Browsing by Author "Bengtsson, Lars"
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Item Kinematic wave model for water movement in municipal solid waste(American Geophysical Union, 1998-11) Bendz, David; Singh, Vijay P.; Rosqvist, H?�kan; Bengtsson, LarsThe movement of water in a large (3.5 m3) undisturbed sample of 22-year-old municipal solid waste has been modeled using a kinematic wave approximation for unsaturated infiltration and internal drainage. The model employs a two-parameter power expression as macroscopic flux law. The model parameters were determined and interpreted in terms of the internal geometry of the waste medium by fitting the model to one set of infiltration and drainage data. The model was validated using another set of data from a sequence of water input events. The results of the validation show that the model performs satisfactorily, but further development of the model to incorporate spatial variability would increase its capability.Item Longitudinal Dispersion Coeffiient in Straight Rivers(2001-11) Bengtsson, Lars; Deng, Zhi-Qiang; Singh, Vijay P.An analytical method is developed to determine the longitudinal dispersion coefficient in Fischer’s triple integral expression for natural rivers. The method is based on the hydraulic geometry relationship for stable rivers and on the assumption that the uniform-flow formula is valid for local depth-averaged variables. For straight alluvial rivers, a new transverse profile equation for channel shape and local flow depth is derived and then the lateral distribution of the deviation of the local velocity from the cross-sectionally averaged value is determined. The suggested expression for the transverse mixing coefficient equation and the direct integration of Fischer’s triple integral are employed to determine a new theoretical equation for the longitudinal dispersion coefficient. By comparing with 73 sets of field data and the equations proposed by other investigators, it is shown that the derived equation containing the improved transverse mixing coefficient predicts the longitudinal dispersion coefficient of natural rivers more accurately.Item Numerical Solution of Fractional Advection-Dispersion Equation(2004-05-01) Bengtsson, Lars; Deng, Zhi-Qiang; Singh, Vijay P.Numerical schemes and stability criteria are developed for solution of the one-dimensional fractional advection-dispersion equation (FRADE) derived by revising Fick’s first law. Employing 74 sets of dye test data measured on natural streams, it is found that the fractional order F of the partial differential operator acting on the dispersion term varies around the most frequently occurring value of F=1.65 in the range of 1.4 to 2.0. Two series expansions are proposed for approximation of the limit definitions of fractional derivatives. On this ground, two three-term finite-difference schemes—‘‘1.3 Backward Scheme’’ having the first-order accuracy and ‘‘F.3 Central Scheme’’ possessing the F-th order accuracy—are presented for fractional order derivatives. The F.3 scheme is found to perform better than does the 1.3 scheme in terms of error and stability analyses and is thus recommended for numerical solution of FRADE. The fractional dispersion model characterized by the FRADE and the F.3 scheme can accurately simulate the long-tailed dispersion processes in natural rivers.