Current Issue : January - March Volume : 2015 Issue Number : 1 Articles : 6 Articles
This paper presents the development of a low cost miniature navigation system for autonomous flying rotary-wing unmanned\naerial vehicles (UAVs). The system incorporates measurements from a low cost single point GPS and a triaxial solid state\ninertial/magnetic sensor unit. The navigation algorithm is composed of three modules running on a micro controller: the sensor\ncalibration module, the attitude estimator, and the velocity and position estimator. The sensor calibration module relies on a\nrecursive least square based ellipsoid hypothesis calibration algorithm to estimate biases and scale factors of accelerometers and\nmagnetometers without any additional calibration equipment. The attitude estimator is a low computational linear attitude fusion\nalgorithm that effectively incorporates high frequency components of gyros and low frequency components of accelerometers and\nmagnetometers to guarantee both accuracy and bandwidth of attitude estimation. The velocity and position estimator uses two\ncascaded complementary filters which fuse translational acceleration, GPS velocity, and position to improve the bandwidth of\nvelocity and position. The designed navigation system is feasible for miniature UAVs due to its low cost, simplicity, miniaturization,\nand guaranteed estimation errors. Both ground tests and autonomous flight tests of miniature unmanned helicopter and quadrotor\nhave shown the effectiveness of the proposed system, demonstrating its promise in UAV systems....
A finite element model of plate partly treated with ACLD treatments is developed based on the constitutive equations of elastic,\npiezoelectric, viscoelastic materials and Hamilton�s principle. The Golla-Hughes-Mctavish (GHM) method is employed to describe\nthe frequency-dependent characteristics of viscoelastic material (VEM).Amodel reduction is completed by using iterative dynamic\ncondensation and balance model reduction method to design an effective control system. The emphasis is concerned on hybrid\n(combined feedback/feedforward) control system to attenuate the vibration of plates with ACLD treatments. The optimal linear\nquadratic Gaussian (LQG) controller is considered as a feedback channel and the adaptive filtered-reference LMS (FxLMS)\ncontroller is used as a feedforward channel. They can be utilized individually or in a hybrid way to suppress the vibration of\nplate/ACLD system. The results show that the hybrid controller which combines feedback/feedforward together can reduce the\ndisplacement amplitude of plate/ACLD system subjected to a complicated disturbance substantially without requiringmore control\neffort. Furthermore, the hybrid controller has more rapid and stable convergence rate than the adaptive feedforward FxLMS\ncontroller.Meanwhile, perfect robustness to phase error of the cancellation path in feedforward controller and the weight matrices\nin feedback LQG controller is demonstrated in proposed hybrid controller. Therefore, its application in structural engineering can\nbe highly appreciated....
This paper presents the development of a tool integrated in the UNS3D code, proprietary of Alenia Aermacchi, for the simulation\nof external aerodynamic flow in a rotating reference frame, with the main objective of predicting propeller-aircraft integration\neffects. The equations in a rotating frame of reference have been formulated in terms of the absolute velocity components; in this\nway, the artificial dissipation needed for convergence is lessened, as the Coriolis source term is only introduced in the momentum\nequation. An Explicit Algebraic Reynolds Stress turbulence model is used. The first assessment of effectiveness of this method is\nmade computing stability derivatives of a NACA 0012 airfoil. Finally, steady Navier-Stokes and Euler simulations of a four-blade\nsingle-rotating propeller are presented, demonstrating the efficiency of the chosen approach in terms of computational cost....
Asimple, nonstandardized material test specimen,which fails along one of two different likely crack paths, is considered herein.The\nresult of deviations in geometry on the order of tenths of a millimeter, this ambiguity in crack pathmotivates the consideration of asmanufactured\ncomponent geometry in the design, assessment, and certification of structural systems.Herein, finite elementmodels\nof as-manufactured specimens are generated and subsequently analyzed to resolve the crack-path ambiguity.The consequence and\nbenefit of such a ââ?¬Å?personalizedââ?¬Â methodology is the prediction of a crack path for each specimen based on its as-manufactured\ngeometry, rather than a distribution of possible specimen geometries or nominal geometry. The consideration of as-manufactured\ncharacteristics is central to the Digital Twin concept. Therefore, this work is also intended to motivate its development....
Mobility control is one of the most essential parts of planetary rovers� research and development. The goal of this research is to let\nthe planetary rovers be able to achieve demand of motion from upper level with satisfied control performance under the rough and\ndeformable planetary terrain that often lead to longitudinal slip. The longitudinal slip influences the mobility efficiency obviously,\nespecially on the major deformable slopes. Compared with the past works on normal stiff terrains, properties of soil and interaction\nbetween wheels and soil should be considered additionally. Therefore, to achieve the final goal, in this paper, wheel-soil dynamic\nmodel for six-wheel planetary rovers while climbing up deformable slopes with longitudinal slip is first built and control based in\norder to account for slip phenomena. These latter effects are then taken into account within terramechanics theory, relying upon\nnonlinear control techniques; finally, a robust adaptive fuzzy control strategy with longitudinal slip compensation is developed to\nreduce the effects induced by slip phenomena and modeling error. Capabilities of this control scheme are demonstrated via full\nscale simulations carried out with a six-wheel robot moving on sloped deformable terrain, whose real time was computed relying\nuniquely upon RoSTDyn, a dynamic software....
The vacuum specific impulse, density vacuum specific impulse, and solid exhaust products were examined for several propellant\nformulations based on the pyrophoric material triethylaluminum (TEA) using CEA thermodynamics code. Evaluation of TEA\nneat and mixed with hydrocarbon fuels with LOX, N2O, N2O4, liquefied air, and HNO3 were performed at stoichiometry. The\nvacuum specific impulse of neat TEA with N2O is comparable to that of nitric acid with the same, but the N2O formulation will\nproduce slightly less solid products during combustion. Additionally, N2O-TEA propellants have vacuum specific impulses and\ndensity vacuum specific impulses within 92.9% and 86.7% of traditional hydrazine propellant formulations under stoichiometric\nconditions....
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