Search

We develop a data-driven clustering method to evaluate a velocity model using surface wave velocity dispersion. This is done by first computing theoretical dispersion curves for 1-D velocity profiles of all the grid locations and then splitting the resulting dispersion curves into a certain number of groups via the K-means clustering. The observed dispersion curves are also clustered following the same procedure and the velocity model is assessed by comparing the spatial patterns obtained for the observed and synthetic data sets. The method is applied to evaluate two community velocity models in southern California, CVM-S4.26 and CVM-H15.1, using phase velocity maps derived for 3–16 s Rayleigh waves. We found a good correlation in the spatial distribution of clusters between the result of CVM-S4.26 and that of the observed data, suggesting that the CVM-S4.26 fits the observed dispersion maps better than the CVM-H15.1 in terms of features extracted from the clustering analysis.

The navigation field of agricultural machinery has entered the intelligent stage, but the navigation control performance of paddy field agricultural machinery represented by rice transplanters is not stable in complex environments. Therefore, this study proposes a method to identify navigation deviation patterns based on Deep Belief Network (DBN) and designs an adaptive preview distance control method based on a driver preview model for each deviation pattern. Among them, the deviation pattern identification method is a two-stage algorithm. First, determine whether the current navigation status is abnormal. Then, the classification was refined for different abnormal states. The adaptive control method is divided into two levels. The main regulator calculates the dynamic preview distance according to the current state variable; the sub-regulator calculates the preview distance adjustment value according to the abnormal state degree. In the performance test of the identification method, all the models show excellent stability and accuracy, and the identification speed of the algorithm meets the high frequency of the rice transplanter navigation system. In the performance test of the control algorithm, compared with the static preview distance, the adaptive preview distance control method proposed in this study can effectively suppress the disturbance deviation of the rice transplanter navigation. [ABSTRACT FROM AUTHOR]

To clarify the influence of the serpentine nozzle configurations on the flow characteristics and aerodynamic performance of aircraft, the flow features and aerodynamic performances of the double-ducted serpentine nozzles with different aspect ratios (AR), length–diameter ratios (LDR) and shielding ratios (SR) are numerically investigated. The results show that the asymmetric nozzle flow occurs due to the curved profile of serpentine nozzles, and a local accelerating effect exists at the S-bend, causing the increase in wall shear stress. The unilateral unsymmetrical expansion of the tail jet in the upward direction interacts with the separated external flow of the afterbody, forming an obvious cross-shock wave and shear layer structure. The surface pressure of the afterbody increases along the external flow direction, and decreases sharply in the separation point of the boundary layer. With the increase in AR and LDR, the local accelerating effect of the nozzle flow weakens, while with the increase in SR, the accelerating effect increases. The total pressure recovery coefficient, flow coefficient and axial thrust coefficient all decrease with the increase in AR, LDR, and SR. The thrust vector angle decreases with the increase in AR but is less affected by LDR and SR. [ABSTRACT FROM AUTHOR]

The bias-graded TiAIN coating was successfully deposited on Ti6AMV alloy substrates using filtered cathodic vacuum arc (FCVA) technology with the bias-graded deposition method. The high-temperature oxidation performance and high-temperature particle erosion resistance of the coating were evaluated. The changes of surface morphology, composition, phase structure, and erosion damage characteristics of the coating before and after the evaluation were tested and characterized. The results showed that after high-temperature oxidation at 400 °C, the surface color of the bias-graded TiAIN coating deepened and remained intact and smooth without significant damage. The oxygen atom fraction on the surface of the bias coating is 20.9% and the mass increase is 0.81 /.ig/mm2. The structure of the bias-graded coating is more dense, inhibiting the inward expansion of oxygen elements, and has better antioxidant performance than bias-50 TiAIN coating. Under high temperature particle erosion conditions at 400 °C, the erosion rates of bias-graded TiAIN coatings at 30° and 90° erosion angles are 0.26 mg/g and 0.24 mg/g, respectively, which are lower than those of bias-50 TiAIN coatings, exhibiting better resistance to high-temperature particle erosion. At 400 °C, there is no significant oxidation damage to the titanium alloy substrate and TiAIN coating, and high-temperature particle erosion damage is the dominant mechanism of erosion. [ABSTRACT FROM AUTHOR]

In the present study, we study formation flight with two flying wing configurations. A low speed wind tunnel test is conducted to validate the accuracy of the Computational Fluid Dynamics (CFD). Two optimization procedures are implemented at a high subsonic speed. The free stream Mach number is kept at 0.85, the lead aircraft's angle of attack is 2°, and the following aircraft's angle of attack is 2° as well. The maximum lift-to-drag ratio of the following aircraft is achieved as the lateral spacing is 0.853 b, and the vertical offset is 0.022 b (b is the wingspan). As much as 24.7% induced drag reduction is achieved at the optimized state. A pair of counter-rotating vortices interact and weaken each other. By analyzing the Kriging model constructed in the optimization procedure, it seems that the following aircraft's aerodynamic performance is sensitive to lateral spacing and vertical spacing, but insensitive to longitudinal spacing in close-formation flight. The best drag reduction position places in the following aircraft's wing tip is positioned at the core of the leading aircraft's wing tip vortex.