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Mitigation of Vortex-Induced Vibrations Using Macro

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Mitigation of Vortex-Induced Vibrations Using Macro Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2012 Mitigation of Vortex-Induced Vibrations in Cables Using Macro-Fiber Composites Gustavo J. Munoz Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY FSU-FAMU COLLEGE OF ENGINEERING MITIGATION OF VORTEX-INDUCED VIBRATIONS IN CABLES USING MACRO-FIBER COMPOSITES By GUSTAVO J. MUNOZ A Thesis submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Master of Science Degree Awarded: Spring Semester, 2012 Gustavo J. Munoz defended this thesis on March 30, 2012. The members of the supervisory committee were: Sungmoon Jung Professor Directing Thesis Michelle Rambo-Roddenberry Committee Member Lisa K. Spainhour Committee Member The Graduate School has verified and approved the above-named committee members, and certifies that the [thesis/treatise/dissertation] has been approved in accordance with university requirements ii I dedicate this manuscript to my mother, father and wife. I love you. iii ACKNOWLEDGMENTS This thesis is a combination of efforts in different ways from many special people. To begin, my advisor, Sungmoon Jung has worked tirelessly and constantly in ensuring my complete understanding of the work needed to complete this project. Not only did he guide me through my thesis work, he pushed me to reach further than minimum requirements -- arguing that we should tap into all of our potential. He also taught me and guided me through a very particular way of analytical thought while stimulating me to blossom in my own way of scientific thinking. I thank him dearly for being an excellent advisor, engineer, and friend. Special thanks to Michelle Rambo-Roddenberry and Lisa Spainhour, my two committee members. It is my aspiration to be as ethical and successful in my work as my advisors are with theirs'. A very warm and special thanks to my mother, Adelina Munoz, father, Gustavo Munoz, sister, Emily Munoz, two beautiful nieces, Samantha and Victoria, godmother, Tualina Matthews, family, Cristi Pertot, Aida Campos and Jorge Ortiz. Without their support and constant encouragement, my thesis would not have been completed with so much enthusiasm and concentration. My mother constantly pushed me to understand the importance of my success and my father was never too tired to help me -- even when it came to constructing portions of my project or giving technical advice. Finally, my friends do not come anywhere far from deserving an enormous amount of gratitude. Edmund P. Rita, my unofficial "professor", was the engine behind my belief in being able to construct a full-scale wind tunnel and have it function as a sophisticated machine. Thanks to him, my department has the immediate facilities to work with wind phenomena. Kunal Joshi, one of my best friends, spent countless hours constructing, troubleshooting and experimenting with me -- much thanks to him. Thanks to Christopher Roberts, Jeyre Lewis and Steven Sullivan, whom all helped in construction of the tunnel. To all others who supported me, Belinda Morris, Rosa Booker, Tom Trimble, Duo Liu, Braketta Ritzenthaler, John Collier, Ching-Jen Chen, Kamal Tawfiq, Amy Chan Hilton and Kirby Kemper, sincerely, thank you very much. This project was funded by a Graduate fellowship through the Florida Space Grant Consortium, NASA. iv TABLE OF CONTENTS List of Figures vi Abstract viii 1.0 Introduction 1 2.0 Literature Review and Motivation 2 2.1 Vortex-Induced Vibration 2 2.2 Vortex-Induced Vibration Control Methods 3 2.3 Macro-Fiber Composite 4 2.4 Motivation for Study 7 3.0 Construction of Wind Tunnel 8 4.0 Experimental Setup 12 4.1 Idealization of Problem 12 4.2 Instrumentation 13 4.3 Method of Perturbation 13 4.4 Calculation of Wind Speed for VIV 15 4.5 Variable Angle Test 17 4.6 Actuation Phase Test 19 5.0 Results and Discussion 21 5.1 Variable Angle Test 21 5.2 Actuation Phase Test 29 6.0 Conclusion and Future Work 34 6.1 Variable Angle Test 34 6.2 Actuation Phase Test 34 APPENDIX 36 REFERENCES 51 BIOGRAPHICAL SKETCH 53 v LIST OF FIGURES 1 Macro-Fiber Composite Schematic 5 2 M-8528-P1 Macro-Fiber Composite Actuator 5 3 Schematic of MFC motion at rest (top) and under actuation (bottom) 6 4 Wind Tunnel Design 9 5 5’ x 5’ Aluminum contraction cone followed by flow straightening section 10 6 Test Section & Diffuser Section 11 7 Open-Circuit Wind Tunnel 11 8 Setup of idealized cable section inside test section of wind tunnel 12 9 Side view of cylinder section placement in wind tunnel 13 10 Schematic of Displacement