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Posts posted by Benja

  1. Hi everyone,

    Despite it's been a while since I started this topic, I think it can always be helpful to share experiences.

    Finally, after a long try and error process, I think we have achieved a reasonable technique.

    To my understanding, the best way to represent a breakwater is as part of the bathymetry, i.e. as an abrupt change of bottoms elevation. Nevertheless, this may lead to numerical problems, since the boussinesq equations that SMS solves, were derived using the assumption of a mild slope bottom. Anyway, this problem can be addressed by putting a typical coastline damping layer.

    With this, I don't take into account the effects of porosity from the wall of the breakwater, since they are one order of magnitude less than thos due to bathymetric change.

    The reason why I, personally, prefer this approach instead of putting a purely damping layer, lies in the numerical tuning that is required to set it up, tuning that can affect greatly the results.

    I hope this can be helpful.


    Benjamin Carrion

    Ingeniero Hidraulico

    Hi John,

    We work extensively with Breakwaters in Bouss2D. I'm not clear where your problem lies, so I will respond to the original queries from Benjamin:

    1) The BOUSS2D manual and associated technical notes indicate that porosity layers can be used to simulate breakwater effects, however we have had limited success with this - note our work is predominantly with rubble mound breakwaters. We generally simulate breakwater effects using damping strings - the manual and Bouss2D page on the SMS Wiki (http://www.xmswiki.com/xms/SMS:BOUSS-2D) provide a chart which can be used to estimate the required damping parameters based on a desired reflection co-efficient for the breawater. Be careful using damping strings in smale scale applications (e.g. entrances to small harbours/inlets where damping strings have the potential to reduce the effective entrance width).

    2) These standing wave effects occur when waves reflected form the structure interact with the incoming wave train. It is important to note that these standing wave effects do occur in reality (this effect is known as clapotis http://en.wikipedia.org/wiki/Clapotis). If your wave maker is too close to the breakwater, or if your reflection coefficient for the breakwater is too high (see number 1 above), these effects may become amplified in a non-realistic manner (this may also cause the model to crash). Some methods to avoid this include:

    - use realistic reflection co-efficients

    - keep your wavemaker at least 4 wavelengths (rule of thumb) from any structures in your domain

    - consider using an internal wavemaker with damping on the seaward boundary

    - if you are not concerned with the region in between the wave maker and the seaward side of the breakwater, consider applying some strong damping to stop the formation of standing waves.

    As noted above, there is some good info on the Wiki regarding these issues (http://www.xmswiki.com/xms/SMS:BOUSS-2D). As a word of caution, remember that these standing wave effects are real before trying to eliminate them. In our work, we sometimes have to carry out additional post processing and analysis to separate the incoming and reflected wave trains.



    JFA Consultants

  2. Hello everyone,

    I've been having the same problem, and I think I could help with this discussion.

    First of all, despite all the good things that bouss2d has, it's worth to know that theirs equations of motion CAN'T represent phenomenons such like of propagations over breakwaters, since its particular set of Boussinesq-type equations is not fully non-linear and overall it assumes in their derivation that the bottom has a mild slope.

    With this in mind, you have to know that any alternative to simulate a breakwater or any similar structure, like using damping layers or similar, will be always and "ad-hoc" approximation and it's not warranty to work successfully in all cases.

    You can here find an excellent paper where this is remarked


    Finally, I'd like to say that despite bouss2d is not the best alternative to model such kind of cases, it's one of the few available commercial alternatives for doing so, without dealing with very academic models, so nevertheless their results will be approximated, they are a good approximation.


    Benjamín Carrión

    Hydraulic Engineer

  3. John,

    Thanks for your reply and advices. I'm working with the 10.0 version and it's working fine... for most cases.

    From your ideas, I'm inclined to think that the problem might have relation with the breakwater that I'm trying to model (http://aquaveo.invisionzone.com/index.php?showtopic=699) since I have represented it as part of the bathymetry and, in fact, it presents slopes in the order of 1:1.75.

    Nevertheless, I'm using a grid discretization (dx=dy=5m) smaller that the one recommended by the model, and smaller time steps, to achieve Courant's Numbers always below 0.5.

    In any case, the model works well for waves with relative shorter periods, up to 12 seconds, and begins to fail from 15 seconds and above, when the cells per wave begin to be fewer, and therefore the model might be unable to reproduce the fast shoaling process, as you suggest.

    Anyway, I see three possible attempts for solving this:

    - Using a smaller dx, since it worked well for shorter waves

    - Try to smooth the scattered data... but I'm not sure if this is a good idea, since there are elevation levels that must be maintained to represent the breakwater

    - Or else, try to represent the breakwater in another way, as a vertical wall like you say, but in that case I'm afraid to alter the output by a bad choice of the damping parameters. In other words, despite the problems that the model might have to deal with large bathymetric variations, it seems to me that this is the most physic way to represent this type of structures.

    Thanks again for your time, and I'll be glad to hear any other consideration.



  4. Dear all,

    I've been working with Bouss2d, and I started to been notified with this error:

    "forrtl: severe (157): Program Exception - access violation"

    As I've found on internet, this might have relation with the program writing in pieces of memory where it is not allowed to write, or with the change of the file's paths.

    In my opinion I haven't done any of this things, but now I keep receiving this message and I cannot finish my models. Please, any help or leads on why this could be happening will be very appreciated.

    Thanks in advance,



  5. Hello everyone,

    I've been trying to run a model with a breakwater on it, but the results I have make me suspicious.

    I represented the breakwater as a part of the bathymetry and I used a porous layer around it (n=0.4), in the interface between the upper part of the breakwater and the submerged one. The width of this porous layer is equal to that used by the slope of the breakwater. The average water depth in this region is 20 meters, and the wave field has an Hs=1.0m and Tp=15s.

    I've used the model in natural bathymetries and have had good and reasonable results, but in the case of this breakwater an standing wave appears in the side of the breakwater that faces the waves, that have 4 or 5 meters of amplitude and therefore couldn't be physically possible.

    My questions, finally, are:

    1. is this the right way to represent an emerging breakwater, or is there any other? because I couldn't find the answer neither on the documentation of the software, or in the examples, or in this forum

    2. could this standing waves be there for any other boundary condition? In fact the wave maker is in the grid boundary and I don't have a damping region behind it... should I use one? is that the real cause or should I pay more attention to the way of representing the breakwater?

    that was a lot more than 2 questions...

    thanks in advance to whoever could (and wanted) to help me



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