Full-Field 3D Experimental Modal Analysis from Dynamic Point Clouds Measured Using a Time-of-Flight Imager

The ability to measure static, high-resolution 3D point cloud data has existed for multiple decades and has been used to great benefit in both civil and mechanical engineering applications. Recently, time-of-flight imagers have emerged that are capable of measuring 3D dynamic point clouds at rates as high as 30 point cloud captures per second with resolutions approaching the millimeter scale. Conventional modal analysis utilizes contact measurements that are captured in the Lagrangian (i.e., material) coordinate system. Imager measurements such as used for DIC are captured in what is approximately an Eulerian frame of reference. However, oftentimes the imager measurements are captured in a small-motion, sub-pixel regime and can be assumed to be captured in a Lagrangian reference frame. As a result, most experimental modal identification algorithms are designed to operate on data captured in a Lagrangian reference frame. Measurements of 3D point clouds of vibrating structures do not necessarily fit into either an Eulerian or Lagrangian framework, particularly in the case where motion of the structure is large. An additional feature of these measurements is that the number of points measured on the structure can change significantly through time as a result of occlusions, the change in angle of the structure, or simply noise in the measurement. This feature of point clouds is significantly different from imagers and contact sensors in which the dimensionality of the measurements does not change through time. In this work we present the first known technique for extracting structural dynamics information from dynamic point clouds

3D structural vibration identification from dynamic point clouds

Video-based measurement has received increased attention for modal analysis and nondestructive evaluation, playing an important role in the development of the next-generation structural sensing technologies. As these techniques have evolved, more quantitative approaches based on computer vision techniques have emerged on full-field unsupervised structural identification, exploiting the benefits provided by the use of video cameras such as high spatial sensor density and low installation costs. More recent work has started to explore the use of laser point cloud data for 3D mapping of scenes and structures. Sensors such as LIDAR provide huge amounts of measurements at high spatial resolution from which it is possible to estimate accurate structural geometry for applications such as the generation of CAD models. Unfortunately to-date, the frame rate and depth resolution of LIDAR and other sensors capable of 3D geometry measurements has not been sufficient for measuring structural dynamics. In this paper, we introduce an approach for efficient and extremely high resolution 3D structural dynamic identification/modal analysis from point cloud data acquired using a commercial, low-cost, time-of-flight imager. Vibration mode shapes and modal coordinates are extracted from this data by creating virtual Lagrangian sensors based on the point clouds parameters. First, time-varying point cloud data are collected from a vibrating structure. Then, a mesh of virtual sensors is created based on the dynamic point cloud data for tracking the structure\u27s displacement over time. Next solutions to the blind source separation problem are employed to estimate high resolution 3D mode shapes, modal coordinates, and resonant frequencies. We demonstrate the potential of our proposed approach on laboratory tests and compare the results to the data collected from conventional laser displacement sensors. This technique represents an advance towards efficiently exploring the full advantages of using dynamic point cloud data for practical monitoring applications and has the potential to be extended for a wide range of 3D motion decomposition problems

Physics and technology of the Next Linear Collider: a report submitted to Snowmass '96

We present the current expectations for the design and physics program of an e+e- linear collider of center of mass energy 500 GeV -- 1 TeV. We review the experiments that would be carried out at this facility and demonstrate its key role in exploring physics beyond the Standard Model over the full range of theoretical possibilities. We then show the feasibility of constructing this machine, by reviewing the current status of linear collider technology and by presenting a precis of our `zeroth-order' design