75 research outputs found
Multiple-Relaxation-Time Lattice Boltzmann Approach to Compressible Flows with Flexible Specific-Heat Ratio and Prandtl Number
A new multiple-relaxation-time lattice Boltzmann scheme for compressible
flows with arbitrary specific heat ratio and Prandtl number is presented. In
the new scheme, which is based on a two-dimensional 16-discrete-velocity model,
the moment space and the corresponding transformation matrix are constructed
according to the seven-moment relations associated with the local equilibrium
distribution function. In the continuum limit, the model recovers the
compressible Navier-Stokes equations with flexible specific-heat ratio and
Prandtl number. Numerical experiments show that compressible flows with strong
shocks can be simulated by the present model up to Mach numbers .Comment: Accepted for publication in EP
Prandtl number effects in MRT Lattice Boltzmann models for shocked and unshocked compressible fluids
For compressible fluids under shock wave reaction, we have proposed two
Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) models [F. Chen, et al,
EPL \textbf{90} (2010) 54003; Phys. Lett. A \textbf{375} (2011) 2129.]. In this
paper, we construct a new MRT Lattice Boltzmann model which is not only for the
shocked compressible fluids, but also for the unshocked compressible fluids. To
make the model work for unshocked compressible fluids, a key step is to modify
the collision operators of energy flux so that the viscous coefficient in
momentum equation is consistent with that in energy equation even in the
unshocked system. The unnecessity of the modification for systems under strong
shock is analyzed. The model is validated by some well-known benchmark tests,
including (i) thermal Couette flow, (ii) Riemann problem, (iii)
Richtmyer-Meshkov instability. The first system is unshocked and the latter two
are shocked. In all the three systems, the Prandtl numbers effects are checked.
Satisfying agreements are obtained between new model results and analytical
ones or other numerical results.Comment: 17 pages, 8 figure
Coseismic fault slip of the 2008 M w 7.9 Wenchuan earthquake estimated from InSAR and GPS measurements
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94993/1/grl26608.pd
Transpressional Rupture Cascade of the 2016 M_w 7.8 Kaikoura Earthquake, New Zealand
Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 M_w 7.8 Kaikoura earthquake, New Zealand, involved the rupture of at least 21 faults, propagating from southwest to northeast for about 180 km. Here we combine space geodesy and seismology techniques to study subsurface fault geometry, slip distribution, and the kinematics of the rupture. Our finite‐fault slip model indicates that the fault motion changes from predominantly right‐lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the Kekerengu and Papatea faults. Teleseismic back projection imaging shows that rupture speed was overall slow (1.4 km/s) but faster on individual fault segments (approximately 2 km/s) and that the conjugate, oblique‐reverse, north striking faults released the largest high‐frequency energy. We show that the linking Conway‐Charwell faults aided in propagation of rupture across the step over from the Humps fault zone to the Hope fault. Fault slip cascaded along the Jordan Thrust, Kekerengu, and Needles faults, causing stress perturbations that activated two major conjugate faults, the Hundalee and Papatea faults. Our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems
Transpressional Rupture Cascade of the 2016 M_w 7.8 Kaikoura Earthquake, New Zealand
Large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults. The 2016 M_w 7.8 Kaikoura earthquake, New Zealand, involved the rupture of at least 21 faults, propagating from southwest to northeast for about 180 km. Here we combine space geodesy and seismology techniques to study subsurface fault geometry, slip distribution, and the kinematics of the rupture. Our finite‐fault slip model indicates that the fault motion changes from predominantly right‐lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the Kekerengu and Papatea faults. Teleseismic back projection imaging shows that rupture speed was overall slow (1.4 km/s) but faster on individual fault segments (approximately 2 km/s) and that the conjugate, oblique‐reverse, north striking faults released the largest high‐frequency energy. We show that the linking Conway‐Charwell faults aided in propagation of rupture across the step over from the Humps fault zone to the Hope fault. Fault slip cascaded along the Jordan Thrust, Kekerengu, and Needles faults, causing stress perturbations that activated two major conjugate faults, the Hundalee and Papatea faults. Our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems
Multiple-relaxation-time lattice Boltzmann model for compressible fluids
We present an energy-conserving multiple-relaxation-time finite difference
lattice Boltzmann model for compressible flows. This model is based on a
16-discrete-velocity model. The collision step is first calculated in the
moment space and then mapped back to the velocity space. The moment space and
corresponding transformation matrix are constructed according to the group
representation theory. Equilibria of the nonconserved moments are chosen
according to the need of recovering compressible Navier-Stokes equations
through the Chapman-Enskog expansion. Numerical experiments showed that
compressible flows with strong shocks can be well simulated by the present
model. The used benchmark tests include (i) shock tubes, such as the Sod, Lax,
Sjogreen, Colella explosion wave and collision of two strong shocks, (ii)
regular and Mach shock reflections, and (iii) shock wave reaction on
cylindrical bubble problems. The new model works for both low and high speeds
compressible flows. It contains more physical information and has better
numerical stability and accuracy than its single-relaxation-time version.Comment: 11 figures, Revte
Coseismic deformation and ionospheric variation associated with Wenchuan earthquake estimated from InSAR
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