[lammps-users] Void growth simulation

Hi Steve
I just want to make sense.
When I use fix deform command, should I use create velocity command to assign a initial
velocity to all atoms? Should I us NVT, NVE, NPT ensemble? Or just only use fix deform?
Thanks.

Yang






09年3月17日,周二, Steve Plimpton [email protected] 写道:


> 发件人: Steve Plimpton [email protected]
> 主题: Re: [lammps-users] Void growth simulation
> 收件人: “amir amiri” <[email protected]…24…>
> 抄送: [email protected]
> 日期: 2009年3月17日,周二,下午10:12
>
> You can apply tension by pulling on boundaries (set initial velocity,
> turn off force, integrate), or using fix deform.
>
> Steve
>
> On Mon, Mar 16, 2009 at 9:23 AM, amir amiri <[email protected]…24…> wrote:
> > Hello everybody,
> >
> > I am a beginner in LAMMPS and am trying to modify the shear.void example of
> > LAMMPS both to learn LAMMPS and to爏tudy the effects of different parameters
> > on the void growth mechanism. I have modified the input file such that the
> > voided body is not under shear anymore and experiences tension. I have a few
> > questions in this regard:
> >
> > 1. How can I get the tensile force induced by the applied velocity? I tried
> > the “fix setforce” command for the upper boundary and lower boundary but it
> > always generates zero force.
> >
> > 2. Why does the failure always take place at the place where the voided body
> > is connected to the upper boundary? This is clearer when the void size is
> > rather small.
> >
> > 3. I modified the ramp velocity command for the tension problem. Does it
> > look OK?
> >
> > Best,
> >
> > Amir
> >
> > Here is the modified script for your information:
> >
> > # 3d metal shear simulation
> >
> > units metal
> >
> > boundary s s p
> >
> > atom_style atomic
> >
> > lattice fcc 3.52
> >
> > region box block 0 30.0 0 30.0 0 2.828427
> >
> > create_box 3 box
> >
> > lattice fcc 3.52 orient x 1 0 0 orient y 0 1 1 orient z 0 -1 1 &
> >
> > origin 0.5 0 0
> >
> > create_atoms 1 box
> >
> > pair_style eam
> >
> > pair_coeff * * Ni_u3.eam
> >
> > neighbor 0.3 bin
> >
> > neigh_modify delay 5
> >
> > region lower block INF INF INF 0.9 INF INF
> >
> > region upper block INF INF 20.1 INF INF INF
> >
> > group lower region lower
> >
> > group upper region upper
> >
> > group boundary union lower upper
> >
> > group mobile subtract all boundary
> >
> > set group lower type 2
> >
> > set group upper type 3
> >
> > # void
> >
> > region void cylinder z 15 10 4 INF INF
> >
> > delete_atoms region void
> >
> > # temp controllers
> >
> > compute new3d mobile temp
> >
> > compute new2d mobile temp/partial 0 1 1
> >
> > # equilibrate
> >
> > velocity mobile create 300.0 5812775 temp new3d
> >
> > fix 1 all nve
> >
> > fix 2 boundary setforce 0.0 0.0 0.0
> >
> > fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0
> >
> > fix_modify 3 temp new3d
> >
> > thermo 25
> >
> > thermo_modify temp new3d
> >
> > timestep 0.001
> >
> > run 100
> >
> > # shear
> >
> > velocity upper set 0 1.0 0
> >
> > velocity mobile ramp vy 0 1.0 y 0.9 20.0 sum yes
> >
> > unfix 3
> >
> > fix 3 mobile temp/rescale 10 300.0 300.0 10.0 1.0
> >
> > fix_modify 3 temp new2d
> >
> > dump 1 all atom 100 dump.shear
> >
> > thermo 100
> >
> > thermo_modify temp new2d
> >
> > reset_timestep 0
> >
> > run 3000
> >
> > ------------------------------------------------------------------------------
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> >
> >
>
> ------------------------------------------------------------------------------
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> easily build your RIAs with Flex Builder, the Eclipse™based development
> software that enables intelligent coding and step-through debugging.
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|

Hi.

I think that one should allways either use the minimize command OR carry out a NPT simultion till equilibration to to make the atomic positions consistent with the potential being used before carrying out the deformation.

Best Regards,

Manoj

2009/3/18 YANG LU <[email protected]…215…>

HI all,

May I know if it is possible to dump atoms velocities at specific intervals like we do for atoms coordinates using dump command?

TIA

dhiraj

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2009/3/18 Dhiraj K. Mahajan <[email protected]…71…>

HI all,

May I know if it is possible to dump atoms velocities at specific intervals like we do for atoms coordinates using dump command?

TIA

Read the documentation for the “dump custom” command:

http://lammps.sandia.gov/doc/dump.html

–AEI

Fix deform doesn't do time integration, so use nve or nvt, etc.
Whether to initialize velocities are not depends on what you
want to do - it has nothing to do with fix deform.

Steve