Simulation Parameters
The simulation parameters govern how the engine performs the model calculations in the hydraulic simulation.
Editing of simulation parameters is not recommended.
It is not normally necessary to amend the network simulation parameters; the default values have been chosen for optimum accuracy and performance.
To view simulation parameters, select Model parameters  Simulation parameters from the Model menu. The simulation parameters for the current network are displayed in the Object Properties Window.
Parameters
Database Table Name: hw_sim_parameters
Field Name  Help text  Database Field  Data Type  Size  Units  Precision  Default  Error Lower Limit  Error Upper Limit  Warning Lower Limit  Warning Upper Limit  

Min base flow depth 
This is the minimum absolute baseflow depth that will be used for base flows in conduits. Valid values: 0 < Minimum base flow depth << Minimum conduit height. This Base Flow used for calculation purposes should not be confused with the Subcatchment Base Flow, which is a real inflow into the system. 
min_base_flow_depth 
Double 

Y 
3 
0.02 m 
0.001 
99 



Base flow factor 
Base flow is necessary to ensure numerical stability of the St. Venant equations. By default the base flow applied is equal to 5% of the conduit height (Base Flow Factor of 0.05) (10% for steeper pipes.) The simulation engine adds base flow to maintain numerical stability at low depths. It does this by altering the true upstream (higher) boundary condition so that there is effectively a wall of the base flow depth at the upstream end of the conduit. The simulation engine then adds the normal flow for the base flow depth to the flows in the conduit. At the true downstream end of the conduit, the boundary condition uses the true flow, so that in effect the base flow is lost between the conduit end and the connected node. This means that node volume balance calculations are based on the true flows.
The base flow factor is used to determine the base flow depth in conduits using the following equation:
Valid values: 0 < Base Flow Factor << 1. 
base_flow_factor 
Double 


3 
.05 
0 
1 



Slope where base flow is doubled 
This is the slope above which the base flow factor is doubled when determining the base flow depth. Valid values: 0 £ Slope where base flow is doubled 
slope_base_flow_x2 
Double 

S 
4 
.01 m/m 
0 
1 



Min space step 
The Space Step parameters determine the number of computational nodes per conduit / river reach. The Space Step is the distance between computational nodes along the conduit / river reach. Valid values are: Minimum Space Step (DXMIN): DXMIN > 0, DXMIN < DXMAX Maximum Space Step (DXMAX): DXMAX > 0, DXMAX > DXMIN In addition, for river reaches:
The Space Step is determined by the Conduit width multiplier:
Minimum Number of Computational Nodes is the global minimum number of computational nodes per conduit. Controls always have 2 computational nodes. The software will allocate at least 5 computational nodes per conduit. If the number of computational nodes determined by the other space step parameters exceeds the minimum, the software will use that number instead.

min_space_step 
Double 

L 
2 
.5 m 
0.01 
9999 



Max space step 
See Min space step 
max_space_step 
Double 

L 
2 
100 m 
0.01 
9999 



Conduit width multiplier 
See Min space step 
width_multiplier 
Double 


2 
20 
0 
999 



Min number of computational nodes 
See Min space step 
min_computational_nodes 



0 
5 
5 
99999999 



Min slot width 
Minimum width of the Preissmann slot (overrides value determined by Celerity ratio). Valid values: 0 < Min slot width << Minimum conduit width. 
min_slot_width 
Double 

