--- Welcome to the official ADCIRCWiki site! The site is currently under construction, with limited information. ---
For general information, see the ADCIRC site, ADCIRC FAQ, or the ADCIRC Wikipedia page. For model documentation not yet available on the wiki, see the ADCIRC site. New content is being continuously added to the ADCIRCWiki, and material from the main ADCIRC site will be gradually transitioned over to the wiki.


Revision as of 23:55, 2 February 2019 by Wpringle (talk | contribs)
Jump to: navigation, search

IM is an important parameter in the fort.15 file that defines numerical model formulation and dimension. Among other things, IM specifies whether ADCIRC is solved in two-dimensional depth-integrated (2DDI) or in three-dimensions (3D), solution of the governing equations is semi-implicit or explicit in time, and whether the model formulation is barotropic or baroclinic.

Shortcut IM Values

The most common combination of options used for simulation can be specified through the shortcut values

Six-digit IM Codes

For fine-grained control of various options six-digit codes for IM can be specified. Each digit represents a specific option regarding the dimension and the formulation of certain terms or integration methods in the GWCE or momentum equations. The available options for each digit are specified below:

Value Digit 1: 2DDI/3D, Lateral Stress in GWCE[1] Digit 2: Advection in GWCE[2] Digit 3: Lateral Stress in Momentum[1] Digit 4: Advection in Momentum[2] Digit 5: Area Integration in Momentum Digit 6: GWCE mass matrix, barotropic/baroclinic
1 (default) 2DDI, Kolar-Gray flux-based Non conservative Integration by parts, velocity-based Non conservative Corrected Consistent (semi-implicit), barotropic
2 2DDI, 2-part flux-based Conservative form 1 Integration by parts, flux-based Conservative form 1 Original Lumped (explicit), barotropic
3 2DDI, 2-part velocity-based Conservative form 2 Integration by parts, velocity-based symmetrical Conservative form 2 - Lumped (explicit), baroclinic (not yet implemented in ADCIRC release version)
4 2DDI, 2-part flux-based symmetrical - Integration by parts, flux-based symmetrical - - -
5 2DDI, 2-part velocity-based symmetrical - 2 Part, velocity-based (not implemented) - - -
6 3D, Kolar-Gray flux-based - 2 Part, flux-based (not implemented) - - -

A common code combination is IM = 111112, which uses default options (same as IM = 0), but simulates in explicit mass-lumping mode. This is a useful alternative to the (default) semi-implicit consistent GWCE mass matrix mode, which requires a matrix solve increasing computational time and memory compared to the explicit mass-lumping mode, which as about twice as fast and scales to fewer grid nodes per computational core.[3]


  1. 1.0 1.1 K.M. Dresback, R.L. Kolar, R.A. Luettich, Jr. (2005). On the Form of the Momentum Equation and Lateral Stress Closure Law in Shallow Water Modeling, in: Estuar. Coast. Model., American Society of Civil Engineers, Reston, VA, 399–418. doi:10.1061/40876(209)23
  2. 2.0 2.1 K.M. Dresback, R.L. Kolar, J.C. Dietrich (2005). On the Form of the Momentum Equation for Shallow Water Models Based on the Generalized Wave Continuity Equation: Conservative vs. Non-Conservative. Advances in Water Resources, 28(4), 345-358. doi:10.1016/j.advwatres.2004.11.011
  3. S. Tanaka, S. Bunya, J.J. Westerink, C. Dawson, R.A. Luettich, Scalability of an Unstructured Grid Continuous Galerkin Based Hurricane Storm Surge Model, J. Sci. Comput. 46 (2011) 329–358. doi:10.1007/s10915-010-9402-1