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The operation of a marine propeller dominates the flow interaction effects and alters the resistance on an upstream hull and the forces on a downstream rudder. A study is carried out into how these effects can be resolved by comparing four different methods. A classical prescribed body force approach in which an averaged nominal wake is used as input for the propeller model with prescribed thrust and torque; Two coupled BEMt-RANS solver which accounts for the non-uniform inflow into the propeller and a time resolved discretize propeller approach employing the use of an Arbitrary Mesh Interface model (AMI). The main differences between these four methods are also outlined quantitatively. The accurate results obtained using the two coupled BEMt-RANS approaches makes them fast and robust methods which can be used for ship resistance and self-propulsion estimation in the initial design phase

As modern supercomputers edge towards exascale, their architectures are becoming more parallel. In order for computational fluid dynamics (CFD) simulations to operate efficiently on newer machines, a complete harmony between hardware, software and numerical algorithms is required. In the work presented here, a typical CFD code is instrumented, and a strong-scalability study performed to identify areas of the execution which require improvement, using the well-known KVLCC2 test case. The effects of changing discretization schemes, mesh structure, turbulence models and linear solvers are all tested. The results show that data exchange among cores and the inner-loop pre-conditioners both have a large impact on performance in a massively-parallel environment, and should be the focus of future developments.

This paper details a set of experimental tests conducted on a NACRA F20 curved dagger board in the University of Southampton’s RJ Mitchell wind tunnel. Digital image correlation (DIC) was used to measure the full field deflection at the board tip and particle image velocimetry (PIV) was used to capture the position and strength of the tip vortex. Preliminary CFD simulations of the rigid experimental geometry are compared to this data

The prediction of a ship’s wake field and self-propulsion capabilities has traditionally been centered on experiments; however with the advancement in modern computing power, this can be achieved through the use of computational methods. An advantage with the use of CFD is its ability to provide insight into flow characteristics close to the wall, which are difficult to obtain through experiments. The most interesting and challenging aspect of using CFD in this analysis, is the influence of the propeller action and the unsteady hydrodynamic of the rudder working in the propeller wake. One approach to address the problem is to discretize the ship, propulsor and the rudder using unsteady RANS computations (Carrica et al., 2011). Due to the small time steps and high computational cost involved, simulations are often performed using representative propeller models or body force method. The level of complexities in the body force propeller approach varies from prescribing the body forces, Badoe et al., (2012), Phillips et al., (2010), through to coupling a more complex propeller performance code which accounts for the non-uniform inflow at the propeller plane, Phillips et al., (2009). There are several self-propulsion computations using body force propeller models reported in the literature. Banks et al., (2010) performed a RANS simulation of multiphase flow around the KCS hull form using a propeller model with force distribution based on the Hough and Ordway thrust and torque distribution (Hough and Ordway, 1965). Simonsen and Stern, (2003) coupled a body force propeller model based on potential theory formulation in which the propeller was represented by bound vortex sheets on the propeller disk and free vortices shed from the downstream of the propeller to a RANS code to simulate the manoeuvring characteristic of the Esso Osaka with a rudder. In the present work an investigation is carried out into the sensitivity with which the wakefield of a container ship in calm water is resolved using a coupled BEMt-RANS sectorial approach.

