Wyniki wyszukiwania - Biblioteka Nauki

1

A new multigrid based method for characteristic diagram based correction of thermo-elastic deformations in machine tools

100%

Naumann C. , Putz M.

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tom Vol. 19, No. 4

42--57

EN

It is a well-known problem of milling machines, that waste heat from motors, friction effects on guides, environmental variations and the milling process itself greatly affect positioning accuracy and thus production quality. An economic and energy-efficient method of correcting this thermo-elastic positioning error is to gather sensor data (temperatures, axis positions, etc.) from the machine tool and the process and to use that information to predict and correct the resulting tool center point displacement using high dimensional characteristic diagrams. The computation of these characteristic diagrams leads to very large sparse linear systems of equations which require a vast memory and computation time to solve. This is particularly problematic for complex machines and varying production conditions which require characteristic diagrams with many input variables. To solve this issue, a new multigrid based method for the computation of characteristic diagrams will be presented, tested and compared to the previously used smoothed grid regression method.

2

Thermal breakdown in semiconductor junction devices

100%

Stepowicz W. J.

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tom Vol. 44, nr 3

365-372

EN

The breakdown phenomenon is found practically in all semiconductor devices with nonlinear pn or ms junctions. It delimits the safe operation area of these devices. On the other hand, some semiconductor devices, for example the Zener diodes and avalanche photodiodes, operate in the breakdown region. So, understanding the performance of semiconductor devices at breakdown is of great importance.

PL

Zjawisko przebicia występuje praktycznie we wszystkich elementach półprzewodnikowych ze złączem pn lub mp spolaryzowanych zaporowo. Ogranicza ono obszar bezpiecznej pracy wielu elementów, jednak, z drugiej strony, praca w zakresie przebicia jest typowa dla takich elementów jak, dla przykładu diody stabilizacyjne i fotodiody lawinowe. Na statycznych charakterystykach i(u) w zakresie przebicia dużym zmianom prądu odpowiadają małe zmiany napięcia. Na charakterystykach tych często występuje punkt, w którym rezystancja różniczkowa elementu zmienia znak z dodatniego na ujemny. Na kształt charakterystyk i(u) w zakresie przebicia mają wpłym zarówno zjawiska elektryczne ( jonizacja zderzeniowa i efekt tunelowy ), jak i termiczne. W ogólnym przypadku, wskutek sprzężenia zjawisk elektrycznych i termicznych, można mówić o przebiciu elektrotermicznym. W pracy wykazano, że w elementach ze złączami pn lub mp, opisanych dobrze znanymi zależnościami i(u), może nastąpić przebicie o charakterze termicznym, spowodowane jedynie zjawiskiem samonagrzewania złącza oraz wyznaczono współrzędne (i l, v t, T jt ) punktu przebicia termicznego. Przebicie termiczne zilustrowano na przykładach diody krzemowej ze złączem pn, diody Schottky'ego oraz tranzystora bipolarnego. Oprócz rozważań teoretycznych przedstawiono wyniki stosowanych pomiarów przeprowadzonych dla wymienionych elementów.

3

Temperature field analysis of optical coatings induced by millisecond and nanosecond lasers

100%

Wang B. , Qin Y. , Ni X. , Shen Z. , Lu J. , Wang X.

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tom Vol. 42, nr 4

783--793

EN

To study the differences between long-pulse and short-pulse laser-induced damage in optical dielectric thin films, temperature distributions in single-layer HfO2 films, multi-layer HfO2/SiO2 films, and HfO2 films with high-absorptive inclusions induced by 1 ms and 10 ns lasers are analyzed based on the temperature field theory. Through our calculations, the damage property differences between millisecond and nanosecond lasers are summarized. The results for single-layer films show that 1 ms laser is easier to damage the substrate than 10 ns laser. For multi-layer films, the laser field effect is weaker when irradiating by 1 ms laser. Furthermore, when inclusions are introduced, the film is easier to be damaged by 10 ns laser, which means that 10 ns laser is more sensitive to the inclusions.

