CONTENTS & ABSTRACTS
InEnglish. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Engineering
Volume 8 No. 4December 2002
Solvingline balancing problems with model checking; 211–222
Jüri Vain, Ingmar Randvee, Tiit Riismaa, andJuhan Ernits
Abstract. A two-step technique for solving large-scale assembly linebalancing problems is proposed. In the first step, an approximate globalsolution is found to the task assignment problem using the algorithmicbranch-and-bound method. In the second step, the workstations with criticalworkload are selected and their load recalculated using local models of finergranularity. The workstation models in the second step are defined as parallelcompositions of timed automata to which the parametric model checking procedurecan be efficiently applied. An illustrative example is given.
Key words: flexible manufacturing, behavioural modelling, timed automata, linebalancing, model checking.
Feed-forwardneural networks for smooth operation of the high voltage power transmissionnetwork; 223–247
Taivo Kangilaski
Abstract. The article describesalgorithms based on feed-forward neural networks for short-term forecast ofhigh-voltage power consumption and fault prediction, implemented in thesoftware “Event Navigator” of Eesti Energia AS.
Key words: high-voltage powertransmission, fault prediction, short-term forecast.
Evaluationof the Gurson–Tvergaard material model by using damage mechanics andthermomechanics; 248–269
Kari Santaoja
Abstract. Gurson–Tvergaard material model has been evaluated by usingdamage mechanics and thermomechanics. The evolution law of Tvergaard for thevoid volume fraction is rigorously derived. It follows that the modificationfor rate of the void volume fraction by Chu and Tvergaard and Tvergaard andNeedleman cannot be accepted since it violates the axiom of conservation ofmass. An extension of the Gurson–Tvergaard model has been derived. Using theextended model it has been shown that under compression there are stress statesby which the Gurson–Tvergaard material model does not satisfy the Clausius–Duheminequality.
Key words: material model, Gurson–Tvergaard model, porous materials,damage mechanics, thermodynamics, thermomechanics.
Simultaneityof the wind power in Estonia; 270–275
Teolan Tomson
Abstract. Analysingsynchronous wind speed and power databases at six characteristic sites in Westand North Estonia, the simultaneous wind power on the Estonian coastal line isstudied. Estonia is big enough not to be covered by the calm totally, but about33% of the time wind turbines over the whole Estonia would be performing at aninsignificant capacity. The wind energy resource in West Estonia is nearlytwice bigger than that in North Estonia due to favourable wind conditions on islands.If wind on islands is not employed (due to environmental restrictions or lackof electrical lines), no big effect can be expected from wind utilization inthe rest of the Estonian territory.
Key words: wind energy, geographical variation of wind.
Influence of wind speed gusts on powergeneration; 276–285
Teolan Tomson and Maire Hansen
Abstract. Based on the analysis of the Estonian offshore and onshore winddatabase, the boundaries of the probability of wind speed gusts and lulls,which lead to disturbances in the electrical grid, are assessed. Theseboundaries are assigned to the probability distribution function (pdf) of windspeed gusts and lulls on one hand and to the pdf of power deflections on theother. The probability of electrical disturbances remains between theseboundaries. For the evaluation of the pdf of gusts and lulls, standarddeviation of the wind speed can be used.
Key words: wind speed gust (lull), wind power gust (lull), disturbances in theelectrical grid.
CHRONICLE
Olav Aarna 60; 286–287
Contents of volume 8; 288
