The non-rigid airship is a low-rigidity and inflatable aircraft which has obvious fluid-structure interaction characteristics. In this paper, the unsteady explicit dynamic fluid-structure interaction analysis framework of non-rigid airship is constructed based on the parametric section (PARSEC) method, the radial basis function (RBF), and the Delaunay mapping method. The reliability and accuracy of the numerical method are verified by the cases of plate impact and the aeroelasticity of NACA0014 wing. The calculation framework is also suitable for unsteady bidirectional fluid-structure interaction analysis of thin-envelope aerostats such as high-altitude balloon. Finally, the time domain and frequency domain responses of one non-rigid airship are simulated by the above framework. The research results show that there is an approximately linear relationship between the dominant frequency of vibration and the pressure difference of the airship.
Aimed at the problem of avoidance strategy of formation satellites when facing the threat of space debris, a non-dominated sorting genetic algorithm (NSGA-II) is improved and used to code satellites. Besides, the improved differential evolution algorithm is used as the orbital generation model, while Pareto dominance is used to select the optimal solution set. By introducing maneuver consumption, collision probability, work efficiency, and other indicators of formation satellites, the avoidance orbits of satellite are screened to ensure that all the indicators of formation satellites are taken into account. Taking the 3-satellite formation of ocean reconnaissance satellite as an example, the phase adjustment, probability calculation, and horizontal dilution of precision (HDOP) calculation models are introduced. The optimal solution of avoiding orbits is obtained by utilzing the multi-objective optimization algorithm. The simulation results show that this method can formulate a more targeted formation satellite avoidance strategy with different objectives.
The transonic flow around a square cylinder at Ma= 0.71 and Re= 4×105 has been studied by using the scale-adaptive simulation (SAS) method, and the characteristics of separated shear layer and wake have been analyzed in depth. To validate the SAS approach, the SAS results are compared with the existing numerical and experimental results. In the present transonic flow, the convective Mach number inside the shear layer is about 0.6. This indicates that the initial evolution of the separated shear layer is dominated by Kelvin-Helmholtz instability, and the roller spanwise eddies in the initial stage of the shear layer can be observed. In the regions near the shear layer and the wake, the doubling frequencies can be obtained indicative of the harmonic phenomenon inside the separated shear layer, which is closely related to the obvious merging of the vortices in the shear layer. Proper orthogonal decomposition of the pressure field shows that the transonic flow field of square cylinder is dominated by the antisymmetric mode, which is associated with the vortex shedding in the wake and the propagation of compression waves induced by the shear layer.
Taking the compressor impeller as the research object, and based on the octagonal truss lattice structure, a novel lightweight lattice compressor impeller is designed, and its machinability is verified by using a SLM280 3D printer. In order to understand its 3D printing performance, the 3D printing process of the lattice impeller is simulated based on the finite element method (FEM). Based on the feasibility of using the numerical method to study the 3D printing process, the printing process of the lattice impeller at different power values is analyzed and compared with the solid compressor impeller under the same working condition. The results show that the layer deformation of the lattice impeller and the solid impeller is a process that increases layer by layer. Under the 7 working conditions studied in this paper, the maximum residual deformation and residual stress of the lattice impeller after printing are less than those of the solid impeller. The maximum residual deformation of the lattice impeller can be 20.19% smaller than that of the solid impeller, and the maximum residual stress can be 10.69% smaller than that of the solid impeller. This means that the lattice impeller is not only lighter, but also has a better printing performance than the solid impeller.
A fault detection method of combined residual is proposed to effectively master the health state of the reaction wheels of in-orbit satellite according to the telemetry data. Based on the characteristics of in-orbit telemetry data, in the proposed method, the XGBoost regression model is used to predict the rotation speed and generate residual with available data of the closed-loop controlled reaction wheel. The sensitivity of viscous friction coefficient to the sudden change of friction torque is also combined with the method. In addition, the fault detection method is verified in view of the incomplete telemetry data in orbit. The result shows that the proposed method has an excellent detection effect on common reaction wheel faults. The combined residual fault detection method does not rely on fault samples and has low requirements for samples, so it has a certain application value in practical fault detection system.
