Mantle thermal structure at northern Mid–Atlantic ridge from improved numerical methods and boundary conditions

2019 ◽  
Author(s):  
Marco Cuffaro ◽  
Edie Miglio ◽  
Mattia Penati ◽  
Marco Viganò
Keyword(s):  
Boundary Conditions ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Geophysical Data ◽  
Mantle Flow ◽  
Viscous Forces ◽  
Versus Domain ◽  
Mid Atlantic Ridge ◽  
Velocity Constraints ◽  
New Formulation

Summary We computed mantle flow and thermal structure beneath a segment of the northern Mid-Atlantic ridge using numerical simulations adopting asymmetric spreading and ridge migration as boundary conditions. The objective is to obtain new insights on mantle processes acting at this ridge segment. We explored different lateral boundary conditions based on velocity, stress and stress-velocity constraints highlighting differences in the depth of the thermal base of the lithosphere versus domain width. Here, we propose a new formulation of lateral and bottom boundary conditions based on the choice of a proper tangential stress at the bottom and on lateral boundaries of the domain accounting for ridge migration. Moreover, dimensional analysis of governing equations suggests that heat generation due to work of the viscous forces cannot be neglected in the computations. Therefore, we included this thermal contribution into the numerical experiments providing an application to the northern Mid-Atlantic ridge at the reference latitude of 43 ○N. Results are compared with available geophysical data in the area, including also mantle tomography models. Asymmetric spreading and ridge migration in numerical modelling account for an asymmetric accretion of the oceanic lithosphere, supporting the evidence of the asymmetries described by geophysical data across the northern Mid-Atlantic ridge segments.

Linking subduction dynamics to back-arc deformation

2020 ◽  
Author(s):  
Valentina Magni ◽  
Manel Prada
Keyword(s):  
Boundary Conditions ◽  
Numerical Models ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Lau Basin ◽  
Crustal Composition ◽  
Lithospheric Extension ◽  
Back Arc ◽  
Existing Structure ◽  
Tyrrhenian Basin

<p> <span>The morphology of back-arc basins shows how complex their formation is and how pre-existing lithospheric structures, rifting and spreading processes, and subduction dynamics all have a role in shaping them. </span><span>Often, back-arc basins present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. Episodes of fast and slow trench retreat can cause rift jumps, migration of magmatism, and pulses of higher crustal production (e.g., Tyrrhenian Basin). The evolution of a back-arc basin is not only tightly linked to subduction dynamics, but it is likely that the composition and the pre-existing structure of the lithosphere play a role in shaping the basin too. </span><span>In this work, we investigate the interplay between these features with numerical models of lithospheric extension with a visco-plastic rheology. We use the finite element code ASPECT to model the rifting of continental and oceanic lithosphere with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically change key parameters such as crustal composition and thickness, initial thermal structure and rheology of the lithosphere, and rate of extension. These models aim at understanding how pre-existing lithospheric structures affect back-arc rifting and spreading and what processes control spreading centres jumps in back-arc settings. Preliminary results show that time-dependent boundary conditions that simulate episodes of fast trench retreat, thus fast extension, play an important role into the style of lithospheric back-arc deformation. Finally, we will compare our model results with the location and timing of back-arc rifting and spreading in different active and inactive back-arc basins.</span></p>

scholarly journals New perspectives for photoelectric phenomena

2016 ◽  
Vol 55 (4) ◽  
Author(s):  
Igor Lashkevych ◽  
Oleg Yu. Titov ◽  
Yuri G. Gurevich
Keyword(s):  
Solar Cells ◽  
Boundary Conditions ◽  
Maxwell’S Equations ◽  
Maxwell's Equations ◽  
Transport Phenomena ◽  
Space Charges ◽  
Recombination Processes ◽  
New Formulation ◽  
Physical Phenomena

The functioning of the solar cells (and photoelectric phenomena in general) relies on the photo-generation of carriers in p–n junctions and their subsequent recombination in the quasi-neutral regions. A number of basic issues concerning the physics of the operation of solar cells still remain obscure. This paper reports on some unsolved basic problems, namely: a model of the recombination processes that does not contradict Maxwell’s equations; boundary conditions; the role played by space charges in the transport phenomena, and the formation of quasi-neutral regions under the presence of nonequilibrium photo-generated carriers. In this work, a new formulation of the theory that explains the underlying physical phenomena involved in the generation of a photo-e.m.f. is presented.

Geoid data and thermal structure of the oceanic lithosphere

1995 ◽  
Vol 22 (14) ◽  
pp. 1913-1916 ◽  
Author(s):  
W. Philip Richardson ◽  
Seth Stein ◽  
Carol A. Stein ◽  
Maria T. Zuber
Keyword(s):  
Thermal Structure ◽  
Oceanic Lithosphere

A New Formulation for Computational Fluid Dynamics

1979 ◽  
Vol 101 (4) ◽  
pp. 453-460
Author(s):  
D. B. Reed ◽  
W. L. Oberkampf
Keyword(s):  
Fluid Dynamics ◽  
Boundary Conditions ◽  
Transport Equation ◽  
Mesh Size ◽  
Channel Length ◽  
Test Case ◽  
Parallel Plates ◽  
Flow Problems ◽  
Vector Quantity ◽  
New Formulation

A new vector quantity in fluid dynamics is defined and a vector transport equation for the quantity is derived. The new vector quantity is defined as the curl of the vorticity and is referred to as the angular vorticity. The transport equation for the new quantity is derived by taking the curl of the vorticity transport equation. The new transport equation combined with Poisson type velocity equations comprises the new angular vorticity-velocity formulation. The major advantage of the new formulaton is that computational boundary conditions for through-flow problems may be significantly relaxed. Boundary conditions for the newly defined variable are derived. A simple test case of laminar incompressible planar flow between parallel plates was executed to determine if the new formulation would produce results comparable to previous solutions. Numerical experiments were conducted using channel length, mesh size, and Reynolds number as parameters. The results are compared to values obtained by other investigators. The results show that the angular vorticity formulation is a feasible method for solution of fluid flow problems where fully developed flow is not attained.

