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=Spherically Symmetric Configurations Synopsis=
=Spherically Symmetric Configurations Synopsis (Using Style Sheet)=


{{LSU_HBook_header}}
{{LSU_HBook_header}}




==New Table Construction==


<p></p>
{| class="wikitable" style="margin: auto; color:black; width:85%;" border="1" cellpadding="12"
{| class="wikitable" style="margin: auto; color:black; width:85%;" border="1" cellpadding="12"
|+ style="height:30px;" | <font size="+1">'''Spherically Symmetric Configurations that undergo Adiabatic Compression/Expansion'''</font> &#8212; adiabatic index, <math>~\gamma</math>
|+ style="height:30px;" | <font size="+1">'''Spherically Symmetric Configurations that undergo Adiabatic Compression/Expansion'''</font> &#8212; adiabatic index, <math>~\gamma</math>
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==Old Table Construction==
<table border="1" cellpadding="8" width="85%" align="center">
<tr>
  <td align="center" colspan="2" bgcolor="lightgreen">
<font size="+1"><b>Spherically Symmetric Configurations that undergo Adiabatic Compression/Expansion</b></font> &#8212; adiabatic index, <math>~\gamma</math>
  </td>
</tr>
<tr>
  <td align="center" colspan="2">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~dV = 4\pi r^2 dr</math>
  </td>
  <td align="center">
and 
  </td>
  <td align="left">
&nbsp;&nbsp;&nbsp;<math>~dM_r = \rho dV ~~~\Rightarrow ~~~M_r = 4\pi \int_0^r \rho r^2 dr</math>
  </td>
</tr>
<tr>
  <td align="right">
<math>~W_\mathrm{grav}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~- \int_0^R \biggl(\frac{GM_r}{r}\biggr) dM_r ~~ \propto ~~ R^{-1}</math>
  </td>
</tr>
<tr>
  <td align="right">
<math>~U_\mathrm{int}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{1}{(\gamma -1)} \int_0^R 4\pi r^2 P dr ~~ \propto ~~ R^{3-3\gamma}</math>
  </td>
</tr>
</table>
  </td>
</tr>
<tr>
  <td align="center" colspan="2" bgcolor="lightgreen">
<font size="+1"><b>Equilibrium Structure</b></font>
  </td>
</tr>
<tr>
  <th align="center" width="50%">
Detailed Force Balance
  </th>
  <th align="center">
Free-Energy Analysis
  </th>
</tr>
<!--  BEGIN MAJOR 4th ROW -->
<tr>
<!--                                          FIRST COLUMN -->
  <td align="left">
<table border="0" cellpadding="5" align="left">
<tr>
  <td align="left">
Given a barotropic equation of state, <math>~P(\rho)</math>, solve the equation of
<div align="center">
<font color="maroon"><b>Hydrostatic Balance</b></font><br />
{{ User:Tohline/Math/EQ_SShydrostaticBalance01 }}
</div>
for the radial density distribution, <math>~\rho(r)</math>.
</td>
</tr>
</table>
  </td>
<!--                                          THIRD COLUMN -->
  <td align="left" rowspan="3">
The Free-Energy is,
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\mathfrak{G}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~W_\mathrm{grav} + U_\mathrm{int} + P_eV</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~-a R^{-1} + bR^{3-3\gamma}+ cR^3 \, .</math>
  </td>
</tr>
</table>
Therefore, also, 
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\frac{d\mathfrak{G}}{dR}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~aR^{-2} +(3-3\gamma)bR^{2-3\gamma} + 3cR^2</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{1}{R}\biggl[ -W_\mathrm{grav} - 3(\gamma-1)U_\mathrm{int} + 3P_eV\biggr]</math>
