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## Parameters in Mflow_02 moveable bed computations

• Dec 13 2021
• bowtiemrh

Hello,

I was wondering if I could get a more detailed explanation than is given in the solver manual of how to properly set the parameters of the moveable be computations in the Mflow_02 solver. Specifically:
– How is the relative weight of bedload material calculated?
– What is the void ratio of the bed material? I see formulas online that give void ratio as, e=V_void/V_total. So is the proper interpretation of this parameter as the degree of soil compaction? How is this parameter utilized in the computations?
-Also, I am not sure what the morphological factor and the secondary flow coefficient and do not see a reference to these in the solver manual.

Thanks

### コメント

1. mineyukigamou says:

Hello,

We will answer some questions. All are input data, but please refer to the following.

The relative weight of bedload material is calculated by s = (σ⁄ρ-1).
ρ: Water density
σ: Gravel density (≅2.65)

The void ratio of the bed material is typically 25-30%. For details, refer to the survey results of each analysis target area.

The secondary flow coefficient is generally around 7.
“Engelund, F .: Flow and Bed Topography in Channel Bend, Jour.of Hydr.Div., ASCE, Vol.100. HY11, pp.1631-1648, 1974.”

2. pritikumaricetpa says:

Mflow_02 is a computer code used for simulating flow and sediment transport in rivers with a moveable bed. The code is based on the one-dimensional Saint-Venant equations, which describe the conservation of mass and momentum for a fluid flow. The moveable bed is modeled using the Exner equation, which describes the evolution of the bed elevation due to sediment transport.
The code has a large number of input parameters that can be adjusted to match the specific characteristics of the river being simulated. Some of the key parameters include:
Flow boundary conditions: The upstream and downstream boundary conditions for the flow must be specified, typically in terms of water surface elevation and flow rate.
Channel geometry: The channel cross-sectional geometry, including width and depth, must be specified at various locations along the channel.
Bed roughness: The Manning’s roughness coefficient is used to describe the resistance to flow due to the roughness of the river bed.
Sediment characteristics: The sediment transport function, which determines the rate of sediment transport, is dependent on the size and characteristics of the sediment particles.
Bed slope: The slope of the river bed can significantly affect the flow and sediment transport dynamics.
Time step size: The time step size is an important parameter in the numerical integration of the equations and must be chosen carefully to ensure stability and accuracy.If you’re looking to improve your coding skills or learn new technologies, Cetpa Infotech offers a range of courses and training programs to help you stay up to date with the latest developments in the field. Check out our website for more information.

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