3D printed feathers with embedded aerodynamic sensing.

Bird flight is often characterized by outstanding aerodynamic efficiency, agility and adaptivity in dynamic conditions. Feathers play an integral role in facilitating these aspects of performance, and the benefits feathers provide largely derive from their intricate and hierarchical structures. Although research has been attempted on developing membrane-type artificial feathers for bio-inspired aircraft and micro air vehicles (MAVs), fabricating anatomically accurate artificial feathers to fully exploit the advantages of feathers has not been achieved.

Longitudinal wave scattering in thin plates with symmetric damage considering oblique incidence.

The interactions between ultrasonic waves and damage provide crucial information for developing effective damage detection techniques in various fields, including non-destructive testing and structural health monitoring, and they can be investigated through wave propagation. Then, this article presents an approach to investigate the longitudinal wave in thin plates with symmetric damage considering oblique incidence. The approach includes a strategy to determine the plate thickness reduction due to the damage presence by considering an oblique incidence of waves generated by the actuator.

Energy considerations and flow fields over whiffling-inspired wings.

Some bird species fly inverted, or whiffle, to lose altitude. Inverted flight twists the primary flight feathers, creating gaps along the wing's trailing edge and decreasing lift. It is speculated that feather rotation-inspired gaps could be used as control surfaces on uncrewed aerial vehicles (UAVs).

Gull dynamic pitch stability is controlled by wing morphing.

Birds perform astounding aerial maneuvers by actuating their shoulder, elbow, and wrist joints to morph their wing shape. This maneuverability is desirable for similar-sized uncrewed aerial vehicles (UAVs) and can be analyzed through the lens of dynamic flight stability. Quantifying avian dynamic stability is challenging as it is dictated by aerodynamics and inertia, which must both account for birds' complex and variable morphology.

Avian whiffling-inspired gaps provide an alternative method for roll control.

Some bird species exhibit a flight behavior known as whiffling, in which the bird flies upside-down during landing, predator evasion, or courtship displays. Flying inverted causes the flight feathers to twist, creating gaps in the wing's trailing edge. It has been suggested that these gaps decrease lift at a potentially lower energy cost, enabling the bird to maneuver and rapidly descend.

Aerodynamic efficiency of gliding birds vs comparable UAVs: a review.

Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency.

Load alleviation of feather-inspired compliant airfoils for instantaneous flow control.

Birds morph their wing shape to adjust to changing environments through muscle-activated morphing of the skeletal structure and passive morphing of the flexible skin and feathers. The role of feather morphing has not been well studied and its impact on aerodynamics is largely unknown. Here we investigate the aero-structural response of a flexible airfoil, designed with biologically accurate structural and material data from feathers, and compared the results to an equivalent rigid airfoil.

Vibration annoyance assessment of train induced excitations from tunnels embedded in rock.

Train movements generate oscillations that are transmitted as waves through the track support system into its surroundings. The vibration waves propagate through the soil layers and reach to nearby buildings creating distractions for human activities and causing equipment malfunctioning. Not only the train components and the rails, but also the surrounding tunnel, soil and rock strata have dynamic characteristics that play significant roles in the vibration levels felt in a nearby structure.

Vibration Damping Mechanism of Fiber-Reinforced Composites with Integrated Piezoelectric Nanowires.

Here, both piezoelectric and nonpiezoelectric nanostructures are used within fiber-reinforced composites to improve the damping capabilities of the host material. This work investigates and isolates the role of both piezoelectricity and the mechanical redistribution of strain on the damping properties of fiber-reinforced composites through the integration of a nanowire interphase between the fiber and matrix. Prior works have successfully studied and reported the effectiveness of modifying the surface of the reinforcing fibers in a composite material using nanowires and other nanostructured interfaces to increase mechanical damping, however, have yet to fully investigate the mechanism dictating the observed behavior.

Adipose-Derived Stromal Vascular Fraction and Cultured Stromal Cells as Trophic Mediators for Tendon Healing.

Adipose-derived stromal vascular fraction (SVF) is a heterogeneous population of cells that yields a homogeneous population of plastic-adherent adipose tissue-derived stromal cells (ASC) when culture-expanded. SVF and ASC have been used clinically to improve tendon healing, yet their mechanism of action is not fully elucidated. The objective of this study was to investigate the potential for ASC to act as trophic mediators for tendon healing.

A Novel Nonlinear Piezoelectric Energy Harvesting System Based on Linear-Element Coupling: Design, Modeling and Dynamic Analysis.

This paper presents a novel nonlinear piezoelectric energy harvesting system which consists of linear piezoelectric energy harvesters connected by linear springs. In principle, the presented nonlinear system can improve broadband energy harvesting efficiency where magnets are forbidden. The linear spring inevitably produces the nonlinear spring force on the connected harvesters, because of the geometrical relationship and the time-varying relative displacement between two adjacent harvesters.

A tale of two tails: developing an avian inspired morphing actuator for yaw control and stability.

Motivated by the lack of research in tailless morphing aircraft in addition to the current inability to measure the resultant aerodynamic forces and moments of bird control maneuvers, this work aims to develop and test a multi-functional morphing control surface based on the horizontal tail of birds for a low-radar-signature unmanned aerial vehicle. Customized macro fiber composite actuators were designed to achieve yaw control across a range of sideslip angles by inducing 3D curvature as a result of bending-twisting coupling, a well-known phenomenon in classical fiber composite theory. This allows for yaw control, pitch control, and limited air break control.

Investigating the thermally induced acoustoelastic effect in isotropic media with Lamb waves.

Elastic wave velocities in metallic structures are affected by variations in environmental conditions such as changing temperature. This paper extends the theory of acoustoelasticity by allowing thermally induced strains in unconstrained isotropic media, and it experimentally examines the velocity variation of Lamb waves in aluminum plates (AL-6061) due to isothermal temperature deviations. This paper presents both thermally induced acoustoelastic constants and thermally varying effective Young's modulus and Poisson's ratio which include the third order elastic material constants.

Experimental and analytical parametric study of single-crystal unimorph beams for vibration energy harvesting.

This research presents an experimental and theoretical energy harvesting characterization of beam-like, uniform cross-section, unimorph structures employing single-crystal piezoelectrics. Different piezoelectric materials, substrates, and configurations are examined to identify the best design configuration for lightweight energy harvesting devices for low-power applications. Three types of piezoelectrics (singlecrystal PMN-PZT, polycrystalline PZT-5A, and PZT-5H-type monolithic ceramics) are evaluated in a unimorph cantilevered beam configuration.

Structural health monitoring using piezoelectric impedance measurements.

This paper presents an overview and recent advances in impedance-based structural health monitoring. The basic principle behind this technique is to apply high-frequency structural excitations (typically greater than 30kHz) through surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred.