Earth Systems Science Computational Centre Publications - UQ eSpace
http://espace.library.uq.edu.au/
The University of QueenslandenFez http://blogs.law.harvard.edu/tech/rssThe Lattice Solid Model to Simulate the Physics of Rocks and Earthquakes: Incorporation of Granular Friction
http://espace.library.uq.edu.au/view/UQ:149052
2008-06-06T15:08:50Z
Place, D. G.; Mora, P. R. The Lattice Solid Model: Towards a realistic simulation model for earthquake micro-physics and the development of a virtual laboratory for the earthquake cycle
http://espace.library.uq.edu.au/view/UQ:150858
2008-06-06T16:50:24Z
Mora, P. R.; Place, D. G.; Abe, S.; Weatherley, D. K.; Keane, T. A. Theoretical and numerical analyses of convective instability in porous media with temperature-dependent viscosity
http://espace.library.uq.edu.au/view/UQ:39745
Exact analytical solutions of the critical Rayleigh numbers have been obtained for a hydrothermal system consisting of a horizontal porous layer with temperature-dependent viscosity. The boundary conditions considered are constant temperature and zero vertical Darcy velocity at both the top and bottom of the layer. Not only can the derived analytical solutions be readily used to examine the effect of the temperature-dependent viscosity on the temperature-gradient driven convective flow, but also they can be used to validate the numerical methods such as the finite-element method and finite-difference method for dealing with the same kind of problem. The related analytical and numerical results demonstrated that the temperature-dependent viscosity destabilizes the temperature-gradient driven convective flow and therefore, may affect the ore body formation and mineralization in the upper crust of the Earth. Copyright (C) 2003 John Wiley Sons, Ltd.2007-08-13T13:54:01Z
Lin, G; Zhao, CB; Hobbs, BE; Ord, A; Muhlhaus, HB Theoretical and numerical analyses of convective instability in porous media with upward throughflow
http://espace.library.uq.edu.au/view/UQ:35706
Exact analytical solutions have been obtained for a hydrothermal system consisting of a horizontal porous layer with upward throughflow. The boundary conditions considered are constant temperature, constant pressure at the top, and constant vertical temperature gradient, constant Darcy velocity at the bottom of the layer. After deriving the exact analytical solutions, we examine the stability of the solutions using linear stability theory and the Galerkin method. It has been found that the exact solutions for such a hydrothermal system become unstable when the Rayleigh number of the system is equal to or greater than the corresponding critical Rayleigh number. For small and moderate Peclet numbers (Pe less than or equal to 6), an increase in upward throughflow destabilizes the convective flow in the horizontal layer. To confirm these findings, the finite element method with the progressive asymptotic approach procedure is used to compute the convective cells in such a hydrothermal system. Copyright (C) 1999 John Wiley & Sons, Ltd.2007-08-13T11:15:11Z
Zhao, CB; Hobbs, BE; Muhlhaus, HB Theoretical and numerical analyses of pore-fluid flow focused heat transfer around geological faults and large cracks
http://espace.library.uq.edu.au/view/UQ:174783
In this paper, theoretical and numerical methods are used to investigate pore-fluid flow focused temperature distribution patterns around geological faults and cracks of any length-scales in hydrothermal systems. If the far field inflow is uniform and the long axis of an elliptical fault of any length-scale is parallel to the far field inflow direction, a complete set of analytical solutions has been presented for the pore-fluid velocity, stream function and excess pore-fluid pressure around the elliptical fault embedded in fluid-saturated porous media. Because the analytical solutions are explicitly expressed in the conventional Cartesian coordinate system, not only can they be used to gain a theoretical insight into the pore-fluid flow patterns around geological faults and large cracks, but also they can be used as valuable benchmark solutions for validating any numerical methods. After a finite element computational model is validated by comparing the numerical solutions with the present analytical solutions, it is used to investigate pore-fluid flow focused heat transfer around geological faults in hydrothermal systems. Some interesting conclusions in relation to the effects of geological faults on pore-fluid flow focused heat transfer have been made through both the theoretical and the numerical analyses.2009-04-08T20:16:41Z
Zhao, Chongbin; Hobbs, Bruce, E.; Ord, Alison; Hornby, peter; Peng, Shenglin; Mühlhaus, Hans Theoretical and numerical analysis of large-scale heat transfer problems with temperature-dependent pore-fluid densities
http://espace.library.uq.edu.au/view/UQ:78347
