User:Tohline/Cylindrical 3D

Equations Cast in Cylindrical Coordinates

Spatial Operators in Cylindrical Coordinates
<math> \nabla f </math>	=	<math> {\hat{e}}_\varpi \biggl[ \frac{\partial f}{\partial\varpi} \biggr] + {\hat{e}}_\varphi {\biggl[ \frac{1}{\varpi} \frac{\partial f}{\partial\varphi} \biggr]} + {\hat{e}}_z \biggl[ \frac{\partial f}{\partial z} \biggr] ; </math>
<math> \nabla^2 f </math>	=	<math> \frac{1}{\varpi} \frac{\partial }{\partial\varpi} \biggl[ \varpi \frac{\partial f}{\partial\varpi} \biggr] + {\frac{1}{\varpi^2} \frac{\partial^2 f}{\partial\varphi^2}} + \frac{\partial^2 f}{\partial z^2} ; </math>
<math> (\vec{v}\cdot\nabla)f </math>	=	<math> \biggl[ v_\varpi \frac{\partial f}{\partial\varpi} \biggr] + {\biggl[ \frac{v_\varphi}{\varpi} \frac{\partial f}{\partial\varphi} \biggr]} + \biggl[ v_z \frac{\partial f}{\partial z} \biggr] ; </math>
<math> \nabla \cdot \vec{F} </math>	=	<math> \frac{1}{\varpi} \frac{\partial (\varpi F_\varpi)}{\partial\varpi} + {\frac{1}{\varpi} \frac{\partial F_\varphi}{\partial\varphi}} + \frac{\partial F_z}{\partial z} ; </math>

Vector Time-Derivatives in Cylindrical Coordinates
<math> \frac{d}{dt}\vec{F} </math>	=	<math> {\hat{e}}_\varpi \frac{dF_\varpi}{dt} + F_\varpi \frac{d{\hat{e}}_\varpi}{dt} + {\hat{e}}_\varphi \frac{dF_\varphi}{dt} + F_\varphi \frac{d{\hat{e}}_\varphi}{dt} + {\hat{e}}_z \frac{dF_z}{dt} + F_z \frac{d{\hat{e}}_z}{dt} </math>
	=	<math> {\hat{e}}_\varpi \biggl[ \frac{dF_\varpi}{dt} - F_\varphi \dot\varphi \biggr] + {\hat{e}}_\varphi \biggl[ \frac{dF_\varphi}{dt} + F_\varpi \dot\varphi \biggr] + {\hat{e}}_z \frac{dF_z}{dt} ; </math>
<math> \vec{v} = \frac{d\vec{x}}{dt} = \frac{d}{dt}\biggl[ \hat{e}_\varpi \varpi + \hat{e}_z z \biggr] </math>	=	<math> {\hat{e}}_\varpi \biggl[ \dot\varpi \biggr] + {\hat{e}}_\varphi \biggl[ \varpi \dot\varphi \biggr] + {\hat{e}}_z \biggl[ \dot{z} \biggr] . </math>

Governing Equations

Introducing the above expressions into the principal governing equations gives,

Equation of Continuity

<math>\frac{d\rho}{dt} + \frac{\rho}{\varpi} \frac{\partial}{\partial\varpi} \biggl[ \varpi \dot\varpi \biggr] + \frac{1}{\varpi} \frac{\partial}{\partial \varphi} \biggl[ \varpi \dot\varphi \biggr] + \rho \frac{\partial}{\partial z} \biggl[ \dot{z} \biggr] = 0 </math>

Euler Equation

<math> {\hat{e}}_\varpi \biggl[ \frac{d \dot\varpi}{dt} - \varpi {\dot\varphi}^2 \biggr] + {\hat{e}}_\varphi \biggl[ \frac{d(\varpi\dot\varphi)}{dt} + \dot\varpi \dot\varphi \biggr] + {\hat{e}}_z \biggl[ \frac{d \dot{z}}{dt} \biggr] = - {\hat{e}}_\varpi \biggl[ \frac{1}{\rho}\frac{\partial P}{\partial\varpi} + \frac{\partial \Phi}{\partial\varpi}\biggr] - {\hat{e}}_\varphi \frac{1}{\varpi} \biggl[ \frac{1}{\rho}\frac{\partial P}{\partial \varphi} + \frac{\partial \Phi}{\partial \varphi} \biggr] - {\hat{e}}_z \biggl[ \frac{1}{\rho}\frac{\partial P}{\partial z} + \frac{\partial \Phi}{\partial z} \biggr] </math>

Adiabatic Form of the
First Law of Thermodynamics

<math>~\frac{d\epsilon}{dt} + P \frac{d}{dt} \biggl(\frac{1}{\rho}\biggr) = 0</math>

