea urchin spines

The endoskeletal structure of the Sea Urchin, Centrostephanus rodgersii, has numerous long spines whose known functions include locomotion, sensing, and protection against predators. These spines have a remarkable internal microstructure and are made of single-crystal calcite. A finite-element model of the spine's unique porous structure, based on micro-computed tomography (microCT) and incorporating anisotropic material properties, was developed to study its response to mechanical loading. Simulations show that high stress concentrations occur at certain points in the spine's architecture; brittle cracking would likely initiate in these regions. These analyses demonstrate that the organization of single-crystal calcite in the unique, intricate morphology of the sea urchin spine results in a strong, stiff and lightweight structure that enhances its strength despite the brittleness of its constituent material

An experimentally validated micromechanical model of a rat vertebra under compressive loading

In recent years, finite element analysis (FEA) has been increasingly applied to examine and predict the mechanical behaviour of craniofacial and other bony structures. Traditional methods used to determine material properties and validate finite element models (FEMs) have met with variable success, and can be time-consuming. An implicit assumption underlying many FE studies is that relatively high localized stress/strain magnitudes identified in FEMs are likely to predict material failure. Here we present a new approach that may offer some advantages over previous approaches. Recently developed technology now allows us to both image and conduct mechanical tests on samples in situ using a materials testing stage (MTS) fitted inside the microCT scanner. Thus, micro-finite element models can be created and validated using both quantitative and qualitative means. In this study, a rat vertebra was tested under compressive loading until failure using an MTS. MicroCT imaging of the vertebra before mechanical testing was used to create a high resolution finite element model of the vertebra. Load-displacement data recorded during the test were used to calculate the effective Young's modulus of the bone (found to be 128 MPa). The microCT image of the compressed vertebra was used to assess the predictive qualities of the FE model. The model showed the highest stress concentrations in the areas that failed during the test. Clearly, our analyses do not directly address biomechanics of the craniofacial region; however, the methodology adopted here could easily be applied to examine the properties and behaviour of specific craniofacial structures, or whole craniofacial regions of small vertebrates. Experimentally validated micro-FE analyses are a powerful method in the study of materials with complex microstructures such as bone

A Three-dimensional fractal model of tamour vasculature

We constructed a three-dimensional fractal model of the vascular network in a tumour periphery. We model the highly disorganised structure of the neoplastic vasculature by using a high degree of variation in segment properties such as length, diameter and branching angle. The overall appearance of the vascular tree is subjectively similar to that of the disorganised vascular network which encapsulates tumours. The fractal dimension of the model is within the range of clinically measured values.4 page(s

Automated mineralogy using finite element analysis and X-ray microtomography

The three-dimensional microstructure of minerals and materials can be visualised in a non-destructive manner using X-ray microtomography. The digitised nature of the tomographic image allows us to generate finite element models which precisely detail the material's microstructure. With a high degree of automation, high resolution models can be created quickly and with little user interaction. The geometry is taken from the microtomographic data, and loads and boundary conditions are applied to the model to simulate various conditions. The finite element analysis results show the deformation and stress distribution in the material. The technique allows us to study the relationship between microstructure and bulk properties of porous minerals, to characterise them in terms of their strength and stiffness, and to simulate their behaviour under known loading conditions. In this paper we present an application of micro-finite element analysis in the study of porous minerals. Micro-finite element analysis can be used to study the behaviour of a variety of minerals, and is especially useful when applied to materials that have a distinct microstructure that affects their bulk properties.7 page(s

Micro-finite element modelling of coke blends using X-ray microtomography

X-ray micro-computed tomography (microCT) is a non-destructive method of visualising specimens in three dimensions at the micrometer scale. Finite element analysis (FEA) is a method for approximating the structural response of systems to mechanical loading. The two methods are readily combined in micro-finite element analysis (microFEA). The microCT image, already in the discretized form of voxels, can be directly converted into a finite element mesh allowing materials with complex microstructures to be modelled. In this paper we present an example of microFEA model construction and use in the study of coke, a porous mineral. MicroCT datasets of different coke blends were used to create finite element models. The models were used to examine the material's structural response to compressive loading by studying the resultant stress distributions and material deformation. MicroFEA can be used to advance our understanding of the relationship between porous materials' microstructure and their bulk properties.5 page(s

Proportional distribution of shear drag to total drag for the bio-realistic and simple wings.

<p>The proportion of shear drag to drag (D_S/D) is plotted against angle of attack (α°) for both the bio-realistic and simple wings for a Reynolds number of 200. The simple wing maintains a noticeably higher proportion of shear drag, at lower angles of attack, however both wings present a very similar proportion of shear drag at the higher angles. This suggests that the corrugations of the bio-realistic wing have less effect on the overall drag at such angles.</p

Pressure distribution along the bio-realistic wing at varying angles.

<p>Pressure distribution on the upper and lower surfaces of bio-realistic wing at angles of attack of 20°, 0° and -10°. The high three-dimensionality of the pressure distribution is significantly more evident when the surface of the wing is more directly in the path of the free stream.</p

Aerodynamic performance comparison of experimental and computational results.

<p>A lift-to-drag (L/D) comparison between experimental results as taken from literature [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124824#pone.0124824.ref014" target="_blank">14</a>] and numerical results determined by computational fluid dynamics (CFD). Two sets of experimental results exist due to differing profiles (cambered and flat) being observed in testing [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124824#pone.0124824.ref014" target="_blank">14</a>]. The CFD results agree with the general trend of the experimental results, and are within expected values at higher angles of attack. Computational results made use of the bio-realistic wing for fair comparison to experimental results.</p

Coefficient of pressure and streakline comparisons at 0° of the bio-realistic and simple wings.

<p>Coefficient of pressure (C_P) plot and streakline comparisons between the bio-realistic and simple wings at A) 0.3 span, B) 0.5 span and C) 0.7 span for a Reynolds number of 200 at an angle of attack of 0°. The fluctuations in pressure across the bio-realistic wing are due to the corrugations—while the coefficient of pressure rarely ever matches that of the flat wing, when integrated over the entire chord the forces correlate with those of the flat wing. D) presents a surface oil-flow of the velocity vectors, where U_∞ is the freestream velocity direction. The surface oil-flow indicates that there exists some recirculation on the upper surface of the bio-realistic wing (left), which is not apparent on the flat wing (right). The maximum pressure coefficient has been truncated to 1.5 for clarity of the pressure distribution along the rest of the wing.</p