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AN EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF WAVE INTERACTION WITH AN OFFSHORE SUBMERGED CYLINDRICAL STRUCTURE

Author
Zarruk, Gustavo
Abstract
The interaction of periodic waves with a model offshore submerged water intake
structure was examined experimentally and analytically. Two wave conditions,
with long and short wavelengths relative to the structure?s characteristic
length scale were tested. Flow kinematics were characterized using particle image
velocimetry and the wave motion measured with capacitance wave gages. Pressure
distributions at key locations around the model as well as inline and uplift forces
were measured with an array of pressure sensors distributed around the model.
The two types of waves tested simulated the maximum and minimum typical conditions
estimated to be present on existing intake structures. Additionally, flow
visualization was carried out for a solitary wave traveling over the structure to
better characterize the processes that occur in the vicinity of the structure. A
complete description of the flow kinematics is presented for the long wave case.
The main vortex patterns are related to the wave motion induced inline and uplift
forces. Large scale vorticity patterns generated on the weather and lee sides of the
structure influence the loading of the structure, primarily the uplift force where
large uplift coefficients were found. The dominant vorticity pattern, a vortex filament
pair, was linked to the maximum uplift coefficient. The inline force coefficient
found is similar to coefficients previously reported for cylindrical structures. The
ratios of total vs two component turbulent kinetic energy were estimated. Results
disagree with typical ratios found in other studies and generally used to estimate
total kinetic energy when one component of velocity is missing. However, large
turbulent kinetic energy uncertainty levels were found and caution is advised when
using this information.
An analytical model based on small amplitude wave theory and irrotational
flow solved using a eigenfunction expansion method is presented. Results are compared
with experimental values measured for a short wavelength case, conducted
specifically to verify and validate the model. Horizontal and vertical velocities as
well as inline and uplift force coefficients are in good agreement. Force coefficients
were also compared with the long wavelength case results and similar maximum
values were obtained. The model is capable of estimating wave scattering, flow
kinematics, and wave induced loading on the structure in the diffraction range.
Date Issued
2004-12-13Subject
wave interaction; cylindrical structure; PIV; analytical solution; eigenfunction expansion method; dynamic forces; solitary wave; flow visualization; force coefficients
Type
dissertation or thesis