Imaging and spectral study on the null point of a fan-spine structure during a solar flare

Using the multi-instrument observations, we make the first simultaneous imaging and spectral study on the null point of a fan-spine magnetic topology during a solar flare. When magnetic reconnection occurs at the null point, the fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the H$\alpha$ images, the fan-spine structure is partly filled and outlined by the bi-directional material flows ejected from the reconnection site. The extrapolated coronal magnetic field confirms the existence of the fan-spine topology. Before and after the flare peak, the total velocity of the outflows is estimated to be about 60 km s$^{-1}$. During the flare, the Si IV line profile at the reconnection region is enhanced both in the blue-wing and red-wing. At the flare peak time, the total velocity of the outflows is found to be 144 km s$^{-1}$. Superposed on the Si IV profile, there are several deep absorption lines with the blueshift of several tens of km s$^{-1}$. The reason is inferred to be that the bright reconnection region observed in Si IV channel is located under the cooler material appearing as dark features in the H$\alpha$ line. The blueshifted absorption lines indicate the movement of the cooler material toward the observer. The depth of the absorption lines also depends on the amount of cooler material. These results imply that this kind of spectral profiles can be used as a tool to diagnose the properties of cooler material above reconnection site.Comment: Accepted for publication in Ap

Simulation of chemical reaction dynamics based on quantum computing

The molecular energies of chemical systems have been successfully calculated on quantum computers, however, more attention has been paid to the dynamic process of chemical reactions in practical application, especially in catalyst design, material synthesis. Due to the limited the capabilities of the noisy intermediate scale quantum (NISQ) devices, directly simulating the reaction dynamics and determining reaction pathway still remain a challenge. Here we develop the ab initio molecular dynamics based on quantum computing to simulate reaction dynamics by extending correlated sampling approach. And, we use this approach to calculate Hessian matrix and evaluate computation resources. We test the performance of our approach by simulating hydrogen exchange reaction and bimolecular nucleophilic substitution SN2 reaction. Our results suggest that it is reliable to characterize the molecular structure, property, and reactivity, which is another important expansion of the application of quantum computingComment: 8 pages, 4 figure

基于雷电物理的风机叶片动态击距与 电气几何模型

The damage of wind turbine blades suffered lightning strikes has been a key factor of the safe and reliable operation of wind farms. The electric geometrical model of wind turbine blades (EGMTB) was presented based on the traditional electric geometrical method and the physical process of lightning leader. The concept of dynamic striking distance was introduced and clarified the physical meaning of striking distance. And the calculation method of blade lightning protection system (LPS) efficiency was deduced. Finally, the effectiveness of EGMTB was validated by the long gap breakdown experiment of blades. The EGMTB was used to analyze the influence factors of blade LPS efficiency. It is indicated that the efficiency of blade LPS reduces with the decrease of lightning current and the angle between the blade and horizontal, and the efficiency of blade LPS can be improved by increasing the side lightning receptors. The EGMTB is intended to provide a theory for lightning protection design and evaluation of wind turbine blades

Numerical study on explosion characteristics of wind turbine blade under lightning induced arc

For enhancing the lightning protection abilities of wind turbine blades, there is the need to study the mechanical explosion characteristics when the blades suffer from lightning induced arc intrusion. In this paper, a magnetohydrodynamic (MHD) model of lightning induced arc intrusion into the blade was developed, and the airflow and gas pressure distribution were calculated accordingly. The simulation results show that the huge pressure generated at the trailing edge of the blade should be the main cause of the trailing edge cracking. The research presented in this paper provides a theoretical basis for improving the structural design of the blade from the lightning protection perspective

Experimental study on lightning attachment manner to rotation wind turbine blade

Lightning strike is one of the most serious damages to the wind turbine blade. The blade is in rotation when lightning strike happens. The influence of the rotation to the lightning attachment manner of wind turbine blade is not fully studied. Experimental work has been done in this paper. A 1:30 scale 3MW wind turbine is built. There are 3 side receptors on each blade according to the real wind turbine blade. A rod electrode is used as the high voltage electrode to simulate the downward leader. Both negative and positive 250/25000μs standard switching impulses are applied. Different blade tip linear speeds, equal to the real wind turbine, are used to study the influence of the blade rotation to attachment process. The results show that the influence of the rotation can be classified into two types, one is the impact on the location of the striking attachment point, the other is the impact on the discharge channel close to the blade. The influence depends on the polarity of the discharge. Positive discharge is more dangerous to wind turbine blade in rotation

Experimental study on lightning discharge attachment to the modern wind turbine blade with lightning protection system

Lightning strike is one of the most severe threats to the wind turbine blades and causes huge damage. Mostly wind turbines are struck by lightning when the blades are rotating. The effect of blade rotation on a lightning discharge attachment is unclear. Therefore, a rod electrode was used in a wind turbine lightning discharge test to investigate the difference in lightning triggering ability when blades are rotating and stationary. A standard switching waveform of 250/2500μs was applied to the rod electrode. Lightning discharge tests of a 1:30 scale wind turbine model with 3m air gaps were performed and the discharge process was observed. Three side receptors were used for Lightning protection system (LPS) of wind turbine blade (WTB). Distance between each receptor was 40cm and 1 st receptor had 5cm distance from tip of the WTB. Standard switching impulses (negative and positive) were applied to the WTB with different orientations and rotating speed. The experimental results demonstrated that when negative switching impulses were applied to the wind turbine blade, all the lightning discharges hit on the 1 st receptor; however, in the case of positive switching impulse, some discharges also hit on the other receptors, blade surface and nacelle of WTB. The attachment points remain same when the blade is stationary or rotating. The analysis revealed that polarity of switching impulse has significant influence on attachment point, and the rotation has little influence during the attachment process. The results can contribute to optimize the design of LPS of wind turbine blade

Experimental study on interception failure of lightning protection system of wind turbine blade

Wind turbine (WT) blades are equipped with lightning protection system (LPS) consisting of receptors and down conductor in order to intercept lightning strikes. However, severe damages caused by lightning strikes still happen frequently, which costs huge losses. In this paper, experiments were conducted to study the lightning interception failure of WT blade LPS, and the results can be useful to improve the optimal design of LPS. Experiments using 5m blade specimen with tip receptor from 1.5MW wind turbine under 3m air gap are conducted to investigate the lightning interception failure of LPS in different orientations and lateral distances (LDs). Factors such as the polarity of lightning strikes, the blade orientation of wind turbine and lateral distance between wind turbine and lightning downward leader were investigated. The lateral distance between downward leader (DL) and wind turbine blade is a key factor which influences the interception efficiency. Three patterns of receptor interception failure are discovered. The protection area shows asymmetry under different lateral distance. Multi-upward leaders (UL) from WT blade have been observed in the experiment