Niell Elvin

The performance of a self-excited fluidic energy harvester

The available power in a flowing fluid is proportional to the cube of its velocity, and this feature indicates the potential for generating substantial electrical energy by exploiting the direct piezoelectric effect. The present work is an experimental investigation of a self-excited piezoelectric energy harvester subjected to a uniform and steady flow. The harvester consists of a cylinder attached to the free end of a cantilevered beam, which is partially covered by piezoelectric patches. Due to fluid?structure interaction phenomena, the cylinder is subjected to oscillatory forces, and the beam is deflected accordingly, causing the piezoelectric elements to strain and thus develop electric charge. The harvester was tested in a wind tunnel and it produced approximately 0.1?mW of non-rectified electrical power at a flow speed of 1.192?m?s?1. The aeroelectromechanical efficiency at resonance was calculated to be 0.72%, while the power per device volume was 23.6?mW?m?3 and the power per piezoelectric volume was 233?W?m?3. Strain measurements were obtained during the tests and were used to predict the voltage output by employing a distributed parameter model. The effect of non-rigid bonding on strain transfer was also investigated. While the rigid bonding assumption caused a significant (>60%) overestimation of the measured power, a non-rigid bonding model gave a better agreement (<10% error).

Interactions of vortices with a flexible beam with applications in fluidic energy harvesting

A cantilever piezoelectric beam immersed in a flow and subjected to naturally occurring vortices such as those formed in the wake of bluff bodies can be used to generate electrical energy harvested in fluid flows. In this paper, we present the pressure distribution and deflection of a piezoelectric beam subjected to controlled vortices. A custom designed experimental facility is set up to study the interaction of individual and multiple vortices with the beam. Vortex tori are generated by an audio speaker and travel at controlled rates over the beam. Particle image velocimetry is used to measure the 2-D flow field induced by each vortex and estimate the effect of pressure force on the beam deflection.

Infrapatellar Straps Decrease Patellar Tendon Strain at the Site of the Jumper’s Knee Lesion: A Computational Analysis Based on Radiographic Measurements

Background: The impetus for the use of patellar straps in the treatment of patellar tendinopathy has largely been based on empirical evidence and not on any mechanistic rationale. A computational model suggests that patellar tendinopathy may be a result of high localized tendon strains that occur at smaller patella–patellar tendon angles (PPTAs). Hypothesis: Infrapatellar straps will decrease the mean localized computational strain in the area of the patellar tendon commonly involved in jumper’s knee by increasing the PPTA. Study Design: Controlled laboratory study. Methods: Twenty adult males had lateral weightbearing and nonweightbearing radiographs of their knees taken with and without 1 of 2 infrapatellar straps at 60° of knee flexion. Morphologic measurements of PPTA and patellar tendon length with and without the straps were used as input data into a previously described computational model to calculate average and maximum strain at the common location of the jumper’s knee lesion during a simulated jump landing. Results: The infrapatellar bands decreased the predicted localized strain (average and maximum) in the majority of participants by increasing PPTA and/or decreasing patellar tendon length. When both PPTA and patellar tendon length were altered by the straps, there was a strong and significant correlation with the change in predicted average localized strain with both straps. Conclusion: Infrapatellar straps may limit excessive patella tendon strain at the site of the jumper’s knee lesion by increasing PPTA and decreasing patellar tendon length rather than by correcting some inherent anatomic or functional abnormality in the extensor apparatus. Clinical Relevance: The use of infrapatellar straps may help prevent excessive localized tendon strains at the site of the jumper’s knee lesion during a jump landing.

Fluidic harvester under train of frozen boxcars (TFB) loading: a parametric study

The Train of Frozen Boxcars (TFB) model has been developed for a continuous piezoelectric cantilever fluidic harvester to simplify the effective one-way interaction between the fluid and the structure for certain flows. The TFB model treats the force due to vortex or turbulent flow as a series of boxcars of different amplitudes, widths and separations advected with a constant velocity over a piezoelectric beam. In this paper, the effect of five parameters, namely the number, amplitude, width, spatial separation and advection speed of the boxcars in the TFB forcing model, is studied for four different forcing scenarios. It has been observed that an increase in the amplitude or advection velocity of the boxcars leads to an increase in the power output, whereas a saturation limit in the power output is observed with an increase in the width or number of boxcars. More importantly, however, it is concluded that the separation between boxcars is the determining factor in maximizing or minimizing the power output from the harvester.