3,895 research outputs found
Geodynamo and mantle convection simulations on the Earth Simulator using the Yin-Yang grid
We have developed finite difference codes based on the Yin-Yang grid for the
geodynamo simulation and the mantle convection simulation. The Yin-Yang grid is
a kind of spherical overset grid that is composed of two identical component
grids. The intrinsic simplicity of the mesh configuration of the Yin-Yang grid
enables us to develop highly optimized simulation codes on massively parallel
supercomputers. The Yin-Yang geodynamo code has achieved 15.2 Tflops with 4096
processors on the Earth Simulator. This represents 46% of the theoretical peak
performance. The Yin-Yang mantle code has enabled us to carry out mantle
convection simulations in realistic regimes with a Rayleigh number of
including strongly temperature-dependent viscosity with spatial contrast up to
.Comment: Plenary talk at SciDAC 200
Implementation and application of adaptive mesh refinement for thermochemical mantle convection studies
Numerical modeling of mantle convection is challenging. Owing to the multiscale nature of mantle
dynamics, high resolution is often required in localized regions, with coarser resolution being sufficient
elsewhere. When investigating thermochemical mantle convection, high resolution is required to resolve
sharp and often discontinuous boundaries between distinct chemical components. In this paper, we present
a 2-D finite element code with adaptive mesh refinement techniques for simulating compressible thermochemical
mantle convection. By comparing model predictions with a range of analytical and previously
published benchmark solutions, we demonstrate the accuracy of our code. By refining and coarsening
the mesh according to certain criteria and dynamically adjusting the number of particles in each element,
our code can simulate such problems efficiently, dramatically reducing the computational requirements
(in terms of memory and CPU time) when compared to a fixed, uniform mesh simulation. The resolving
capabilities of the technique are further highlighted by examining plume‐induced entrainment in a thermochemical
mantle convection simulation
The "Yin-Yang Grid": An Overset Grid in Spherical Geometry
A new kind of overset grid, named Yin-Yang grid, for spherical geometry is
proposed. The Yin-Yang grid is composed of two identical component grids that
are combined in a complemental way to cover a spherical surface with partial
overlap on their boundaries. Each component grid is a low latitude part of the
latitude-longitude grid. Therefore the grid spacing is quasi-uniform and the
metric tensors are simple and analytically known. One can directly apply
mathematical and numerical resources that have been written in the spherical
polar coordinates or latitude-longitude grid. The complemental combination of
the two identical component grids enables us to make efficient and concise
programs. Simulation codes for geodynamo and mantle convection simulations
using finite difference scheme based on the Yin-Yang grid are developed and
tested. The Yin-Yang grid is suitable for massively parallel computers.Comment: 9 figure
Large-scale adaptive mantle convection simulation
A new generation, parallel adaptive-mesh mantle convection code, Rhea, is described and benchmarked. Rhea targets large-scale mantle convection simulations on parallel computers, and thus has been developed with a strong focus on computational efficiency and parallel scalability of both mesh handling and numerical solvers. Rhea builds mantle convection solvers on a collection of parallel octree-based adaptive finite element libraries that support new distributed data structures and parallel algorithms for dynamic coarsening, refinement, rebalancing and repartitioning of the mesh. In this study we demonstrate scalability to 122 880 compute cores and verify correctness of the implementation. We present the numerical approximation and convergence properties using 3-D benchmark problems and other tests for variable-viscosity Stokes flow and thermal convection
Deformation-Induced Mechanical Instabilities at the Core-Mantle Boundary
Post-Perovskite: The Last Mantle Phase Transition
Our understanding of the core-mantle boundary (CMB) region has improved significantly over the past several years due, in part, to the discovery of the post-perovskite phase. Sesimic data suggest that the CMB region is highly heterogeneous, possibly reflecting chemical and physical interaction between outer core material and the lowermost mantle. In this contribution we present the results of a new mechanism of mass transfer across the CMB and comment on possible repercussions that include the initiation of deep, siderophile-enriched mantle plumes. We view the nature of core-mantle interaction, and the geodynamic and geochemical ramifications, as multiscale processes, both spatially and temporally. Three lengthscales are defined. On the microscale (1-50 km), we describe the effect of loading and subsequent shearing of the CMB region and show how this may drive local flow of outer core fluid upwards into D". We propose that larger scale processes operating on a mesoscale (50-300 km) and macroscale regimes (> 300 km) are linked to the microscale, and suggest ways in which these processes may impact on global mantle dynamics
An extreme-scale implicit solver for complex PDEs: highly heterogeneous flow in earth's mantle
Mantle convection is the fundamental physical process within earth's interior responsible for the thermal and geological evolution of the planet, including plate tectonics. The mantle is modeled as a viscous, incompressible, non-Newtonian fluid. The wide range of spatial scales, extreme variability and anisotropy in material properties, and severely nonlinear rheology have made global mantle convection modeling with realistic parameters prohibitive. Here we present a new implicit solver that exhibits optimal algorithmic performance and is capable of extreme scaling for hard PDE problems, such as mantle convection. To maximize accuracy and minimize runtime, the solver incorporates a number of advances, including aggressive multi-octree adaptivity, mixed continuous-discontinuous discretization, arbitrarily-high-order accuracy, hybrid spectral/geometric/algebraic multigrid, and novel Schur-complement preconditioning. These features present enormous challenges for extreme scalability. We demonstrate that---contrary to conventional wisdom---algorithmically optimal implicit solvers can be designed that scale out to 1.5 million cores for severely nonlinear, ill-conditioned, heterogeneous, and anisotropic PDEs
Confinement of rotating convection by a laterally varying magnetic field
Spherical shell dynamo models based on rotating convection show that the flow
within the tangent cylinder is dominated by an off-axis plume that extends from
the inner core boundary to high latitudes and drifts westward. Earlier studies
explained the formation of such a plume in terms of the effect of a uniform
axial magnetic field that significantly increases the lengthscale of convection
in a rotating plane layer. However, rapidly rotating dynamo simulations show
that the magnetic field within the tangent cylinder has severe lateral
inhomogeneities that may influence the onset of an isolated plume. Increasing
the rotation rate in our dynamo simulations (by decreasing the Ekman number
) produces progressively thinner plumes that appear to seek out the location
where the field is strongest. Motivated by this result, we examine the linear
onset of convection in a rapidly rotating fluid layer subject to a laterally
varying axial magnetic field. A cartesian geometry is chosen where the finite
dimensions mimic in cylindrical coordinates. The lateral
inhomogeneity of the field gives rise to a unique mode of instability where
convection is entirely confined to the peak-field region. The localization of
the flow by the magnetic field occurs even when the field strength (measured by
the Elsasser number ) is small and viscosity controls the smallest
lengthscale of convection. The lowest Rayleigh number at which an isolated
plume appears within the tangent cylinder in spherical shell dynamo simulations
agrees closely with the viscous-mode Rayleigh number in the plane layer linear
magnetoconvection model. The localized excitation of viscous-mode convection by
a laterally varying magnetic field provides a mechanism for the formation of
isolated plumes within Earth's tangent cylinder.Comment: 12 figures, 3 table
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