due to MFC Actuation 14 11 MFC Mechanism mounted inside Cylinder at 60-degree Orientation 14 12 Aluminum Plates with MFC glued on both sides 14 13 Schematic of Cylinder with Actuator mounted inside 15 14 Free Vibration Cylinder at 12 seconds 16 15 Free Vibration Cylinder at 1 second 16 16 Boundary Layer Separation 18 17 4 Angles of Perturbation 18 18 Detailed Schematic of Cylinder System at 60 degrees 19 19 Schematic of phase difference 20 20 0-degree Orientation Spectrum 21 21 Average Maximum Displacement @ 2.2 m/s and 0 degrees 22 22 Maximum Displacement @ 2.2 m/s and 0 degrees 22 vi 23 VIV undergoing 5.5 Hz actuation at 2.2 m/s 23 24 VIV undergoing 6.0 Hz actuation at 2.2 m/s 23 25 VIV undergoing 6.5 Hz actuation at 2.2 m/s 24 26 Average Maximum Displacement @ 2.35 m/s and 0 degrees 24 27 Maximum Displacement @ 2.35 m/s and 0 degrees 25 28 VIV undergoing 5.5 Hz actuation at 2.35 m/s 25 29 VIV undergoing 6.0 Hz actuation at 2.35 m/s 26 30 VIV undergoing 6.5 Hz actuation at 2.35 m/s 26 31 Average Maximum Displacement @ 2.6 m/s and 0 degrees 27 32 Maximum Displacement @ 3.0 m/s and 0 degrees 27 33 VIV undergoing 5.5 Hz actuation at 2.6 m/s 28 34 VIV undergoing 6.0 Hz actuation at 2.6 m/s 28 35 VIV undergoing 6.5 Hz actuation at 2.6 m/s 28 36 Effect of Frequencies Near fv on Vortex-Induced Vibrations 29 37 VIV Magnitude at Re = 6400 30 38 Cylinder undergoing VIV with 3 Hz perturbation at Re = 6400 (Trial 1) 30 39 Cylinder undergoing VIV with 3 Hz perturbation at Re = 6400 (Trial 2) 31 40 Cylinder undergoing VIV with 3 Hz perturbation at Re = 6400 (Trial 3) 31 41 Phase difference between 180o and 270o (Trial 1) 32 42 Phase difference between 180o and 270o (Trial 2) 32 43 Phase difference between 180o and 270o (Trial 3) 33 vii ABSTRACT Vortex-Induced Vibration (VIV) in cables is a prevalent phenomenon affecting the structural health of bridges and their components. Past studies have shown both passive and active methods are beneficial in the reduction of vibrations, however, a number of issues such as excessive base moment, transformation of geometry, intrusive implementation and fatigue limit the effectiveness of current engineering. A method involving no intrusion, no geometrical manipulation and a mechanism to prevent and mitigate VIV is needed. A "skin" of material embedded with Macro-Fiber Composite (MFC) material and with the capabilities of perturbing the surface near the separation point of vortex shedding is explored and tested. Simplifications of the proposed material are made in order to understand the effects of the capabilities of a perturbing skin of MFC material. Construction of a 17-ft Open-circuit wind tunnel is done in order to make the VIV condition to be tested with the near method of VIV control. The VIV on cables is recorded. Experiments are run inside the tunnel at a Re of 11400 and 6400. In order to see the effects of surface perturbations, an MFC actuation mechanism is made and a cable section effectively able to cause surface perturbations is built. A test is then run to find the effect of different angles of perturbation. Finally, a testing and analysis of a phase- difference of a signal, at prescribed perturbation frequencies is done. This is analyzed against surface vortex formation theory. The data are analyzed in order to see the capabilities of an MFC skin on VIV of cables. The mechanism shows promise in both reducing VIV and providing for a low-key, non-intrusive control mechanism. viii CHAPTER 1 INTRODUCTION Structures, heavily or partially supported by cables may undergo Vortex-Induced Vibrations (VIV) when subject to wind or other fluid flow, due to boundary layer flow separation. This characteristic of flow behavior may cause detrimental effects to the support cables of bridges. Several issues arise with modern bridge structures being subject to wind. Long span slender structures are affected by VIV as well as the inclined cables supporting them. Due to very low damping of the cables, VIV are fairly common [Matsumoto et al, 2003]. Although many control methods have been used in prototypes and have been implemented in real cable-stayed bridges, fatigue from constant vibrations is found in connections of cables to damping mechanisms. Certain bridges such as two cable-stayed bridges in Shanghai and Nanjing China have suffered from heavy cable vibrations due to rain-wind-induced vibrations, causing severe damage to the outside protective casing of the cables [Gu et al, 1998]. Hikami reproduced wind induced vibration of cables which had occurred naturally on the Meiko Nishi Bridge to demonstrate the effects of VIV [Hikami, 1986].
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