Abstracts:In this paper, supervised machine learning is applied to the parameter estimation for optimal asteroid transfer trajectories. Efficient models for the estimation of important trajectory parameters are developed based on the Gaussian Process Regression (GPR) technique. The essence of constructing the GPR-based model is to learn the correlation between the trajectory parameters and the selected features. The asteroid orbital elements are considered as an original feature set due to their decisive influence on transfer trajectories. Two strategies are introduced to enhance the prediction performance of GPR-based models. The first one, the grouping strategy, is able to improve the prediction accuracy by dividing the candidate asteroids into several groups. The second one is that two new compound features are constructed based on the idea of feature extraction, whose function is to provide more crucial information for the inference of transfer time. The efficiency of the proposed models is substantiated by evaluating the global optimal two-impulse transfers to inner main-belt asteroids. This paper provides a basic framework for evaluating the interplanetary trajectories by using supervised machine learning. The proposed approach can be easily extended to solve other trajectory optimization and analysis problems.

Abstracts:This paper presents a generic global matrix formulation for the dynamics of flexible multibody systems with variable-speed control moment gyroscopes (VSCMGs). The flexible bodies are assumed to exhibit only small deformation, and they are connected in a tree topology by hinges permitting large rotation and translation. A cluster of VSCMGs is mounted on each body for actuation; it is assumed that the VSCMGs are statically and dynamically balanced, and their rotors are axisymmetric. A minimum set of dynamic equations are derived systematically via a mixed use of Kane's method and Newton–Euler equations. The parameters of each flexible body are augmented to take into account the inertias of the attached VSCMGs. Moreover, a skew-symmetric gyroscopic matrix and three control-input-mapping matrices are defined to represent the passive and the active gyroscopic torques of the VSCMGs in a global matrix manner. Three examples are given to show the usefulness, versatility, and correctness of the proposed formulation. As an additional contribution, also presented are linear dynamic equations for a spacecraft with flexible appendages and embedded VSCMGs.

Abstracts:Dealing with meteorological uncertainty poses a major challenge in air traffic management (ATM). Convective weather (commonly referred to as storms or thunderstorms) in particular represents a significant safety hazard that is responsible for one quarter of weather-related ATM delays in the US. With commercial air traffic on the rise and the risk of potentially critical capacity bottlenecks looming, it is vital that future trajectory planning tools are able to account for meteorological uncertainty. We propose an approach to model the uncertainty inherent to forecasts of convective weather regions using statistical analysis of state-of-the-art forecast data. The developed stochastic storm model is tailored for use in an optimal control algorithm that maximizes the probability of reaching a waypoint while avoiding hazardous storm regions. Both the aircraft and the thunderstorms are modeled stochastically. The performance of the approach is illustrated and validated through simulated case studies based on recent nowcast data and storm observations.

Abstracts:As a novel approach to control the relative motion of a spacecraft formation, electromagnetic formation flight (EMFF) has some prominent advantages, such as no propellant consumption and no plume contamination. The relative motion actuated by inter-craft electromagnetic force/torque is characterized by equilibrium states which could be utilized to accomplish particular missions, such as close formation, interferometer, etc. However, to maneuver among and maintain these equilibrium configurations, the control capability would be insufficient with only electromagnetic actuation and the inertial thrust is required, so an optimal method which exploits the invariant manifold theory is investigated in this paper. Firstly, the nonlinear translational dynamic model of two-craft electromagnetic formations is derived, and then relative equilibrium configurations and their stabilities are analytically studied. Secondly, the manifolds displaying characteristics of equilibria for the unstable equilibrium configurations are analyzed for the first time. Based on these manifolds, a novel and generalized method is proposed to formulate and parameterize optimal reconfigurations from one electromagnetic equilibrium configuration to another with the electromagnetic control inputs from the initial value to the target value. Specifically, the system's uncontrolled and discontinuous flows along manifolds compose majority of the transfer trajectories, and then optimal controls are applied to a portion of the discontinuous trajectories to differentially correct them to match continuity. By defining the control histories as a finite set of time independent variables, the optimal control problem is converted to a parameter optimization problem and solved by Particle Swarm Optimization. The method can attain the shape-changing ability and consume as little inertial thrust as possible, in exchange for added electromagnetic control effort. Lastly, numerical simulations are presented to verify the feasibility and optimality of the designed method.

Abstracts:The parameter adjusting in Automatic Carrier Landing System (ACLS) is a time-consuming and tedious task. In order to improve the efficiency of the adjusting task and overcome the difficulties in the manual parameter adjustment, a multilayer optimization strategy, in which ACLS is clearly divided into four layers including inner loop, autopilot, guidance control and guidance compensation, is proposed in this study and adopted for the parameter design. Besides, a novel algorithm, named Cauchy Mutation Pigeon-Inspired Optimization (CMPIO) which is inspired by Cauchy distribution, is proposed to optimize ACLS parameters in each layer. Comparative simulations are conducted to verify the feasibility of the multilayer design strategy and the superiority of CMPIO. To enhance the authenticity of the simulations in the guidance compensation layer, some stochastic conditions are considered with different deck motion, air wake and radar noise turbulences alleviated by several rejection methods. The simulation results prove that the designed ACLS based on the multilayer design strategy satisfies the acknowledged criteria including the time and the frequency domain. Furthermore, the stability of the inner loop and the autopilot integrated with Approach Power Compensation System (APCS) are confirmed.

