# HW6 - MAE 290b Numerical Methods HW6 Qiyun Zhao March 7...

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Unformatted text preview: MAE 290b Numerical Methods HW6 Qiyun Zhao March 7, 2011 MAE290b HW6 Qiyun Zhao Problem 1 (a) Solve the problem using an explicit method (1) Use EE and finite difference du i,j dt + u n i,j u n i +1 ,j- u n i- 1 ,j 2Δ x + v n i,j u n i,j +1- u n i,j- 1 2Δ y = ν ( u n i +1 ,j- 2 u n i,j + u n i- 1 ,j Δ x 2 + u n i,j +1- 2 u n i,j + u n i,j- 1 Δ y 2 ) dv i,j dt + u n i,j v n i +1 ,j- v n i- 1 ,j 2Δ x + v n i,j v n i,j +1- v n i,j- 1 2Δ y = ν ( v n i +1 ,j- 2 v n i,j + v n i- 1 ,j Δ x 2 + v n i,j +1- 2 v n i,j + v n i,j- 1 Δ y 2 ) Then we can obtain: du i,j dt =- u n i,j u n i +1 ,j- u n i- 1 ,j 2Δ x- v n i,j u n i,j +1- u n i,j- 1 2Δ y + ν ( u n i +1 ,j- 2 u n i,j + u n i- 1 ,j Δ x 2 + u n i,j +1- 2 u n i,j + u n i,j- 1 Δ y 2 ) dv i,j dt =- u n i,j v n i +1 ,j- v n i- 1 ,j 2Δ x- v n i,j v n i,j +1- v n i,j- 1 2Δ y + ν ( v n i +1 ,j- 2 v n i,j + v n i- 1 ,j Δ x 2 + v n i,j +1- 2 v n i,j + v n i,j- 1 Δ y 2 ) where i = 1 , 2 ,...,M- 1 j = 1 , 2 ,...,N- 1 , n = 1 , 2 ,.... Use the explicit method to calculate u n +1 i,j and v n +1 i,j , say EE. u n +1 i,j = u n i,j + Δ t [- u n i,j u n i +1 ,j- u n i- 1 ,j 2Δ x- v n i,j u n i,j +1- u n i,j- 1 2Δ y + ν ( u n i +1 ,j- 2 u n i,j + u n i- 1 ,j Δ x 2 + u n i,j +1- 2 u n i,j + u n i,j- 1 Δ y 2 )] v n +1 i,j = v n i,j + Δ t [- u n i,j v n i +1 ,j- v n i- 1 ,j 2Δ x- v n i,j v n i,j +1- v n i,j- 1 2Δ y + ν ( v n i +1 ,j- 2 v n i,j + v n i- 1 ,j Δ x 2 + v n i,j +1- 2 v n i,j + v n i,j- 1 Δ y 2 )] where i = 1 , 2 ,...,M- 1 j = 1 , 2 ,...,N- 1 , n = 0 , 1 , 2 ,.... As Let Δ x = Δ y = h , from the linear case, we can get Δ t ≤ h 2 4 ν U i,j +1 U i- 1 ,j U i,j U i +1 ,j U i,j- 1 (2)Use EE to get started for Adamas-Bashforth AB method: y n +1 = y n + h 2 [3 f ( y n ,t n )- f ( y n- 1 ,t n- 1 )] u n +1 i,j = u n i,j + Δ t 2 { 3[- u n i,j u n i +1 ,j- u n i- 1 ,j 2Δ x- v n i,j u n i,j +1- u n i,j- 1 2Δ y + ν ( u n i +1 ,j- 2 u n i,j + u n i- 1 ,j Δ x 2 + u n i,j +1- 2 u n i,j + u n i,j- 1 Δ y 2 )]- [- u n- 1 i,j u n- 1 i +1 ,j- u n- 1 i- 1 ,j 2Δ x- v n- 1 i,j u n- 1 i,j +1- u n- 1 i,j- 1 2Δ y + ν ( u n- 1 i +1 ,j- 2 u n- 1 i,j + u n- 1 i- 1 ,j Δ x 2 + u n- 1 i,j +1- 2 u n- 1 i,j + u n- 1 i,j- 1 Δ y 2 )] } 1 MAE290b HW6 Qiyun Zhao 0.2 0.4 0.6 0.8 1 0.5 1-1-0.5 0.5 1 x u using explicit method y z 0.2 0.4 0.6 0.8 1 0.5 1 0.5 1 1.5 x v using explicit method y z Figure 1: Solution use AB (b) Solve the problem using ADI combined with EE u n + 1 2- u n =- Δ t 2 ( u n ∂u n ∂x + v n ∂u n ∂y ) + ν Δ t 2 ( ∂ 2 u n + 1 2 ∂x 2 + ∂ 2 u n ∂y 2 ) u n +1- u n + 1 2 =- Δ t 2 ( u n ∂u n ∂x + v n ∂u n ∂y ) + ν Δ t 2 ( ∂ 2 u n + 1 2 ∂x 2 + ∂ 2 u n +1 ∂y 2 ) Use finite difference in space, we obtain: u n + 1 2 i,j- u n i,j =- Δ t 2 [ u n i,j u n i +1 ,j- u n i- 1 ,j 2Δ x + v n i,j u n i,j +1- u n i,j- 1 2Δ y ] + ν Δ t 2 ( u n +1 / 2 i +1 ,j- 2 u n +1 / 2 i,j + u n +1 / 2 i- 1 ,j Δ x 2 + u n i,j +1- 2 u n i,j + u n i,j- 1 Δ y 2 ) u n +1 i,j- u n + 1 2...
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## This note was uploaded on 03/13/2011 for the course MAE 290B taught by Professor Marsden during the Winter '11 term at UCSD.

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HW6 - MAE 290b Numerical Methods HW6 Qiyun Zhao March 7...

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