Analysis of coupling fault correlation and nonlinear vibration of multi-stage gear transmission system

In the multistage gear transmission system, when multiple faults are coupled, the faults with weak signals are often hidden and hard to identify. Multi-fault coupling may also cause new coupling fault characteristics, such as new peaks or side bands in the spectrum. These characteristics are likely to contain fault information. Studying the sources of frequency components in coupled fault signals will help to decouple the signals and dig out the correlation characteristics between faults. The coupling fault of fixed-axis gear crack and planetary gear tooth broken was studied in this paper. The nonlinear dynamic model of the multi-stage gear transmission system was used for simulation, and the fault frequency characteristics of the system varying with the excitation frequency were obtained. The short-time Fourier transform (STFT) and waterfall plot analysis were applied to the experimental signals to separate the fault features. By comparing the theoretical and experimental signals, we found the natural frequency of the system, the side frequency characteristics of single fault and coupling fault, and the cause of new peaks. This study has a guiding significance for the separation and identification of coupling faults of the multi-stage gear transmission system

Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface

Recent theories and experiments have suggested that strong spin-orbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic entanglement effects. Such systems feature two-dimensional surface states whose electrodynamic properties are described not by the conventional Maxwell equations but rather by an attached axion field, originally proposed to describe strongly interacting particles. It has been proposed that a topological insulator with a single spin-textured Dirac cone interfaced with a superconductor can form the most elementary unit for performing fault-tolerant quantum computation. Here we present an angle-resolved photoemission spectroscopy study and first-principle theoretical calculation-predictions that reveal the first observation of such a topological state of matter featuring a single-surface-Dirac-cone realized in the naturally occurring Bi$_2$Se$_3$ class of materials. Our results, supported by our theoretical predictions and calculations, demonstrate that undoped compound of this class of materials can serve as the parent matrix compound for the long-sought topological device where in-plane surface carrier transport would have a purely quantum topological origin. Our study further suggests that the undoped compound reached via n-to-p doping should show topological transport phenomena even at room temperature.Comment: 3 Figures, 18 pages, Submitted to NATURE PHYSICS in December 200

Coupling fault transfer characteristics of fixed-axis gear crack and planetary gear missing tooth

The test signal of multistage gear transmission system is complex. When coupling faults occur in the system, it is often difficult to accurately extract all kinds of fault features. In the past studies, we found that the fault signals have modulation and coupling effects. The failure of a gear is often reflected in the power spectrum in the form of associated changes in the meshing frequency of other stages. The separation of these features will facilitate the analysis of the coupling effects of multiple faults. The transfer characteristic method provides an effective method for decomposing such signal features. In this paper, through the analysis of transfer characteristics, the coupling fault transfer characteristics and the associated influence relationship of fixed-axis gear crack and planetary gear missing tooth are revealed. The contact force signals of each pair of gears with the coupling fault are obtained by dynamic simulation. The test signals of the fixed-axis gearbox and planetary gearbox are obtained under normal and coupling fault states. According to the method of system identification, the corresponding transfer function model of each path is established. The transfer process is revealed by the analysis of transfer characteristics. The association between two kinds of faults is found, which does not exist in a single fault and is difficult to obtain by signal analysis. This study reveals the association and vibration mechanism of the coupled fault, which provides a theoretical basis for fault diagnosis of multistage gears

Slip energy barriers in aluminum and implications for ductile versus brittle behavior

We conisder the brittle versus ductile behavior of aluminum in the framework of the Peierls-model analysis of dislocation emission from a crack tip. To this end, we perform first-principles quantum mechanical calculations for the unstable stacking energy $\gamma_{us}$ of aluminum along the Shockley partial slip route. Our calculations are based on density functional theory and the local density approximation and include full atomic and volume relaxation. We find that in aluminum $\gamma_{us} = 0.224$ J/m$^2$. Within the Peierls-model analysis, this value would predict a brittle solid which poses an interesting problem since aluminum is typically considered ductile. The resolution may be given by one of three possibilites: (a) Aluminum is indeed brittle at zero temperature, and becomes ductile at a finite temperature due to motion of pre-existing dislocations which relax the stress concentration at the crack tip. (b) Dislocation emission at the crack tip is itself a thermally activated process. (c) Aluminum is actually ductile at all temperatures and the theoretical model employed needs to be significantly improved in order to resolve the apparent contradiction.Comment: 4 figures (not included; send requests to [email protected]

