DROP: Dynamics Responses from Human Motion Prior and Projective Dynamics

Synthesizing realistic human movements, dynamically responsive to the environment, is a long-standing objective in character animation, with applications in computer vision, sports, and healthcare, for motion prediction and data augmentation. Recent kinematics-based generative motion models offer impressive scalability in modeling extensive motion data, albeit without an interface to reason about and interact with physics. While simulator-in-the-loop learning approaches enable highly physically realistic behaviors, the challenges in training often affect scalability and adoption. We introduce DROP, a novel framework for modeling Dynamics Responses of humans using generative mOtion prior and Projective dynamics. DROP can be viewed as a highly stable, minimalist physics-based human simulator that interfaces with a kinematics-based generative motion prior. Utilizing projective dynamics, DROP allows flexible and simple integration of the learned motion prior as one of the projective energies, seamlessly incorporating control provided by the motion prior with Newtonian dynamics. Serving as a model-agnostic plug-in, DROP enables us to fully leverage recent advances in generative motion models for physics-based motion synthesis. We conduct extensive evaluations of our model across different motion tasks and various physical perturbations, demonstrating the scalability and diversity of responses.Comment: SIGGRAPH Asia 2023, Video https://youtu.be/tF5WW7qNMLI, Website: https://stanford-tml.github.io/drop

Preliminary system design of a Three Arm Capture Mechanism (TACM) flight demonstration article

The overall objective of the Three Arm Capture Mechanism (TACM) is to serve as a demonstration of capability for capture of objects in space. These objects could be satellites, expended boosters, pieces of debris, etc.; anything of significant size. With this capability we can significantly diminish the danger of major collisions of debris with valuable space assets and with each other, which would otherwise produce many smaller, high velocity pieces of debris which also become concerns. The captured objects would be jettisoned into the atmosphere, relocated in 'parking' orbits, or recovered for disposition or refurbishment. The dollar value of satellites launched into space continues to grow along with the cost of insurance; having a capture capability takes a positive step towards diminishing this added cost. The effort covered is a planning step towards a flight demonstration of the satellite capture capability. Based on the requirement to capture a communication class satellite, its associated booster, or both, a preliminary system definition of a retrieval kit is defined. The objective of the flight demonstration is to demonstrate the techniques proposed to perform the mission and to obtain data on technical issues requiring an in situ space environment. The former especially includes issues such as automated image recognition techniques and control strategies that enable an unmanned vehicle to rendezvous and capture a satellite, contact dynamics between the two bodies, and the flight segment level of automation required to support the mission. A development plan for the operational retrieval capability includes analysis work, computer and ground test simulations, and finally a flight demonstration. A concept to perform a selected mission capturing a precessing communications satellite is described. Further development efforts using analytical tools and laboratory facilities are required prior to reaching the point at which a full commitment to the flight demonstration design can be made

Importance of vegetation in tsunami mitigation: evidence from large eddy simulations with fluid-structure interactions

Communities worldwide are increasingly interested in nature-based solutions like coastal forests for the mitigation of coastal risks. Still, it remains unclear how much protective benefit vegetation provides, particularly in the limit of highly energetic flows after tsunami impact. The present thesis, using a three-dimensional incompressible computational fluid dynamics model with a fluid-structure interaction approach, aims to quantify how energy reflection and dissipation vary with different degrees of rigidity and vegetation density of a coastal forest. In this study, tree trunks are represented as cylinders, and the elastic modulus of hardwood trees such as pine or oak is used to characterize the rigidity of these cylinders. To capture tsunami bore propagation in onshore, dam break flow is used over the wet surface in the numerical studies. After validating numerical code against experimental studies, multi-cylinder configurations are incorporated and Froude Number is used to scale the flow parameters and vegetation flow parameter (VFP) to scale the tree parameters such as elastic modulus, the diameter of the trunk, etc. Numerical tests are conducted for different cylinder diameters, densities, and elastic moduli. The numerical results show that energy reflection increases with rigidity only for a single cylinder. In the presence of multiple cylinders, the difference in energy reflection created by varying rigidity diminishes as the number of cylinders increases. Instead of rigidity, the blockage area created by the presence of multiple tree trunks is found to dominate energy reflection. As tree trunks are deformed by the hydrodynamic forces, they alter the flow field around them, causing turbulent kinetic energy generation in the wake region. As a consequence, trees dissipate flow energy, highlighting the importance of coastal forests in reducing the onshore energy flux of tsunamis by means of both reflection and dissipation

