Monitoring the Technical Condition of Dams of Hydroelectric Power Plants with an Automated Monitoring and Earthquake Registration System

An approach is described that has been developed for auxiliary monitoring of technical condition of hydropower plant dams. It is based on analysis of changes in dynamic characteristics of dams obtained by an automated monitoring and earthquake registration system that records microseismic vibrations of structures. The configuration of the system as well as the results of seismometric monitoring of the dam of Krasnoyarsk hydroelectric power plant are described. To study behavior of the dam under normal and extreme loads it was proposed to develop a model of the dam with the use of the finite element method.     

Scalable minimum fatigue control of dispatchable wind farms

As wind energy penetration increases, wind power plants may be required to regulate their power production according to the load‐balancing needs of the power system. This presents an opportunity: when a wind farm tracks a power set‐point, its wind turbines are free to continuously vary their power production as long as the sum of their productions meets the power demand. Here, we present an intuitive wind turbine coordination policy that uses this flexibility to minimize the aggregate fatigue load on the turbines. An important property is that the policy is scalable enough to be applied to any wind farm size. Specifically, the computational effort required to compute and reconfigure the optimal coordination policy is the same as that of a single stand‐alone turbine, and the only centralized information processing needed to implement it is a single averaging operation. The efficiency of the coordination policy is illustrated in a simulation study based on real wind farm data. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of spurious diffraction orders in arbitrary multifoci patterns produced via phase-only holograms

We analyze the effect of spurious diffraction orders when generating functional multifoci patterns produced by illuminating a phase-only hologram with a single Gaussian beam. Using a practical device for encoding a hologram generates an undesirable zero order and high-diffraction orders at the Fourier plane. This translates to the fact that a significant fraction of the incident light does not necessarily convert to functional multifoci patterns. In most applications, the zero order can be avoided by generating foci patterns shifted off the optical axis, which further increases the amount of light distributed to spurious high-diffraction orders owing to the reduction of light directed to the desired foci pattern. We analyze the amount of light dispersed to spurious orders and show that these unwanted orders can be a major limiting factor for most applications based on arbitrary multifoci patterns.     

Dependence of gold nanoparticle production on pulse duration by laser ablation in liquid media

The dependence on laser fluence and laser pulse duration of size, size distribution and concentration of gold nanoparticles synthesized by laser ablation in liquid media was investigated. It was demonstrated that increasing laser energy from 1 to 5 mJ/pulse enhances the ablation rate by a factor of 100. The behavior of the ablation rate, hence of the nanoparticle concentration, as a function of pulse duration (varied from 40 fs to 200 ps) was found to strongly differ from that in air, which can be explained by photoionization and important losses of laser energy in the femtosecond regime. The optimal pulse duration for maximum ablation rate in liquid media was found to be equal to 2 ps.     

Magnesium gasar as a potential monolithic hydrogen absorbent

The study focuses on the aspect of using the structure of gasars, i.e. materials with directed open porosity, as a potential hydrogen storage. The structure of the tested gasar is composed of a large number of thin, open tubular pores running through the entire longitudinal section of the sample. This allows hydrogen to easily penetrate into the entire sample volume. The analysis of pore distribution showed that the longest diffusion path needed for full penetration of the metal structure with hydrogen is about L = 50–70 μm, regardless of the external dimensions of the sample. Attempts to hydrogenate the magnesium gasar structure have shown its ability to accumulate hydrogen at a level of 1 wt%. The obtained results were compared with the best result was obtained for the ZK60 alloy after equal channel angular pressing (ECAP) and crushed to a powder form. The result obtained exceeded 4 wt% of hydrogen accumulated in the metal structure, at theoretical 6.9 wt% maximum capacity. A model analysis of the theoretic absorption capacity of pure magnesium was also carried out based on the concentration of vacancies in the metal structure. The theoretical results obtained correlate well with experimental data.