The design and implementation of a Bayesian CAD modeler for robotic applications

We present a Bayesian CAD modeler for robotic applications. We address the problem of taking into account the propagation of geometric uncertainties when solving inverse geometric problems. The proposed method may be seen as a generalization of constraint-based approaches in which we explicitly model geometric uncertainties. Using our methodology, a geometric constraint is expressed as a probability distribution on the system parameters and the sensor measurements, instead of a simple equality or inequality. Tosolve geometric problems in this framework, we propose an original resolution method able to adapt to problem complexity. Using two examples, we show how to apply our approach by providing simulation results using our modeler.     

Stochastic Optimisation Methods for Biomolecular Structure Prediction

We discuss the use of stochastic optimization methods for biomolecular structure prediction, particularly applied to protein structure prediction and receptor ligand docking. After a brief introduction we give an overview of the dominating physical effects that are important for protein structure prediction and outline our strategy to address this problem. We discuss the strengths and weaknesses of several possible optimization methods, including the stochastic tunneling method. Finally we give examples of applications of this methodology both for protein structure prediction and receptor ligand docking.     

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

Abstract

There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)₂ saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.     

Flow pattern and alloy dissolution during tapping of steel furnaces

Abstract

Alloying of steel during tapping from BOFs and EAFs has been studied by computational fluid dynamics in two-dimensional axisymmetric models of two ladles. The flow patterns and particle trajectories have been computed for six different levels of steel in the tapping ladle, five different alloy sizes, two alloy injection points, and three types of bulk alloy (FeMn, SiMn, and FeSi75). Based on the fluid dynamics in the ladle and a definition of good alloying practice, conclusions with regard to alloy sizing and timing of alloy addition have been established. The computational results support findings in plant tests, which show the benefit of using small sized alloys. Furthermore, a method that allows us to estimate the optimum feeding rate for alloy additions during steelplant operation has been developed. Results from full scale tests in steelplants are shown.     

COMPARISON OF TWO METHODS TO INCREASE TIP CLEARANCE AND ITS EFFECT ON PERFORMANCE OF TURBOCHARGER CENTRIFUGAL COMPRESSOR STAGE

Tip clearance between the blade tip and casing of a centrifugal compressor can be varied through two methods:by changing the blade height(M1)or by changing the casing diameter(M2). Numerical simulations are carried out to compare these two methods and their effect on the stage and impeller performance.The impeller and diffuser are connected through rotor stator boundary using frozen rotor approach.Overall stage performance and the flow configuration have been investigated for nine tip clearance levels from no gap to 1 mm.Impeller and diffuser performances are also pre- sented separately.It has been found that the overall and impeller performance are comparatively better for M1 below tip clearance of 0.5 mm whereas M2 is found advantageous above 0.5 mm of tip clear- ance.Both M1 and M2 show performance degradation with the increase in tip clearance.Two models have been proposed for the stage total pressure ratio and efficiency,which are found to be in agree- ment with experimental results.The impeller efficiency and the pressure ratio are found to be maxi- mum at tip clearance of 0.1 mm for both the cases however minimum diffuser effectiveness is also observed at the same clearance level.Diffuser effectiveness is found to be maximum at zero gap for both cases.As it is practically impossible to have zero gap for unshrouded impellers so it is concluded that the optimum thickness is 0.5 mm onwards for M1 and 0.5 mm for M2 in terms of diffuser effec- tiveness.Mass averaged flow parameters,entropy,blade loading diagram and relative pressure fields are presented,showing the loss production within the impeller passage with tip clearance.     

Determination of inhibition effects of various imidazole derivatives on copper corrosion in 0·1M HCl media

Abstract

In the present study the inhibitive behaviour of 1H-imidazole, 1-methyl imidazole, imidazolidin-2-one, 4-(imidazole-1-yl)acetophenone, 4-(imidazole-1-yl) phenol and L-hystidine on the corrosion of copper in 0·1 M HCl has been investigated by potentiodynamic polarisation and polarisation resistance techniques. Except for 2-imidazolidone, the tested imidazole derivatives were found to behave as cathodic inhibitors. 1-methyl imidazole, 4-(imidazole-1-yl) acetophenone, 4-(imidazole-1-yl) phenol and L-hystidine were adsorbed on copper surface according to Temkin isotherm model. By using semi-empirical quantum chemical methods, physical parameters such as charge on the heteroatoms of imidazole derivatives q _n, energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and dipole moments were calculated. Possible correlations between these calculated physical parameters and inhibitor efficiencies were considered. Finally, the mechanistic information relating to the inhibition process was elucidated.     

Experimental and numerical investigations of NH4Cl solidification in a mould Part 2: numerical results

Abstract

This paper deals with the validation of a multiphase solidification model based on a benchmark experiment presented in Part 1. For the numerical modelling of NH₄Cl–H₂O solidification, the three different phases liquid, columnar dendrite trunks and equiaxed grains have been considered. The mass, momentum, energy conservation and species transport equations for each phase have been solved. The multiphase Eulerian-Eulerian model equations have been implemented in the Finite Volume Method based commercial software FLUENT-ANSYS using User-Defined Functions (UDF). The simulation of the NH₄Cl–H₂O solidification has been numerically investigated as a twodimensional unsteady process representing a cross-section of a 100 × 80 × 10 mm experimental benchmark. During the experiment both columnar and equiaxed growth of NH₄Cl were observed, therefore both phenomena were considered in the simulation. The predicted distribution of the solidification front has been compared with the measurements.     

Numerical investigation of grid influence on formation of macrosegregation

Abstract

The investigation of grid influence on numerical prediction of the formation of macrosegregation is an important issue in the point of view of numerical modelling. The estimation of numerical accuracy for the simulation of complex multiphase phenomena is a difficult modelling process, since the thermophysical properties depend on the temperature and concentration as well. The numerical stability and accuracy of the modelling also depend on the chosen time step and grid size. This paper focuses on the grid influence and modelling questions on macrosegregation in a benchmark ingot using Fe-0·34 wt-%C steel. The FLUENT-ANSYS v6·3 commercial software does not have built-in multiphase solidification and melting module for simulating columnar to equiaxed transition. Therefore, a multiphase model was implemented using User-Defined Functions. The number of grid cells has been increased from 180 to 4300 to define an optimal grid size, to prove the reliability of the model implementation based on solution accuracy. The results show, the macrosegregation pattern does not change significantly above a well-chosen number of grid cells.     

Calibration of X-Ray Film Used in the Detection of Soft X-Rays from the CTR Device Sceptre

To assist in the interpretation of X-ray pinhole photographs in thermonuclear research with the toroidal pinch device Sceptre, with a view to applying such photographs to the study of the energy spectrum of the electron flux incident upon the torus walls (constructed from aluminium and copper), experiments have been performed to determine the photographic effect of the X-rays produced from a known flux of electrons of given energy. A demountable X-ray tube was made in which the target was alternately copper or aluminium foil, indirectly heated, and in which a beam of electrons of known energy was focused on the foil. X-rays from the target fell upon llford Industrial G type X-ray flim, after passing through one or more metal foils. By maintaining a known beam current for different times, a range of exposures was given to different parts of the same film specimen and density-log exposure curves were compiled. Results of such experiments are presented for target elements of aluminium and copper and various thicknesses of absorbing foil, for electron energies in the range 1.8-8.4 KeV. A method is suggested by which data accumulated in this way may be used in analysis of electron energy spectra.