Wyniki wyszukiwania - Biblioteka Nauki

1

Dynamic behavior of an imbalanced and warped Jeffcott rotor with asymmetric stiffness

100%

Lin F. , Meng G. , Fang T.

International Journal of Applied Mechanics and Engineering

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2007

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tom Vol. 12, no 4

1039-1048

EN

The dynamic behaviour of an imbalanced and warped Jeffcott rotor with asymmetric stiffness was studied theoretically and experimentally. The rotor response was analyzed and discussed under different rotating speeds and angle ranges between the directions of the bend and imbalance. It was noted that the angle between the directions of the warp and the imbalance plays a key role in controlling the rotor response and effect of the angle varied by the magnitude of bend. If the angle is larger than [...] and smaller than [...] in radian, the rotor response will decrease due to imbalance. Particularly for sufficiently large angles, the response amplitude will decrease with increasing rotating speed. This effect will take place before passing the first critical rotating speed, if the magnitude of the warp is smaller than the eccentricity; and will take place after passing the first critical rotating speed, if the magnitude of the warp is larger than the eccentricity. A double frequency response also happened in an imbalanced rotor with initial bow and asymmetric stiffness; the supposed stationary response will lose its stability as the rotating speed lies in the range between the first two critical speeds. Good agreement was achieved between the numerical solutions and the experimental results to verify the proposed model capability, which may contribute to the diagnosis of asymmetric stiffness and the residual warp of the rotor.

2

Characteristics of elastic wave propagation in thick beams - when guided waves prevail?

88%

Peng H. , Ye L. , Meng G. , Sun K. , Li F.

Journal of Theoretical and Applied Mechanics

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2011

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tom Vol. 49 nr 3

807-823

EN

Characteristics of wave propagation in thick beams are analyzed using a three-dimensional (3-D) spectral element method (SEM) for the purpose of damage detection. Analysis of wave propagation in beams of different thickness under excitations with different central frequency reveals that when the thickness of the beam is comparable to the wavelength of the elastic wave, a local wave mode, besides quasi-symmetric and quasi-anti-symmetric modes, exist simultaneously in the beam. In particular, when the wavelength is more than two times the beam thickness, the local wave modes are suppressed and the wave modes in the beam can be regarded as traditional guided waves, i.e., Lamb waves. It is demonstrated that the central frequency of wave signals can be selected according to the dimensions of the beam to obtain simple wave modes like those in thin beams. The characteristics of wave propagation in an intact beam and beams with a lateral crack are analyzed and the results are also validated by experiments, where wave propagation signals in thick steel beams are activated and captured using PZT elements.

PL

Praca przedstawia problem detekcji uszkodzeń w belkach o znacznej grubości za pomocą trójwymiarowej metody elementów spektralnych (SEM) ze szczególnym uwzględnieniem charakterystyk propagacji fal w ośrodku. Analiza rozchodzenia się fal w belkach o różnej grubości poddanych wymuszeniom o różnej częstotliwości centralnej ujawniła, że gdy grubość belki jest porównywalna z długością fali sprężystej, to oprócz quasi-symetrycznych i quasi-antysymetrycznych postaci pojawia się lokalna postać własna fali. Gdy długość fali przekracza co najmniej dwukrotnie grubość belki, postacie lokalne zanikają i postacie fal mogą zostać uznane jako tradycyjne fale prowadzone, tj. fale Lamba. Pokazano, że centralna częstotliwość sygnałów falowych może zostać dobrana do konkretnych rozmiarów belki tak, aby otrzymać proste postacie własne fal przypominające kształt fal rozchodzących się w belkach cienkich. W pracy zbadano charakterystyki propagacji fal w belce nieuszkodzonej i belce z pęknięciem poprzecznym. Rezultaty tych badań zweryfikowano doświadczalnie poprzez generowanie i rejestrację sygnałów w grubych stalowych belkach aktuatorami i czujnikami piezoelektrycznymi.

3

Synthesis of V2O3/C composites with different morphologies by a facile route and phase transition properties of the compounds

75%

Zhang Y. , Wang N. , Huang Y. , Huang C. , Mei X. , Meng G.

Materials Science Poland

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2014

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tom Vol. 32, No. 2

236--242

EN

V2O3 and amorphous carbon composites (V2O3/C composites) with different morphologies (e.g. nanospheres, nanorods and nanosheets) were, for the first time, successfully synthesized by a facile hydrothermal route and subsequent calcination. The as-obtained samples were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometery (EDS), elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The morphology of V2O3/C composites could be easily controlled by varying the reaction time, and, as a result, V2O3/C composites with nanospheres, nanorods and nanosheets were selectively synthesized. Furthermore, the phase transition property of V2O3/C composites was measured by differential scanning calorimetry (DSC), suggesting that V2O3/C composites exhibit the phase transition similar to V2O3, which could expand the potential applications of materials related to V2O3 in the future.