Add solid fake for perpendicular flap tutorial

[NiklasVin]

I added a solid fake implemented in Python to the perpendicular flap tutorial, similar to the already existing fluid-fake.

[MakisH]

Is this ready for review?
Don't forget to add it into the README of the tutorial. I can generate some of the plots when reviewing.

I will fix the markdownlint, it is failing also elsewhere.

[MakisH]

@NiklasVin please rebase/merge from develop, the markdownlint issue is now fixed.

[NiklasVin]

Is this ready for review? Don't forget to add it into the README of the tutorial. I can generate some of the plots when reviewing.

I will fix the markdownlint, it is failing also elsewhere.

Yes, now this should be ready for review.

[MakisH]

@NiklasVin can you please enable edits by maintainers? It's a checkbox on the right.

[BenjaminRodenberg]

I checked the case with fluid-openfoam. Generally runs and VTK output looks good. Only a minor point is left + some readability comments.

[BenjaminRodenberg]

Suggested change

	# first, get displacement independent of x, only dependent on y and t
	# maximal displacement at flap tip should be 0.5
	# initially, flap's displacement is 0
	x_displ = np.minimum(((np.sin(3 * np.pi * t + np.arcsin(-0.95)) + 0.95) / 8) * y / flap_tip_y, 0.5 * y / flap_tip_y)
	# first, get displacement independent of x, only dependent on y and t
	# initially, flap's displacement is 0
	max_x_displacement = 0.5
	x_displ = np.minimum(((np.sin(3 * np.pi * t + np.arcsin(-0.95)) + 0.95) / 8) * y / flap_tip_y, max_x_displacement * y / flap_tip_y)

I would generally try to avoid raw numbers and rather use descriptive names. This often allows you to completely save some comments.

What does the 0.95, the 3 * np.pi and the /8 do? Generally, I think if the formula you are using here works we can keep it. But a brief comment about the general rationale behind the arcsin and sin would be helpful.

[NiklasVin]

I added some comments that hopefully clarify the idea behind the formula

[BenjaminRodenberg]

Thank for the changes! Looks good now. Let's get this merged 🎉