用于三维软组织实时切割的混合凝聚有限元模型

随着近几年来微创外科的迅速发展，虚拟内窥镜手术模拟系统作为手术训练、规划的有效手段，已逐渐成为研究的热点。根据实际手术的需要，虚拟手术系统应该不仅能够实时模拟软组织的变形，而且也同样可以对软组织的切割、缝合操作进行实时模拟。该文提出了一个用于虚拟手术模拟、三维软组织变形以及切割的有限元模型－混合凝聚有限元模型。该模型的显著优点在于其可以在当前的PC机平台上有效地对软组织变形及具有拓扑改变的切割操作进行实时模拟。     

多精度混合弹性变形及其交互模拟

固体的弹性变形模拟作为计算机物理动画领域的重要内容,如何在保证模拟真实感的同时尽可能地提高计算效率以满足交互应用,一直是其研究难点.为此,提出一种多精度混合弹性变形模型来高效地模拟固体的弹性变形及其交互.该模型通过对物体计算空间进行物理和几何区域的用户自定义比例划分,并混合处理交界面处计算结点,实现2种变形区域的稳定耦合;利用虚拟顶点算法对物理变形区域进行稳定和光滑的虚拟切割模拟;提出自适应边界粒子采样的固流耦合算法模拟固流交互.实验结果表明,文中模型通过调整2种区域计算结点的比例,控制和调整弹性变形模拟的效率和精度,可以满足虚实交互和固流交互模拟中稳定和高效的性能需求.     

基于模型约简和GPU加速的软组织实时仿真

为了得到虚拟外科手术中人体软组织的实时变形仿真,采用了基于模态分析的模型约简方法,同时结合了GPU加速技术,实现了人体软组织的实时仿真计算,为虚拟手术提供了良好的人机交互.模型约简以有限元理论为基础,将软组织模型的动力学方程投射到约筒子空间,减少系统自由度.在实时仿真过程中,首先需在子空间中对低维动力学模型进行数值计算,然后利用GPU通用计算技术来加速重建原始空间中的形变向量.以心脏大变形实时仿真为例,验证方法的性能,实验结果表明心脏的变形仿真可以在很高的刷新率下运行.提出的模型约简和GPU加速方法,为人体软组织的变形实现了实时仿真,为虚拟手术提供了理论基础和技术支撑.     

虚拟手术中顶点复制切割算法的设计研究

为了解决虚拟内镜手术中软体组织切割模拟仿真问题,论述并实现了虚拟手术中软组织切割仿真技术.使用四面体网格模型,利用刀具移动简化模型,构造用于切割操作的切割树,设计了通过划分切割区域,复制和移动顶点,在实现切割分裂时,减少网格单元结构数量增加的切割分裂和切割细化算法.通过仿真实验,文中算法的耗时与切割长度程线性关系;使用该算法实施切割后,网格结构中单元结构数量的增加相比传统的算法有明显减少.     

虚拟手术中血流特效场景仿真的研究

血流特效场景可以增强虚拟手术的真实感。虚拟手术中的血流特效场景包括了有交互的血液模拟及血管壁模拟。首先基于光滑粒子流体动力学,使用Physx物理引擎模拟血液流动的物理形态,并利用Screen Space Flow算法对血流表面进行实时渲染。然后基于质点-弹簧模型,提出使用Physx物理引擎模拟可交互、有弹性形变及可切割的血管壁。最后实现两个实验场景:场景一实现肺动脉内大规模血液流动的特效;场景二实现在用户交互下的血管壁形变和切割,并通过触发事件实现血管壁破裂流血的特效。实验结果表明,该血流及血管壁模拟方法在40 000个粒子下仍能保证实时绘制,满足虚拟手术的需求。     

用于软组织变形仿真的层状菱形链连接模型

为提高软组织变形仿真的精度与实时性,提出一种新颖的、基于物理意义的层状菱形链连接模型.该模型中每层各个链结构单元相对位移的叠加对外等效为物体表面的变形,与之相连的弹簧弹性力的合力等效为物体表面接触力.利用6-DOFDelta手控器构建了力触觉交互实验系统,使用虚拟软组织模型进行按压、拉拽等交互操作,并通过反馈力产生触觉感.实验结果表明,该模型不仅计算简单,而且能够保证触觉接触力和变形计算具有较高精度;同时在交互过程中,力触觉感觉平稳、模拟效果逼真、满足虚拟现实系统对精细作业和实时性的要求.     

