Underwater topography detection of Shuangzi Reefs with SAR images acquired in different time

Imaging mechanism of underwater topography by SAR and a underwater topography SAR detection model built on the theory of underwater topography detection with SAR image presented by Yuan Yeli are used to detect the underwater topography of Shuangzi Reefs in the Nansha Islands with three scenes of SAR images acquired in different time. Detection results of three SAR images are compared with the chart topography and the detection errors are analyzed. Underwater topography detection experiments of Shuangzi Reefs show that the detection model is practicable. The detection results indicate that SAR images acquired in different time also can be used to detect the underwater topography, and the detection results are affected by the ocean conditions in the SAR acquiring time.

ROV模糊控制导航方法

本文提出一种水下 ROV(Remotely Operated Vehicles)的模糊导航方法和基于该方法的控制器结构 .通常由于水下环境光照不足或是水质混浊 ,很难依赖摄像机准确地为 ROV导航 ,引导 ROV到达预定目标 ,尤其是工作空间存在障碍物时 ,ROV很可能发生碰撞 .文中提出的模糊控制方法 ,将 ROV在 3D空间运动的状态、局部环境信息以及导航规划数据表示为多重模糊条件 ,然后结合 ROV的导航特点 ,建立了一个三级模糊控制器 ,该控制器使用同一种控制模式完成 ROV有障碍和无障碍的导航任务 .仿真实验结果验证了所提出方法的有效性

虚拟监控遥操作水下机器人控制系统的研究

随着海洋科学考察和水下工程的日益增多，人类的研究趋势不断地向海洋深处发展。然而，水下环境与陆地和空间环境相比更加恶劣，对人类的威胁更大，因此水下机器人作为人的替代者，正在越来越多地在实际水下操作中应用。传统的水下机器人是采用主从遥操作控制，陆地上或母船上的操作员借助水下摄像机观察机器人的工作情况，通过主手或操纵杆操纵机器人，这种工作方式已不能满足当前水下作业的需要，所以研制具有高效率、高操作精度的水下机器人系统成为当今机器人领域的研究热点。本论文的研究内容是国家“863”高技术计划研究项目“虚拟监控遥操作水下机器人系统”的重要组成部分，以水下机器人检查海底石油钻井平台导管架焊缝的实际工作为背景，建立了一个完整的水下机器人实验系统，详细研究了虚拟遥操作控制、机器人监控控制及ROV(Remotely Operated Vehicles)模糊控制导航方法，并将这些控制方法应用到所建立的机器人系统中，完成实际操作实验。为了解决运动学逆解无解析解一类机械手的实时控制问题，本文提出一种适合于实时求解的算法--“跟踪搜索算法"，并使用该算法实现了5DOF水下机械手的运动学解算和实时控制。水下机器人载体ROV的导航问题一直被研究者们关注，在水下机器人控制中占重要地位。本文提出一种模糊控制导航方法，使用统一控制模式实现ROV在3D空间的导航，避免了ROV水下导航中多模控制切换点难以确定和切换过程造成ROV波动的问题。根据对ROV和机械手运劫特征的分析，以及水下环境的先验知识，建立了机器人和水下环境的虚拟模型。为了适应机器人在非结构化环境中工作的要求，提出“交互虚攒建模”方法，在环境发生变化时，重新建立虚拟环境模型，使虚拟环境反映真实环境的变化。在此基础上，建立了一个多功能虚拟仿真平台。监控控制是目前水下机器人最好的控制方法，本论文将虚拟现实技术应用在机器人监控系统中，提出虚拟监控系统的双层结构，发展了监控思想。研究并实现了四种虚拟监控控制方法：(1)基于虚拟显示的控制方法，(2)基于虚拟视觉的控制方法，(3)虚拟层任务规划，(4)虚拟投射控制。将上述各部分集成，设计并实现了虚拟监控遥操作控制系统，以该控制系统为核心，连接真实水下机器人和视觉系统，建立了虚拟监控遥操作水下机器人实验系统。本论文提出的系统结构、虚拟建模方法、模糊导航方法，虚拟监控控制方法均应用到机器人实验系统中。实际操作结果和仿真实验结果验证了所提出的虚拟监控系统结构的合理性，方法的正确性，体现了这些结构和方法的先进性。该实验系统和上述实验结果作为“863”项目“虚拟监控遥操作水下机器人系统”的重要组成部分，通过了专家组的验收，得到专家们的肯定。此外，为了适应开展网络遥操作研究的需要，本论文基于Internet网络技术，建立了机器人的网络通讯框架，使本论文中建立的机器人系统具有网络扩展性。论文的研究工作为研制可实用的高性能水下机器人系统奠定了基础，研究成果对水下机器人遥操作具有理论指导意义，为其实际应用提供了技术实现的途径。

