Thrust ripple analysis for improved modular tubular permanent magnet synchronous linear motor

Various technologies have ever been developed to minimize the detent force of linear motors. Although the traditional modular structure can effectively reduce the detent force, the width of the flux barrier and the number of units severely limit its application. To solve these, this paper proposes a new modular type of tubular permanent magnet synchronous linear motor (TPMSLM), which consists of two identical unit motors. For simplification, a subdomain analytical method of the unit motor is firstly established, and its accuracy is verified by a comparison with that of the finite element method. Using the two approaches, the important parameters of the motor are analyzed. A modified two-unit modular TPMSLM is also proposed through the star vectograms of the electromotive force, which achieves thrust performance similar to the traditional three-unit modular TPMSLM with a smaller axial size. Moreover, to make full use of the volume of the flux barrier, end teeth are added at both ends of the unit motors. The simulation results indicate that a reasonable end tooth structure can not only reduce the magnetic leakage phenomenon of the end but also effectively improve the thrust of the motor.

Kinematic Analysis of Water Polo Player in the Vertical Thrust Performance to Determine the Force-Velocity and Power-Velocity Relationships in Water: A Preliminary Study

Background: To date, studies on muscle force and power-velocity (F-v and P-v) relationships performed in water are absent. Aim: The goal of this study is to derive the F-v and P-v regression models of water polo players in water vertical thrust performance at increasing load. Methods: After use of a control object for direct linear transformation, displacement over the water and elapsed time was measured, by using a high-speed 2D-videoanalysis system, on 14 players involved in the study. Results: Intra-operator and player’s performance interclass correlation coefficient (ICC) reliability showed an excellent level of reproducibility for all kinematic and dynamic measurements considered in this study with a coefficient of variation (CV) of less than 4.5%. Results of this study have shown that an exponential force-velocity relationship seems to explain better the propulsive force exerted in the water in lifting increasing loads compared to the linear one, while the power and velocity have been shown to follow a second-order polynomial regression model. Conclusion: Given the accuracy of the video analysis, the high reliability and the specificity of the results, it is pointed out that video analysis can be a valid method to determine force-velocity and power-velocity curves in a specific environment to evaluate the neuromuscular profile of each water polo player.

Experimental Investigation of Detonation Propagation Modes and Thrust Performance in a Small Rotating Detonation Engine Using C2H4/O2 Propellant

A small rotating detonation engine (RDE) model and the corresponding experimental setup were constructed for the experimental investigation of the detonation propagation characteristics and thrust performance of a circular RDE. Experiments were conducted at a range of 0.3–2.5 equivalence ratio with a total mass flow rate of less than 180.0 g/s using a C2H4/O2 mixture. Irregularly unstable detonative combustion occurs immediately after the detonation initiation, which includes initiation, propagation, decaying, and the merging of detonation waves. Following this, periodically unsteady detonative combustion occurs in the circular channel, resulting in the stable operation of the RDE. During stable operation, two detonation waves are predominant, rotating along the wall at a speed lower than the Chapman–Jouguet (CJ) detonation speed. The characteristic velocity efficiency is approximately 73% on average. The low characteristic velocity efficiency is presumed to be caused by the unoptimized combustion channel and the poor mixing efficiency owing to the two-dimensional injector configuration. The effect of the RDE component design and the RDE flow field characteristics need to be further investigated for improving the performance of the RDE.