Trimming aircraft on the ground is an absolutely necessary for flight simulators. In order to carry out this task, the aircraft-runway dynamic model is analyzed, and then an elite re-optimized hybrid genetic algorithm for trimming the model is designed, which combines the merits of a genetic algorithm and pattern search. It does not only avoid being trapped by a local optimum, but also improves the precision of results and saves on the time for trimming. Because this trim method requires only in-out information of the dynamic model, it is a universal tool and can be used on different trim works of different simulated aircraft. Its efficiency is then validated in a flight simulator, which reveals its engineering significance.
This paper addresses the problem of how to control spacecraft formation with coupled translational and rotational dynamics with optimized fuel usage using a single body fixed thruster and reaction wheels. The orientation of the thrust vector is constrained by the attitude and angular velocity. In particular, the star camera cannot point at the sun during formation maneuvering. The formation coupled control, which is a difficult problem with nonlinear and nonconvex attitude dynamics, is posed as a nonlinear optimal control problem and solved via direct transcription using the Gauss pseudospectral method. Examples demonstrate application of the proposed approach with simulated trajectory optimization of a dual-spacecraft formation initialization and a three-spacecraft reconfiguration problem.
Satellite attitude is usually controlled by plume exhaust from thrusters into the vacuum of space. To study the plume effects in the highly rarefied region, the Direct Simulation Monte Carlo (DSMC) method is usually used, because the plume flow field contains the entire range of flow regime from the near-continuum near the nozzle exit through the transitional state to free molecular state at the far field region from the nozzle. The purpose of this study is to investigate the behavior of a small monopropellant thruster plume in the vacuum region numerically by using the DSMC method. To obtain more accurate results, the preconditioned Navier-Stokes algorithm is introduced to calculate continuum flow fields inside the thruster to predict nozzle exit properties, which are used for inlet conditions of DSMC method. As a result, the plume characteristics in the highly rarefied flow, such as strong nonequilibrium near nozzle exit, large back flow region, etc., are investigated.
Liquid propellant sloshing, which induces perturbations to dynamic behavior of spacecraft, is a serious problem. This paper proposes an approach based on equivalent mechanics theory and Computational Fluid Dynamics (CFD) technology to estimate the dynamic influence of propellant sloshing on spacecraft. A mechanical model was built by CFD technique and packed as a “sloshing” block utilized in the spacecraft Guidance Navigation and Control (GNC) simulation loop. The block takes the motion characteristics of the spacecraft as inputs and outputs perturbative force and torques induced by propellant sloshing. It is more convenient to utilize in analysis of the coupling effect between propellant sloshing dynamics and spacecraft GNC than CFD packages directly. A validation case is taken to validate the accuracy and the superiority of the approach. The deducing process is applied to practical cases, and the simulation results are presented to demonstrate the proposed approach is efficient in identifying the problems induced by sloshing and evaluating effectiveness of several typical schemes for suppressing sloshing.
Today Global Navigation Satellite Systems (GNSS) are widely used for determining position. Within the city environment, however, in which there are many tall buildings, GNSS signals are frequently interrupted, making it difficult for users to obtain information on their exact position. This paper analyzed the availability and positioning performance of a GPS augmented system within the Seoul urban area using the Japanese QZSS (Quasi-Zenith Satellite System) and a geostationary satellite. A 3-dimensional reproduction of Seoul that was based on the 3D GIS (Geographic Information System) Digital Map and a satellite tracking algorithm using Ray-Triangle Intersection algorithm were discussed. A satellite tracking algorithm was verified through filed testing and the QZSS orbit simulator was realized using Keplerian parameter. DOP (Dilution of Precision) and availability in the urban area of Seoul were analyzed using a GPS/QZSS/geostationary satellite separately and simultaneously.
This paper presents the experimental results of the effect of Higher Harmonic Control (HHC) and Active Flap on the Blade/Vortex Interaction (BVI) noise. Wind tunnel tests were performed with a 1-bladed rotor system to evaluate the simplified BVI phenomenon avoiding the complicated aerodynamic interference which is characteristically and inevitably caused by a multi-bladed rotor. Another merit to use this 1-bladed rotor system is that the several objective active techniques can be evaluated under the same condition installed in the same rotor system. The effects of the active techniques on the BVI noise reduction were evaluated comprehensively by the sound pressure, the blade/vortex miss distance obtained by Laser light Sheet (LLS), the blade surface pressure distribution and the tip vortex structure by Particle Image Velocimetry (PIV). The correlation among these quantities to describe the effect of the active techniques on the BVI conditions is well obtained. The experiments show that the blade/vortex miss distance is more dominant for BVI noise than the other two BVI governing factors, such as blade lift and vortex strength at the moment of BVI.
Much research is in progress to develop a next-generation rotor system for various aircrafts, including unmanned aerial vehicles (UAV) with multi-rotor systems, such as coaxial and tandem rotors. Development and design of such systems requires accurate estimation of rotor performance. The most serious problem encountered during analysis is wake prediction, because wake-wake and wake-rotor interactions make the problem very complex. This study analyzes the aerodynamic characteristics based on the free-wake method, which is both efficient and effective for predicting wake. This code is modified to include the effect of complex planforms as well as thickness by using an unsteady 3D panel method. A time-marching free-wake model is implemented based on the source-doublet panel method that assigns panels to the surface and analyzes them. The numerical wake instability, the most critical problem for analysis, is resolved by adopting slow start-up and by including viscous effects. Also, the instability due to wake interference in tandem rotor analysis is resolved by configuring the initial shapes of the multi-rotor wake as that of a single rotor wake trajectory. The developed code is verified by comparing with previous experimental data for coaxial and tandem rotors.
A comprehensive design method for a LOX/Liquid-Methane (L-CH4) rocket engine combustor with a coaxial injector and the preliminary design of the regenerative cooling combustor with 100-kN thrust in vacuum at a combustion pressure of a 3.43 MPa are presented. Reasonable dimensions for the combustor that satisfy the targeted C* efficiency of more than 98% and combustion stability are obtained.