Computational Fluid Dynamics (CFD) has enjoyed the speed-up available from supercomputer technology advancements for many years. In the coming decade, however, the architecture of supercomputers will change, and CFD codes must adapt to remain current.Based on the predictions of next-generation supercomputer architectures it is expected that the first computer capable of 1018 floating-point-operations-per-second (1 ExaFLOPS) will arrive in around 2020. Its architecture will be governed by electrical power limitations, whereas previously the main limitation was pure hardware speed. This has two significant repercussions. Firstly, due to physical power limitations of modern chips, core clock rates will decrease in favour of increasing concurrency. This trend can already been seen with the growth of accelerated “many-core” systems, which use graphics processing units (GPUs) or co-processors. Secondly, inter-nodal networks, typically using copper-wire or optical interconnect, must be reduced due to their proportionally large power consumption. This places more focus on shared-memory communications, with distributed-memory communication (predominantly MPI - “Message Passing Interface”) becoming less important.The current most powerful computer, Tianhe-2, capable of 33 PFlops, consists of 3,120,000 cores. The first exascale machine, which will be 30 times more powerful, is likely to be 300-times more parallel – which is a massive acceleration in parallelization compared to the last 50 years. This concurrency will come primarily from intra-node parallelization. Whereas Tianhe-2 features an already-large O(100) cores per node, an exascale machine must consist of O(1k-10k) cores per node.CFD has benefited from weak scalability (the ability to retain performance with a constant elements-per-core-ratio) for many years; its strong scalability (the ability to reduce the elements-per-core ratio) has been poor and mostly irrelevant. With the shift to massive parallelism in the next few years, the strong scalability of CFD codes must be investigated and improved.In this paper, a brief summary of earlier results is given, which identified the linear-equation system solver as one of the least-scalable parts of the code. Based on these results, a chaotic iterative solver, which is a totally-asynchronous, non-stationary, linear solver for high-scalability, is proposed. This paper focuses on the suitability of such a solver, by investigating the linear equation systems produced by typical CFD problems. If the results are optimistic, future work will be carried out to implement and test chaotic iterative solvers.

For an AUV to perform a long-range mission with its maximum endurance, its energy consumption during transit must be kept to a minimum. This paper presents an improved cost function for a grid-based genetic algorithm (GA) path planning in 2D static environments. The proposed function consists of energy consumption terms that are estimated according to dynamics of a hover-capable AUV - notably Delphin2 AUV. It seeks for a path that requires least effort for the vehicle to move along. A simulation was written in Matlab and the outcomes of the GA with the improved cost function are compared with the ones of a GA with an optimal distance approach as well as an A* approach. It is found that outcomes of an improved cost function require less energy compared with the other techniques

The passive resistance of a swimmer on the free surface has previously been researched experimentally. The contribution of wave resistance to total drag for a swimmer with a velocity around 2.0 m.s-1 was found to vary from 5% for Vorontsov and Rumyantsev (2000), to 21 % for Toussaint et al. (2002) and up to 60% according to Vennell et al. (2006). The exact resistance breakdown of a swimmer remains unknown due to difficulties in the direct measurement of wave resistance. As noted by Sato and Hino (2010), this lack of experimental data makes it difficult to validate numerical simulations of swimmers on the free surface.This study is therefore aimed at presenting direct measurements of a swimmer’s total drag and wave resistance, along with the longitudinal wave cuts which may be used to validate numerical simulations. In this paper, experimental data of a swimmer’s resistance are presented at two different velocities (case 1 = 1.7 m.s-1 and case 2 = 2.1 m.s-1). Total drag was measured using force block dynamometers mounted on a custom-built tow rig (Webb et al., 2011). Moreover, a longitudinal wave cut method was used to directly evaluate wave resistance (Eggers, 1955).The two conditions tested were simulated using the open-source Computational Fluid Dynamics (CFD) code OpenFOAM (OpenFOAM® (2013)). The body geometry is a generic human form, morphed into the correct attitude and depth using the above- and under-water video footage recorded during the experiment. 3D Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations were performed using the Volume of Fluid (VOF) method to solve the air-water interface. A similar numerical technique was used by Banks (2013a) to assess the passive resistance of a swimmer. Two cases were simulated and the error in total drag compared to the experimental data was found to be 1 % and 22 % respectively. In this paper, the resistance components over a swimmer’s typical range of speeds are investigated and compared with the experimental data

The flow past a sphere located at the free-surface, was studied over the critical Reynolds number range: 2x10^5 to 4x10^5. Experiments were carried out in the Lamont tank at the University of Southampton. Due to the inclusion of a free-surface, the solver interFoam (version OF-2.2.0) was used to simulate the flow past the sphere with a Courant number of 1.2 to allow the simulations to run faster without compensating on the results’ accuracy. Maximum wave resistance occurs when the sphere is half-submerged due the maximum crosssectional area of the sphere. The wave resistance component becomes negligible at an immersion depth greater than 175%D.

