Wyniki wyszukiwania - BazTech

1

Estimation of random friction forces on the microbearing cooperating surfaces

Wierzcholski Krzysztof, Miszczak Andrzej

Journal of KONES

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2019

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Vol. 26, No. 2

167--174

EN

Presented paper concerns a new mathematical form of stochastic theory of hydrodynamic friction forces occurring on the real cooperating surfaces in computer micro bearing fan and computer microbearing in hard disc driver HDD. This paper presents particularly a new-review of stochastic analytical considerations realized by the authors for friction forces estimation during hydrodynamic lubrication performed on the ground of the measurements of the gap height between two roughness surfaces. After numerous experimental measurements directly follows that the random unsymmetrical increments and decrements of the gap height of computer microbearings have important influence on the load carrying capacities and finally on the friction forces and wear of cooperating surfaces. The main topic demonstrates the influence of the variations of expectancy values and standard deviation of the computer microbearing gap height on the friction forces occurring in the HDD and microbearing fan. Moreover, it is observed the evident connection between the apparent dynamic viscosity and the features of the microbearing superficial surface. Hence after abovementioned remarks follows the corollary that the influence of the microbearing gap height stochastic variations connected with the surface roughness tend moreover indirect from the apparent viscosity into the friction forces variations. The synthetic, complex elaboration of obtained results indicates finally the influence of the random roughness in micro and nano level of microbearing surfaces on the friction forces distribution. A new results contained in this paper are obtained taking into account 3D variations of dynamic viscosity of the non-Newtonian lubricant, particularly variations crosswise the film thickness and influences of surface superficial layer features on the lubricant apparent viscosity.

2

Numerical review of friction forces in microbearings with curvilinear journals

Wierzcholski K.

Acta Mechanica et Automatica

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2008

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Vol. 2, no. 4

102-105

EN

The research showed in this paper lead to presentation of hydrodynamic HDD micro-bearing with orthogonal curvilinear profile of journal for example for conical, hyperbolic and other cooperating micro-bearing surfaces. Pressure distributions and load carrying capacity values on the conical micro-bearing journals are calculated. The formulae describing the friction forces and friction coefficients for micro-bearing curvilinear journals are derived. Up to now, the dynamic behavior of HDD micro-bearings was considered mostly by Jang at al. (2005). Presented paper indicates that on the memory capacity have influence not only herringbone or spiral grooves but in many cases the shapes of micro-bearing journals and sleeves too.

3

Microbearings and microturbines - possibilities of dynamic state assessment.

Kiciński J.

Zagadnienia Eksploatacji Maszyn

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2007

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Vol. 42, nr 2

91-107

EN

The article discusses tendencies in development of turbines, from the macro to micro scale, and their possible application in dispersed cogeneration, i.e. in home power installations. In the small scale, turbines and bearings are a source of specific problems connected with securing stable rotor operation and their susceptibility to some material imperfections, such as shaft cracks. New research tools composing the computer system MESWIR are presented, and results of system stability investigations taking into account thermoelastic deformations of bearing bushes and various variants of their fixing are discussed, along with the results of investigations of the effect of crack depth propagation on the dynamic state of the entire system. The obtained results are rather surprising and frequently in opposition to a so-called engineering intuition. The machine selected for investigations is a three-support rotating machine with two discs, in operation in conditions specific for microturbines (low Sommerfeld numbers). The developed research tools have turned out extremely applicable for assesing vibroacoustic threats generated by this type of machines.

PL

W pracy przedstawione zostały rozważania dotyczące tendencji rozwojowych turbin od makroskali do mikroskali i możliwości ich aplikacji w kogeneracji rozproszonej, czyli w tzw. "domowych" instalacjach energetycznych. Turbiny i łożyska w małej skali generują specyficzne problemy związane z utrzymaniem stabilnej pracy wirnika i wrażliwością na niektóe imperfekcje materiałowe takie jak np. pęknięcia wału. Przedstawione zostały nowe narzędzia badawcze w postaci systemu komputerowego MESWIR i zaprezentowane wyniki badań stabilności układu z uwzględnieniem deformacji termosprężystych panwi łożyskowych i różnych wariantów ich zacisku, a także wyniki badań dotyczące wpływu propagacji głębokości pęknięcia wału na stan dynamiczny całego układu. Otrzymano wyniki dość zaskakujące, często sprzeczne z tzw. "intuicją inżynierską". Do analizy przyjęta została trójpodporowa maszyna wirnikowa z dwoma dyskami pracująca w warunkach właściwych dla mikroturbin (małe liczby Sommerfelda). Opracowane narzędzia badawcze okazały się bardzo przydatne w ocenie zagrożeń wibroakustycznych tego typu urządzeń.

4

Microturbines in dispersed cogeneration - vibroacoustic threats

Kiciński J.

Archives of Acoustics

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2007

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Vol. 32, No. 2

263-277

EN

The article discusses tendencies in development of turbines, from the macro to micro scale, and their possible application in dispersed cogeneration, i.e. in home power installations. In the small scale, turbines and bearings are a source of specific problems connected with securing stable rotor operation and their susceptibility to some material imperfections, such as shaft cracks. New research tools composing the computer system MESWIR are presented, and results of system stability investigations taking into account thermoelastic deformations of bearing bushes and various variants of their fixing are discussed, along with the results of investigations of the effect of crack depth propagation on the dynamic state of the entire system. The obtained results are rather surprising and frequently in opposition to a so-called engineering intuition. The machine selected for investigations is a three-support rotating machine with two discs, in operation in conditions specific for microturbines (low Sommerfeld numbers). The developed research tools have turned out extremely applicable for assessing vibroacoustic threats generated by this type of machines.