The Flash Center is pleased to announce the alpha release of the next<br>
version of the FLASH code, version 4 alpha. FLASH 4 alpha includes<br>
several new physics capabilities and resolves many bugs found in<br>
previous releases up to 3.3.<br>
<br>
<br>
Capabilities added since the FLASH3.3 release take the growth of FLASH<br>
into two new directions simultaneously. One is a new set of physics<br>
solver capabilities that enable the code to simulate phenomena in<br>
High-Energy-Density Physics (HEDP). The second is inclusion of<br>
patch-based AMR with Chombo. Much remains to be done in both these new<br>
directions, however, they are both usable for a limited collection of<br>
real calculations.<br>
<br>
The HEDP capabilities are :<br>
<br>
* Ability to model 2 temperatures and radiation in the fluid<br>
<br>
* Diffusion and Conduction with implicit solvers<br>
<br>
* Opacities<br>
<br>
* Radiation transfer with multigroup diffusion<br>
<br>
* Laser energy deposition<br>
<br>
* Multimaterial EOS (gamma law). A tabulated version is currently<br>
under testing. It will soon be released as a patch. In the meantime<br>
it can be obtained as-is by contacting the Flash Center.<br>
<br>
* Hybrid PIC (contributed by Mats Holmstrom). Please contact Mats<br>
(<a href="mailto:matsh@irf.se" target="_blank">matsh@irf.se</a>) for support on this section of the code.<br>
<br>
Other new physics capabilities are :<br>
<br>
* 3D MHD with unsplit staggered mesh implementation included<br>
in the release<br>
<br>
* Super time-stepping<br>
<br>
* Oscillation suppression in Hydro<br>
<br>
* A new, more robust implementation of the multipole method<br>
for solving the Poisson equation<br>
<br>
* Quiet start<br>
<br>
The new infrastructural capabilities are :<br>
<br>
* Chombo (fully functional in UG mode, AMR functional with<br>
restrictions)<br>
<br>
* Mesh replication, which allows processors to be divided into<br>
groups where each group gets a copy of some or all of mesh variables.<br>
The non-replicated mesh variables are distributed among the groups<br>
such that each group has a unique set.<br>
<br>
* A new, more efficient PnetCDF based I/O implementation. The implementation<br>
is dependent upon some feature of MPI-2, therefore does not work with<br>
MPI-1.<br>
<br>
Enhancements to the existing capabilities since FLASH 3.3 are :<br>
<br>
* Values of physical constants maintained by the PhysicalConstants<br>
unit have been updated to the recommended values of K. Nakamura<br>
et al. (Particle Data Group), J. Phys. G 37, 075021 (2010).<br>
Note in particular a relatively large change to the value of<br>
Newton's gravitational constant from 6.6725985E-8 to 6.67428E-8.<br>
This change could strongly affect simulations that depend on<br>
a balance between gravitational and other forces, and/or for which<br>
initial conditions where computed with a different value of the<br>
constant.<br>
<br>
* Generalization of the GridParticles subunit so that it can now<br>
be used for moving many types of non-Eulerian data structures<br>
through the mesh. It is now used with PIC and Laser ray-trace in<br>
addition to its traditional role with Lagrangian particles.<br>
<br>
* A longer list of changes is contained in the User's Guide in Section 1,<br>
What's New in This Release.<br>
<br>
<br>
<br>
Issues that have become known since the FLASH3.3 release and have been<br>
fixed in FLASH 4 alpha include:<br>
<br>
* A bug was discovered in the mapping of particles to mesh which led<br>
to non-conservation of mass by small amounts. The fix was<br>
originally distributed on the Flash mailing list as a patch for<br>
FLASH 3.3.<br>
<br>
* A bug was found in the Paramesh point to point implementation of<br>
mapping particles to mesh. Please see Section 1 of the FLASH<br>
User's Guide.<br>
<br>
<br>
Notes / Limitations:<br>
<br>
* Multitemperature Hydro has not been tested in 3D.<br>
<br>
* The new multipole solver is missing the ability to treat<br>
a non-zero minimal radius for spherical geometries, and the<br>
ability to specify a point mass contribution to the potential.<br>
<br>
* Unsplit diffusion does not work in 3D.<br>
<br>
* HYPRE needs to be installed to use Unsplit Diffusion, Unsplit diffusion<br>
uses hypre-2.7.0b (might not be backward compatible).<br>
<br>
* Usage of HYPRE Split solver in FLASH4 is only for internal debugging purposes<br>
and is not generally recommended for usage.<br>
<br>
* Split diffusion has not been tested with PARAMESH.<br>
<br>
* Interoperability of Unsplit hydro and diffusion solver has not been<br>
tested extensively.<br>
<br>
* Some configurations of hydrodynamic test problems with Chombo grid<br>
show worse than expected mass and total energy conservation. Please<br>
see the Chombo section in Hydro chapter of the FLASH User's Guide for<br>
details.<br>
<br>
* We have experienced the following abort when running<br>
IsentropicVortex problem with Chombo Grid:<br>
"MayDay: TreeIntVectSet.cpp:1995: Assertion `bxNumPts != 0' failed. !!!"<br>
We are currently in contact with the Chombo team to resolve this<br>
issue.<br>
<br>
<br>
The release is available at:<br>
<br>
<a href="http://flash.uchicago.edu/site/flashcode/" target="_blank">http://flash.uchicago.edu/site/flashcode/</a><br>
<br>
A stripped down version of FLASH3 that may be downloaded without a<br>
license is also available at the same site. This is essentially the<br>
FLASH framework without any implementations.<br>
<br>
The Flash Center continues to provide support for "add-ons" to the<br>
code.<br>
<br>
Additionally, the FLASH testing software FlashTest, which became<br>
available with the alpha release, continues to be available for<br>
download at:<br>
<br>
<a href="http://flash.uchicago.edu/site/flashcode/" target="_blank">http://flash.uchicago.edu/site/flashcode/</a><br>
<br>
The code architecture and most interfaces of FLASH4 are compatible<br>
with FLASH3. Many, but not all parts are also backward compatible<br>
with FLASH2. The Flash Center has written extensive documentation<br>
detailing how to make the transition from FLASH2 to FLASH3 as smooth<br>
as possible. The user should look to:<br>
<br>
<a href="http://flash.uchicago.edu/site/flashcode/user_support/" target="_blank">http://flash.uchicago.edu/site/flashcode/user_support/</a><br>
<br>
The website also contains other documentation including a User's Guide<br>
and a developer's section. A new feature from FLASH3 onward is the<br>
online description of the public interface routines to various code<br>
units.<br>
<br>
<br>
Development of the FLASH Code was funded by the DOE-supported<br>
ASC/Alliance Center for Astrophysical Thermonuclear Flashes,<br>
and continues to be funded by DOE NNSA and OASCR. We<br>
acknowledge support received from Lawrence Livermore National<br>
Laboratory and the University of Chicago.<br>
<br>
All publications resulting from the use of the FLASH Code must<br>
acknowledge the Flash Center for Computational Science.<br>
Addition of the following text to the paper acknowledgments<br>
will be sufficient.<br>
<br>
"The software used in this work was in part developed by the<br>
DOE-supported Flash Center for Computational Science<br>
at the University of Chicago."<br clear="all"><br>--- The Flash Center, and the FLASH code team.<br>