Slam and Response Reconstruction for High-Speed Catamarans

  • Hirdaris, S. (Examiner)
  • Damien Holloway (Supervisor)
  • Tim Finnigan (Chair)

Aktiviteetti: Väitöskirjan esitarkastajana tai vastaväittäjänä toimiminen tai jäsenyys tohtorikoulutusneuvostossa

Description

Wave-piercing catamarans are used in high-speed transport applications where they constantly encounter sea wave loads. To ensure sufficient strength and fatigue life at low cost, knowledge to predict or reconstruct wave slamming forces and the subsequent responses is required, which is difficult due to the complex fluid-structure interaction. The slamming wave force over the bow area produces significant responses in addition to the non-slamming global wave load responses, which are measured using multiple sensors on the vessels. In this thesis, the slam force and the relationship between sensors are investigated analytical and numerically combined with sea trials data.

A simplified analytical model to predict severe slam force on a catamaran in head sea was developed. The method was validated by transverse impact experiments on a free-free beam. The ship was represented by a beam, the local hydroelasticity and air-water mixture compressibility by a spring, and the water interaction by an added mass. The model parameter values were based on the geometry of the catamaran, natural frequencies and relative bow velocities measured during sea trials. The peak force was found to be in the order of the vessel weight. It was found that increased flexibility between beam and striker reduced peak impact force. For very stiff vessels, a single degree of freedom mass-spring system could predict the slam force.

Slamming and global wave load responses were reconstructed using the transmissibility concept based on linear response theory to demonstrate redundancy and potentially reduce the number of sensors on the high-speed catamaran HSV 2 Swift using full-scale sea trials on various operating conditions. A transmissibility function was derived between two responses from the data using a typical impact event. The transmissibility function could reconstruct the desired response when the sea state and vessel heading did not change. For general operating conditions the transmissibility matrix, which relates a set unknown response to a set of known responses, was derived from some of the data. It successfully reconstructed desired responses on all operating conditions. A single transmissibility matrix can be used for head, port bow, and starboard bow sea vessel directions in all the sea states and vessel speeds tested.
Slam force reconstruction on the 98 m catamaran HSV 2 Swift was investigated using sea trials data combined with direct transient finite element analysis of the full-scale vessel. This inverse analysis was carried out using the Tikhonov regularisation. This was first validated using the beam experiment data for a single force and multiple superposed forces. The slam force on the vessel was divided into four regions over the bow area and was reconstructed using four measured longitudinal bending strains. Thus, the method could be used for a variety of vessel headings. It was found the peak force was around the weight of the vessel, and that slams are typically asymmetric even in head seas. The technique enables to accurately determine slam force profiles and impact location trajectories.
Aikajakso30 tammik. 2024
TutkittavaSebhatleb Gebrezgabir
Tutkimuksen ajankohta
  • University of Tasmania
Tunnustuksen arvoInternational

Open science

  • This is related to promoting open science

Open science keywords

  • Researcher evaluation
  • Wide scientific knowledge dissemination

Research ethics and research integrity

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