L 
5 
0.001 m 
0.00001 
99 



Celerity ratio 
The Preissmann slot is used in the hydraulic simulation to model pressurised flow in closed conduits. The Celerity ratio determines the width of the Preissmann slot used in the software to model surcharged flow. The slot width is such that the celerity in the slot is Celerity ratio x the celerity at half conduit height. The standard ratio was chosen so that surcharged flows could be modelled robustly and accurately. This results in a slot that is 2% of the width of the conduit (slightly different for some conduit shapes). If the software is being used to model storage in large surcharged trunk sewers you may want to reduce the slot width to reduce the additional storage that it generates (note that the slot transition generally adds 45% area depending on shape). To do this, increase the value of Celerity ratio  a value of 14.414 produces a slot that is 1% of conduit width. Note that narrower slots may make the model less stable. The slot width is inversely proportional to Celerity ratio. Valid values: Celerity ratio > 0 The equations used to calculate the slot width are as follows:

celerity_ratio 
Double 


2 
10 
0 
9999 



Lower Froude number 
This is the characteristic Froude number above which the inertia terms in the SaintVenant equations are phased out for a conduit. The characteristic Froude number for a conduit is determined at half depth. Valid values: 0 < Lower Froude number < Upper Froude number 
lower_froude_number 
Double 


3 
.8 
0 
99 



Upper Froude number 
This is the characteristic Froude number above which the inertia terms in the SaintVenant equations are dropped. Note that using a value above 1.0 may result in instabilities during simulation. The conduits with the inertia terms dropped will be solved faster by the hydraulic simulation. Valid values: Upper Froude number > 0, Upper Froude number > Lower Froude number 
upper_froude_number 
Double 


3 
1 
0 
99 



Start timestep (s) 
The Initialisation Parameters are used if an initial simulation has not been included in the Simulation State section of the Schedule Hydraulic Run Dialog. The hydraulic system is initialised in a steady state.
The simulation engine will perform up to five initialisation phases. Each time initialisation fails, the phasein time will be multiplied by a factor of 10 and restartedf from the initial (dry) condition. 
start_timestep 
Double 


2 
7.5 
0.01 
9999 



Max timestep (s) 
Maximum allowed timestep during initialisation process. See Start timestep 
max_timestep 
Double 


2 
1920 
0.01 
9999 



Phasein time (min) 
Time over which the boundary conditions (initial inflows and tide levels) are linearly phased in during initialisation. See Start timestep 
phase_in_time 
Double 


2 
15 
0.01 
99999 



Steady state flow tolerance 
See Start timestep 
steady_tol_flow 
Double 

Q 
6 
.0005 m3/s 
0.000001 
999 



Steady state depth tolerance 
See Start timestep 
steady_tol_depth 
Double 

Y 
6 
.005 m 
0.000001 
999 



Max number of timestep halvings  initialisation 
Maximum number of timestep halvings to allow convergence of the NewtonRaphson method during the initialisation process. 
ini_max_halvings 



0 
10 
1 
30 



Max number of iterations  initialisation 
Maximum number of iterations per timestep during the initialisation process. 
ini_max_iterations 



0 
10 
1 
999 



Max number of iterations after doubling  initialisation 
Maximum number of iterations allowed after the timestep has been doubled during the initialisation process. (Rapid convergence of the NewtonRaphson method may result in the timestep being doubled). 
ini_max_iterations_x2 



0 
7 
1 
999 



Tolerance for flow 
During the initialisation process, convergence is achieved when:

ini_tolerance_flow 
Double 


4 
.01 
0.0001 
9 



Flow tolerance scaling factor  initialisation 
See Tolerance for flow  initialisation 
ini_scaling_flow 
Double 


3 
1 
0.001 
999 



Tolerance for depth 
See Tolerance for flow  initialisation 
ini_tolerance_depth 
Double 


4 
.01 
0.0001 
9 



Depth tolerance scaling factor  initialisation 
See Tolerance for flow  initialisation 
ini_scaling_depth 
Double 


3 
1 
0.001 
999 



Tolerance for level 
See Tolerance for flow  initialisation 
ini_tolerance_level 
Double 


4 
.01 
0.0001 
9 



Level tolerance scaling factor  initialisation 
See Tolerance for flow  initialisation 
ini_scaling_level 
Double 


3 
1 
0.001 
999 



Min depth in conduits  initialisation 
Minimum depth imposed by the simulation engine during the initialisation process. 
ini_min_depth 
Double 

