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time steps in transient heat transfer in solids
Hello,
Is there any criteria for the time steps doing transient calculation with heat transfer in solids? I found one for the convective mass transport saying 2*dt*nu/rho < L^2 L ... mean mesh size dt ... time step rho ... density nu ... dynamic viscosity Is that criteria correct? Is it possible to compare the energy-equation with the one for mass transport, so that I get a similar criteria for heat transport in solids?: 2*dt*lambda/(rho*cp) < L^2 L ... mean mesh size dt ... time step rho ... desnity lambda ... heat conduct. of solid cp ... spec. heat Thanks in advance for every answer Mike |

Re: time steps in transient heat transfer in solid
Hi,
It depends on whether you use an explicit or implicit method for time discretization. Usually: Explicit: 2*dt*lambda/(rho*cp) < L^2 (as you have pointed out) Implicit: No restrictions for convergence (only for accuracy) Semi-implicit (Crank-Nicolson): No retrictions for convergence but a restriction to avoid unphysical results: dt*lambda/(rho*cp) < L^2 Hope this helps, Gorka |

Re: time steps in transient heat transfer in solid
Hello,
Thank you very much - that really helps a lot, Gorka. I have an implicit scheme, so it should be only a question of accuracy. Do you have any advice how I can measure or see accuracy without having experimental data? Or is there any hint how to choose the time steps in fully imclicit scheme? Mike |

Re: time steps in transient heat transfer in solid
Hi,
The Implicit scheme is first order accurate unless you use results from the two previous time-steps (n and n-1, being n+1 the new time step, in which you evaluate the terms). Therefore, you should use small time steps if you want to obtain accurate results. Sorry but I donīt know any specific criterium. Gorka |

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