The Experts below are selected from a list of 3393 Experts worldwide ranked by ideXlab platform

Shoucheng Zhang - One of the best experts on this subject based on the ideXlab platform.

Jing Wang - One of the best experts on this subject based on the ideXlab platform.

Uijttewaal W.s.j. - One of the best experts on this subject based on the ideXlab platform.

  • Transverse Momentum Exchange Induced by Large Coherent Structures in a Vegetated Compound Channel
    2019
    Co-Authors: Truong S. H., Uijttewaal W.s.j.
    Abstract:

    In floodplains of vegetated channels, transverse exchange processes of mass and momentum are of primary importance as these are directly linked to the river bank stability, sedimentation, and nutrient transport. Despite its importance, knowledge about this phenomenon is still incomplete especially in the context of the presence of the large horizontal coherent structures (LHCSs). As a result, although various exchange models have been developed, their applicability in different circumstances is still unclear as their validity is usually restricted to a narrowly ranging experiment data set. A proper model for this exchange in a compound channel geometry with or without vegetation is lacking. In order to obtain more insight, a laboratory experiment of a shallow flow field in a compound vegetated channel has been conducted. A quadrant analysis of the Reynolds shear stresses has been applied to study the connection between the cycloid flow events induced by the LHCSs and transverse momentum exchange in the channel. It is suggested that local variability leads to differences in the transverse exchange of momentum. Furthermore, the experimental data were used to verify state-of-the-art momentum exchange models. As the limitations of those models were analyzed, for the first time a hybrid eddy viscosity model based on the occurrence of LHCSs and the presence of vegetation was proposed and validated using a variety of experimental data sets. The results suggest that the transverse momentum exchange can be well modeled with the new eddy viscosity model for quite a range of different setups and scenarios by varying only a Coefficient of Proportionality β, which is related to the transverse slope between the main channel and the floodplain

  • Transverse Momentum Exchange Induced by Large Coherent Structures in a Vegetated Compound Channel
    'American Geophysical Union (AGU)', 2019
    Co-Authors: Truong S. H., Uijttewaal W.s.j.
    Abstract:

    In floodplains of vegetated channels, transverse exchange processes of mass and momentum are of primary importance as these are directly linked to the river bank stability, sedimentation, and nutrient transport. Despite its importance, knowledge about this phenomenon is still incomplete especially in the context of the presence of the large horizontal coherent structures (LHCSs). As a result, although various exchange models have been developed, their applicability in different circumstances is still unclear as their validity is usually restricted to a narrowly ranging experiment data set. A proper model for this exchange in a compound channel geometry with or without vegetation is lacking. In order to obtain more insight, a laboratory experiment of a shallow flow field in a compound vegetated channel has been conducted. A quadrant analysis of the Reynolds shear stresses has been applied to study the connection between the cycloid flow events induced by the LHCSs and transverse momentum exchange in the channel. It is suggested that local variability leads to differences in the transverse exchange of momentum. Furthermore, the experimental data were used to verify state-of-the-art momentum exchange models. As the limitations of those models were analyzed, for the first time a hybrid eddy viscosity model based on the occurrence of LHCSs and the presence of vegetation was proposed and validated using a variety of experimental data sets. The results suggest that the transverse momentum exchange can be well modeled with the new eddy viscosity model for quite a range of different setups and scenarios by varying only a Coefficient of Proportionality β, which is related to the transverse slope between the main channel and the floodplain.Environmental Fluid Mechanic

S M Hassanizadeh - One of the best experts on this subject based on the ideXlab platform.

  • The effect of dynamic capillarity in modeling saturation overshoot during infiltration
    'Soil Science Society of America', 2019
    Co-Authors: Zhuang Luwen, Duijn, Cj Hans Van, S M Hassanizadeh
    Abstract:

    \u3cp\u3eGravity-driven fingering has been observed during downward infiltration of water into dry sand. Moreover, the water saturation profile within each finger is non-monotonic, with a saturation overshoot at the finger tip. As reported in the literature, these effects can be simulated by an extended form of the Richards equation, where a dynamic capillarity term is included. The Coefficient of Proportionality is called the dynamic capillarity Coefficient. The dynamic capillarity Coefficient may depend on saturation. However, there is no consensus on the form of this dependence. We provide a detailed traveling wave analysis of four distinctly different functional forms of the dynamic capillarity Coefficient. In some forms, the Coefficient increases with increasing saturation, and in some forms, it decreases. For each form, we have found an explicit expression for the maximum value of saturation in the overshoot region. In current formulations of dynamic capillarity, if the value of the capillarity Coefficient is large, the value of saturation in the overshoot region may exceed unity, which is obviously nonphysical. So, we have been able to ensure boundedness of saturation regardless of the value of the dynamic capillarity Coefficient by extending the capillary pressure–saturation relationship. Finally, we provide a qualitative comparison of the results of traveling wave analysis with experimental observations.\u3c/p\u3

  • saturation dependent solute dispersivity in porous media pore scale processes
    Water Resources Research, 2013
    Co-Authors: Amir Raoof, S M Hassanizadeh
    Abstract:

