Introduction to CFD Questions & Answers  
Question by Student 201227147
Professor, I have a question about Assignment #7. Last class, you changed mf as 1, 2, and 4 and grid became as $21*21$, $41*41$, and $81*81$ because $is=1$ and $ie=1+round(20*mf)$. But, I think $ie$ should be $round(20*mf)$ so that grid becomes $20*20$, $40*40$, and $80*80$. Why $ie=1+round(20*mf)$?
05.15.17
This is to make sure that there is one node at $x=0,~y=0$. If ie would be set to 20, 40, etc, instead of 21, 41, etc, then there wouldn't be a node precisely at the origin. 1 point bonus.
Question by Student 201227141
Professor, at assign#7 i just changed mf and xiverge then i got this wrong picture.
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I can't understand what i did wrong.
05.17.17
There's not enough information provided for me to help you. You need to isolate the problem and indicate clearly what change in the control file created this problem.
Question by Student 201427142
Professor, I have problem with Q#2 at Ass. #7. You said $r=\sqrt2$. However, when I set $mf=2\sqrt2$, there is no (0, 0) point instead ($\pm$0.0175439,$\pm$0.0175439). You intend to reduce the scale, but I think it cannot be done. How can I to do about it?
That's correct: I did this on purpose so you need to find a way to approximate $\delta_x P$ at the origin as well as possible when there is no node exactly at the origin. There are several ways this can be done. Explain clearly in your solutions how you do this. 2 points bonus.
Question by Student 201227147
In class, you defined $\epsilon _f^{rel}$ as following: $\epsilon _f^{rel}$ $\equiv$ $\vert\frac{(\delta_{x}\phi)_{c}-(\delta_{x}\phi)_{f}}{(\delta_{x} \phi)_f}\vert$. However, in the table you uploaded, it says that $\epsilon _f^{disc, rel}$ $\equiv$ $\frac{(\delta_{x}\phi)_{f}-(\delta_{x}\phi)_{c}}{(\delta_{x} \phi)_f}$. Which definition is right?
05.18.17
Good observation. It's better to use the definition in the tables. Make modifications to your class notes accordingly. 2 points bonus.
Question by Student 201527110
Professor, I have one question during finding order of accuracy P. In definition, $$P=\frac{1}{ln(R)}*ln(\frac{(\delta_xP)_3-(\delta_xP)_2}{(\delta_xP)_2-(\delta_xP)_1})$$, however what if the value in log function is negative? Is it okay to take absolute value for that sequence?
Well, if the value is within the second log is negative it means you're not within the asymptotic range of convergence.. 2 points bonus.
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