1,721,183 research outputs found
Ship wake field analysis using a coupled BEMt-RANS approach
No full textThe 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.<br/
A method for analysing fluid structure interactions on a horizontal axis tidal turbine
No full textFree 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
Design metrics for evaluating the propulsive efficiency of future ships
No full textThere is an increasing need for the ship design process to take account of environmental issues such as the emission of greenhouse gases and the likely extension of a carbon dioxide charging mechanism to international shipping. These issues, together with the need for economic viability, provide further incentives to improve the efficiency of propulsion of ships. The main components of powering are firstly reviewed. Individual components and other power saving devices are identified which should contribute to improvements in the overall efficiency of propulsion. Suitable design metrics and procedures, taking into account economic and environmental factors, are recommended for the design of future ships
Development of high performance composite bend-twist coupled blades for a horizontal axis tidal turbine
No full textDevelopment of a design methodology for a composite, bend-twist coupled, tidal turbine blade has been undertaken. Numerical modelling was used to predict the response of the main structural member for the adaptive blade. An experimental method for validation is described. The analysis indicates a non-linear blade twist response
Numerical propeller rudder interaction studies to assist fuel efficient shipping
No full textReducing the fuel consumption of shipping presents opportunities for both economic and environmental gain. From a resistance and propulsion standpoint, a more holistic propeller/hull/rudder interaction strategy has the potential to reduce fuel consumption, and minimise the risk of cavitation. The goal of this paper is to demonstrate that powering requirements can be reduced by optimizing the interaction between a ship’s rudder and propeller. In this paper, ongoing investigation regarding the design of an energy efficient rudder by adapting the local rudder incidence across the span to the effective inflow angle due to propeller swirl is presented. Numerical simulations are performed using an open-source RANS CFD code, Open FOAM, due to its ease with complex topology. Propeller effects are simulated using a body force model approach with special emphasis on ensuring the correct inflow to the rudde
Use of cryogenic buoyancy systems for controlled removal of heavy objects from the seabed
No full textThe 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
Tidal turbines that survive?
No full textTidal 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
Fluid-structure interactions of anisotropic thin composite materials for application to sail aerodynamics of a yacht in waves
No full textIn 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 couplin
The effect of swimsuit resistance on freestyle swimming race time.
No full textIt is known that swimming equipment (suit, cap and goggles) can affect the total resistance of a swimmer, and therefore impact the resulting swimming speed and race time. After the 2009 swimming world championships (WC) the international swimming federation (FINA) banned a specific type of full body suit, which resulted in an increase in race times for subsequent WC events. This study proposes that the 2009 suits provided a reduction in swimming resistance and aims to quantify this resistance reduction for male and female freestyle events. Due to the practical difficulties of testing a large sample of swimmers a simulation approach is adopted. To quantify the race time improvement that the 2009 suits provided, an equivalent 2009 “no-suit” dataset is created, incorporating the general trend of improving swimming performance over time, and compared to the actual 2009 times. A full race simulation is developed where the start, turn, underwater and surface swimming phases are captured. Independent resistance models are used for surface and underwater swimming; coupled with a leg propulsion model for underwater undulatory swimming and freestyle flutter kick, and a single element arm model to simulate freestyle arm propulsion. A validation is performed to ensure the simulation captures the change in swimming speed with changes to resistance and is found to be within 5% of reality. Race times for an equivalent “no-suit” 2009 situation are simulated and the total resistance reduced to achieve the actual 2009 race times. An average resistance reduction of 4.8% provided by the 2009 suits is identified. A factor of 0.47 ± 10%, to convert resistance changes to freestyle race time changes is determine
Parametric definition of complex multi-appended bodies for marine and aerospace application: a user guide to Adaptflexi
No full textAn overview is given of the powerful geometry (solid model) creation program Adaptflexi. A detailed user guide and a number of worked examples are given to illustrate how the code can be used as part of a design investigation for realistic marine or aerospace vehicles. The software can either be run interactively or using previously created scripts that allow multiple parametric variations of the specified problem. A range of input format and output format allows straightforward coupling to other CAD/ship lines software and to analysis using CFD or FEA. Useful features include: the ability to generate ab initio parametric definitions of complex shapes; creation of multiple object problems; definition of multiple phase domain problems; independent manipulation of sub assemblies of components; systematic control of surface and volume mesh creation process; and visualisation tools for assessing mesh quality and flow solutions. The report describes all the available functionality as well as giving worked examples for a number of typical marine and aerospace applications
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