Purpose - In many scientific and engineering fields, large-scale heat transfer problems with temperature-dependent pore-fluid densities are commonly encountered. For example, heat transfer from the mantle into the upper crust of the Earth is a typical problem of them. The main purpose of this paper is to develop and present a new combined methodology to solve large-scale heat transfer problems with temperature-dependent pore-fluid densities in the lithosphere and crust scales. Design/methodology/approach - The theoretical approach is used to determine the thickness and the related thermal boundary conditions of the continental crust on the lithospheric scale, so that some important information can be provided accurately for establishing a numerical model of the crustal scale. The numerical approach is then used to simulate the detailed structures and complicated geometries of the continental crust on the crustal scale. The main advantage in using the proposed combination method of the theoretical and numerical approaches is that if the thermal distribution in the crust is of the primary interest, the use of a reasonable numerical model on the crustal scale can result in a significant reduction in computer efforts. Findings - From the ore body formation and mineralization points of view, the present analytical and numerical solutions have demonstrated that the conductive-and-advective lithosphere with variable pore-fluid density is the most favorite lithosphere because it may result in the thinnest lithosphere so that the temperature at the near surface of the crust can be hot enough to generate the shallow ore deposits there. The upward throughflow (i.e. mantle mass flux) can have a significant effect on the thermal structure within the lithosphere. In addition, the emplacement of hot materials from the mantle may further reduce the thickness of the lithosphere. Originality/value - The present analytical solutions can be used to: validate numerical methods for solving large-scale heat transfer problems; provide correct thermal boundary conditions for numerically solving ore body formation and mineralization problems on the crustal scale; and investigate the fundamental issues related to thermal distributions within the lithosphere. The proposed finite element analysis can be effectively used to consider the geometrical and material complexities of large-scale heat transfer problems with temperature-dependent fluid densities.2007-08-15T07:40:19Z
Zhao, CB; Hobbs, B; Ord, A; Lin, G; Muhlhaus, HB Theoretical investigation of convective instability in inclined and fluid-saturated three-dimensional fault zones.
http://espace.library.uq.edu.au/view/UQ:74649
The convective instability of pore-fluid flow in inclined and fluid-saturated three-dimensional fault zones has been theoretically investigated in this paper. Due to the consideration of the inclined three-dimensional fault zone with any values of the inclined angle, it is impossible to use the conventional linear stability analysis method for deriving the critical condition (i.e., the critical Rayleigh number) which can be used to investigate the convective instability of the pore-fluid flow in an inclined three-dimensional fault zone system. To overcome this mathematical difficulty, a combination of the variable separation method and the integration elimination method has been used to derive the characteristic equation, which depends on the Rayleigh number and the inclined angle of the inclined three-dimensional fault zone. Using this characteristic equation, the critical Rayleigh number of the system can be numerically found as a function of the inclined angle of the three-dimensional fault zone. For a vertically oriented three-dimensional fault zone system, the critical Rayleigh number of the system can be explicitly derived from the characteristic equation. Comparison of the resulting critical Rayleigh number of the system with that previously derived in a vertically oriented three-dimensional fault zone has demonstrated that the characteristic equation of the Rayleigh number is correct and useful for investigating the convective instability of pore-fluid flow in the inclined three-dimensional fault zone system. The related numerical results from this investigation have indicated that: (1) the convective pore-fluid flow may take place in the inclined three-dimensional fault zone; (2) if the height of the fault zone is used as the characteristic length of the system, a decrease in the inclined angle of the inclined fault zone stabilizes the three-dimensional fundamental convective flow in the inclined three-dimensional fault zone system; (3) if the thickness of the stratum is used as the characteristic length of the system, a decrease in the inclined angle of the inclined fault zone destabilizes the three-dimensional fundamental convective flow in the inclined three-dimensional fault zone system; and that (4) the shape of the inclined three-dimensional fault zone may affect the convective instability of pore-fluid flow in the system. (C) 2004 Published by Elsevier B.V.2007-08-15T05:21:52Z
