Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Monroy R, Zdravkovic L, Ridley AM, 2015,

    Mechanical behaviour of unsaturated expansive clay under K-0 conditions

    , ENGINEERING GEOLOGY, Vol: 197, Pages: 112-131, ISSN: 0013-7952
  • Journal article
    Cui W, Gawecka KA, Taborda DMG, Potts DM, Zdravkovic Let al., 2015,

    Time-step constraints in transient coupled finite element analysis

    , International Journal for Numerical Methods in Engineering, Vol: 106, Pages: 953-971, ISSN: 1097-0207

    In transient finite element analysis, reducing the time-step size improves the accuracy of the solution. However, a lower bound to the time-step size exists, below which the solution may exhibit spatial oscillations at the initial stages of the analysis. This numerical ‘shock’ problem may lead to accumulated errors in coupled analyses. To satisfy the non-oscillatory criterion, a novel analytical approach is presented in this paper to obtain the time-step constraints using the θ-method for the transient coupled analysis, including both heat conduction–convection and coupled consolidation analyses. The expressions of the minimum time-step size for heat conduction–convection problems with both linear and quadratic elements reduce to those applicable to heat conduction problems if the effect of heat convection is not taken into account. For coupled consolidation analysis, time-step constraints are obtained for three different types of elements, and the one for composite elements matches that in the literature. Finally, recommendations on how to handle the numerical ‘shock’ issues are suggested.

  • Journal article
    Ormo J, Melero-Asensio I, Housen K, Wunnemann K, Elbeshausen D, Collins GSet al.,

    Scaling and reproducibility of craters produced at the Experimental Projectile Impact Chamber (EPIC), Centro de Astrobiología, Spain

    , Meteoritics & Planetary Science, ISSN: 1086-9379
  • Journal article
    Xu S, Freeman SPHT, Rood DH, Shanks RPet al., 2015,

    Decadal <sup>10</sup>Be, <sup>26</sup>Al and <sup>36</sup>Cl QA measurements on the SUERC 5 MV accelerator mass spectrometer

    , Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, Vol: 361, Pages: 39-42, ISSN: 0168-583X

    © 2015 Elsevier B.V.All rights reserved. We quantify the routine performance and uncertainties of cosmogenic 10Be, 26Al and 36Cl QA measurements made on the SUERC 5 MV accelerator mass spectrometer since 2004. Our analysis compiles data from primary (NIST SRM4325 for 10Be, Purdue Z92-0222 for 26Al and Purdue Z93-0005 for 36Cl) and secondary (Nishiizumi's series for 10Be, 26Al and 36Cl) reference samples with 10Be/9Be, 26Al/27Al and 36Cl/Cl ratios ranging between 10-11 and 10-13. Our decadal datasets indicate that the 10Be, 26Al and 36Cl secondary standard samples have average standard deviations 1.1%-2.4%, 1.1%-2.8% and 3.0%-3.1%, respectively. The average statistical uncertainties based on counting statistics are 1.0%-1.8%, 0.9%-2.8% and 2.5%-2.7% for 10Be, 26Al and 36Cl, respectively. These indicate additional uncertainties (0.6%-1.6% for 10Be, 0.5%-2.4% for 26Al and 1.4%-1.7% for 36Cl) above those calculated from counting statistics alone. The average differences between the measured and the nominal values are within ±1% in 13 of 14 secondary samples.

  • Journal article
    Van Reeuwijk M, Craske J, 2015,

    Energy-consistent entrainment relations for jets and plumes

    , Journal of Fluid Mechanics, Vol: 732, Pages: 333-355, ISSN: 1469-7645

    We discuss energetic restrictions on the entrainment coefficient for axisymmetric jets and plumes. The resulting entrainment relation includes contributions from the mean flow, turbulence and pressure, fundamentally linking to the production of turbulence kinetic energy, the plume Richardson number Ri and the profile coefficients associated with the shape of the buoyancy and velocity profiles. This entrainment relation generalises the work by Kaminski et al. (J. Fluid Mech.vol. 526, 2005, pp. 361{376) and Fox (J. Geophys. Res. vol. 75, 1970, pp. 6818{6835). The energetic viewpoint provides a unified framework with which to analyse the classical entrainment models implied by the plume theories of Morton, Taylor and Turner (Proc. Roy. Soc. London A vol. 234, 1955, pp.1{23) and Priestley and Ball (Q. J. R. Meteorol. Soc. vol. 81, 1954, pp. 144{157). Datafor pure jets and plumes in unstratified environments indicate that to first order the physics are captured by the Priestley and Ball entrainment model, implying that 1) the profile coefficient associated with the production of turbulence kinetic energy has approximately the same value for pure plumes and jets; 2) the value of for a pure plume is roughly a factor 5/3 larger than for a jet; and 3) the enhanced entrainment coefficient in plumes is primarily associated with the behaviour of the mean flow and not with buoyancy-enhanced turbulence. Theoretical suggestions are made on how entrainment can be systematically studied by creating constant Ri flows in a numerical simulation or laboratory experiment.

