SMS:BOUSS2D
BOUSS2D  

BOUSS2D Screenshot  
Model Info  
Model type  Boussinesq Wave Model for Coastal Regions and Harbors. 
Developer 
Okey George Nawogu, Ph.D. 
Web site  BOUSS2D web site 
Tutorials 
General Section
Models Section
Several sets of sample problems and case studies are available. These include:

BOUSS2D is a comprehensive model for simulating the propagation and tranformation of waves in coastal regions and harbors based on a timedomain solution of Boussinesqtype equations. It is based on Boussinesqtype equations derived by Okey Nwogu and has been under development since 1993. The equations are depthintegrated for the conservation of mass and momentum for nonlinear waves propagating in shallow and intermediate water depths.
The BOUSS2D model can be added to a paid edition of SMS.
Functionality
BOUSS2D computes nearshore wave fields including mean wave heights, mean current direction, mean water level breaking and transient representation of water levels, currents, and wave breaking.
BOUSS2D is a comprehensive numerical model for simulating the propagation and transformation of waves in coastal regions and harbors based on a timedomain solution of Boussinesqtype equations. The governing equations are uniformly valid from deep to shallow water and can simulate most of the phenomena of interest in the nearshore zone and harbor basins including:
 Reflection/diffraction near structures
 Energy dissipation due to wave breaking and bottom friction
 Crossspectral energy transfer due to nonlinear wavewave interactions
 Breakinginduced longshore and rip currents
 Wavecurrent interaction
 Wave interaction with porous structures
The governing equations in BOUSS2D are solved in the time domain with a finitedifference method. Input waves may be periodic (regular) or nonperiodic (irregular), and both unidirectional or multidirectional sea states may be simulated. Waves propagating out of the computation domain are either absorbed in damping layers or allowed to leave the domain freely. The SI engineering units are used in BOUSS2D calculations.
Output Options
See Output Options in the BOUSS2D Simulations article.
Saving BOUSS2D
When completing a File  Save As... command, the following files get saved in the *.sms
 *.mat referenced to new save location
 *.map referenced to new save location
 Damping files saved to temp folder
 *.par referenced to new save location
 *.sol referenced to original save location unless rerun
 *.h5 referenced to new save location
Using the Model / Practical Notes
BOUSS2D can be applied to a wide variety of coastal and ocean engineering problems, including complex wave transformation over small coastal regions (15 km), wave agitation and harbor resonance studies, wave breaking over submerged obstacles, breakinginduced nearshore circulation patterns, wavecurrent interaction near tidal inlets, infragravity wave generation by groups of short waves, and wave transformation around artificial islands.
As with many numerical models, BOUSS2D can terminate or crash due to numerical instabilities. These are usually caused by problems related to the grid, the boundary conditions, or model parameters. The following lists describe common causes of instability and methods to correct them.
Instability due to the grid/geometry
 Model stability requires a low Courant number throughout the domain. SMS computes an approximate maximum time step to maintain a Courant number below 0.5. In some cases, it is desired to lower the time step even more. Additionally, some may want to truncate the computational domain to areas with depth above a specified minimum. Another option is to increase resolution by using smaller computational cells. Either of these options increase run time, so before applying them, look at the other causes of instability.
 Abrupt changes in elevation from one cell to another in the computational domain could result in instabilities. It may be helpful to smooth the grid. (A smoothing command is available by right clicking on the grid object in the project explorer in the SMS interface.)
 Computation nodes surrounded on three or four sides by land may be created during the grid creation process. These "isolated" cells may become unstable and generally don't have an impact on the wave climate. They can be converted to land cells.
Instability due to the boundary conditions
 Generally, avoid placing damping or porosity layers along structures and shorelines.
 Wave makers are more stable on the edges of the domain. Therefore, generally speaking, the wave maker should be placed on the boundary of the domain in constant (or nearly constant) depth water. (The SMS interface offers to extend the grid and transition to constant depth if a wave maker is created in a location with more that 20% variation in depth.) This is especially true in real world applications where reflected waves are of no concern. Also, when simulating large waves, the greater stability of external wavemakers may be required.
 Wave makers should be placed far enough from shore to avoid interaction between the wave maker and reflecting waves. This is because the external boundary behind the wave maker is treated as a vertical wall.
 Exceptions, or applications in which internal wavemakers (i.e. wavemakers placed inside the domain) are recommended include:
 In applications with significant reflections from structures inside the computational domain. When reflected are caused by coastlines, structures, or bathymetry (reflected wave sources), the simulated seastate will become less uniform spatially, and the simulation may not reach a steadystate condition. The resulting wave field in such simulations will generally consist of nodes and antinodes that resemble a standing wave pattern, where waves appear to be bouncing back and forth inside the domain. If reflected waves cannot escape through boundaries of the modeling domain (or are constrained to exit the domain), a steadystate condition technically cannot be reached irrespective of the length of simulation. When reflected waves intercept external wavemakers, the extremes (lows and highs) in the calculated wavefield may keep building and can eventually lead to model instabilities.
 Internal wavemakers should be used for finite domains and especially for limited area physical modeling studies, and with the above specified guidance.
 If wavemakers are placed on the interior of the domain, they should cross the entire domain to avoid potential "end effects", and have a damping layer placed behind (on the seaward side of) the internal wavemakers to absorb reflected waves. There should also be a gap (at least one nondamped cell) between the internal wavemaker and the damping layer located offshore.
 In the absence of laboratory or field data to calibrate damping and porous layers for an application, consider multiple simulations with a range of damping widths and/or coefficients. This graph from BOUSS2D's technical report illustrates the variation of effective reflectivity given various damping coefficients and damping layer widths. To use this graph:
 Compute L (the wavelength for the incident wave).
 Select a w/L ratio. Use this ratio to compute w (damping width).
 Select an expected reflection percentage. Follow a horizontal line for this percentage on plot to intersect the graph for selected w/L ratio. Read associated damping coefficient from plot.
 Note that the reflection coefficient is very sensitive to a change in damping coefficient when the coefficient is small (< 0.3) and much less sensitive when the coefficient is larger.
 This process may require the damping parameters be changed when different wave conditions are considered.
 It should be observed that this plot is for normally incident waves. Different reflection coefficients would be obtained for obliquely incident waves.
 Damping layers should be 5–10 cells wide.
Instability due to model parameters
 The model includes a Smagorinsky term to account for subgrid turbulence. If the turbulence is known, it is expected this term can be left at the default (0.0), however, it may be increased to increase stability. (This should be done with caution. Remember, don't suppress the wiggles, they are trying to say something.)
Test Cases
 Test 1 – Simple test demonstrating the use of an internal wavemaker.
External Links
 BOUSS2D User Manual
 CHL BOUSS2D website [1]
 May 2007 ERDC/CHL CHETNI73 InfraGravity Wave Input Toolbox (IGWT): User’s Guide [2]
 May 2005 ERDC/CHL CHETNI70 BOUSS2D Wave Model in SMS: 2. Tutorial with Examples [3]
 Mar 2005 ERDC/CHL CHETNI69 BOUSS2D Wave Model in the SMS: 1. Graphical Interface [4]
 Aug 2011 Tsunami Modeling Example Study  A Joint Hydraulic/Structural Methodology for the Rehabilitation of the Crescent City Marina [5]
 Apr 2014 Tsunami Modeling Article [6]
Related Topics
 BOUSS2D Graphical Interface
 Cartesian Grid Module
 BOUSS2D Files
 BOUSS2D Model Control Dialog
 BOUSS2D Calculators
 CGWAVE
 SMS Models page
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