4

Parameterization of environmental influences by automated characteristic diagrams for the decoupled fluid and structural-mechanical simulations

88%

Glänzel J. , Kumar T. S. , Naumann C. , Putz M.

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tom Vol. 19, No. 1

98--113

EN

Thermo-elastic effects contribute the most to positioning errors in machine tools especially in operations where high precision machining is involved. When a machine tool is subjected to changes in environmental influences such as ambient air temperature, velocity or direction, then flow (CFD) simulations are necessary to effectively quantify the thermal behaviour between the machine tool surface and the surrounding air (fluid). Heat transfer coefficient (HTC) values effectively represent this solid-fluid heat transfer and it serves as the boundary data for thermo-elastic simulations. Thereby, deformation results can be obtained. This two-step simulation procedure involving fluid and thermo-structural simulations is highly complex and time-consuming. A suitable alternative for the above process can be obtained by introducing a clustering algorithm (CA) and characteristic diagrams (CDs) in the workflow. CDs are continuous maps of a set of input variables onto a single output variable, which are trained using data from a limited number of CFD simulations which is optimized using the clustering technique involving genetic algorithm (GA) and radial basis function (RBF) interpolation. The parameterized environmental influences are mapped directly onto corresponding HTC values in each CD. Thus, CDs serve as look-up tables which provide boundary data (HTC values along with nodal information) under several load cases (combinations of environmental influences) for thermo-elastic simulations. Ultimately, a decoupled fluid-structural simulation system is obtained where boundary (convection) data for thermo-mechanical simulations can be directly obtained from CDs and would no longer require fluid simulations to be carried out again. Thus, a novel approach for the correction of thermo-elastic deformations on a machine tool is obtained.

5

Efficient quantification of free and forced convection via the decoupling of thermo-mechanical and thermo-fluidic simulations of machine tools

88%

Glaenzel J. , Ihlenfeldt S. , Naumann C. , Putz M.

Journal of Machine Engineering

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2018

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tom Vol. 18, No. 2

41--53

EN

Thermo-elastic deformations represent one of the main reasons for positioning errors in machine tools. Investigations of the thermo-mechanical behaviour of machine tools, especially during the design phase, rely mainly on thermo-elastic simulations. These require the knowledge of heat sources and sinks and assumptions on the heat dissipation via convection, conduction and radiation. Forced convection such as that caused by moving assemblies has both a large influence on the heat dissipation to the surrounding air. The most accurate way of taking convection into account is via computational fluid dynamics (CFD) simulations. These simulations compute heat transfer coefficients for every finite element on the machine tool surface, which can then be used as boundary conditions for accurate thermo-mechanical simulations. Transient thermo-mechanical simulations with moving assemblies thus require a CFD simulation during each time step, which is very time-consuming. This paper presents an alternative by using characteristic diagrams to interpolate the CFD simulations. The new method uses precomputed thermal coefficients of a small number of load cases as support points to estimate the convection of all relevant load cases (i.e. ambient conditions). It will be explained and demonstrated on a machine tool column.

6

Nieizotermiczne parametry małosygnałowe elementów półprzewodnikowych

75%

Stepowicz W. J. , Zarębski J.

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tom Vol. 44, nr 3

345-364

PL

Zjawiska termiczne wpływają w istotny sposób na własności i parametry elementów półprzewodnikowych oraz układów scalonych. Dotyczy to zarówno ich modeli sałoprądowych jak i modeli dla prądu zmiennego. W sytuacjach, kiedy zjawiska termiczne odgrywają istotną rolę, modele elementow różnią się zasadniczo, zarówno jakościowo jak i ilościowo, od ich odpowiedników znanych z klasycznej teorii nie uwzględniającej tych zjawisk. Z kolei, postać modeli elementów wpływa na parametrty robocze, określające własności funkcjonalne, układów elektronicznych skonstruowanych z wykorzystaniem tych elementów. W pracy przedstawiono metodę wyznaczania nieizotermicznych modeli małosygnałowych elementów półprzewodnikowych i pokazano takie modele dla wybranych elementów, uzyskane na podstawie tej metody. Na kilku przykładach zilustrowano wpływ nieizotermicznej postaci modeli małosygnałowych elementów na własności układów, a także przytoczono inne konsekwencje i korzyści wynikające ze stosowania takich modeli.

