Publication:
Free Vibration Response Comparison of Composite Beams with Fluid Structure Interaction

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Authors
Priest, Eric M.
Subjects
Composite
Mode Shape
Fluid Structure Interaction
Digital Image Correlation
Impact Hammer Test
Advisors
Kwon, Young W.
Gordis, Joshua H.
Date of Issue
2012-09
Date
Sep-12
Publisher
Monterey, California. Naval Postgraduate School
Language
Abstract
The analysis of the dynamic response of a vibrating structure in contact with a fluid medium can be interpreted as an added mass effect known as the Fluid Structure Interaction (FSI) problem. This effect is critical in the study of composites for marine applications since the densities of the composites and water are relatively close to one another. In this study, experimental testing was conducted to compare the free vibration response of composite beams in air with those in FSI immersed in water. Composite beams with six layers of non-biased, plain weave, 6 oz E-glass were used with two different layer orientations and boundary conditions. Five samples were layered at the 0 and 90 degree orientations and five samples were layered at the plus and minus 45 degree orientation. The Digital Image Correlation (DIC) technique was used to test each of the ten samples in a cantilever boundary condition with an initial displacement to induce a free vibration response both in air and immerse in water. A High Speed Camera (HSC) was also used to gain further frequency information during each of these tests. A second set of two composite beams were constructed with 16 layers at both of the described orientations. These were instrumented with accelerometers to conduct a modal analysis from an impact hammer test. These tests were conducted with the beams in a free-free boundary condition while in air and immersed in water. Prior to conducting these tests, an aluminum beam was tested with the same conditions to verify the waterproofing of the accelerometers and to ensure valid data was collected. The findings of this study will provide a better understanding for the use of composite materials in marine applications where various excitations can occur.
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Department
Mechanical Engineering
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Approved for public release; distribution is unlimited.
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