[FLASH-USERS] shock waves in water

[Matthias Broenner]

Dear Dr Maksim Kozlov,


1) You can define additional species in the FLASH code and give them 
different Equations of State and starting conditions.

You need to define a new species in the config file of your simulation 
and write a custom Simulation_initBlock, to define the placement of the 
species.

2) The imaginary sound speed problem stems from an area in the lower 
temperature part of the equation of state, where the pressure drops with 
rising density.

As far as I know it is only a problem below 600 K.

So you have two options for this: Either you modify the equation of 
state table with some kind of Maxwell construction an ensure that with 
rising density the pressure also rises, or you can give your simulation 
a smallt>600.0 (You can just use this in the flash.par file).

This could remedy this problem.

3) I am speculating here, but maybe you could define a custom variable 
in your cells that rises sharply around the axis and add this variable 
to the refine_var_#.

I hope that helps.

All the best,

Matthias Brönner


Am 03.07.2022 um 10:11 schrieb Maksim Kozlov:
> Dear Flash users,
> I would really appreciate it if somebody could help me with the 
> following issues. I am trying to use FLASH code to simulate 
> convergence of cylindrical shock waves in water. Shock waves are 
> initiated by deposition of energy into the strip of water. 5kJ of 
> energy is introduced into a strip of water (width of strip ~1mm and 
> radius ~4.5 mm) with sub-microsecond pulse FWHH~0.25 microseconds. 
> Height of the simulated cylinder is  ~ 50 mm. Pressure and sound speed 
> are calculated from the tabulated Equation of state (Los Alamos SESAME 
> database) using a 2D spline-interpolation algorithm. I managed to 
> simulate converging shock using the HLL Riemann solver provided with 
> FLASH code. Results of my simulations were recently published in PoP 
> (please see attached). However I encounter the following problems
> 1) I am unable to simulate realistic experiments where energy is 
> deposited into an array of copper wires. This would require simulation 
> of two different substances and I believe FLASH code does not have 
> such capabilities
> 2) When I am trying to introduce power into narrower strip of water 
> (~100 microns) gradients become much higher which results in 
> significant oscillations around shock front and consequent crush of 
> the code (imaginary sound speed). I tried to use different Riemann 
> solvers and artificial flattening but these did not help.
> 3) As far as I understand, the adaptive mesh capability of FLASH code 
> increases resolution around shock fronts (high gradients).  Is there 
> any way to add additional geometric conditions for increasing 
> resolution in such a way that resolution is increased only around the 
> axis of the cylinder where shock converges.
> I would really appreciate any advice on how to solve the above issues 
> or at least give me reference to publications on this subject.
> Thank you very much!
> Dr Maksim Kozlov
>
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