基于复合模型的软组织变形模拟算法

为满足虚拟手术中软组织变形的精确性和实时性要求,提出一种基于复合模型的软组织变形模拟算法。该复合变形模型包括复合网格的建立,复合网格中粗糙体网格应用有限元模型,精细表面网格应用基于位置动力学模型,通过变形计算流程实现变形模拟。复合模型与传统的有限元模型和基于位置的动力学模型相比,变形的精确性和实时性取得了更好的平衡。通过变形实例,表明复合模型对于实例模型也具有很好的展示效果。     

虚拟手术中的模型实时绘制

实时的视觉反馈在虚拟手术中可以加强操作者的沉浸感。该文分析了体绘制和面绘制的优缺点,在系统实时性的要求下,实现了基于立体纹理映射的三维体模型的面绘制。算法在容许实时交互的同时,为操作者提供了真实感较强的视觉反馈。由于文中立体纹理生成及纹理坐标计算的特殊性,对虚拟手术中的拉压变形和切割等操作也能很好地处理。     

人体软组织建模与实时仿真

虚拟手术系统在医学中实时仿真以建立可供手术前规划和手术时参考的虚拟环境.由于人体器官大多由软组织构成,有限元法能够精确地进行软组织几何大变形仿真.加速有限元仿真有多种方法,文章采用基于模态分析的模型约简方法,对软组织有限元模型进行模态分析,将约简子空间中的形变向量重构到原始空间,从而实现软组织实时仿真.实验结果表明,采...     

应用于网上虚拟手术的自适应变形模型

提出并开发了一种适用于网上虚拟手术的自适应变形模型.在这个模型里,外力逐层地传播到软组织里,从而导致变形.通过控制外力的渗透深度,变形只局限在某些区域内发生,而模拟的计算量和准确性亦得以优化.该方法避免了在传统的质点弹簧模型中建立刚度矩阵的繁复程序.实验结果表明,这个模型可以用来模拟不同机械特性的材料,亦可用于在虚拟环境里模拟多用户的协同工作,或与多自由度的触觉式设备结合使用.     

Microdrive operational and non-operational shock and vibration testing

Commercially available microdrives were tested using linear and rotary shock and vibration testing equipment. Several microdrives designed with different slider and disk configurations were tested to track hard and soft errors as well as head/disk failures. The shock amplitude for operational and non-operational shock was gradually increased to determine the maximum shock that a microdrive could withstand before failure. After failure, the microdrive was examined to determine whether a mechanical failure occurred or whether the failure was due to a magnetic hard/soft error. During a shock event, the displacement and frequency of the vibrations of the microdrive were examined at various locations on the arm and suspension. A scanning laser Doppler vibrometer (LDV) was also used to determine the amplitude and frequency of the vibrations of the front cover and to investigate whether these vibrations contribute to failure of the head/disk interface. A finite element model of the disk drive was also developed to simulate the shock response. The maximum amplitude for failure to occur was determined numerically for operational and non-operational conditions using a pulse width of 2 ms. A comparison of experimental and numerical results is given.     

Non-operational shock analysis and design of head gimbal assembly in spinning data storage devices

The work presented in this paper was motivated by the experimental observation of de-bonding phenomena between head gimbal assembly (HGA) and suspension for a commercial 3.5-in. enterprise HDD under non-operational 250?G shock test, which leads to revisit design of HGA/suspension with objective placed on withstanding shocks between the head slider and the suspension. In this study experimental observation and numerical finite element studies were conducted to understand such effect on the mechanical failure of HGA when it is subjected to non-operational shock in parked position on ramp. It was observed that by changing flexure angle in HGA, shock stress can be reduced. FEA simulation results have been presented to verify the findings.     

Manufacturing cost estimation for machined parts based on manufacturing features

The purpose of this paper is to present a feature-based cost estimating system for machined parts. Since cost estimation provides designers with valuable information, it must be quick and accurate. In this paper, manufacturing features are classified into four categories. Cost estimation for all features in a category is based on manufacturing activities. Early cost estimations did not consider the manufacturing activity, hence they were not accurate. Machining cost is proportional to machining time, which includes operational time and non-operational time. Operation time includes rough cutting time and finish cutting time. Tool approach time and non-operation time are taken from past experience and approximated for modification into mathematical forms. This paper develops a cost estimation system based on manufacturing features. It is an approximation system which inputs information on machining activities.     

