[Mesa-users] convergence problem
sheyda najafi
sh.najafi8590 at gmail.com
Tue May 14 10:59:02 EDT 2019
Dear Pablo
I have added the extra term to HSE equation and for high values in
free parameter space of my model(beta) it seems that the star becomes
unstable.
(where if beta=0 ==> extra_dpdm=0)
I have changed mixing_length_alpha and mass_loss to check how the
result depends on these parameters and still the star was unstable
for high values of (beta>200).
I found that this instability relates to my extra_dpdm since for high
values of (beta) it overcomes the gravitational term in HSE equation,
becomes positive in some radius and makes the star unstable(dp/dr > 0)
in some radius near the surface. which seems reasonable, in my
opinion.
then I thought that maybe the reason to see such instability is that
some equations are not changed due to the new force, like
pressure_scale_height equation.
So you mean keeping the pressure_scale_height equation unchanged in my
model, can not be the cause of instability.
Thank you very much
Sheyda
On 5/14/19, Pablo Marchant <pamarca at gmail.com> wrote:
> On Tue, May 14, 2019, 08:57 sheyda najafi <sh.najafi8590 at gmail.com> wrote:
>
>> Dear Pablo
>>
>> Thank you very much.
>>
>> I thought that by adding the new acceleration as extra_dpdm in HSE
>> equation of MESA code, other equations which depend on acceleration,
>> change due to gravitational force + extra force.
>>
>> 1)So there is no relation that relates grav to extra_dpdm or
>> dlnp_dm_qhse?
>>
>
> That scale height is derived from the standard eqn for hydrostatic
> equilibrium
>
> dP/dr = -rho g
>
> Where grav is just the standard gravity. In your case, you could write your
> equations in dP/dr form and get the value for the scale height as well.
>
> 2)what might happen to the star if I add extra_dpdm to HSE equation
>> and do not change pressure_scale_height?
>>
>
> The scale height is mostly used for convective energy transport as well for
> overshooting.
>
> 3)Do you think it would have impact on stability of the star?
>>
>
> Would not expect to affect stability at all. If you're thinking about this
> in terms of making non-working simulations work I would not recommend it.
>
> Cheers
>
>
>> Thank you
>> Sheyda
>>
>> On 5/14/19, Pablo Marchant <pamarca at gmail.com> wrote:
>> > Hi Sheyda,
>> >
>> > The pressure scale height is set in star/private/mlt_info.f90, assuming
>> > standard hydrostatic equilibrium, so its set as
>> >
>> > scale_height = P / (grav*rho)
>> >
>> > If you want to modify the pressure scale height then you'll have to
>> adjust
>> > this accordingly. You can reimplement mlt using the other_mlt hook,
>> > just
>> > copy all what's neccesary from mlt_info into your run_star_extras and
>> > adjust the line above. Note that you also have to set properly the
>> partial
>> > derivatives for the scale height, which are required by the newton
>> solver,
>> > this is currently done in mlt_info in this way
>> >
>> > d_scale_height_dvb = scale_height*(dP_dvb/P - d_grav_dvb/grav -
>> > dRho_dvb/Rho)
>> >
>> > Here the variables denoted as *_dvb are arrays containing the partial
>> > derivatives with respect to each variable. You should be able to figure
>> out
>> > how itworks by digging a bit in mlt_info. From your modifications,
>> > you'll
>> > need to figure out how to get the partial derivatives for dphi with
>> respext
>> > to the structure variables.
>> >
>> > Cheers
>> >
>> > On Tue, May 14, 2019, 07:06 sheyda najafi via Mesa-users <
>> > mesa-users at lists.mesastar.org> wrote:
>> >
>> >> Dear MESA users
>> >>
>> >> I have changed extra_dpdm to add a new acceleration term to HSE
>> >> equation in MESA code.
>> >> (p(i-1)- p(i))/dm_bar(i)=( -standard_cgrav*m(r))/(4*pi* s% r(i)**4) -
>> >> beta*(clight**2) *rho_face(i) (dphi/dm_bar)
>> >> therefore
>> >> extra_dpdm(i)= - beta*(clight**2) *rho_face(i) dphi/dm_bar
>> >>
>> >> which i have asked about the quantities and the shape of this new term
>> >> in previous emails.
>> >>
>> >> My question is how does this extra acceleration change the pressure
>> >> scale height in the code. I can not find the relation. I know that
>> >> pressure scale height depends on p_face and rho_face and grav. The
>> >> extra_dpdm has impact on density and pressure but I can not find the
>> >> relation between grav and extra_dpdm in the code.
>> >>
>> >> Thank you very much
>> >> Sheyda Najafi
>> >>
>> >> On 5/7/19, sheyda najafi <sh.najafi8590 at gmail.com> wrote:
>> >> > Dear Mesa users
>> >> >
>> >> > I have another question regarding my previous emails.
>> >> >
>> >> > As i said I wanted to study the evolution of 1 solar mass star in
>> >> > the
>> >> > presence of
>> >> > new extra acceleration term :(-beta*(clight**2)*(dphi/dr)).
>> >> > i have changed the
>> >> > extra_dPdm subroutine of MESA code to add
>> >> > the extra term (-beta*rho(clight**2)*(dphi/dm)) ==>( in lagrangian
>> >> > framework) .