  • Journal article
    Monteux J, Collins GS, Tobie G, Choblet Get al., 2015,

    Consequences of large impacts on Enceladus' core shape

    , Icarus, Vol: 264, Pages: 300-310, ISSN: 1090-2643

    The intense activity on Enceladus suggests a differentiated interior consisting of a rocky core, an internal ocean and an icy mantle. However, topography and gravity data suggests large heterogeneity in the interior, possibly including significant core topography. In the present study, we investigated the consequences of collisions with large impactors on the core shape. We performed impact simulations using the code iSALE2D considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0.24 and 2.4 km/s. Our simulations showed that the main controlling parameters for the post-impact shape of Enceladus’ rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core. For low energy impacts, the impactors do not pass completely through the icy mantle. Subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly. For moderately energetic impacts, the impactors completely penetrate through the icy mantle, inducing a negative core topography surrounded by a positive anomaly of smaller amplitude. The depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity. For highly energetic impacts, the rocky core is strongly deformed, and the full body is likely to be disrupted. Explaining the long-wavelength irregular shape of Enceladus’ core by impacts would imply multiple low velocity (<2.4 km/s) collisions with deca-kilometric differentiated impactors, which is possible only after the LHB period.

  • Journal article
    Allen PA, Armitage JJ, Whittaker AC, Michael NA, Roda-Boluda D, D'Arcy Met al., 2015,

    Fragmentation model of the grain size mix of sediment supplied to basins

    , Journal of Geology, Vol: 123, Pages: 405-427, ISSN: 1537-5269
  • Journal article
    Castelltort S, Whittaker AC, Verges J, 2015,

    Tectonics, sedimentation and surface processes: from the erosional engine to basin deposition

    , Earth Surface Processes and Landforms, Vol: 40, Pages: 1839-1846, ISSN: 1096-9837
  • Journal article
    Wan X, Liu JG, Yan H, 2015,

    The Illumination Robustness of Phase Correlation for Image Alignment

    , IEEE Transactions on Geoscience and Remote Sensing, Vol: 53, Pages: 5746-5759, ISSN: 0196-2892

    Phase correlation (PC) is a well-established imagematching algorithm. It is robust to the variation of image contrastand brightness, but whether it is invariant to local illuminationchange, particularly sun angle change, is yet to be investigated.This paper presents our study to prove and demonstrate therobustness of illumination invariance of the PC algorithm viamathematical analysis and image matching experiments. First, a3-D space named slope-aspect-intensity (SAI) is proposed to characterizethe 3-D relationship between image intensity and terrainslope/aspect angles for a given illumination geometry. Based onthe SAI space, the mathematical relationship between PC crosspowerspectra and illumination direction (e.g., solar azimuth andzenith angles) is analyzed. The impact of illumination angle variationbetween two images for matching is then rigorously investigatedvia experiments using simulated terrain shading imagesfrom a digital elevation model and real optical images taken underdifferent sun illumination conditions. Our study confirms that PCis robustly invariant to illumination and therefore can achievereliable matching between images taken under different solarillumination conditions for various remote sensing applications.

  • Journal article
    Abushaikha AS, Blunt MJ, Gosselin OR, Pain CC, Jackson MDet al., 2015,

    Interface control volume finite element method for modelling multi-phase fluid flow in highly heterogeneous and fractured reservoirs

    , JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 298, Pages: 41-61, ISSN: 0021-9991
  • Conference paper
    Martinez Calonge D, Gawecka KA, Zdravkovic L, Sim WW, Taborda DMGet al., 2015,

    Development of a new temperature-controlled triaxial apparatus for saturated soils

    , 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing

    In recent years, the study of the Thermo-Hydro -Mechanical (THM) behaviour of geomaterials has become a growing area in geotechnical engineering due to the increasing interest in energy geostructures and underground nuclear waste disposal. Advanced laboratory testing is essential in gaining an understanding of the THM behaviour of soils and solving these complex geomechanical problems. This paper describes the development of a new triaxial apparatus at the Imperial College Geotechnics Laboratory, capable of testing saturated soils at temperatures up to 85°C and pressures up to 800kPa. In order to aid its design, numerical analysis of the thermal response of the cell was conducted using the Imperial College Finite Element Program (ICFEP) with its newly developed THM capabilities.

