MATLAB在运用系统建模处理南海气象数据过程中应用

介绍了MATLAB语言特点和系统建模方法的基本理论.根据南海气象数据的实际建模处理过程,给出了建模的详细步骤及其MATLAB实现过程以及MATLABTM的主要实现程序.试验讨论和结果表明利用MATLAB语言可以方便地对南海气象数据用系统建模方法进行建模和处理,MATLAB在运用系统建模法处理南海气象数据方面具有明显的优越性.     

我国新一代VLBI数字基带转换器研制进展

数字化是目前设备研制发展的趋势,介绍了中国科学院上海天文台利用超大规模集成电路结合软件无线电技术,自主研发的我国新一代VLBI数字基带转换器(Chinese Data Acquisition System,简称CDAS).文中描述了设备的工作原理及其组成,并以VLBI观测实验数据证明其可行性.与原有的模拟设备(Anal...     

Experimental and numerical study on vortex-induced motions of a deep-draft semi-submersible

An experimental study on vortex-induced motions (VIM) of a deep-draft semi-submersible (DDS) was carried out in a towing tank, with the aim to investigate the VIM effects on the overall hydrodynamics of the structure. In order to study the fluid physics associated with VIM of the DDS, a comprehensive numerical simulation was conducted to examine the characteristics of vortex shedding processes and their interactions due to multiple cylindrical columns. The experimental measurements were obtained for horizontal plane motions including transverse, in-line and yaw motions as well as drag and lift forces on the structure. Spectral analysis was further carried out based on the recorded force time history. These data were subsequently used to validate the numerical model. Detailed numerical results on the vortex flow characteristics revealed that during the “lock-in”, the vortex shedding processes of the upstream columns enhance the vortex shedding processes of the downstream columns leading to the rapid increase of the magnitude of VIM. In addition to the experimental measurements, for the two uniform flow incidences (0° and 45°) investigated, comprehensive numerical data of the parametric study on the VIM characteristics at a wide range of current strength will also serve as quality benchmarks for future study and provide guidance for practical design.     

基于AD9956的任意频率合成器研制

为满足精密时间测量和高性能星载原子钟等国家重要研究课题的实验应用需求,研制了主要由AD9956芯片和8位高性能单片机构成的一种DDS(直接数字合成)任意频率合成器。在分析DDS的基本原理和特点的基础上,从硬、软件等方面较为详细地介绍了该频率合成器的设计,对同时完成的专用于控制该合成器工作的计算机应用软件也作了介绍。实际使用结果表明:研制的合成器符合实验使用要求,并对促进课题的研究完成发挥了积极作用。     

基于GIS技术的城市房地产开发决策支持系统

主要阐述建立城市房地产开发决策支持系统的重要意义和目标原则，探讨如何进行城市房地产开发决策支持系统的GIS数据库设计，同时给出基于组件GIS的系统技术框架和决策支持系统实现过程模型。     

应用于数字下变频中CORDIC算法的FPGA实现

正余弦信号在GNSS接收终端的数字下变频中有着重要的应用,CORDIC算法是实现正余弦信号的最重要方法。立足于DDS与CORDIC算法的基本原理,针对CORDIC算法实现主要存在的3个问题,结合变象限法、流水线技术及相幅量化数据格式,在FPGA上通过实现CORDIC算法可在一个时钟周期内计算出正余弦信号幅值。仿真结果表明：与传统CORDIC算法实现相比,本文实现的正余弦信号精度高且速度快,并能满足GNSS接收终端数字下变频对正余弦信号的需求。     

相位量化误差对导航模拟信号伪距生成精度的影响分析

导航信号模拟源器是接收机性能验证的重要技术手段,目前的研究多关注于高动态场景实现和伪距误差分析,对于静态伪距和恒定多普勒等高精度测量场景中的伪距精度少有分析。本文针对高精度测试场景,分析了相位量化误差的产生原因,推导了由此引起的伪距误差公式并给出了仿真验证。分析和仿真结果表明：相位累加字量化误差影响伪距稳定度。进位相位截断误差引起的相位抖动影响伪距零值测量结果,两种误差均不可忽略。为高精度卫星导航信号模拟器的设计提供了理论依据。     

A hybrid optimization approach for efficient calibration of computationally intensive hydrological models

ABSTRACT

The calibration of hydrological models is formulated as a blackbox optimization problem where the only information available is the objective function value. Distributed hydrological models are generally computationally intensive, and their calibration may require several hours or days which can be an issue for many operational contexts. Different optimization algorithms have been developed over the years and exhibit different strengths when applied to the calibration of computationally intensive hydrological models. This paper shows how the dynamically dimensioned search (DDS) and the mesh adaptive direct search (MADS) algorithms can be combined to significantly reduce the computational time of calibrating distributed hydrological models while ensuring robustness and stability regarding the final objective function values. Five transitional features are described to adequately merge both algorithms. The hybrid approach is applied to the distributed and computationally intensive HYDROTEL model on three different river basins located in Québec (Canada).     

基于DDS和FPGA的数字函数信号发生器设计和实现

采用现场可编程逻辑器件（FPGA）,辅以必要的模拟电路,设计实现了一个基于直接数字式频率合成（DDS）技术的数字函数信号发生器.主要模块有键盘、波形表生成、频率控制、数模转换及幅度控制、显示控制和后级处理.其中键盘用来设定频率和幅度的大小以及波形的选择;FPGA用来改变DDS频率控制字,并由FPGA来实现波形表生成和频率控制,即DDS算法实现模块;将FPGA产生的波形数据送入到AD7520进行D/A转换.幅度控制由DAC0832内部的电阻分压网络实现;后级采用低通滤波器和OCL电路来提高输出波形质量并增强其带负载能力.     

计算机控制的高精度频率源设计

通过对通用串行总线(USB)协议和直接数字合成(DDS)技术的研究和分析,设计实现了一种采用DDS技术的高精度频率源,并且能通过计算机应用软件对其进行实时控制.给出了该设计的硬件结构与部分关键程序的结构,同时给出了对该设计性能参数的测量结果,并对其进行了简单分析和探讨.