Geometric Optimization Design System Incorporating Hybrid GRECO-WM Scheme and Genetic Algorithm

This article seeks to outline an integrated and practical geometric optimization design system (GODS) incorporating hybrid graphical electromagnetic computing-wedge modeling (GRECO-WM) scheme and the genetic algorithm (GA) for calculating the radar cross section (RCS) and optimizing the geometric parameters of a large and complex target respectively. A new wedge modeling (WM) scheme is presented for calculating the high-frequency RCS of wedge with only one visible facet based on the method of equivalent currents (MEC). The applications of GODS to 2D cross-section and 3D surface are respectively implemented by choosing an average of monostatic RCS values corresponding to a series of incident angles over a frequency band as the optimum objective function. And the results demonstrate that the RCS can be effectively and conveniently reduced by the GODS presented in this article.     

基于产品三维模型的工艺几何特征快速建模方法

开展基于产品三维模型的工艺几何特征快速建模的研究,深入分析工艺几何特征建模所依据的各个要素,研究依据这些要素进行快速建模的算法流程并开发实现,从而实现工艺几何特征的快速建模.     

基于系统集成的HLA协同仿真系统的研究与实现

HLA以其优越的互操作能力和可重用性成为开发大规模协同仿真系统先进的框架标准,但是它本身并没有提供具体的联邦开发规范。在总结传统HLA仿真系统开发经验的基础上,以集成作为构建仿真联邦的出发点,将集成的要求贯穿于联邦开发的各个阶段,并制定为相应的开发规范,从而形成了基于系统集成的HAL协同仿真系统开发方法。使用这种开发方法简化了联邦及成员开发的过程,降低了系统的实现难度．提高系统的开发效率。     

云的建模与渲染技术

云的建模和渲染技术对仿真系统的研究有着重要的理论和现实意义.该文利用粒子系统,结合了云的运动规律和光照规律对其进行建模.并对其运动模型、光照模型以及相函数都进行了简化.渲染时考虑了风速、光源等因素,提出两阶段算法来渲染云.试验结果表明,该文采用的运动模型,光照模型和渲染方法有较好的真实感和良好的实时性.     

MEMS惯性器件误差建模和补偿方法研究综述

针对MEMS惯性器件的特点,结合国内外相关文献资料,讨论了MEMS陀螺、加速度计这两类惯性器件的误差建模和误差补偿方法,文中将其误差分静态、动态和随机三类,详细地分析了各自的误差模型、参数标定方法和误差补偿方法,重点讨论陀螺随机误差建模及补偿技术,供广大研究人员参考。     

直升机复合材料桨叶铺层三维几何建模方法

针对直升机复合材料桨叶铺层几何建模过程中存在的效率低、工作繁琐重复等问题,提出了一种桨叶铺层三维几何建模方法。首先系统归纳了典型的桨叶铺层类型,提出了一种面向复合材料铺层几何建模的铺层信息参数化表达方案,并通过一个智能向导引导设计人员对各铺层进行定义和描述,在此基础上由软件算法自动生成桨叶铺层设计表格;根据桨叶理论外形和桨叶铺层设计表格,通过铺层区域裁剪复制和分片逐次等距方法构造桨叶当前铺层几何模型,并实现整个桨叶铺层几何模型的自动生成。通过实例验证表明,该方法能够快速、高效地实现复合材料桨叶铺层的三维几何建模。     

一种BT.656到XGA视频格式转换结构的FPGA实现

本文简化了常用的BT.656接口复合视频信号向1024×768的XGA视频信号转换的结构,在matlab中对该结构的核心转换模块进行了算法建模和仿真。在此基础上用HDL描述语言描述了整个转换结构的功能模型,并用matlab生成视频数据文件供modelsim工具作为输入,仿真后输出图像数据经matlab处理显示结果正确。最后在FPGA验证板上对整个视频格式转换模块进行了原型验证,输出视频信号清晰地显示在显示器上。     

不同外形建模方法对机翼气动特性的影响

飞机设计和制造过程中外形建模方法对飞机气动特性有较大影响。针对一种大型商用飞机机翼外形方案,基于样条曲线曲面理论,以内外翼整体或分段造型、调整曲面特征截面数量等不同方法进行三维外形建模,同时借助CFD数值计算得出巡航状态下各外形的气动参数,对比分析几种建模方法对机翼外形和气动特性的影响,并总结出一些关于飞机机翼外形建模的基本原则,对飞机设计和制造工程有一定参考价值。     

Performance of GPS-based accelerometry: A simulation experiment

Recent studies have shown that with the availability of high-quality CHAMP and GRACE gravity field models, it is feasible to determine accurate non-gravitational accelerations for low Earth orbiting satellites indirectly from precise GPS satellite-to-satellite observations. Possible applications of this so-called GPS-based accelerometry approach consist of accelerometer calibration and atmospheric density and wind computations. With the growing number of high-quality space-borne GPS receivers, this method could be applied to a large range of satellites. In this paper an extensive simulation study has been carried out, based on real accelerometer data from the GRACE mission, in order to determine the optimal processing strategy and the resulting accuracy of the estimated non-gravitational accelerations. It is shown that the optimal processing strategy consists of a piecewise linear parameterization of the estimated empirical accelerations, together with short 6-h orbit arcs. The GPS-based accelerometry approach makes use of triple-differenced GPS observations and the impact of considering the correlated observation noise was found to be marginal in the presence of other error sources such as GPS ephemeris errors. Using a priori non-gravitational force models improves the recovery of low temporal resolution accelerations, except during huge geomagnetic storms. With this strategy, non-gravitational accelerations can be recovered during high solar activity with an accuracy of better than 10% of the total signal in along-track direction and around 25–40% in cross-track direction, at time resolutions of around 8–20 min. During solar minimum conditions, the relative recovery error will increase to approximately 50% in along-track direction and around 60–70% in cross-track direction, due to the reduced atmospheric drag signal. Unfortunately, GPS-based accelerometry is hardly sensitive in the radial direction.     

面向对象的虚拟组织集成建模方法

提出了一种适应虚拟组织业务过程动态变化的虚拟组织集成建模方法(VOIM,Virtual Organization Integrated modeling),该方法集标准化面向对象的建模语言(UML,Unified Modeling Language)、功能建模集成化定义方法(IDEF0,Integration Definition for Function Modeling)和事件驱动过程链(EPC,Event-driven Process Chain)为一体,以弥补单一方法的不足,适合复杂系统特别是虚拟组织的建模,其中:IDEF0对虚拟组织的功能建模,EPC对功能视图进行细化,UML通过实体映射关系把虚拟组织模型的各个视图有机结合起来,有利于实现系统的模块化和模型的重用;同时对建模过程中UML到EPC之间的转换方法进行了研究.最后对模型进行了形式化描述,从而使VOIM具备严格定义的抽象语法和语义,为模型的验证和仿真提供了良好的基础.