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Title: Efficient methods for solving water flow in variably saturated soils under prescribed flux infiltration
Contributor(s): Zhang, Xiaoxian (author); Bengough, A Glyn (author); Crawford, John W (author); Young, Iain  (author)
Publication Date: 2002
DOI: 10.1016/S0022-1694(01)00598-4
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Abstract: The non-linear solvers in numerical solutions of water flow in variably saturated soils are prone to convergence difficulties. Many aspects can give rise to such difficulties and in this paper we address the gravity term and the prescribed-flux boundary in the Picard iteration. The problem of the gravity term in the Picard iteration is iteration-to-iteration oscillation as the gravity term is treated, by analogy with the time-step advance technique, 'explicitly' in the iteration. The proposed method for the gravity term is an improvement of the 'implicit' approach of Zhang and Ewen [Water Resour. Res. 36 (2000) 2777] by extending it to heterogeneous soil and approximating the inter-nodal hydraulic conductivity in the diffusive term and the gravity term with the same scheme. The prescribed-flux boundary in traditional methods also gives rise to iteration-to-iteration oscillation because there is no feedback to the flux in the solution at the new iteration. To reduce such oscillation, a new method is proposed to provide such a feedback to the flux. Comparison with traditional Picard and Newton iteration methods for a wide range of problems show that a combination of these two proposed methods greatly improves the stability and consequently the computational efficiency, making the use of small time step and/or under-relaxation solely for convergence unnecessary.
Publication Type: Journal Article
Source of Publication: Journal of Hydrology, v.260, p. 75-87
Publisher: Elsevier BV
Place of Publication: The Netherlands
ISSN: 0022-1694
Field of Research (FOR): 050399 Soil Sciences not elsewhere classified
060208 Terrestrial Ecology
050305 Soil Physics
050303 Soil Biology
Socio-Economic Objective (SEO): 961402 Farmland, Arable Cropland and Permanent Cropland Soils
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
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Appears in Collections:Journal Article
School of Environmental and Rural Science

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