Wyniki wyszukiwania - BazTech

1

Wybrane modele chłodzenia płyty stalowej w powietrzu i ich walidacja

Hadała B., Malinowski Z., Szajding A.

Hutnik, Wiadomości Hutnicze

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2017

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Vol. 84, nr 4

178--183

PL

W pracy przedstawiono wyniki analizy wybranych modeli warunku brzegowego opartego o efektywny współczynnik wymiany ciepła wykorzystywany w symulacjach numerycznych procesów metalurgicznych. Badania miały na celu wytypowanie zależności pozwalających otrzymać jak najlepsze odwzorowanie pola temperatury płyty pionowej chłodzonej swobodnie w powietrzu od temperatury 900°C. Warunki brzegowe zostały zaimplementowane do programu wyliczającego zmianę temperatury płyty z rozwiązania metodą elementów skończonych równania przewodzenia ciepła. Otrzymane wyniki zostały porównane z pomiarem zmian temperatury płyty podczas chłodzenia. Dokonano również oceny dokładności zastosowanego modelu warunku brzegowego przez jego porównanie ze współczynnikiem wymiany ciepła uzyskanym z rozwiązania odwrotnego. Wykonane testy wykazały, że modele warunku brzegowego typu radiacyjnego oparte na efektywnym współczynniku wymiany ciepła pozwalają najdokładniej modelować zmiany temperatury płyty chłodzonej w powietrzu.

EN

Selected models of the boundary condition for the steel plate cooling in air have been analyzed. The models which utilize effective heat transfer coefficient for modeling steel plates cooling in metallurgical processes have been tested. The research was focused on selection the most accurate boundary condition model for natural cooling of steel plate from a high initial temperature of 900°C. The boundary conditions have been implemented in the finite element software employed for computing the plate temperature from the heat condition equation. The results of the computed plate temperature have been compared with the measurements. Further, the heat transfer coefficient distributions calculated from the selected boundary condition models have been compared with the effective heat transfer coefficient variation obtained from the inverse solution. The conducted research has shown that the radiation type boundary condition utilizing the effective heat transfer coefficient have given the best accuracy in the plate temperature simulations.

2

Towards the Applications of Algorithms for Inverse Solutions in EEG Brain-Computer Interfaces

Jagodzińska U.

International Journal of Electronics and Telecommunications

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2013

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Vol. 59, No. 3

277-283

EN

Locating the sources of EEG signals (signal generators), i.e. indicating the places in the brain that the signals come from is the objective of the inverse problem in BCI applications using EEG. The two algorithms based on the methods used in the inverse problem: the linear least squares method and the LORETA1 method were compared. An analysis of the accuracy of locating the sources generating EEG signals on the basis of the two above mentioned methods was carried out with the use of the MATLAB programme. The findings made it possible to determine both the complexity of calculation involved in the methods under consideration and to compare the accuracy of the results obtained. Tests were done in which the inverse problem was solved on the basis of the data that were entered from the electrodes. Then potentials on electrodes were found by means of solving the forward problem once again ɸ (ɸ→ɸ). Moreover, tests were conducted on simulated data describing current density at selected places in the brain. In this case potentials on the electrodes were found by means of solving the forward problem. Subsequently the inverse problem was solved and potentials at selected places in the brain were specified J(J→Ĵ). In the case of J(J→Ĵ) only the relative error was examined, while the variance was studied in both cases. As a result of doing the tests, it was proved that relative errors were the same in the SVD and PINV methods, while in the LORETA method the error was similar. The variance computed for these methods was more differentiated for each of the cases, which made it possible to compare the algorithms in a better way. Differentiation of the variances under 0.2 shows that the algorithms that have been analyzed work properly. On the basis of knowing the results of the inverse problem, an attempt was made to make a selection of the best features of the EEG signal which differentiates the classes. In the present work tests were conducted to examine the differentiation of selected classes. Welch’s t-statistics was used to differentiate and order them. The results of the tests present the order for three classes of thought tasks, i.e. imagining moving one’s left hand, imagining moving one’s right hand, imagining generating words beginning with a randomly chosen letter. The present work is an introduction to a wider classification of features which are made with the use of inverse solutions.

3

Applying algorithms for inverse solutions in classifying EEG signals

Jagodzińska U.

Elektronika : konstrukcje, technologie, zastosowania

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2013

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Vol. 54, nr 9

144-147

EN

The article presents selected algorithms in inverse solutions in the EEG signal. When undertaking the calculations, it was assumed that the data obtained from electrodes on the surface of the head were preprocessed. As a result of using these algorithms it is possible to specify both the areas of the brain that the signals come from and the current density of the signals read by means of electrodes placed on the surface of the head. On the basis of knowing the solution to the inverse problem, an attempt was made to select the features of the signals. Then t-statistics was used to differentiate and order them.

PL

W artykule przedstawiono wybrane algorytmy rozwiązywania zagadnień odwrotnych w sygnale EEG. Przystępując do obliczeń założono, że dane uzyskane z elektrod rozmieszczonych na powierzchni głowy zostały wstępnie przetworzone. Wynikiem działania tych algorytmów jest lokalizacja obszarów mózgu, z których pochodzą sygnały oraz natężenia tych sygnałów odczytywanych za pomocą elektrod rozmieszczonych na powierzchni głowy. Znając rozwiązania zagadnienia odwrotnego podjęto też próbę selekcji cech. Wykorzystano t-statystykę do ich zróżnicowania i uszeregowania.