Computer modelling of the combined effects of plant conditions and coal quality on burnout in utility furnaces

The aim of this paper is to describe the latest steps in the development of a computer model to predict the combined effects of plant conditions and coal quality on burnout. The work was conducted as part of RWE’s contribution to the recent ECSC project ‘Development of a carbon-in-ash notification system (CARNO)’. A burnout predictor code has been developed and validated; it includes both coal and plant effects and includes a burnout model based closely on CBK8. The agreement between predicted c-in-ash and plant data is encouraging, but further improvements are still desirable. The predictions obtained from the burnout predictor show that the calculated sensitivities to changes in plant condition can be very dependent on state of plant.     

Timing HIV infection with a simple and accurate population viral dynamics model

Clinical trials for HIV prevention can require knowledge of infection times to subsequently determine protective drug levels. Yet, infection timing is difficult when study visits are sparse. Using population nonlinear mixed-effects (pNLME) statistical inference and viral loads from 46 RV217 study participants, we developed a relatively simple HIV primary infection model that achieved an excellent fit to all data. We also discovered that Aptima assay values from the study strongly correlated with viral loads, enabling imputation of very early viral loads for 28/46 participants. Estimated times between infecting exposures and first positives were generally longer than prior estimates (average of two weeks) and were robust to missing viral upslope data. On simulated data, we found that tighter sampling before diagnosis improved estimation more than tighter sampling after diagnosis. Sampling weekly before and monthly after diagnosis was a pragmatic design for good timing accuracy. Our pNLME timing approach is widely applicable to other infections with existing mathematical models. The present model could be used to simulate future HIV trials and may help estimate protective thresholds from the recently completed antibody-mediated prevention trials.     

Canonical transformation and stabilization of generalized Hamiltonian systems

This paper introduces generalized canonical transformations for generalized Hamiltonian systems which convert a generalized Hamiltonian system into another one, and preserve the generalized Hamiltonian structure of the original. As in classical mechanics, it is expected that canonical transformations will provide new insights and fundamental tools for both analysis and synthesis of those systems. Firstly, the class of generalized canonical transformations and some of their properties are indicated. Secondly, it is shown how to stabilize the generalized Hamiltonian systems using canonical transformations. In addition, some examples illustrate how such transformations are utilized for control systems design.     

An iterative linearised solution to the sinusoidal parameter estimation problem

Signal processing applications use sinusoidal modelling for speech synthesis, speech coding, and audio coding. Estimation of the model parameters involves non-linear optimisation methods, which can be very costly for real-time applications. We propose a low-complexity iterative method that starts from initial frequency estimates and converges rapidly. We show that for N sinusoids in a frame of length L, the proposed method has a complexity of O(LN), which is significantly less than the matching pursuits method. Furthermore, the proposed method is shown to be more accurate than the matching pursuits and time-frequency reassignment methods in our experiments.     

Numerical design for cathodic protection systems for concrete

Cathodic protection (CP) has become a successful method for the rehabilitation of concrete structures affected by chloride-induced corrosion of reinforcing steel. CP involves applying an electrical current from an external anode through the concrete to the reinforcement. The current causes steel polarisation, electrochemical reactions and ion transport. Normally the anode is placed over relatively large surface areas, including those where the steel is passive. Conventional views assume that protection current will not significantly flow outside the anode area. In many cases this results in a conservative design. This paper presents principles and first results of numerical calculations for design of an example CP system by finite element modelling. The final objective is to develop a tool for more economical CP system design. In particular, a CP system for the protection of local damage in bridges (e.g. at leaking joints) has been simulated. The corroding area with respect to the size of the anode is varied. Current and potential distributions and depolarisation values are predicted, both close to and more distant from the anode. It appears that current densities required to achieve sufficient polarisation are much higher than those usually found in the field. Neglecting time-dependent repassivation processes is likely to be the main cause and further work is needed to include them. The present model can be used with reasonable confidence for preventive application to passive steel.     