EN

The thermal phenomena influence models of semiconductor devices considerably; it concerns the d.c. characteristics and the small - signal circuits as well. In the well - known models the effect of the ambient temperature is only taken into account, and therefore these models can be denominated as isothermal. In fact, due to the selfheating phenomenon, the junction (inside) temperature differs from the ambient temperature. Under steady - state, the junction temperature rise above the ambient temperature depends on the thermal resistance of the device and on the dissipated power. Under any a. c. current or voltage exitation, the a. c. component of the junction temperature appears. The models including selfheating can be denominated as nonisothermal. In some cases in ICs, the mutual thermal interactions between the devices have to be taken into considerations, additionally. In this paper the a. c. nonisothermal small - signal models of some semiconductor devices are discoussed. Due to the thermal effects, in the low frequency range the small - signal nonisothermal parameters of the devices become complex. Since in this range the electrical inertia resulting in the diffusion and junction capacitances can be neglected, the thermal inertia leads to the small - signal circuits with the new capacitances and inductances. In the paper the influence of the nonisothermal small - signal parameters on the performance of some circuits: the voltage amplifier and current source is shown. As well, some results concerning the 1/f noise model of the pn diode are given, and a new method of the thermal resistance measurement sof the BJT, based on its nonisothermal uotput conductance, is presented.

7

Cyclic steady states of a thick-walled reactor with stress concentrators

63%

Widłak G. , Zieliński A.

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tom R. 107, z. 4-M

157-166

EN

The paper deals with elastic-plastic stress states in vicinity of a radial cross-bore in a thick-walled reactor loaded by variable internal pressure and a temperature gradient. In the description of material, the linear Prager model of hardening has been applied. The mechanism of development of reverse plastification in each load cycle has been observed. The termal effect is presented on an example of the steady stress states. The transient states (starting and closing work periods of the reactor) have been investigated in the PhD thesis of the first author.

PL

W artykule badano sprężysto-plastyczne stany naprężeń w pobliżu otworu grobościennego reaktora obciążonego zmiennym ciśnieniem wewnętrznym i różnicą temperatur. W opisie materiału stosowano liniowy model wzmocnienia Pragera. Obserwowano mechanizm rozwoju przeciwzwrotnego uplastycznienia występujący przy każdym cyklu obciążenia. Efekty termiczne pokazano na przykładzie stanów ustalonych. Stany nieustalone (rozruch i wygaszanie reaktora) były badane w ramach rozprawy doktorskiej pierwszego autora.

8

Investigation of thermal effects of water vapor adsorption on zeolites

63%

Gwadera M. , Kupiec K. , Rakoczy J.

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tom R. 109, z. 1-M

87--94

EN

Temporal variations of temperatures in an adsorbent bed have been studied in this paper. Separation of an ethanol-water vapor mixture on zeolites has been considered. Temperature of the bed was determined both experimentally and numerically on the basis of a mathematical model of the process. The conformity between experimental and numerical values was satisfactory. It was found that maximum temperature in the bed depends mainly on water content in the raw material.

PL

W artykule podano badania czasowych zmian temperatur w złożu adsorbentu. Pomiary dotyczyły rozdzielania parowej mieszaniny etanol-woda na zeolitach. Przebiegi temperatur złoża zostały określone zarówno eksperymentalnie, jak i obliczeniowo w oparciu o model matematyczny procesu. Zgodność wyników doświadczalnych i obliczeniowych była zadowalająca. Stwierdzono, że maksymalna temperatura w złożu zależy głównie od zawartości wody w odwadnianym surowcu.