Ethernet based time synchronization for Raspberry Pi network improving network model verification for distributed active turbulent flow control

Friction drag primarily determines the total drag of transport systems. A promising approach to reduce drag at high Reynolds numbers(> 104) are active transversal surface waves in combination with passive methods like a riblet surface. For the application in transportation systems with large surfaces such as airplanes, ships or trains, a large scale distributed real-time actuator and sensor network is required. This network is responsible for providing connections between a global flow control and distributed actuators and sensors. For the development of this network we established at first a small scale network model based on Simulink and True Time. To determine timescales for network events on different package sizes we set up a Raspberry Pi based testbed as a physical representation of our first model. These timescales are reduced to time differences between the deterministic network events to verify the behavior of our model. Experimental results were improved by synchronizing the testbed with sufficient precision. With this approach we assure a link between the large scale model and the later constructed microcontroller based real-time actuator and sensor network for distributed active turbulent flow control.

Hybrid-panel-based new design idea for large reflector antenna

Large reflector antennas are widely used as radio telescopes and active main reflectors are generally applied to improve the surface accuracy. Considering that the high cost has been one important problem in engineering, it is worth discussing whether it is necessary to install actuators on all the panels. Thus, in this paper, a hybrid-panel-based new design idea for large reflector antenna is proposed. Assuming that the actuators are installed only in the region of the reflector with large deformations and there are no actuators in other region to reduce the actuator number, the surface accuracies and the corresponding electromagnetic(EM) performances calculated by three different panel adjustment strategies are compared. The most effective method is that the deformed reflector should be first preadjusted to reduce the gravity deformation and then the panels equipped with actuators should be adjusted to the locations determined by the best fitting reflector(BFR) derived by the deformed reflector with no actuators. A 35 m reflector antenna is adopted as an example to calculate the surface accuracy and EM performance when parts of the panels are equipped with actuators. The simulation results show that there is no need to install actuators on all panels and the presented method can greatly reduce the number of actuators with guaranteed surface accuracy. Thus, during the antenna structural design phase, once the surface accuracy requirement is given, the number of actuators can be minimized to reduce the manufacturing and maintenance costs as much as possible. This paper can provide valuable guidance for the design of an active main reflector with hybrid panels.