The traditional load-sensing hydraulic system is an energy-saving fluid power transmission, which supply ''on-demand'' flow at a prescribed pressure margin greater than the highest load pressure of the system. In this paper, a novel loadsensing system that has a variable pressure margin through overriding differential pressure control via integrating an electro-proportional three-way type pressure reducing valve into the hydro-mechanical load-sensing valve is proposed. Also, a bond graph model taking into account the dynamic characteristics of load-sensing valve and load-sensing path is constructed, and three group experiments are performed to verify the validation of the model. Based on the bond graph model, a series of theoretical simulations are carried out to prove that the proposed Load-Sensing system enables a satisfactory balance between energy efficiency and rapid dynamic response over a wide range of operating conditions. In addition, due to overriding differential pressure control, mode selection and power limit regulation can also be achieved.
The Wenchuan Earthquake of May 12, 2008 triggered large numbers of geo-hazards. The heavy rain on 13 August 2010 triggered debris flows with total volume of more than 6 million cubic meters and the debris flows destroyed 500 houses and infrastructure built after the Wenchuan Earthquake. The study area Qingping Town was located in the northwestern part of the Sichuan Basin of China, which needs the second reconstructions and the critical evaluation of debris flow. This study takes basin as the study unit and defines collapse, landslide and debris flow hazard as a geo-hazard system. A multimode system composed of principal series system and secondary parallel system were established to evaluate the hazard grade of debris flow in 138 drainage basins of Qingping Town. The evaluation result shows that 30.43% of study basins (42 basins) and 24.58% of study area, are in extremely high or high hazard grades, and both percentage of basin quantity and percentage of area in different hazard grades decrease with the increase of hazard grade. According to the geo-hazard data from the interpretation of unmanned plane image with a 0.5-m resolution and field investigation after the Wenchuan Earthquake and 8.13 Big Debris Flow, the ratio of landslides and collapses increased after the Wenchuan Earthquake and the ratios of extremely high or high hazard grades were more than moderate or low hazard grades obviously. 23 geo-hazards after 8.13 Big Debris Flow in Qingping town region all occurred in basins with extremely high or high hazard grades, and 9 debris flows were in basins with extremely high hazard grade. The model of multimode system for critical evaluation could forecast not only the collapse and landslide but also the debris flow precisely when the basin was taken as the study unit.
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