Poisson Equation

<math> \frac{1}{\varpi} \frac{\partial }{\partial\varpi} \biggl[ \varpi \frac{\partial \Phi}{\partial\varpi} \biggr] + \frac{1}{\varpi^2} \frac{\partial^2 \Phi}{\partial \varphi^2} + \frac{\partial^2 \Phi}{\partial z^2} = 4\pi G \rho . </math>

Eulerian Formulation

Each of the above simplified governing equations has been written in terms of Lagrangian time derivatives. An Eulerian formulation of each equation can be obtained by replacing each Lagrangian time derivative by its Eulerian counterpart. Specifically, for any scalar function, <math>f</math>,

<math> \frac{df}{dt} \rightarrow \frac{\partial f}{\partial t} + (\vec{v}\cdot \nabla)f = \frac{\partial f}{\partial t} + \biggl[ \dot\varpi \frac{\partial f}{\partial\varpi} \biggr] + \biggl[ \dot\varphi \frac{\partial f}{\partial\varphi} \biggr] + \biggl[ \dot{z} \frac{\partial f}{\partial z} \biggr] . </math>

Hence,

Equation of Continuity

<math> \frac{\partial\rho}{\partial t} + \biggl[ \dot\varpi \frac{\partial \rho}{\partial\varpi} \biggr] + \frac{\rho}{\varpi} \frac{\partial}{\partial\varpi} \biggl[ \varpi \dot\varpi \biggr] + \biggl[ \dot\varphi \frac{\partial \rho}{\partial\varphi} \biggr] + \frac{1}{\varpi} \frac{\partial}{\partial \varphi} \biggl[ \varpi \dot\varphi \biggr] + \biggl[ \dot{z} \frac{\partial \rho}{\partial z} \biggr] + \rho \frac{\partial}{\partial z} \biggl[ \dot{z} \biggr] = 0 </math>

<math> \Rightarrow ~~~ \frac{\partial\rho}{\partial t} + \frac{1}{\varpi} \frac{\partial}{\partial\varpi} \biggl[ \rho \varpi \dot\varpi \biggr] + \frac{1}{\varpi} \frac{\partial}{\partial \varphi} \biggl[ \rho \varpi \dot\varphi \biggr] + \frac{\partial}{\partial z} \biggl[ \rho \dot{z} \biggr] = 0 </math>

Linearize each term of the Continuity Equation assuming ...
<math> Q(\varpi, \phi, z, t) = [q_i(\varpi, z) + \delta q(\varpi, z, t) e^{i m \varphi}] ~~~ \mathrm{and} ~~~ \delta q/q_i \ll 1 </math>			<math> \mathrm{and} ~~~ \dot\varpi_i = \dot z_i = 0 </math>
<math>\frac{\partial\rho}{\partial t}</math>	<math>~~ \rightarrow ~~</math>	<math> \cancel{ \frac{\partial (\rho_i) }{\partial t} } + e^{im\varphi} \biggr[ \frac{\partial (\delta\rho) }{\partial t} \biggr] </math>
<math>\frac{1}{\varpi} \frac{\partial}{\partial\varpi} \biggl[ \rho \varpi \dot\varpi \biggr] = \frac{\rho \dot\varpi}{\varpi} + \rho\frac{\partial \dot\varpi}{\partial\varpi} + \dot\varpi \frac{\partial \rho}{\partial\varpi} </math>	<math>~~ \rightarrow ~~</math>	<math> \frac{ (\rho_i + e^{im\varphi} \delta\rho) ( {\dot\varpi_i} + e^{im\varphi} \delta\dot\varpi)}{\varpi} </math> <math> + (\rho_i + e^{im\varphi} \delta\rho) \frac{\partial ( {\dot\varpi_i} + e^{im\varphi} \delta\dot\varpi)}{\partial\varpi} </math> <math> + ( {\dot\varpi_i} + e^{im\varphi} \delta\dot\varpi) \frac{\partial (\rho_i + e^{im\varphi} \delta\rho)}{\partial\varpi} </math>
	<math>~~ \rightarrow ~~</math>	<math> e^{im\varphi} \biggl[ \frac{ \rho_i \dot\varpi_i}{\varpi} + \frac{ \rho_i }{\varpi} ( \delta\dot\varpi ) + \frac{ \dot\varpi_i }{\varpi} ( \delta\rho ) + \cancel{ \frac{ (\delta\rho) ( \delta\dot\varpi)}{\varpi} } </math> <math> + (\rho_i + \delta\rho) \frac{\partial {\dot\varpi_i} }{\partial\varpi} + (\rho_i + \cancel{\delta\rho}) \frac{\partial ( \delta\dot\varpi)}{\partial\varpi} </math> <math> + ( {\dot\varpi_i} + \delta\dot\varpi) \frac{\partial \rho_i }{\partial\varpi} + ( {\dot\varpi_i} + \cancel{\delta\dot\varpi}) \frac{\partial (\delta\rho)}{\partial\varpi} \biggr] </math>	<math>~~~~ \rightarrow ~~~~</math>	<math> e^{im\varphi} \biggl[ \cancel{ \frac{ \rho_i \dot\varpi_i}{\varpi} } + \frac{ \rho_i }{\varpi} ( \delta\dot\varpi ) + \cancel{ \frac{ \dot\varpi_i }{\varpi} ( \delta\rho ) } </math> <math> + \cancel{ (\rho_i + \delta\rho) \frac{\partial {\dot\varpi_i} }{\partial\varpi} } + (\rho_i ) \frac{\partial ( \delta\dot\varpi)}{\partial\varpi} </math> <math> + ( \cancel{\dot\varpi_i} + \delta\dot\varpi) \frac{\partial \rho_i }{\partial\varpi} + \cancel{ ( {\dot\varpi_i} ) \frac{\partial (\delta\rho)}{\partial\varpi} } \biggr] </math>
<math>\frac{1}{\varpi} \frac{\partial}{\partial\varphi} \biggl[ \rho \varpi \dot\varphi \biggr] = \frac{\rho}{\varpi} \frac{\partial (\varpi \dot\varphi) }{\partial\varphi} + \dot\varphi \frac{\partial \rho}{\partial\varphi} </math>	<math>~~ \rightarrow ~~</math>	<math> e^{im\varphi} \biggl[ \frac{ (\rho_i + \delta\rho) ( {\dot\varpi_i} + \delta\dot\varpi)}{\varpi} </math> <math> + (\rho_i + \delta\rho) \frac{\partial ( {\dot\varpi_i} + \delta\dot\varpi)}{\partial\varpi} </math> <math> + ( {\dot\varpi_i} + \delta\dot\varpi) \frac{\partial (\rho_i + \delta\rho)}{\partial\varpi} \biggr] </math>

