Daniel Weihs

Pied kingfishers (Ceryle rudis) capture fish by plunge diving from hovering that may last several minutes. Hovering is the most energy-consuming mode of flight and depends on active wing flapping and facing headwind. The power for hovering is mass dependent increasing as the cube of the size, while aerodynamic forces increase only quadratically with size. Consequently, birds above a certain body mass can hover only with headwind and for very short durations. Hummingbirds are referred to as the only birds capable of hovering without wind (sustained hovering) due to their small size (ca. 2-20 gr), high wing-beat frequency and unique anatomy.We studied the hovering characteristics of pied kingfishers in relation to wind and sun orientation, in 139 hovers. Furthermore, plunge diving necessitates the coping with the visual effects of light at the air/water interface. The kingfishers oriented their body axis towards the wind more than towards the sun. Hovering in little or no wind was com...

... Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida. ... Session BM: Aerodynamics. 11:00 AM–12:44 PM, Sunday, November 19, 2006. Tampa Marriott Waterside Hotel and Marina Room: Meeting Room 10 Chair: Jamey Jacob, Oklahoma State University Abstract ID ...

Drafting in cetaceans is defined as the transfer of forces between individuals without actual physical contact between them. This behavior has long been surmised to explain how young dolphin calves keep up with their rapidly moving mothers. It has recently been observed that a significant number of calves become permanently separated from their mothers during chases by tuna vessels. A study of the hydrodynamics of drafting, initiated in the hope of understanding the mechanisms causing the separation of mothers and calves during fishing-related activities, is reported here. Quantitative results are shown for the forces and moments around a pair of unequally sized dolphin-like slender bodies. These include two major effects. First, the so-called Bernoulli suction, which stems from the fact that the local pressure drops in areas of high speed, results in an attractive force between mother and calf. Second is the displacement effect, in which the motion of the mother causes the water in...

Swimming movements in boxfishes were much more complex and varied than classical descriptions indicated. At low to moderate rectilinear swimming speeds (<5 TL s(-1), where TL is total body length), they were entirely median- and paired-fin swimmers, apparently using their caudal fins for steering. The pectoral and median paired fins generate both the thrust needed for forward motion and the continuously varied, interacting forces required for the maintenance of rectilinearity. It was only at higher swimming speeds (above 5 TL s(-1)), when burst-and-coast swimming was used, that they became primarily body and caudal-fin swimmers. Despite their unwieldy appearance and often asynchronous fin beats, boxfish swam in a stable manner. Swimming boxfish used three gaits. Fin-beat asymmetry and a relatively non-linear swimming trajectory characterized the first gait (0--1 TL s(-1)). The beginning of the second gait (1--3 TL s(-1)) was characterized by varying fin-beat frequencies and ampli...

A theoretical model describes how an intermittent swimming style can be energetically advantageous over continuous swimming at high average velocities. Kinematic data are collected from high-speed ciné pictures of free swimming cod and saithe at high velocities in a burst-and-coast style. These data suggest that fish make use of the advantages shown by choosing initial and final burst velocities close to predicted optimal values. The limiting role of rapid glycogen depletion in fast white anaerobic muscle fibres is discussed.

The flow through and around a finite row of parallel slender bodies in close proximity moving in a viscous incompressible fluid is studied. The motion occurs under creeping flow (Re {≪} 1) conditions. This row is a model of a comb-wing configuration found in insects of the Thrips family and being developed for use for flying vehicles of mm size,

A mathematical model describing growth of an internal vapor bubble produced by homogeneous nucleation within a liquid droplet during explosive boiling is presented. Existing experimental results for explosive boiling of superheated droplets confirm the predictions of the model. The difference between the present model and the classical theories of bubble growth is discussed.