The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.B...The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.By fitting the identified nonlinear coefficients under different excitation amplitudes,the nonlinear vibration responses of the system are predicted.The results show that the accuracy of the BWM is higher than that of the CSFM,especially in the non-resonant region.However,the optimization time of the BWM is longer than that of the CSFM.展开更多
The objects of our paper are aluminum alloy samples (AASs) contained the different amount of Cu, Mn, Mg, Si and Li. We are modeling the features of microstructure of potential relief of an AAS and studying its transfo...The objects of our paper are aluminum alloy samples (AASs) contained the different amount of Cu, Mn, Mg, Si and Li. We are modeling the features of microstructure of potential relief of an AAS and studying its transformation under both imposed fatigue deformation and wetted by liquid metals (Ga;or Hg;Li;In). We illustrate the main ideas by using only the “time series” allied with effective internal friction Q-1eff of an AAS. AASs like B-95 or 7075 are heterogeneous materials for which the more energy can be absorbed by selected micro-regions of a tested sample. So micro-crack in the space of AAS and alarm state of AAS arises. Each micro-region will to contribute the Q-1k (the internal friction Q-1k belong to k-th micro-region) to the effective internal friction— Q-1eff accordance with fit statistic . We find a number of micro-regions—L and series gk & Qk from the experimental data like as the internal friction (Q-1)eff versus both the number of cycles—N and the deformation—е. Series gk & Qk (k=1,2,3,...,L) present the microstructures of AASs. In this paper also is presented the original technology to forecast fatigue damage of an AAS. Here the fatigue sensitive element (FSE) used. We made multiphase heterogeneous mixtures (MHMs) which contents a variable volume of initial components. It is selected MHMs are using for produce FSEs. The present paper is aimed to establish the correlation of the FSEs microstructures changes and corresponding changes of the aluminum alloy microstructures at imposing the same spectra deformation on both of them. A change of FSEs microstructure investigated by using their effective electrical resistance Reff data.展开更多
In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack...In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack. Also, local stiffness changes at the crack location are considered to be a nonlinear amplitude-dependent function and it is assumed that during one half a cycle, the frequencies and mode shapes of the beam vary continuously with time. In addition, by using the experimental tests, it is shown that the local stiffness at the crack location varies continuously between the two extrerae values corresponding to the fully closed and the fully open cases of the crack. Then, by using the mechanical energy balance the dynamic response of the cracked beam is obtained at every time instant. The results show that for a specific crack depth, by approaching the crack location to the fixed end of the beam, more reduction in the fundamental frequency occurs. Furthermore, for a specific crack location, the fundamental frequency diminishes and the nonlinearity of the system increases by increasing the crack depth. In order to validate the results, the variations of the fundamental frequency ratio against the crack location axe compared with experimental results.展开更多
The problem on the Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper, ...The problem on the Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper, we shall examine the hypothesis more rigorous than that which has been carried yet. A new deconvolution method for Fourier transform is suggested. Using this method, the polar motion data since 1900 are analysed and the varying process of the Chandlerian period and amplitude are given. The analytical results show that the Chandler period is not stable and is indeed amplitude-dependent. The probable explanation for this phenomenon is that it might be caused by non-equilibrium response of the ocean.展开更多
文摘The cubic stiffness force model(CSFM)and Bouc-Wen model(BWM)are introduced and compared innovatively.The unknown coefficients of the nonlinear models are identified by the genetic algorithm combined with experiments.By fitting the identified nonlinear coefficients under different excitation amplitudes,the nonlinear vibration responses of the system are predicted.The results show that the accuracy of the BWM is higher than that of the CSFM,especially in the non-resonant region.However,the optimization time of the BWM is longer than that of the CSFM.
文摘The objects of our paper are aluminum alloy samples (AASs) contained the different amount of Cu, Mn, Mg, Si and Li. We are modeling the features of microstructure of potential relief of an AAS and studying its transformation under both imposed fatigue deformation and wetted by liquid metals (Ga;or Hg;Li;In). We illustrate the main ideas by using only the “time series” allied with effective internal friction Q-1eff of an AAS. AASs like B-95 or 7075 are heterogeneous materials for which the more energy can be absorbed by selected micro-regions of a tested sample. So micro-crack in the space of AAS and alarm state of AAS arises. Each micro-region will to contribute the Q-1k (the internal friction Q-1k belong to k-th micro-region) to the effective internal friction— Q-1eff accordance with fit statistic . We find a number of micro-regions—L and series gk & Qk from the experimental data like as the internal friction (Q-1)eff versus both the number of cycles—N and the deformation—е. Series gk & Qk (k=1,2,3,...,L) present the microstructures of AASs. In this paper also is presented the original technology to forecast fatigue damage of an AAS. Here the fatigue sensitive element (FSE) used. We made multiphase heterogeneous mixtures (MHMs) which contents a variable volume of initial components. It is selected MHMs are using for produce FSEs. The present paper is aimed to establish the correlation of the FSEs microstructures changes and corresponding changes of the aluminum alloy microstructures at imposing the same spectra deformation on both of them. A change of FSEs microstructure investigated by using their effective electrical resistance Reff data.
文摘In this paper, a new approach to free vibration analysis of a cracked cantilever beam is proposed. By considering the effect of opening and closing the crack during the beam vibration, it is modeled as a fatigue crack. Also, local stiffness changes at the crack location are considered to be a nonlinear amplitude-dependent function and it is assumed that during one half a cycle, the frequencies and mode shapes of the beam vary continuously with time. In addition, by using the experimental tests, it is shown that the local stiffness at the crack location varies continuously between the two extrerae values corresponding to the fully closed and the fully open cases of the crack. Then, by using the mechanical energy balance the dynamic response of the cracked beam is obtained at every time instant. The results show that for a specific crack depth, by approaching the crack location to the fixed end of the beam, more reduction in the fundamental frequency occurs. Furthermore, for a specific crack location, the fundamental frequency diminishes and the nonlinearity of the system increases by increasing the crack depth. In order to validate the results, the variations of the fundamental frequency ratio against the crack location axe compared with experimental results.
文摘The problem on the Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper, we shall examine the hypothesis more rigorous than that which has been carried yet. A new deconvolution method for Fourier transform is suggested. Using this method, the polar motion data since 1900 are analysed and the varying process of the Chandlerian period and amplitude are given. The analytical results show that the Chandler period is not stable and is indeed amplitude-dependent. The probable explanation for this phenomenon is that it might be caused by non-equilibrium response of the ocean.
