Combination resonance analysis of a multi-DOF controllable close-chain linkage mechanism system

The two-DOF controllable close-chain linkage mechanism system is investigated in this paper. Based on the air-gap field of the non-uniform airspace of motors caused by the eccentricity of rotor, the electromechanical coupling relation in the real running state of motors is analyzed. The electromechanical coupling dynamic model of the system is established by means of the finite element method. The dynamic equation constitutes the basis on which the combination resonance characteristics of the system caused by electromagnetic parameter excitations of the two motors are analyzed by the multiple scales method. The first-order stationary solution is obtained under that condition, and the stability conditions of the stationary solution are also given. Finally, an experiment is presented. Results indicate that it is feasible and beneficial to explain some unexpected strong vibration phenomena in the high-speed operation of such multi-DOF controllable close-chain linkage mechanism using nonlinear combination resonance theories

A Robust Method to Suppress Jamming for GNSS Array Antenna Based on Reconstruction of Sample Covariance Matrix

The Global Navigation Satellite System (GNSS) receiver is vulnerable to active jamming, which results in imprecise positioning. Therefore, antijamming performance of the receiver is always the key to studies of satellite navigation system. In antijamming application of satellite navigation system, if active jamming is received from array antenna main-lobe, main-lobe distortion happens when the adaptive filtering algorithm forms main-lobe nulling. A robust method to suppress jamming for satellite navigation by reconstructing sample covariance matrix without main-lobe nulling is proposed in this paper. No nulling is formed while suppressing the main-lobe jamming, which avoids main-lobe direction distortion. Meanwhile, along with adaptive pattern control (APC), the adaptive pattern of array antenna approaches the pattern without jamming so as to receive the matching navigation signal. Theoretical analysis and numerical simulation prove that this method suppresses jamming without main-beam distortion. Furthermore, the output SINR will not decrease with the main-lobe distortion by this method, which improves the antijamming performance

Combination resonance analysis of a multi-DOF controllable close-chain linkage mechanism system

The two-DOF controllable close-chain linkage mechanism system is investigated in this paper. Based on the air-gap field of the non-uniform airspace of motors caused by the eccentricity of rotor, the electromechanical coupling relation in the real running state of motors is analyzed. The electromechanical coupling dynamic model of the system is established by means of the finite element method. The dynamic equation constitutes the basis on which the combination resonance characteristics of the system caused by electromagnetic parameter excitations of the two motors are analyzed by the multiple scales method. The first-order stationary solution is obtained under that condition, and the stability conditions of the stationary solution are also given. Finally, an experiment is presented. Results indicate that it is feasible and beneficial to explain some unexpected strong vibration phenomena in the high-speed operation of such multi-DOF controllable close-chain linkage mechanism using nonlinear combination resonance theories

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-C-14 ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-C-14 dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn&#39;t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12 +/- 18.50)x10(-5)) and delta O-18 ((1.76 +/- 1.03)parts per thousand) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11 +/- 0.41)x10(-5) and delta O-18=(-4.82 +/- 0.96)parts per thousand). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and delta O-18 ratios than modem Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today&#39;s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km(2) during the Ming Dynasty, approximately similar to 5% larger than it is today.</p