Dissertation
Free running 6 degree of freedom CFD for high-speed small craft
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2022
DOI: 10.25820/etd.006789
Abstract
CFD simulations of a high-speed small craft, the Generic Prismatic Planing Hull (GPPH), are performed with 6DoF motions including 2DoF captive motion, free running self-propulsion, turning circles in calm water and waves, acceleration, and avoidance line tests. Both a single-phase flow solver and multi-phase flow solver are used for the calculations including variable fidelity modeling (VFM) and high fidelity (HF) methods. In the VFM simulations, the propeller and gear case force models are used to replace the actual geometry propeller used for the HF calculations. The hull form and propulsor of the GPPH are scaled to match a deep V fishing boat (DVFB). The on water experimental data of the DVFB was collected by Mercury Marine (MM) for self-propulsion, which is used for qualitative validation.
Both the captive and 3DoF self-propulsion simulations show that the trim angle and heave decrease with the gear case. The simulation with the gear case also shows a larger resistance than the VFM due to the differences between the VFM and the gear case towing tank experiment. For the self-propulsion simulations, the 6DoF simulations show reasonable force and moment balances for all of directions including surge, sway, heave, roll, pitch, and yaw. The 3DoF simulations, however, only show the balances with surge, heave, and pitch. The tilt angle effect study shows that the resistance decreases, and the pitch angle increases with tilt angles for the HF simulations, which agrees with the experiment. The simulations of turning circle maneuvering show reasonable force-moment balance in all degrees of motion, and the VFM results show reasonable agreement with the HF for stable turnings but show spin-out phenomenon for the steering angle of 25 deg. When the unstable turning spin-out occurs, the yaw rate and drift angle are highly increased and the ship-speed is significantly reduced. The simulations of maneuvering in waves show that the yaw rate and drift angle are highly increased, and the speed is significantly reduced, which is similar to the spin-out case in calm water. The avoidance line tests show the results satisfies the safety criteria and a large centrifugal acceleration over 2.2g is predicted during the 90deg quick turns, which is dangerous as it may lead to ejection of the crew from the vessel.
The present work is the first known CFD study for the free running of high-speed small craft with 6DoF motions and is exploratory in nature. The accuracy and performance of the VFM methods are evaluated with the issues identified. Other issues for the simulations of the high-speed small craft are also discussed such as the optimum grid sizes, submerged depth of the gear case, and instabilities. All of these can be provided as recommendations for future research improvements.
Details
- Title: Subtitle
- Free running 6 degree of freedom CFD for high-speed small craft
- Creators
- Sungtek Park
- Contributors
- Frederick Stern (Advisor)Zhaoyuan Wang (Advisor)Ching-Long Lin (Committee Member)Moustafa Abdel-Maksoud (Committee Member)James Buchholz (Committee Member)Corey Markfort (Committee Member)John Scherer (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Mechanical Engineering
- Date degree season
- Autumn 2022
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006789
- Number of pages
- xix, 138 pages
- Copyright
- Copyright 2022 Sungtek Park
- Language
- English
- Description illustrations
- Illustrations, charts, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 135-138).
- Public Abstract (ETD)
Numerical simulation of high-speed small craft with 6DoF motions is challenging and difficult since it involves high Reynolds number multiphase turbulent flows interacting with moving bodies of complex geometries. Most previous maneuvering studies for high-speed small craft are focused on system based maneuvering methods. The system based maneuvering method can well predict ship motions with proper set-up of the hydrodynamic coefficients. However, many captive tests are needed to cover all ranges of ship motions to obtain the required hydrodynamic coefficients. Moreover, the system based maneuvering model cannot predict the ship motion properly when abrupt changes occur in ship motions, such as the spin-out phenomenon.
In the present study, computational fluid dynamics (CFD) simulations of a high-speed small craft are performed with 6DoF motions. Both CFDShip-Iowa V4.5 and V5.5 are used for the calculations including variable fidelity modeling (VFM) and high fidelity (HF) methods. In the VFM simulations, the propeller and gear case force models are used to replace the actual geometry propeller. Many captive and free running conditions are considered including 2DoF captive motion, free running self-propulsion, turning circles in calm water and waves, acceleration, and avoidance line tests. The very challenging multi-phase flow simulations involving air, water, exhaust gas, and cavitation are also conducted.
The present work is the first known CFD study for the free running of high-speed small craft with 6DoF motions. It also should be noted that the present study is exploratory in nature and the project limitations required the differences in the CFD and experimental geometries. The optimum grid sizes and VFM were not known a priori but rather are issues, which are identified in the present research and provided as recommendations for future research improvements.
- Academic Unit
- Mechanical Engineering
- Record Identifier
- 9984362557602771
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