Development and performance evaluation of tropospheric scintillation model on Ku-band satellite link over Akure,Nigeria

Existing amplitude scintillation prediction models often perform less satisfactorily when deployed outside the regions where they were formulated. This necessitates the need to evaluate the performance of scintillation models developed in one region using data data from other regions while documenting their relative errors. Due to its variation with elevation angle, frequency, other link parameters and meteorological factors, we employed three years (January 2016 to December 2018) of concurrently measured satellite radio beacons and tropospheric weather parameters to develop a location-based amplitude scintillation prediction model over the Earth-space path of Akure (7.17^oN, 5.18^oE), South-western Nigeria. The satellite beacon measurement used Tektronix Y400 NetTek Analyzer at 1 s integration time while meteorological parameters, namely; temperature, pressure and relative humidity were measured using Davis Vantage Vue weather station at 1 min integration time. Comparative study of the model’s performance with nine (9) existing scintillation prediction models indicates that the best and worst performing models, in terms of root mean square error (RMSE), are the Statistical Temperature and Refractivity (STN) and direct physical and statistical prediction (DPSP) models with values 11.48 and 51.03 respectively. Also, worst month analysis indicates that April, with respective enhancement and fade values of 0.88 and 0.90 dB for 0.01% exceedance, is the overall worst calendar month for amplitude scintillation.     

Topology optimization in lightweight design of a 3D-printed flapping-wing micro aerial vehicle

Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength. Whether the optimization results meet the actual needs mainly depends on the accuracy of the material properties and the boundary conditions, especially for a tiny Flapping-wing Micro Aerial Vehicle (FMAV) transmission system manufactured by 3D printing. In this paper, experimental and numerical computation efforts were undertaken to gain a reliable topology optimization method for the bottom of the transmission system. First, the constitutive behavior of the ultraviolet (UV) curable resin used in fabrication was evaluated. Second, a numerical computation model describing further verified via experiments. Topology optimization modeling considering nonlinear factors, e.g. contact, friction and collision, was presented, and the optimization results were verified by both dynamic simulation and experiments. Finally, detailed discussions on different load cases and constraints were presented to clarify their effect on the optimization. Our methods and results presented in this paper may shed light on the lightweight design of a FMAV.     

基于随机维纳过程的航空发动机性能衰退研究

针对发动机下发间隔预测的问题，研究了发动机性能衰退规律。基于发动机排气温度裕度（EGTM）数据，建立了随机维纳模型，并使用严酷度因子修正模型，表征不同的工作条件对发动机的影响。利用期望最大化（EM）算法结合贝叶斯定理，对模型参数求解，最终得到了基于性能衰退的发动机平均下发间隔。研究结果表明，在严酷度因子为1.2696的使用条件下，某型号航空发动机性能衰退平均下发间隔为8219循环；基于该模型预测的发动机平均下发间隔与厂商建议的下发时间之间的误差仅为1.7%。     

涡轮基组合循环发动机分布式控制系统通信网络混合拓扑结构优化方法

涡轮机组合循环(Turbine based combined cycle,TBCC)发动机控制系统通信网络拓扑结构是其分布式控制系统方案设计的重要部分,优化网络拓扑结构可提高发动机推重比和控制系统可靠性。本文基于智能优化算法提出TBCC分布式控制系统网络拓扑结构优化方法。基于图论建立TBCC几何模型和网格模型,以重量和可靠性为优化性能指标,同时考虑发动机表面高温区域以及控制节点的工作可靠性,分别采用粒子群算法和遗传算法优化星形结构中智能中央节点位置、中央节点的环形拓扑结构,获得星形-环形混合拓扑结构。仿真实例表明,基于本文方法优化所得的混合拓扑结构相较于星形集中式控制结构,系统重量降低了51.9%。     

An innovative approach for integrated airline network and aircraft family optimization