  </td>
</tr>
</table>
Equilibrium configurations exist at extrema of the free-energy function, that is, they are identified by setting <math>~d\mathfrak{G}/dR = 0</math>.  Hence, equilibria are defined by the condition,
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~0</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~W_\mathrm{grav} + 3(\gamma-1)U_\mathrm{int} - 3P_eV\, .</math>
  </td>
</tr>
</table>
  </td>
</tr>
<!--  END MAJOR 4th ROW -->
<tr>
  <th align="center">Virial Equilibrium</th>
</tr>
<tr>
  <td align="left">
<table border="0" cellpadding="5" align="left">
<tr>
  <td align="left">
Multiply the hydrostatic-balance equation through by <math>~rdV</math> and integrate over the volume:
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~0</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~-\int_0^R r\biggl(\frac{dP}{dr}\biggr)dV - \int_0^R r\biggl(\frac{GM_r \rho}{r^2}\biggr)dV</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~-\int_0^R 4\pi r^3 \biggl(\frac{dP}{dr}\biggr) dr - \int_0^R \biggl(\frac{GM_r}{r}\biggr)dM_r</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~-\int_0^R\biggl[ \frac{d}{dr}\biggl( 4\pi r^3P \biggr) - 12\pi r^2 P\biggr] dr + W_\mathrm{grav}</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\int_0^R 3\biggl[ 4\pi r^2 P \biggr]dr - \int_0^R \biggl[ d(3PV)\biggr] + W_\mathrm{grav}</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~3(\gamma-1)U_\mathrm{int}  + W_\mathrm{grav} - \biggl[ 3PV \biggr]_0^R \, .</math>
  </td>
</tr>
</table>
</td>
</tr>
</table>
  </td>
</tr>
<tr>
  <td align="center" colspan="2" bgcolor="lightgreen">
<font size="+1"><b>Stability Analysis</b></font>
  </td>
</tr>
<tr>
  <th align="center" width="50%">
Perturbation Theory
  </th>
  <th align="center">
Free-Energy Analysis
  </th>
</tr>
<!--  BEGIN MAJOR STABILITY ROW -->
<tr>
<!--  BEGIN 1ST LEFT STABILITY COLUMN -->
  <td align="left">
Given the radial profile of the density and pressure in the equilibrium configuration, solve the [[User:Tohline/SSC/VariationalPrinciple#Ledoux_and_Pekeris_.281941.29|eigenvalue problem defined]] by the,
<div align="center">
<font color="#770000">'''LAWE: &nbsp; Linear Adiabatic Wave''' (or ''Radial Pulsation'') '''Equation'''</font><br />
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~0</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\frac{d}{dr}\biggl[ r^4 \gamma P ~\frac{dx}{dr} \biggr]
+\biggl[ \omega^2 \rho r^4 + (3\gamma - 4) r^3 \frac{dP}{dr} \biggr] x
</math>
  </td>
</tr>
</table>
</div>
to find one or more radially dependent, radial-displacement eigenvectors, <math>~x \equiv \delta r/r</math>, along with (the square of) the corresponding oscillation eigenfrequency, <math>~\omega^2</math>.
  </td>
<!--  END 1ST LEFT STABILITY COLUMN -->
<!--  BEGIN 1ST RIGHT STABILITY COLUMN -->
  <td align="left" rowspan="5">
The second derivative of the free-energy function is,
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\frac{d^2 \mathfrak{G}}{dR^2}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
-2aR^{-3} + (3-3\gamma)(2-3\gamma)b R^{1-3\gamma} + 6cR
</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{1}{R^2}\biggl[
2W_\mathrm{grav} - 3(\gamma-1)(2-3\gamma)U_\mathrm{int} + 6P_e V
\biggr] \, .
</math>
  </td>
</tr>
</table>