Accurate prediction of the hydrodynamic forces and moments acting on a manoeuvring marine vehicle using Reynolds averaged Navier–Stokes simulations requires sufficient mesh resolution to capture off-body vortical structures. Because the path of these structures is not known a priori, a vortex identification and capture strategy is required alongside an iterative mesh adaption process. An improved version of the VORTFIND algorithm, which can identify multiple vortices of variable strength and rotational direction using a K-means algorithm is described. The algorithm is applied to velocity fields generated from Reynolds averaged Navier–Stokes simulations to increase the mesh resolution in the vortex core region, ensuring sufficient mesh density to capture the downstream propagation of the vortex for a submarine hull at drift and ship propeller–rudder interaction

With the increase in fuel prices and growing pressure on the marine industry to reduce greenhouse gas emissions, there is a demand for both new and current ships in operation to develop novel ways to reduce their fuel consumption. In January 2013, the International Maritime Organisation (IMO) provided mandatory methods on how both new and existing ships will be assessed on their emissions via the Energy Efficiency Design Index (EEDI)and the Ship Energy Efficiency Management Plan (SEEMP) respectively. Existing ships are less suitable for major design changes, so they must rely on engine room systems upgrades or the use of retro-fit devices. This research paper presents how the efficiency of an existing tanker hull form could be increased by 10% with the use of cost-effective retro-fit solutions. A method, involving CFD simulations performed using OpenFOAM and validated with wind tunnel tests, is explained. An in-house code, based on the Blade-Element Momentum Theory (BEMT), is used to provide some propeller characteristics: efficiency, torque and thrust coefficients.Although, the efficiency output from the BEMT code is not the propulsive coefficient, the different appendage configurations may still be directly compared using this efficiency, denoted BEMT throughout this paper. This procedure successfully detects changes in propeller efficiency at model scale due to devices and thus provides a route to investigate a wide variety of devices. Preliminary results highlightes that efficiency gains up to 3% could be obtained with vanes and up to 9% with flow increasing ducts

An overview is given of current research in maritime CFD using the open source flow solver OpenFoam through examples of unsteady propulsors representations, free surface capture and hull-propulsor-rudder interaction for energy efficient shipping. Fundamental unsteady flow as hydroacoustic sources on a 2D foil is also solved.

The importance of a rudder cannot be understated; although relatively small, the hydrodynamic forces and moments developed on it are essential in the assessment of the manoeuvring characteristics of a ship. Additionally, ship rudders are almost always placed downstream of the propeller so they can take advantage of the increased local velocity due to the presence of the propeller. The knowledge of the interaction effects between the rudder and the propeller is a focal aspect for the improvement of ship’s performance. Propeller and rudder are considered as a propulsion unit in which the former is an active device that generates the thrust to keep the ship on move and the latter a control surface that produces the transverse force to keep the ship on course (Kracht 1992). In this paper, a method for rapidly computing the flow field and integrated forces acting on a rudder in a propeller race is presented.

The education of naval architects, marine engineers and others who are the active contributors to the ship design processes is heavily focussed on engineering fundamentals, often aligned with traditional university course constraints. The concept of a research collegium is described whose aim is to provide an environment where young people in their formative postgraduate years can learn and work in a small, mixed discipline group drawn from the worldwide maritime community to develop their skills whilst completing a project in advanced ship design. The brief that initiates each project sets challenging user requirements which encourage each team to develop an imaginative solution, using their individual knowledge and experience, together with learning derived from teaching which form a common element of the early part of the collegium

Marine local scour is understood as the removal of sediment from around the base of an object on the seabed caused by waves and currents. The introduction of a flow obstruction to the seafloor will have a significant impact on the local hydrodynamics, causing acceleration, pressure gradients, boundary-layer separation and increased turbulence at the seabed and in the wake of the object. Where the seabed cannot resist the increased magnitude of impinging shear forces, e.g. in non-cohesive mobile sediment such as sands, sediment will be eroded to form a characteristic scour hole. Scour, left unchecked can cause structural damage and major economic losses. The ability to predict scour, both vertical and lateral, is thus a prerequisite for the optimised design of a structure and provision of scour protection.At present, empirical equations are used for simple two-dimensional objects such as vertical and horizontal cylindrical type in the forecast of maximum scour depths. Fewer relations are available for the quantification lateral scour extent and evolution of the scour pit with time. For a more comprehensive scour prediction or assessment of more complex structures, expensive and time-consuming physical model experiments are required.The aim of this PhD project is to develop a numeric method for scour modelling in openFOAM CFD which will be capable of predicting scour around complex three-dimensional seabed structures. In this study, we will focus on the discussion of the available approaches for scour modelling using CFD methods.

