nima103
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thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
Hi Rahul Thanks for you response but I have to disagree with you. The reason that simulation of GAJENDRA KUMAR NHAICHANIYA on the other thread is not converging is not singularity, He has the wrong boundary condition because he has introduced a heat source without a heat sink, that means you have a closed unit and you only heat it up, of course the temperature will only rise until it reaches the maximal long number that the software can handle. that means the energy balance is not holding now if you introduce a spc temperature and fix some nodes with some temperature, the iteration will not go on and has to stop but the temperature results wont be accurate. In my model I have been entering the QVOL and QBDY1 which are multiplied with element volume and element area. Now if the element volume has deviated a very small amount from what your CAD model that means discrepency between energy input and output which leads to not converging. QVOLxVolume = QBDY1xArea I would expect however that the software would be able to handle thisw deviation since they are very small but as you see they magnify with each iteration. However I found a work around which is to read the volume and area using command consule with 17digits of precision and then enter QVOL and QBDY1 values with 17 digits and run it on cluster and without determining any temperature constraints. In this case all the models would converge and calculate a dT. furthermore the test that you made by adding the temperature would lead to very bigger deviations once you have a more comlex geometry and more elements. 
thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
Yes I am in contact with Altair and the solutions that were devised didn't work. I am able to read the volume and enter the flux B.C. with high precision but still the energy equation doesn't hold fully and the simulation wpnt converge. 
thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
that is correct, the boundary condition that I have defined should only be able to calculate the temperature difference (that is ΔT in Fourier's law q=k.ΔT/L or ∇T in matrix presentation: Q=K∇T) but In order to do that the simulation should first converge. The converging of simulation is highly dependant on mesh orientation while in reality it should not. It seems like optistruct is not handling a simulation with heat source and heat sink correctly, or independant of mesh orientation. 
thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
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thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
Thanks Rahul but my problem is not how to do thermal simulation, my problem is that I have a negative and positive heat source with the same magnitude and the simulation isn't converging 
thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
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thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
Thanks Rahul, few words Regarding the meshing for the model that converges: I have created 2D elements and dragged them along to create 1 big 3D component, then I have deleted some elements until I have reached the model that you see, therefore the element material directions are on the same orientation. for meshing of the other model, the meshing is done in differenet directions. Although I have tried to orient all material direction and element normals of the notconvergingmodel, still this model is not converging. Therefore I assume material direction and element normals dont have influence. 
thermal equilibrium between positive and negative heat source
nima103 replied to nima103's topic in Altair OptiStruct
As you can see here 1.fem file converges with sensible results while 2.fe file does not converge ! does anybody have any idea? 
thermal equilibrium between positive and negative heat source
nima103 posted a topic in Altair OptiStruct
Hi everyone, I am trying to perform thermal simulation with heat source and sink as boundary condition. I have a positive heat flux(as QVOL acting on solid elements) and a negative heat flux (as QBDY1 acting on conduction interface). However most of the time I could see that the simulation does not converge and the Temperature results are very big. Attached here I have 2 fem files with exactly the same geometry and boundary condition and element size, but different meshing directions. the 1.fem file yields correct results while 2.fem doesn not converge. I have tried to experiment with changing element normal and changing material direction all to be along heat transfer direction but still 2.fem file does not converge and I cant find what makes the difference in simulation results. can anybody check to see if you can converge the 2.fem file ? and what makes 2.fem file not converge? thanks and looking forward to hear from you Rafezi 2.fem 1.fem 13 replies

 heat transfer
 thermal simulation

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Rahul R liked a post in a topic: Thermal equiblium between conduction and convetion

Thermal equiblium between conduction and convetion
nima103 replied to nima103's topic in Altair OptiStruct
I found out Rahul, the simulation is correct, I have a mistake in calculation. I shoud have used 35 as thikness instead of 0.35 
Thermal equiblium between conduction and convetion
nima103 replied to nima103's topic in Altair OptiStruct
Hi Rahul, yes sure model.fem 
Hi every one, I am trying to simulate a convection and conduction model and compare it with analytic results. I have a cube with K value of 100 as it can be seen in the attachment, with upper surface temperature of 40. The lower surface is exposed to free convection with amb. temp of 20 and H value of 40. The thinkness if cube is 0.35m. Analytical calculation of problem would yield lower surface temp. of 37.3 while simulation results always gets very close to ambient temperature. can anyone explain why there is a difference ? T1 = 40 K = 100 H = 40 Tamb = 20 L = 0.35 T2 = ? k.(T1T2)/L = H(T2  Tamb) T2 = 37.3