Zhao, CB; Hobbs, BE; Ord, A; Peng, SL; Muhlhaus, HB; Liu, LM The physics of crustal faulty systems, numerical simulation, and earthquake prediction: recent advances and challenges for the 21-st century
http://espace.library.uq.edu.au/view/UQ:96788
2007-08-24T00:48:11Z
Mora, P. R.; Place, D. G.; Weatherley, D. K.; Abe, S. The plausibility of long-wavelength stress correlation or stress magnitude as a mechanism for precursory seismicity: Results from two simple elastics models
http://espace.library.uq.edu.au/view/UQ:142333
2008-06-10T13:23:33Z
Winter, M. The practice of decision making v decision theory
http://espace.library.uq.edu.au/view/UQ:161343
Judges, arbitrators, business people and others must routinely decide "close cases," and often, must articulate their reasons publicly. Some preliminary work has been done, from first principles, toward defining methods of training professionals to make a fair and thorough decision, and also toward defining performance-based methods of identifying people who have a high aptitude for decision-making. But how well do these designs "map" onto the emerging research in decision theory? Much of this research seems to suggest that typical decision making is "from the gut" --- or from prejudice --- and supported ex post facto by "reasoning" that selectively emphasizes the facts and arguments that support the decision already made. What does decision theory say about the training necessary to overcome such tendencies? Furthermore, is there a role for "facilitative judging," i.e. a version of judging which blends dispute resolution skills with judging skills --- or must these be considered as separate domains?2009-01-21T09:37:47Z
Sourdin, Tania; Honeyman, Christopher; O'Conner, Kathleen; Wade, John The rapid development of high performance numerical models in mantle convection
http://espace.library.uq.edu.au/view/UQ:101683
2007-08-23T20:20:12Z
Davies, M.; Muhlhaus, H. B.; Gross, L. Thermal and Hydraulic coupled modeling of hot fractured rock geotermal reservoir
http://espace.library.uq.edu.au/view/UQ:104930
2007-08-23T22:42:29Z
Xing, H; Wyborn,; XU,; Yin, C.; Mora, P R Thermal effects in the evolution of initially layered mantle material
http://espace.library.uq.edu.au/view/UQ:13257
A simpliﬁed model for anisotropic mantle convection based on a novel class of rheologies, originally developed for folding instabilities in multilayered rock (MUHLHAUS et al., 2002), is extended ¨ through the introduction of a thermal anisotropy dependent on the local layering. To examine the eﬀect of the thermal anisotropy on the evolution of mantle material, a parallel implementation of this model was undertaken using the Escript modelling toolkit and the Finley ﬁnite-element computational kernel (DAVIES et al., 2004). For the cases studied, there appears too little if any eﬀect. For comparative purposes, the eﬀects of anisotropic shear viscosity and the introduced thermal anisotropy are also presented. These results contribute to the characterization of viscous anisotropic mantle convection subject to variation in thermal conductivities and shear viscosities.2007-03-29T11:48:24Z
Davies, Matt; Muhlhaus, Hans; Gross, Lutz Thermal Effects in the Evolution of Initially Layered Mantle Material
http://espace.library.uq.edu.au/view/UQ:9143
A simplied model for anisotropic mantle convection based on a novel class of rheologies, originally developed for folding instabilities in multilayered rock, is extended through the introduction of a thermal anisotropy dependent on the local layering. To examine the eect of the thermal anisotropy on the evolution of mantle material, a parallel implementation of this model was undertaken using the Escript modelling toolkit and the Finley nite element computational kernel. For the cases studied, there appears to little if any eect. For comparative purposes, the eects of anisotropic shear viscosity and the introduced thermal anisotropy are also presented. These results contribute to the characterisation of viscous anisotropic mantle convection subject to variation in thermal conductivities and shear viscosities.2005-10-07T00:00:00Z
Davies, Matt; Muhlhaus, Hans-Bernd; Gross, Lutz Thermal evolution models of the moon
http://espace.library.uq.edu.au/view/UQ:104974
2007-08-23T22:44:16Z
Gottschaldt, K.; Breuer, D.; Muhlhaus, H. B.; Baumgardner, R. Thermal evolution models of the moon
http://espace.library.uq.edu.au/view/UQ:104976
2007-08-23T22:44:20Z
Gottschaldt, K.; Breuer, D.; Muhlhaus, H. B.; Baumgardner, R. Thermal stability of poly(lactic acid) before and after g-radiolysis
http://espace.library.uq.edu.au/view/UQ:143311
