# Non linear wave propagation

(Difference between revisions)
 Revision as of 01:51, 25 December 2005 (view source)← Older edit Latest revision as of 14:03, 19 July 2007 (view source)Jola (Talk | contribs) m (Reverted edits by Mansoor (Talk); changed back to last version by Harish gopalan) (6 intermediate revisions not shown) Line 2: Line 2: :$\frac{\partial u}{\partial t}+ u \frac{\partial u}{\partial x}=0 :[itex] \frac{\partial u}{\partial t}+ u \frac{\partial u}{\partial x}=0$ [/itex] + == Domain == == Domain == - x=[-5,10] + :$x \in \left[-5,10\right]$ + == Initial Condition == == Initial Condition == - :$u(x,0)=0 ,x <=0$ + :$u(x,0) = - :[itex] u(x,0)=1 ,x >0$ + \begin{cases} + 0 & x \le 0 \\ + 1 & x > 0 + \end{cases} + [/itex] + == Boundary condition == == Boundary condition == - u[0]=0 + :$u(0,t)=0$ == Exact solution == == Exact solution == - :$u(x,t)=0 ,x<=0$ + :[itex]u(x,t) = - :[itex] u(x,t)=x/t, 0

## Problem definition

$\frac{\partial u}{\partial t}+ u \frac{\partial u}{\partial x}=0$

## Domain

$x \in \left[-5,10\right]$

## Initial Condition

$u(x,0) = \begin{cases} 0 & x \le 0 \\ 1 & x > 0 \end{cases}$

## Boundary condition

$u(0,t)=0$

## Exact solution

$u(x,t) = \begin{cases} 0 & x \le 0 \\ x/t & 0 < x < t \\ 1 & \mbox{otherwise} \end{cases}$

## Numerical method

### Space

#### Explicit Scheme (DRP)

${(\frac{\partial u}{\partial x})}_i=\frac{1.0}{dx}\sum_{k=-3}^3 a_k u_{i+k}$

The coefficients can be found in Tam(1993).At the right boundaries use fourth order central difference and fourth backward difference.At left boundaries use second order central difference for i=2 and fourth order central difference for i=3.The Dispersion relation preserving (DRP) finite volume scheme can be found in Popescu (2005).

#### Implicit Scheme(Compact)

Domain: $\alpha v_{i-1} + v_i + \alpha v_{i+1}=\frac{a}{2h}(u_{i+1}-u_{i-1})$
Boundaries: $v_1+\alpha v_2=\frac{1}{h}(au_1+bu_2+cu_3+du_4)$

where v refers to the first derivative.For a general treatment of compact scheme refer to Lele (1992).In this test case the following values are used

$\mbox{Domain:} \alpha=0.25 , a=\frac{2}{3}(\alpha+2)$
$\mbox{Boundary:} \alpha=2 ,a=-(\frac{11+2\alpha}{6}),b=\frac{6-\alpha}{2},c=\frac{2\alpha-3}{2},d=\frac{2-\alpha}{6}$

Both the schemes are 4th order accurate in the domain.The compact scheme has third order accuracy at the boundary.

### Time (4th Order Runga-Kutta)

$\frac{\partial u}{\partial t}=f$
$u^{M+1} =u^M + b^{M+1}dtH^M$
$H^M=a^MH^{M-1}+f^M$

,M=1,2..5 .The coefficients a and b can be found in Williamson(1980)

## Reference

Mihaela Popescu, Wei Shyy , Marc Garbey (2005), "Finite volume treatment of dispersion-relation-preserving and optimized prefactored compact schemes for wave propagation", Journal of Computational Physics, Vol. 210, pp. 705-729.

Tam and Webb (1993), "Dispersion-relation-preserving finite difference schemes for computational acoustics", Journal of Computational Physics, Vol. 107, pp. 262-281.

SK Lele (1992), "Compact finite difference schemes with spectrum-like resolution", Journal of Computational Physics, Vol.103, pp.16-42.

Williamson (1980), "Low Storage Runge-Kutta Schemes", Journal of Computational Physics, Vol.35, pp.48–56.