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ObjectiveThis study aims to investigate the influence and mechanism of a cup structure on the hydrodynamic performance of a surface-piercing propeller. MethodsBased on the RANS method and combined with the volume of fluid (VOF) and sliding mesh methods, a numerical simulation is carried out on an 841-B surface-piercing propeller with a cup structure modification under natural ventilation conditions. On the basis of verifying the effectiveness of the numerical simulation method, the trailing edge angle is adjusted according to the dichotomy method to change the cup structure of the benchmark surface-piercing propeller, and a series of propellers is obtained for simulation calculation and research. ResultsChanging the cup structure has a significant impact on the thrust and torque of the surface-piercing propeller, but relatively little impact on its efficiency. Enlarging the cup structure allows more water to be attached to the blades when it emerges from the free surface, resulting in increased waves and droplet splashing behind the propeller. ConclusionThe method and results of this paper can provide useful references for the design of surface-piercing propellers.

ObjectivesThis paper aims to research the effects of the temperature and compressibility of liquid water on the super-cavitation phenomenon of an ultra-high-speed underwater vehicle and its motion characteristics. Methods First, based on CFD general software Fluent 19.2, the free motion of transonic and supersonic vehicles is computed using a numerical model that considers both the compressibility and temperature of the water. Qualitative and quantitative comparisons with the experimental results of reference [1] are made, and the effectiveness of the numerical method is verified. The motion characteristics at different initial speeds are then analyzed using the range at the sailing time of 0.008 s as the comparison base. Finally, the influence of the launch depth and environment temperature on the motion characteristics is discussed. Results It is found that when the speed is greater than 2 000 m/s, increasing the initial speed does not significantly increase the effective range; the critical speed is found between 1 450 m/s and 1 475 m/s, where the range variation is less than 3% with or without the influence of the temperature; as the launch depth increases, the resistance of the vehicle becomes greater and the sailing range gradually decreases; and the higher the environment temperature, the shorter the effective range. Conclusions It is shown that the numerical model proposed herein, which considers both the temperature and compressibility of liquid water, can provide valuable references for the motion analysis of ultra high-speed underwater vehicles and corresponding practical applications.

Surface-enhanced Raman scattering (SERS) is widely used for trace detection of substances, and the key to this technology lies in the preparation of the substrate material. In this study, a composite SERS material of Au NRs/4-MBA/PAM was constructed and characterized to better immobilize the reference molecule 4-mercaptobenzoic acid (4-MBA). Electron transmission microscopy results demonstrated that the PAM film helps Au NRs to pack closely, enhancing the stability of the material structure and reducing the interference of external environmental factors on the response of 4-MBA, thus improving the accuracy of quantitative determination. Comparative experimental results with the Au NRs/4-MBA substrate showed that the relative standard deviations (RSDs) of the detection results for MG on different batches of Au NRs/4-MBA/PAM were less than 8.0%, and the RSDs of different points on the same material were less than 10.0%, indicating that the Au NRs/4-MBA/PAM has higher uniformity, better reproducibility, and higher sensitivity in detecting malachite green (MG). Applying this material in the recovery determination of fish extract showed that the recovery rates of MG were between 75.60% and 83.24%. Therefore, the Au NRs/4-MBA/PAM substrate can accurately detect and quantify veterinary drug residue in complex matrices such as food tissue.

In this work, a simple, low-cost, green, and mild method for the preparation of three-dimensional nanocomposite materials of gold nanorods (Au NRs)@TiO2 is reported. The surface of Au NRs was coated with TiO2 in situ reduction at room temperature without a complicated operation. The synthetic Au NRs@TiO2 nanocomposites were used as surface-enhanced Raman spectroscopy (SERS) active substrates for the reusable and sensitive detection of environmental pollutants. The results showed that the pollutants on Au NRs@TiO2 nanocomposites have higher SERS activity and reproducibility than those on the Au NR substrate without the presence of TiO2. Moreover, the SERS substrate can be readily recycled by UV-assisted self-cleaning to remove residual analyte molecules. Malachite green (MG) and crystal violet (CV) were used as examples to demonstrate the feasibility of the proposed sensor for the sensitive detection of environmental pollutants. The results showed that the limit of detections (LODs) were 0.75 μg/L and 0.50 μg/L for MG and CV, respectively, with the recoveries ranging from 86.67% to 91.20% and 83.70% to 89.00%. Meanwhile, the SERS substrate can be easily regenerated by UV light irradiation. Our investigation revealed that within three cycles, the Au NRs@TiO2 substrates still maintained the high SERS enhancement effect that they showed when first used for SERS detection. These results indicated that the method can be used to detect MG and CV in really complex samples. Due to the high sensitivity, reusability, and portability and the rapid detection property of the proposed sensor, it can have potential applications in the on-site detection of environmental pollutants in a complex sample matrix.