Investigation on Thrust Force Conversion Method of Oscillating Caudal Fin Based on Wake Vortex Field Structure

The wake field of the flexible oscillating caudal fin is investigated using the Digital Particle Image Velocity (DPIV) system. The distributions of the vorticity with different Strouhal numbers are presented, and a self-developed program is used for calculating the velocity circulation of the vortex ring. Quantitative analysis of the wake field such as velocity circulation of the vortex ring, vortex radius, and the center-to-center spacing of vortex pair is presented. A three-dimensional vortex ring chain model of oscillating caudal fin is introduced. A conversion model between velocity circulation and dynamic moment of the vortex ring is presented according to the vortex dynamics theory, and a self-developed program is used for the calculation, in which the conversion of the thrust force based on wake field of oscillating caudal fin is carried out. Comparisons of the results of the two kinds flexible caudal fins thrust force conversion with the result of tricomponent balance system have been done in this paper. The relative errors are 5.86% and 3.44%, respectively. It is shown that the thrust force conversion model of flexible oscillating caudal fin is accurate and reliable, and the method presented in the paper provides an effective model for the quantitative conversion between the flow field and the thrust force of the caudal fin.

Effect of ionization waves on dust chain formation in a DC discharge

An interesting aspect of complex plasma is its ability to self-organize into a variety of structural configurations and undergo transitions between these states. A striking phenomenon is the isotropic-to-string transition observed in electrorheological complex plasma under the influence of a symmetric ion wake field. Such transitions have been investigated using the Plasma Kristall-4 (PK-4) microgravity laboratory on the International Space Station. Recent experiments and numerical simulations have shown that, under PK-4-relevant discharge conditions, the seemingly homogeneous direct current discharge column is highly inhomogeneous, with large axial electric field oscillations associated with ionization waves occurring on microsecond time scales. A multi-scale numerical model of the dust–plasma interactions is employed to investigate the role of the electric field in the charge of individual dust grains, the ion wake field and the order of string-like structures. Results are compared with those for dust strings formed in similar conditions in the PK-4 experiment.

Physics of magnetized dusty plasmas

In this review, we summarize recent advances in the field of dusty plasmas at strong magnetic fields. Special emphasis is put on situations where experimental laboratory observations are available. These generally comprise dusty plasmas with magnetized electrons and ions, but unmagnetized dust. The fundamental parameters characterizing a magnetized (dusty) plasma are given and various effects in dusty plasmas under magnetic fields are presented. As examples, the reaction of the dust component to magnetic-field modified plasma properties, such as filamentation, imposed structures, dust rotation, nanodusty plasmas and the resulting forces on the dust are discussed. Further, the behavior of the dust charge is described and shown to be relatively unaffected by magnetic fields. Wake field formation in magnetized discharges is illustrated: the strength of the wake field is found to be reduced with increased magnetic field. The propagation of dust acoustic waves in magnetized dusty plasmas is experimentally measured and analyzed indicating that the wave dynamics are not heavily influenced by the magnetic field. Only at the highest fields ($$B> 1$$ B > 1 T) the wave activity is found to be reduced. Moreover, it is discussed how dust-cyclotron waves might be used to indicate a magnetized dust component. Finally, implications of a magnetized dusty plasma are illustrated.

Effect of piezoelectric material on vibration of vessel of marine transportation

The drive arrangement of normal marine vessels involves a propeller coupled to a progression of shafts and diary orientation which is at last associated with a push bearing which sends the propeller pivotal power into the frame of the boat through a push block coupled to the mass head. For effortlessness, the framework is improved to a propeller, a solitary shaft, diary bearing and a push bearing. As the vessel travels through the sea, a wake is produced. This non-uniform wake field is the inflow to the propeller. The power produced by the propeller is additionally non-uniform. The impetus arrangement of a marine vessel is the principle supporter of commotion emanated from the vessel. It is along these lines important to diminish the commotion sent from the propeller into the sea and consequently the vibration that is created by the propeller that is thus communicated into the body. The inspiration for lessening commotion and vibration remembers diminishing mechanical wear for segments, expanding secrecy limit of military vessels, improving traveler and group solace, and decreasing the effect on marine conditions. The point of this theory is to dissect the shaky power created by the propeller, the power transmission ways, and techniques to quantify the power transmission through the push bearing continuously.

Determining Actuator Requirements for Cyclic Varying Pitch Propeller for Ships

In marine applications, a cyclic varying pitch (CVP) propeller is a propeller in which the propeller blade can be cyclic-pitched. This cyclic pitching of the propeller blades is used to adapt to the local flow conditions in the non-uniform wake field that the propeller operates in, behind the ship hull. This has the potential to improve the performance of the propulsion system relative to a propeller which has fixed pitch for each revolution. The potential performance improvements include increasing the propulsion efficiency and reducing the cavitation, pressure pulses, vibrations and noise problems. However, the CVP propeller is not on the market today, and several challenges have to be addressed before the CVP propeller may be realized. One of these challenges is how to design the individual cyclic pitch mechanism for the propeller. However, before the cyclic pitch mechanism can be designed, it is necessary to know the requirements for it, such as the required pitching power and torque. The focus of the current paper is therefore to present a model for the propeller, by which it is possible to determine the loads acting on the CVP propeller blades during the cyclic pitching, and hence the actuator force/torque and power requirements. To illustrate the usefulness of the model, an example is presented, in which the loads on a CVP propeller are determined, together with the requirements for the individual cyclic pitch mechanism. The efficiency results presented are, however, not representative of the efficiency improvement that may be obtained, as neither the propeller nor the pitch trajectory has been optimised. The results do, however, serve to show the benefit and validity of the model.