Document Type

Thesis

Date of Degree

Fall 2015

Degree Name

MS (Master of Science)

Degree In

Mechanical Engineering

First Advisor

Frederick Stern

Second Advisor

Sayyed M. Mousaviraad

Abstract

High-fidelity CFD-MBD FSI (Computational Fluid Dynamics - Multi Body Dynamics Fluid-Structure Interaction) code development and validation by full-scale experiments is presented, for a novel hull form, WAM-V (Wave Adaptive Modular Vessel). FSI validation experiments include cylinder drop with suspended mass and 33 ft WAM-V sea-trials. Calm water and single-wave sea-trails were with the original suspension, while the rough-water testing was with a second generation suspension. CFDShip-Iowa is used as CFD solver, and is coupled to Matlab Simulink MBD models for cylinder drop and second generation WAM-V suspension. For 1DOF cylinder drop, CFD verification and validation (V&V) studies are carried out including grid and time-step convergence. CFD-MBD results for 2DOF cylinder drop show that 2-way coupling is required to capture coupled physics. Overall, 2-way results are validated with an overall average error value of E=5.6%DR for 2DOF cylinder drop. For WAM-V in calm water, CFD-MBD 2-way results for relative pod angle are validated with E=14.2%DR. For single-wave, CFD-MBD results show that 2-way coupling significantly improves the prediction of the peak amplitude in pontoon motions, while the trough amplitudes in suspension motions are under-predicted. The current CFD-MBD 2-way results for single-wave are validated with E=17%DR. For rough-water, simulations are carried out in regular head waves representative of the irregular seas. CFD-MBD 2-way results are validation with E=23%D for statistical values and the Fourier analysis results, which is reasonable given the differences between simulation waves and experiments.

Public Abstract

A wave adaptive modular vessel (WAM-V) is studied and computer models, simulating the coupled suspension dynamics and pontoon hydrodynamics, are developed and validated against sea-trial data. A WAM-V is a class of suspension sea-going vessel that conforms to the surface of waves through flexible catamaran style pontoons, a suspension system that independently articulates, and hinged engine pods.

Simulations are performed and validated independently, simulating the hydrodynamics (water-pontoon interaction), and simulating the suspension dynamics, and coupled, where the dynamic motions of the suspension are accounted for in the hydrodynamic simulation. This coupling method is referred to as fluid structure interaction, and is the objective of this thesis.

Experiments are used to validate independent and coupled simulations for both a full scale WAM-V and a simple pontoon-sprung-mass system. The pontoon-sprung-mass experiments are used to initially validate hydrodynamic modeling, suspension modeling, and simulation coupling methodology. The WAM-V experiments are used to validate suspension system modeling and coupled simulations in calm water, over a single stern wake of a freighter ship, and in rough waters.

The results from the independent simulations for the pontoon-sprung-mass experiments and the WAM-V show good agreement with experimental data. The results from the coupled simulations compared to the independent simulations show that it is necessary in cases with complex coupled physics to have a coupled simulation to capture important phenomena that is missed in independent simulations.

Keywords

publicabstract, Computational Fluid Dynamics, Coupling, Fluid Structure Interactions, Mulit-Body Dynamics, Ship Hydrodynamics

Pages

xi, 76 pages

Bibliography

Includes bibliographical references (pages 73-76).

Copyright

Copyright 2015 Michael Anthony Conger

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