In human skin, the ability to spatially discriminate an individual indentation from two simultaneous indentations is tailored to the need of the specific area of application on the human body. While the spatial resolution is comparatively low over wide areas of the human body, there are no insensitive spots. In addition, the measuring range is tuned to the expected loads on the respective part of the human body. Within this study these observations are utilized to solve some of the key challenges on the way towards an artificial skin as a whole-body cover for robotic systems. To enable the reliable detection of collision events which are commonly of very short duration the reaction time of the artificial skin system has to be minimized. In order to do so, the goal conflict between the required number of taxels and the required high readout frequencies has to be solved. We present the DLR approach towards scalable transduction hardware and readout electronics as a basis for the acquisition of tactile information from future whole-body covers. First experiments with prototypes of the DLR Artificial Skin demonstrate the scalability of the transduction hardware with respect to size, spatial resolution and measuring range.
The dual-bell nozzle is an altitude-adaptive nozzle concept. It combines the advantages of a nozzle with small area ratio under sea-level conditions and a large area ratio nozzle under high-altitude conditions. Reynolds-averaged Navier-Stokes and unsteady Reynolds-averaged Navier-Stokes simulations on two-dimensional axisymmetric grids were conducted at DLR, German Aerospace Center in Lampoldshausen to investigate the transition from one mode to the other of a dual-bell nozzle model with positive pressure gradient extension. A cold flow test campaign conducted at DLR's cold flow test facility P6.2 provided validation data for the numerical approach. The present study investigates the influence of different turbulence models and feeding pressure gradients on the dual-bell flow transition behavior. Better results were achieved for the Spalart-Allmaras and Reynolds stress turbulence model. A clear impact of the feeding pressure ramp on the dual-bell transition pressure ratio and the flow separation position velocity was shown. The transition nozzle pressure ratio was predicted with an accuracy of 1%. For the hysteresis between transition and retransition nozzle pressure ratio, an accuracy of approximately 10% was reached. The calculated values of the experimental and numerical transition duration were on the same order of magnitude. Nomenclature A = area, m 2 H = hysteresis gap, % L = length, m R = radius, m y = dimensionless wall spacing α = angle, deg ϵ = expansion ratio Subscripts b = base nozzle e = nozzle extension i = inflection retr = retransition t = total th = nozzle throat tr = transition
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