Evaluating this second derivative for an equilibrium configuration &#8212; that is by calling upon the (virial) equilibrium condition to set the value of the internal energy &#8212; we have,
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~3(\gamma-1)U_\mathrm{int}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~3P_e V - W_\mathrm{grav} </math>
  </td>
</tr>
<tr>
  <td align="right">
<math>~\Rightarrow~~~ R^2 \biggl[\frac{d^2\mathfrak{G}}{dR^2}\biggr]_\mathrm{equil}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~2W_\mathrm{grav} - (2-3\gamma)\biggl[3P_e V - W_\mathrm{grav}  \biggr] + 6P_e V
</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~(4-3\gamma)W_\mathrm{grav} + 3^2\gamma P_e V \, .
</math>
  </td>
</tr>
</table>
  </td>
<!--  END 1ST RIGHT STABILITY COLUMN -->
</tr>
<tr>
  <th align="center" width="50%">
Variational Principle
  </th>
</tr>
<!--  BEGIN ANOTHER MAJOR STABILITY ROW -->
<tr>
<!--  BEGIN 2ND LEFT STABILITY COLUMN -->
  <td align="left">
Multiply the LAWE through by <math>~4\pi x dr</math>, and integrate over the volume of the configuration gives the,
<div align="center">
<font color="#770000">'''Governing Variational Relation</font><br />
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~0</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\int_0^R 4\pi r^4 \gamma P \biggl(\frac{dx}{dr}\biggr)^2 dr
- \int_0^R 4\pi (3\gamma - 4) r^3 x^2 \biggl( \frac{dP}{dr} \biggr) dr
</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>~
- 4\pi \biggr[r^4 \gamma Px \biggl(\frac{dx}{dr}\biggr) \biggr]_0^R
- \int_0^R 4\pi \omega^2 \rho r^4 x^2 dr \, .
</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\int_0^R x^2 \biggl(\frac{d\ln x}{d\ln r}\biggr)^2 \gamma 4\pi r^2P  dr
- \int_0^R (3\gamma - 4)x^2 \biggl( - \frac{GM_r}{r}  \biggr) 4\pi \rho r^2 dr
</math>
  </td>
</tr>
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>~
+ \biggr[\gamma 4\pi r^3 Px^2 \biggl(-\frac{d\ln x}{d\ln r}\biggr) \biggr]_0^R
- \int_0^R 4\pi \omega^2 \rho r^4 x^2 dr \, .
</math>
  </td>
</tr>
</table>
</div>
Now, by setting <math>~(d\ln x/d\ln r)_{r=R} = -3</math>, we can ensure that the pressure fluctuation is zero and, hence, <math>~P = P_e</math> at the surface, in which case this relation becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\omega^2</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\frac{\gamma (\gamma -1) \int_0^R x^2 \bigl(\frac{d\ln x}{d\ln r}\bigr)^2 dU_\mathrm{int}
- \int_0^R (3\gamma - 4)x^2 dW_\mathrm{grav}
+ 3^2 \gamma  x^2  P_eV}{ \int_0^R  x^2 r^2  dM_r}
</math>
  </td>
</tr>
</table>
</div>
  </td>
<!--  END 1ST LEFT STABILITY COLUMN -->
</tr>
<tr>
  <th align="center" width="50%">
Approximation: &nbsp; Homologous Expansion/Contraction
  </th>
</tr>
<!--  BEGIN ANOTHER MAJOR STABILITY ROW -->
<tr>
<!--  BEGIN 2ND LEFT STABILITY COLUMN -->
  <td align="left">
If we ''guess'' that radial oscillations about the equilibrium state involve purely homologous expansion/contraction, then the radial-displacement eigenfunction is, <math>~x</math> = constant, and the governing variational relation gives,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\omega^2 \int_0^R  r^2  dM_r</math>
  </td>
  <td align="center">
<math>~\approx</math>
  </td>
  <td align="left">
<math>~
(4- 3\gamma) W_\mathrm{grav}+ 3^2 \gamma  P_eV \, .
</math>
  </td>
</tr>
</table>
</div>
  </td>
</tr>
</table>