Distribution and evolution of uranium in the oceanic lithosphere

1979 ◽  
Vol 291 (1381) ◽  
pp. 423-431 ◽  
Keyword(s):  
Sea Water ◽  
Oceanic Lithosphere ◽  
Uranium Content ◽  
Major And Trace Elements ◽  
Ultramafic Rocks ◽  
Layer 2 ◽  
Secondary Enrichment ◽  
Layer 4 ◽  
Mid Atlantic Ridge ◽  
Fractionation Trend

Induced fission track techniques permit us to determine quantitatively the microscopic distribution of uranium in rocks, in their constituent minerals, and in percolating fluids. Both primary magmatic variations and secondary mobilization of uranium can be discerned. Concentrations of uranium in phenocrysts and fresh glasses of oceanic basalts and gabbros are very low (2-80 parts/10 9 ) and are comparable to concentrations in the same minerals of the associated ultramafic rocks. Variations with depth in D.S.D.P. holes show several distinct cyclic variations of uranium, accompanied by parallel trends in some major and trace elements. In Hole 332B (mid-Atlantic ridge, 36 °N), uranium and other elements can be shown to fall into two distinct groupings, each group following its own characteristic fractionation trend, suggesting that two distinct magmas differentiated independently beneath the median valley, the two magmas alternating in their contribution to the formation of oceanic layer 2. Earlier investigations of the uranium distribution in surface pillows and other dredged rocks exposed to sea water had shown that, owing to halmyrolysis, the uranium concentration increases systematically with distance from the axis of a midoceanic ridge. Subsequent investigations on rocks drilled from horizons deeper into oceanic layer 2 indicate that secondary enrichment or redistribution of uranium is confined to specific zones of altered basalt, near fractures, pillow and flow margins, and especially along horizontal planes of breccias and sediments in between massive flow where convective water circulation is thought to occur. Ultramafic rocks from the base of layer 3 and top of layer 4 are also enriched in uranium when hydrated by sea water during the process of serpentinization. A combination of these processes may double the uranium content of an oceanic lithospheric plate between the time of its formation and its eventual subduction.

scholarly journals Buckling of the oceanic lithosphere from geophysical data and experiments

Tectonics ◽  
1992 ◽  
Vol 11 (3) ◽  
pp. 537-548 ◽  
Author(s):  
Jonathan M. Bull ◽  
Joseph Martinod ◽  
Philippe Davy
Keyword(s):  
Oceanic Lithosphere ◽  
Geophysical Data

Calculation of Optimal Surface Roughness With Respect to Lift/Drag Forces Acting on Wind Turbine Blade

2014 ◽  
Author(s):  
Xuerui Mao ◽  
Simon Hogg
Keyword(s):  
Surface Roughness ◽  
Boundary Conditions ◽  
Smooth Surface ◽  
Adjoint Equation ◽  
Turbine Blades ◽  
Leading Edge ◽  
Sensitivity Study ◽  
Small Magnitude ◽  
Viscous Forces ◽  
Drag Forces

Roughness on the surface of turbine blades induced by icing, dirt, erosion or manufacturing imperfections changes the aerodynamic configurations of wind turbines and reduces the power generation efficiency. In this work, a modified NACA0024 aerofoil is adopted to study effects of surface roughness on lift/drag forces. Three Reynolds numbers, 1000, 2000 and 5000 and a range of angles of attack [0°,20°] are studied. Since the magnitude of the roughness is small, it can be modelled as non-zero velocity boundary conditions imposed on the smooth surface without roughness. The flow with surface roughness can be therefore decomposed as the sum of a flow without roughness and a flow induced by roughness (or the velocity boundary conditions). The first flow can be obtained by solving the Navier-Stokes (NS) equation while the second one is governed by the linearized NS equation. Correspondingly the lift and drag forces acting on the aerofoil can be also decomposed as the sum of a force without considering roughness and a force induced by roughness. Instead of studying a particular type or distribution of roughness, we calculate the optimal roughness, which changes aerodynamic forces most effectively. This optimal roughness is obtained through a sensitivity study by solving an adjoint equation of the linearized NS equation. It is found that the optimal roughness with respect to both drag and lift forces is concentrated around the trailing edge and upper leading edge of the aerofoil and the lift is much more sensitive to roughness than the drag. Then the optimal roughness with a small magnitude is added to the smooth aerofoil geometry and this new geometry is tested through direct numerical simulations (DNS). It is found that the optimal roughness with a small magnitude (e-norm, defined as the square integration of the roughness around the surface, 0.001) induces over 10% change of the lift. Comparing the forces acting on the smooth surface and on the rough surface, it is noticed that the roughness changes the pressure force significantly while has little influence on the viscous forces. The pressure distribution is further inspected to study mechanisms of the effects of roughness on forces.

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