Electroconvective instability in a fluid layer

Electroconvective instabilities in fluid laye

The improvement of aluminium casting process control by application of the new CRIMSON process

All The traditional foundry usually not only uses batch melting where the aluminium alloys are melted and held in a furnace for long time, but also uses the gravity filling method in both Sand Casting Process (SCP) and Investment Casting Process (ICP). In the gravity filling operation, the turbulent behaviour of the liquid metal causes substantial entrainment of the surface oxide films which are subsequently trapped into the liquid and generate micro cracks and casting defects. In this paper a new CRIMSON process is introduced which features instead of gravity filling method, using the single shot up-casting method to realize the rapid melting and rapid filling mould operations which reduce the contact time between the melt and environment thus reducing the possibility of defect generation. Another advantage of the new process is the drastic reduction of energy consumption due to shortened melting and filling time. Two types of casting samples from SCP and ICP were compared with the new process. The commercial software was used to simulate the filling and solidification processes of the casting samples. The results show that the new process has a more improved behaviour during filling a mould and solidification than the two conventional casting processes

Assessment of casting filling by modeling surface entrainment events using CFD

The reliability of cast components is dependent on the quality of the casting process. During this highly transient filling phase the prevention of free surface turbulence and consequential oxide entrainment is critical to ensure the mechanical integrity of the component. Past research has highlighted a number of events that lead to entrainment of surface oxides. Using FLOW-3D, flow structures that result in surface entrainment events have been simulated and an algorithm developed that allows entrainment and defect motion to be tracked. This enables prediction of the quantity and motion of oxide film generated from each event. The algorithm was tested experimentally and compared to experimental data from previously published work. A quantitative criterion is proposed to assess the damage of each type of event. Complete running systems have also been studied to understand how they could be assessed for quality of filling based on the flows within them

The modelling of oxide film entrainment in casting systems using computational modelling

As Campbell stated in 2006, “the use of entrainment models to optimise filling systems designs for castings has huge commercial potential that has so far being neglected by modellers”. In this paper a methodology using computational modelling to define entraining events and track the entrained oxide films is presented. Research has shown that these oxide films present within the casting volume are highly detrimental to casting integrity, thus their entrainment during mould filling is especially undesirable. The method developed for the modelling of oxide entrainment has been validated against previously published data by Green and Campbell (1994) [31]. The validation shows good quantitative correlation with experimental data. However there is scope for further development which has the potential to both improve the accuracy and further validate the technique

Continuous data assimilation with blurred-in-time measurements of the surface quasi-geostrophic equation

An intrinsic property of almost any physical measuring device is that it makes observations which are slightly blurred in time. We consider a nudging-based approach for data assimilation that constructs an approximate solution based on a feedback control mechanism that is designed to account for observations that have been blurred by a moving time average. Analysis of this nudging model in the context of the subcritical surface quasi-geostrophic equation shows, provided the time-averaging window is sufficiently small and the resolution of the observations sufficiently fine, that the approximating solution converges exponentially fast to the observed solution over time. In particular, we demonstrate that observational data with a small blur in time possess no significant obstructions to data assimilation provided that the nudging properly takes the time averaging into account. Two key ingredients in our analysis are additional boundedness properties for the relevant interpolant observation operators and a non-local Gronwall inequality.Comment: 44 page

A Purely Functional Computer Algebra System Embedded in Haskell

We demonstrate how methods in Functional Programming can be used to implement a computer algebra system. As a proof-of-concept, we present the computational-algebra package. It is a computer algebra system implemented as an embedded domain-specific language in Haskell, a purely functional programming language. Utilising methods in functional programming and prominent features of Haskell, this library achieves safety, composability, and correctness at the same time. To demonstrate the advantages of our approach, we have implemented advanced Gr\"{o}bner basis algorithms, such as Faug\`{e}re's $F_4$ and $F_5$, in a composable way.Comment: 16 pages, Accepted to CASC 201

An investigation into the psychosocial impact of therapeutic recreation summer camp for youth with serious illness and disability

OBJECTIVES: This study aimed to evaluate the impact on emotional, social, physical and educational functioning of a therapeutic recreation camp provided by ‘Over The Wall’, a UK charity for children and young people with chronic illness or disability. METHOD: Two hundred and sixty four people registered to attend camp were sent the Pediatric Quality of Life Inventory version Child Self-Report Scale before camp, immediately after camp, 1 month after camp and 3 months after camp. RESULTS: Of those invited to participate, 178 children completed the pre-camp survey (67% response rate). Of those, 105 completed both the post-camp 1 and pre-camp questionnaires (59% of pre-camp respondents), and 60 of those participants subsequently completed the 1-month post-camp questionnaire as well (34% of pre-camp respondents). Only 32 participants completed the 3-month follow-up data (18% of pre-camp respondents). Across the first three timepoints (pre-Camp, post-Camp and 1 month follow-up), a repeated measures ANOVA indicated a significant improvement in emotional and social functioning, but not physical or school functioning (p < 0.05). Post-hoc analyses on pre-camp and post-camp scores revealed small-medium effect sizes of 0.317 and 0.272 for emotional and social functioning, respectively. DISCUSSION: The therapeutic recreation summer camp provided for children and young people with health challenges had a significant, positive impact on emotional and social functioning. Such camps can therefore be considered as having empirical support for their aims. Further work is warranted to increase the response rate to establish the longer term impact of the camps and the wider impact of the camps on the wider family

Thermodiffusion in model nanofluids by molecular dynamics simulations

In this work, a new algorithm is proposed to compute single particle (infinite dilution) thermodiffusion using Non-Equilibrium Molecular Dynamics simulations through the estimation of the thermophoretic force that applies on a solute particle. This scheme is shown to provide consistent results for simple Lennard-Jones fluids and for model nanofluids (spherical non-metallic nanoparticles + Lennard-Jones fluid) where it appears that thermodiffusion amplitude, as well as thermal conductivity, decrease with nanoparticles concentration. Then, in nanofluids in the liquid state, by changing the nature of the nanoparticle (size, mass and internal stiffness) and of the solvent (quality and viscosity) various trends are exhibited. In all cases the single particle thermodiffusion is positive, i.e. the nanoparticle tends to migrate toward the cold area. The single particle thermal diffusion 2 coefficient is shown to be independent of the size of the nanoparticle (diameter of 0.8 to 4 nm), whereas it increases with the quality of the solvent and is inversely proportional to the viscosity of the fluid. In addition, this coefficient is shown to be independent of the mass of the nanoparticle and to increase with the stiffness of the nanoparticle internal bonds. Besides, for these configurations, the mass diffusion coefficient behavior appears to be consistent with a Stokes-Einstein like law