  • Conference paper
    Byrne BW, McAdam RA, Burd HJ, Houlsby GT, Martin CM, Gavin K, Doherty P, Igoe D, Zdravkovic L, Taborda DMG, Potts DM, Jardine RJ, Sideri M, Schroeder FC, Muir Wood A, Kallehave D, Skov Gretlund Jet al., 2015,

    Field testing of large diameter piles under lateralloading for offshore wind applications

    , 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing

    Offshore wind power in the UK, and around Europe, has the potential to deliver significant quantities of renewable energy. The foundation is a critical element in the design. The most common foundation design is a single large diameter pile, termed a monopile. Pile diameters of between 5m and 6m are routinely used, with diameters up to 10m or more, being considered for future designs. Questions have been raised as to whether current design methods for lateral loading are relevant to these very large diameter piles. To explore this problem a joint industry project, PISA, co-ordinated by DONG Energy and the Carbon Trust, has been established. The aim of the project is to develop a new design framework for laterally loaded piles based on new theoretical developments, numerical modelling and bench-marked against a suite of large scale field pile tests. The project began in August 2013 and is scheduled to complete during 2015. This paper briefly outlines the project, focusing on the design of the field testing. The testing involves three sizes of pile, from 0.27m in diameter through to 2.0m in diameter. Two sites will be used; a stiff clay site and a dense sand site. Tests will include monotonic loading and cyclic loading. A suite of site investigation will be carried out to aid interpretation of the field tests, and will involve in-situ testing, standard laboratory testing and more advanced laboratory testing.

  • Conference paper
    Dubasaru V, Zdravkovic L, Taborda DMG, Hardy Set al., 2015,

    Influence of pile raft stiffness on building behaviour in a tunnel-pile clash scenario

    , 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing

    In a modern urban environment, the underground space becomes increasingly congested due to the high value of the land that forces the new infrastructure projects to be constructed deeper into the ground. For each new project, the potential of both expected and unexpected clashes between new tunnel alignments and the foundations of the existing structures becomes more probable. However, to date, the research on tunnel-pile clashes has been scarce. In the current study, the effects of such a situation are studied by carrying out finite element analyses for a scenario that is typical in the London ground profile. A parametric study was conducted to investigate the influence of the pile raft bending stiffness on the building settlement and the change in piles’ axial forces. It is shown that an increased raft bending stiffness helps to transfer the load from the trimmed pile to the adjacent piles, thus reducing the settlement of the trimmed pile. In the process of tunnel excavation, the pile settles due to the soil-induced downdrag and the loss of both its base and part of its shaft capacity. It is concluded that the tunnel-pile clash has a large impact on the surface structure, piles and tunnel itself.

  • Conference paper
    Gawecka KA, Cui W, Potts DM, Taborda DMG, Zdravkovic Let al., 2015,

    Numerical modelling of open-loop ground source energy systems

    , 16th European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: ICE Publishing

    The environmental and economic benefits of utilising the ground for extracting and storing heat have been known for a long time. However, only recently have government sustainability policies and rising energy prices encouraged the use of this renewable energy resource. In open-loop systems water is abstracted from one well and re-injected into another after exchanging energy with a building’s heating/cooling system using a heat pump. In order to guarantee a good performance of the system, it is fundamental that the possibility of thermal breakthrough occurring is minimised, i.e. that the temperature of the water being abstracted remains unaffected by the injection of warmer/cooler water at the other well. In this paper, the Imperial College FiniteElement Program (ICFEP), which is capable of simulating fully coupled thermo-hydro-mechanical behaviour of porous materials, was used to perform two-dimensional analyses of open-loop ground source heat systems. The parametric studies carried out highlight the relative impact on the occurrence of thermal break-through of the hydraulic ground conditions andthe geometric characteristics of the system, providing an invaluable insight into possible improvements to the current design procedure.

  • Journal article
    Prelat A, Pankhania S, Jackson CA-L, Hodgson DMet al., 2015,

    Slope gradient and lithology as controls on the initiation of submarine slope gullies; insights from the North Carnarvon Basin, Offshore NW Australia

    , Sedimentary Geology, Vol: 329, Pages: 12-17, ISSN: 0037-0738

    Slope-confined submarine gullies are present on many continental margins, yet the controls on their initiation and demise are poorly understood because modern or recently active systems are rarely if ever monitored, and exhumed systems, typically formed in very fine-grained successions, are poorly preserved at outcrop. We use 3D seismic reflection and borehole data from offshore NW Australia to investigate long-term (~ 40 Myr) variations in the geomorphology of Eocene-to-Miocene gullies that developed in mixed carbonate–clastic clinothems. Through time, clinoform slope gradient increases from 1.6° to 3.2°, with gullies forming when the clinoform slope exceeds 2.5°. After their inception, gullies increase in width (from 350 m to 770 m) and depth (from 37 m to 60 m). Slope steepening appears to coincide with a change from poorly cemented, fine-grained carbonate to better-cemented, coarse-grained carbonate, implying a secondary, lithological control on slope dip and, ultimately, gully formation.

