shock simulation

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#1

Dear Ray Shan and lammps users,

I am attaching the video as well as plot (velocity_time_ region wise) got from my shock simulation through porous medium , I was trying to use your logic to build the script initially. Thanks for helping me by sharing the script , from that I really have learnt how to use wall/reflect to generate a shock in classical method.
After a long steps my system behaves in peculiar way, the last region behind the shock front approaches opposite to the shock direction while the system dimension along shock direction increases gradually, finally my simulation stops showing error related to memory allocation.

my particle velocity was 2km/s. I had used your logic almost directly only change was system topology and force field information,here my script portion

variable SHOCKVEL equal 2 # km/s
variable xleftwall equal -0.0749979
variable xrightwall equal 812.925
variable Nshock equal 1.10*(v_xrightwall/0.00005)/(v_SHOCKVEL/0.10)

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fix 4 all wall/reflect xlo {xleftwall} xhi {xrightwall} units box

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variable vel equal ${SHOCKVEL}*-10.000 # A/ps

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velocity all set {vel} 0.0 0.0 sum yes units box fix 1 all nve fix 4 all wall/reflect xlo {xleftwall} xhi ${xrightwall} units box

run ${Nshock}

Why the shock front cant reach the right wall before that the last portion behaves in such a manner. Please need your valuable comment. Please give some insights into this regarding the video and as well as plot.

Thanks in advance.

Thanks

&

Regards

Oxem Selesta

shock_result_animation.avi (3.33 MB)

vel_time.jpg

#2

Selesta,

I don't understand your question, if there even was one. This has
become a non LAMMPS-related question, and the mailing list is not
suitable for interpreting your shock results.

Anyhow, your velocity unit is wrong - default velocity is in A/fs for
real units, not in A/ps. You were actually using a 2000 km/s piston
velocity. Might explain your run ended with a seg fault?

Ray

#3

Dear Ray,
Thanks for your reply,I had used metal unit, so my velocity unit is A/ps not default A/fs. Here particle velocity was 2km/s.

The shock front was propagating from left to right(along +ve X dirn) but before reaching the right-wall, it seems that it have stopped, in this time the last 20% of the material near the right wall start motion towards -ve X dirn.
Please comment.
Thanks in advance.

#4

Selesta,

Wish I could help, but this question goes beyond my actual knowledge in physics, and i’m kinda lazy to read all the information. I’m more of a MD software user, not an MD expert. However I would recommend to read references in regard shock propagation in porous media. My little knowledge I posses about MD was obtained thanks to “Reading” (perhaps you may want to contact Eduardo Ebringa) He has been working in porous media. (so yeah he may be willing to give ideas). I’m not sure about your plot of time vs velocity ? . What method You use to find Speed vs time ? . I dont like the fact that the speed in the first plot, increase asymptotically

A Salute
Oscar G.