Free stream tidal turbines are rotating bodies in fast flowing tidal currents, and as such are exposed to fluctuating loads from the surrounding fluid. These time varying forces will cause the blades to deform dynamically, potentially deflecting the blade shape away from the optimum orientation as well as exciting resonant responses that may enhance fatigue loading. It is important to understand this hydroelastic response for all but the stiffest blades. A loosely coupled, modular approach to fluid structural interactions (FSI) has been developed for the analysis of horizontal axis tidal turbine blades (HATTs). This paper discusses the methodology behind the FSI process and illustrates the technique through a case study of a 20m diameter, three bladed, horizontal axis tidal turbine, in which the deflection of the blades is examined through the iterative procedure.

A commercial RANS code is used to investigate the multiphase flow field surrounding the KCS hull form. Results are presented for the associated wave pattern (case 2.1), dynamic sinkage and trim (case 2.2b) and self propulsion parameters for the hull using a body force propeller model (case 2.3a)

This investigation first focuses on modelling the flow around cantilever plates in normal oscillation, providing key guidance for attaining sufficient accuracy for most engineering applications, in terms of turbulence modelling, mesh refinement and time step selection. The modelling approach is then applied to the hydrodynamics of a ship-like section fitted with vertical bilge keels, rolling at free surface. The results obtained from RANS are compared to available experimental data and predictions obtained from potential flow analysis. Viscous effects arising from the presence of the bilge keels are shown to influence more hydrodynamic coefficients than just roll fluid damping. Finally, empirical formulae commonly used to allow for the influence of viscous roll damping are compared to RANS predictions and experimental data.

In our days, when environmental protection and low petroleum consumption are the top priorities of a marine engineer and a naval architect, the design and construction of fully optimized engines, smart installations and exploitation of the highest percentage of energy produced is required. As a result innovations, optimization, new concept design and simulation play a significant role in marine industry. Although 93% of the world’s trade is done by ships and by the year 2011 the emissions of CO2 will contribute to 4% of world’s CO2 emissions as well as 37% and 28% of NOx¬ and SOx emissions respectively, the marine sector is targeted.The problem of high emissions exists, when the engine operates in the non optimum condition, a percentage relevant to engine’s MCR, tuned by the engine manufacturer. This means that in transient load (project SMOKERMEN, 2002; project HERCULES, 2007) large amounts of smoke, particle matter, NOx and SOx hazardous gasses are produced. Two stroke engines on board ships are directly coupled to the propeller using a rotating shaft. While ships operate in constantly changing environment and chartering commands change during voyage, propulsion unit have to adapt its speed and produced torque. Therefore engine loading changes to less efficient points and the SFOC is increased. Meanwhile, temperature of combustion and pressure differ from the most efficient and connected to them formulation of NOx increases along with increase in SOx, CO2¬ and smoke. Our work is based on real operational data provided by a Greek maritime corporation with a fleet of 65 cargo ships. The obtained data contains information from 3 Post Panamax new built sister vessels, regarding fuel consumption, engine loading, weather and sea conditions along with bunker characteristics (e.g. Sulphur percentage). Phase one of the project is separated into 3 parts. The first part includes worldwide adopted methods for emission calculation. Project utilizes the “activity based method” (NTUA - Laboratory of Marine Transportations, 2008) which uses proper emission factors taken from relevant literature (VDMA Engines and Systems, 2008; MARPOL, 2005; EMEP/ CORINAIR, 2000). The second part, utilizes the voyage data of the vessels, correlates the consumption and engine loading with the weather characteristics. Furthermore, applies the assumption of constant loading of diesel engines and the existence of storage medium in order to estimate the fuel savings of the hybrid vessel. At the third part, industrial and market research was performed to find the proper storage medium. As first step, batteries were examined and different types were compared, judging by their energy density, weight, operational factors and restrictions. Also a proposal for sizing the alternative propulsion system was done and economical assessment was performed. Finally conclusions were discussed and they are summarized below:Hybrid Technology has significant fuel savings that can be increased due to further optimization of Turbochargers and by the operation of engine in smaller margin. Furthermore emission reduction in NOx is successful due to lower combustion temperatures. Moreover, ship design and cargo capacity will be affected making the overall task difficult. Finally, Hybrid Technology is economically feasible and the Internal Rate of Return of investment varies between 4.7% until 20.7% depending on the storage medium type and the availability of kWh.

