International Journal of Aerospace Engineering

In this paper, in order to clarify the influence of structural parameters of laminates on the modal characteristics of high-aspect-ratio wings under prestress, the CFD/CSD coupling method was used to study the modal characteristics of nonlinear structures under the influence of layering angle, layering unbalanced coefficient, and layering reference direction. The results show that the first six order modal frequencies of wing structure increase with the increase of layering angle, and the increment change of frequency increases with the increase of layering angle. The frequency results of positive and negative layering angles are basically the same, and there is no great difference. The modal frequency of airfoil structure is not very sensitive to the change of unbalanced coefficient. The modal frequencies obtained by the mixed angle layering scheme are obviously larger than those obtained by the layering scheme composed of only two angles. With the change of the reference direction of laying, the lowest frequency is generally present in the 0° reference direction and has one or two minima in each order of modal frequency. The layer reference direction angle mainly in the second quadrant is beneficial to the enhancement of modal frequency. After determining the related layer parameters, the appropriate adjustment of the layer reference direction will be beneficial to change the vibration characteristics of the wing structure.

Detecting the infrared characteristics of the contrails is a reasonable approach to tracing the rocket, and the particle properties of the contrails are the basis of the infrared analysis. The conventional numerical approach to obtaining the particle properties is a Euler/Lagrange method or a simple Euler/Euler method, difficultly obtaining more accurate results because it ignores the particle size distribution in parcels or cells. A modified Euler/Euler method is applied to simulate the contrail formation in the near field of a solid rocket motor at different altitudes, which considers the size distribution by adding the first- to second-order particle radius moments based on the simple Euler/Euler method. The simulation results show that the crystals are generated at altitudes from 10 km to 20 km and that the contrails are visible at altitudes from 10 km to 15 km, where the radii of the crystals are from 0.1 μm to 0.3 μm. The visible contrails indicate that aviation vehicles are cruising at altitudes from 10 km to 15 km, and the smaller crystals indicate that the contrails are generated by rockets, not aircraft. Our work can provide important insight for the follow-up infrared analysis of the contrails based on the obtained particle radii.

Image edge detection plays a crucial role in image analysis and recognition. However, when dealing with color images captured by unmanned aerial vehicles (UAVs), there are certain limitations, such as large operations, multiple noise sources, easy distortion, and missing information in edge detection. To address these shortcomings, this study proposes a UAV color image edge detection method based on an enhanced fireworks algorithm. In this method, the color image pixels of the UAV are represented using quaternions. The explosion amplitude formula of the fireworks is divided into two categories based on the mean value of the number of fireworks explosions. For each category, an explosion formula is proposed, and the explosion mutation operator of the fireworks algorithm is improved accordingly. By applying the proposed algorithm, the preliminary edges of a UAV color image are obtained. Additionally, a novel approach for color image edge refinement is introduced. This approach involves classifying the edge points based on their degree of attachment, which leads to the formation of the edges in a UAV color image. Experimental results demonstrate that the algorithm proposed in this study offers several advantages, including fast calculation, strong denoising capability, and high-quality edge detection.

In this paper, a network coupling mechanism is studied to couple the air sector network, airport network, and air route network into a multilayer air network model. Then, the altitude layers are divided into three: high, medium, and low, and the arrival and departure flight procedures are also considered. By defining the association between the altitude layers and the waypoints, a multilayer air network model considering the altitude layer is constructed. Then, the line graph theory is used to redefine the nodes and edges, and the network is reconstructed to obtain a new single-layer one which is easy to calculate. Finally, a case study is carried out in Chengdu control area. The results show that the proposed model is closer to the reality, and the invulnerability performance is more referential. Besides, it also reflects the impact of altitude layers on the efficiency of airspace. The results are helpful for air traffic controllers to manage airspace better and have significance for promoting air traffic safety and stability.

In this study, the effect of the axial gap on the mechanical response of a cartridge-loaded propellant grain under vibration loads is investigated. The wide strain rate range of uniaxial compression tests () on the composite modified double base (CMDB) propellant was carried out by using a universal testing machine, a hydraulic testing machine, and a split Hopkinson pressure bar system, respectively. A linear viscoelastic constitutive model of the CMDB propellant was developed by using the experimental measurements. The results show the studied CMDB propellant has a strong strain rate dependence, exhibiting an initial linear elasticity followed by a strain hardening region. The dynamic process of collision between the propellant grain and the motor case in the axial direction induced by vibration loads was simulated with the developed constitutive model by using the finite element method. The effects of the gap size between the propellant grain and the case and the vibration frequency on the mechanical response of the grain were studied. This shows that with a constant vibration frequency, the stress of the grain increases first and then decreases with increasing gap size. Moreover, the stress increases with increasing vibration loads.

To further investigate the fracture response in propellant grain, numerical methodology is proposed to cope with crack propagation simulation especially for the mixed mode condition. The numerical discrete scheme of the propellant linear viscoelastic constitutive model is proposed, which provides a key means for the simulation of crack propagation. In order to simulate the cohesive traction distribution on the new crack surface, the extrinsic Park-Paulino-Roesler (PPR) cohesive zone model (CZM) is introduced. To let the crack propagate along any direction determined, element splitting technique and its corresponding topological operations are proposed step by step. Then, computational simulation implementation process is explained in greater detail. Typical fracture problem, single edge-notched tension test (SENT) is solved to demonstrate the efficiency and accuracy of the proposed method. In addition, double edge-notched tension test (DENT) as well as plate tension test with a slant crack is conducted to show the special fracture characters in viscoelastic solid propellant, like time dependence. Computational results reveal that the method proposed can be utilized in further fracture investigation in solid propellant combined with the experimental findings.