FLEXIBLE MULTI-BODY DYNAMICS MODEL OF A BIO-INSPIRED ORNITHOPTER WITH EXPERIMENTAL VALIDATION

There is currently a large effort underway to understand the physics of avian-based flapping wing vehicles, known as ornithopters. There is a need for small aerial robots to conduct a variety of civilian and military missions. Efforts to model the flight physics of these vehicles have been complicated by a number of factors, including nonlinear elastic effects, multi-body characteristics, unsteady aerodynamics, and the strong coupling between fluid and structural dynamics. Experimental verification is crucial in order to achieve accurate simulation capabilities. A multi-disciplinary approach to modeling requires the use of tools representing individual disciplines, which must be combined to form a comprehensive model. In the framework of this research a five body flexible vehicle dynamics model and a novel experimental verification methodology is presented. For the model development and verification of the modeling assumptions, a data set providing refined wing kinematics of a test ornithopter research platform in free flight was used. Wing kinematics for the verification was obtained using a Vicon motion capture system. Lagrange equations of motion in terms of a generalized coordinate vector of the rigid and flexible bodies are formulated in order to model the flexible multi-body system. Model development and verification results are presented. The `luff region" and "thrust flap region" of the wing are modeled as flexible bodies. A floating reference frame formulation is used for the ornithopter. Flexible body constraints and modes are implemented using the Craig-Bampton method, which incorporates a semi-physical subspace method. A quasi-steady aerodynamic model using Blade Element Theory was correlated and verified for the problem using the experimental wing kinematics. The aerodynamic model was then formulated in terms of generalized coordinates of the five-body flexible multi-body system and is used in the resulting model in order to account for aero-elasticity. Modeling assumptions were verified and simulation results were compared with experimental free flight test data

Crosslinking and Mechanical Properties Significantly Influence Cell Attachment, Proliferation, and Migration Within Collagen Glycosaminoglycan Scaffolds.

Crosslinking and the resultant changes in mechanical properties have been shown to influence cellular activity within collagen biomaterials. With this in mind, we sought to determine the effects of crosslinking on both the compressive modulus of collagen-glycosaminoglycan scaffolds and the activity of osteoblasts seeded within them. Dehydrothermal, 1-ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde crosslinking treatments were first investigated for their effect on the compressive modulus of the scaffolds. After this, the most promising treatments were used to study the effects of crosslinking on cellular attachment, proliferation, and infiltration. Our experiments have demonstrated that a wide range of scaffold compressive moduli can be attained by varying the parameters of the crosslinking treatments. 1-Ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde treatments produced the stiffest scaffolds (fourfold increase when compared to dehydrothermal crosslinking). When cells were seeded onto the scaffolds, the stiffest scaffolds also showed increased cell number and enhanced cellular distribution when compared to the other groups. Taken together, these results indicate that crosslinking can be used to produce collagen-glycosaminoglycan scaffolds with a range of compressive moduli, and that increased stiffness enhances cellular activity within the scaffolds

Flight Testing of Novel Compliant Spines for Passive Wing Morphing on Ornithopters

Unmanned Aerial Vehicles (UAVs) are proliferating in both the civil and military markets. Flapping wing UAVs, or ornithopters, have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number flight regimes. The purpose of this paper is to present new free flight experimental results for an ornithopter equipped with one degree of freedom (1DOF) compliant spines that were designed and optimized in terms of mass, maximum von-Mises stress, and desired wing bending deflections. The spines were inserted in an experimental ornithopter wing spar in order to achieve a set of desired kinematics during the up and down strokes of a flapping cycle. The ornithopter was flown at Wright Patterson Air Force Base in the Air Force Research Laboratory Small Unmanned Air Systems (SUAS) indoor flight facility. Vicon motion tracking cameras were used to track the motion of the vehicle for five different wing configurations. The effect of the presence of the compliant spine on wing kinematics and leading edge spar deflection during flight is presented. Results show that the ornithopter with the compliant spine inserted in its wing reduced the body acceleration during the upstroke which translates into overall lift gains