User Forum of Software BASEMENT

Yang He

User

Registered: 2024-06-02

Posts: 8

Error (Newton-iteration) and Warnings in Suspended Load Modeling

Hello,

I am currently working on modeling suspended load transportation in a 56 km river, which includes 3,065 cross-sections with 20 m gaps between each. The river five tributaries.

The simulation I am conducting is based on hydraulic steady-state results. I assumed clear water conditions (SSC = 0 g/L) throughout the river, with a constant discharge and 0 g/L SSC for the upper boundary and tributaries 2, 3, 4, and 5. Only tributary 1 has varying discharge and SSC inputs to observe how suspended sediment is transported.

However, I encountered the following warning multiple times:

WARNING -> Bedload control volume mixtures differ more than 0.1 percent, is
   sumofbeta = 1.02956, thickness = 0.02, element = IP_cs_68_cs_69_0.39544669

WARNING -> Bedload control volume mixtures differ more than 0.1 percent, is
   sumofbeta = 1.04673, thickness = 0.02, element = IP_cs_68_cs_69_0.39544669

Additionally, I received the following error, which caused the model to stop:

ERROR -> Newton-iteration to calculate water surface elevation (z) as a function
   of the wetted area (A) failed for cross section
   'IP_cs_195_cs_196_0.33305671'. Maximal number of iteration (1000) was
   reached.
   Requested A = 4.2739e+32
   Current z   = 0
   A-Anew      = 1000
   [z0,z1]     = [1300.2, 1342.06]
   [A0,A1]     = [0, 2344.58]
   Please try to (1) start simulation with wetted initial condition, (2) check
   tags in HYDRAULICS -> PARAMETERS -> SECTION_COMPUTATION.

To address the "Newton-iteration" error, I have already tried the suggested solutions found here (https://forum.basement.ethz.ch/viewtopic.php?id=5503). Specifically, I defined the main channel and bottom ranges, checked the potentially problematic cross-sections, and adjusted the downstream slope. I also experimented with changing the “min_interval” and “max_interval” settings. While these adjustments delayed the error, they did not resolve the issue.

Below is the current configuration of “SECTION_COMPUTATION” in my model:

"PARAMETER": {
              "SECTION_COMPUTATION": {
                "internal_levees": "on",
                "type": "table",
                "max_interval": 0.005,
                "min_interval": 0.001
              },
              "minimum_water_depth": 0.01,
              "riemann_solver": "roe",
              "simulation_scheme": "explicit",
              "stretch_boundary_elem": "yes"

And here is setting of “SUSENDED LOAD”

"SUSPENDED_LOAD": {
              "BOUNDARY": [
                {
                  "string": "upstream",
                  "type": "suspension_discharge",
                  "file": "ssc_initial.txt",
                  "mixture": "unique"
                },
                {
                  "string": "downstream",
                  "type": "out_down"
                }
              ],
              "INITIAL": {
                "concentration": 0.0,
                "mixture": "unique",
                "type": "global_value"
              },
              "PARAMETER": {
                "scheme": "quickest",
                "sediment_exchange": "on",
                "diffusion_factor_dynamic": 1,
                "sink_velocity_type": "vanrijn",
                "local_slope": "off",
                "exchange_type": "concentrations",
                "settling_velocities": [
                  0.152
                ],
                "pickup_factor": 0.0
              }
Error and warnings happen when I set the "sediment_exchange" to be "on"

I would greatly appreciate any advice or insights you might have on how to resolve these issues.

Thank you for your time and assistance.

Best regards,
Yang