Nonlinear hydro turbine model having a surge tank.

yesThis paper models a hydro turbine based on the dynamic description of the hydraulic system having a surge tank and elastic water hammer. The dynamic of the hydraulic system is transformed from transfer function form into the differential equation model in relative value. This model is then combined with the motion equation of the main servomotor to form the nonlinear model of the hydro turbine, in which the power of the hydro turbine is calculated using algebraic equation. A new control model is thus proposed in which the dynamic of the surge tank is taken as an additional input of control items. As such, the complex hydraulic system is decomposed into a classical one penstock and one machine model with an additional input control. Therefore, the order of the system is descended. As a result, the feasibility of the system is largely improved. The simulated results show that the additional input of the surge tank is effective and the proposed method is realizable.National Natural Science Foundation of China (50839003, 50949037, 51179079), Natural Science Foundation of Yunnan Province (No. 2008GA027

Social Media, Gender and the Mediatisation of War: Exploring the German Armed Forces’ Visual Representation of the Afghanistan Operation on Facebook

Studies on the mediatisation of war point to attempts of governments to regulate the visual perspective of their involvements in armed conflict – the most notable example being the practice of ‘embedded reporting’ in Iraq and Afghanistan. This paper focuses on a different strategy of visual meaning-making, namely, the publication of images on social media by armed forces themselves. Specifically, we argue that the mediatisation of war literature could profit from an increased engagement with feminist research, both within Critical Security/Critical Military Studies and within Science and Technology Studies that highlight the close connection between masculinity, technology and control. The article examines the German military mission in Afghanistan as represented on the German armed forces’ official Facebook page. Germany constitutes an interesting, and largely neglected, case for the growing literature on the mediatisation of war: its strong antimilitarist political culture makes the representation of war particularly delicate. The paper examines specific representational patterns of Germany’s involvement in Afghanistan and discusses the implications which arise from what is placed inside the frame of visibility and what remains out of its view

Smoothing control of wind generator output fluctuations by PWM voltage source converter and chopper controlled SMES

Since the mechanical power extracted from wind is proportional to the cube of the wind speed, the output of the wind turbine generator system fluctuates considerably due to wind speed variations. Therefore, high penetration of wind power to the power grid causes fluctuation of the grid frequency, which has adverse effects on power system stability and reliability. Since a superconducting magnetic energy storage (SMES) system has the ability to provide both active and reactive power simultaneously and quickly, the SMES system can be an effective tool to mitigate frequency fluctuations under such conditions. In the present study, a PWM voltage source converter and two-quadrant DC-DC-chopper-controlled SMES system is proposed, which can significantly decrease the voltage and output power fluctuations of the wind farm and consequently mitigate the grid frequency fluctuation. A computational method by which to determine the SMES power rating needed to minimize the grid frequency fluctuation is analyzed. Moreover, the required minimum energy storage capacity of the SMES unit is determined. The simulation analyses were performed using PSCAD/EMTDC