Reduced numerical integration in thermal transient finite element analysis

The stability and accuracy of the so-called “ga-family”, two level time integration algorithms for thermal transient problems are considered. In particular, the influence on the solution characteristics of the order of numerical integration rule employed in the evaluation of the element matrices is examined. Consideration is restricted to the four node bilinear and eight node biquadratic isoparametric elements. The time integration schemes considered in detail are the Crank Nicolson, Galerkin, Modified Galerkin and Euler Backward algorithms. The stability of each process is related to both the eigenproperties of the conductivity and heat capacity matrices and to the eigenvalue spectrum of the thermal equation system. It is shown that inaccuracies and instabilities can arise in solution which are associated with the poor prediction of the element properties by reduced numerical integration rules. For eight node biquadratic elements, the source of error is the inadequate modelling of the eigenvalue spectrum of the heat capacity matrix by reduced quadrature; with both full and reduced integration rules providing very similar values for the conductivity (or stiffness matrix). However, for four node bilinear elements, reduced quadrature can result in an inadequate representation of both the conductivity and heat capacity matrices. It is shown that these inaccuracies are confined to the higher thermal frequencies which can be dominant in the initial stages of a transient response and cause deterioration of the numerical solution. Therefore an “adaptive” scheme is proposed in which a full integration order is used for the first few timesteps, after which a reduced integration rule is employed. Recommendations are made for the selection of time integration algorithms, quadrature rules and element dimensioning which are substantiated by the solution of several numerical examples.     

On a generalisation of the root iterations for polynomial complex zeros in circular interval arithmetic

Consider a polynomialP (z) of degreen whose zeros are known to lie inn closed disjoint discs, each disc containing one and only one zero. Starting from the known simultaneous interval processes of the third and fourth order, based on Laguerre iterations, two generalised iterative methods in terms of circular regions are derived in this paper. These interval methods make use of the definition of thek-th root of a disc. The order of convergence of the proposed interval methods isk+2 (k≧1). Both procedures are suitable for simultaneous determination of interval approximations containing real or complex zeros of the considered polynomialP. A criterion for the choice of the appropriatek-th root set is also given. For one of the suggested methods a procedure for accelerating the convergence is proposed. Starting from the expression for interval center, the generalised iterative method of the (k+2)-th order in standard arithmetic is derived.     

A uniform numerical method for quasilinear singular perturbation problems without turning points

A numerical method for singularly perturbed quasilinear boundary value problems without turning points is proposed: the continuous problem is transformed by introducing a special new independent variable and then finite-difference schemes are applied. The first order convergence uniform in the perturbation parameter is proved in the discreteL ¹-norm. The numerical results show the pointwise convergence, too.     

Proof rules for gotos

Summary We offer a program specification format adapted to statements with multiple exits, and use it to present proof rules to replace the somewhat unsatisfactory treatment of jumps in [3]. We justify the bridled use of gotos in return exits, failure exits, and loops with jumps in the middle. To exemplify our methodology, we prove the function Lookup.     

Robot control: Tracking with the required settling time

A recently developed concept of the finite-time tracking is studied within the framework of robot control. All the robot non-linearities are incorporated. Finite-time tracking and tracking with the required settling time are defined. The general sufficient conditions for all these tracking features are proved. They provide algorithms for control assuring the special tracking property. Their application to a rotational robot is shown via digital simulation. The simulation results illustrate the theory developed in the paper and show the excellent tracking behaviour of the robot.     

Stream water temperature prediction based on Gaussian process regression

The prediction of stream water temperature presents an interesting topic since the water temperature has a significant ecological and economical role, such as in species distribution, fishery, industry and agriculture water exploitation. The prediction of stream water temperature is usually based on appropriate mathematical model and measurements of different atmospheric factors. In this paper, a probabilistic approach to daily mean water temperature prediction is proposed. The resulting model is a combination of two Gaussian process regression models where the first model describes the long-term component of water temperature and the other model describes the short-term variations in water temperature. The proposed approach is developed even further by modeling the short-term variations with multiple Gaussian process regression models instead with a single one. Apart from that, variable selection procedure based on mutual information is presented which is suitable for input variable selection when nonlinear models for stream water prediction are developed. The proposed approach is compared with traditional modeling approaches on the measurements obtained on the Drava river in Croatia. The presented methodology can be used as a basis of the predictive tools for water resource managers.     

Understanding the new digital divide—A typology of Internet users in Europe

The purpose of this study is to better understand the digital divide by identifying the variety of ways in which people in Europe use the Internet. First, by using cluster analysis on survey data (N=12,666/age: 16–74 years) from Eurostat on Internet usage in Norway, Sweden, Austria, the UK, and Spain, we identified five user types: Non-Users (42%), Sporadic Users (18%), Instrumental Users (18%), Entertainment Users (10%), and Advanced Users (12%). These user types differ in their distributions over country, age, access, household members, and gender. An alarming finding is that 60% of the population was found to be either Non-Users or Sporadic Users, which reflects a large digital divide in Europe. Second, we conducted a logistic regression to identify the predictors for different user types. We found on a cross-national level that age and Internet access are the most salient predictors, whereas gender and household seems to be less relevant. However, the amount of variance explained differs between countries. We also suggested a future increase in the digital divide between the identified user types—a user type divide. The user typology and the identified predictors might help researchers, practitioners, and decision makers to better understand Internet users and the multi-complex variations among individuals and countries. This knowledge will also serve as a means to understand the digital divide by providing a more nuanced perspective on Europeans' unequal usage of the Internet and participation in an increasingly digital society.     

Protus 2.0: Ontology-based semantic recommendation in programming tutoring system

With the development of the Semantic web the use of ontologies as a formalism to describe knowledge and information in a way that can be shared on the web is becoming common. The explicit conceptualization of system components in a form of ontology facilitates knowledge sharing, knowledge reuse, communication and collaboration and construction of knowledge rich and intensive systems. Semantic web provides huge potential and opportunities for developing the next generation of e-learning systems. In previous work, we presented tutoring system named Protus (PRogramming TUtoring System) that is used for learning the essence of Java programming language. It uses principles of learning style identification and content recommendation for course personalization. This paper presents new approach to perform effective personalization highly based on Semantic web technologies performed in new version of the system, named Protus 2.0. This comprises the use of an ontology and adaptation rules for knowledge representation and inference engines for reasoning. Functionality, structure and implementation of a Protus 2.0 ontology as well as syntax of SWRL rules implemented for on-the-fly personalization will be presented in this paper.     

Intelligent control of DC motor driven electromechanical fin actuator

In this paper modeling, simulation and control of an electromechanical actuator (EMA) system for aerofin control (AFC) with permanent magnet brush DC motor driven by a constant current driver are investigated. Nonlinear model of the EMA-AFC system has been developed and experimentally verified in actuator test bench. Model has been used as the starting point for PID position controller synthesis. To improve performances of the system, computational intelligence has been applied. Genetic PID optimization, genetic algorithm (GA) optimized fuzzy supervisory PID control and finally GA optimized nonlinear PID algorithm modification are proposed. Improved transient response and system behavior have also been experimentally validated.