A comprehensive comparison of fuel options for fuel cell vehicles in China

Fuel cell vehicles (FCVs) offer the potential of ultra-low emissions combined with high efficiency. Proton exchange membrane (PEM) fuel cells being developed for vehicles require hydrogen as a fuel. Due to the various pathways of hydrogen generation, both onboard and off-board, the question about which fuel option is the most competitive for fuel cell vehicles is of great current interest. In this paper, a life-cycle assessment (LCA) model was made to conduct a comprehensive study of the energy, environmental, and economic (3E) impacts of FCVs from well to wheel (WTW). In view of the special energy structure of China and the timeframe, 10 vehicle/fuel systems are chosen as the study projects. The results show that methanol is the most suitable fuel to serve as the ideal hydrogen source for fuel cell vehicles in the timeframe and geographic regions of this study. On the other hand, gasoline and pure hydrogen can also play a role in short-term and regional applications, especially for local demonstrations of FCV fleets. (c) 2004 Elsevier B.V All rights reserved.

Nonlinear Acoustics in Underwater and Biomedical Applications: Array Performance Degradation and Time Reversal Invariance

This dissertation describes a model for acoustic propagation in inhomogeneous flu- ids, and explores the focusing by arrays onto targets under various conditions. The work explores the use of arrays, in particular the time reversal array, for underwater and biomedical applications. Aspects of propagation and phasing which can lead to reduced focusing effectiveness are described. An acoustic wave equation was derived for the propagation of finite-amplitude waves in lossy time-varying inhomogeneous fluid media. The equation was solved numerically in both Cartesian and cylindrical geometries using the finite-difference time-domain (FDTD) method. It was found that time reversal arrays are sensitive to several debilitating factors. Focusing ability was determined to be adequate in the presence of temporal jitter in the time reversed signal only up to about one-sixth of a period. Thermoviscous absorption also had a debilitating effect on focal pressure for both linear and nonlinear propagation. It was also found that nonlinearity leads to degradation of focal pressure through amplification of the received signal at the array, and enhanced absorption in the shocked waveforms. This dissertation also examined the heating effects of focused ultrasound in a tissue-like medium. The application considered is therapeutic heating for hyperther- mia. The acoustic model and a thermal model for tissue were coupled to solve for transient and steady temperature profiles in tissue-like media. The Pennes bioheat equation was solved using the FDTD method to calculate the temperature fields in tissue-like media from focused acoustic sources. It was found that the temperature-dependence of the medium's background prop- erties can play an important role in the temperature predictions. Finite-amplitude effects contributed excess heat when source conditions were provided for nonlinear ef- fects to manifest themselves. The effect of medium heterogeneity was also found to be important in redistributing the acoustic and temperature fields, creating regions with hotter and colder temperatures than the mean by local scattering and lensing action. These temperature excursions from the mean were found to increase monotonically with increasing contrast in the medium's properties.

Modelling collisions of rail vehicles with deformable objects

This study utilized the latest computing techniques to analyze the driver's cab of a railroad vehicle colliding with deformable objects. It explored the differences between a collision with a deformable object and a collision with a rigid object. It also examined the differences between a collision with a large simple shaped object and a collision with a life-like object. Tools of analysis included vehicle dynamics analysis and finite element analysis.

A Marine Environmental Recorder

An inexpensive Marine Environmental Recorder is described. The instrument system is small, lightweight and of low-power consumption. It is flexible, simple to operate and economical. It can be used remotely in a moored, buoyed or towed instrument system, recording measurements continuously for up to 24 h, or intermittently for 1 min every hour, for a period of up to 60 d. It has been used extensively in the Continuous Plankton Recorder and the Undulating Oceanographic Recorder to measure temperature, depth and occasionally chlorophyll and radiant energy; as a temperature recorder, it has a resolution of 0.1 Co, an uncertainty of measurement of ±0.1 Co and a stability of calibration within ±0.1 Co over a period of several months. With optional additional sensors for pitch, roll, vibration, acceleration and water-flow, the instrument system has been used to measure the performance of underwater towed vehicles and plankton samplers. The Marine Environmental Recorder is being incorporated into an instrument system in a data buoy, for automatically monitoring the marine environment in estuaries around the British Isles.