1,721,021 research outputs found
A study of auditors' skeptical characteristics and their relationship to skeptical judgments and decisions
Full text linkGroot, T.L.C.M. [Promotor]Wright, A.M. [Copromotor
Convective cell approach for solving incompressible Euler flows: explicit flux vector splitting scheme using artificial compressibility
No full textArtificial compressibility has been used to model three dimensional steady state incompressible fluid flow. The numerical scheme applies the finite volume method to the Euler equations via multi-stage explicit time integration and flux vector splitting spatial discretisation. To allow the modelling of complex geometries arbitrary polyhedra control volumes have been used, defined by connectivity of geometrical entities. In addition moving meshes are allowed and the provision for adaptive meshing is provided. Solutions of flow over a two dimensional hump and around a Wigley hullform have produced acceptable convergence histories but are as yet unvalidated as to their accuracy. Ongoing work includes the validation of data, the imposition of a free surface boundary and the ability to model unsteady flow
Efficient multi-level adaption methods for unstructured polyhedral computational meshes
No full textThe definition of a computational mesh uniquely suited to a given model is a difficult and time consuming process. Using spatial and flow property quality definitions a method has been developed to adapt and optimise any given mesh. Through complex data structures, efficient surface definition and statistical analysis efficient cellular and interface manipulation routines are initiated. Cellular fission/fusion, nodal convection and interface manipulation are detailed and benefits of the adaption listed. The development of such techniques into a fully automated grid generation process is discussed
Techniques for assessing the flow and spatial quality of arbitrary 3D computational meshes
No full textThe solution accuracy of any model using computational fluid dynamics is dependent upon the quality of the discretised mesh. This report details the range of spatial and flow properties affecting the accuracy and stability of any solution and comments upon their individual effects. Methods of calculating these properties upon an arbitrary 3D mesh are defined and statistical analysis provides a unique quantative value upon any given mesh. As a result volumes of poor grid quality can be identified without user interpretation, as well as the most suitable form of rectification
Directly coupled fluid structural model of a ship rudder behind a propeller
No full textA computational method is presented that models fluid structural interaction problems for three-dimensional marine structures. Flow can be modelled with either potential or viscous incompressible flow. The structure deformation is modelled by a shell finite element formulation. The two fields are coupled by a domain decomposition approach that uses virtual surfaces to transfer information. A typical spade rudder has been modelled for steady-state three-dimensional problems in a free stream and in way of a propeller race. These computational models have been tested for mesh dependancy in both the fluid and structural domains as well as the virtual surface definition. The results show increased correlation to experimental data from uncoupled hydrodynamic modelling as well as detailed structural deformation. Of note is the variation in rudder stock bending moment from that utilised by classification society scantling rules
An analysis of the interaction between slider physique and descent time for the bob skeleton
No full textA single degree of freedom simulator has been developed to analyse the effect of athlete physique on descent timein the bob skeleton. A human proportions model is used to predict frontal and total surface area of an athlete for a given weight and height. Descent time data for a range of typical athlete physiques has been acquired. Descent times for the top 15 male competitors at the 2007 world championships are compared to the simulated descent time for each athlete. Results demonstrate the gains in aerodynamics made from being taller for a given mass and also for increased overall mass. Sleds used to equalise overall mass show an advantage in the athlete being lighter for a given height. Normalisation of the world championship results so that start time is not taken into account shows correlation between athlete experience and descent time
Development of a web based, collaborative working environment for maritime computational fluid dynamics
No full textA report is given on the developments so far on a DtI/Wolfson Unit funded projects to use GRID technologies to facilitate CFD analysis of marine vessels. A web enabled front end allows remote access to appropriate CFD tools and facilities. The user is guided through the process of solid model creation, mesh generation, quality assessment, CFD analysis, result interpretation, and visualisation of the computed solution. Issues such as data security, appropriate access to commercially sensitive calculations and automated access to cost-effective computational platforms are discussed. Examples will be given of calculations for the seakeeping assessment of the Series 60 hull form and the upwind performance of a fully appended IACC hull
Methodology for improving stern gear design of high speed craft using cfd simulation
No full textStern gear design for luxury high speed yachts currently relies on an estimation of the inflow velocity at the propeller plane and the propeller race. These components are often located within tunnel features on the hull and the flow regime will be influenced by the vessel trim and planning speed. Typically, the flow into the propeller is taken as an average over the entire propeller area and does not take into account the variation of the flow into the propeller due to appendages and hull shape. Computational fluid dynamics (CFD) simulations allow this variation to be calculated. These data are coupled with a potential based lifting surface program and are used to improve propeller design.In order to optimise the design of the rudder, the propeller race must be known. A method of introducing the propeller forces back into the CFD flow is investigated. This improved method has the advantage of providing a more accurate flow field into the rudder, which allows the rudder design to be improved. It is expected that this procedure will reduce the rudder drag and cavitation. The development and validation of this CFD methodology applied to high speed planning craft propulsion using open source software is illustrated with regard to two case studies for P bracket and propeller design optimisation, and to estimate the toe-in angle for the rudder in order to align it with the propeller race
The use of CFD in modelling blanketing effects for yacht race simulations
No full textA detailed examination of the performance of a typical upwind sail rig arrangement was carried out for different heel and yaw angles using a commercial Computational Fluid Dynamics (CFD) solver. Experimental wind tunnel data provided by the Wolfson Unit for Marine Technology and Industrial Aerodynamics were used to validate the calculated CFD results. The computed results demonstrate good agreement and the effect of mesh density on the flow solution is presented. The purpose of this work is to identify the downwind position and track of the resultant sail vortex system. The ability to model correctly this behaviour within a yacht race simulation is critical to identifying the blanketing effect between two yachts
- …
