We theoretically and experimentally study the mechanical response of silkworm and spider silks against stretching and the relationship with the underlying structural factors. It is found that the typical stress-strain profiles are predicted in good agreement with experimental measurements by implementing the “β-sheet splitting” mechanism we discovered and verified, primarily varying the secondary structure of protein macromolecules. The functions of experimentally observed structural factors responding to the external stress have been clearly addressed, and optimization of the microscopic structures to enhance the mechanical strength will be pointed out, beneficial to their biomedical and textile applications.
Abstract:The volatility of wind power poses great challenges to the operation of power systems. This paper deals with the economic dispatch problems presented by energy storage in wind integrated systems. A policy iteration algorithm for deriving the cost optimal policy of real-time scheduling is proposed, taking the effect of wind forecast uncertainties into account. First, energy loss and use of fast-ramping generation are selected as the performance metrics. Then, a policy iteration algorithm is developed using the Perturbed Markov decision process. This algorithm has a two-level optimization structure in which both the long-term and short-term behaviors of real-time scheduling policy are optimized. In addition, a unified optimal storage control strategy is presented. The feasibility of the proposed methodology is demonstrated via the wind power archive of Electric Reliability Council of Texas (ERCOT). Through comparative numerical experiments, both the performance of the policy iteration algorithm in the short-term and long-term are verified and the consistency, robustness, good convergence and high computational efficiency of the proposed algorithm are also corroborated.
Forced oscillations (FOs), or low-frequency oscillations (LFOs) caused by periodic, continuous, small power disturbances, threaten the security and stability of power systems. Flexible AC transmission system (FACTS) devices can effectively mitigate LFOs via stability control. We propose a novel method that mitigates FOs by shifting the resonant frequency. Based on the features of the linearized swing equation of a generator, a resonant frequency shift can be achieved by controlling the synchronous torque coefficient using a unified power flow controller (UPFC). Because of the resonance mechanism, the steady-state response of an FO can be effectively mitigated when the resonant frequency changes from the original one, which was close to the disturbance frequency. The principle is that a change in resonant frequency affects the resonance condition. Simulations are conducted in a single-machine infinite-bus (SMIB) system, and the simulation results verify that the method is straightforward to implement and can significantly mitigate FOs. The controller robustness when the resonant frequency is not accurately estimated is also analyzed in the simulations.
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