Hello dear all, I don’t know whether it is the right place to post what follows… I am trying to resolve a differential equation like (namely Rayleigh-Plesset eq): R*d²R/dt²+3/2*dR/dt=P where P is a constant, say. Previously I correctly resolved the Schrodinger equation for a particle in a 1D-box…

[image] aquarelle332: Does the code appear “correct” for you? i.e., Am I on the right way? No, you’re missing a ./R on the second term. This should be it: using OrdinaryDiffEq, Plots #Parameters P = 75.0 #pression 50 => collapse #initial conditions R₀ = [5.0] dR₀ = [1.0] tspan …

Thank you Chris for your reply. Sorry for my stupid error.

Hello dear all, Continuing my work on the Rayleigh-Plesset equation, I wrote this code: using OrdinaryDiffEq, Plots #SI units #external parameters Pₕ = 1.01325e5 #hydrostatic pressure (Pa) #Parameters (liquid = water) Pᵥ = 2.5e3 #vapour pressure (Pa) σ = 73.…

Oh, this is a debugging technique I always hope will work in Julia, and I think it does here! The Unitful.jl package provides the tools to define quantities with units in the type. I added types to all your parameters, evaluated the expression to be integrated, and got this error: using OrdinaryDif…

That looks promising! With DPRKN6(), I get the error below. Should this be reported as a bug? I played around a bit and couldn’t find an integrator for second order systems that didn’t have a problem like this, is there some integrator in particular that is known to work with Unitful? ERROR: LoadEr…

https://github.com/SciML/DifferentialEquations.jl/issues/393 It’s hard case because the element type of the array is not well-defined.

Thank you all very much for your help. I understand that there is a difficulty to compute directly the R-t curve as described above, i.e., in its dimensional form. Moreover I greatly appreciated to learn on Unitful.jl (… immediately installed and tested :wink:).

Independently of the solution of the RP equation as written above, the difference of units between right-side terms (m^3/s² vs m/s²) results from the precedence of multiplication on “/” division (it is not trivial because it depends on both scientific communities and the use of / vs ÷): (1/ρ*R) sho…

Finally the RP equation was solved in its dimensional form with DPRKN6(). For low values of acoustic pressure (< 1.28e5 Pa), there is no problem. [RP_test_2] For higher values, the collapse is very sharp and (of course) I get: Warning: dt <= dtmin. Aborting. There is either an error in your mod…

Trying to solve a second order differential equation. Your advices

Specific Domains Optimization (Mathematical)

ericphanson June 21, 2020, 11:17pm 6

I believe units should work with the pure Julia solvers; see this chart: https://docs.sciml.ai/stable/basics/compatibility_chart/#

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Trying to solve a second order differential equation. Your advices

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