| Author | Message | ||||
     Mehdi Naderi (mnader4) Member Username: mnader4 Post Number: 40 Registered: 12-2006 |
Dear Mr. Nelson, Happy New Year, I will apprecite if you help me. Complete form of Heat equation in Fpde is below form: Div(k*grad(temp))=c*ro*dt(temp)+source in my example ( the beam fixed at one end), attached file)thermal conductivity in a specific region will reduce with time. I expect that when thermal conductivity is very low temperarue shoots up very high at that specific region. But in my program at the end there is just a little temperature rise. I dont know where is the mistake. Maybe Fpde has a specific rule for such this type of equation. Regards, Mehdi
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| Marek Nelson (mgnelson) Moderator Username: mgnelson Post Number: 16 Registered: 07-2007 |
It looks to me as if you just need to run longer. Try running to a later time like 500 or 600. You stop at time 290, but the significant change of the thermal conductivity happened after time 280. There has not been enough time for the system to react. This is supported by the fact that the temperature plot has just started to rise when the time 290 is reached and the run stops. Attached graphic shows a run to time 600.  | ||||
| Mehdi Naderi (mnader4) Member Username: mnader4 Post Number: 41 Registered: 12-2006 |
Dear Mr. Nelson, Thank you for your answer. First of all, my problem is so that the system will stop at t=290 (or will break).I can not increase the time. The virging k=237 and when t=265 , k=227 while time is going to 290, thermal conductivity: k= 226.6363283 226.1934931 225.7157842 225.1734763 224.6101849 223.9905514 223.2712904 222.4601281 221.5645141 220.501815 219.3162422 217.9205655 216.285706 214.1941298 211.6327305 208.39354 203.9709313 197.8755883 189.1870305 174.7095106 146.199389 55.44624753 0.11 Fpde has to sense low thermal conductivity after t=265. But I dont know why fpde is not very sensitive to thermal conductivity change. | ||||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 1041 Registered: 06-2003 |
Your conductivity is still 146 at t=288. Even if the conductivity dropped to zero, the temperature could only rise at 0.4 (Source/rho/cp) degrees per time unit. From 288 to 290 is 2 units, or 0.8 degrees rise best case (which yours isn't). This isn't a question of what FlexPDE does or doesn't do. It's inherent in your specification of the system. | ||||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 1042 Registered: 06-2003 |
PS How do you get Aluminum to stop conducting heat? And at a precise second in time? This sounds like Alchemy. | ||||
| Mehdi Naderi (mnader4) Member Username: mnader4 Post Number: 42 Registered: 12-2006 |
Dear Mr. Nelson, Thank you so much. Actually,if you remeber my problem is a fluctuating beam. Fatigue phenamenon occurs after no. of cycles. t=290 is taken from an experiment. it means that at t=290 the beam seperates. every material in fatigue has degradation and micro and macrocrak which will reduce thermal conductivity and density (I have to change density too in my model). in experiment between t=265 and 290 we saw huge temeperature rise. So I am trying to model it and see the temperature rise at the end. because the beam fails at the fixed point I tried to define a small region and force the change of material properties there. | ||||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 1045 Registered: 06-2003 |
If you have an experimental result, you can use the data to compute how long the conductivity must be shut off and what the source term must be. (Temp2-Temp1)/(time2-time1)=Source/rho/cp Conductivity must be zero (not 146) from time1 at the latest. |
beam with time dependent thermal conductivity
thermal conductivity