<math>\varpi</math> Component of Euler Equation

<math> \frac{d \dot\varpi}{dt} - \varpi {\dot\varphi}^2 = - \frac{1}{\rho}\frac{\partial P}{\partial\varpi} - \frac{\partial \Phi}{\partial\varpi} </math>

<math> \rightarrow ~~~ \frac{\partial \dot\varpi}{\partial t} + \biggl[ \dot\varpi \frac{\partial \dot\varpi}{\partial\varpi} \biggr] + \biggl[ \dot\varphi \frac{\partial \dot\varpi}{\partial\varphi} \biggr] + \biggl[ \dot{z} \frac{\partial \dot\varpi}{\partial z} \biggr] - \varpi {\dot\varphi}^2 = - \frac{1}{\rho}\frac{\partial P}{\partial\varpi} - \frac{\partial \Phi}{\partial\varpi} </math>

<math>\varphi</math> Component of Euler Equation

<math> \frac{d (\varpi\dot\varphi) }{dt} + \dot\varpi \dot\varphi = - \frac{1}{\varpi} \biggl[ \frac{1}{\rho}\frac{\partial P}{\partial \varphi} + \frac{\partial \Phi}{\partial \varphi} \biggr] </math>

<math> \rightarrow ~~~ \frac{\partial (\varpi\dot\varphi)}{\partial t} + \biggl[ \dot\varpi \frac{\partial (\varpi\dot\varphi)}{\partial\varpi} \biggr] + \biggl[ \dot\varphi \frac{\partial (\varpi\dot\varphi)}{\partial\varphi} \biggr] + \biggl[ \dot{z} \frac{\partial (\varpi\dot\varphi)}{\partial z} \biggr] + \dot\varpi \dot\varphi = - \frac{1}{\varpi} \biggl[ \frac{1}{\rho}\frac{\partial P}{\partial \varphi} + \frac{\partial \Phi}{\partial \varphi} \biggr] </math>

<math>z</math> Component of Euler Equation

<math> \frac{d \dot{z} }{dt} = - \frac{1}{\rho}\frac{\partial P}{\partial z} - \frac{\partial \Phi}{\partial z} </math>

<math> \rightarrow ~~~ \frac{\partial \dot{z}}{\partial t} + \biggl[ \dot\varpi \frac{\partial \dot{z}}{\partial\varpi} \biggr] + \biggl[ \dot\varphi \frac{\partial \dot{z}}{\partial\varphi} \biggr] +\biggl[ \dot{z} \frac{\partial \dot{z}}{\partial z} \biggr] = - \frac{1}{\rho}\frac{\partial P}{\partial z} - \frac{\partial \Phi}{\partial z} </math>

See Also

© 2014 - 2021 by Joel E. Tohline |   H_Book Home   |   YouTube   | Appendices: | Equations | Variables | References | Ramblings | Images | myphys.lsu | ADS | Recommended citation:   Tohline, Joel E. (2021), The Structure, Stability, & Dynamics of Self-Gravitating Fluids, a (MediaWiki-based) Vistrails.org publication, https://www.vistrails.org/index.php/User:Tohline/citation