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The research challenges for electric propulsion technologies are examined in the context of s-curve development cycles. It is shown that the need for research is driven both by the application as well as relative maturity of the technology. For flight qualified systems such as moderately-powered Hall thrusters and gridded ion thrusters, there are open questions related to testing fidelity and predictive modeling. For less developed technologies like large-scale electrospray arrays and pulsed inductive thrusters, the challenges include scalability and realizing theoretical performance. Strategies are discussed to address the challenges of both mature and developed technologies. With the aid of targeted numerical and experimental facility effects studies, the application of data-driven analyses, and the development of advanced power systems, many of these hurdles can be overcome in the near future.

A tandem propeller is a kind of propulsion device that is installed on the outer axis and the inner axis with the same axis respectively and rotates positively and negatively. Taking DTMB tandem thrusters as an example, which consists of propeller3689 and propeller3849, the hydrodynamic characteristic simulation of the tandem thrusters is completed, using sound analogy theory. The simulation results are consistent with the experimental results. The speed distribution of the tandem thrusters and the hydrodynamic wake of the tandem thrusters are analyzed. Through the analysis of acoustic radiation characteristics, it can be concluded that the noise characteristics of tandem thrusters are more complex than those of ordinary propellers, and there are more line spectrum characteristics in them.

This article conducts unsteady numerical calculations on lateral thrusters under arrival conditions, revealing the induced unsteady force characteristics under the interference between lateral thrusters and pod packages. The calculation results show that the lateral force and torque of the lateral propeller point towards the bow of the ship, and the main characteristic frequencies of pressure pulsation are blade frequency and its harmonics; The thrust and torque pulsation of the side thrusters on the bow side of the ship have maximum values; The bottom of the lateral thrust channel exhibits stronger pressure pulsation compared to other positions. The calculation results of this article determine the position and characterization form of the excitation force of the lateral thruster, providing a basis for the design of low-noise lateral thrusters.

AbstractThe results of studies on the use of solid-state infrared lasers in combination with special targets for obtaining primary electrons in ionization chambers of plasma-ion thrusters are presented. Such thrusters being equipped with free molecular air intakes for using the surrounding atmosphere as a propellant for air-breathing electric thrusters, which are highly efficient for long-term maintenance of spacecraft in ultra-low orbits, providing significant advantages in Earth remote sensing and telecommunications. It is shown that the method of electron emission proposed can be an alternative to the current-heated cathodes used today, significantly increasing their lifetime.

Robot designs can take many inspirations from nature, where there are many examples of highly resilient and fault-tolerant locomotion strategies to navigate complex terrains by recruiting multi-functional appendages. For example, birds such as Chukars and Hoatzins can repurpose wings for quadrupedal walking and wing-assisted incline running. These animals showcase impressive dexterity in employing the same appendages in different ways and generating multiple modes of locomotion, resulting in highly plastic locomotion traits which enable them to interact and navigate various environments and expand their habitat range. The robotic biomimicry of animals’ appendage repurposing can yield mobile robots with unparalleled capabilities. Taking inspiration from animals, we have designed a robot capable of negotiating unstructured, multi-substrate environments, including land and air, by employing its components in different ways as wheels, thrusters, and legs. This robot is called the Multi-Modal Mobility Morphobot, or M4 in short. M4 can employ its multi-functional components composed of several actuator types to (1) fly, (2) roll, (3) crawl, (4) crouch, (5) balance, (6) tumble, (7) scout, and (8) loco-manipulate. M4 can traverse steep slopes of up to 45 deg. and rough terrains with large obstacles when in balancing mode. M4 possesses onboard computers and sensors and can autonomously employ its modes to negotiate an unstructured environment. We present the design of M4 and several experiments showcasing its multi-modal capabilities. The biomimicry of animals’ appendage repurposing can be applied to robot designs, resulting in unparalleled capabilities. Sihite et al. report a Multi-Modal Mobility Morphobot (M4) that negotiate unstructured, multi-substrate environments, including land and air, by employing its components in different ways as wheels, thrusters, and legs.

