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Due to thermal expansion of the mechanical structure, assembly processes, bearing wear, and long-term vibration during operation, a clearance fit may occur between the bearing outer ring and its pedestal. The clearance fit may result in relative motion between the bearing outer ring and pedestal, thereby altering the support characteristics of the rotor and subsequently impacting the dynamic characteristics of the rotor-bearing system. The stable operation of the system may be at risk in this case. In this paper, the dynamic model of the coupling system of a dual rotor-bearing outer ring-pedestal-casing with clearance fit is established based on the finite element method and lumped parameter method. The dimensionality of the system equation is reduced using the fixed-interface component mode synthesis (CMS) method and solved numerically. The impact of clearance fit on the vibration characteristics of the system is investigated under three operational conditions: imbalance of the inner rotor, imbalance of the outer rotor, and simultaneous imbalance of both two rotors. Furthermore, an analysis is conducted to evaluate the motion state of the system with clearance fit. Lastly, the vibration transmission characteristics between the rotor-bearing outer ring-pedestal-casing are studied. The results indicate that the harmonic components corresponding to the rotational speed frequency of rotors will appear on the spectrum and envelope spectrum of the system with clearance fit. The natural frequency of the system may be excited in the resonance region. Due to the influence of gravity, the dynamic characteristics of the system vary significantly at low and high rotational speeds. Additionally, the vibration transmission characteristics of the system are significantly influenced by both the rotational speeds and clearance fit. [ABSTRACT FROM AUTHOR]

This paper presents a method for structural modifications for achieving desired eigenstructures based on receptances, by adding multiple mass-spring systems to some locations of the primary system. This method has the benefit that not only neither analytical nor modal models are needed, but also the original mass and stiffness of the primary system are maintained. Moreover, when a complex structure or machine is designed for some special functions so that its inner structure is not allowed to be modified, it is an effective way in practice to achieve desired dynamical performance resulted from adding several external simple substructures. The theory is presented in this paper, which is suitable for linear undamped systems. Numerical experiment is set up, and the results of the modifications are compared with the method proposed by Braun and Ram. Both theoretical derivation and numerical results demonstrate the effectiveness of this method. [ABSTRACT FROM AUTHOR]

Micro- and nano-sized SiC/fluoroelastomer (FKM) composites were prepared by a mechanical mixing method. These composites were first characterized by a rotorless rheometer. Then the effects of micro- and nano-sized SiC on hardness, static and dynamic mechanical properties of the composites were investigated. The increasing amount of the SiC filler increased the curing efficiency of the biphenyl curing system, which was evident from the rheometric properties of the resulting composites. The tensile properties of composite increased with the increasing of micro- and nano-sized SiC content. When the micro- and nano-sized SiC content was higher than 20 phr, the composites showed almost unchanged tensile properties. The increasing of the tensile property was mainly attributed to the well dispersed micro- and nano-sized SiC particles characterized by SEM images. Compared to pure FKM, the composites exhibited a higher glass transition temperature and lower tan δ peak value. [ABSTRACT FROM AUTHOR]

Zircon LA-ICP-MS U-Pb dating of the Jingju syenogranites in the southwestern part of Zhejiang Province shows that these rocks were crystallized in the Late Triassic at 215±2 Ma, rather than in the Cretaceous as previously proposed. The Jingju syenogranites are characterized by relatively high KO and FeO*, and low MgO. They have high concentrations of large ion lithophile elements (LIL) and LREE, such as K, Th, La, and Ce, but are depleted in high field strength elements (HFSE) such as Nb, Ta, and Ti. Their 10Ga/Al ratios and (Zr+Nb+Ce+Y) contents are also high. These characteristics are similar to those of A-type granites. The syenogranites have high I (0.7179-0.7203), low ɛ( t) (from −14.2 to −13.2), and relatively old T ages, similar to those of the ancient metamorphic basement in the Cathaysia Block. It is suggested that the Jingju syenogranites were formed by partial melting of the Cathaysia basement rocks during tectonic extension. This identification of Indosinian A-type granite in Jingju has significant implications for understanding the early Mesozoic tectonic evolution of South China. [ABSTRACT FROM AUTHOR]