=See Also=
=See Also=

Revision as of 01:28, 19 June 2017


Spherically Symmetric Configurations Synopsis (Using Style Sheet)

Whitworth's (1981) Isothermal Free-Energy Surface
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Spherically Symmetric Configurations that undergo Adiabatic Compression/Expansion — adiabatic index, <math>~\gamma</math>

<math>~dV = 4\pi r^2 dr</math>

and

   <math>~dM_r = \rho dV ~~~\Rightarrow ~~~M_r = 4\pi \int_0^r \rho r^2 dr</math>

<math>~W_\mathrm{grav}</math>

<math>~=</math>

<math>~- \int_0^R \biggl(\frac{GM_r}{r}\biggr) dM_r ~~ \propto ~~ R^{-1}</math>

<math>~U_\mathrm{int}</math>

<math>~=</math>

<math>~\frac{1}{(\gamma -1)} \int_0^R 4\pi r^2 P dr ~~ \propto ~~ R^{3-3\gamma}</math>

Equilibrium Structure
Detailed Force Balance Free-Energy Analysis
Given a barotropic equation of state, <math>~P(\rho)</math>, solve the equation of

Hydrostatic Balance

LSU Key.png

<math>~\frac{dP}{dr} = - \frac{GM_r \rho}{r^2}</math>

for the radial density distribution, <math>~\rho(r)</math>.

The Free-Energy is,

<math>~\mathfrak{G}</math>

<math>~=</math>

<math>~W_\mathrm{grav} + U_\mathrm{int} + P_eV</math>

 

<math>~=</math>

<math>~-a R^{-1} + bR^{3-3\gamma}+ cR^3 \, .</math>

Therefore, also,

<math>~\frac{d\mathfrak{G}}{dR}</math>

<math>~=</math>

<math>~aR^{-2} +(3-3\gamma)bR^{2-3\gamma} + 3cR^2</math>

 

<math>~=</math>

<math>~\frac{1}{R}\biggl[ -W_\mathrm{grav} - 3(\gamma-1)U_\mathrm{int} + 3P_eV\biggr]</math>

Equilibrium configurations exist at extrema of the free-energy function, that is, they are identified by setting <math>~d\mathfrak{G}/dR = 0</math>. Hence, equilibria are defined by the condition,

<math>~0</math>

<math>~=</math>

<math>~W_\mathrm{grav} + 3(\gamma-1)U_\mathrm{int} - 3P_eV\, .</math>

Virial Equilibrium

Multiply the hydrostatic-balance equation through by <math>~rdV</math> and integrate over the volume:

<math>~0</math>

<math>~=</math>

<math>~-\int_0^R r\biggl(\frac{dP}{dr}\biggr)dV - \int_0^R r\biggl(\frac{GM_r \rho}{r^2}\biggr)dV</math>

 

<math>~=</math>

<math>~-\int_0^R 4\pi r^3 \biggl(\frac{dP}{dr}\biggr) dr - \int_0^R \biggl(\frac{GM_r}{r}\biggr)dM_r</math>

 

<math>~=</math>

<math>~-\int_0^R\biggl[ \frac{d}{dr}\biggl( 4\pi r^3P \biggr) - 12\pi r^2 P\biggr] dr + W_\mathrm{grav}</math>

 

<math>~=</math>

<math>~\int_0^R 3\biggl[ 4\pi r^2 P \biggr]dr - \int_0^R \biggl[ d(3PV)\biggr] + W_\mathrm{grav}</math>

 

<math>~=</math>

<math>~3(\gamma-1)U_\mathrm{int} + W_\mathrm{grav} - \biggl[ 3PV \biggr]_0^R \, .</math>

Stability Analysis
Perturbation Theory Free-Energy Analysis

Given the radial profile of the density and pressure in the equilibrium configuration, solve the eigenvalue problem defined by the,

LAWE:   Linear Adiabatic Wave (or Radial Pulsation) Equation

<math>~0</math>

<math>~=</math>

<math>~ \frac{d}{dr}\biggl[ r^4 \gamma P ~\frac{dx}{dr} \biggr] +\biggl[ \omega^2 \rho r^4 + (3\gamma - 4) r^3 \frac{dP}{dr} \biggr] x </math>

to find one or more radially dependent, radial-displacement eigenvectors, <math>~x \equiv \delta r/r</math>, along with (the square of) the corresponding oscillation eigenfrequency, <math>~\omega^2</math>.