Some NASA contributions to human factors engineering: A survey

This survey presents the NASA contributions to the state of the art of human factors engineering, and indicates that these contributions have a variety of applications to nonaerospace activities. Emphasis is placed on contributions relative to man's sensory, motor, decisionmaking, and cognitive behavior and on applications that advance human factors technology

Orbiting Geophysical Observatory Attitude Control Subsystem design survey

Development history and design modifications for attitude control subsystem of OG

Advancing Thoracic Spine Biomechanical Research

The long term objective of this research was to elucidate issues with current thoracic spine testing methods and develop more accurate ways to quantify the biomechanical impact of surgical procedures or medical devices. The ability to perform thoracic spine testing with a rib cage is limited by test machine variability and experimental design inconsistency, so surgeons are left with little reliable information on the biomechanical impacts of procedures and implants. This research sought to validate a novel spine test machine, provide biomechanical data to support the inclusion of an intact rib cage when testing the thoracic spine, and quantify the biomechanical impacts of sequential Ponte osteotomies. Specific Aim 1 validated the accuracy of the spine test machine for rigidity ranges that represent cadaveric specimen rigidities present in the spine. Cervical, thoracic, and lumbar spine specimens were modeled with synthetic rubber that represented the breadth of rigidities, and testing was conducted in bending and axial rotation. The maximum machine displacement error was less than 2° for lumbar and thoracic specimens, so it is suggested that researchers use an external motion-tracking system in conjunction with the test machine when high accuracy measurements are required. Specific Aim 2 quantified the biomechanical differences of testing full cadaveric thoracic spine specimens with and without an intact rib cage. While it was presumed that the rib cage provides structural stability to the thoracic spine, the extent to which the rib cage contributes to spinal motion had not been fully quantified. Testing quantified the motion and stiffness values of an intact thoracic spine specimen, and results showed that testing without a rib cage changes both motion and stiffness values. Specific Aim 3 quantified the biomechanical impact of sequential Ponte osteotomies in cadaveric thoracic spine specimens with intact rib cages. Overall and regional changes in motion due to Ponte osteotomies were analyzed, and results showed increased flexibility in the sagittal plane on both overall and regional levels. The results from this work could provide researchers and surgeons the tools they need to better understand and improve spine procedures and implants, which could ultimately improve the quality of life for patients

Tracking dynamic regions of texture and shape

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 137-142).The tracking of visual phenomena is a problem of fundamental importance in computer vision. Tracks are used in many contexts, including object recognition, classification, camera calibration, and scene understanding. However, the use of such data is limited by the types of objects we are able to track and the environments in which we can track them. Objects whose shape or appearance can change in complex ways are difficult to track as it is difficult to represent or predict the appearance of such objects. Furthermore, other elements of the scene may interact with the tracked object, changing its appearance, or hiding part or all of it from view. In this thesis, we address the problem of tracking deformable, dynamically textured regions under challenging conditions involving visual clutter, distractions, and multiple and prolonged occlusion. We introduce a model of appearance capable of compactly representing regions undergoing nonuniform, nonrepeating changes to both its textured appearance and shape. We describe methods of maintaining such a model and show how it enables efficient and effective occlusion reasoning. By treating the visual appearance as a dynamically changing textured region, we show how such a model enables the tracking of groups of people. By tracking groups of people instead of each individual independently, we are able to track in environments where it would otherwise be difficult, or impossible. We demonstrate the utility of the model by tracking many regions under diverse conditions, including indoor and outdoor scenes, near-field and far-field camera positions, through occlusion and through complex interactions with other visual elements, and by tracking such varied phenomena as meteorological data, seismic imagery, and groups of people.by Joshua Migdal.Ph.D