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Timestamp:
Mar 13, 2007 2:52:40 AM (17 years ago)
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raasch
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  • palm/trunk/DOC/app/chapter_2.0.html

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    6   <title>PALM chapter 2.0</title>
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    8   <meta content="Marcus Oliver Letzel" name="AUTHOR">
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    11   <meta content="parallel LES model" name="KEYWORDS">
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    19 <h2 style="line-height: 100%;"><font size="4">2.0 Basic techniques of
     2<html><head>
     3<meta content="text/html; charset=windows-1252" http-equiv="CONTENT-TYPE"><title>PALM chapter 2.0</title> <meta content="StarOffice 7 (Win32)" name="GENERATOR"> <meta content="Marcus Oliver Letzel" name="AUTHOR"> <meta content="20040719;14534028" name="CREATED"> <meta content="20041117;10385730" name="CHANGED"> <meta content="parallel LES model" name="KEYWORDS"> <style>
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     9<body style="direction: ltr;" lang="en-US"><h2 style="line-height: 100%;"><font size="4">2.0
     10Basic techniques of
    2011the LES model and its parallelization </font>
    21 </h2>
    22 <p style="line-height: 100%;">LES models generally permit the
     12</h2><p style="line-height: 100%;">LES models
     13generally permit the
    2314simulation of turbulent flows, whereby those eddies, that carry the
    2415main energy are resolved by the numerical grid. Only the
    … …  
    2819simulated directly (they are explicitly resolved) and their effects are
    2920represented by the advection terms. </p>
    30 <p style="font-style: normal; line-height: 100%;">PALM is based on the
     21<p style="font-style: normal; line-height: 100%;">PALM is
     22based on the
    3123non-hydrostatic incompressible Boussinesq equations. It contains a
    3224water cycle with cloud formation and takes into account infrared
    3325radiative cooling in cloudy conditions. The model has six prognostic
    34 quantities in total – u,v,w, liquid water potential temperature
    35 <font face="Thorndale, serif">&#920;</font><sub>l </sub>(BETTS,
     26quantities in total &ndash; u,v,w, liquid water potential
     27temperature
     28<font face="Thorndale, serif">&Theta;</font><sub>l
     29</sub>(BETTS,
    36301973), total water content q and subgrid-scale turbulent kinetic energy
    3731e. The
    … …  
    45391993). The water cycle is closed by using a simplified version of
    4640KESSLERs scheme (KESSLER, 1965; 1969) to parameterize precipitation
    47 processes (MÜLLER and CHLOND, 1996). Incompressibility is
     41processes (M&Uuml;LLER and CHLOND, 1996). Incompressibility is
    4842applied by means of a Poisson equation for pressure, which is solved
    4943with a direct method (SCHUMANN and SWEET, 1988). The Poisson equation
    … …  
    5852horizontal directions. At the lower surface, either temperature/
    5953humidity or their respective fluxes can be prescribed. </p>
    60 <p style="font-style: normal; line-height: 100%;">The advection terms
     54<p style="font-style: normal; line-height: 100%;">The
     55advection terms
    6156are treated by the scheme proposed by PIACSEK and WILLIAMS (1970),
    6257which conserves the integral of linear and quadratic quantities up to
    … …  
    6661with the third-order Runge-Kutta scheme. A second-order Runge-Kutta
    6762scheme, a leapfrog scheme and an Euler scheme are also implemented.</p>
    68 <p style="line-height: 100%;">By default, the time step is computed
     63<p style="line-height: 100%;">By default, the time step is
     64computed
    6965with respect to the different criteria (CFL, diffusion) and adapted
    7066automatically. In case of a non-zero geostrophic
    7167wind the coordinate system can be moved along with the mean wind in
    7268order to maximize the time step (Galilei-Transformation). </p>
    73 <p style="font-style: normal; line-height: 100%;">In principle a model
     69<p style="font-style: normal; line-height: 100%;">In
     70principle a model
    7471run is carried out in the following way: After reading the control
    7572parameters given by the user, all prognostic variables are
    … …  
    9087corrected with the help of the pressure solver. Following this, all
    9188diagnostic turbulence quantities including possible
    92 Prandtl-layer–quantities are computed. At the end of a time
     89Prandtl-layer&ndash;quantities are computed. At the end of a time
    9390step the data output requested by the user is made
    9491(e.g. statistic of analyses for control purposes or profiles and/or
    9592graphics data). If the given end-time was reached, binary data maybe
    9693be saved for restart. </p>
    97 <p style="font-style: normal; line-height: 100%;">The model is based
     94<p style="font-style: normal; line-height: 100%;">The
     95model is based
    9896on the originally non-parallel LES model which has been operated at the
    9997institute since 1989
    … …  
    109107Users can choose between a two- and a one-dimensional domain
    110108decomposition. A 1D-decomposition is preferred on machines with a
    111 slow&nbsp; network interconnection. In case of a 1D-decomposition, the
     109slow&nbsp; network interconnection. In case of a 1D-decomposition,
     110the
    112111grid points along x direction are
    113112distributed among the individual processors, but in y- and z-direction
    114113all respective grid points belong to the same PE. </p>
    115 <p style="line-height: 100%;">The calculation of central differences or
     114<p style="line-height: 100%;">The calculation of central
     115differences or
    116116non-local arithmetic operations (e.g. global
    117117sums, FFT) demands communication and an appropriate data exchange
    … …  
    126126y-direction, the data which lie distributed on the individual central
    127127processing elements, have to be collected and/or relocated before.
    128 This happens by means of the routine <tt>MPI_ALLTOALLV</tt>. Certain
     128This happens by means of the routine <tt>MPI_ALLTOALLV</tt>.
     129Certain
    129130global operations like e.g. the search for absolute maxima or minima
    130131within the 3D-arrays likewise require the employment of special MPI
    131132routines (<tt>MPI_ALLREDUCE</tt>). </p>
    132 <p style="line-height: 100%;">Further details of the internal model
     133<p style="line-height: 100%;">Further details of the
     134internal model
    133135structure are described in the <a href="../tec/index.html">technical/numerical
    134136documentation</a>. <br>
    135137&nbsp; </p>
    136 <hr><font color="#000080"><font color="#000080"><br>
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    144 <p style="line-height: 100%;"><span style="font-style: italic;">Last
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    148 </html>
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