Date

2014

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Grenestedt, Joachim L.

Other advisers/committee members

Grenestedt, Joachim L.; Harlow, D. Gary; Nied, Herman F.; Pakzad, Shamim N.

Abstract

This dissertation consists of three parts - analytical modeling of slamming on a simplified bottom structure (Papers 1-2), manufacturing of sandwich panels and installing them on the Numerette high-speed offshore research boat, and experimental evaluation of slamming using the Numerette (Paper 3). In the first part, the responses of boat hull bottom panels under slamming loads are studied analytically using a linear elastic Euler-Bernoulli beam as a representation of the cross section of a bottom panel. The slamming pressure is modeled as a high-intensity peak followed by a lower constant pressure, traveling at constant speed along the beam. The problem is solved using a Fourier sine integral transformation in space and a Laplace-Carson integral transformation in time. The response of the beam is solved analytically. Deflection and bending moment as functions of time and position for different slamming speeds, bending stiffnesses, etc. are given. The response during both the initial structural inertia phase and the subsequent free vibration phase are studied and compared. In particular the effect of slamming load traveling speed on structural response of the simplified bottom structure is investigated. It is found that rather large deflections and bending moments are encountered at certain speeds of the pressure, which suggests that bottom panels may benefit from tailoring their stiffness and mass properties such that loads are reduced. The importance of the high-intensity pressure peak often encountered during slamming is also studied. In the second part some analysis of the structure plus manufacturing of sandwich panels for the Numerette craft is outlined. In the third part, experimentally obtained data from slamming on the bottom of the Numerette is studied. By combining traditional steel with modern composite materials, a creative steel/composite hybrid ship structure concept is developed and adopted in the design and manufacturing of the test boat. This slamming load test facility is also an attempt to shed some light on a new concept of building high-speed crafts with hybrid ship structures. With this new concept, the high-speed craft could be superior in certain aspects to traditional steel ship designs. The eventual goal is to develop the technology required to build a destroyer size ship using the steel/composite hybrid concept. Sea trials of the steel/composite hybrid boat were performed to evaluate the structural design of the steel/composite hybrid hull concept, as well as to investigate the response of bottom structures of high speed craft under slamming loads. A considerable amount of valuable data was collected with the onboard data acquisition system. Preliminary data analysis was accomplished. Typical strain and acceleration signals of bottom panels under real slamming loads were identified.Finally the conclusions and future work are briefly summarized in the last chapter of this dissertation.

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