Dynamics of nonlinear fluidic energy harvesters and arrays

Unique opportunities exist to increase the power harvested with fluidic piezoelectric generators by almost two -orders of magnitude higher than existing methods by exploiting dynamic nonlinearities and deploying multielement arrays in carefully selected positions in a flow field. These ac-coupled generators convert fluid kinetic energy, which otherwise would be wasted, into electrical energy. The available power in a flowing fluid is proportional to the cube of its velocity and if it is properly harvested can be used for continuously powering very small electronic devices or can be rectified and stored for intermittent use. Our earlier and current experimental and analytical works involving the testing of short length, flexible piezoelectric energy harvesters with different tip shapes in a large scale wind tunnel under resonance and random excitation have shown that it is possible to generate high levels of voltages through interactions with uniform flows, vortices, and turbulence in a boundary layer or in nearly homogeneous and isotropic flows. Additional experimental study has shown that nonlinear arrays of such energy harvesters can produce high output voltages in a very broadband range of frequencies. In our study, we investigate the effect of geometric parameters such as spatial arrangement of and the mutual interference between the elements of a nonlinear array have on their overall performance and efficiency characteristics. The study also includes the synergistic development of analytical and computational tools based on the nonlinear van der Pol oscillator and the lattice Boltzmann method in Finite Element formulation for a Large Eddy Simulation platform, which are being used to obtain pertinent performance parameters

Subsurface damage detection using a novel fiber optic sensing technique

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1998.Includes bibliographical references (p. 107-110).The detection of subsurface damage is important in ensuring the safety and timely repair of structures. Existing methods for non-destructive evaluation of structural elements tend to be either expensive or unreliable for monitoring large scale systems. The novel fiber optic based technique developed in this research overcomes many of the limitations of traditional non-destructive evaluation methods by providing an interferometric sensing technique coupled with a simple mechanical test. The method is based on monitoring the phase change in an integral interferometric fiber optic sensor caused by moving a mechanical load over the damaged structure. The method has been shown to unambiguously detect both the position and size of damage. The theoretical and experimental validation of the proposed method is presented for the case of open cracks in which the faces are not allowed to come into contact. The effect of damage position and damage size on sensor performance for two typical structural elements is also presented. A closed loop fiberoptic interferometer with modulated load is shown to overcome the traditional problems of environmental drift such as material creep, temperature and ambient noise. This interferometric technique is also shown to be one of the few fiber-optic based techniques that have adequate sensitivity for integral damage detection. Many traditional non-destructive evaluation methods tend to be insensitive in detecting closed cracks. Thus the closed crack problem represents a special challenge for structural damage monitoring. A fast iterative based boundary element method has been developed to solve this problem. This method is used to show the theoretical feasibility of detecting closed cracks with the developed novel sensing method.by Niell Elvin.Ph.D

Infrapatellar Straps Decrease Patellar Tendon Strain at the Site of the Jumper’s Knee Lesion

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

Damage detection in civil and aerospace structures with fiber optic sensors

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995.Includes bibliographical references.by Niell Glen Elvin.M.S

fatigue monitoring

floating gate injector for self-powere