  • Journal article
    Aghakouchakn A, Sim WW, Jardine RJ, 2015,

    Stress-path laboratory tests to characterise the cyclic behaviour of piles driven in sands

    , SOILS AND FOUNDATIONS, Vol: 55, Pages: 917-928, ISSN: 0038-0806

    Recent publications have emphasised the importance of addressing cyclic behaviour when designing piled foundations. Laboratory tests may be conducted to provide site-specific cyclic soil characteristics, but questions arise concerning: (i) how to take into account the pile installation process and (ii) how to apply the results to assess pile capacity and deformation responses under cyclic loads. This paper describes an investigation into the cyclic behaviour of Dunkerque and NE34 Fontainebleau sands, performed to support and to help analyse field-scale and model pile cyclic loading tests on the same soils. Forty computer-controlled, locally instrumented, cyclic and static triaxial tests were performed, following testing schemes that were developed to reflect the conditions adjacent to the pile shafts. Assessments were made of how the cyclic variations in stress imposed during installation and the period allowing for the two types of sand to creep following such ‘installation’ effects, affect the response to subsequent cycling. Constant-volume cyclic tests, involving up to 4500 cycles, were imposed from alternative sets of initial conditions that revealed the relationships among the cyclic deviatoric amplitude, the changes in mean effective stress and the number of cycles as well as the permanent strain accumulation and the cyclic stiffness characteristics. Monotonic compression and extension tests are also presented for both sands to help frame their strength, stiffness and critical state properties. A synthesis with previously obtained cyclic pile test trends confirms the practical applicability of the results obtained.

  • Journal article
    Potter RWK, Kring DA, Collins GS, 2015,

    Scaling of basin-sized impacts and the influence of target temperature

    , Geological Society of America Special Papers, Vol: 518, Pages: 99-113, ISSN: 0072-1077

    We produce a set of scaling laws for basin-sized impacts using data from a suiteof lunar basin numerical models. The results demonstrate the importance of preimpacttarget temperature and thermal gradient, which are shown to greatly infl uencethe modifi cation phase of the impact cratering process. Impacts into targets withcontrasting thermal properties also produce very different crustal and topographicprofi les for impacts of the same energy. Thermal conditions do not, however, signifi -cantly infl uence the excavation stage of the cratering process; results demonstrate,as a consequence of gravity-dominated growth, that transient crater radii are generallywithin 5% of each other over a wide range of thermal gradients. Excavationdepth-to-diameter ratios for the basin models (~0.12) agree well with experimental,geological, and geophysical estimates, suggesting basins follow proportional scaling.This is further demonstrated by an agreement between the basin models andPi- scaling laws based upon fi rst principles and experimental data. The results of thiswork should also be applicable to basin-scale impacts on other silicate bodies, includingthe Hadean Earth.

  • Journal article
    Craske J, Debugne ALR, van Reeuwijk M, 2015,

    Shear-flow dispersion in turbulent jets

    , Journal of Fluid Mechanics, Vol: 781, Pages: 28-51, ISSN: 0022-1120

    We investigate the transport of a passive scalar in a fully developed turbulent axisymmetric jet at a Reynolds number of Re = 4815 using data from direct numerical simulation. In particular, we simulate the response of the concentration field to an instantaneous variation of the scalar flux at the source. To analyse the time evolution of this statisticallyunsteady process we take an ensemble average over 16 independent simulations. We find that the evolution of Cm(z, t), the radial integral of the ensemble-averaged concentration, is a self-similar process, with front position and spread both scaling as √t. The longitudinal mixing of Cm is shown to be primarily caused by shear-flow dispersion.Using the approach developed by Craske & van Reeuwijk (J. Fluid Mech., vol. 763, 2014,pp. 538–566), the classical theory for shear-flow dispersion is applied to turbulent jets to obtain a closure that couples the integral scalar flux to the integral concentration Cm. Model predictions using the dispersion closure are in good agreement with the simulation data. Application of the dispersion closure to a two-dimensional jet results in an integraltransport equation that is fully consistent with that of Landel et al. (J. Fluid Mech., vol.711, 2012, pp. 212–258)

  • Conference paper
    Summersgill FC, Kontoe S, Potts DM, 2015,

    Finite element investigation of vertical stabilisation piles in a stiff clay excavated slope using a nonlocal strain softening model

    , XVI ECSMGE Geotechnical Engineering for Infrastructure and Development
  • Conference paper
    Colombero R, Kontoe S, Foti S, Potts DMet al., 2015,

    Numerical modelling of wave attenuation through soil

    , XVI ECSMGE Geotechnical Engineering for Infrastructure and Development

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=833&limit=20&page=5&respub-action=search.html Current Millis: 1582322493976 Current Time: Fri Feb 21 22:01:33 GMT 2020