Lightning Performance of Copper-Mesh Clad Composite Panels: Test and Simulation

According to simulation lightning experiments and eddy current analysis results, a three-dimensional finite element model of composite laminated plates with shield is established. By applying electric-thermal boundary and the coupling relationship between them, the lightning strike damage results under the protection of shield are realistically simulated with the commercial finite element analysis software, ABAQUS. Considering the coupling effect of heat, electricity, and force during lightning strike, the load distribution field of copper mesh and carbon fiber panel with lightning current inducted is analyzed. Comparing the thermal stress distribution of the specimen surface under various current loads, it is shown that the stress of carbon fiber panel is significantly lower than the one of the copper screen when the specimen structure suffers heavy current, since the copper network plays a role of endergonic protection. Simulation data are consistent with the test results, thus the method can be used for other similar research

Parametric geometry modeling of flying wing UAV configuration integrated with intake and exhaust

Flying wing is a preferred configuration for unmanned combat air vehicle（UCAV），in which its airframe is highly integrated with intake and exhaust of propulsion system. To implement rapid geometric model of flying wing UCAV concept，a parametric geometry modeling method for flying wing UCAV configuration integrated with the intake and exhaust is proposed in this paper. Firstly，parametric models for configuration of the flying wing airframe and the intake and exhaust are established using class function/shape function. Then，the related geometry parameters between the flying wing airframe and the intake and exhaust are identified，and the correlative control rules are set to match airframe-propulsion interactions. 3D geometric models of the flying wing UCAV configuration are automatically generated by use of the parametric geometry model and CATIA API. Application examples indicate that flying wing UCAV configurations can automatically adjust its shape to match the different intake and exhaust concepts by use of the proposed method. The method can effectively improve efficiency for flying wing UCAV conceptual design

Reliability-Based Multidisciplinary Optimization for Aircraft Wing Design

Aircraft wing design typically involves multiple disciplines such as aerodynamics and structure. Multidisciplinary design optimization (MDO) has been recently used to deal with the multidisciplinary efforts in wing design. when reliability is considered, MDO for the wing design becomes much more computationally intensive. To improve the efficiency, the strategy of using Sequential Optimization and Reliability Assessment (SORA) in MDO is proposed with the application of a simplified wing design problem. The overall reliability-based MDO is decomposed into sequential cycles of deterministic MDO and reliability analysis. The reliability analysis is therefore decoupled from the MDO loop, and the number of reliability analyses is then reduced significantly. It is shown that the use of the SORA method is efficient through the demonstration of a light aircraft wing design problem

Improved Reliability-Based Optimization with Support Vector Machines and its Application in Aircraft Wing Design

A new reliability-based design optimization (RBDO) method based on support vector machines (SVM) and the Most Probable Point (MPP) is proposed in this work. SVM is used to create a surrogate model of the limit-state function at the MPP with the gradient information in the reliability analysis. This guarantees that the surrogate model not only passes through the MPP but also is tangent to the limit-state function at the MPP. Then, importance sampling (IS) is used to calculate the probability of failure based on the surrogate model. This treatment significantly improves the accuracy of reliability analysis. For RBDO, the Sequential Optimization and Reliability Assessment (SORA) is employed as well, which decouples deterministic optimization from the reliability analysis. The improved SVM-based reliability analysis is used to amend the error from linear approximation for limit-state function in SORA. A mathematical example and a simplified aircraft wing design demonstrate that the improved SVM-based reliability analysis is more accurate than FORM and needs less training points than the Monte Carlo simulation and that the proposed optimization strategy is efficient

An Improved Method for Initial Sizing of Airbreathing Hypersonic Aircraft

One essential problem in aircraft conceptual design is initial sizing in which the aircraft primary parameters such as weight, size, and thrust are estimated for given design requirements. The airbreathing hypersonic aircraft is a type of novel aircraft and has significant differences from conventional aircraft in terms of its flight speed and propulsion system. Traditional initial sizing methods are not suitable for this type of novel aircraft. This paper presents an improved initial sizing method for the conceptual design of airbreathing hypersonic aircraft. An illustrative airbreathing hypersonic aircraft is used to describe the detailed procedure of the method. The weight and size of the aircraft are estimated through the simultaneous solution of the weight equation and the volume equation. Constraint analysis is applied to determine the solution space of the thrust-to-weight ratio and the wing loading. A thrust trade is conducted to find the minimum takeoff gross weight of the aircraft. The impacts of technology parameters on the weight, size, and thrust are investigated by sensitivity analyses. The presented method is based on rational derivation. It can be expected that the initial sizing results from the method are reasonable and satisfactory for conceptual design of the airbreathing hypersonic aircraft

Sequential Reliability-Based Optimization with Support Vector Machines

Traditional reliability-based design optimization (RBDO) is either computational intensive or not accurate enough. In this work, a new RBDO method based on Support Vector Machines (SVM) is proposed. For reliability analysis, SVM is used to create a surrogate model of the limit-state function at the Most Probable Point (MPP). The uniqueness of the new method is the use of the gradient of the limit-state function at the MPP. This guarantees that the surrogate model not only passes through the MPP but also is tangent to the limit-state function at the MPP. Then Importance Sampling (IS) is used to calculate the probability of failure based on the surrogate model. This treatment significantly improves the accuracy of reliability analysis. For optimization, the Sequential Optimization and Reliability Assessment (SORA) is employed, which decouples deterministic optimization from the SVM reliability analysis. The decoupling makes RBDO more efficient. The two examples show that the new method is more accurate with a moderately increased computational cost

Annihilation Mechanism of Low-Angle Grain Boundary in Nanocrystalline Metals

Due to the high density of grain boundaries (GBs), nanocrystalline metals possess superior properties, including enhanced strength, work hardening, and fatigue resistance, in comparison to their conventional counterparts. The expectation of GB migration is critical for grain coarsening and GB annihilation in these materials, significantly affecting the polycrystalline network and mechanical behavior. Here, we perform molecular dynamics (MD) simulations on gold (Au) nanocrystals containing multiple parallelly arranged GBs, with a focus on the investigation of annihilation mechanisms of low-angle grain boundaries (LAGBs). It is observed that the shear-coupled motion of LAGBs, consisting of dislocations, gives rise to their preliminary migration with the reduced separation distance between GBs. With subsequent GB motion, the LAGBs encountered with neighboring GBs, and can be annihilated by various mechanisms, including dislocations interpenetration, dislocations interaction, or dislocations absorption, depending on the specific configuration of the neighboring GB. These findings enhance our understanding of GB interactions and shed light on the controlled fabrication of high-performance nanocrystalline metals