About 2D modelling in ICM

2D Modelling:

Removes some of the assumptions made when undertaking 1D modelling.

Leads to greater confidence in outputs.

Better method for understanding the impact on communities such as large rural areas with significant overland flow.

Used to enhance existing 1D models with 2D overland routing, allowing simulation and understanding of more complex systems.

2D Visual Outputs:

Represent the true power of 2D modelling.

Remove reliance on theorized flood cones and assumptions about the impacts that the flooding has on surrounding properties.

Allow impacts to be displayed clearly with a 2D model added to a map.

Facilitate detailed flood damage calculations based on the flood depth to individual properties.

Shallow water equations (SWE), the depth-average version of the Navier-Stokes equations, used for mathematical representation of 2D flow.

ICM uses unstructured mesh to represent 2D zone for robust simulation of rapidly varying flows (shock capturing) as well as super-critical and transcritical flows.

Refer to Autodesk InfoWorks ICM Help topic, Basic 2D Hydraulic Theory, for more information on the ICM 2D solver.

2D Zones:

Used to define the area required for mesh generation and 2D calculations.

Can be imported via the Open Data Import Centre (ODIC) or digitized directly on the GeoPlan.

Each model contains either small discrete 2D zones or a single large 2D zone.

No interaction between different 2D zones.

Where the boundary of multiple 2D zones is coincident, should be merged to ensure continuity of the hydraulic calculations.

For river modelling, no need to have a separate 2D zone for either side of the river.

 

2D Boundaries:

Defined primarily by the boundary edge of the 2D zone.

Used to define alternative boundary conditions along a section of a 2D zone boundary.

Overrides 2D zone boundary.

Boundary type, set in 2D zone properties, defines how flow is allowed out of the 2D zone.

Can also be used to bring flows into the model.

2D Mesh:

Comprised of 2D elements often triangular in shape, due to the underlying routine, but which can take any amalgamated shape.

Irregular Mesh:

Used by ICM rather than a gridded mesh, making ICM different from many other 2D hydraulic modelling software.

Enables a more exact representation of underlying topology and geometry of structures.

Allows modelling of detailed areas and less detailed areas as desired, resulting in more effective resource management due to an ideal number of 2D elements for analysis.

The more elements and therefore calculation points in a model, the longer calculations take, and the more results data generated.

For 2D mesh to be generated, need to import an appropriate ground model that covers the extent of the 2D zone.

Often a resolution of 2m or less for city scale models.

Ground level for mesh element calculated by sampling ground model within 2D triangles making up the element, and then taking average of sample point levels.

Mesh Comparison:

Two methods of mesh generation for InfoWorks networks:

Classic:

• Present in ICM since first release.
• Populates entire mesh with triangles, then attempts to amalgamate small ones to meet minimum element area criteria.

Clip meshing:

• Makes use of primary and secondary meshing phases.
• Particularly suited to models with complex geometry and objects that may be approximately coincident.
• Typically leads to generation of fewer elements and avoids complications with small triangle generation.

A comparison of the two techniques along a detailed river bank:

Classic meshing: Created lots of small elements along boundary edge which is typically undesirable and could impact simulation stability and run time.

Clip meshing: Primary elements have been clipped to the river reach boundary, giving it its name.

Terrain Sensitive Meshing:

Used to increase resolution of mesh in areas with rapid variation in height, without increasing number of elements in relatively flat areas.

More accurately represents the underlying topography than a lower resolution mesh.

Can be seen in image below, where darker regions indicate areas of small dense elements.

Allows identification of main flow paths from mesh alone.

Meshing Jobs:

Treated in the same way as a simulation.

Turns green once mesh generation is complete.

Can be used to generate multiple meshes at the same time for different models or scenarios.

Validates data used to create mesh prior to mesh generation.

Creates mesh log with error messages, which must be corrected before mesh generation.