Aquaveo & Water Resources Engineering News

Ghost node correction (GNC) package in GMS

The GMS team just added support for the ghost node correction (GNC) package in GMS. This will be available in GMS 10.1. A wiki page has already been created to document the interface.

The GNC package can be used to improve the accuracy of a model in which there are grid cells that do not follow the assumptions of the finite volume method - namely that the line connecting the center points of adjacent cells is also a perpendicular bisector of the face between the cells. This situation arises with quadtree, octree, and nested type grids, as well as with many other types of grids. Regular (quadrilateral) grids and voronoi grids do not have this issue. All of these types of grids can easily be created in GMS.

Ghost node conceptualization for nested grids.1

GMS can calculate all the ghost node data automatically, or the user can enter the data manually. When done automatically, GMS uses an algorithm developed with input from Sorab Panday (author of MODFLOW-USG). The algorithm is illustrated in the following figure:

Ghost node placement - general case.

Ghost node locations are calculated using the perpendicular bisector of the face between adjacent cells and its intersection with the lines connecting cell centers. AlphaJ values are calculated based on the distances from the ghost nodes to the adjacent cells. A new tutorial was created to teach how to use the new GNC functionality in GMS. The GNC package typically increases the accuracy of a model by a small amount and is therefore often unnecessary.

1. Panday, Sorab, Langevin, C.D., Niswonger, R.G., Ibaraki, Motomu, and Hughes, J.D., (2013), MODFLOW-USG, version 1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly coupled processes using a control volume finite-difference formulation: U.S. Geological Survey Techniques and Methods, book 6, chap. A45, 66 p., Reston, Virginia

GMS Sprint October 2014

Some of the more notable things completed by the GMS team during the month.

  • Fixed 5 bugs
  • Flow observations for MODFLOW-USG completed
  • Model checker now has checks for valid USG geometry
  • Boundary elements on voronoi grids have effective cell center on outer edge
  • Support for point and cell based datasets on UGrids
  • GNC package (ghost node correction) completed
  • Python script to properly convert gsf files to vtk created
  • mod-PATH3DU progress
  • Nodal functions for interpolation on UGrids improved
  • New tutorial for MODFLOW-USG calibration created
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GMS Sprint September 2014

Some of the more notable things completed by the GMS team during the month.

  • Fixed 8 bugs
  • MODFLOW-USG duplicated when duplicating UGrid
  • More progress on observations with MODFLOW-USG and PEST
  • Expanded/collapsed state of items in the Project Explorer now saved
  • mod-PATH3DU interface mostly completed
  • Progress on new datasets to be used with VTK
  • User now asked about inactive cells when converting to MODFLOW-USG
  • Switching to MODFLOW-NWT now prompts to switch the solver to NWT
  • GUI testing for UGrid interpolation added
  • MODFLOW code and solution changed to reduce all the dlls
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GMS Spring August 2014

Some of the more notable things completed by the GMS team during the month.

  • Fixed 6 bugs
  • Good progress on MODFLOW-USG observations with PEST
  • Progress on VTK hypergridtree
  • Added "Do not show again" for warning about pathlines not displaying
  • Standardized on "dataset", not "data set" throughout interface
  • Pushed SAMG code for MODFLOW-USG into dev and 10.0
  • Table view dialog added read-only and no insert/delete capabilities
  • Testing added image comparison tolerance
  • Test added for Getting Started tutorial
  • Tutorial durations and dependencies updated
  • UGrid interpolation added
  • Units default to users locale, and saved in settings
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