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Dynamic global and torsional loads of high-speed wave-piercing catamarans through full-scale FEA and CFD simulation

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Almallah, I ORCID: 0000-0003-2398-8691 2021 , 'Dynamic global and torsional loads of high-speed wave-piercing catamarans through full-scale FEA and CFD simulation', PhD thesis, University of Tasmania.

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Abstract

Wave-piercing catamaran hull forms are widely used for high-speed ferry applications due to the hull slenderness suitable for achieving high speeds. Internal global loads acting on a catamaran's hull are of great interest as there is limited knowledge on determining the real-time magnitude of the loads, in particular when operating in random sea conditions. As a twin-hull vessel, catamarans experience additional types of global loads compared to monohull ships, especially in the transverse direction. In this thesis, the estimation of global loads of high-speed wave-piercing catamarans in full-scale is investigated through numerical simulations in particular to investigate torsional loads acting on the hull structure.
Several finite element load cases are developed in order to achieve conversion between local strain values and prevailing global loads. Records of strain signals are collected from sea trials runs of 98 m Incat HSV-2 Swift wave-piercing highspeed catamaran. Det Norske Veritas Germanischer Lloyd (DNV GL) load cases are applied to a finite element model to estimate unit conversion of strain to load. Longitudinal bending moment (LBM), pitch connecting moment (PCM) and transverse bending moment (TBM) were estimated for selected number of sea trials runs through single gauge records. Each strain gauge was positioned at the appropriate location to pick up a specific dominant loading response of the vessel. It was found that this method is relatively reliable for the prediction of hull global loads in the absence of slamming.
A transformation matrix is generated using the concept of ordinary least squares in order to convert the combined strain responses of multiple gauges to the equivalent global load cases. This is applied to determine global loads during several sea trials runs in different heading angles and speeds of 10, 20 and 35 knots. These loads then are compared to show each global load severity at specific speed or heading angle.
Full-scale computational fluid dynamics (CFD) simulations are undertaken to investigate slamming torsional and global loads acting on 98 m Incat HSV2 Swift high-speed wave-piercing catamaran in irregular sea waves. Validation of wave motion responses was carried out by comparing motion responses of CFD with sea trials data. The rigid body dynamics method is applied to estimate internal global loads at different sections of the vessel based on the relative hydrodynamic and inertia forces. The estimated global loads are compared with design loads limits provided by (DNVGL) rules. LBM, TBM, PCM, TorM, split force and prying moment were estimated for each of these CFD runs. Those runs were performed at different sea headings at 20 knots of forward speed. Headseas and bow quartering seas were investigated and slam loads were recorded and compared with sea trials load records. Peak values of each load are plotted against corresponding wave height, pitch and roll accelerations for each major slam event. It was found from these CFD simulations the maximum LBM load reached 65% of the DNV GL design load limit.

Item Type: Thesis - PhD
Authors/Creators:Almallah, I
Keywords: wave-piercing catamaran, full-scale, global wave loads, torsional loads, finite element method (FEM), computational fluid dynamics (CFD), sea trials, hull monitoring
DOI / ID Number: 10.25959/100.00046063
Copyright Information:

Copyright 2021 the author

Additional Information:

Chapter 3 appears to be the equivalent of a pre-print version of an article published as: Almallah, I., Lavroff, J., Holloway, D. S., Shabani, B., Davis, M. R., 2020. Global load determination of high-speed wave-piercing catamarans using finite element method and linear least squares applied to sea trial strain measurements, Journal of marine science and technology, 25, 901-913.

Chapter 4 appears to be the equivalent of a pre-print version of an article published as: Almallah, I., Ali-Lavroff, J., Holloway, D. S., Shabani, B., Davis, M. R., 2021. Slam load estimation for high-speed catamarans in irregular head seas by
full-scale computational fluid dynamics, Ocean engineering, 234, 109160.

A conference paper related to chapter 4 has been published. It is: Almallah, I., Lavroff, J., Holloway, D. S., Shabani, B., Davis, M. R., 2019. Real time structural loads monitoring for a large high-speed wave-piercing catamaran using numerical simulation and linear regression. IMC 2019 Pacific International Maritime Conference, 8 - 10 October 2019, Sydney Australia.

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