Automated Computation of the Fundamental Matrix for Vision-Based Construction Site Applications

Estimating the fundamental matrix (F), to determine the epipolar geometry between a pair of images or video frames, is a basic step for a wide variety of vision-based functions used in construction operations, such as camera-pair calibration, automatic progress monitoring, and 3D reconstruction. Currently, robust methods (e.g., SIFT + normalized eight-point algorithm + RANSAC) are widely used in the construction community for this purpose. Although they can provide acceptable accuracy, the significant amount of required computational time impedes their adoption in real-time applications, especially video data analysis with many frames per second. Aiming to overcome this limitation, this paper presents and evaluates the accuracy of a solution to find F by combining the use of two speedy and consistent methods: SURF for the selection of a robust set of point correspondences and the normalized eight-point algorithm. This solution is tested extensively on construction site image pairs including changes in viewpoint, scale, illumination, rotation, and moving objects. The results demonstrate that this method can be used for real-time applications (5 image pairs per second with the resolution of 640 × 480) involving scenes of the built environment.

A subdivision-based implementation of the hierarchical b-spline finite element method

A novel technique is presented to facilitate the implementation of hierarchical b-splines and their interfacing with conventional finite element implementations. The discrete interpretation of the two-scale relation, as common in subdivision schemes, is used to establish algebraic relations between the basis functions and their coefficients on different levels of the hierarchical b-spline basis. The subdivision projection technique introduced allows us first to compute all element matrices and vectors using a fixed number of same-level basis functions. Their subsequent multiplication with subdivision matrices projects them, during the assembly stage, to the correct levels of the hierarchical b-spline basis. The proposed technique is applied to convergence studies of linear and geometrically nonlinear problems in one, two and three space dimensions. © 2012 Elsevier B.V.

Interaction between Fe-based oxygen carriers and n-heptane during chemical looping combustion

Chemical looping combustion (CLC) uses a metal oxide (the oxygen carrier) to provide oxygen for the combustion of a fuel and gives an inherent separation of pure CO2 with minimal energy penalty. In solid-fuel CLC, volatile matter will interact with oxygen carriers. Here, the interaction between iron-based oxygen carriers and a volatile hydrocarbon (n-heptane) was investigated in both a laboratory-scale fluidised bed and a thermogravimetric analyser (TGA). Experiments were undertaken to characterise the thermal decomposition of the n-heptane occurring in the presence and in the absence of the oxygen carrier. In a bed of inert particles, carbon deposition increased with temperature and acetylene appeared as a possible precursor. For a bed of carrier consisting of pure Fe2O3, carbon deposition occurred once the Fe2O3 was fully reduced to Fe. When the Fe2O3 was doped with 10 mol % Al2O3 (Fe90Al), deposition started when the carrier was reduced to a mixture of Fe and FeAl2O4, the latter being very unreactive. Furthermore, when pure Fe2O3 was fully reduced to Fe, agglomeration of the fluidised bed occurred. However, Fe90Al did not give agglomeration even after extended reduction. The results suggest that Fe90Al is promising for the CLC of solid fuels. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Sensors based on SAW and FBAR technologies

Over the last few years a number of sensing platforms are being investigated for their use in drug development, microanalysis or medical diagnosis. Lab-on-a-chip (LOC) are devices integrating more than one laboratory functions on a single device chip of a very small size, and typically consist of two main components: microfluidic handling systems and sensors. The physical mechanisms that are generally used for microfluidics and sensors are different, hence making the integration of these components difficult and costly. In this work we present a lab-on-a-chip system based on surface acoustic waves (for fluid manipulation) and film bulk acoustic resonators (for sensing). Coupling surface acoustic waves into liquids induces acoustic streaming and motion of micro-droplets, whilst it is well-known that bulk acoustic waves can be used to fabricate microgravimetric sensors. Both technologies offer exceptional sensitivity and can be fabricated from piezoelectric thin films deposited on Si substrates, reducing the fabrication time/cost of the LOC devices. © 2013 SPIE.

A coupled hydro-mechanical analysis for prediction of hydraulic fracture propagation in saturated porous media using EFG mesh-less method

The details of the Element Free Galerkin (EFG) method are presented with the method being applied to a study on hydraulic fracturing initiation and propagation process in a saturated porous medium using coupled hydro-mechanical numerical modelling. In this EFG method, interpolation (approximation) is based on nodes without using elements and hence an arbitrary discrete fracture path can be modelled.The numerical approach is based upon solving two governing partial differential equations of equilibrium and continuity of pore water simultaneously. Displacement increment and pore water pressure increment are discretized using the same EFG shape functions. An incremental constrained Galerkin weak form is used to create the discrete system of equations and a fully implicit scheme is used for discretization in the time domain. Implementation of essential boundary conditions is based on the penalty method. In order to model discrete fractures, the so-called diffraction method is used.Examples are presented and the results are compared to some closed-form solutions and FEM approximations in order to demonstrate the validity of the developed model and its capabilities. The model is able to take the anisotropy and inhomogeneity of the material into account. The applicability of the model is examined by simulating hydraulic fracture initiation and propagation process from a borehole by injection of fluid. The maximum tensile strength criterion and Mohr-Coulomb shear criterion are used for modelling tensile and shear fracture, respectively. The model successfully simulates the leak-off of fluid from the fracture into the surrounding material. The results indicate the importance of pore fluid pressure in the initiation and propagation pattern of fracture in saturated soils. © 2013 Elsevier Ltd.