Evaluation of an Uncoupled Method for Analyzing the Seismic Response of Wind Turbines Excited by Wind and Earthquake Loads

There is a significant interaction between wind and earthquakes for large-scaled wind turbines due to an aeroelastic effect. This study evaluates the accuracy of an uncoupled method extensively utilized to analyze the seismic response of wind turbines at the operational state. Initially, the oscillation of the blade for the National Renewable Energy Laboratory (NREL) 5 MW wind turbine excited by wind and wind-earthquake combination, respectively, is compared using the fully coupled method to verify the assumption in this uncoupled method. Subsequently, the influence of ground motions on the aerodynamic loadings of the rotor is discussed to evaluate the interaction between wind and earthquake loads. In addition, the accuracy of the uncoupled method is assessed by comparing the analysis results of the coupled and uncoupled methods, where different mean wind speed and equivalent aerodynamic damping ratio are considered. The results indicate that the oscillation velocity of blades and thrust on the rotor are significantly influenced by ground motions. Moreover, the amplitude of thrust variations caused by earthquakes increases monotonously with the oscillation velocity amplitude of blade-root. The errors between the two models are beyond the engineering margins for some earthquakes, such that it is difficult to optimize a consistent aerodynamic damping in the uncoupled model to accurately predict the seismic response of wind turbines.

Dynamics of neutrino wave packet in the Tachyon-like Dirac equation

In this study the tachyon-like Dirac equation, formulated by Chodos to describe superluminal neutrino, is solved. The analytical solutions are Gaussian wave packets obtained using the envelope method. It is shown that the superluminal neutrino behaves like a pseudo-tachyon, namely a particle with subluminal velocity and pure imaginary mass that fulfils the energy-momentum relation typical of classical tachyons. The obtained results are used to prove that the trembling motion of the particle position around the median, known as Zitterbewegung, also takes place for the superluminal neutrino, even if the oscillation velocity is always lower than the speed of light. Finally, the pseudo-tachyon wave packet is used to calculate the probability of oscillation between mass states, obtaining a formula analogous to the one obtained for the ordinary neutrino. This suggest that in the experiments concerning neutrino oscillation is not possible to distinguish tachyonic neutrinos from ordinary ones.

Dynamics of Neutrino Wave Packet in the Tachyon-like Dirac Equation

In this study the tachyon-like Dirac equation, formulated by Chodos to describe superluminal neutrino, is solved. The analytical solutions are Gaussian wave packets obtained using the envelope method. It is shown that the superluminal neutrino behaves like a pseudo-tachyon, namely a particle with subluminal velocity and pure imaginary mass that fulfils the energy-momentum relation typical of classical tachyons. The obtained results are used to prove that the trembling motion of the particle position around the median, known as Zitterbewegung, also takes place for the superluminal neutrino, even if the oscillation velocity is always lower than the speed of light. Finally, the pseudo-tachyon wave packet is used to calculate the probability of oscillation between mass states, obtaining a formula analogous to the one obtained for the ordinary neutrino. This suggest that in the experiments concerning neutrino oscillation is not possible to distinguish tachyonic neutrinos from ordinary ones.

Adsorption of molybdenum (VI) in contaminated water using Fe3O4/CTS magnetic nanoparticles

To solve the problem of excess molybdenum, a new composite nanomaterial was prepared for adsorption and removal of Mo (VI). Chitosan-modified magnetic nanoparticles (Fe3O4/CTS) were prepared by the method of glutaraldehyde crosslinking. The morphology of the composite nanoparticles was characterized by a scanning electron microscope, and the magnetic properties of the nanoparticles were characterized by an external magnetic field. The content of Mo (VI) was determined by thiocyanate spectrophotometry. The relationship between adsorbent dosage, oscillation velocity, contact time and removal of Mo (VI) was studied. The results showed that when the dosage of Fe3O4/CTS magnetic nanoparticles was 0.4 g, the oscillation speed was 100 r min-1, and the contact time was 10 min, 100 ml of Mo (VI) solution was treated under the condition of initial pH =4, and the removal effect of Fe3O4/CTS magnetic nanoparticles on Mo (VI) was the best. Treatment effluent can reach the comprehensive sewage discharge standard in Liaoning Province. At the same time, it is proved that Fe3O4/CTS magnetic nanoparticles are a kind of adsorbent which is easy to recover, easy to separate magnetically, and has the ability to remove Mo (VI) efficiently.

Effect of Normal Contact Vibration on Nano-Scale Friction

In this work, we investigate the effect of contact vibration on the friction of sliding single asperity contacts of different adhesion strength over a wide range of load and vibration amplitude. We convert the amplitude of vibration to its equivalent modulation force and tip-oscillation velocity. We observe a logarithmic relationship between friction and the ratio of the modulation force to the normal force and between friction and the ratio of sliding velocity to the tip-oscillation velocity. We discuss these logarithmic dependencies based on an induced corrugation of the tip-sample interaction potential.

Aeroacoustic analysis using natural Helmholtz–Hodge decomposition

The analysis of aeroacoustic phenomena is crucial for a deeper understanding of the damping mechanisms of a sound-absorbing bias flow liner (BFL). For this purpose, simultaneous measurements of the sound field and the flow field in a BFL are required. The fluid velocity can serve as the measurand, where both the acoustic particle velocity and the aerodynamic flow velocity contribute and, thus, can be acquired simultaneously. However, there is a need to separate these two quantities to distinguish between them. This is challenging because they generally coincide with each other in the time domain. Due to the interaction of sound and flow in a BFL, both velocities also overlap in the temporal frequency domain, having a coherent oscillation at the acoustic frequency. For this reason, the recently developed natural Helmholtz–Hodge decomposition (NHHD) is applied to separate both quantities from the measured oscillation velocity field in the spatial domain. The evaluation of synthetic vector field data shows that the quality of the decomposition is enhanced when a smaller grid size is chosen. The velocity field in a generic BFL, necessarily recorded within a three-dimensional region of interest at more than 4000 measurement locations, is evaluated using NHHD. As a result, the measured oscillation velocity in the BFL is dominated by the flow that is related to vortices and also by irrotational aerodynamic flow. Moreover, indications for an aeroacoustic source near the facing sheet of the liner are revealed.

Asymmetry in Solar Torsional Oscillation

Solar torsional oscillations are migrating bands of slower and faster than average rotation, which are thought to be related to the Sun’s magnetic cycle. We perform the first long-term study (16 years) of hemispherical asymmetry in solar torsional oscillation velocity using helioseismic data. We explore the spatial and temporal variation of North-South asymmetry using zonal flow velocities obtained from ring diagram analysis of the Global Oscillation Network Group (GONG) Doppler images. We find a strong correlation between the asymmetries of near-surface torsional oscillation with magnetic flux and sunspot number, with the velocity asymmetry preceding in both the cases. We speculate that the asymmetry in torsional oscillation velocity may help in predicting the hemispherical asymmetry in the sunspot cycle.