in order to my master thesis i must build a MFA model for rice cultivation.
first as i recently imported some of the values in my model and then calculated it. i became an erorr regarding contradiction in my model. as i modelled 2 crop and three cropping season in one model and the values i inserted are actually the same for both (because of the difference of the fields of the two type of cultivation i had to consider them seperately). all i want to say ist, in my model the contradiction error that i got is for 2 crop rice cultivation (RZM2) and NOT for three crop rice cultivation (RZM3), which is wired. i entered mass of rice production in good layer and N concentration which goes with the product as mass fraction of product but it seems to be a contradiction for STAN?! could you look at my model in attachment and see if there is something wrong with my model?
secondly i wanted to ask if it is right in order to MFA rules to consider all the goods in one layer of goodl?! because i have water balances in the area and then seed and rice as production and also some other stuff like fertilizer and pesticides etc. and i dont know if i should consider the subgood for every singel good i have in my model or it is actually ok to consider all of them as one good layer?
and the last thing i would like to know is that: for gas emissions it souldnt/couldnt be defined a mass. so if i define N losses to air according to the mass of applied N fertilizer in N layer and no mass for these losses (because obviously they havent any ) it souldnt be a problem. am i right?
P.S.sorry if my questions are maybe a little at beginner level, but i try to write my thesis and had no knowledge of MFA before i started my thesis so even that i saw all the tutorials there is some missing knowledge parts which i have to fill !
The computational problems you encounter (contradiction warning) might be due to some numerical instabilities in the computation algorithm "Cencic 2012" in connection with the additional relations you entered. I tested the computation with the commercial algorithm "IAL-IMPL2013" and there the computation was partially successful (i.e., not all unknown quantities could be calculated).
As you consider the substance layers N and P, you have to model all of your goods on the layer of goods.
If enough data is given, the unknown losses of N to air should be able to be computed from the mass balances of the N flows going in and out of the respective processes. Of course, you can also estimate the percentage of losses and state them as transfer coefficients.
thanks for your suggestion.
i tried to modell my system a lot easier and then i entered my data and tried with both algorithm to calculate the model. the one with cencic 2012 shows me that the stock which i entered in one process has controdiction in the first period. but i don't get, what it means. actually the sum of in and outflows should go into stock but will add as stock change rate in each period. am i right?
with the other IAL-IMPL2013 calculation method the calculation will be abort with 100 iteration!
i really don't know what to do to fix this error.
non of the flows are calculated. Even the given mass concentrations are not calculated as mass balances.
i think maybe i need to add data uncentainty for my model!
i upload my model as well, to take a look at it.
i will be appriciated.
Some of your flows have zero mass values on the layer of goods but mass values different from zero on the layers P and N. This can' be correct.
Additonal, mass values of flows of goods that you know to be zero have to be manually set to zero (e.g. the change in stock of NR2 and NR3). Otherwise, you will get problems during computation because when the calculation algorithm is converging to its solution there will be a division by zero error that prevents conversion.