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| This is the problem of numerical methods for PDE. First, we cannot use automatic method selection, because we get a warning NDSolveValue::ibcinc: Warning: boundary and initial conditions are inconsistent. When using `Method ->... |
| You possibly did not realize that there is no slipping between the disks, therefore $r\psi =R \phi -(R-r) \theta $. Then $(\psi ')^2=(R \phi '-(R-r) \theta ')^2/r^2$. |
| It should be noted that z1 is a vector `{z1[[1]],z1[[2]]}`. The signs of the remaining expressions can be clarified. z1 = {-R*W*Sin[W*t] + l'[t]*Sin[\[Phi][t]] + l[t]*(\[Phi]'[t])*Cos[\[Phi][t]], R*W*Cos[W*t] -... |
| No, you're not right, we made this replacement in `(divsig0 /. uif -> uif[i - 1])` in line `Do[
]`. If you want to make this replacement earlier, then make it so that there is no error due to the coincidence of the names of the iterator ... |
| Ok! Thank you, this image works. Why didn't you add a legend bar for `Tension map` and `Pressure map`? |
| Publish the code, we will check. |
| I will show a numerical solution q = {U[t] + 3 U[t]^2 + 6 V[t] + 3 V[t]^2 + 5 W[t] + 2 W[t]^2 + 4 U[t]*V[t] == 2 U'[t], 6 U[t] + 3 U[t]^2 + 3 V[t] + 4 V[t]^2 + 8 W[t] + 4 W[t]^2 + 3 U[t]*V[t] == V'[t], 5... |
| To test the effectiveness of all algorithms, I used a 1D type solution $Us[\tau, \xi]=Us[\tau-\xi]$ as the initial and boundary conditions. Unfortunately, all the algorithms turned out to be ineffective in the sense that the error in reproducing the... |
| Paul, attach file with code, perhaps we will find a solution. |
| This is a duplicate from the site https://mathematica.stackexchange.com/questions/185957/interpretation-of-polarplot I will postpone my answer. Here we have an example of incorrect use of the polar radius function `r[t]`, which by definition must... |