Hydrodynamic simulation in itself is an


extremely useful tool, but it is only when fully integrated into the design process and coupled with other computer aided engineering (CAE) techniques such as structural analysis and control system design that the full potential can be realised. The CFMS initiative, part funded by


the Technology Strategy Board, has led the way in developing these techniques. A pan-industry cooperative programme involving Airbus, BAE Systems, MBDA, Rolls-Royce and Williams F1 among others, the programme aims to deliver a paradigm shiſt in the capability of fluid mechanics simulation systems. As lead marine contributor to the programme, Frazer- Nash has focussed on coupling established geometry, optimisation, and simulation packages to allow fully constrained, multi-objective optimisation to be performed on high-speed planing craſt. Frazer-Nash said that it has demonstrated the ability to optimise hull forms for minimum slamming loads, vertical accelerations and resistance through a variety of rough sea conditions in a single automated optimisation operation taking less than one day. Te logical next step for this tool is to


combine the hydrodynamic simulation with finite element analysis of the structural response and to evaluate the seakeeping response of the vessel under helm inputs. In this way it is possible to automatically produce a hull design that is optimised for hydrodynamic, structural and manoeuvring performance for a specific range of likely operating scenarios. With today’s high powered computing clusters, and sophisticated optimisation and automation systems, such a simulation is no longer a pipe dream and has become a reality.


Beyond hydrodynamics Automated optimisation can theoretically be applied to any problem where the inputs can be parametrically defined, and the output mathematically quantified; as such, the possibilities for optimisation in the future are seemingly endless. Similarly the use of CFD itself in the marine industry is not limited to hydrodynamics. To the CFD user, water is merely another continuum material which can be discretized and simulated using a computer, and CFD is increasingly being used to simulate both external and internal


The Naval Architect July/August 2010


aerodynamic, rather than hydrodynamic, effects.


External and internal aerodynamics Engineers at Frazer-Nash have brought the full range of CFD tools to bear on the external aerodynamics of aircraſt carriers. Te airwake over the carrier deck has been simulated using CFD in order to characterise the turbulent structures over the flight deck. Tis information has been used to inform take-off and landing procedures and allow pilots to train more effectively for future carrier operations. Airwake assessment is more commonly


used in helideck operations, across defence, superyacht and container platforms. Te maturity of CFD techniques has been recognised to such a degree that CFD simulations are now considered reliable and accurate enough to provide sufficient evidence for helideck certification. Frazer- Nash has been actively involved in the MCA committee developing the LY2 regulations and has successfully assessed helicopter operations across a number of platforms. Te external aerodynamics of superyachts


are of particular concern for designers since passenger comfort is a primary design driver. CFD can be used to predict the dispersion of engine and ventilation exhaust gases over the vessel in order to gain an understanding of likely passenger exposure. Te CFD models can then be used to drive design changes in order to reduce and mitigate this exposure. Whilst the external aero and


hydrodynamics are of key importance to the design of many vessels, Frazer-Nash has frequently found that the HVAC system can be a high risk in a vessel’s design, both in terms of performance and safety, and can be easily overlooked. Insufficient or arduous intake or extract flows to main propulsion or secondary systems will clearly lead to sub optimal system performance. However in many cases it is insufficient engine cooling, both in terms of fluid and air conditioning systems that will lead to downtime. Frazer-Nash have used CFD simulations to evaluate losses in pipework systems where performance does not meet design expectations and have redesigned engine room ventilation systems across a variety of platforms in order to provide more effective, targeted cooling. Te scale


of these simulations has ranged from luxury superyachts to large naval vessels.


Simulation: the future As discussed previously, the future of CFD technology lies in simplifying and speeding up the transition from geometric model to useful simulation result. Tis allows for automated optimisation runs to be completed in a timely manner, and increases the feasibility of one-off simulations to evaluate design changes on an ad-hoc basis. Designers can then use CFD to understand and predict performance prior to manufacture rather than only to understand the root causes of problems which have been designed and built into the finished vessel, as has been the case in the past. The potential for increased throughput


is dependent on development in four key areas, specifically: computational power, automated meshing, automated simulation, and automated post processing. Te final two areas are now well established, and it is in computational power and automated meshing that real gains are being seen. The majority of readers will be familiar


with the concept of parallel processing and multi-processor clusters. Machines of this class can now be found on home desktops, and high-performance computer clusters consisting of 64 or more processing cores are now commonplace in the CFD industry. However, an interesting recent development has been in the application of Graphics Processing Units (GPUs), originating in the computer games industry, to CFD simulations. Cambridge University has recently been able to demonstrate a speed up in the simulation of flow through a gas turbine from 12 hours on a single processor to nine minutes using a GPU. Another interesting development has been


in the use of mesh-free methods for fluids simulation. This side-steps the need for automated meshing in the optimisation process by using advance modelling techniques such as smoothed particle hydrodynamics (SPH). Tese methods are increasingly finding their way out of academia and into real world applications in the marine industry as they are particularly suited to modelling the flow of water under gravity. Exploiting the combined potential of these


exciting soſtware and hardware developments will allow the full potential of these methods to be unleashed to the benefit of designers, manufacturers and operators alike. NA


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