Vibration Control for Two Air Compressor Units Used in Tandem

The paper presents the vibration control for two air compressors used in tandem to an oxygen generating station. The compressors are identical in terms of constructive and functional properties, and are both located on similar foundations. Each compressor is supported on a foundation made from one massive block of concrete, provided with some elastic and damping parts. This anti vibrating structure insulates the machines compared to other station equipment. During operation, were observed dangerous levels of vibration at one of the machines, which forced some unwanted stoppages for the station. Two hypotheses have been promoted. One of them referred to a pronounced wear of one compressor, although this was relatively new. The second hypothesis has taken in consideration the appearance of some cracks in the foundation massive concrete block. Experimental research conducted on the spot led to the identification of some errors done at foundation fabrication. The experimental results and some theoretical investigations are presented in this paper.

Spatio-temporal Variations in Plantation Forests'Disturbance and Recovery of Northern Guangdong Province Using Yearly Landsat Time Series Observations(1986-2015)

Forest disturbance plays a vital role in modulating carbon storage,biodiversity and climate change.Yearly Landsat imagery from 1986 to 2015 of a typical plantation region in the northern Guangdong province of southern China was used as a case study.A Landsat time series stack(LTSS) was fed to the vegetation change tracker model(VCT) to map long-term changes in plantation forests' disturbance and recovery,followed by an intensive validation and a continuous 27-yr change analysis on disturbance locations,magnitudes and rates of plantations' disturbance and recovery.And the validation results of the disturbance year maps derived from five randomly identified sample plots with 25 km^2 located at the four corners and the center of the scene showed the majority of the spatial agreement measures ranged from 60% to 83%.A confusion matrix summary of the accuracy measures for all four validation sites in Fogang County showed that the disturbance year maps had an overall accuracy estimate of 71.70%.Forest disturbance rates' change trend was characterized by a decline first,followed by an increase,then giving way to a decline again.An undulated and gentle decreasing trend of disturbance rates from the highest value of 3.95% to the lowest value of 0.76% occurred between 1988 and 2001,disturbance rate of 4.51% in 1994 was a notable anomaly,while after 2001 there was a sharp ascending change,forest disturbance rate spiked in 2007(5.84%).After that,there was a significant decreasing trend up to the lowest value of 1.96% in 2011 and a slight ascending trend from 2011 to 2015(2.59%).Two obvious spikes in post-disturbance recovery rates occurred in 1995(0.26%) and 2008(0.41%).Overall,forest recovery rates were lower than forest disturbance rates.Moreover,forest disturbance and recovery detection based on VCT and the Landsat-based detections of trends in disturbance and recovery(LandT rendr) algorithms in Fogang County have been conducted,with LandT rendr finding mostly much more disturbance than VCT.Overall,disturbances and recoveries in northern Guangdong were triggered mostly by timber needs,policies and decisions of the local governments.This study highlights that a better understanding about plantations' changes would provide a critical foundation for local forest management decisions in the southern China.

ROBUSTNESS OF MULTIPLE-LIMB MANIPULATION SYSTEMS

The characteristic that multiple limb manipulation systems can resist disturbance external forces without relying on the feedback control of joint torques, called the robustness, has been addressed by several researchers. Based on their results, a further study of robustness is presented in this paper. By decomposing the space of external forces into two subspaces, the necessary and sufficient condition for a system to have robustness is given and a definition of robustness which is applicable to any multiple limb systems is also proposed. For the purpose of the evaluation of robustness, a new quality measure — critical disturbance external force and its algorithm are put forward. Finally, two examples of robustness analysis are presented.

Visualization of Coherent Structures in Acoustically Forced, Gas-Particle Turbulent Round Jet

To show the effects of the particles and forced disturbances on the instantaneous large-scale vortex structures in a gas-particle round jet, coherent structures in gas-particle turbulent round jets were investigated experimentally by flow visualization. The 45-μm and 350-μm diameter glass beads were used as the particles in the experiments. An acoustic speaker was used to introduce velocity perturbations at the jet exit. The Strouhal number based on the nozzle diameter, exit velocity, and forcing frequency was varied from 0,1 to 0.9. The Reynolds number was 9400. The coherent structures were visualized in unforced and forced single-phase jet flows and unforced and forced particle-laden jet flows with different diameter glass beads. The experimental results show that the particles have significant effects on the gas phase coherent structures. The coherent structures are controlled by the large 350-μm diameter particles, while the structures are mainly dominated by the forced disturbances in the flows w