In order to investigate the characteristics of solid attitude control system (SACS) using proportional pintle thrusters, an ACS comprised of dual collaborative thrusters was designed and studied by theory and cold-flow test. Experiments were conducted to ascertain thrust variation at different pintle locations. With the purpose of studying thrust control principle, the thrust, chamber pressure and pintle displacement of two thrusters were measured, which worked differentially in the process. Results show that a nearly linear relationship is found between the thrust and valve pintle position and the two thrusters can work synchronous to produce a resultant force, whose direction and value can vary continuously. Besides, collaborative work mode of dual thrusters is conducive to the stabilization of chamber pressure which is beneficial to the choice of propellant.
The prominent properties owned by T-spline, such as flexibility, continuity, local refinement, water tightness, make it extensively applied in CAD & CAE integrating scenarios. But the local fairness may dissatisfy in damaged areas or even on the entire surface of industry applications. Under these circumstances, local protrusion and sharp features appeared seriously affect the fairness of T-spline surfaces. Derived from the geometric properties of T-spline control points, we propose a smoothing algorithm based on the 1-ring neighborhood space angle to deal with local abruptions of T-spline surfaces. We also demonstrate the availability of the proposed algorithm through several experiments. Results show that this method is suitable for removing sharp features and smoothing unstructured T-spline surfaces.
In this paper, we investigate covert communications for an unmanned aerial vehicle (UAV)-aided rate-splitting multiple access (RSMA) system in which the UAV transmits to the covert and public users separately while shielding covert transmissions from a warden. Under the RSMA principles, the messages of the covert and public users are converted to common and private streams for air-to-ground transmissions. Subject to the quality of service (QoS) requirements of the public user and covertness constraint of the UAV-aid RSMA (UAV-RSMA) system, the aim of covert communication design is to maximize the covert rate by jointly optimizing the transmit power allocation, common rate allocation, and UAV hovering height, which each contribute to the uncertainty of the warden’s binary decision and attempts to enhance communication performance. To address the non-convex covert rate maximization problem in addition to the highly coupled system parameters, we decouple the original problem into three subproblems of transmit power allocation, common rate allocation, and UAV hovering height. We derive the optimal solutions for each of the subproblems of the transmit power and rate allocations and formulate a signomial programming problem to tackle UAV hovering height optimization. The simulation results indicate the superior covert rate performance achieved by the proposed AO algorithm and demonstrate that the proposed UAV-RSMA scheme achieves a higher covert rate than the benchmark schemes.
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