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GENERAL
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HIT3DP is a pseudospectral DNS code, that is, it performs direct numerical 
simulation of incompressible isotripic homogeneous turbulence with or without 
forcing.  The code has capability of carrying passive scalars, Lagrangian 
particles and Large Eddy Simulation


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EXTRA PACKAGES
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The code is written in Fortran 90 and uses the two open libraries:
- Open-MPI  (www.open-mpi.org)
- FFTW3	    (www.fftw.org)

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LICENSING
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The code is distributed under the terms of GNU GPLv3 license.  You can read
the full text of the license at http://www.gnu.org/licenses/gpl.html

Copyright (C) 2006-2010 Sergei Chumakov, Natalia Vladimirova, Misha Stepanov


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COMPILING THE CODE
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First, edit the Makefile:
- add a section that corresponds to the name of your machine.  Ideally it should
  be a wrapper from your MPI implementation.
- define the name of the F90 compiler
- define FCFLAGS and LDFLAGS.  They should include the include directories, the
  flags that link FFTW3 and MPI implementation.

Run "gmake".

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RUNNING THE CODE
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The directory "scripts" provides some examples of the batch job submission files.

The directory "scripts" contains the following files:

00_example.in 	a sample input file

snapshot.gp	a Gnuplot instruction file that creates two plots that 
 		can get attached to the notification emails 

coyote.sub	Running script for the Coyote cluster at LANL
wcr.sub     	Example script for WCR cluster at Center for Turbuience Research 
		at Stanford University

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THE INPUT FILE
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NX,NY,NZ  Number of grid points in one dimension.  The grid will be NX x NY x NZ.
	  The physical dimensions will be 2*pi x 2*pi x 2*pi

ITMIN	The timestep number of the restart file.  The restart files have names 
	such as "test__this.64.123456".  Here, "test__this" is the run name, 
	"64" signifies that the file is written with double precision and 
	"123456" is the timestep number.  If the ITMIN is set to 0, the 
	subroutine that defines	the initial conditionis for the flow is called.

ITMAX	The maximum number of timesteps in the simulation.

IPRNT1	How often to generate the statistics.

IPRNT2	How often to write restart files

IWRITE4	How often to write the real*4 files that are used for post-processing.

TMAX	The runtime of the simulation (not the wallclocok time)

TRESCALE  The time at which to rescale the velocity.  This is used in decaying
	  simulations when we want to establish some correlations first and 
	  then rescale the velocity field so it has higher kinetic energy.

TSCALAR	  When to start moving the passive scalars.

flow_type Parameter that switches the flow type
	  0 - decaying turbulence
	  1 - forced turbulence

RE	  The local Reynolds number (1/nu, where nu is viscosity)

DT	  The timestep.
	  If DT is negative, then the timestep is fixed to be (-DT)
	  If DT is positive, the timestep is found from the stability
	  criteria for the time-stepping scheme that is used.

ISPCV1   Initial spectrum type (see init_velocity.f90)
mv1      initial infrared exponent in the spectrum
wm0v1    initial peak wavenumber in the spectrum


force_type	   The type of the forcing that is applied for the case of
		   forced turbulence.
		   1 - forcing from Michaels PRL paper (PRL #79(18) p.3411)
		   So far no other forcing has been implemented

KFMAX	The upper bound for the forcing band in the Fourier space.

FAMP	The magnitude of the forcing (usually set to 0.5)

det_rand 	The parameter that switches the random generation for the
		random seeds for the code.
	DEFUNCTIONAL.  In the current version of the code, the seeds for the
	random number generator are fixed and are taken from the input file.
	The fixed seeds have the effect of producing the initial data that
	looks similar for different resolutions (the large features of 
	initial flow in 32^3 simulation will look similar to the large features
	of a 1024^3 simulation if the seeds are the same).

RN1, RN2, RN3  - random number seeds


DEALIAS		The parameter that switches between the dealiasing algorithms.
	0 - the standard 3/2-rule (or 2/3 rule).  Faster computations, but
	fewer modes.
	1 - the phase shift combined with truncation.  This retains much more
	modes than the 2/3-rule, while increasing the computations 60% or so.
	The most economical mode for DNS in terms of flops per the number of
	Fourier modes in the resulting data.

np	The number of Lagrangian particles

*       particle tracking mechanism:
	0 - trilinear interpolations
	1 - 4-point cubic interpolation
	
time_p  time in the simulation when to release the particles in the flow

particle_filter_size
        The particles can be advected by fully resolved field or by locally averaged
	field.  The filter size determines the size of the filter that is applied
	to the velocity field before computing the particles' velocities.

les_model  The LES model.  See m_les.f90 for list of the current models.

NUMS  The number of passive scalars to carry around

The last section contains the parameters of the passive scalars.  Each scalar
must have the type, Schmidt number, infrared exponent, peak wavenumber and 
reaction rate.

TYPE:
0	The scalar that is forced by the mean gradient.
1-9	The initial conditions for the scalar are generated using Fourier space.
	1: Exponential spectrum
	2: von Karman spectrum
	3: double-delta PDF
>10	The initial conditions for the scalar are generated in the real space.
	11: single slab of the scalar.
	12: two slabs of the scalar
	13: 1-D sinusoidal wave of the scalar


The reaction rate parameter is defunctional in this version of the code.

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ANY QUESTIONS?
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email Sergei Chumakov at [email protected]