    [1] It is known that in variably saturated porous media, dispersion Coefficient depends on Darcy velocity and water saturation. In one-dimensional flow, it is commonly assumed that the dispersion Coefficient is a linear function of velocity. The Coefficient of Proportionality, called the dispersivity, is considered to depend on saturation. However, there is not much known about its dependence on saturation. In this study, we investigate, using a pore network model, how the longitudinal dispersivity varies nonlinearly with saturation. We schematize the porous medium as a network of pore bodies and pore throats with finite volumes. The pore space is modeled using the multidirectional pore-network concept, which allows for a distribution of pore coordination numbers. This topological property together with the distribution of pore sizes are used to mimic the microstructure of real porous media. The dispersivity is calculated by solving the mass balance equations for solute concentration in all network elements and averaging the concentrations over a large number of pores. We have introduced a new formulation of solute transport within pore space, where we account for different compartments of residual water within drained pores. This formulation makes it possible to capture the effect of limited mixing due to partial filling of the pores under variably saturated conditions. We found that dispersivity increases with the decrease in saturation, it reaches a maximum value, and then decreases with further decrease in saturation. To show the capability of our formulation to properly capture the effect of saturation on solute dispersion, we applied it to model the results of a reported experimental study.

L Borselli - One of the best experts on this subject based on the ideXlab platform.

  • Clod movement and tillage tool characteristics for modeling tillage erosion
    Journal of Soil and Water Conservation, 2002
    Co-Authors: Dino Torri, L Borselli
    Abstract:

    Soil erosion caused by tillage is proportional to the local slope curvature. The value of the Coefficient of Proportionality (tillage transport Coefficient) depends on the interaction between tillage tool and soil. These interactions have been modeled as a three-phase motion: drag (depending only on tool characteristics), when the soil is in contact with the instrument; jump (not necessarily present for all tools), when the soil loses contact with the tool and is ejected; and rolling, when the clods roll and jump in relatively close contact with the soil surface. Three sets of equations have been proposed and assembled into a computer program (SETi, from Soil Erosion by Tillage). The model simulates the 3D behavior of the transported soil. The performance e of SETi is illustrated for the case of the moldboard plow. The simulated trends closely resemble those observed in experimental studies of tillage translocation. The major improvement with respect to previous models is that tool characteristics are explicitly taken into account. Tillage erosion is one of the major soil redistributing processes within the field border. Recent research has shown that that tillage erosion is often proportional to the local slope curvature (i.e., the rate at which slope gradient varies per unit of length). In present-day models, the Proportionality Coefficient is considered to be a black-box Coefficient, depending on tillage tool and soil characteristics. To make the relationship between tillage translocation, soil, and tool characteristics more explicit the process of soil translocation must be better understood. We have found that there are three phases of motion, each described by its own set of equations, namely, drag, jump and rolling. Each phase depends on measurable characteristics of the tillage tools and of the soil, These equations have been implemented in the SETi computer model. At present, the model has been parameterized for a moldboard plow. The simulated soil transport reproduces the trends shown in the literature, indicating that the model behaves realistically. In its present form it can already be used for calculating the tillage transport Coefficient needed by the existing tillage erosion models, as well as for designing less erosive tillage tools.

  • clod movement and tillage tool characteristics for modeling tillage erosion
    Journal of Soil and Water Conservation, 2002
    Co-Authors: Dino Torri, L Borselli
    Abstract:

    ABSTRACT: Soil erosion caused by tillage is proportional to the local slope curvature. The value of the Coefficient of Proportionality (tillage transport Coefficient) depends on the interaction between tillage tool and soil. These interactions have been modeled as a three-phase motion: drag (depending only on tool characteristics), when the soil is in contact with the instrument; jump (not necessarily present for all tools), when the soil loses contact with the tool and is ejected; and rolling, when the clods roll and jump in relatively close contact with the soil surface. Three sets of equations have been proposed and assembled into a computer program (SETi, from Soil Erosion by Tillage). The model simulates the 3D behavior of the transported soil. The performance of SETi is illustrated for the case of the moldboard plow. The simulated trends closely resemble those observed in experimental studies of tillage translocation. The major improvement with respect to previous models is that tool characteristics are explicitly taken into account. Tillage erosion is one of the major soil redistributing processes within the field border. Recent research has shown that that tillage erosion is often proportional to the local slope curvature (i.e., the rate at which slope gradient varies per unit of length). In present-day models, the Proportionality Coefficient is considered to be a black-box Coefficient, depending on tillage tool and soil characteristics. To make the relationship between tillage translocation, soil, and tool characteristics more explicit the process of soil translocation must be better understood. We have found that there are three phases of motion, each described by its own set of equations, namely, drag, jump and rolling. Each phase depends on measurable characteristics of the tillage tools and of the soil. These equations have been implemented in the SETi computer model. At present, the model has been parameterized for a moldboard plow. The simulated soil transport reproduces the trends shown in the literature, indicating that the model behaves realistically. In its present form it can already be used for calculating the tillage transport Coefficient needed by the existing tillage erosion models, as well as for designing less erosive tillage tools.