Non-monotonicity of the frictional bimaterial effect

Sliding along frictional interfaces separating dissimilar elastic materials is qualitatively different from sliding along interfaces separating identical materials due to the existence of an elastodynamic coupling between interfacial slip and normal stress perturbations in the former case. This bimaterial coupling has important implications for the dynamics of frictional interfaces, including their stability and rupture propagation along them. We show that while this bimaterial coupling is a monotonically increasing function of the bimaterial contrast, when it is coupled to interfacial shear stress perturbations through a friction law, various physical quantities exhibit a non-monotonic dependence on the bimaterial contrast. In particular, we show that for a regularized Coulomb friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is a non-monotonic function of the bimaterial contrast, and provide analytic insight into the origin of this non-monotonicity. We further show that for velocity-strengthening rate-and-state friction, the maximal growth rate of unstable interfacial perturbations of homogeneous sliding is also a non-monotonic function of the bimaterial contrast. Results from simulations of dynamic rupture along a bimaterial interface with slip-weakening friction provide evidence that the theoretically predicted non-monotonicity persists in non-steady, transient frictional dynamics.Comment: 14 pages, 5 figure

Limitations of Quantum Simulation Examined by Simulating a Pairing Hamiltonian using Nuclear Magnetic Resonance

Quantum simulation uses a well-known quantum system to predict the behavior of another quantum system. Certain limitations in this technique arise, however, when applied to specific problems, as we demonstrate with a theoretical and experimental study of an algorithm to find the low-lying spectrum of a Hamiltonian. While the number of elementary quantum gates does scale polynomially with the size of the system, it increases inversely to the desired error bound $\epsilon$. Making such simulations robust to decoherence using fault-tolerance constructs requires an additional factor of $1/ \epsilon$ gates. These constraints are illustrated by using a three qubit nuclear magnetic resonance system to simulate a pairing Hamiltonian, following the algorithm proposed by Wu, Byrd, and Lidar.Comment: 6 pages, 2 eps figure

Stability of faults with heterogeneous friction properties and effective normal stress

Abundant geological, seismological and experimental evidence of the heterogeneous structure of natural faults motivates the theoretical and computational study of the mechanical behavior of heterogeneous frictional fault interfaces. Fault zones are composed of a mixture of materials with contrasting strength, which may affect the spatial variability of seismic coupling, the location of high-frequency radiation and the diversity of slip behavior observed in natural faults. To develop a quantitative understanding of the effect of strength heterogeneity on the mechanical behavior of faults, here we investigate a fault model with spatially variable frictional properties and pore pressure. Conceptually, this model may correspond to two rough surfaces in contact along discrete asperities, the space in between being filled by compressed gouge. The asperities have different permeability than the gouge matrix and may be hydraulically sealed, resulting in different pore pressure. We consider faults governed by rate-and-state friction, with mixtures of velocity-weakening and velocity-strengthening materials and contrasts of effective normal stress. We systematically study the diversity of slip behaviors generated by this model through multi-cycle simulations and linear stability analysis. The fault can be either stable without spontaneous slip transients, or unstable with spontaneous rupture. When the fault is unstable, slip can rupture either part or the entire fault. In some cases the fault alternates between these behaviors throughout multiple cycles. We determine how the fault behavior is controlled by the proportion of velocity-weakening and velocity-strengthening materials, their relative strength and other frictional properties. We also develop, through heuristic approximations, closed-form equations to predict the stability of slip on heterogeneous faults. Our study shows that a fault model with heterogeneous materials and pore pressure contrasts is a viable framework to reproduce the full spectrum of fault behaviors observed in natural faults: from fast earthquakes, to slow transients, to stable sliding. In particular, this model constitutes a building block for models of episodic tremor and slow slip events

Motor current signal analysis using a modified bispectrum for machine fault diagnosis

This paper presents the use of the induction motor current to identify and quantify common faults within a two-stage reciprocating compressor. The theoretical basis is studied to understand current signal characteristics when the motor undertakes a varying load under faulty conditions. Although conventional bispectrum representation of current signal allows the inclusion of phase information and the elimination of Gaussian noise, it produces unstable results due to random phase variation of the sideband components in the current signal. A modified bispectrum based on the amplitude modulation feature of the current signal is thus proposed to combine both lower sidebands and higher sidebands simultaneously and hence describe the current signal more accurately. Based on this new bispectrum a more effective diagnostic feature namely normalised bispectral peak is developed for fault classification. In association with the kurtosis of the raw current signal, the bispectrum feature gives rise to reliable fault classification results. In particular, the low feature values can differentiate the belt looseness from other fault cases and discharge valve leakage and intercooler leakage can be separated easily using two linear classifiers. This work provides a novel approach to the analysis of stator current for the diagnosis of motor drive faults from downstream driving equipment

Fault-Tolerant Exact State Transmission

We show that a category of one-dimensional XY-type models may enable high-fidelity quantum state transmissions, regardless of details of coupling configurations. This observation leads to a fault- tolerant design of a state transmission setup. The setup is fault-tolerant, with specified thresholds, against engineering failures of coupling configurations, fabrication imperfections or defects, and even time-dependent noises. We propose the implementation of the fault-tolerant scheme using hard-core bosons in one-dimensional optical lattices.Comment: 5 pages and 4 figure