The thermal degradation of poly(lactic acid) has been studied using thermal gravimetric analysis over the temperature range 300-700 K, and following a sterilization dose of 50 kGy under vacuum, nitrogen or air. Isothermal weight loss studies have been found to follow complex kinetics with activation energies determined by the MacCallum method for various fractional conversions in the range 72-103 kJ mol(-1). Dynamic thermogravimetric analysis at heating rates from 10 to 25 K min(-1) showed the maximum rate of weight loss occurs in the range 550-650 K with the onset of degradation being in the range 450-500 K. The thermograms observed for the unirradiated polymer under a nitrogen atmosphere showed a very small shoulder on the low temperature side of the thermograms. The Kissinger expression, which is based on the temperature for the maximum rare of weight loss, yielded an activation energy of 109 kJ mol(-1) for thermal degradation under nitrogen and 131 kJ mol(-1) under oxygen. Compared with those of unirradiated samples, the weight-loss profiles under nitrogen for samples irradiated under vacuum or nitrogen were shifted towards higher temperatures, but the profiles for the samples irradiated in air did not change significantly. The shift to higher temperatures for the former two samples was attributed to modification of chain-end hydroxyl groups. (C) 1999 Society of Chemical industry.2008-06-10T14:11:37Z
Babanalbandi, A.; Hill, D. T.; Hunter, D. S.; Kettle, L. The role of mobile belts for the longevity of deep cratonic lithosphere: The crumple zone model
http://espace.library.uq.edu.au/view/UQ:36346
Many Archean cratons are surrounded by Proterozoic mobile belts that have experienced episodes of tectonic re-activation over their lifetimes. This suggests that mobile belt lithosphere may be associated with long lived, inherited weakness. It is proposed that the proximity of this weakness can increase the longevity of deep Archean lithosphere by buffering Archean cratons from mantle derived stresses. The physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere. Within the simulations, the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels.2007-08-13T11:42:55Z
Lenardic, A; Moresi, L; Muhlhaus, H The transition from endogenous to exogenous growth of lava domes with the development of shear bands
http://espace.library.uq.edu.au/view/UQ:120607
The transition from an endogenous to an exogenous regime of lava dome growth must be achieved by the formation of discontinuities within the dome. Such transitions (and vice versa) are an important characteristic of most long-lived lava domes and often coincide with significant changes in the dynamics of magma supply and lava dome collapse events. For the purpose of this paper, following recent experimental and observational evidence, we assume that such a transition occurs when shear bands are generated. A model for the formation of shear bands, and therefore the growth transition within a dome and coupled conduit domain is presented. Shear bands are most likely to initiate at the junction of the conduit and base of the dome, where the shear stress experienced between new lava entering the dome and existing lava is greatest. Stress accumulation within the shear bands is likely to lead to brittle shear, resulting in the formation of fractures. Finite element modelling of lava flow shows that such shear bands only develop for certain extrusion rates and lava viscosities. Similarly, the growth regime of the lava dome will depend upon the extrusion rate and viscosity within the conduit, which is largely controlled by volatile loss and the growth of crystals in the upper part of the conduit. We consider a simplified rheology during lava dome growth considering isothermal conditions with crystal growth. The development of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for Soufrière Hills Volcano, Montserrat. During October to December 1996 this lava dome-forming eruption experienced a transition from endogenous to exogenous growth as it grew in height by about 90 m. Modelling indicates that the observed fall in magma extrusion rate from about 2.0 m3s-1 to 0.5 m3s-1, as a result of the increased pressure head from the dome and the evolution in viscosity, could have subsequently changed the dome growth regime due to the development of shear bands. Our models provide insight into the shear stress fields possible within the conduit and the shear stresses required for shear band development.2007-12-12T13:16:00Z
Hale, Alina J.; Wadge, Geoff The weakness of earthquake faults
http://espace.library.uq.edu.au/view/UQ:145093
Numerical experiments using: the particle based lattice solid model produce simulated earthquakes. Model faults with a thin gouge layer are sufficiently weak relative to those without gouge to explain the heat flow paradox (HFP). Stress drop statistics are in agreement with field estimates. Models with a thick granular fault zone exhibit a strong evolution effect. Results are initially similar to those of laboratory experiments but after a sufficient time, the system self-organizes into a weak state. The long time :required for self-organization could explain why weak gouge has not been observed in the laboratory. The new results suggest an HFP explanation without the so called fatal flaws of previously proposed solutions. They demonstrate that fault friction potentially undergoes a strong evolution effect and could be dependent on gouge microstructure. This raises questions about the extent to which laboratory derived friction laws can be used in macroscopic domain earthquake simulation studies.2008-06-10T15:40:40Z
