GMS:NWT Package

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Flow: BCF6, HUF, LPF, UPW
Solvers:

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UZF1
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Example of the MODFLOW NWT Solver dialog.

The Newton package (NWT) is one of the solvers available in MODFLOW-NWT. The NWT package is only used with the UPW Package. Using the NWT solver requires twice the memory of other MODFLOW solvers because using the Newton method results in an asymmetric matrix. Because of the asymmetric matrix a different matrix solver must be used. The NWT package provides an option to use one of two matrix solvers: a generalized-minimum-residual (GMRES) solver and an Orthomin/stabilized conjugate-gradient solver called χMD (chi-MD).

General Options

  • Comments (Text)
  • Max head change between outer iterations (L)(HEADTOL)
  • Max root-mean-squared flux difference between outer iterations (L^3/T) (FLUXTOL)
  • Max number of iterations allowed for outer problem (MAXITEROUT)
  • Portion of cell thickness used for adjusting coefficients to zero (THICKFACT)
  • Matrix solver to be used (LINMETH)
  • Print additional info to listing file (IPRNWT)
  • Correct head relative to cell-bottom if surrounded by d-watered cells (IBOTAV)
  • Options (OPTIONS)

General Specified Options

  • Coefficient to reduce weight applied to head change (DBDTHETA)
  • Coefficient to increase weight applied to head change (DBDKAPPA)
  • Factor used to weight the head change for iterations n&ndashl1 and n (DBGGAMMA)
  • Momentum coefficient (MOMFACT)
  • Use residual control (BACKFLAG)
  • Max number of reductions (backtracks) in head change (MAXBACKITER)
  • Proportional decrease in root-mean-squared error (BACKTOL)
  • Reduction factor for residual control that reduces head change (BACKREDUCE)

GMRES Specified Options

  • Max number of iterations for the linear solution (MAXITINNER)
  • Method of incomplete factorization used as preconditioner (ILUMETHOD)
  • Fill limit for ILUMETHOD 1 or level of fill for ILUMETHOD 2 (LEVFILL)
  • Tolerance for convergence of linear solver (STOPTOL)
  • Number of iterations between restarts of GMRES (MSDR)

χMD Specified Options

  • Acceleration method (IACL)
  • Scheme of ordering unknowns (NORDER)
  • Level of fill for incomplete LU factorization (LEVEL)
  • Number of orthogonalization for the ORTHOMIN acceleration scheme (NORTH)
  • Reduced system preconditioning (IREDSYS)
  • Use drop tolerance in preconditioning (IDROPTOL)
  • Drop tolerance for preconditioning (EPSRN)
  • Head closure criteria for inner (linear) iterations (HCLOSEXMD)
  • Max number of iterations for linear solution (MXITERXMD)

References

For more information on the NWT package see the USGS documentation at: water.usgs.gov/nrp/gwsoftware/modflow2000/MFDOC/nwt_newton_solver.htm


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