The second derivative of the free-energy function is,

<math>~\frac{d^2 \mathfrak{G}}{dR^2}</math>

<math>~=</math>

<math>~ -2aR^{-3} + (3-3\gamma)(2-3\gamma)b R^{1-3\gamma} + 6cR </math>

 

<math>~=</math>

<math>~\frac{1}{R^2}\biggl[ 2W_\mathrm{grav} - 3(\gamma-1)(2-3\gamma)U_\mathrm{int} + 6P_e V \biggr] \, . </math>

Evaluating this second derivative for an equilibrium configuration — that is by calling upon the (virial) equilibrium condition to set the value of the internal energy — we have,

<math>~3(\gamma-1)U_\mathrm{int}</math>

<math>~=</math>

<math>~3P_e V - W_\mathrm{grav} </math>

<math>~\Rightarrow~~~ R^2 \biggl[\frac{d^2\mathfrak{G}}{dR^2}\biggr]_\mathrm{equil}</math>

<math>~=</math>

<math>~2W_\mathrm{grav} - (2-3\gamma)\biggl[3P_e V - W_\mathrm{grav} \biggr] + 6P_e V </math>

 

<math>~=</math>

<math>~(4-3\gamma)W_\mathrm{grav} + 3^2\gamma P_e V \, . </math>

Variational Principle

Multiply the LAWE through by <math>~4\pi x dr</math>, and integrate over the volume of the configuration gives the,

Governing Variational Relation

<math>~0</math>

<math>~=</math>

<math>~ \int_0^R 4\pi r^4 \gamma P \biggl(\frac{dx}{dr}\biggr)^2 dr - \int_0^R 4\pi (3\gamma - 4) r^3 x^2 \biggl( \frac{dP}{dr} \biggr) dr </math>

 

 

<math>~ - 4\pi \biggr[r^4 \gamma Px \biggl(\frac{dx}{dr}\biggr) \biggr]_0^R - \int_0^R 4\pi \omega^2 \rho r^4 x^2 dr \, . </math>

 

<math>~=</math>

<math>~ \int_0^R x^2 \biggl(\frac{d\ln x}{d\ln r}\biggr)^2 \gamma 4\pi r^2P dr - \int_0^R (3\gamma - 4)x^2 \biggl( - \frac{GM_r}{r} \biggr) 4\pi \rho r^2 dr </math>

 

 

<math>~ + \biggr[\gamma 4\pi r^3 Px^2 \biggl(-\frac{d\ln x}{d\ln r}\biggr) \biggr]_0^R - \int_0^R 4\pi \omega^2 \rho r^4 x^2 dr \, . </math>

Now, by setting <math>~(d\ln x/d\ln r)_{r=R} = -3</math>, we can ensure that the pressure fluctuation is zero and, hence, <math>~P = P_e</math> at the surface, in which case this relation becomes,

<math>~\omega^2</math>

<math>~=</math>

<math>~ \frac{\gamma (\gamma -1) \int_0^R x^2 \bigl(\frac{d\ln x}{d\ln r}\bigr)^2 dU_\mathrm{int} - \int_0^R (3\gamma - 4)x^2 dW_\mathrm{grav} + 3^2 \gamma x^2 P_eV}{ \int_0^R x^2 r^2 dM_r} </math>

Approximation:   Homologous Expansion/Contraction

If we guess that radial oscillations about the equilibrium state involve purely homologous expansion/contraction, then the radial-displacement eigenfunction is, <math>~x</math> = constant, and the governing variational relation gives,

<math>~\omega^2 \int_0^R r^2 dM_r</math>

<math>~\approx</math>

<math>~ (4- 3\gamma) W_\mathrm{grav}+ 3^2 \gamma P_eV \, . </math>


See Also

Whitworth's (1981) Isothermal Free-Energy Surface

© 2014 - 2021 by Joel E. Tohline
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