UDF Radiation model for combustion
Hi,,,This is siva kumar from IIT MADRAS....while am interpret my udf the error is showing like.....
Error: FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: () this error is coming in my fluent model when i interpret the source code as shown in below....fuel is methane #include "udf.h" DEFINE_SOURCE(energy,c,t,ds,eqn) { /*FILE *fp;*/ real source,tep,sigma,Pamb,tamb; real MW[18]; real Xh2o,Xco,Xco2,Xch4,ph2o,pco,pco2,pch4; real MWmix,sum=0; real kapa,absh2o,absco,absco2,absch4; real a0,a1,a2,a3,a4,a5; real b0,b1,b2,b3,b4,b5; real c0,c1,c2,c3,c4; real d0,d1,d2,d3,d4; int i; /*fp=fopen("properties.txt","w");*/ tep=C_T(c,t); MW[0]=1; MW[1]=32; MW[2]=17; MW[3]=16; MW[4]=2; MW[5]=18; MW[6]=33; MW[7]=28; MW[8]=44; MW[9]=16; MW[10]=15; MW[11]=14; MW[12]=30; MW[13]=29; MW[14]=31; MW[15]=34; MW[16]=13; MW[17]=28; sigma=0.000000056697; Pamb=1.0; tamb=298.0; a0=18.741; a1=121.310; a2=273.500; a3=194.05; a4=56.31; a5=5.8169; b0=0.23093; b1=1.12393; b2=9.4153; b3=2.99880; b4=0.51382; b5=.000018684; c0=6.6334; c1=0.0035686; c2=0.000000016682; c3=0.00000000025611; c4=0.000000000000026558; if(tep<=750) { d0=4.7869; d1=0.06953; d2=0.000295775; d3=0.000000425732; d4=0.000000000202894; } else if(tep>750) { d0=10.09; d1=0.01183; d2=0.0000047753; d3=0.000000000587209; d4=0.000000000000025334; } for(i=0;i<18;i++) { sum=sum+C_YI(c,t,i)/MW[i]; } MWmix=1/sum; Xh2o=C_YI(c,t,5)*MWmix/18; Xco=C_YI(c,t,7)*MWmix/28; Xco2=C_YI(c,t,8)*MWmix/44; Xch4=C_YI(c,t,9)*MWmix/16; ph2o=Xh2o*Pamb; pco=Xco*Pamb; pco2=Xco2*Pamb; pch4=Xch4*Pamb; absch4=c0+(c1*tep)+(c2*pow(tep,2))+(c3*pow(tep,3)) +(c4*pow(tep,4) ); absco2=a0+(a1*(1000/tep))+(a2*pow(1000/tep,2))+(a3*pow(1000/tep,3 ))+(a4*pow(1000/tep,4))+(a5*pow(1000/tep,5)); absco=d0+(d1*tep)+(d2*pow(tep,2))+(d3*pow(tep,3))+ (d4*pow(tep,4)) ; absh2o=b0+(b1*(1000/tep))+(b2*pow(1000/tep,2))+(b3*pow(1000/tep,3 ))+(b4*pow(1000/tep,4))+(b5*pow(1000/tep,5)); kapa=(absch4*pch4)+(absco*pco)+(absco2*pco2)+(absh 2o*ph2o); source=(4*sigma*kapa*(pow(tep,4)pow(tamb,4))); /*fprintf(fp,"%f%f%f\n",tep,source,MWmix);*/ ds[eqn]=0; return source; } why the error is coming i don't know please help me?????? 
Hello Siva,
Notice the space into your variable: kapa=(absch4*pch4)+(absco*pco)+(absco2*pco2)+(absh 2o*ph2o); Delete that space and it should be ok: kapa=(absch4*pch4)+(absco*pco)+(absco2*pco2)+(absh2o*ph2o); Have a good day. Micaël 
Thank u very much Micaël
i willl try that.....thank u very much for ur reply...keep in touch with me,,,,,

hey Micaël
i have tried but it is not working man,,,,,???

Sorry, I had not tried the UDF, only saw this space and reported it. Now I can see too that there is another problem, more difficult to find.
That is not clear to me, but the problem seems to come from C_YI(c,t,i). Using only a Species Transport model, I can successfully use your UDF. Which model do you use? Someone reported problem using C_YI(c,t,i) with a pdf combustion model: http://university.fluent.com/forum/v...814ae1a27f690d Hope this can helps. Micaël 
Micaël
hi,,,,miceal,,,am using species transport model .......how can it be solved...?
see miceal am not using pdf combustion model am using only species transport model......??? 
Here is what I did:
I enabled Species Transport. I choose "mixturetemplate" in the Mixture Material dropdown list. In the Materials panel, I added arbitrary fluid materials in that mixture up to 18. Finally, I hooked the UDF in the boundaries panel, adding energy source in the fluid zone. I did few iterations without bug. Do you use it that way? If you have less then 18 species defined in your mixture there is a bug here in your code: for(i=0;i<18;i++) { sum=sum+C_YI(c,t,i)/MW[i]; } You can easily see how many species you have: Define > Models > Species > Transport & Reaction Just look at the right of "Number of Volumetric Species" 
u have run that file...
did get running the fluent with out error....but mine is error is coming again,,,??? 
You have defined 18 species in your mixture?
If yes, then I don't know what is the problem. 
miceal..
hi miceal my problem is 2 step methane combustion....total products are 6 how can i give 18 products ,,,,
i think we need to change the udf into 6 species,,,,,,isn't it??? 
Did your write this UDF yourself? What it does? What is "MW"?
I thought you have 18 species because of this: for(i=0;i<18;i++) { sum=sum+C_YI(c,t,i)/MW[i]; } i in C_YI(c,t,i) is species index (integer) What this loop intend to do? Since you have 6 species, now it is clear to me that the problem is there.;) Don't give up. 
absorption
Dear friends,
as I saw the UDF you are calculating absorption for each species that are present in the domain and give it as a source value. how is this source define in fluent because the heat is only absorped in the cell where these species are present en not else were. I want to used DPM to inject particle and that calculate the absorpted heat by radiation. how could I used this UDF please help 
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