基于块体离散元法的多面体接触重叠算法

近年来随着非连续介质力学方法的发展,离散元法成为了颗粒材料的物理力学特性研究的重要工具。而对于任意形状复杂块体,精确的接触检测算法一直是离散元法的难题之一。本文基于几何对偶理论,在耦合模拟器CoSim (Coupling Simulator)的块体离散元框架下开发了多面体接触重叠算法。该算法融合了GJK (Gilbert-Johnson-Keerthi)和快速凸包等算法,能够准确计算重叠多面体,进而从接触重叠体中提取接触点、法线方向、接触面积和嵌入深度等接触特性。通过颗粒碰撞测试和砌体结构破坏试验,验证了该算法的准确性和适用性,能够解决多面体的接触问题。     

星载测量通信系统模拟器设计与实现

为了在地面对星载测量通信系统之间互联互通性能进行测试评估,设计了一种可替代星载测量通信系统的地面模拟器,该模拟器由收发信机,时频单元,信道仿真器以及管理控制计算机构成,收发信机采用双FPGA架构设计,支持星间信号的收发处理,在功能性能指标方面与星载设备具有良好的一致性,信道仿真器能够实现信号传输延时、多普勒以及衰落特性的实时仿真,可显著增强试验场景的真实性以及评估结论的可信性。互联互通试验过程表明,该模拟器功能齐全、性能可靠、操控简单并且易于搬运,试验结果有效验证了星间互联互通方案的可行性。     

A Virtual Numerical Simulator for Aeration Effects in Lake Eutrophication

In this paper, the eutrophication process in reservoirs is briefly presented, then one of the best remedial actions against it, i.e. aeration, is developed. Multiphase flows are then described to show the complexity of the process and related modeling issues. A first order approximation is then suggested through one-phase flow analysis based on the conventional Navier-Stokes equations to simulate virtually aeration effects in natural reservoirs or lakes by prescribing appropriate internal conditions for velocity to simulate air injection. Though the flow features three-dimensional aspects with variable density, only two-dimensional incompressible fluid flow configurations are considered in this paper to demonstrate the feasibility of the methodology developed. Numerical experiments are then run for scenario analysis. Though the results are somewhat qualitative, they are encouraging and with some kind of validation and calibration a cheap alternative can be offered for studying the aeration process.     

飞行模拟转台非线性干扰观测器反步滑模控制器设计

本文针对考虑不确定性的飞行模拟转台伺服系统,提出了一种基于非线性干扰观测器的反步全局滑模补偿控制方法。该方法采用反步控制方法设计转速期望虚拟控制,然后利用非线性干扰观测器观测系统不确定干扰,进而对引入非线性干扰观测器的系统设计自适应全局滑模控制器,实现了飞行模拟转台伺服系统期望转角信号的鲁棒跟踪控制,仿真结果表明,该方法控制效果良好,具有很好的工程应用价值。     

基于IODELAY原语SAR载荷模拟器延迟单元设计

针对星载合成孔径雷达中数传分系统接收数据时序拉偏测试需求,本文提出一种基于FPGA原语的SAR载荷模拟器延时单元设计与实现。该延迟单元采用IODELAY原语,通过时序约束实现正反向时钟拉偏功能。仿真与试验结果表明,该延迟单元时序调整范围可达-6ns至6ns,步进1ns,系统运行稳定,满足设计要求。     

一种矢量水听器基阵模拟器的设计

矢量水听器的每个阵元同时测量声场中声矢量和质点振速的3个分量,相对于声压水听器阵来说,矢量阵获取声场中更多的信息。利用矢量阵所获得速度场的信息可以去除目标方位估计中的 180°模糊。模拟器可以模拟实际海洋环境中目标的辐射特性和噪声特性,应用模拟器可以有效地缩短声纳的研制周期。本文提出一种矢量水听器基阵模拟器的设计方案,该方案解决了矢量阵中宽带信号的90°移相问题、时延精确控制问题和宽带噪声的谱状控制问题。     

Analog simulation of a simple system with state-dependent diffusion

We have constructed an electronic simulator of a simple bistable system driven by noise, whose intensity is determined by the instantaneous value of the coordinate. We observe that the most probable state of the system can be reversed by altering the noise intensity only in the neighborhood of the barrier, an effect pointed out by Landauer many years ago in the context of discussions on entropy-related stability criteria for nonequilibrium systems. We compare detailed measurements on the system with the recent white noise calculations of Landauer and van Kampen. The system also has interesting possibilities for tests of contemporary colored noise theory which we illustrate with an example.