Y 
5 
.01 m 
0.00001 
9 



Min plan area at nodes  initialisation 
Minimum node plan area imposed by the simulation engine during the initialisation process. 
ini_min_node_area 
Double 

NA 
3 
1 m2 
0 
9999 



Time weighting factor 
q is used in the Preissmann 4point scheme. The 4point scheme is only unconditionally stable when q > 0.5. The value of q = 1.0 provides maximum numerical dispersion during initialisation. 
ini_time_weighting 
Double 


3 
1 
0 
1 
0.5 


Tolerance for volume balance 
If Tolerance for volume balance is set to 0.0 (default), no volume balance checking will be carried out. To enable volume balance checking, define a value greater than zero. The recommended value to use is 0.01. When volume balance checking is enabled the simulation engine checks the volume balance at each node at each iteration where the flow, depth, and level increments are within tolerance. If volume balance / (volume balance scaling factor + largest volume in/out/change in storage) is greater than the Tolerance for volume balance then the engine will do another iteration, unless the engine has already done the maximum number of iterations for this timestep, in which case the engine will halve the timestep. 
ini_tolerance_volbal 
Double 


4 
0 
0 
9 



Volume balance tolerance scaling factor  initialisation 
See Tolerance for volume balance (Initialisation) 
ini_scaling_volbal 
Double 


3 
1 
0 
999 



Relax tolerance from run t/s  initialisation 
During the initialisation phase:
It is strongly recommended that this option is checked for networks that contain 2D Zones. 
ini_relax_tol 
Boolean 


0 
True 





Max number of timestep halvings  simulation 
Maximum number of timestep halvings to allow convergence of the NewtonRaphson method during the simulation. 
sim_max_halvings 



0 
10 
1 
30 



Max number of iterations  simulation 
Maximum number of iterations allowed per timestep. 
sim_max_iterations 



0 
10 
1 
999 



Max number of iterations after doubling  simulation 
Maximum number of iterations allowed after the timestep has been doubled. (Rapid convergence of the NewtonRaphson method may result in the timestep being doubled). 
sim_max_iterations_x2 



0 
7 
1 
999 



Tolerance for flow  simulation 
During the simulation, convergence is achieved when:

sim_tolerance_flow 
Double 


4 
.01 
0.0001 
9 



Flow tolerance scaling factor  simulation 
See Tolerance for flow  simulation 
sim_scaling_flow 
Double 


3 
1 
0.001 
999 



Tolerance for depth  simulation 
See Tolerance for flow  simulation 
sim_tolerance_depth 
Double 


4 
.01 
0.0001 
9 



Depth tolerance scaling factor  simulation 
See Tolerance for flow  simulation 
sim_scaling_depth 
Double 


3 
1 
0.001 
999 



Tolerance for level  simulation 
See Tolerance for flow  simulation 
sim_tolerance_level 
Double 


4 
.01 
0.0001 
9 



Level tolerance scaling factor  simulation 
See Tolerance for flow  simulation 
sim_scaling_level 
Double 


3 
1 
0.001 
999 



Min depth in conduits  simulation 
Minimum depth imposed by the simulation engine 
sim_min_depth 
Double 

Y 
5 
.01 m 
0.00001 
9 



Min plan area at nodes  simulation 
Minimum node plan area imposed by the simulation engine 
sim_min_node_area 
Double 

NA 
3 
1 m2 
0 
9999 



Time weighting factor  simulation 
q is used in the Preissmann 4point scheme. The 4point scheme is only unconditionally stable when q > 0.5; the value of q = 0.65 used during simulation introduces a small degree of numerical dispersion. 
sim_time_weighting 
Double 