Mora, P. R.; Place, D. Three dimensional finite element modeling of thermomechanical frictional contact between finite deformation bodies using R-minimum strategy
http://espace.library.uq.edu.au/view/UQ:115491
An algorithm for analyzing the transient thermal coupling with the frictional contact between the multiple elastic-plastic bodies in finite deformation is presented using the R-minimum strategy. An arbitrarily shaped contact element strategy, named as node-to-point contact element strategy, is proposed to handle the thermomechanical frictional contact between finite deformation bodies. Assuming the material properties to be temperature dependent, the constitutive equations for both the thermomechanical frictional contact and the thermal-elastic-plastic materials are deduced respectively and applied in our finite element code. Finally, two examples are presented to show the efficiency and usefulness of this algorithm. (C) 2002 Elsevier Science B.V. All rights reserved.2007-10-17T11:30:55Z
Xing, HL; Makinouchi, A Three-dimensional finite element simulation of large-scale nonlinear contact friction problems in deformable rocks
http://espace.library.uq.edu.au/view/UQ:183170
2009-09-03T10:20:28Z
Xing, H. L.; Makinouchi, A.; Zhao, Chongbin Time homogenization for clays subjected to large numbers of cycles
http://espace.library.uq.edu.au/view/UQ:306554
2013-08-11T00:18:15Z
Papon, A.; Yin, Z. -Y.; Riou, Y.; Hicher, P. -Y. Towards a Modeling Environment for Earth Systems Simulations
http://espace.library.uq.edu.au/view/UQ:107937
The developments of models in Earth Sciences, e.g. for earthquake prediction and for the simulation of mantel convection, are fare from being finalized. Therefore there is a need for a modelling environment that allows scientist to implement and test new models in an easy but flexible way. After been verified, the models should be easy to apply within its scope, typically by setting input parameters through a GUI or web services. It should be possible to link certain parameters to external data sources, such as databases and other simulation codes. Moreover, as typically large-scale meshes have to be used to achieve appropriate resolutions, the computational efficiency of the underlying numerical methods is important. Conceptional this leads to a software system with three major layers: the application layer, the mathematical layer, and the numerical algorithm layer. The latter is implemented as a C/C++ library to solve a basic, computational intensive linear problem, such as a linear partial differential equation. The mathematical layer allows the model developer to define his model and to implement high level solution algorithms (e.g. Newton-Raphson scheme, Crank-Nicholson scheme) or choose these algorithms form an algorithm library. The kernels of the model are generic, typically linear, solvers provided through the numerical algorithm layer. Finally, to provide an easy-to-use application environment, a web interface is (semi-automatically) built to edit the XML input file for the modelling code. In the talk, we will discuss the advantages and disadvantages of this concept in more details. We will also present the modelling environment escript which is a prototype implementation toward such a software system in Python (see www.python.org). Key components of escript are the Data class and the PDE class. Objects of the Data class allow generating, holding, accessing, and manipulating data, in such a way that the actual, in the particular context best, representation is transparent to the user. They are also the key to establish connections with external data sources. PDE class objects are describing (linear) partial differential equation objects to be solved by a numerical library. The current implementation of escript has been linked to the finite element code Finley to solve general linear partial differential equations. We will give a few simple examples which will illustrate the usage escript. Moreover, we show the usage of escript together with Finley for the modelling of interacting fault systems and for the simulation of mantel convection.2007-08-27T12:58:16Z
Gross, L.; Davies, M.; Gerschwitz, J. C.; Muhlhaus, H. B.; Hornby, P. Towards an integrated simulator for enhanced geothermal reservoirs
http://espace.library.uq.edu.au/view/UQ:237681