Abstracts:Inspired by insect flapping wings, a novel flapping wing rotor (FWR) has been developed for micro aerial vehicle (MAV) application. The FWR combines flapping with rotary kinematics of motions to achieve high agility and efficiency of flight. To demonstrate the feasibility of FWR flight and its potential MAV application, an extensive and comprehensive study has been performed. The study includes design, analysis, manufacture, experimental and flight test of a flyable micro FWR model of only 2.6 g weight. By experiment, the FWR kinematic motion and aerodynamic lift were measured using high speed camera and load cells. Within a range of input power, the difference between the measured aerodynamic force and the analytical results by a quasi-steady model was found to be within 3.1%–15.7%. It is noted that the FWR aeroelastic effect plays a significant role to obtain an ideal large angle of attack especially in up-stroke and enhance the FWR performance. Further analysis of the unsteady aerodynamic characteristics has been carried out based on the detailed airflow field of the FWR in a flapping cycle by CFD method. A successful vertical take-off and short hovering flight of the micro FWR model has been achieved for the first time in the research field. The flight test demonstrates the FWR feasibility and its unique feature of flight dynamics and stability for the first time. These characteristics have also been simulated by using ADAMS software interfaced with the aerodynamic model.

Abstracts:This communication presents additional results on a recently published work of the author [1], which addressed the stationary coarse alignment (CA) stage of strapdown inertial navigation systems (SINS). As main contribution of this communication, the error analysis proposed in [1] is extended, and novel general expressions for the SINS CA errors are derived, which are valid regardless of the inertial measurement unit (IMU) orientation, and present hence, greater practical applicability. The general error expressions prove to be similar to the simplified equations derived in [1], but with body frame coordinates replaced by navigation frame coordinates. Simulation results validates the adequacy of the outlined verifications, and are in agreement with experimental results found in the literature.

Abstracts:The mean flow compressibility effects greatly influence the behavior of turbulent flows, as long as the flow is compressible. The fact is even though Favre average has taken into account the variation of the density, less accurate CFD results are always obtained when the flow is compressible. Thus, many compressibility corrections are made for high Mach number flows. As for the transonic turbulence flow, the mean flow compressibility effects are not mentioned. In this paper, it is demonstrated that the mean flow compressibility effects are not ignorable in transonic flows on some flow features. The mean flow compressibility effects are taken into account by introducing a characteristic turbulence length scale. The key is a new definition of vorticity by the curl of momentum. A compressible von Kármán length scale is introduced to obtain a new turbulence model CKDO (Compressible Kinetic Dependent Only) for complex compressible flows on the basis of the KDO. The only two empirical coefficients in the KDO model are not changed, which were calibrated by a slice of the incompressible flat plate boundary layer flow. Numerical simulations of transonic flows around RAE2822 airfoil, axisymmetric bump pipe and ONERA-M6 wing show that compressibility is non-negligible, and the new length scale definition can improve the prediction accuracies of aerodynamic features, such as the onset locations of shock waves, skin friction and pressure coefficients.

Abstracts:To predict ice accretion on the helicopter rotor more accurately, a three-dimensional Eulerian method with a shadow zone dispersion model is developed for calculating the water collection efficiency on blades in the unsteady vortex flowfield of the rotor. Firstly, the unsteady vortex flowfield of the rotor is calculated using a CLORNS code. Secondly, considering the 3-D effect of the rotor deeply, the droplet flowfield on the same embedded grids is solved by the Eulerian method to overcome the defects of traditional 2-D calculation methods for predicting rotor icing. To increase the stability and efficiency of the Eulerian method, the shadow zone dispersion model is presented. Thirdly, the calculated results are respectively validated through the ice amount comparisons with experimental results of UH-1H rotor and SRB rotor. The simulated results show that the blade-tip vortex has a significant effect on the water collection efficiency and causes a drop in the water collection amount along the blade spanwise direction. Finally, the effects of the advance ratio and the forward tilting angle of the rotor shaft on the water collection efficiency are calculated and analyzed, and some new conclusions are obtained. In forward flight, the blade-tip vortex has a more obvious effect on the water collection efficiency in the advancing blade than that in the retreating blade, and this effect decreases with the increase of the advance ratio and the forward tilting angle.

Abstracts:This study explores the effects of wing flexibility on several characteristics of flight, in this case the trim conditions, power requirements and dynamic stability of an insect-like flapping-wing micro-air vehicle (FWMAV) based on the hawkmoth Manduca sexta. The wing structure is analyzed by the finite-element method. A potential-based aerodynamic model which encompasses the unsteady panel method and the extended unsteady vortex-lattice method is employed to compute the aerodynamic forces. The motions of the FWMAV are obtained using a flexible multibody dynamics program coupled with the potential-based aerodynamic model. The results of this study show that the trim conditions of insect-like flexible and rigid FWMAVs may differ significantly from each other. When the flight speed is less than 3.0 m/s, using flexible wings is favorable, as they help the FWMAV reduce the power requirement and stabilize the lateral dynamics. However, at 3.0 m/s, these advantages are almost unnoticeable, while at 4.0 m/s, the flexible insect-like FWMAV requires even more mechanical power than its rigid counterpart.