3 
.65 
0 
1 
0.5 


Tolerance for volume balance  simulation 
If Tolerance for volume balance is set to 0.0, no volume balance checking will be carried out. To enable volume balance checking, define a value greater than zero. The recommended value to use is 0.01. When volume balance checking is enabled the simulation engine checks the volume balance at each node at each iteration where the flow, depth, and level increments are within tolerance. If volume balance / (volume balance scaling factor + largest volume in/out/change in storage) is greater than the Tolerance for Volume Balance then the engine will do another iteration, unless the engine has already done the maximum number of iterations for this timestep, in which case the engine will halve the timestep. 
sim_tolerance_volbal 
Double 


4 
0.01 
0 
9 



Volume balance tolerance scaling factor 
See Tolerance for volume balance  simulation 
sim_scaling_volbal 
Double 


3 
1 
0 
999 



Relax tolerance from run t/s  simulation 
During the simulation phase:
It is strongly recommended that this option is checked for networks that contain 2D Zones. 
sim_relax_tol 
Boolean 


0 
True 





Use SWMM5 RDII 
A check in the box (default) indicates that SWMM5 RDII (Rainfall Derived Infiltration and Inflow) is to be used in the simulation. If unchecked, the preSWMM 5 RDII implementation will be used in the simulation. Note
PreSWMM 5 RDII does not support the monthly variation and initial abstraction functionality that is available in SWMM5 RDII for Monthly RTK Hydrographs, but does allow multiple subcatchments that use RTK Hydrographs (not necessarily the same one) to drain to a single node. 
swmm5_rdii  Boolean  0  True  
Stay pressurised 
A pipe should only be pressurised if it is to stay pressurised throughout the simulation. However it is very common that people model pressurised pipes that are not in fact pressurised. By default, the simulation engine will switch to the full solution model for the rest of the simulation if a pressure pipe is not surcharged. You may want to check the Stay pressurised option if you have, for example, a rising main that numerically temporarily goes out of surcharge because of water hammer effects when a pump switches on or off. The simulation may fail in this case, if you have inappropriately set a conduit as a pressure pipe. You should only use the pressurised pipe model for conduits that you know remain permanently surcharged. The field settings are:

stay_pressurised 
Boolean 


0 
False 





Don't linearise conveyance 
In culverts, the conveyance is greater just before the culvert becomes full than at the point when the culvert becomes surcharged. This effect is most pronounced in wide rectangular culverts, and occurs due to the effect of the roughness of the roof of the culvert. When this is option is unchecked (default), conveyance tables are linearised to the pipe full value to eliminate turning points in the conveyance function used by the solver. This is shown by the red line on the graph below. This results in the underestimation of flow capacity in rectangular culverts. However, it is more stable mathematically. When this option is checked, the simulation engine does not linearise conveyance tables (see the black line on the graph). Using this option may result in instabilities when the conduit enters/leaves surcharge.
Conduit Conveyance 
dont_linearise_k 
Boolean 


0 
False 





No. of geometry table entries 
This field determines the number of entries the simulation uses for conduit crosssection geometry lookup tables between the invert and soffit. More entries provide a more accurate representation of the geometry, at the expense of memory use and computational effort. You may need to change this parameter to get a more accurate representation of pipe behaviour close to pipe full when you turn on the Don't linearise conveyance option above. 
geometry_table_entries 



0 
15 
15 
999 



Use full area for headloss calculations 
By default the checkbox is unchecked. The value of velocity passed through to the headloss calculations is calculated from:
When this option is checked headloss calculations are carried out using the full cross section area of the pipe. 
use_full_area_for_hl 
Boolean 


0 
False 





The value of this field affects the way in which the simulation engine handles inflow as defined in the Inflow field of conduit, river reach, channel and bridge links. For new models, Innovyze recommend that this field is checked. However, if you want to reproduce the behaviour of the simulation engine prior to InfoWorks ICM, version 6.5 then do not check this field.

