Packing Characteristics of Different Shaped Proppants for use with Hydrofracing - A Numerical Investigation using 3D FEMDEM

Imperial Users onl

Capturing Hands in Action using Discriminative Salient Points and Physics Simulation

Hand motion capture is a popular research field, recently gaining more attention due to the ubiquity of RGB-D sensors. However, even most recent approaches focus on the case of a single isolated hand. In this work, we focus on hands that interact with other hands or objects and present a framework that successfully captures motion in such interaction scenarios for both rigid and articulated objects. Our framework combines a generative model with discriminatively trained salient points to achieve a low tracking error and with collision detection and physics simulation to achieve physically plausible estimates even in case of occlusions and missing visual data. Since all components are unified in a single objective function which is almost everywhere differentiable, it can be optimized with standard optimization techniques. Our approach works for monocular RGB-D sequences as well as setups with multiple synchronized RGB cameras. For a qualitative and quantitative evaluation, we captured 29 sequences with a large variety of interactions and up to 150 degrees of freedom.Comment: Accepted for publication by the International Journal of Computer Vision (IJCV) on 16.02.2016 (submitted on 17.10.14). A combination into a single framework of an ECCV'12 multicamera-RGB and a monocular-RGBD GCPR'14 hand tracking paper with several extensions, additional experiments and detail

Computing fast search heuristics for physics-based mobile robot motion planning

Mobile robots are increasingly being employed to assist responders in search and rescue missions. Robots have to navigate in dangerous areas such as collapsed buildings and hazardous sites, which can be inaccessible to humans. Tele-operating the robots can be stressing for the human operators, which are also overloaded with mission tasks and coordination overhead, so it is important to provide the robot with some degree of autonomy, to lighten up the task for the human operator and also to ensure robot safety. Moving robots around requires reasoning, including interpretation of the environment, spatial reasoning, planning of actions (motion), and execution. This is particularly challenging when the environment is unstructured, and the terrain is \textit{harsh}, i.e. not flat and cluttered with obstacles. Approaches reducing the problem to a 2D path planning problem fall short, and many of those who reason about the problem in 3D don't do it in a complete and exhaustive manner. The approach proposed in this thesis is to use rigid body simulation to obtain a more truthful model of the reality, i.e. of the interaction between the robot and the environment. Such a simulation obeys the laws of physics, takes into account the geometry of the environment, the geometry of the robot, and any dynamic constraints that may be in place. The physics-based motion planning approach by itself is also highly intractable due to the computational load required to perform state propagation combined with the exponential blowup of planning; additionally, there are more technical limitations that disallow us to use things such as state sampling or state steering, which are known to be effective in solving the problem in simpler domains. The proposed solution to this problem is to compute heuristics that can bias the search towards the goal, so as to quickly converge towards the solution. With such a model, the search space is a rich space, which can only contain states which are physically reachable by the robot, and also tells us enough information about the safety of the robot itself. The overall result is that by using this framework the robot engineer has a simpler job of encoding the \textit{domain knowledge} which now consists only of providing the robot geometric model plus any constraints

Computation of ground waves from pile driving and their effects on structures

Present guidance on levels of vibration generated by pile driving is primarily empirical, conservative and often contradictory. The objective of this research was to model the ground waves generated by pile driving using the ABAQUS finite element program in order to predict the free ground surface response resulting from installation by both impact and vibratory hammers. New procedures including infinite element and quiet boundary formulations have been developed for the computation of ground surface vibrations caused by impact and vibratory driving of pre-formed piles. The procedures do not require a detailed knowledge of site conditions and are therefore particularly useful as a preliminary design tool and for modelling the large amount of site data that currently exists in order to assist in the development of more rational guidance. The work has brought together research from several areas of study in order to produce computational procedures for modelling vibrations from pile driving. The new models have been validated by comparisons with measurements from various piling sites. The new methods now need to be applied to a large number of varied sites in order to develop site specific guidance. It is envisaged that this guidance could be in the form of design charts or simple formulae for incorporation into the relevant British Standards or Eurocodes. A range of common building forms has been incorporated into the models. The results indicate that slender frames can be analysed by transient displacements imposed on the foundations; however, a full three-dimensional analysis with soil-structure interaction is required for walls and infilled panels so that the reduced foundation displacements are modelled correctly. The techniques developed during this project could be usefully extended to model the effects of pile driving on various geotechnical structures and pipelines and also other forms of excitation, such as vibrocompaction