# How to map a domain changing in length with time

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 November 26, 2011, 16:37 How to map a domain changing in length with time #1 New Member   amgotsikmeme Join Date: Nov 2011 Posts: 6 Rep Power: 7 Hi all; I have a problem with my CFD project and need help. The problem is I have a 1-D domain which is given by L=L_0+delta(sin(wt)) and I try to map it into a domain that has one fixed length by using fixed number of grid points at all times. I need to find a mapping function. Thanks for your concern Last edited by bababanamzdaalma; November 26, 2011 at 17:14.

 November 26, 2011, 20:13 #2 New Member   Carlos Join Date: Nov 2011 Location: The Netherlands Posts: 17 Rep Power: 7 If I understand this correctly, you need a 1D domain of fixed length where only the nodes change position in time? So in your simulation you would get that some cell faces are elongating while others or shortening, yet the sum of lengths is constant in time.You could start with a simpler example, by having an uniform motion of nodes: for i = 0:N loc_0(i) = L * i/N + L_0 end for t = 0:T_end for i = 1:N-1 loc(i,t) = loc_0(i) + L/N*sin(w*t) end end This would get your nodes to move uniformly to the right and back. If this is not want you meant, please post some additional information! __________________ "Do not worry about your difficulties in Mathematics. I can assure you mine are still greater." - Albert Einstein

 November 26, 2011, 20:32 #3 New Member   amgotsikmeme Join Date: Nov 2011 Posts: 6 Rep Power: 7 the domain can be considered as 1-D engine piston. I have to figure out an algebraic function that maps the current domain in a constant length one by using constant number of grid points.

 November 27, 2011, 06:30 #4 Senior Member   cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 13 maybe i misunderstand you, but that should be easy: you know your domain size (physically) at each time t, so just map that your unit interval as a function of t .... your domain length is some fct of t: L(t), with a=X(x=0) and b=X(x=L(t)) so your projection is just: [0,1]-> [a,b(t)] with equidistant nodes....

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