The determination of optimal aerial transport networks and their associated flight frequencies is crucial for the strategic planning of airlines, as well as for carrying out market research, to establish target markets, and for aircraft and crew rostering. In addition, optimum airplane types for the selected networks are crucial to improve revenue and to provide reduced operating costs. The present study proposes an innovative approach to determine the optimal aerial transport network simultaneously with the determination of the optimum fleet for that network, composed of three types of airplanes (network and vehicle integrated design). The network profit is maximized. The passenger’s demands between the airports are determined via a gravitational model. An embedded linear programming solution is responsible for obtaining potential optimal network configurations. The optimum fleet combination is determined from a database of candidate aircraft designs via genetic algorithm. A truly realistic airplane representation is made possible thanks to accurate surrogate models for engine and aerodynamics is adopted. An accurate engine deck encompassing a compression map and an innovative engine weight calculation besides an aerodynamical artificial neural network module enable a high degree of accuracy for the mission analysis. The proposed methodology is applied to obtain the optimum network comprised of twenty main Brazilian airports and corresponding fleet.     

最小二乘直线函数的特性分析

证明了最小二乘直线函数是一种严格的凸函数。F(a,b)=∑(y-ax_i-b)~2是一个椭圆抛物面。a=[n∑x_iy_i-∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]和b=[∑x_i^2∑y_i-∑x_i∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]仅表示极值点。a=∑x_iy_i/∑x_i和 b=[∑x_i^2∑y_i-∑x_i∑x_iy_i]/[n∑x_i^2]在某些情况下可以是极值点,但不是在每种情况下都是极值点。     

关于疲劳裂纹扩展数学模型的参数寻优

本文通过引入工程设计中的优化方法，分别对室内空气环境下铝合金（ＬＹ１２－ＣＺ）材料疲劳裂纹扩展的数学模型，以及环境条件下（３．５％ＮａＣｌ水溶液浸泡）该材料腐蚀疲劳裂纹扩展的数学模型进行了探讨。在已知标准试样在不同的环境下疲劳裂纹扩展实验ｄａｄＮｉ，ΔＫｉ的条件下，采用优化方法进行参数寻优，可方便地得到与其对应的疲劳裂纹扩展的ｄａｄＮ～ΔＫ最优数学模型     

满足约束的Gn连续过渡曲面的构造

在Erich Hartmann提出的由两基曲面线性组合构造G^n连续过渡曲面方法的基础上，针对该方法存在很难找到合适的参数变换的问题，提出了一种基于基曲面局部区域重新参数化构造G^n连续过渡曲面的方法。通过对基曲面上切触线附近区域部分曲面重新参数化，再由重新参数化局部基曲面线性组合构造G^n连续过渡曲面。这样将两基曲面间构造过渡曲面的问题转化为在重新参数化局部基曲面间构造过渡曲面。以构造G^1连续的翼身融合面为例，讨论了满足约束要求条件时G^2连续过渡面的构造方法。即先对基曲面上过渡切触线附近的局部区域进行重新参数化，后通过优化求解来确定比例因子和偏移量、平衡因子和调配因子，使过渡曲面满足前后边条线约束，最后利用线性组合来构造G^2连续的过渡面。约束过渡曲面的形状可通过改变重新参数化基曲面的大小来调整．     

基于粒子群优化算法的不完全数据的处理

不完全信息下的数据挖掘是一个困难的问题，但它在实际决策中是不可避免的。在介绍几种处理方法的基础上，提出了基于粒子群优化算法的处理方法。对适应函数进行了讨论，实例表明该方法比较有效。     

A Novel Onboard-gateway-based Mechanism to Improve TCP Performance in Aeronautical Satellite Networks

The IP-based networks on aircraft serve to support Internet services via satellites. However, in aeronautical satellite hybrid net- works,the TCP protocol performance often deteriorates due to improper decreases and slow recovery of the congestion window. This paper proposes a window size determination and notification mechanism, onboard-gateway-based mechanism (OGBM), which is based on the onboard gateway in the networks on aircraft. A cross-layer approach is adopted by the onboard gateway to obtain the satellite link bandwidth information. And then, by the gateway, through changing the receiver’s advertised window field in ACK packets, TCP sources are notified of the window size of each TCP source calculated on the ground of bandwidth delay product and flow numbers. The mechanism is able to avoid improper changes of TCP window and serve multiple users. Simulation results show that the mechanism with the fairness index close to 1 improves TCP performance in aeronautical satellite networks.