I. Masters

Design optimisation of aluminium recycling processes using Taguchi technique

Abstract In this paper, a robust design method is developed for reducing cost and improving quality in aluminium recycling. An experimental investigation into the process parameter effects is presented to determine the optimum configuration of design parameters for performance, quality and cost. The Taguchi method is applied initially to plan a minimum number of experiments. Orthogonal array techniques are used to investigate the simultaneous variation of several parameters and the investigation of interactions between parameters. Matrix experiments using standard L4 and L9 orthogonal arrays are employed to evaluate the effects of parameters in recycling of aluminium dross and scrap materials. A statistical analysis of signal-to-noise ratio is followed by performing an analysis of variance (ANOVA), in order to estimate the optimum levels and determine the relative magnitude of the effect of various factors. Finally, a historical data analysis based on the response surface methodology is carried out using a Taguchi orthogonal analysis. Experimental results are shown for an L18 orthogonal array illustrating a good agreement between the optimum factor levels suggested by the signal-to-noise ratios and those obtained from the response surfaces.

A robust blade element momentum theory model for tidal stream turbines including tip and hub loss corrections

Blade Element Momentum Theory (BEMT) performance models for wind turbines lead to a robust BEMT model of marine current or tidal stream turbines. It is shown that numerical convergence methods for models reported in the literature are problematic when away from the normal operating range and this paper reports a robust numerical scheme using combined Monte Carlo and sequential quadratic optimisation. The model is extended by Prandtl corrections for losses at the blade tip and hub. Results are validated against an industrial code, Garrad Hassan’s Tidal Bladed Software (GH Tidal Bladed) evaluation version, and a lifting line theory model.

Similarity Measures for Enhancing Interactive Streamline Seeding

Streamline seeding rakes are widely used in vector field visualization. We present new approaches for calculating similarity between integral curves (streamlines and pathlines). While others have used similarity distance measures, the computational expense involved with existing techniques is relatively high due to the vast number of euclidean distance tests, restricting interactivity and their use for streamline seeding rakes. We introduce the novel idea of computing streamline signatures based on a set of curve-based attributes. A signature produces a compact representation for describing a streamline. Similarity comparisons are performed by using a popular statistical measure on the derived signatures. We demonstrate that this novel scheme, including a hierarchical variant, produces good clustering results and is computed over two orders of magnitude faster than previous methods. Similarity-based clustering enables filtering of the streamlines to provide a nonuniform seeding distribution along the seeding object. We show that this method preserves the overall flow behavior while using only a small subset of the original streamline set. We apply focus + context rendering using the clusters which allows for faster and easier analysis in cases of high visual complexity and occlusion. The method provides a high level of interactivity and allows the user to easily fine tune the clustering results at runtime while avoiding any time-consuming recomputation. Our method maintains interactive rates even when hundreds of streamlines are used.

Permanent magnet generator control and electrical system configuration for Wave Dragon MW wave energy take-off system

A permanent magnet generator (PM) control scheme and electrical system configuration for Wave Dragon MW wave energy power take off system is presented in this paper. The characteristics of low pressure hydro turbine are introduced first. To achieve the maximum energy conversion efficiency, a variable speed control scheme of low-head hydro-turbine using IGBT AC/DC converter is described. The electrical system configuration, operation and grid connection issues are also discussed. Voltage source PWM inverters are employed to control the output power to utility grid. Simulation model has been built, and the control of tracking maximum turbine efficiency is simulated.

Automatic Stream Surface Seeding: A Feature Centered Approach

The ability to capture and visualize information within the flow poses challenges for visualizing 3D flow fields. Stream surfaces are one of many useful integration based techniques for visualizing 3D flow. However seeding integral surfaces can be challenging. Previous research generally focuses on manual placement of stream surfaces. Little attention has been given to the problem of automatic stream surface seeding. This paper introduces a novel automatic stream surface seeding strategy based on vector field clustering. It is important that the user can define and target particular characteristics of the flow. Our framework provides this ability. The user is able to specify different vector clustering parameters enabling a range of abstraction for the density and placement of seeding curves and their associated stream surfaces. We demonstrate the effectiveness of this automatic stream surface approach on a range of flow simulations and incorporate illustrative visualization techniques. Domain expert evaluation of the results provides valuable insight into the users requirements and effectiveness of our approach.

Numerical modelling of the rotary furnace in aluminium recycling processes

Abstract In this paper, a numerical simulation involving fluid flow and heat transfer is presented in order to improve the understanding of rotary furnaces. The finite element model is employed to simulate the furnace rotation and analyse the energy flows inside the furnace. A transient dynamic analysis is carried out to predict the evolution and distribution of temperatures in a rotary furnace by modelling and analysing the furnace under different flame positions. The finite element modelling system ELFEN is used to develop models of the furnace. The results clearly indicate the temperature distribution for different angular velocities along with a comparison of temperature variation under different flame positions.

Cavitation inception and simulation in blade element momentum theory for modelling tidal stream turbines

Blade element momentum theory (BEMT) is an analytical modelling tool that describes the performance of turbines by cross-referencing one-dimensional momentum theory with blade element theory. Each blade is discretised along its length and the dynamic properties of torque and axial force are determined. A compatible cavitation detection model is introduced to indicate any cavitating blade elements. Cavitation occurrence is dependent on proximity to the free surface, the incident flow velocity and inflow angle and the blade cross-section aerofoil shape. The shock waves associated with cavitation can significantly damage the blade surface and reduce performance; therefore, this model is a useful addition to BEMT and can be used in turbine design to minimise cavitation occurrence. The results are validated using the cavitation experiment observations.

Why you should consider object‐oriented programming techniques for finite element methods

Object‐oriented programming, as an alternative to traditional, procedural programming methods for finite element analysis, is growing rapidly in importance as algorithms and programs become more complex. This paper reviews some of the literature and seeks to explain some of the concepts of object‐oriented thinking most useful to the finite element programmer, using as an example a C++ implementation of a heat transfer and solidification program.

AUTOMATIC TIMESTEP SELECTION FOR THE SUPER-TIME-STEPPING ACCELERATION ON UNSTRUCTURED GRIDS USING OBJECT-ORIENTED PROGRAMMING

The super-time-stepping algorithm is an improved timestepping scheme. It can significantly increase the performance of explicit methods, by reducing the restrictive timestep limits that exist. One of the drawbacks of the method is that the improvements are dependent on a set of parameters which are generally unknown. An investigation is performed to find the effect of these parameters and a method is described that estimates them. The technique is applied to a real problem and the results show a considerable improvement over a standard explicit timestepping scheme. The technique is implemented in an object-oriented manner, and details are given in an Appendix.

The Variation in Wake Structure of a Tidal Stream Turbine with Flow Velocity

A combined Blade Element Momentum—Computational Fluid Dynamics (BEM-CFD) model is applied to a 10 m diameter tidal stream turbine blade and the supporting nacelle and tower structure in a 700 m long rectangular channel. The modelling approach is computationally efficient and is suitable for capturing the time-averaged influence of the turbine on the flow. A range of simulations are conducted for the purpose of undertaking a comparative study of the influence of the turbine on mean flow characteristics. Variations in flow structure around the turbine for different flow conditions were evaluated.