| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | July 18, 2014 |
| Latest Amendment Date: | March 6, 2015 |
| Award Number: | 1363231 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Irina Dolinskaya
idolinsk@nsf.gov (703)292-7078 CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | September 1, 2014 |
| End Date: | August 31, 2018 (Estimated) |
| Total Intended Award Amount: | $325,000.00 |
| Total Awarded Amount to Date: | $330,000.00 |
| Funds Obligated to Date: |
FY 2015 = $5,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
506 S WRIGHT ST URBANA IL US 61801-3620 (217)333-2187 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1901 S. First Street, Suite A Champaign IL US 61820-7473 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Dynamics, Control and System D |
| Primary Program Source: |
01001516DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
Fluid-structure interaction is ubiquitous across a range of engineering applications, from flutter and divergence in aerodynamics, to vibration of fuel rods in nuclear power reactors, tension legs in offshore platforms, wind turbine towers, and hydrokinetic energy harvesting. A major aim of this work is to demonstrate that using intentionally designed nonlinear oscillators inside a bluff body it is possible to passively suppress vortex induced vibrations - VIVs, partially stabilize the wake past the body, and reduce the drag force exerted by the surrounding fluid without any external modification. This research can have broad and significant impact in diverse fields. For example, the reduction of the drag forces on a bluff body through the action of internal nonlinear oscillators might significantly affect the design of future air vehicles and boats by enhancing their performance, enlarging their range of operation and decreasing fuel consumption. Also, enhanced and economical hydrodynamic vibration energy harvesting could be achieved by appropriate design and optimization of internal nonlinear oscillators inside a body undergoing VIVs.
In this research, the dynamic interactions of a strongly nonlinear finite-dimensional oscillator with an infinite-dimensional fluid flow will be studied. This is important in understanding not only fluid-structure interaction in a variety of contexts, but also, in a broader sense, because it serves as a testbed for understanding the nonlinear dynamical behavior of a variety of other mechanical (and nonmechanical) systems involving nonlinear interactions of coupled finite- and infinite-dimensional parts. The fundamental importance of dealing with an intermediate-to-high range of Reynolds number -- Re -- lies in the fact that our preliminary results show that the dimension of the attractor in the two-dimensional laminar case is less than four, while in the turbulent case, it is expected to grow as Re to the 9/4 power. This system thus provides a unique opportunity to understand the dynamics of fluid-structure interaction, where the dimension of the attractor varies from one (for periodic response) to much larger values. We will also study the heretofore unexplored role of angular momentum in VIV. Finally, the capacity of strongly nonlinear internal oscillating elements to drastically modify the wake of a bluff body and reduce its drag coefficient at both intermediate and higher Re will be explored. The research will be performed using slow/fast dynamical decompositions, invariant slow manifold considerations, nonlinear system identification, and reduced-order modeling techniques. High-fidelity fluid-structure interaction computations will be performed in the laminar, transition, and turbulent regimes.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The problem of vortex-induced-vibrations (VIVs) when bluff or flexible bodies dynamically interact with a surrounding fluid is central in many practical applications. For example, this problem is of interest in off-shore oil platforms with their pylons being subject to water wave excitations; in devices that harvest energy from underwater currents or surface waves; but also in more common types of engineering applications such as (high-speed) commercial planes cruising in air, high-performance automobiles experiencing drag resistance from air, or boats experiencing drag from the sea.
The scope of this project was two-fold: First, to explore the effects that strongly nonlinear, oscillating or rotating internal attachments inside a bluff body can have on the fluid-structure interaction (FSI) of that body; and second, to perform a preliminary study of the efficacy of this type of internal rotating nonlinear attachments for hydroelectric energy harvesting from the surrounding fluid. To this end, a simple system was selected for the study, namely an in-flow linearly sprung cylinder allowed to undergo transverse oscillations orthogonally to the direction of the incoming flow. This system, although of simple geometry and configuration, provided a prototypical model to study the qualitative and qualitative features of the nonlinear FSI dynamics under consideration.
Advanced techniques were employed for this project, including asymptotic techniques that allowed for slow/fast partitions of the FSI dynamics of the cylinder, the internal nonlinear attachment and the fluid modes; nonlinear system identification techniques yielding accurate and robust reduced-order models of the nonlinear FSI; as well as high-fidelity spectral element computational techniques based on the state-of-the-art code NEK 5000.
The study was carried out in two phases, considering first the laminar flow regime – with Reynolds numbers (Re) of about 100, and then the turbulent flow regime with Re up to 10,000. Considering first the low-Re laminar regime, it was found that the addition of an internal rotating nonlinear dissipative attachment to the cylinder can have surprising and unexpected results on its interaction with the surrounding fluid. First, the internal attachment can act as a nonlinear energy sink (NES), passively absorbing and locally dissipating vibration energy from the fluid, thus suppressing the VIVs of the cylinder. Different modes of suppression were studied in detail. Second, it was proven that the action of the internal NES may drastically affect the dynamics of the surrounding fluid, that it, it may intermittently, partially stabilize the fluid motion in the wake of the cylinder. This intermittent nonlinear phenomenon is accompanied with significant reduction of the drag and lift coefficients of the cylinder. Hence, it was proven that an internal strongly nonlinear attachment may affect the FSI interaction of the bluff body in which it is contained. This exciting new finding paves the way for passively reducing the drag coefficients of bluff bodies in-water or in-air through appropriately optimized internal nonlinear attachments.
Extending the study to the high-Re turbulent regime, it was found that the significant drag reduction of the cylinder due to the action of an internal rotating NES appears to be preserved in the turbulent regime as well. This highlights the practical significance of implementing internal NESs in engineering applications involving FSI of bluff or flexible bodies. In addition, a preliminary study of using the internal rotating NES as energy harvester was performed, indicating that the NES is capable of absorbing a significant portion of the energy induced by the flow to the cylinder. This provides a preliminary demonstration of the efficacy of the proposed nonlinear design for hydroelectric energy harvesting.
The proposed concept of using internal nonlinear elements for suppressing VIV and affecting the wake of bluff bodies holds potential for applications in broad fields such as offshore structures (passively reducing their vibrations due to sea wave excitations), aeroelastic structures (partially stabilizing flutter regimes, and extending the flight envelopes due to passive drag reduction), and reducing wind-induced oscillations of high rise structures, e.g., bridges and chimneys. Moreover, the data-based reduced-order modeling and analysis techniques that were developed in this project can find applications in studies of complex dynamical interactions involving nonlinear substructures coupled to linear or nonlinear main structures, so that predictive design based on rigorous analysis can be performed. Finally, the motion (translation or rotation) of the nonlinear attachment can be utilized in energy harvesting schemes, potentially providing a new paradigm for clean-energy harvesting, with potential benefits compared to current designs. That is, providing minimal interference and disturbance of aquatic life, and being environmentally friendly, as it is minimally intrusive to the environment.
Last Modified: 11/29/2018
Modified by: Alexander F Vakakis
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