New Frontiers Fellow Dr Joe Banks and PhD student Artur Lidtke represented FSI at Tokyo 2015.  The Ship Hydordynamics workshop, organised by and held at the facilities of National Maritime Research Institute (NMRI) of Japan, attracted a large number of attendees from academic and industrial backgrounds alike. Over 30 groups submitted results to allow for an assessment of the state of the art in hydrodynamic prediction methods related to ship flows. Investigated cases included the Korean Container Ship (KCS), ONR tumblehome ship (ONRT), as well as a completely new bulk carried hull, the Japanese Bulk Carrier (JBC).

The latter proved to be particularly challenging to evaluate numerically due to its high block coefficient and the resultant complex vortex structure in the wake. Most of the participants were able to predict the global forces acting on the hull and propeller with reasonable accuracy, but only the most advanced highly-resolved LES and Reynolds Stress transport RANS models were found to be capable of capturing the nature of the hook-shaped vortex in the stern region.

 The submission by the FSI group focused on the towed and self-propelled JBC cases. The former were found to agree well with similar submissions from other institutions. FSI was the only participant to evaluate the same case using more than one code using nearly-identical numerical setup and the same grid. Doing so helped to distinguish between prediction errors due to fundamental shortcomings of the RANS method used and implementation- and user-induced inaccuracies.

The Southampton maritime CFD team are the only UK based group to participate regularly in these workshops that originated from the International Towing Tank Conference in the 1980’s. They have presented their work in Gothenburg in 2000 and 2010 and previously in Tokyo in 2005.  A number of those involved in those years attended as representatives from other organisations worldwide.

Figure1: Breaking wave formation in the towing tank

Research has recently been undertaken utilising the new 138m towing tank at the University of Southampton.  Funded by the Higher Education Innovation Fund (HEIF) via the Southampton Marine and Maritime Institute (SMMI), the research is a collaboration between Dr Sally Bennett (Fluid-Structure Interactions) and Prof. Robert Marsh (Ocean and Earth Sciences) which looks at the characterisation of freak wave groups for safer ship routing. The research strongly links with PhD research being undertaken by Alex Cattrell within the Fluid-Structure Interactions group at University of Southampton.

The recent testing focussed on the characterisation of freak waves and freak wave groups in terms of their formation and shape.  Waves were generated at a scale of 1:22.  A combination of photography, video imagery and state-of-the-art ultrasonic wave probe technology was used to analyse the wave formation including breaking wave characteristics where appropriate.   A video of some of the testing can be found at https://youtu.be/EQ05QXMoShg.
Following this investigation into the wave groups themselves, this project will continue by looking at the influence of these waves on a ship, and how to manoeuvre the vessel through the waves to minimise structural loading, and therefore damage.
 

GDP2 at Boldrewood Innovation Campus

Last but not least of our series introducing this years Group Design Projects run from the ship science programme.  The project aims to solve many problems that hull fouling causes, both environmentally and financially. To name a few:

• 39% of invasive species transported by shipping are found in the hull fouling (Molnar et al., 2008)
• A fouled hull leads to increased fuel consumption and carbon emissions (M.P. Schultz, 2010)
• Existing cleaning methods require the ship to remain in port

We are undertaking the design build and test of an autonomous hull cleaning robot, capable of regularly cleaning the hull of a ship while the ship is at operational speeds.


To achieve this we are going to:

• Develop an attachment method capable of resisting the forces the robot is subject to at operational ship speeds.
• Develop the autonomous system which is able to navigate a defined area, maintaining knowledge of its position within the domain and avoiding obstacles.
• Design and test a body form which is optimised to aid the attachment method
• Manufacture the various elements of the robot to be tested individually
• Test the ability of the final assembly to perform under simulated operating conditions

FSI Seminar on Thursday 10th December in 176/L1107,
Boldrewood Innovation Campus
to be given by Christian Klettner, Research associate, Mechanical Engineering, University College London
 
Risers from the sea floor to installations at the sea surface are an integral part of the flow assurance of deep sea oil exploration, which has become necessary in the last decade. These risers are subjected to various hydrodynamic forcing, particularly sea currents, wakes of upstream installation members and surface waves, which can result in vortex or wake induced vibrations and these in turn can result in riser fatigue or collision. The free stream flow past groups of cylinders has been studied for two- and three-dimensions for Re=100(based on the cylinder diameter) by Nicolle & Eames (2011) (direct numerical simulations) and ReO(10000) by Chang \& Constantinescu (2015) (large eddy simulations) respectively. In this study we will be focusing on the first two aspects listed above, numerical simulations will be performed to investigate the effect of an upstream truss on an array of cylinders. The main diagnostic will be how varying the void fraction of the array of cylinders affects the frequency and magnitude of the drag and lift forces on the cylinders.
 
Brief CV
Christian Klettner received his BEng in 2006 and PhD in 2010 from University College London. His PhD, under the supervision of Ian Eames, was on aspects of solitary waves propagating over different topography using numerical simulations.  He was in at National University Hospital Singapore as a post doc for 2.5 years developing numerical models and performing small scale  experiments on transport in hospital rooms.  He is now a post doc at UCL Department of Mechanical Engineering  working on the project URBANWAVES which is in collaboration with UCL Civil Engineering Department. The project will investigate the forces exerted on coastal installations during tsunami and storm surge inundation which will require the development of various numerical methods. The intention is to calibrate a shallow water model with large scale numerical simulations of the flow past a building with varying blockage ratio. These can then be incorporated into city wide shallow water models.