A Balanced IIRS Model for Investigating the Dynamics of Damped Rotor Bearing System

In this paper the application of the balanced Iterative Improved Reduction model techniques to complex rotor-bearing systems is investigated. It is demonstrated that, Iterative Improved Reduction System (IIRS) improves the matrix reductions by ensuring that the transformation matrix for each reduction is optimized. This reduction technique also benefices the problem due to skew symmetric matrices, which arises for inclusion of gyroscopic effect and internal damping. Numerical examples are solved to demonstrate the validity and efficiency of the reduced order model in representing the dynamics of the actual rotor system. Under these conditions, the complex behaviour of the rotor-shaft is studied to get an insight of the dynamic characteristics of the system, in terms of Campbell Diagram, Decay rate plot and Unbalance Response. Many researchers adopted different methodology for obtaining the model reduction but their work is limited up to undamped system. This work is started by motivation of the absentia of work for damped rotor bearing system.

Effects of the vertical and horizontal availability of food resources: the diet selection of sheep grazing on natural grassland

SUMMARYThe relationship between sheep diet selection and the vertical/horizontal availability of plant species on complex natural Leymus chinensis grassland was investigated. Two plots (low and high stocking rate plots) with different vegetation availabilities, created by adjusting sheep numbers, were studied for 3 months (June, July and August). In each month, the sheep's diet composition was estimated using n-alkanes in combination with long-chain alcohols and/or fatty acid markers. Vertical (sward surface height) and horizontal food availability (proportion cover of individual plant species) were determined simultaneously. The results revealed that sheep diet composition varied greatly according to seasonal variations in vegetation availability, and that sheep diet selection was related to the vertical and horizontal availability of plant species on both plots. Horizontal availability, which turned out to be the main influencing factor, was strongly and positively correlated with sheep diet composition in each month on both plots. On the low stocking rate plot, vertical availability affected sheep consumption in June, July and August. In contrast, a significant correlation between diet composition and vertical availability was only observed in July on the high stocking rate plot. These results suggest that the relative importance of vertical and horizontal availability differed between plots depending on vegetation availability. Horizontal availability played a more important role than vertical availability when sheep grazed freely on natural L. chinensis grassland. Finally, the changing selectivity index for each plant species in each grazing period on both plots indicated different grazing impacts on vegetation communities when vegetation availability differed.

Viscoelastic effects during unloading in depth-sensing indentation

With polypropylene as a prototype viscoelastic material at room temperature, it was found that a “nose” may appear in the unloading segment of the load–displacement curve during nanoindentation when the holding time at peak load is short and/or the unloading rate is small, and when the peak load is high enough. The load at which the nose appears was also found to decrease linearly with decreasing unloading rate. A linear viscoelasticity analysis was performed to interpret this effect. The analysis predicts a linear variation between the nose load and the unloading rate, and the slope of such a linear variation is also shown to be proportional to the viscosity parameter of the material. Thus, by measuring the slope of the nose-load versus unloading rate plot at a given temperature, the viscosity parameter of the specimen can be found. This is a new way of measuring the viscosity parameter of a material in addition to the existing method of force modulation and noting the frequency response of the displacement.