某水电站厂房结构固有频率及共振分析

水电站厂房作为水利工程中的一个重要水工建筑物,应首先保证其运行的安全可靠性,其次再考虑经济性。设计时应利用合理的技术措施,确保厂房工程质量,取得工程投资建设的经济效益和社会效益。因此,对厂房进行结构动力分析具有重要意义。笔者以某引水式水电站工程的厂房结构为研究对象,选取其中典型机组段,建立机组段三维有限元模型,对厂房进行地震作用分析以及厂房结构固有频率分析与共振校核,为该工程的设计和安全运行提供合理的依据。

Facile preparation of self-assembled MXene@Au@CdS nanocomposite with enhanced photocatalytic hydrogen production activity

Photocatalytic hydrogen production is considered a promising approach to generating clean sustainable energy.However,the conventional co-catalyst(e.g.,Pt)used in photocatalytic hydrogen production is high-cost and difficult to obtain.Here,we designed and prepared a ternary nanocomposite MXene@Au@Cd S,which can be used in the field of efficient and excellent photocatalytic hydrogen production.The MXene@Au@Cd S has a hydrogen production rate of 17,070.43μmol g^-1h^-1(tested for 2 h),which is 1.85 times that of pure Cd S nanomaterials.The improved hydrogen production performance of the MXene@Au@Cd S is attributed to:(i)MXene provides more active adsorption sites and reaction centers for Au and Cd S nanoparticles;(ii)the synergistic effect of Au’s strong surface plasmon resonance expands the optical response range of Cd S.Therefore,this work solves the problem of the solid connection between the surface functional groups of photocatalyst,and achieves rapid interface charge transfer and long-term stability during the hydrogen production.

Electron dynamics and wave activities associated with mirror mode structures in the near-Earth magnetotail

We report the observation of mirror mode structures by Cluster spacecraft at around X^-16 RE in the Earth’s magnetotail.The wavelength of the mirror structure is larger than 7000 km,corresponding to tens of ion gyroradii.Features of the mirror structures are similar to those detected in the magnetosheath:the anti-correlation between the magnetic field strength and plasma density,zero phase velocity in the plasma rest frame and linear polarization.The structures were observed in a region bounded by two dipolarizations during a substorm intensification.Thus,the dipolarization process may provide a plasma condition facilitating the growth of the mirror mode structures.Another interesting feature is the electron dynamics within the mirror structures.Thermal electron energy flux has an enhancement at 0°and 180°pitch angles inside the magnetic dips of the first three mirror structures and an enhancement at 90°pitch angle inside the magnetic dip of the last structure.The different electron distribution inside the mirror structures might be a result of different evolution stages of the mirror wave.The last structure may be in the nonlinear stage of the mirror instability,whereas the three others with quasi-sinusoidal waveforms may be in the linear stage.In addition,we found that intense whistler waves were confined within the magnetic dips.We conjecture that whistler waves observed in the first three dips were generated in a remote region,then they were trapped in the mirror mode troughs and transported toward the spacecraft;while the whistler wave detected in the last dip was excited locally by the electron anisotropy instability.

Numerical Analysis of a Wells Turbine at Different Non-dimensional Piston Frequencies

Wave energy is one of the renewable energy sources with the highest potential.Several pilot plants have been built based on the principle of the Oscillating Water Column(OWC).Among the different solutions that have been suggested,the Wells turbine has gained particular attention due to its simplicity and reliability.The majority of available studies concentrate on the steady operation of the Wells turbine,while only few analyze its performance under an unsteady and bi-directional air flow,as determined by the presence of the OWC system.In this work,experimental and numerical performance of a high-solidity Wells turbine with NACA0015 profiles have been compared,at different non-dimensional piston frequencies.The numerical simulations have been conducted using commercial CFD software and focus on unsteady predictions,with particular attention to the behavior of the flow upstream and downstream of the rotor,flow hysteresis between acceleration and deceleration phases and differences between intake and exhaust strokes due to the non-symmetrical configuration of the machine.