Ship rudders are almost always placed downstream of the propeller so they can take advantage of the increased local velocity due to the presence of the propeller race. The methods discussed in this paper replicate the flow integrated effects of the propeller which generates an accelerated and swirled onset flow onto the rudder. As long as the radial variation in axial and tangential momentum (including hull and rudder interaction effects) generated by the propeller are included, then the influence of the unsteady propeller flow can be removed and ’steady’ calculations performed to evaluate propeller rudder interaction. Three different body force propeller models will beconsidered and numerical results will be compared with experiments by Molland and Turnock [1, 2, 3], using the modified Wageningen B4.40 propeller and Rudder No.2

In recent years technological innovations has allowed large improvements to be made in sail design and construction. Sails and in particular kite-sails have application for sport, ships’ auxiliary propulsion and even power generation. Sails are divided into upwind and downwind sails (Fig.1), where upwind sails operate as lifting surfaces with small angles of attack whereas traditional downwind sails acted as drag device. New designs of downwind sails have reduced the area of separated flow and increased the lifting behaviour of the sails. In order to capture the lifting behaviour and regions of separation present in both types of sail careful application of computational fluid dynamic analysis tools are required. Solutions of the Reynolds averaged Navier- Stokes equations (RANSE) are often used as a part of the design process of high performance sailing yachts.The present paper discusses some initial investigations and future guidelines in order to get a more detailed description of the physics involved in sail FSI. Three main fields are therefore covered: the use of CFD in order to accurately capture flow features and a comparison with experimental results; structural modelling; and approach to coupling

Tidal turbines offer an exciting opportunity to exploit ocean current flows to generate sustainable energy. However, a key to their success is the ability to operate with minimal intervention in the ocean over extended periods (15-20 years). This talk explored the likely design and operational issues that will influence satisfactory performance associated with material corrosion and biofouling. The main difficulty is that turbine economic viability is capital driven so whole system, including operation and maintenance needs to be as cost-effective as possible. Although can use approaches developed from those applied for ship design and in the offshore industry there is a need to appreciate that cost-drivers are different. For instance a ‘Gold plated’ technology approach from oil and gas industry may not deliver cost-effective solutions.

The concept design of a lightweight cryogenic marine heavy lift buoyancy system has been investigated. The approach makes use of a novel cryogenic system for provision of buoyancy within the ocean environment. The objective is to be able to lift or lower large displacement objects under full remote control. The nature of subsea lifting and lowering operations requires a high degree of precise control for operational safety, reasons and to preserve the structural integrity of the load. The lift operation occurs in two phases: Development of lift to overcome seabed suction, and then rapid reduction of buoyancy to maintain a controlled ascent. Descent involves controlled release of the buoyancy. The proposed buoyancy system consists of a buoyancy chamber and an integral cryogenic gas generation unit. The application of an on-board gas generation unit allows the removal of the engineering challenges associated with use of compressors and the concomitant complex manifold of connecting umbilical pipe work. It provides for a fully remote system completely eliminating all risk associated with extensive physical surface to subsea connection throughout the entire lift operation. The opening stages of the project work include the development of a system that will operate efficiently and effectively to a depth of 350m. An initial general arrangement for the buoyancy system has been developed. A number of these systems involve considerable design and development, these include: structural design of the buoyancy chamber, mechanical systems to control and connection to the lift device, the cryogenic system itself and overall process control systems. As part of the design process for such an arrangement, numerical simulation of the complete system has been undertaken in order to develop mechanical, cryogenic and process control systems efficiently and effectively. This system simulation has been developed using Matlab Simulink. This paper considers the overall design concept and associated system development issues. These are illustrated through use of the time accurate simulation of alternative design configurations that confirm the viability of the concept. A main conclusion is that minimisation of the dry weight of the system is critical to cost-effective operation of the project.