Changes between Version 1 and Version 2 of ModellingQuestions

Oct 20, 2008, 1:39:05 PM (15 years ago)



  • ModellingQuestions

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    99See the chapter on "Restrictions and Limitations" in the [ User Manual].
     11== Can I start the simulation at an arbitrary time? ==
     13Yes, using {{{domain.set_time()}}} you can specify an arbitrary
     14starting time. This is for example useful in conjunction with a
     15file_boundary, which may start hours before anything hits the model
     16boundary. By assigning a later time for the model to start,
     17computational resources aren't wasted.
     19== Can I change values for any quantity during the simulation? ==
     21Yes, by using {{{domain.set_quantity()}}} inside the domain.evolve
     22loop you can change values of any quantity. This is for example
     23useful if you wish to let the system settle for a while before
     24assigning an initial condition. Another example would be changing
     25the values for elevation to model e.g. erosion.
     27== Can I change boundary conditions during the simulation? ==
     29Yes, see the example in the section "Changing boundary conditions on the fly" in the
     30[ User Manual].
     32== How do I access model time during the simulation? ==
     34The variable {{{t}}} in the evolve for loop is the model time.
     35For example to change the boundary at a particular time (instead of basing this on the state
     36of the system as in the "Changing boundary conditions on the fly" section of the manual)
     37one would write something like
     39for t in domain.evolve(yieldstep = 0.2, duration = 40.0):
     40    if Numeric.allclose(t, 15):
     41        print 'Changing boundary to outflow'
     42        domain.set_boundary({'right': Bo})
     44The model time can also be accessed through the public interface {{{domain.get_time()}}},
     45or changed (at your own peril) through {{{domain.set_time()}}}.
     47== Why does a file_function return a list of numbers when evaluated? ==
     49Currently, file_function works by returning values for the conserved
     50quantities {{{stage}}}, {{{xmomentum}}} and {{{ymomentum}}} at a given point in time
     51and space as a triplet. To access, or example, {{{stage}}} one must specify element 0 of the
     52triplet returned by file_function, to access {{{xmomentum}}} one must specify element 1 of the triplet, etc.
     54== How do I use a DEM in my simulation? ==
     56You use {{{dem2pts}}} to convert your DEM to the required .pts format. This .pts file is then called
     57when setting the elevation data to the mesh in {{{domain.set_quantity}}}.
     59== What sort of DEM resolution should I use? ==
     61Try and work with the '''best''' you have available. Onshore DEMs
     62are typically available in 25m, 100m and 250m grids. Note, offshore
     63data is often sparse, or non-existent.
     65Note that onshore DEMS can be much finer as the underlying datasets from which they
     66are created often contain several datapoints per squate metre.
     67It may be necessary to thin out the data so that it can be imported
     68without exceeding available memory. One tool available on the net is called 'decimate'. (Need reference?).