Taking stratospheric airship as the research object, considering the transmission characteristics of the airship surface and the absorption rate and emissivity of the inner filling gas to radiation, the thermodynamic equations of the airship surface skin and inner filling gas are deduced. The thermodynamic simulation model of the airship considering the transmittance of the skin is established by using the sub-method, and the thermodynamic characteristics of airship under typical skin materials are analyzed and compared. Through airship shape modeling and surface discretization, the transient thermal characteristics of each unit and internal gas are calculated, and the influence of the mesh division and time step in the simulation model on the calculation results is analyzed. The data verifies the reliability and validity of the established model and its solution method, and the thermal characteristics and the changing laws of airships with different characteristics of skin materials are analyzed and compared.
High-resolution simulation of shear layer oscillation induced by ridge ice in post-stall condition is conducted via the improved delayed detached-eddy simulation (IDDES) method. The flow-field evolution characteristics of large scale separation in high Reynolds number condition are described. It is shown that the ridge ice and trailing edge of the lower surface induce the development of shear flow at the same time. The wall is not reattached by the shear layer induced by ridge ice, and the “up-wash” flow from the lower surface is interacted with the shear layer, which lead to the formation of large-scale coherent structures. Combined with the spectral analysis, the pressure pulsation located in the shear layer is characterized by two typical frequencies, which are associated with Kelvin-Helmholtz instability and appear as the vortex pairing and shedding. Based on the proper orthogonal decomposition, the dominant mode of pressure pulsation between shear layers is extracted as large-scale coherent structures. The same peak value is shown in power density spectrum of dominant mode temporal coefficient and lift coefficient, which indicates that the large-scale coherent structure is connected with lift fluctuation.
In order to explore the influencing factors of the effectiveness and stability for stall recovery and its flow mechanism when the antisurge valve is opened quickly, the dynamic stall recovery processes are simulated and the recovery processes at different discharging speeds are emphatically compared. Two numerical simulation methods, i.e., the distributed speed-changeable MG (Moore-Greitzer) model and the RANS (Reynolds Averaged Navier-Stokes) equation are used. The performance curves predicated by the two models agree well. The results of RANS show that the flow field changes are essentially the same when the valve is opened at different speeds. The disturbance, affected by the high-speed air flow generated at the inlet, moves downstream and finally reaches the leading edge of the rotor, whose scale will be further reduced with the impact of axial high-speed flow until completely dissipated. A comparison of different valve opening speeds indicates that the faster the valve is opened, the stronger the high-speed air flow generated at the inlet, shortening the stall recovery time. The greater the disturbance weakening degree, the faster the circumferential propagation speed of the disturbance, and the closer to the rotor speed. In the process of valve opening, the air flow fluctuation is more intense, and more energy is lost.
In view of the issue that surface catalysis has a significant influence on aerodynamic heating of hypersonic vehicle heatshield and is difficult to accurately predict, a four-step surface heterogeneous catalytic model including physisorption, chemisorption, Eley-Rideal (ER) recombination, and Langmuir-Hinshelwood (LH) recombination was established by combining theoretical analysis and numerical simulation. Based on the model, the nonequilibrium flow and the aerodynamic heat around a two-dimensional cylinder were simulated. The influence of the fraction of occupied physisorption and chemisorption sites on the catalysis rate and the aerodynamic heat was analyzed. The results show that the established model can improve the prediction accuracy of the aerodynamic heat. The surface adsorption has a nonlinear influence on the aerodynamic heat due to the competing and promoting between different reaction pathways. Based on the real physicochemical process, the model can reflect the catalytic properties of different materials and further provides theoretical support for the lightweight and low redundancy design of the thermal protection system.
Aimed at the problem of weak coordination and low balance of distributed resources under multiple parallel deicing tasks, a cooperative control method of aircraft ground deicing resources based on multi-agent negotiation was proposed, which combined airport deicing resource allocation and space-time distribution. A framework for collaborative operation of multi-agent deicing resources was established, and a resource optimization method for the bidding mechanism of a global collaborative consortium was designed to improve the overall task balance. Based on the operating plan, an autonomous multi-agent resource collaborative optimization model was constructed. The model predictive control method was applied to generate a collaborative control strategy, and the feasibility was verified in actual scenarios. The results demonstrate that the resource coordination and anti-interference ability of the proposed method are significantly enhanced while meeting the real-time requirements. Compared with the results obtained by other methods, the average takeoff tolerance is 4.89 min, increased by 1.015 min, and the average utilization rate is increased by 15.28%, which can ensure the safety and synergy of deicing resources.
