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Search Results: 1 - 10 of 15493 matches for " Yongsheng Ren "
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 International Journal of Differential Equations , 2009, DOI: 10.1155/2009/714357 Abstract: We present new oscillation criteria for the differential equation of the form [()()]
 Shock and Vibration , 2014, DOI: 10.1155/2014/765875 Abstract: A dynamical model is developed for the rotating composite shaft with shape-memory alloy (SMA) wires embedded in. The rotating shaft is represented as a thin-walled composite of circular cross-section with SMA wires embedded parallel to shaft’s longitudinal axis. A thermomechanical constitutive equation of SMA proposed by Brinson is employed and the recovery stress of the constrained SMA wires is derived. The equations of motion are derived based on the variational-asymptotical method (VAM) and Hamilton’s principle. The partial differential equations of motion are reduced to the ordinary differential equations of motion by using the Galerkin method. The model incorporates the transverse shear, rotary inertia, and anisotropy of composite material. Numerical results of natural frequencies and critical speeds are obtained. It is shown that the natural frequencies of the nonrotating shaft and the critical rotating speed increase as SMA wire fraction and initial strain increase and the increase in natural frequencies becomes more significant as SMA wire fraction increases. The initial strain of SMA wires appears to have marginal effect on dynamical behaviors of the shaft. The actuation performance of SMA wires is found to be closely related to the ply-angle. 1. Introduction Composite materials have found the increased applications for replacement of the conventional metallic materials in the rotating flexible shaft employed for drive shafts of helicopters, steam, and gas turbines. This is likely attributed to high stiffness and strength/weight ratios of composite shaft compared with its metallic counterparts. The development trend in design of light-weight composite shafts is towards higher operating speeds, which gives rise to the problems of high vibration amplitude and stability. Seeking the solution of these problems has caused great research effort [1] in the dynamic of composite rotor. A review on the literature in this area has shown that composite shafts have high whirling resistance capability and are less susceptible to dynamic instability associated with metallic shafts [2]. Several attempts to develop mathematical models of spinning composite shafts are reported in the literature. These models include the shaft models based on shell theories [3], or beam theories combined with the strain—displacement relations of the shell theories [4], or a thin-walled beam theory [5]. Song et al. [5] developed the composite thin-walled shaft model based on a thin-walled beam theory of Rehfield [6]. This model was used to investigate the natural frequencies and
 Shock and Vibration , 2014, DOI: 10.1155/2014/123271 Abstract: The dynamical analysis of a rotating thin-walled composite shaft with internal damping is carried out analytically. The equations of motion are derived using the thin-walled composite beam theory and the principle of virtual work. The internal damping of shafts is introduced by adopting the multiscale damping analysis method. Galerkin’s method is used to discretize and solve the governing equations. Numerical study shows the effect of design parameters on the natural frequencies, critical rotating speeds, and instability thresholds of shafts. 1. Introduction The rotating composite material shafts are being used as structural elements in many application areas involving the rotating machinery systems. This is likely to contribute to the high strength to weight ratio, lower vibration level, and longer service life of composite materials. A significant weight saving can be achieved by the use of composite materials. Also by appropriate design of the composite layup configuration, orientation, and number of plies the improved performance of the shaft system can be obtained. Furthermore, the use of composite would permit the use of longer shafts in the supercritical range than what is possible with conventional metallic shafts. In the last few years, there exist numerous researches related to predicting critical speeds and natural frequencies of composite shaft. Zinberg and Symonds [1] investigated the critical speeds of rotating anisotropic cylindrical shafts based on an equivalent modulus beam theory (EMBT), and dos Reis et al. [2] evaluated the shaft of Zinberg and Symonds [1] by the finite element method. Kim and Bert [3] adopted the thin- and thick-shell theories of first-order approximation to derive the motion equations of the rotating composite thin-walled shafts. They used this model to obtain a closed form solution for a simply supported drive shaft and to analyze the critical speeds of composite shafts. Singh and Gupta [4] developed two composite spinning shaft models employing EMBT and layerwise beam theory (LBT), respectively. It was shown that a discrepancy exists between the critical speeds obtained from both models for the unsymmetric laminated composite shaft. Chang et al. [5] presented a simple spinning composite shaft model based on a first-order shear deformable beam theory. The finite element method is used here to find the approximate solution of the system. The model was used to analyze the critical speeds, frequencies, mode shapes, and transient response of a particular composite shaft system. Gubran and Gupta [6] presented a modified
 环境科学学报(英文版) , 2010, Abstract: The adsorption of Methyl Violet (MV) cationic dye from aqueous solution was carried out by using crosslinked poly (acrylic acid-co-acrylamide)/attapulgite (Poly(AA-co-AM)/ATP) composite as adsorbent. The factors influencing adsorption capacity of the composite such as pH, concentration of the dye, temperature, contact time, adsorbent dosage, ionic strength and surfactant were systematically investigated. The equilibrium data fitted very well to the Langmuir isotherm and the maximum adsorption capacity reach...
 American Journal of Industrial and Business Management (AJIBM) , 2013, DOI: 10.4236/ajibm.2013.34045 Abstract: Enterprise logistics risk early warning is an essential part of enterprise logistics risk management, which has been increasingly drawing the attentions of both practical and academic world. However, enterprise logistics risk early warning hasn’t been radically put into practice yet. Therefore, the factors hinder the proceeding of enterprise logistics risk early warning become the key to starting the engine of enterprise logistics risk early warning. In this paper, review of researches on enterprise logistics risk early warning is provided, a questionnaire has been designed according to both exterior and internal factors influencing enterprise logistics risk early warning and a survey on manufacturing industries in Beijing area has been carried out, logistics risk early warning status and influencing elements have been analyzed based on previous survey and advices proposed are concluded to provide valuable references.