N12A-T011 TITLE: High Resolution Measurement of the Coupled Velocity and Acceleration Fields of both the Fluid and Structure in Hydrodynamic Fluid Structure Interactions associated with Marine Vehicles

TECHNOLOGY AREAS: Materials/Processes

ACQUISITION PROGRAM: NAVSEA 073R, Advanced Submarine Systems Development (ASSD)

OBJECTIVE: Develop a low-cost, non-invasive approach to measure time-resolved fluid and structural velocity and acceleration fields that occur in a coupled fluid structure interaction associated with marine vehicles.

DESCRIPTION: Innovative non-invasive approaches are sought for simultaneous acquisition of the velocity and acceleration fields of both a fluid and solid undergoing a fully-coupled fluid-structure interaction. The coupled velocity and acceleration fields of a fluid and structure for a fluid around a moving structure are sought. Techniques which do not require the alternation of the structure to accommodate invasive sensors, such as optical techniques, are particular preferred (see references). Spatial resolution of measurement methods must also allow fine enough spatio-temporal resolution to capture large and small scale flow eddies near the solid surface, turbulent flow shear layer characteristics and structural response modes. Of particular importance is that the proposed method possesses sufficient time resolution to enable accurate measurement of the fluid and structure acceleration fields. The apparatus and technique should be capable of simultaneously characterizing the fluid and structure motions, be usable in large-scale test scenarios, capable of mounting to test vehicle, and should be capable of synchronization with other measurement acquisition. Any velocity/acceleration measurement method that meets the above requirements will be considered.

Modern composite structures are being designed to flex or deform under fluid loading to attain desired performance gains. The resulting fluid/structure interactions, not easily modeled by classical analytical approaches, have recently motivated development of advanced methods to simulate coupled flow and structural motion. The success of these advanced computational methods depends critically on high-quality, high-fidelity, validation measurements. In addition, once a full-scale device made from composite materials is built, its performance must be accurately characterized to ensure it meets design specifications. The accurate characterization of the fluid and structure acceleration field is also essential to accurate acoustic predictions.

The various commonly used velocity field measurement methods used to spatially map a flow field are either inadequate for coupled measurement of both the fluid and structural velocity and acceleration fields, or involve expensive, specialized high frame rate cameras and high firing rate lasers as an illumination source. For example, Particle Image Velocimetry (PIV) methods, can be extended to measure acceleration. For many users, the cost of a system capable of high-speed measurement is prohibitive due to the high cost of camera and laser. Often there is an inherent between illumination intensity and acquisition rate. This can be minimized in small-scale experimental setups, because the optical paths are short. However, it is desirable to allow high-speed acquisition in larger test rigs to accommodate larger-scale testing in a tow tank, flume, water tunnel, or in the field.

PHASE I: Define and develop a concept of an imaging method capable of simultaneous measurement of the velocity and acceleration fields of both the fluid and flexible structure undergoing coupled fluid-structure interaction. Evaluate the spatial and temporal resolution limits and identify approaches to improve resolution. Evaluate the velocity and acceleration measurement accuracy. Define the potential for development of low-cost version of the method. Address potential for on-board deployment in a test model. Contractor may make use of public domain flow facilities, such as wind and water tunnels operated by academic institutions.

PHASE II: Extend the Phase I methodology to improve any deficiencies, such as spatial or temporal resolution, and measurement uncertainty. Develop and deliver a prototype capable of meeting the objectives outlined above and capable of being used in large scale test facilities; such as tow tanks, flumes, water tunnels, or field trials. Improve upon the Phase I laboratory method to enable practical, low-cost version for future commercialization. Any differences between Phase I and Phase II methodologies are to be noted and explained.

PHASE III: Further develop the measurement method to commercially viable form, or to a service provided for private sector and other government uses.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The ability of current optical technology tools to characterize both the fluid and solid components of a fully-coupled fluid-structure interaction is limited by several factors. If successful, it is expected that this technology will provide excellent benefits for marine vehicle designers in both the commercial and military sectors and will be generally useful as a research and engineering tool. Significant benefits will be gained over a wide variety of marine and medical device applications. A large segment of these communities would be potential customers of this method. Finally, the emphasis on low cost solutions will encourage adoption by academic institutions as a teaching tool.

REFERENCES:
1. Govardhan, R., and CHK Williamson. "Modes of vortex formation and frequency response of a freely vibrating cylinder." Journal of Fluid Mechanics 420 (2000): 85-130. MAE.Cornell.edu. 2000 Cambridge University Press. 13 Apr. 2011 <http://www.mae.cornell.edu/fdrl/publications/Govardhan_Williamson.pdf>.

2. Hover, F. S., A. H. Techet, and M. S. Triantafyllou. "Forces on oscillating uniform and tapered cylinders in a crossflow." Journal of Fluid Mechanics 363 (1998): 97-114. DSpace.MIT.Edu. Cambridge University Press. 13 Apr. 2011 <http://hdl.handle.net/1721.1/25616>.

3. Muller, Susan J. "Velocity measurements in complex flows of non-Newtonian fluids." Velocity measurements in complex flows of non-Newtonian fluids 14 (2002): 93-105. Korea-Australia Rheology Journal. 13 Apr. 2011 <http://infosys.korea.ac.kr/PDF/KARJ/KR14/KR14-3-0093.pdf>.

4. Sarpkaya, T. "A critical review of the intrinsic nature of vortex-induced vibrations." Journal of Fluids and Structures 19 (2004): 389-447. DTIC.mil. Elsevier Science Ltd. 13 Apr. 2011 <http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA417156&Location=U2&doc=GetTRDoc.pdf>.

5. Wang, X. J., et. al., "Characterization of fluid flow velocity by optical Doppler tomography." Optics Letters., Vol. 20, Issue 11 (1995).

KEYWORDS: Flow; Visualization; Velocimetry; Acceleration; Interaction; Hydroelasticity

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