Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Grenestedt, Joachim L.

Other advisers/committee members

Harlow, D. Gary; Nied, Herman F.; Jaworski, Justin; Yu, Yue

Abstract

This dissertation consists of four articles on the experimental investigation of slamming in high speed craft. The investigation utilizes data from the purpose-built 9 meter high-speed offshore research boat Numerette. The unique hybrid steel/composite construction and high-speed, high channel count instrumentation and data acquisition system have enabled collection of the wealth of experimental data that is analyzed in these articles. In the first article the role of hull bottom panel stiffness in slamming is investigated. Two panels of differing construction are mounted on starboard and port on the Numerette, which is run at relatively high speeds in the Atlantic Ocean. Displacements of the two different panels are compared. The structural response under slamming loading is then compared with the behavior under static loading. It is shown that the static stiffness relationship is not directly reflected in the experimental slamming data; rather the relative response falls somewhere between the case of a static loading and the dynamic response of a simple mass-spring system. In the second article, the structural response of bottom panels to slamming loads is investigated further. Experiments are described and results presented for modal and static analysis of the Numerette bottom panels in free air. Strain data is then presented from slamming experiments, investigating the influence of wave encounter conditions and vessel rigid body motions on response in the time and frequency domains.The third article presents an analysis technique that uses the wavelet transform to provide insight into the behavior of marine structures subjected to slamming loads. Pressure, strain, acceleration and displacement data for an isolated slamming event are presented in the time domain and in the frequency domain with Fourier transforms and wavelet transforms. Two periods of high acceleration are identified and using the wavelet transform are shown to be vibration at the dry and then wet eigenfrequencies. Mode shapes are identified during these two phases using data from an array of accelerometers. The optimal time-frequency resolution of the wavelet transform makes it a powerful tool in analyzing slamming data, revealing non-stationary behavior that the Fourier transform obscures. Identifying such behavior can be critical, in particular in hull structures with reduced stiffness where strong hydroelastic effects are expected.The final article presents the validation of a high fidelity CFD/FE FSI code using data from Numerette. The CFD code CFDShip-Iowa and finite element solver Ansys are used. Hydrodynamic simulations are performed at a range of Froude numbers and sea conditions. Good agreement is shown with experimental data in calm seas. A one-way fluid structure interaction study is performed and strains show a qualitative agreement between numerical and experimental data.These articles give insight to the designer of high speed craft by comparing the response of panels of varying, but relevant constructions to slamming loads. Additionally, the time-frequency analysis tool presented enables evaluation of structural response and identification of behavior that can be critical in slamming. Finally the collected data is used to validate a CFD/FE FSI code that could be used early in the design phase to optimize a structure and hull geometry under realistic conditions.

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