Scour going deeper than the layer thickness?

Marulke · 2020-10-23 10:54:19

Hi,
I am running a sediment transport model in Baseplane 2.8. I use only bed load transport (Engelund Hansen) with one grain size (d = 0,25 mm). I have defined only one soil layer for the entire model. The layer has a "bottom elevation" = -0.1 m.

When I run the model I get areas with deeper scouring. The maximum delta-z is -0.22 m.

As I understand the documentation the fixed bed level (max scour depth) is defined as the bottom of the lowest defined soil layer. In this case -0.1 m.

Any suggestions as to why I have scouring below the bottom elevation of the only soil layer?

Regards,
Marulke

Matteo Facchini · 2020-10-29 15:40:48

Hi Marulke,

can you post or attach your bmc file?

Thanks

Marulke · 2020-11-06 14:24:38

Hi Matteo,
you will find my bmc below. (I hope its OK to post it in this way?)

There is one layer, and the thickness is -0.01. However, delta_Z gets much lower.

Kind regards,
Marulke

//---------------------------------------------------
// BASEMENT file
// generated by BASEview
//---------------------------------------------------
PROJECT {
title = B_lab_model_sediment_transport
}
DOMAIN {
BASEPLANE_2D {
region_name = B_reservoir
GEOMETRY {
type = 2dm
file = 20201021_A1.2dm
STRINGDEF {
name = US_boundary
node_ids = (2 129 130 131 132 133 134 135 136 137 1)
upstream_direction = right
}
STRINGDEF {
name = DS_boundary
node_ids = (47 138 139 140 141 142 143 144 145 146 48)
upstream_direction = right
}
}
HYDRAULICS {
PARAMETER {
minimum_water_depth = 0.01
riemann_solver = exact
}
FRICTION {
type = manning
default_friction = 0.033
wall_friction = on
}
INITIAL {
type = continue
file = Restart_Q4000m3s_577masl_nosed.cgns
restart_solution_time = -1
}
BOUNDARY {
name = US_boundary
type = hydrograph
string_name = US_boundary
file = Inflow_4000_steady.txt
slope = 200
}
BOUNDARY {
name = DS_boundary
type = zhydrograph
file = DS_HQ_boundary_577_for_4000m3s.txt
string_name = DS_boundary
}
}
TIMESTEP {
CFL = 0.98
total_run_time = 94500
start_time = 0
}
OUTPUT {
console_time_step = 1000
SPECIAL_OUTPUT {
type = BASEviz
output_time_step = 1000
}
SPECIAL_OUTPUT {
type = node_centered
output_time_step = 1000
values = (depth velocity wse deltaz)
format = sms
}
SPECIAL_OUTPUT {
type = boundary_history
output_time_step = 1000
boundary_values = (Q Qsed)
}
}
MORPHOLOGY {
PARAMETER {
local_slope_angle_repose = 30.0
}
BEDMATERIAL {
GRAIN_CLASS {
diameters = (0.25)
}
MIXTURE {
name = Model_sand_d_025
volume_fraction = (100)
}
SOIL_DEF {
name = Model_sandbed
LAYER {
mixture = Model_sand_d_025
bottom_elevation = -0.01
}
}
SOIL_ASSIGNMENT {
index = (1)
soil = (Model_sandbed)
}
}
INITIAL {
type = continue
file = Restart_Q4000m3s_577masl_nosed.cgns
}
BEDLOAD {
FORMULA {
bedload_formula = engelundhansen
local_slope_correction = local_slope_vanrijn
}
PARAMETER {
use_cell_averaged_bedload_flux = on
}
DIRECTION {
lateral_transport_type = curvature_effect_dynamic
lateral_index = (1)
radius_calculation_type = velocity_vectors
}
BOUNDARY {
type = sediment_discharge
file = US_bedload_inflow_2kg_per_min.txt
string_name = US_boundary
mixture = Model_sand_d_025
}
BOUNDARY {
type = IODown
string_name = DS_boundary
}
}
}
}
PARALLEL {
number_threads = 0
}
}

Matteo Facchini · 2020-11-06 17:50:59

That's strange!

Is your restart file related to a fixed bed simulation or not?

Best
Matteo

Marulke · 2020-11-08 21:05:17

Hi Matteo,
you solved the problem.

When I changed MORPH \ INITIAL from "continue" to "initial mesh" the scouring stopped at the bottom elevation defined in LAYER \ bottom elevation (-0.01).

The restart file, which was originally called in MORPH / INITIAL was from a pure hydraulic simulation. There was no MORPH block defined for that simulation.

I assume that the simulation should use the bottom elevation defined in the actual bmc, not in the restart file? Maybe a bug?

Thanks,
Marulke

Matteo Facchini · 2020-11-09 10:28:10

Hi marulke,

I am glad you solved your issue!

Cheers,
Matteo

User Forum of Software BASEMENT

#1 2020-10-23 10:54:19

Scour going deeper than the layer thickness?

#2 2020-10-29 15:40:48

Re: Scour going deeper than the layer thickness?

#3 2020-11-06 14:24:38

Re: Scour going deeper than the layer thickness?

#4 2020-11-06 17:50:59

Re: Scour going deeper than the layer thickness?

#5 2020-11-08 21:05:17

Re: Scour going deeper than the layer thickness?

#6 2020-11-09 10:28:10

Re: Scour going deeper than the layer thickness?

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