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Research Papers

Optimal Compliant Flapping Mechanism Topologies With Multiple Load Cases

[+] Author and Article Information
Bret Stanford

U.S. Air Force Research Laboratory, Wright-Patterson AFB, OH 45433bret.stanford@wpafb.af.mil

Philip Beran

U.S. Air Force Research Laboratory, Wright-Patterson AFB, OH 45433philip.beran@wpafb.af.mil

J. Mech. Des 134(5), 051007 (Apr 25, 2012) (10 pages) doi:10.1115/1.4006438 History: Received April 13, 2011; Revised February 10, 2012; Published April 24, 2012; Online April 25, 2012

The conceptual design of effective actuation mechanisms for flapping wing micro air vehicles presents considerable challenges, with competing weight, power, authority, and life cycle requirements. This work utilizes topology optimization to obtain compliant flapping mechanisms; this is a well-known tool, but the method is rarely extended to incorporate unsteady nonlinear aeroelastic physics, which must be accounted for in the design of flapping wing vehicles. Compliant mechanism topologies are specifically desired to perform two tasks: (1) propulsive thrust generation (symmetric motions of a left and a right wing) and (2) lateral roll moment generation (asymmetric motions). From an optimization standpoint, these two tasks are considered multiple load cases, implemented by scheduling the actuation applied to the mechanism’s design domain. Mechanism topologies obtained with various actuation-scheduling assumptions are provided, along with the resulting flapping wing motions and aerodynamic force/moment generation. Furthermore, it is demonstrated that both load cases may be used simultaneously for future vehicle control studies: gradual transition from forward flight into a turning maneuver, for example.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Compliant mechanism and flapping wings

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Figure 2

Finite element model of both the mechanism and the wing

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Figure 3

Multiple load cases for topology optimization: two possible scenarios

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Figure 4

Wing section and coordinate system used for aerodynamic modeling

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Figure 5

Optimal mechanism topologies: hatched areas are clamped

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Figure 6

Five snapshots of the flapping motion for mechanism 1: symmetric (left row) and asymmetric flapping (right row)

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Figure 7

Time-history of the flapping rotation due to the input actuation (positive angle corresponds to wingtips up)

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Figure 8

Five snapshots of the flapping motion for mechanism 3: symmetric (left row) and asymmetric flapping (right row)

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Figure 9

Time-periodic thrust coefficient (symmetric flight) and rolling moment coefficient (asymmetric flight) orbits

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Figure 10

Aeroelastic response of mechanism 3 to simultaneous in-phase sinusoidal forces from the left and the right actuators

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