Search Results (3)

By introducing fractional exponentiation into a three-dimensional chaotic system, a jerk system with only six terms is designed. It has the property of total amplitude control, where a single non-bifurcation parameter can directly rescale all system variables without affecting the dynamics. It also features two-dimensional offset boosting, where a single parameter can realize direct offset boosting while another provides interlocked cross-dimensional offset boosting. Furthermore, this jerk system has a parameter-dominated symmetric attractor, which means that symmetric attractors appear successively as the parameter changes from positive to negative. Circuit experiments confirm the feasibility of analog fractional exponentiation using the 444 circuit and the complete control, including amplitude control and offset boosting, of the resulting system. The proposed circuit may facilitate applications of chaotic signal generators where signal versatility is important and exemplifies the generative potential of analog fractional exponentiation. Full article

Reducing the volume of distributing chamber by shortening its width is one of the ways to obtain good metallurgical effects for a large two-strand induction heating tundish. A multi-field coupling numerical model was established to figure out the effect of distributing chamber volume on the flow field, temperature field of molten steel, and removal of inclusions. Three tundishes with distributing chamber widths of 1.216 m (tundish A), 0.838 m (tundish B), and 0.606 m (tundish C) were modeled. The results indicated that reducing the width of the distributing chamber from 1.216 m to 0.838 and 0.606 m could improve the fastest heating rate from 0.4 K/min to 0.6 and 0.8 K/min and reduce the energy consumption from 476 kWh to 444 and 434 kWh. The temperature fluctuation of molten steel in the distributing chamber rose with the decrease in distributing chamber volume during the continuous casting process. Besides, tundish B performs the best temperature uniformity. The flow field in the distributing chamber was no longer symmetrical, and a short-circuit flow appeared when the width was reduced to 0.606 m. As a result, the floating ratio and removal ratio of inclusions decreased and the ratio of inclusions flowing into the mold sharply increased in tundish C. When the width was reduced from 1.216 to 0.838 m, the floating ratio of inclusions had little change and the removal ratio increased slightly. The floating efficiency increased with the decrease in the volume of distributing chamber, and the removal efficiency is the highest in tundish B. Taken together, tundish B should be adopted. Full article

Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The draft tube cavitation surge is a hydraulic phenomenon that appears in Francis turbines below and above its Best Efficiency Point (BEP). It is a low frequency phenomenon consisting of a vortex rope in the runner outlet and draft tube, which can become unstable when its frequency coincides with a natural frequency of the hydraulic circuit. At this situation, the output power can significantly swing, endangering the electrical grid stability. This study is focused on the detection of these instabilities in Francis turbines and their relationship with the output power swings. To do so, extensive experimental tests for different operating conditions have been carried out in a large prototype Francis turbine (444 MW of rated power) within the frame of the European Project Hyperbole (FP7-ENERGY-2013-1). Several sensors have been installed in the hydraulic circuit (pressure sensors in the draft tube, spiral casing, and penstock), in the rotating and static structures (vibration sensors, proximity probes, and strain gauges in the runner and in the shaft), as well as in the electrical side (output power, intensity, and voltage). Moreover, a numerical Finite Element Method (FEM) has been also used to relate the hydraulic excitation with the output power swing. Full article