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SIMULTANEOUS STRUCTURE AND MECHANISM DESIGN FOR AN ADAPTIVE WING USING TOPOLOGY OPTIMIZATION
James J. Joo Aerospace Mechanics Division University of Dayton Research Institute Dayton, OH 45469, USA
Brian Sanders Air Vehicles Directorate AirForce Research Laboratory Wright-Patterson AFB, Ohio 45433, USA
ABSTRACT
A synthesis technique using a topology optimization scheme for an adaptive wing structure and mechanism design will be described.This enables the design of energy efficient adaptive structures with controllable deformation characteristice.This is accomplished by using a multi-objective function that minimizes strain energy and maximizes mutual potential energy to design the structure and mechanism simultaneously.To enable simultaneous design for structure and mechanism, the reference structure is composed of three layers; a membrane layer for skin, a frame element layer for structure, and truss element layer for an efficient mechanism. The attachment points between mechanism and structure are also identified with linear springs that are located between mechanism and structure layers. We focus on a simultaneous design of a wing structure and mechanism for large shape change applications. The geometrically large deformation analysis scheme is also added to the synthesis to capture nonlinear effects in design and it will be compared with linear synthesis results.
INTRODUCTION
Adaptive structures are a multidisciplinary technology that requires the efficient integration of power systems, structures, mechanisms, and actuators to achieve the desired performance. Adaptive systems will have a dramatic impact on the design of air vehicle systems if new devices can be synergistically
integrated into systems. The basic research community has suggested a plethora of innovative concepts ranging from structural health monitoring to adaptive shape control using energy intensive smart materials. Smart material technologies have increased its potential application to provide a new opportunity for active/adaptive structure systems that fully integrate actuators and structures. The Defense Advanced Research Projects Agency (DARPA) recognizes the potential of this technology and initiated the Smart Materials and Structures Demonstration Program to demonstrate the use of smart materials to achieve aerodynamic and hydrodynamic flow control and to reduce noise and vibration in a variety of structures (Sanders, et. al, 2004).
New materials synthesized at the atomic level to produce new functionality are ideal for this application but the technology is very immature. Until now, smart materials or other adaptive technologies have been added to an existing structure to achieve a desired shape change a structure already designed to avoid deformation. For example, aircraft wings are designed to be stiff as possible to control aeroelastic effects, and then smart materials are attached on to it to get a higher lift coefficient by change airfoil shape. This system becomes very energy inefficient because you are trying to deform a structure that was alreadydesigned to prevent deformation. For this reason, researchers have designed in flexibility for their structure design. Lu and Kota (2003) have designed a compliant leading edge that matches a desired shape with a single actuation force. Others are investigating new design techniques for these applications. Maute et. al. (2005) used the topology optimization technique to design mechanisms in morphing aircraft structures including actuator characteristics. Also Mauteand Reich (2004) showed the simultaneous optimization of the mechanism layout of adaptive wing and aerodynamic tasks outperformed the decomposed two step procedure.
Designed properly, these structural concepts have the potential to revolutionize aircraft design and basic functionality. For example, the use of adaptive systems within unmanned air vehicles (UAV) will enable a multi-mission (e.g., hunter-killer) UAV by allowing the vehicle configuration to efficiently adapt to a wide range of mission roles, such as loiter and high speed dash. Here the best wings for each purpose have radically different planforms. Current research on morphing aircraft that exhibit very large shape changes requires more efficient ways of synthesizing out three major components; rigid-body mechanisms, structures and skins. In this paper, we propose to design an energy efficient adaptive structure for shape control purposes by designing structures and mechanisms simultaneously. A three-layer model is developed that is composed of a ground truss layer for mechanism design and a membrane and beam layers for structure design. A multi-objective function to maximize mutual potential energy to increase flexibility in desired direction and minimizing strain energy to withstand drag is adopted here.
NOMENCLATURE
Uo Dummy force in the desired output direction
Ui Dummy force in the input direction.
Fin Input force
Fex External force
[K] Global stiffness matrix
djenzi2 Displacement vector
{f} Force vector
Km Element stiffness matrix of membrane element
Kt Element stiffness matrix of truss element
Kf Element stiffness matrix of frame element
Ks Element stiffness matrix of spring element
Maximum volume of truss element
Maximum volume of frame element
N* Maximum number of spring
P Penalty
ρf, s, t Density of frame, spring, and truss elements
REFERENCE STRUCTURE
The reference element composed of three layers is shown in Figure 1 below; the membrane element layer is for stretchable flexible skin. The truss element layer is for an energy efficient mechanism that generates motion using rigid body rotation rather than the deformation of elements to change the shape. Using frame elements, most of energy will be stored in the mechanism rather than transformed to the output port which results in an inefficient mechanism. Also this truss element with rigid body rotation is more appropriate for large shape changing applications than frame elements due to the similar reason. This truss element layer is connected to the membrane elements layer by springs and this is for identifying connection points between structure and mechanism. Spring stiffness is chosen based on the following criteria (Chandrupatla 1997) to bond mechanism and membrane layer together:
C=max∣kij∣×103 (1
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