Aerodynamic analysis of multirotor vehicles using a higher-order potential flow method

A higher-order potential flow method is adapted for the aerodynamic performance prediction of small rotors used in multirotor unmanned aerial vehicles. The method uses elements of distributed vorticity which results in numerical robustness with both a prescribed and relaxed wake representation. The radial loading and wake shapes of a rotor in hover were compared to experiment to show strong agreement for three disk loadings. The advancing flight performance prediction of a single rotor was compared to a single rotor was compared to a blade element momentum theory based approach and to experiment. Comparison showed good thrust and power agreement with experiment across a range of advance ratios and angles of attack. Prediction in descending flights showed improvements in comparison to the blade element momentum theory approach. The model was extended to a quadrotorm configuration showing the differences associated to vehicle orientation and rotor rotational direction.

Aerodynamic analysis of multirotor vehicles using a higher-order potential flow method

A higher-order potential flow method is adapted for the aerodynamic performance prediction of small rotors used in multirotor unmanned aerial vehicles. The method uses elements of distributed vorticity which results in numerical robustness with both a prescribed and relaxed wake representation. The radial loading and wake shapes of a rotor in hover were compared to experiment to show strong agreement for three disk loadings. The advancing flight performance prediction of a single rotor was compared to a single rotor was compared to a blade element momentum theory based approach and to experiment. Comparison showed good thrust and power agreement with experiment across a range of advance ratios and angles of attack. Prediction in descending flights showed improvements in comparison to the blade element momentum theory approach. The model was extended to a quadrotorm configuration showing the differences associated to vehicle orientation and rotor rotational direction.

Femoral mechanical performance of precocial and altricial birds: a simulation study

BackgroundAs the major load-bearing structures, bones exhibit various properties related to mechanical performance to adapt to different locomotor intensities. The habits and ontogenetic changes of locomotion in animals can, thus, be explored by assessing skeletal mechanical performance.MethodsIn this study, we investigated the growing femoral mechanical performance in an ontogenetic series of Cabot’s Tragopans (Tragopan caboti) and Pigeons (Columba livia domestica). Micro-computed tomography-based finite element analysis was conducted to evaluate the stress, strain, and strain energy density (SED) of femora under axial and radial loading.ResultsFemora deflected medio-laterally and dorso-ventrally under axial and radial loading, respectively. Femora deformed and tensed more severely under radial loading than axial loading. In adult individuals, Cabot’s Tragopans had lower strain and SED than pigeons. During ontogeny, the strain and SED of pigeons decreased sharply, while Cabot’s Tragopans showed moderately change. The structural properties of hatchling pigeons are more robust than those of hatchling Cabot’s Tragopans.ConclusionsLimb postures have dominant effect on skeletal deformation. The erect posture is preferred by large mammals and birds to achieve a high safety factor of bones during locomotion. Adult Cabot’s Tragopans have stronger femora than pigeons, reflecting a better bone adaption to the terrestrial locomotion of the studied pheasant species. Changes in strain and SED during growth reflect the marked difference in locomotor ability between precocial and altricial hatchlings. The femora of hatchling Cabot’s Tragopans were built with better energy efficiency than deformation resistance, enabling optimized mechanical performance. In contrast, although weak in mechanical function at the time of hatching, pigeon femora were suggested to be established with a more mature structural design as a prerequisite for rapid growth. These results will be helpful for studies regarding developmental patterns of fossil avian species.

Thoracic Aortic Parallel Stent-Graft Behaviour When Subjected to Radial Loading

To manage complex aortic arch disease using minimally invasive techniques, interventionalists have reported the use of multiple stent-graft devices deployed in a parallel configuration. The structural device-device and device-artery interactions arising during aortic arch parallel endografting, also known as chimney thoracic endovascular aortic repair (ch-TEVAR), is not well understood. Through the use of a radial force testing system we sought to characterise both the loading and deformation behaviour of parallel endografts in representative ch-TEVAR configurations. Four commercially available devices (Bentley BeGraft, Gore TAG, Gore Viabahn, and Medtronic Valiant) were subjected to uniform radial load individually, and in six combinations, to quantify loading profiles. Image data collected during testing were analysed to evaluate mechanical deformations in terms of gutters, chimney and main endograft compression, as well as graft infolding. Parallel endografting was found to increase radial loads when compared to standard TEVAR. Chronic outward force during ch-TEVAR was dependent on main endograft manufacturer, with TAG combinations leading to consistently higher loads than Valiant, but independent of chimney graft type. Endograft deformations were dependent on chimney graft type, with Viabahn combinations presenting with lower gutter areas and increased lumen compression than BeGraft. Chimney graft deformations were also influenced by deployment arrangement in the case of double ch-TEVAR. This study emphasizes the significant variability in both radial loads and mechanical deformations between clinically relevant ch-TEVAR configurations.