A unified approach to modelling the performance of concurrent systems

Quantitative design is crucial to ICT and it is therefore important to integrate performance modelling techniques into support environments that facilitate the correct construction of computer systems. We consider Performance Modelling Interchange Formats (PMIFs), which allow models to be specified in a uniform way and ported to a number of tools that solve them. We focus on extending the class of models describable in a PMIF that can be solved analytically – specifically, yielding a product-form solution for their equilibrium state probabilities. We use an extension of an established theorem, called the ‘reversed compound agent theorem’ (RCAT) as the basis of the analytical modelling tool into which the extended PMIF feeds models. We describe the RCAT methodology in practical terms, how it is integrated into an extended PMIF, and illustrate our methodology with three examples.     

A survey of partial differential equations in geometric design

Computer-aided geometric design is an area where the improvement of surface generation techniques is an everlasting demand, since faster and more accurate geometric models are required. Traditional methods for generating surfaces were initially mainly based upon interpolation algorithms. Recently, partial differential equations (PDE) were introduced as a valuable tool for geometric modelling, since they offer a number of features from which these areas can benefit. This work summarizes the uses given to PDE surfaces as a surface generation technique together with some other applications to computer graphics.     

Prediction of capillary tubes with alternative refrigerants to CFC‐502

A numerical model is presented in this paper, for predicting capillary tube performance using new alternative refrigerants to CFC‐502. The model has been established after the fluid flow conservation equations written for a homogeneous azeotropic refrigerant fluid flow under saturated, sub‐cooled and two‐phase conditions. The study was limited to the following azeotropic mixtures; R‐507, R‐404A, and quaternary mixture (R32/R125/R134a/R143a). Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R‐507 would experience smaller pressure drop across the capillary compared to the other alternatives under question. Copyright © 2001 John Wiley & Sons, Ltd.     

A constraint‐based approach to the modelling and analysis of packaging machinery

To enable packaging machinery manufacturers to compete at an international level, it is necessary to introduce them to more advanced design methods and technologies. For years, the evolution of packaging machinery has relied heavily on trial‐and‐error methods. The demands for continual increases in the performance capabilities of the machines, escalating legislation, environmental directives and changes in the characteristics of the product require rapid development of existing machine designs and the creation of new machines. This paper discusses the needs of SME packaging machinery manufacturers and identifies their requirements for methods in support of the design and redesign of packaging machinery. The need to identify, capture and manipulate design knowledge is critical for SMEs, where all too often design records are incomplete. Furthermore, a systems modelling approach that provides for support over the conceptual, embodiment and detailed design phases is essential for the rapid and effective development of designs. In order to meet these requirements, a methodology is proposed which incorporates ‘constraint modelling’ techniques. The methodology provides for experimental investigation and computer‐based modelling, which together aid the designer in gaining a fundamental understanding of the design problem. This enables the identification and representation of design knowledge, the determination of the limitations of an existing design, the evaluation of alternative designs and redesign strategies, as well as the embodiment, refinement and optimization of design solutions. The theory of ‘constraint modelling’ is discussed and the various phases of the methodology described. The applications of the methodology to a new machine design and a redesign program are also detailed. Copyright © 2001 John Wiley & Sons, Ltd.     

Modelling of convection during solidification of metal and alloys

The role of convection during solidification is studied with the help of a mathematical model. The effect of various mush models on convection and consequent macrosegregation is examined with the help of numerical simulations. The predicted macrosegregation profiles are compared with published experimental data. Subsequently, the importance of proper auxiliary relationship for thermo-solutal coupling in the mushy region is highlighted through some careful numerical simulations. Finally, the role of material parameters on double-diffusive convection is illustrated through comparative study of solidification of aqueous ammonium chloride, iron-carbon and lead-tin binary systems. Important results of these studies are presented and discussed.