This paper introduces the current state in computer modelling of geothermal reservoir system and then focuses on our research efforts in high performance simulation of enhanced geothermal reservoir system. PANDAS - Parallel Adaptive static/dynamic Nonlinear Deformation Analysis System - a novel supercomputer simulation tool has been developing for simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials at different spatial and temporal scales. It is applied to simulate and visualise the enhanced geothermal system (EGS), such as (1) visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e. the permeability) for the further numerical analysis; (2) converting the available fractured rock image/fracture data to lattice grid and further simulating the fluid flow in the complicated fractures involving the detailed description of fracture dimension and geometry by the Lattice Boltzmann method; (3) interacting fault system simulation to determine the relevant complicated dynamic rupture process; (4) multiphase coupled thermo-fluid flow analysis of a geothermal reservoir system. A few of benchmark and application examples are presented to show its accuracy, stability and usefulness in simulating the enhanced geothermal reservoir system.2011-03-21T11:03:22Z
Xing, H.L.; Gao, J.; Zhang, J.; Liu, Y. Towards a Self Consistent Plate Mantle Model that Includes Elasticity: Simple Benchmarks and Application to Basic Modes of Convection
http://espace.library.uq.edu.au/view/UQ:9040
One of the difficulties with self consistent plate-mantle models capturing multiple physical features, such as elasticity, non-Newtonian flow properties, and temperature dependence, is that the individual behaviours cannot be considered in isolation. For instance, if a viscous mantle convection model is generalized naively to include hypo-elasticity, then problems based on Earth-like Rayleigh numbers exhibit almost insurmountable numerical stability issues due to spurious softening associated with the co-rotational stress terms. If a stress limiter is introduced in the form of a power law rheology or yield criterion these difficulties can be avoided. In this paper, a novel Eulerian finite element formulation for visco-elastic convection is presented and the implementation of the co-rotational stress terms is addressed. The salient dimensionless numbers of visco-elastic plastic flows such as Weissenberg, Deborah and Bingham numbers are discussed in a separate section in the context of Geodynamics. We present an Eulerian formulation for slow temperature dependent, visco-elastic-plastic flows. A consistent tangent (incremental) formulation of the governing equations is derived. Numerical and analytical solutions demonstrating the effect of visco-elasticity, co-rotational terms are first discussed for simplified benchmark problems. For flow around cylinders we identify parameter ranges of predominantly viscous and visco-plastic and transient behavior. The influence of locally high strain rates on the importance of elasticity and non-Newtonian effects is also discussed in this context. For the case of simple shear we investigate in detail the effect of different co-rotational stress rates and the effect of power law creep. The results show that the effect of the co-rotational terms is insignificant if realistic stress levels are considered (e.g. deviatoric invariant smaller than 1/10 of the shear modulus say). We also consider the basic convection modes of stagnant lid, episodic resurfacing and mobile lid convection as applicable to a cooling planet. The simulations show that elasticity does not have a significant effect on global parameters such as the Nusselt number and the qualitative nature of the basic convection pattern. Our simple benchmarks show, however, also that elasticity plays a significant role for instabilities on the local scale of an individual subduction zone.2005-10-25T00:00:00Z
Muhlhaus, Hans-Bernd; Regenauer-Lieb, Klaus Towards A Unified Model For The Dynamics Of Planets
http://espace.library.uq.edu.au/view/UQ:9149
The way a planet deforms in response to thermal or gravitational driving forces, depends on the material properties of its constituents. The Earth's behaviour is unique in that its outermost layer consists of a small number of continuously moving plates. Venus, another planet of similar size and bulk composition to the Earth displays signs of active volcanism but there is no evidence of plate movements or plate tectonics. In this article we review Eulerian finite element (FE) schemes and a particle-in-cell (PIC) FE scheme.1 Focussing initially on models of crustal deformation at a scale of a few tens of km, we choose a Mohr-Coulomb yield criterion based upon the idea that frictional slip occurs on whichever one of many randomly oriented planes happens to be favorably oriented with respect to the stress field. As coupled crust/mantle models become more sophisticated it is important to be able to use whichever failure model is appropriate to a given part of the system. We have therefore developed a