# michielm

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bio website tudelft.nl location Delft, Netherlands age 25 member for 5 months seen 1 hour ago profile views 15

I am a PhD student in the field of fluid dynamics and soft matter.

 2d comment Existence and uniqueness of Stokes flow@Qmechanic Ok! I have corrected the referencing. 2d comment Existence and uniqueness of Stokes flowDon't pin me down on it, but I believe the situation is only unsolvable if the far-field is unbounded May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipseok, this is pretty embarrassing. The mistake was in a function call where I had swapped the parameters of 2 ellipses. So I got the shape-plot for 1 ellipse (with b=2.5) while I got the integral for a different one (with b=0.52). Anyway, it's solved. Thanks for the effort and sorry about the dumb mistake May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipseAh ok, so I am at least getting the same number. So maybe the error is already somewhere earlier: in the value of $\phi_s$. I will look into it and come back here when I sorted things out. Thanks for the help!! It's much appreciated May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipseYou're right, they both are the same (I was missing a bracket), but still I get a much higher value. What I noticed by the way is that you use b=2.5 while I have b=0.52. What do you get with that smaller b? May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipsemmm that's odd. I found this for the integrand: $$a b \sqrt{\frac{b^4 \cos^2\phi+a^4 \sin^2\phi}{(b^2\cos^2\phi+a^2\sin^2\phi)^3}}$$ which is supposed to be the same according to ($\cos^2\phi+\sin^2\phi=1$) but apparently it is not???? May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipseBy the way: I agree that a different parametrization would be better. The thing is that I also need the polar angle so I will have to do a bit of work connecting the parametrization you suggest with the polar angle May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipseyeah, I see that now. Do you have a symbolic answer to the integrand? Then at least I can start looking for my mistake from there! Anyways, Thanks for the quick help!! May3 comment Inaccuracy in numerical calculation of arclength of part of an ellipse@your first comment: sorry I wrote down the value in degrees instead of radian, I fixed it in the post. The relative distance comes from the fact that I know where the tip of the ellipse and the point $\phi_s$ are ---- your second comment: So you are saying that the problem is most likely caused by the parametrization in combination with round-off errors? Apr29 comment Wisdom of the crowd in estimative calculation@joriki yes, I think it is safe to assume that the estimates for the individual quantities are normally distributed Apr18 comment Incomplete elliptic integral of the second kind and the arc length of an ellipse - does a simple relation exist?Awesome, thanks!! Could you add this into your answer so I can except it?! (comments tend to be less permanent) Apr18 comment Incomplete elliptic integral of the second kind and the arc length of an ellipse - does a simple relation exist?Thanks! I corrected the equations in my post. Unfortunately, I was more sloppy in typing up the post then I was in my derivation, in which I did have the correct expressions. So my question still holds Apr4 comment Approximations of the incomplete elliptic integral of the second kindGreat, I will give that a try! Thanks! Apr4 comment Approximations of the incomplete elliptic integral of the second kind@J.M. I need the approximation to determine $l=f(\phi)$ such that I can rewrite it in a form $\phi=f(l)$. With the exact elliptic integral that doesn't seem possible. Apr4 comment Approximations of the incomplete elliptic integral of the second kind@J.M. the use of pade approximants seems to me to be a fairly involved approach in which I have to determine all the prefactors, which I would probably need a computer for so then I don't see the point in using the approximation over the 'real' incomplete elliptic integral Apr3 comment Approximations of the incomplete elliptic integral of the second kindI hadn't seen it yet, but after taking a look it doesn't get much clearer for me. I can see that Eq 21 in the link is an approximation, but I am not sure how I would go about applying it? Apr3 comment Detect values in array that are statistically inconsistentThat's a good point. I guess you have to know quite a bit about the physics/chemistry of what you're measuring to be able to set a sensible absolute or relative threshold. Mar31 comment Problems with votesPretty sure that there should be, but that is a bit too tough a nut to crack for me. Mar31 comment Determine if the Series Converges and Explain approachOk, I agree, formally I cannot write $2^\frac{1}{\infty+1}=1$ but I figured that it is obvious that this is correct in the limit of infinity Mar31 comment Geometric calculation: two kneading discsDo you know the exact geometry of 1 of the discs? or only the area? If you know the function describing the long edge of the discs then it shouldn't be too hard to come up with an answer