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Underwater vehicles typically rely on batteries or other energy sources for operation, where drag reduction can significantly lower energy consumption and extend operational endurance. Inspired by the skin structure of loaches, a flexible structure with scales and mucus pores was designed. First, numerical simulations were conducted. To accurately demonstrate the interaction between the flexible flow field and the fluid flow field and to capture the movement boundaries of the plates, a bidirectional fluid–structure interaction simulation method was used. The numerical results indicate that the flexible structure has a positive effect on drag reduction. In channel experiments, the drag reduction effects of flexible and non-flexible structures were compared. Both showed optimal drag reduction at a water flow speed of 2 m/s and mucus flow speed of 0.1 m/s. The maximum drag reduction rate for the flexible structure was 28.5%, compared to 22.8% for the non-flexible structure. This difference is attributed to the flexible structure altering the flow pattern of the near-wall boundary layer, reducing the velocity gradient of the boundary layer, and increasing its thickness. The findings of this study can provide guidance for future research on flexible surface drag reduction technologies. [ABSTRACT FROM AUTHOR]

Reducing the surface resistance of underwater vehicles plays an important role in improving cruising speed and cruising mileage. The epidermis of loaches is not only covered with a layer of scale structure but also secretes mucus tissue with a lubricating effect, which makes loaches swim rapidly in muddy water. Study the morphology and structure of the skin of loach and establish a two-stage biomimetic drag reduction model. Adjust the different structural parameters of the model and select the parameters with the best drag reduction rate for the modeling design. The numerical simulation results show that the optimal drag reduction rate of the two-stage drag reduction structure is greater than 21%. In the flow channel test experiment, the drag reduction rate is slightly lower than the simulation results. Numerical simulation and experimental data show that the underwater drag reduction function can be realized by simulating the microstructure of loach skin. Finally, analyze the velocity gradient, vortices, etc., and search for the drag reduction mechanism. The simulation design of the microstructure of the loach skin can increase the thickness of the boundary layer, promote the vortex structure near the wall surface, change the flow mode of the solid–liquid interface, and reduce the wall resistance. At the same time, the drag reduction model provides key technical support for the practical application of reducing surface resistance, such as in underwater vehicles. [ABSTRACT FROM AUTHOR]

The aggregation of the remaining battery capacity of electric vehicles (EVs) can be used as distributed energy storage to participate in the microgrid optimisation through vehicle‐to‐grid (V2G) technology. However, the reliability of this service to be delivered is affected by the uncertainty of EVs' behaviour. The un‐reliable service will bring risks in the operation of microgrid when EVs' V2G electricity is regarded as an important flexibility resource. This paper, first proposes an analytical method to quantify the reliability of EV aggregation's (EVA's) V2G electricity based on the analysis of historical charging data and compound Poisson process. Based on this model, electric vehicles aggregators can evaluate the V2G bid quantity for any time slot on day t+1 according to the reliability requirements. Secondly, an optimal operation model of microgrid with consideration of V2G's reliability is considered. Finally, a test system with photovoltaics (PVs) and EVA on top of the original IEEE 33‐node system is used to verify the effectiveness of the proposed model. The results show that with the proposed reliability evaluation method of V2G electricity, the optimal operation of the microgrid can be reached with appropriate evaluation of the capability of the EVA. [ABSTRACT FROM AUTHOR]

The nitrogen vacancy (NV) color center in diamonds is an electron spin that can measure magnetic fields with high sensitivity and resolution. Furthermore, the robustness of an NV-based quantum system should be improved for further application in other sensing methods and in the exploration of basic physics. In this work, the robustness of an NV magnetometer is improved by the double driving method. The sensitivity of the NV magnetometer was improved 2.1 times by strengthening the pumping power from 100 to 600 mW. In this process, thermal drift was introduced, which affects the measurement accuracy. The temperature drift of a diamond matrix was measured using an infrared camera, and the temperature change of a diamond host drifted to ∼80 K under high laser and microwave power. To address the drift of temperature owing to sensitivity improvement by pumping enhancement, the double driving method was introduced, to suppress the drift of the resonance frequency, to improve the robustness of a continuous-wave NV magnetometer. The magnetic noise density was improved from 10 to 1.2 nT/Hz1/2. This study checked the source of temperature noise in the process of measuring with the NV color centers and proposes a double driving measurement method to track the resonant frequency change due to environmental temperature drift and improve sensitivity. The findings of this study are useful in applying complex pulse protocols in high-level sensing applications based on solid-state spin. [ABSTRACT FROM AUTHOR]