Efficient numerical methods for aeroelastic analysis of wing-propeller configuration compound helicopters

Efficient numerical methods for time-domain aeroelastic analysis of a wing structure under a propeller-wing configuration is described in the paper. A linear beam model with deformable elastic axis under torsion and flapping is considered to simulate a wing structure with a tipmounted propeller, relying on efficient, analytical formulations. The complete aeroelastic system of equations is then solved using Galerkin’s approach, and numerically integrated by the Newmark-beta method. The computational tool developed is able to efficiently predict in the time domain the wing aeroelastic transient behaviour and the wing-propeller interaction effects. The purpose of the tool developed is to provide accurate enough predictions of the system aeroelastic response to be included in structural optimisation and control synthesis procedures. A detailed analysis on the solver used and an aeroelastic case study of a Eurocopter X3-like compound helicopter wing/propeller configuration are demonstrated

Three-systems for visual numerosity: A single case study

Abstract Humans possess the remarkable capacity to assess the numerosity of a set of items over a wide range of conditions, from a handful of items to hundreds of them. Recent evidence is starting to show that judgments over such a large range is possible because of the presence of three mechanisms, each tailored to specific stimulation conditions. Previous evidence in favour of this theory comes from the fact that discrimination thresholds and estimation reaction times are not constants across numerosity levels. Likewise, attention is capable of dissociating the three mechanisms: when healthy adult observers are asked to perform concurrently a taxing task, the judgments of low numerosities

Spontaneous perception of numerosity in humans

Humans, including infants, and many other species have a capacity for rapid, nonverbal estimation of numerosity. However, the mechanisms for number perception are still not clear; some maintain that the system calculates numerosity via density estimates—similar to those involved in texture—while others maintain that more direct, dedicated mechanisms are involved. Here we show that provided that items are not packed too densely, human subjects are far more sensitive to numerosity than to either density or area. In a two-dimensional space spanning density, area and numerosity, subjects spontaneously react with far greater sensitivity to changes in numerosity, than either area or density. Even in tasks where they were explicitly instructed to make density or area judgments, they responded spontaneously to number. We conclude, that humans extract number information, directly and spontaneously, via dedicated mechanisms

Subitizing but not estimation of numerosity requires attentional resources

The numerosity of small numbers of objects, up to about four, can be rapidly appraised without error, a phenomenon known as subitizing. Larger numbers can either be counted, accurately but slowly, or estimated, rapidly but with errors. There has been some debate as to whether subitizing uses the same or different mechanisms than those of higher numerical ranges and whether it requires attentional resources. We measure subjects' accuracy and precision in making rapid judgments of numerosity for target numbers spanning the subitizing and estimation ranges while manipulating the attentional load, both with a spatial dual task and the "attentional blink" dual-task paradigm. The results of both attentional manipulations were similar. In the high-load attentional condition, Weber fractions were similar in the subitizing (2-4) and estimation (5-7) ranges (10-15%). In the low-load and single-task condition, Weber fractions substantially improved in the subitizing range, becoming nearly error-free, while the estimation range was relatively unaffected. The results show that the mechanisms operating over the subitizing and estimation ranges are not identical. We suggest that pre-attentive estimation mechanisms works at all ranges, but in the subitizing range, attentive mechanisms also come into play

Time-domain aeroelastic model for compound helicopter propeller-wing configuration

A simplified numerical model for time-domain aeroelastic analysis of a wing structure in a propeller-wing configuration is described in the paper. A linear beam model with deformable elastic axis under torsional deformation and out-of-plane bending is considered to simulate a wing structure with tip mounted propeller, relying on efficient, analytical formulations. The complete aeroelastic system of equations is solved using Galerkin’s approach, and numerically integrated by the Newmark-beta method. The computational tool developed is able to predict the wing aeroelastic transient behaviour and the wing-propeller interaction effects in the time domain. The purpose of such a tool is to provide accurate enough predictions of the system aeroelastic response to be included in structural optimisation and control synthesis procedures. A complete analysis on the solver used and an aeroelastic analysis of a Eurocopter X3-like compound helicopter wing/propeller configuration are demonstrated