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The propagation of water waves can be manipulated via artificial structures. However, such structures usually need to possess a large volume ratio in water, and it may not be easy to build and move them in practical ocean engineering. Here, we theoretically propose and experimentally demonstrate a fixed, shallow-draft cylinder array that can refract and focus water waves within a wide range of wavelengths. When impinging upon the cylinder array from a region of water without structures, water waves can be slightly reflected at the surface of the array and speeded up in the array. As a result, favorable focusing performances such as a short focal length and high intensity at the focal point are observed. [ABSTRACT FROM AUTHOR]

A novel control strategy based on finite time control and super-twisting observer is proposed to improve the control performance and robustness for permanent magnet synchronous linear motor (PMSLM) drive system. First of all, the velocity-current single loop control which called non-cascade structure control is proposed by the finite time control, then the response velocity of the PMSLM drive system can be improved. Secondly, to improve the disturbance rejection performance, a super-twisting observer is designed to feedforward the load. Furthermore, the strictly convergence of the proposed control strategy is implemented. Finally, comparative simulations and experiments are designed on PI control, sliding mode control, and the proposed control method. Results demonstrate that the proposed method has better robustness and control performance. [ABSTRACT FROM AUTHOR]

In order to study the application effect of advanced support in deep buried tunnels, this paper simulated the comparative tests of tunnel three-step excavation based on the Xiangshan Tunnel project of Yinchuan-Lanzhou High-speed Railway, and studied the stability analysis of bolt support on the face and surrounding rock by analyzing the changes of earth pressure and the deformation of the face and the peak change of bolt micro strain at different positions. The results obtained show that: (1) The bolt support has a good limiting effect on soil deformation, and the vertical soil restriction is better than that in the horizontal direction; (2) The reinforcement of the soil in front of the tunnel face by the bolt support limits the deformation range of the surrounding rock above and indirectly improves the stability of the surrounding rock. (3) After the bolt support, the final deformation of the tunnel face is reduced by 0. 92 mm, and the displacement is reduced by nearly half in the excavation where the displacement changes occur; (4) The support effect in the middle position of the tunnel face after the bolt support is the best, while the upper bolt is deformed greatly, and it is recommended to cooperate with the small conduit and pipe shed under special circumstances. The research results can provide a theoretical reference for the stability of the advance support of the hammer during tunnel construction. [ABSTRACT FROM AUTHOR]

A non-singular terminal sliding mode control based on finite time observer is designed to achieve speed direct control for the permanent magnet synchronous motor (PMSM) drive system. Speed and current are regulated in one loop under the non-cascade structure, taking place of the cascade structure control method in the vector control of PMSM. Based on the second-order speed function of the PMSM, the disturbance and parameters uncertainties are estimated by the designed finite time observer (FTO), and compensate to the drive system. The estimated value of the finite time observer will converge to the actual disturbance value in a finite time. A second-order non-singular terminal sliding mode controller is proposed to realize the speed and current single-loop, which can track the reference speed and reference current in a finite time. Rigorous stability analysis is established. Comparative results verified that the proposed method has faster speed tracking performance and disturbance rejection property. [ABSTRACT FROM AUTHOR]

Spatiotemporal vortex pulses are wave packets that carry transverse orbital angular momentum, exhibiting exotic structured wave fronts that can twist through space and time. Existing methods to generate these pulses require complex setups like spatial light modulators or computer-optimized structures. Here, we demonstrate a new approach to generate spatiotemporal vortex pulses using just a simple diffractive grating. The key is constructing a phase vortex in frequency-momentum space by leveraging symmetry, resonance, and diffraction. Our approach is applicable to any wave system. We use a liquid surface wave (gravity wave) platform to directly demonstrate and observe the real-time generation and evolution of spatiotemporal vortex pulses. This straightforward technique provides opportunities to explore pulse dynamics and potential applications across different disciplines.

Achieving Goos-Hänchen shift enhancement with high transmittance or reflectance based on the resonance effect is challenging due to the drop in the resonance region. This Letter demonstrates the realization of large transmitted Goos-Hänchen shifts with high (near 100%) transmittance based on a coupled double-layer grating system. The double-layer grating is composed of two parallel and misaligned subwavelength dielectric gratings. By changing the distance and the relative dislocation between the two dielectric gratings, the coupling of the double-layer grating can be flexibly tuned. The transmittance of the double-layer grating can be close to 1 in the entire resonance angle region, and the gradient of the transmissive phase is also preserved. The Goos-Hänchen shift of the double-layer grating reaches ∼30 times the wavelength, approaching 1.3 times the radius of the beam waist, which can be observed directly.