Unbonded flexible risers consist of several helical and cylindrical layers, which can undergo large bending deformation and can be installed to different configurations to adapt to harsh marine environments, and is a key equipment in transporting oil and gas resources from Ultra Deep Waters (UDWs) to offshore platforms. The helical interlayer of an unbonded flexible riser makes the structural behavior difficult to predict. In this paper, the axial tensile behavior and the axial tensile ultimate strength of an unbonded flexible riser are studied based on a typical 2.5-inch eight-layer unbonded flexible riser model, and verified through a theoretical method considering the contact between adjacent layers. First, the balance equation of separate layers is deduced by a functional principle, and then the overall theoretical model of an unbonded flexible riser is established considering the geometric relationship between adjacent layers. Then, the numerical model considering the detailed geometric properties of an unbonded flexible riser is established to simulate the axial tensile behavior. Finally, after being verified through the experimental results, the axial tensile stiffness and axial tensile strength of an unboned flexible riser considering the elasticity of the tensile armor layer are studied using the proposed two methods. Additionally, the effect of frictional coefficients is conducted. The numerical and theoretical results show good agreement with the test results, and the friction between adjacent layers would increase the axial tensile stiffness of an unbonded flexible riser.

This paper studies the synchronization problem for a class of chaotic systems subject to disturbances. The nonlinear functions contained in the master and slave systems are assumed to be incremental quadratic constraints. Under some assumptions, a feedback law is designed so that the error system behaves like the $H^{\infty }$ performance. Meanwhile, the detailed algorithm for computing the incremental multiplier matrix is also given. Finally, one numerical example and one practical example are simulated to show the effectiveness of the designed method.

When diamond scribing knives are used to grind silicon wafers at ultra-high speeds, slight changes in the structure of the diamond scribing knives and changes in the grinding parameters will have a large impact on the processing accuracy and appearance of the silicon wafers. In order to reduce the defective rate of silicon wafers, improve the service life of diamond scribing knives and grinding efficiency. To address this issue, the working mechanism of the scribing knife grinding is analysed in the paper, the influence of spindle speed and feed rate on the quality of the silicon wafer slit when the scribing knife is grinding is studied, and the chipping of silicon wafers is observed through the scanning electron microscope and optical microscope, so as to analyse the shape of the cross-section, length of the cutting edge, concentration of diamond particles in the cutting edge, thickness of the cutting edge and determine the structure of the scribing knife, and to test its influence on the silicon wafer slit by means of the grinding experiments. The structure of the scribing knife was determined, and its influence on the quality of silicon wafer slit was tested by grinding experiment. The results show that the wear rate of diamond particles, slit quality and processing efficiency of the scribing knife are optimal when grinding silicon wafers at 50,000 r/min and 60-80 mm.sec-1. The above study can help to further understand the wear mechanism of the scribing knife in the process of ultra-high-speed grinding of silicon wafers, improve the machining efficiency, and prolong the service life of the tool. Scribing knife Grinding mechanism Tool structure optimization Parameter optimization

To investigate and quantify the effect of grids as well as different numerical models on the propeller open water simulation results and to evaluate the confidence level of the simulation results, numerical simulation of open water and uncertainty assessment are necessary. The propeller open water performance was calculated using the SST k-ω method with MRF (Multiple Reference Frames) and SM (Sliding Mesh) models under different grid densities. Following ITTC (International Towing Tank Conference) (2021) procedures, CFD (Computational Fluid Dynamics) uncertainty evaluation and flow field analysis of the numerical models were carried out. The principles of the "verification" and "validation" steps were introduced. Three grids of different densities were numerically simulated to obtain the thrust coefficient K_T, torque coefficient K_Q and open water efficiency η at different advance coefficient, J. CFD calculation result uncertainty analysis was implemented. Comparisons were made of near-wall Y+ distribution, wakefield, velocity distribution, and surface pressure distribution at J=0.6. Results show that: 1) the trends of the three grids' results were consistent, and the SM model was more sensitive to grids, but its converged results were closer to the true value; 2) near-wall Y+ distribution, wakefield and velocity distribution showed noticeable differences due to grid discrepancies, while pressure distributions were approximate. Calculation results monotonically converged in "verification" and were validated in "validation". Thus, calculation results meet application requirements and model settings can provide an engineering reference.

Ultra-high-speed permanent magnet synchronous motors (PMSMs) have been widely applied in aerospace, advanced manufacturing, and consumer products due to their small size, high reliability, and high-power density. As the rotational speed increases, losses, cooling requirements, excitation forces, bearing losses, and noise characteristics of the motor are significantly different from those of conventional motors. To minimize iron losses and improve efficiency, ultra-high-speed motors typically employ a low pole count configuration, exemplified by the prevalent 2-pole 3-slot (2P3S) design. In 2-pole machines, low-order electromagnetic excitation forces may cause significant electromagnetic vibration and noise. Reducing electromagnetic noise, especially the two-times mechanical rotational frequency (2f) noise in 2P3S motors, is critical. Therefore, the noise reduction strategies for a 120,000 rpm PMSM are investigated. First, the electromagnetic excitation frequencies and magnitudes of the motor are analyzed. Through changing the pole-slot configuration (such as transitioning from 2P3S to 2P6S), the unbalanced magnetic pull (UMP) in the original 2P3S design is eliminated, significantly reducing the main source of vibration. Then, the impact of the stator assembly gap on electromagnetic excitation is examined using a segmented stator structure. Effective control of this assembly gap further reduces the electromagnetic noise of the motor. Finally, experimental tests demonstrate a significant noise reduction in the 2f frequency band, with a sound pressure level reduction of about 9 dB. The reduction validates the effectiveness of this pole-slot optimization and stator assembly gap control strategies.