From Fireflies to Fault-Tolerant Swarms of Robots

One of the essential benefits of swarm robotic systems is redundancy. In case one robot breaks down, another robot can take steps to repair the failed robot or take over the failed robot's task. Although fault tolerance and robustness to individual failures have often been central arguments in favor of swarm robotic systems, few studies have been dedicated to the subject. In this paper, we take inspiration from the synchronized flashing behavior observed in some species of fireflies. We derive a completely decentralized algorithm to detect non-operational robots in a swarm robotic system. Each robot flashes by lighting up its on-board light-emitting diodes (LEDs), and neighboring robots are driven to flash in synchrony. Since robots that are suffering catastrophic failures do not flash periodically, they can be detected by operational robots. We explore the performance of the proposed algorithm both on a real-world swarm robotic system and in simulation. We show that failed robots are detected correctly and in a timely manner, and we show that a system composed of robots with simulated self-repair capabilities can survive relatively high failure rates.      

生物软组织力反馈触觉建模测试系统研制

设计了一种结构新颖的用于生物软组织力反馈触觉建模的测试系统。阐述了系统结构与工作原理,介绍了系统的机械设计、硬件电路和系统软件。系统采用计算机测量并控制带有力和位置传感器的单自由度机械手,通过插针实验与动物软组织交互得到软组织的力反馈触觉模型。以猪肝为标本进行实验,实验结果和现有的理论模型较为符合,该系统可以用于软组织触觉建模实验研究。     

Maintaining censorship resistance in the iTrust network for publication,search and retrieval

This paper presents the architecture of the iTrust system together with algorithms for maintaining censorship resistance. In iTrust, metadata describing documents, and requests containing keywords, are distributed to randomly chosen nodes in the iTrust network. If a node receives a request containing keywords that match metadata it holds, it sends the URL of the matching document to the requesting node, which then retrieves the document from the source node. A novel detection algorithm estimates the proportion of operational nodes in the iTrust network, by comparing the empirical probabilities of the number of responses received for a node’s request with the analytical probabilities for a match, for various proportions of operational nodes. A novel defensive adaptation algorithm increases the number of nodes to which the requests are distributed, in order to maintain the same high probability of a match when some of the nodes are non-operational or malicious as when all of the nodes are operational. Extensive experimental evaluations demonstrate the effectiveness of the architecture and the algorithms for maintaining censorship resistance in the iTrust network.     

A study of non-operational dynamic responses of disk in 3.5 in. hard disk drive to impact load

Hard disk drives have to be designed to sustain operational and non-operational shock. There are many analytical models and numerical schemes proposed and many experiments conducted for analyzing the transient impact responses of hard disk drives. The existing researches have been focused on the slider-suspension responses at the head-disk interface in which the linear models have been used and the effects of spindle motor have been ignored. In this study, the complex vibrations of disk of 3.5 in. hard disk drive (HDD) under shock are experimentally investigated. The hammer impact test and linear drop test are conducted for the HDD to study the effect of shock on the disk responses. The results show that the nonlinear rock modes substantially contribute to the vibrations of disk when HDD is under shock impact. The nonlinear properties of the disk responses and the mode damping ratio are evaluated by using empirical mode decomposition approach.     

基于水平集方法的软组织图像序列分割

医学图像分割是医学图像处理中的关键问题之一.图像序列的分割操作是医学图像三维重建的必要准备,而软组织图像分割则是医学图像分割中的一大难点.基于曲线演化理论的,借助偏微分方程等数学工具的水平集方法已经被广泛应用于医学图像分割领域.介绍了水平集方法的数学模型,并设计了一种基于窄带水平集方法的,专门针对软组织图像分割的算法.用边界追踪等方法提取第一层图片中的软组织相关轮廓;将它们作为初始水平集曲线,再利用窄带水平集方法进行演化;经过两个阶段的迭代处理,最终自动分割出整个软组织图像序列.实验表明该算法具有较高效率、分割结果精确,所产生的分割结果可以作为三维重建的合适的数据集.     

回转窑煅烧过程运用软测量的建模方法及应用

为了解决工业回转窑的生产过程中存在工艺复杂、建模困难和控制目标只能离线检测等控制难点的问题,在分析锌钡白回转窑煅烧过程运行机理和工艺流程的基础上,运用软测量的方法建立煅烧过程的控制模型。结合熟练工人的操作经验,采用模糊控制的方法对控制模型的PID参数进行自动整定,详细介绍了控制模型的建立过程和模糊参数自整定控制器的设计方法。现场运行取得了满意的效果。     

一种基于逐次逼近法求解软组织力平衡的方法

进行腹腔微创手术操作时,为获得软组织变形的图形反馈,需要进行软组织的力平衡求解.建立了胆囊及其附属管路的几何模型,对其赋予弹簧一质点力学模型,提出了一种基于逐次逼近法的力平衡算法求解软组织力平衡.该算法编程量较少,易于实现,仿真实时性也较好.仿真实验表明,该算法可以产生较为真实的软组织图形反馈,可以实际应用于软组织仿真...