UFOWTs (Unmoored Floating Offshore Wind Turbines) are a new concept of floating offshore wind turbine in which mooring lines are replaced by thrusters. This approach has several advantages, e.g it may open exploitation of far offshore wind, but only if the thrusters power consumption is kept low enough. This research aims at estimating the annual production of UFOWTs. To do so, a steady state model is implemented, taking into account environmental loads from wind and waves, based on realistic meteocean data from ERA-5 database. The results are promising, as they indicate that a UFOWT can achieve 56 % to 69 % of the production of a conventional FOWT depending on how far the UFOWT is allowed to drift away from its initial position.

Underwater robots have been promoted a significant interest in monitoring the marine environment. In some complex situation, robots sometimes need to keep moving fast, sometimes need to keep low speed and low noise. To address this issue, a novel spherical underwater robot (SUR IV) with hybrid propulsion devices including vectored water-jet and propeller thrusters is proposed in this paper. The diversity of the movement modes is also proposed for the different targets as remote or hover and general or silent. To analyze the hydrodynamic characteristics of the hybrid thruster, the computational fluid dynamics simulation is calculated in ANSYS CFX by using the multi-reference frame method. The simulation results show the interaction between the propeller and water-jet thruster. The thrust experiment to evaluate the performance of the improved hybrid thruster is also conducted. The maximum thrust of the hybrid thruster is increased 2.27 times than before. In addition, a noise comparison experiment is conducted to verify the low noise of the water-jet thruster. Finally, the 3 DoF motions which include the surge, heave and yaw for the SUR IV were carried out in the swimming pool. The improvement of the overall robot is assessed by the experimental results.

An inductive pulsed plasma thruster (IPPT) operates by pulsing high current through an inductor, typically a coil of some type, producing an electromagnetic field that drives current in a plasma, accelerating it to high speed. The IPPT is electrodeless, with no direct electrical connection between the externally applied pulsed high-current circuit and the current conducted in the plasma. Several different configurations were proposed and tested, including those that produce a plasma consisting of an accelerating current sheet and those that use closed magnetic flux lines to help confine the plasma during acceleration. Specific impulses up to 7000 s and thrust efficiencies over 50% have been measured. The present state-of-the-art for IPPTs is reviewed, focusing on the operation, modeling techniques, and major subsystems found in various configurations. Following that review is documentation of IPPT technology advancement paths that were proposed or considered.

A brand new non-penetrating tunnel thruster (short for NPT thruster) is proposed in this paper. The tunnel structural parameters of the thruster are optimized, and the performance and optimization effect are verified by experiments. First, the design and function of the NPT thruster are introduced. Second, the computational fluid dynamics method is used to calculate the hydrodynamic performance of the NPT thruster and to analyze the static mooring thrust performance. Third, the tunnel structural parameters of the NPT thruster are optimized with the method of the response surface methodology. The pressure distributions and the flow fields on the tunnel surface of the NPT thrusters before and after optimization are compared with simulations. Finally, the mooring static thrust of the NPT thrusters is tested with experiments. The results show that the average increase in the mooring static thrust for the optimized thruster is 12.4%, and the maximum increase can reach 21.79% when the rotational speed is from 3000 rpm to 6500 rpm.

To address the issues of excessive observation equipment and discontinuous observation points in tethered discrete profiling observations, a mobile profiling observation platform with mooring and cable-traversing capabilities has been designed. This platform is propelled by electric thrusters and incorporates a mooring mechanism that clamps onto the tether to achieve clinging positioning. A dynamic simulation model of the mobile platform was established to analyse the thrust required for traversing the cable and the clamping force and torque needed during mooring. The study reveals that the magnitude of horizontal flow velocity is the primary factor influencing the thruster thrust and clamping torque, both of which increase with higher flow velocities. The designed cable-traversing mobile observation platform provides a methodological approach for conducting profiling observations on tethered marine observation platforms.