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# Non-Newtonian Flow Options

In GeoHECRAS, the Non-Newtonian Flow Options panel of the Unsteady Flow Computational Options dialog box allows the user to define the parameters necessary for performing a Non-Newtonian flow analysis with HEC-RAS.

By default, the Non-Newtonian Flow Options checkbox is unchecked, and the content of this panel is disabled (i.e., grayed out). The user can select the Non-Newtonian Flow Options checkbox to enable the content of this panel and perform the Non-Newtonian flow computations.

The following sections describe how to interact with the Non-Newtonian Flow Options panel of the Unsteady Flow Computational Options dialog box.

## Computational Options

This section allows the user to define the Non-Newtonian flow computational method to be used for computations.

The following options are provided in this section:

• Flow computational method: This dropdown combo box allows the user to select one of the five available computational methods: Bingham Equation, Clastic Grain-Flow, Herschel-Bulkley Equation, Newtonian Flow (Clear Water), and O’Brien Quadratic Equation, as shown below.

## Concentration and Bulking

This section allows the user to define the volumetric concentration of the solid particles in the flow and select the appropriate bulking method.

The following parameters are provided:

• Volumetric concentration (Cv): This entry field is used to define the volumetric concentration in percent. Clicking on the [Convert Concentration] button displays the Convert Concentration Calculator dialog box, which converts various concentration conventions to percentage volumetric concentration (%).
The user is required to enter the following options in the Convert Concentration Calculator dialog box for the concentration conversion.

1. Input concentration units: This dropdown combo box allows the user to select one of the four available concentration conventions. The four available options are Concentration by Weight (%), mg/l, ppm, and Water Content (wt) (%).
2. Input concentration: This entry field allows the user to enter the concentration value.
3. Specific gravity: This entry field allows the user to enter the specific gravity value of the solids.
4. Volumetric concentration (Cv): Clicking the [Compute] button places the computed value of volumetric concentration in this read-only field.
The software will then close the dialog box, convert the defined input concentration to volumetric concentration (%), and place the computed value into the Volumetric concentration (Cv) input field.
• Select bulking method: This dropdown combo box allows the user to select the appropriate bulking method depending on whether the volume of solids is included in the flow or not. Two available options are as follows:
1. Bulk Fluid Volume
2. Do Not Bulk (default)

## Shear Stress Components

This section allows the user to define the various parameters which will be used in the computation.

Note that based on the Flow computational method selected, the options of this section get enabled or disabled, as described below.

ParameterFlow computational method
Bingham EquationClastic Grain-FlowHerschel-Bulkley EquationNewtonian Flow (Clear Water)O’Brien Quadratic Equation
Yield strength methodEnabledDisabledEnabledDisabledEnabled
Mixture dynamic viscosityEnabledDisabledDisabledDisabledEnabled
Max CvDisabledDisabledDisabledDisabledEnabled
Representative grain sizeDisabledDisabledDisabledDisabledEnabled
Generalized Herchel-Bulkley parameter KDisabledDisabledEnabledDisabledDisabled
Generalized Herchel-Bulkley parameter nDisabledDisabledEnabledDisabledDisabled
Clastic methodsDisabledEnabledDisabledDisabledDisabled

The following options are provided for the user:

• Yield Strength Method: This dropdown combo box allows the user to select one of the following yield strength methods: Coulomb, Exponential, and User Yield.

1. Coulomb: This method is used when the concentration is very high and particle interactions transition from collision to inter-particle friction. On selecting this method, the software enables the Coulomb model of the Clastic Methods dropdown combo box.
2. Exponential: This method incorporates two empirical parameters into an exponential function of the volumetric concentration. On selecting this method, the software enables the Calibration coefficient a and Calibration coefficient b entry fields, as shown below.
These coefficients vary widely, so they are often calibration parameters. But these values can serve as a starting point for calibration. Clicking on the […] button will display a Calibration Coefficients lookup table dialog box.
3. User Yield: On selecting this method, the software enables the Yield strength entry field to enter the yield strength value. The yield strength value represents the range of stress over which the mixture does not move.
• Mixture Dynamic Viscosity: This dropdown combo box allows the user to select one of the following mixture dynamic viscosity methods: Defined Viscosity, Exponential, Maron and Pierce, and Viscosity Ratio, as shown below.
Based on the type of Mixture Dynamic Viscosity selected by the user, the following options will be enabled or disabled.

1. Max Cv: This entry field gets enabled when the user selects the Maron and Pierce option for Mixture dynamic viscosity. It defines the maximum possible concentration. By default, the software uses 61.5 %. However, the user can enter a different value. Note that Max Cv is always greater than Volume concentration (Cv).
2. Exponential multiplier B: This entry field gets enabled when the user selects the Exponential option for Mixture dynamic viscosity. It allows the user to specify the exponential multiplier to compute the viscosity. Clicking on the […] button will display an Exponential Multiplier coefficient lookup table dialog box.
3. Dynamic viscosity: This entry field gets enabled when the user selects the Defined Viscosity option for Mixture dynamic viscosity. It allows the user to enter the viscosity.
4. Viscosity ratio: This entry field gets enabled when the user selects the Viscosity Ratio option for Mixture dynamic viscosity. It allows the user to enter the viscosity ratio used to compute the dynamic viscosity of the mixture as the water viscosity times the user-specified ratio.
5. Dynamic temperature: This option gets enabled when the user selects the Viscosity Ratio option for Mixture dynamic viscosity. Clicking on the [Define] button displays the Time Series Water Temperature dialog box, which allows the user to define a new time series water temperature data.
• Representative grain size: This entry field allows the user to enter the representative grain (particle) size.
• Generalized Herschel-Bulkley parameter K: This entry field allows the user to enter the consistency factor.
• Generalized Herschel-Bulkley parameter n: This entry field allows the user to enter the power index or exponent, which can be greater or less than 1. Note that when n < 1, the fluid/mixture is shear-thinning, and when n > 1, the fluid/mixture is shear thickening.
• Clastic method: This dropdown combo box allows the user to select one of the following clastic methods: Coulomb and Voellmy, as shown below.
Based on the type of Clastic methods selected, the following options will be enabled or disabled.

1. Friction angle F: This entry field allows the user to enter the angle of friction to compute the threshold of the motion. This field is enabled for both Coulomb and Voellmy Clastic methods.
2. Voellmy coefficient x: This entry field gets enabled when the user selects the Voellmy option for Clastic methods. It allows the user to enter the voellmy coefficient for performing the unsteady flow computation.
Notes:
• The Voellmy Clastic method is enabled only when the user selects the Clastic Grain-Flow flow computational method.
• For other Non-Newtonian flow computational methods, the Clastic methods dropdown combo box is enabled when the user selects the Coulomb option for the Yield strength method. However, the Voellmy option of Clastic methods dropdown remains disabled.