inflow_is_lateral 
Boolean 


0 
False 





Bottom of headloss transition 
The Bottom of headloss transition and Top of headloss transition parameters are used to define a transition zone in which headloss in conduits is phased out, with the purpose of eliminating unrealistically high headloss results for links with flows at low depths.
The values are given as a proportion of conduit height minus sediment depth:

hl_trans_bottom 
Double 


3 
0 
0 
1 



Top of headloss transition 
Used to define a transition zone in which headloss in conduits is phased out, with the purpose of eliminating unrealistically high headloss results for links with flows at low depths. See Bottom of headloss transition for further details. 
hl_trans_top 
Double 


3 
0 
0 
1 



Use Villemonte equation 
When this field is checked the simulation will use the Villemonte equation for drowned weir flow. 
use_villemonte 
Boolean 


0 
False 





Drop inertia in pressure pipes 
Check this parameter to exclude modelling of inertia in pressure pipes. See Pressurised Pipe Model for more information. 
pressure_drop_inertia 
Boolean 


0 
True 





Drowned bank linearisation threshold 
When calculating bank flow for a drowned spill segment, linearised flow equations will be used when the head difference at both ends of the segment is below this threshold. Applicable to lateral banks, inline banks and irregular weirs; this parameter is used to avoid oscillating flows as the head difference over the bank approaches zero. If set to null, a value of zero is assumed (no linearisation). 
drowned_bank_threshold  Double  Y  3  0.01 m  
Node level affects groundwater infiltration 
Check this parameter to make groundwater infiltration depend on the depth in the groundwater destination node. In existing networks (created before Version 8.0) this option will be unchecked. In new networks this option will be checked. 
sim_node_affects_infiltration  Boolean  0  True  
Weight Manning roughness by n 
The simulation engines uses the equivalent roughness concept to provide a roughness value for a wetted perimeter that has more than one roughness value. This parameter allows you to choose whether the perimeter is weighted using n (N) or 1/n (MANNING) to represent roughness. Check this parameter to weight Manning roughness by n. If unchecked (default), Manning roughness will be weighted by 1/n. 
weight_by_n  Boolean  0  False  
Use 2d elevations instead of depths 
Used as a measure to avoid oscillating flows due to ground level discrepancy between manholes and 2D mesh elements. Check this parameter to use the elevation in 2D zones to set the elevation at 1D nodes connected to the 2D zone. If this option is unchecked, the engine will use the depth in 2D zones to set the depth above ground at 1D nodes. See Defining 2D Nodes for more information. Note
This setting is overridden by the setting on the 1D2D linkage basisfield for individual nodes. See Node Data Fields for further information. 
use_2d_elevations  Boolean  0  False  
Inflowbased node2d link 
Check this parameter to use the net inflow into an element when calculating maximum flow that can be exchanged between the 2D element and a 1D node within the element. This method monitors the error between the head in the element (measured head) and the corresponding head given by the net inflow into the element (equilibrium head). A PID controller is used to minimise the error by adjusting the maximum flow that can be exchanged between the 2D and 1D network. If this option is unchecked, the engine will use the volume in the element to calculate the maximum flow that can be exchanged. This method may result in discrepancies between head in the 2D mesh and inflow to the 1D network, particularly in cases where 1D nodes are located within small elements and when using long timesteps. 
inflow_manhole_link  Boolean  0  True  
Ground slope term correction 
Check this parameter if the ground slope term at the faces is to be based on a constant slope connecting the adjacent element ground levels. Using this method, the resulting flow under uniform conditions will follow the Manning's equation for any ground slope subject to the 2D Parameters set in a run. This maybe useful when calibrating models in areas with steep slopes. However, using this parameter may result in large flow velocities which may cause a reduction of the engine time step and therefore an increase in run times. To alleviate this issue, it is recommended to reduce the Maximum velocity parameter on the Advanced tab of the 2D Parameters dialog. If this option is unchecked (default), the ground slope term is based on a discontinuous step connecting the adjacent element ground levels. The results using both approaches tend to the same values in areas where the shallow water equation hypothesis is fulfilled, i.e. areas with low to moderate slopes of both the free surface and the ground level. 
ground_slope_correction  Boolean  0  False 