>> >> > where phi depends on local density of each layer(cell density: s%
>> >> > rho).
>> >> > which is named (xn) in the code. and beta is a constant.
>> >> > i have added the extra term as follows
>> >> >
>> >> > do k = 1,2
>> >> > s% extra_dPdm(k) = -( (( xn(k)- xn(k+1))/(s%
>> >> > dm_bar(k+1)))*((beta*(clight**(2.0d0)))*(s% rho_face(k))) )
>> >> >
>> >> > end do
>> >> >
>> >> > do k = 2, s% nz-1
>> >> > s% extra_dPdm(k) = -( ((( xn(k)- xn(k+1))/(s%
>> >> dm_bar(k+1)))+
>> >> > &
>> >> > (( xn(k-1) - xn(k))/(s% dm_bar(k))))
>> >> > *((beta*(clight**(2.0d0)))*(s% rho_face(k))*(1.d0/2.d0)) )
>> >> >
>> >> > end do
>> >> >
>> >> > do k = s% nz-1, s% nz
>> >> > s% extra_dPdm(k) = -( (( xn(k-1) - xn(k))/(s%
>> >> > dm_bar(k)))*((beta*(clight**(2.0d0)))*(s% rho_face(k))) )
>> >> >
>> >> > end do
>> >> >
>> >> > I noticed that s% dm_bar(s%nz) = s%dm(s% nz) + s%dm(s%nz-1)/2
>> >> > and not (s% dm(s% nz) + s% dm(s%nz-1))/2.
>> >> >
>> >> > i am not sure that dm_bar must be used in extra_dpdm or (s% dm(s%
>> >> > nz)
>> >> > + s% dm(s%nz-1))/2.
>> >> >
>> >> > Thank you very much
>> >> > Sheyda Najafi
>> >> >
>> >> >
>> >> > On 10/21/18, sheyda najafi <sh.najafi8590 at gmail.com> wrote:
>> >> >> Dear Josiah and MESA users
>> >> >>
>> >> >>
>> >> >> I have another question regarding my previous emails. i have asked
>> >> >> it
>> >> >> before but unfortunately no one answered.
>> >> >>
>> >> >> As i said I wanted to study the evolution of 1 solar mass star in
>> the
>> >> >> presence of
>> >> >> new extra acceleration term :(-beta*(clight**2)*(dphi/dr)).
>> >> >> i have changed the
>> >> >> extra_dPdm subroutine of MESA code to add
>> >> >> the extra term (-beta*rho(clight**2)*(dphi/dm)) ==>( in lagrangian
>> >> >> framework) .
>> >> >> where phi depends on local density of each layer(cell density: s%
>> >> >> rho).
>> >> >> which is named (xn) in the code. and beta is a constant.
>> >> >>
>> >> >> do k = 1,2
>> >> >> s% extra_dPdm(k) = -( (( xn(k)- xn(k+1))/(s%
>> >> >> dm_bar(k+1)))*((beta*(clight**(2.0d0)))*(s% rho_face(k))) )
>> >> >>
>> >> >> end do
>> >> >>
>> >> >> do k = 2, s% nz-1
>> >> >> s% extra_dPdm(k) = -( ((( xn(k)- xn(k+1))/(s%
>> >> >> dm_bar(k+1)))+
>> >> >> &
>> >> >> (( xn(k-1) - xn(k))/(s% dm_bar(k))))
>> >> >> *((beta*(clight**(2.0d0)))*(s% rho_face(k))*(1.d0/2.d0)) )
>> >> >>
>> >> >> end do
>> >> >>
>> >> >> do k = s% nz-1, s% nz
>> >> >> s% extra_dPdm(k) = -( (( xn(k-1) - xn(k))/(s%
>> >> >> dm_bar(k)))*((beta*(clight**(2.0d0)))*(s% rho_face(k))) )
>> >> >>
>> >> >> end do
>> >> >>
>> >> >> Since i did not know the value of s%rho(0) i did'nt have xn(0) to
>> >> >> write extra_dpdm it in 1 part therefore i have split it in three
>> >> >> parts. how it is possible to write this term in 1 part. i mean if i
>> >> >> want to write the extra term as :
>> >> >>
>> >> >> do k = 1, s% nz
>> >> >> s% extra_dpdm(k)= -(( xn(k-1)- xn(k)) / s% dm_bar(k)) * beta*
>> >> >> (clight**2)* ( s%rho_face(k)).
>> >> >> end do
>> >> >>
>> >> >> I will have problem in finding the value of xn(0). because xn is
>> >> >> related to cell density s%rho(0) via
>> >> >>
>> >> >> xn(i)= (( n1*(lambda**(4.d0+n1)) )/(((mpl)**(n1))*clight*beta*s%
>> >> >> rho(i)))**(1.d0/(n1+1.d0))
>> >> >>
>> >> >> lambda, mpl, n1 and beta are constant.
>> >> >>
>> >> >> which density should i use as rho(0) ??
>> >> >>
>> >> >> (for your kindly information my codes are attached in the email)
>> >> >> Thank you in advance
>> >> >>
>> >> >>
>> >> >> Sheyda
>> >> >>
>> >> >
>> >> _______________________________________________
>> >> mesa-users at lists.mesastar.org
>> >> https://lists.mesastar.org/mailman/listinfo/mesa-users
>> >>
>> >>
>> >
>>
>
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