CHS: Small: Fast simulation of geometrically complex multibody systems in contact and self-contact

模拟复杂机械接触的能力在工程实践中广泛适用。它可以用于虚拟培训，比如重型机械的操作。也许最重要的是，它可以用来在虚拟现实中组装和测试复杂的机械结构(使用包括触觉反馈的人机界面)。这种通常被称为虚拟样机的技术极大地缩短了设计周期，减少了错误，提高了产品安全性，并节省了数百万美元的研发成本。在飞机、汽车、火车、宇宙飞船、发电厂、建筑物、工具、重型设备等必须由许多部件设计和制造的复杂结构的任何地方都可以找到应用程序。在这个项目中，PI将开发计算高效的碰撞检测和接触解决方法，以适应由许多物体组成的复杂系统，这些物体通过关节连接并进行接触和自接触。他的目标是设计足够快的算法，以适应高更新率(触觉的模拟步数为每秒1000步或更多)，并扩展到通常由数百万个三角形代表的复杂现实世界机制，例如内燃机或整个汽车引擎舱，飞机起落架或飞机门，或挖掘机机器。此外，尽管以前快速成功的基于工业惩罚的方法通常仅限于接触的对象对，但在本研究中，PI的目标是处理更复杂和真实的情况，包括刚性对象、关节、摩擦和自接触。由于复杂几何形状对计算和稳定性的严格要求，快速模拟接触的多体系统是具有挑战性的。这样的模拟经常涉及分布式接触，也就是说，接触涉及许多不同表面积和法向的碰撞地点，这些地点随着时间的推移而迅速变化。由于基于约束的方法在高更新率下稳定地解决这种接触是具有挑战性的，首席调查者将利用点和隐式函数(距离场或体素图)之间经过行业验证的惩罚方法，并且他将扩展该方法，该方法迄今仅限于接触的对象对，以适应任意接触的N=2个对象，以及通过关节连接并经历主动控制的对象。技术挑战包括如何稳定地解决N=2个对象之间的时间步长分布接触，如何在存在约束(关节)的情况下稳定地模拟和渲染六自由度分布接触，以及如何在保持高更新率的同时处理自接触和考虑摩擦(或者在极端接触的情况下优雅地降低它们)。由于首席调查员的初步经验表明，当前算法的离散性质是实践中的一个重要限制，他还将研究点和距离场之间的连续碰撞检测。项目成果将通过PI与多家高科技虚拟样机行业领先者的持续合作，转化为工程实践，并将推动计算机图形、触觉、机器人和虚拟现实领域的最先进水平。

The ability to simulate complex machinery in contact is broadly applicable to engineering practice. It can be used for virtual training, say in the operation of heavy machinery. Perhaps most importantly, it can be used to assemble and test complex mechanical structures in virtual reality (using a human-computer interface that includes haptic feedback). Such virtual prototyping, as it is commonly called, greatly shortens design cycles, decreases errors, improves product safety and saves millions of dollars in R&D costs. Applications can be found anywhere a complex structure must be designed and manufactured out of many component parts: airplanes, cars, trains, spaceships, power plants, buildings, tools, heavy equipment, etc. In this project the PI will develop computationally efficient collision detection and contact resolution methods that can accommodate complex systems consisting of many objects that are connected by joints and undergoing contact and self-contact. His goal is to devise algorithms that are sufficiently fast to accommodate high update rates (1,000 simulation steps per second for haptics, or more), and that scale to complex real-world mechanisms typically represented by millions of triangles, such as an internal combustion engine or an entire car engine compartment, an airplane landing gear or airplane doors, or excavator machines. Furthermore, whereas previous fast successful industrial penalty-based methods have typically been limited to pairs of objects in contact, in this research the PI's objective is to deal with more complex and realistic situations including rigid objects, joints, friction and self-contact.Fast simulation of multi-body systems in contact is challenging due to the severe computational and stability requirements imposed by complex geometry. Such simulations frequently involve distributed contact, that is to say contact involving many collision sites of varying surface areas and normal orientations that change rapidly over time. Because it is challenging for constraint-based methods to resolve such contact stably at high update rates, the Principal Investigator will exploit industry-proven penalty methods between points and implicit functions (distance fields or voxmaps), and he will extend the approach, which has to date been limited to pairs of objects in contact, to accommodate N = 2 objects in arbitrary contact, as well as objects connected with joints and undergoing active control. The technical challenges include how to stably resolve and time-step distributed contact between N = 2 objects, how to stably simulate and render 6-DOF distributed contact in the presence of constraints (joints), and how to handle self-contact and incorporate friction, all the while maintaining high update rates (or gracefully degrading them in case of extreme contact). Because the Principal Investigator's preliminary experience suggests that the discrete nature of current algorithms is an important limitation in practice, he will also investigate continuous collision detection between points and distance fields. Project outcomes will be transitioned to engineering practice via the PI's ongoing collaborations with a number of industrical leaders in high-tech virtual prototyping, and will advance the state of the art in computer graphics, haptics, robotics and virtual reality.