Wyniki wyszukiwania - BazTech

1

Bifurcation and chaos analysis of a gear-rotor-bearing system

Gou X., Zhu L., Qi C.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 3

585--599

EN

To study chaos and bifurcation of a gear system, a five-degree-of-freedom nonlinear dynamic model of a gear-rotor-bearing system is established. It consists of a gear pair, supporting shafts, bearings and other auxiliary components. The effects of frequency, backlash, bearing clearance, comprehensive transmission error and stiffness on nonlinear dynamics of the system are investigated according to bifurcation diagrams, phase portraits and Poincar´e maps by a numerical method. Some nonlinear phenomena such as grazing bifurcation, Hopf bifurcation, inverse-Hopf bifurcation, chaos and coexistence of attractors are investigated. Different grazing bifurcations and their causes are discussed. The critical parameters are identified, too.

2

Evaluation of Strength and Failure of Brittle Rock Containing Initial Cracks under Lithospheric Conditions

Li X., Qi C., Shao Z., Ma C.

Acta Geophysica

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2018

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Vol. 66, no. 2

141--152

EN

Natural brittle rock contains numerous randomly distributed microcracks. Crack initiation, growth, and coalescence play a predominant role in evaluation for the strength and failure of brittle rocks. A new analytical method is proposed to predict the strength and failure of brittle rocks containing initial microcracks. The formulation of this method is based on an improved wing crack model and a suggested micro-macro relation. In this improved wing crack model, the parameter of crack angle is especially introduced as a variable, and the analytical stress-crack relation considering crack angle effect is obtained. Coupling the proposed stresscrack relation and the suggested micro-macro relation describing the relation between crack growth and axial strain, the stress-strain constitutive relation is obtained to predict the rock strength and failure. Considering different initial microcrack sizes, friction coefficients and confining pressures, effects of crack angle on tensile wedge force acting on initial crack interface are studied, and effects of crack angle on stress-strain constitutive relation of rocks are also analyzed. The strength and crack initiation stress under different crack angles are discussed, and the value of most disadvantaged angle triggering crack initiation and rock failure is founded. The analytical results are similar to the published study results. Rationality of this proposed analytical method is verified.

3

Wpływ minerałów ilastych na właściwości zaczynu cementowego z dodatkiem naftaleno-sulfonianu sodowego

Tan H., Lin C., Yang H., Ma B., Qi C., Li X.

Cement Wapno Beton

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2015

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R. 20/82, nr 3

193--200

PL

W pracy zbadano wpływ dodatku minerałów ilastych do cementu, a mianowicie kaolinitu i montmorillonitu na właściwości zaczynu z równoczesnym dodatkiem superplastyfikatora naftalenowego. Przeprowadzone doświadczenia wykazały, że adsorpcja plastyfikatora przez kaolinit i montmorillonit, badane za pomocą spektrometru promieniowania ultrafioletowego, była mniejsza niż cementu. Jednak szereg właściwości zaczynu uległo pogorszeniu, a szczególnie skurcz suszenia zaczynu cementowego zwiększył się, a wytrzymałość na ściskanie uległa zmniejszeniu. Wodożądność wzrosła bardzo znacznie, a konsystencja zaczynu uległa pogorszeniu. W podsumowaniu można stwierdzić, że należy unikać występowania w betonie minerałów ilastych, gdyż mają one niekorzystny wpływ na właściwości tego kompozytu.

EN

In the paper the investigations of the effect of clay minerals addition, namely kaolinite and montmorillonite, to cement on the properties of cement paste with sodium naphthalene sulfonate superplasticizer(NS) are presented. The studies have shown that the adsorption of NS by kaolinite and montmorillonite, determined by UV-VIS spectrophotometer, was lower than that of cement, but several cement paste properties were worse. Particularly the drying shrinkage of cement paste was increasing and the compressive strength was much lower as well as water demand was drastically increased and consistency of the paste was decreased. Summarizing the presence of clay minerals should be avoided in concrete because they have very disadvantage effect on the properties of this composite.

4

Multimode VCSEL Thermal and Spatial Model

Shi X., Qi C., Wang G.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 7b

248--251

EN

We present a VCSEL model that addresses the spatial dependence and thermal behavior of VCSELs based on multimode rate equations without sacrificing the numerical efficiency demanded by the circuit-level simulation of optoelectronic systems. The model is more comprehensive and parameters are easier to determine. The equivalent circuit of the model and expressions of circuit elements are given. It is implemented into SPICE-like simulators to simulate the dc, ac and transient features of VCSELs. The simulated results exhibit good agreements with references.

PL

Zaprezentowano model lasera typu VCSEL (vertical cavity surface emitting laser). Analizowano właściwości przestrzenne i termiczne. Zaproponowano schemat zastępczy modelu i przeprowadzono symulacje.