way to represent Mohr-Coulomb failure within a mantle-convection fluid dynamics code. With the modelling of lithosphere deformation we use an orthotropic viscous rheology (a different viscosity for pure shear to that for simple shear) to define a preferred plane for slip to occur given the local stress eld. The simple-shear viscosity and the deformation can then be iterated to ensure that the yield criterion is always satisfied. We again assume the Boussinesq approximation -neglecting any effect of dilatancy on the stress field. Turning to the largest planetary scale, we present an outline of the mechanics of unified models plate-mantle models and then show how computational solutions can be obtained for such models using Escript. The consequent results for different types of convection are presented and the stability of the observed flow patterns with respect to different initial conditions and computational resolutions is discussed.2005-10-05T00:00:00Z
Muhlhaus, Hans; Moresi, Louis; Davies, Matt; Gottschaldt, Klaus Towards realistic simulations of lava dome growth using the level set method
http://espace.library.uq.edu.au/view/UQ:12910
The level set method has been implemented in a computational volcanology context. New techniques are presented to solve the advection equation and the reinitialisation equation. These techniques are based upon an algorithm developed in the finite difference context, but are modified to take advantage of the robustness of the finite element method. The resulting algorithm is tested on a well documented Rayleigh–Taylor instability benchmark [19], and on an axisymmetric problem where the analytical solution is known. Finally, the algorithm is applied to a basic study of lava dome growth.2007-03-12T11:52:31Z
Bourgouin, Laurent; Muhlhaus, Hans-Bernd; Hale, Alina Jane; Arsac, Antonin Towards simulation based seismic hazard assessment in Queensland, Australia
http://espace.library.uq.edu.au/view/UQ:103211
2007-08-23T21:26:07Z
Weatherley, D. K.; Parmiter,; Saez, E.; Mora, P. R. Trans-boundary parks and collaborative stakeholder planning: The case of Zimbabwe's Great Limpopo Transfrontier Park (GLTP)
http://espace.library.uq.edu.au/view/UQ:186348
2009-11-16T16:52:51Z
Doppelfeld, M.; Ritchie, Brent W. Unconventional gas mining: insights from pore to mine scale simulations
http://espace.library.uq.edu.au/view/UQ:289939
Modern computational techniques are invaluable components of every engineer’s toolkit and every scientist’s laboratory. The main challenge for computational analysis of unconventional gas mining is to consider the multiscale heterogeneity and the related phenomena in natural and/or enhanced geo-materials. Heterogeneous materials typically possess a multitude of mechanically significant scales and each of these scales requires appropriate modeling. Heterogeneous structures on the microscale (i.e. mineral grains, pore space and micro-cracks) are often close in size to a characteristic length for the macroscopic pattern for such as subsurface flow and transport. Hence these structures strongly influence macroscale processes. To analyze and depict complicated unconventional gas behaviours across different scales in fractured porous media, an Enhanced Multiscale Heterogeneous Porous Media Computational Model (EMHPM) is proposed based on analytical solution for fluid flow in a nano pipe and lattice Boltzmann method (LBM), and implemented in PANDAS (i.e. PANDAS/LBM). We apply the conventional LBM (CLBM) algorithm for simulating the microscale processes based on a micro-structural high resolution X-ray/CT/MRI/SEM measurement data. Upon completion of a solution step, the micro models return with the upscale material properties such as permeability for macroscale analysis. The macroscale model which distinguishing fractures, solids and matrix with some certain permeability by stating its local physical properties from the microscale simulation will be simulated. PANDAS/LBM has been benchmarked and applied in analysis of unconventional gas mining, and the quantitative description of gas migration in porous media at extreme conditions has demonstrated advantages of the proposed algorithm for an improved understanding and assessing the unconventional gas flow phenomena in practical mining processes.2013-01-25T15:41:57Z
Xing, Huilin; Gao, Jinfang; Wang, Geoff; Muhlhaus, Hans Unstructured mesh construction and finite element modelling of the fault system of Sumatra area
http://espace.library.uq.edu.au/view/UQ:103215
2007-08-23T21:26:15Z
Xing, H.; Mora, P. R. Using a lattice solid model for vertical seismic profiles
http://espace.library.uq.edu.au/view/UQ:99715
2007-08-24T12:53:48Z
Filippidou, N.; Abe, S.; Drijkoningen, G.G. Using FCD mapper software and landsat images to detect breaks in forest canopies in landscapes in Australia and the Philippines
http://espace.library.uq.edu.au/view/UQ:102510
2007-08-23T20:58:18Z
