The regolith sampling process is risky but a key procedure in planet exploration. It not only accounts for the uncertainty of the soil particles that interacted with the bucket, but also the automated operation of the sampling manipulator. In this paper, the sampling process for lunar regolith, which involves the coupling between the microscopic lunar soil particles and macroscopic sampling mechanism, is analyzed. A discrete element model (DEM) that considers the torsion, bending and equivalent attraction between two particles is proposed for lunar soil modeling, whose microscopic parameters are calibrated based on tri-axial experimental results. Then a dynamic model for a lunar sampling manipulator is established using Lagrange formulations, and operation space control is applied to the manipulator to make the bucket move along the expected excavation trajectory. The numerical results show the whole sampling procedure, which considers the interaction between lunar soil and the bucket approaching a realistic situation. The operation space control schema is validated during the excavation simulation process, confirming the methods and model can support the performance analysis and design of a sampling mechanism for lunar explorations.
Combustion stability characteristics in a small-scale combustor with seven liquid-liquid bi-swirl coaxial injectors were studied experimentally. Liquid oxygen and kerosene (Jet A-1) were burned in a fuel-rich combustor simulating a liquid rocket engine gas generator. While changing mixture ratios between 0.286 and 0.370, static pressure, temperature, and dynamic pressure data in the propellant manifolds and combustion chamber were acquired. In addition, chamber pressures were varied between 47.9 bar and 69.0 bar, which covered the sub- and supercritical pressures of oxygen. When the chamber pressure was above the critical pressure of oxygen, dominant pressure waves were not encountered. However, when the chamber pressure was below the critical pressure of oxygen, low-frequency pressure oscillations were found to develop in the manifolds and combustion chamber. Additionally, the amplitude of such low-frequency pressure oscillations increased as the pressure drop across the fuel-side injector was reduced. Accordingly, the effects of chamber pressure and pressure drop across the injectors must be carefully considered when designing a swirl coaxial injector operating in fuel-rich conditions.
Yaw and roll damping measurements of a flapping-wing aircraft during hover are taken with a load cell. Yaw damping is also estimated by analyzing the vibration of the suspended flapping-wing aircraft. The damping values obtained using the two methods increase with the increase of angular frequencies of yaw and rolling motions. They are also calculated using quasi-steady analysis. Furthermore, yaw damping is also estimated using the equation proposed by Hedrick et al. for flying animals. When the angular frequencies of yawing and rolling motions are smaller than 10% of the frequency of flapping motion, the theoretical values from the quasi-steady analysis and the equation of Hedrick et al. agree well with the experimental values.
Flight vehicle high-speed spin movement has caused difficulties in the application of the strap-down inertial navigation system due to gyroscope performance limits. One method for designing a low-cost untwisting spin platform used for high-speed spin flight vehicle is proposed. A permanent magnet synchronous motor (PMSM) is selected as the drive motor. The platform and PMSM rotor are directly connected to reduce the influence of the gear clearance on inertial measurement unit measurement accuracy. Signal transmission between the spin flight vehicle and micro-electro-mechanical system (MEMS) gyroscope is carried out by a slip ring. The PMSM is controlled by a speed loop and current loop without angle loop, which is able to achieve fast tracking of flight vehicle spin movement and reduce the MEMS gyroscope output noise influence on platform performance. The demand on gyroscope performance is also decreased. The design method is verified experimentally and results show that the method can not only effectively isolate the inertial measurement unit from the spin movement of the flight vehicle, but also decrease the attitude angle error.
This paper discusses algorithms for the self-separation of aircraft operating in a high-density air corridor. An air corridor is a tube or band-shaped piece of airspace that connects congested airports, high-demand city areas, etc. Aircraft in the corridor all fly in the same direction, and only aircraft capable of self-separation may operate in the corridor. An appropriate self-separation algorithm is indispensable for realizing high traffic throughput while maintaining safety. In this paper, we augment a previously developed basic self-separation function with a new algorithm that determines heading changes based on the relative speed of other traffic. The basic self-separation function uses the relative lateral positions of other aircraft to determine heading changes for conflict avoidance assuming that all aircraft intend to fly along the corridor. Numerical traffic simulations show that the new algorithm, based on relative speed, leads to the formation of groups of aircraft with similar speed. It is clarified that the introduction of a simple common rule concerning turn direction achieves a drastic improvement in the degree of control while maintaining safety. It is also found that the control amount is equalized regardless of the flight speed and its variability.
An approach for the aerodynamic optimization design of elastic configurations is implemented and tested. Aeroelastic analysis was carried out by combining an Euler equations solver and finite-element structural solver. Two important techniques used in high-fidelity aerostructural design optimization are discussed: the grid deformation method and finite-element mesh (FEM) update. An improved grid deformation methodology based on transfinite interpolation (TFI) and the radial basis function (RBF) method is presented. It adapts to complex configurations very well. The technique to update the FEM is based on a bilinear interpolation method and RBF method, and it adapts to any grid of finite-element model. The discrete adjoint method is used to get the gradient of the objective function with respect to design variables. Optimizations of a wing and a more realistic wing-body configuration are done to demonstrate the effectiveness of the proposed approach. Results show that the lift-to-drag ratio can be improved with constraints through optimization, which indicates that the present methodology can be successfully applied to design optimization of jig shapes of aircraft.
This paper proposes a parallel model predictive control (MPC) scheme for planning conflict-free trajectories for multiple aircraft, in which each aircraft's computer synchronously solves mixed-integer quadratically constrained quadratic programming (MIQCQP) problems. The main contribution of this paper is the formulation of compatibility constraints for the separation of aircraft, which guarantees recursive feasibility and enables synchronous calculations. Moreover, the constraints on the velocity and acceleration, which are often overly simplified in existing studies, are tightly formulated in the framework of mixed-integer linear constraints. Through numerical simulations, the effectiveness of the scheme is confirmed in terms of the scalability, the recursive feasibility, and the validity of the trajectories.