Baynes, J. Using quicksand to improve debugging practice in post-novice level students
http://espace.library.uq.edu.au/view/UQ:286425
The ability to debug existing code is an important skill to develop in student programmers. However, debugging may not receive the same amount of explicit teaching attention as other material and the main expression of debugging competence is students' ability to undo problems which they themselves have injected into their assignments. Further, as the literature points out, debugging skills do not necessarily develop at the same rate as code writing skills. This paper discusses an intervention in a second year course designed to improve students' application of simple debugging techniques. We use a puzzle based approach where students are graded based on the number of attempts they take to locate misbehaving code in a program which they did not write but whose function they understand. An existing assignment component addresses another aspect of debugging practice.2012-11-28T14:28:43Z
Fenwick, Joel; Sutton, Peter Using the level set method to model endogenous lava dome growth
http://espace.library.uq.edu.au/view/UQ:24537
Modeling volcanic phenomena is complicated by free-surfaces often supporting large rheological gradients. Analytical solutions and analogue models provide explanations for fundamental characteristics of lava flows. But more sophisticated models are needed, incorporating improved physics and rheology to capture realistic events. To advance our understanding of the flow dynamics of highly viscous lava in Peléean lava dome formation, axi-symmetrical Finite Element Method (FEM) models of generic endogenous dome growth have been developed. We use a novel technique, the level-set method, which tracks a moving interface, leaving the mesh unaltered. The model equations are formulated in an Eulerian framework. In this paper we test the quality of this technique in our numerical scheme by considering existing analytical and experimental models of lava dome growth which assume a constant Newtonian viscosity. We then compare our model against analytical solutions for real lava domes extruded on Soufrière, St. Vincent, W.I. in 1979 and Mount St. Helens, USA in October 1980 using an effective viscosity. The level-set method is found to be computationally light and robust enough to model the free-surface of a growing lava dome. Also, by modeling the extruded lava with a constant pressure head this naturally results in a drop in extrusion rate with increasing dome height, which can explain lava dome growth observables more appropriately than when using a fixed extrusion rate. From the modeling point of view, the level-set method will ultimately provide an opportunity to capture more of the physics while benefiting from the numerical robustness of regular grids.2007-07-30T12:26:42Z
Hale, Alina Jane; Bourgouin, Laurent; Muhlhaus, Hans Bernd Validation of using Gumbel probability plotting to estimate Gutenberg-Richter seismicity parameters
http://espace.library.uq.edu.au/view/UQ:104986
2007-08-23T22:44:44Z
TURNBULL,; Weatherley, D K Virtual rock laboratory - A grid portal enabling computational geoscience research
http://espace.library.uq.edu.au/view/UQ:188780
Virtual Rock Lab (VRL) is a secure web portal designed to enable users without programming skills to construct and execute ESyS-Particle simulations. The portal covers all steps of the work flow combining interfaces that allow users to create and edit input scripts through dialogues, submit jobs to a supercomputer connected to the AuScope Grid and browse a simulation journal to access past simulations and monitor active ones. Thus, authorised users need nothing more than a computer with a web browser to use the system and require no programming skills.2009-12-02T10:10:31Z
Altinay, Cihan; Weatherley, Dion Viscoelastic plastic model of continental deformation
http://espace.library.uq.edu.au/view/UQ:104967
2007-08-23T22:43:58Z
Moresi,; LEMIALE,; Muhlhaus, H B; May, Visualization of large particle systems
http://espace.library.uq.edu.au/view/UQ:98356
2007-08-24T01:53:49Z
Abe, S.; Place, D. G.; Mora, P. R. Voltage control of exchange coupling in phosphorus doped silicon
http://espace.library.uq.edu.au/view/UQ:72679
Motivated by applications to quantum computer architectures we study the change in the exchange interaction between neighbouring phosphorus donor electrons in silicon due to the application of voltage biases to surface control electrodes. These voltage biases create electro-static fields within the crystal substrate, perturbing the states of the donor electrons and thus altering the strength of the exchange interaction between them. We find that control gates of this kind can be used to either enhance or reduce the strength of the interaction, by an amount that depends both on the magnitude and orientation of the donor separation.2007-08-15T04:17:51Z
Wellard, C.J.; Hollenberg, L.C.L.; Kettle, L. M.; Goan, H. S.