Dropped Variable

[bradcarman]

The following produces the error: ERROR: UndefVarError: vol2₊rho not defined, which as can be seen is defined.
 

using ModelingToolkit
using ModelingToolkit: D_nounits as D, t_nounits as t
import ModelingToolkitStandardLibrary.Blocks as B
import ModelingToolkitStandardLibrary.Mechanical.Translational as T
import ModelingToolkitStandardLibrary.Hydraulic.IsothermalCompressible as IC
using OrdinaryDiffEq
using Plots


liquid_pressure(rho, rho_0, bulk) = (rho/rho_0 - 1)*bulk
gas_pressure(rho, rho_0, p_gas, rho_gas) = rho * ((0 - p_gas) / (rho_0 - rho_gas))
full_pressure(rho, rho_0, bulk, p_gas, rho_gas) = ifelse( rho >= rho_0, liquid_pressure(rho, rho_0, bulk), gas_pressure(rho, rho_0, p_gas, rho_gas))
    

@component function Volume(;

    #parameters
    area,
    direction = +1,
    x_int,
    name)

    pars = @parameters begin
        area = area
        x_int = x_int
        rho_0 = 1000
        bulk = 1e9
        p_gas = -1000
        rho_gas = 1
    end

    vars = @variables begin
        x(t)=x_int
        dx(t), [guess=0]
        p(t), [guess=0]
        f(t), [guess=0]
        rho(t), [guess=0]
        m(t), [guess=0]
        dm(t), [guess=0]
    end

    systems = @named begin
        port = IC.HydraulicPort()
        flange = T.MechanicalPort()
    end

    eqs = [
        # connectors
        port.p ~ p
        port.dm ~ dm
        flange.v * direction ~ dx
        flange.f * direction ~ -f

        # differentials
        D(x) ~ dx
        D(m) ~ dm

        # physics
            p ~ full_pressure(rho, rho_0, bulk, p_gas, rho_gas)

        f ~ p * area
        m ~ rho * x * area]

    return ODESystem(eqs, t, vars, pars; name, systems)
end

systems = @named begin
    fluid = IC.HydraulicFluid(; bulk_modulus = 1e9)

    src1 = IC.Pressure(;)
    src2 = IC.Pressure(;)

    vol1 = Volume(;area=0.01, direction = +1, x_int=0.1)
    vol2 = Volume(;area=0.01, direction = +1, x_int=0.1)

    mass = T.Mass(; m = 10)

    sin1 = B.Sine(; frequency = 0.5, amplitude = +0.5e5, offset = 10e5)
    sin2 = B.Sine(; frequency = 0.5, amplitude = -0.5e5, offset = 10e5)
end

eqs = [connect(fluid, src1.port)
        connect(fluid, src2.port)
        connect(src1.port, vol1.port)
        connect(src2.port, vol2.port)
        connect(vol1.flange, mass.flange, vol2.flange)
        connect(src1.p, sin1.output)
        connect(src2.p, sin2.output)]

initialization_eqs = [
    mass.s ~ 0.0
    mass.v ~ 0.0
]

@mtkbuild sys = ODESystem(eqs, t, [], []; systems, initialization_eqs)
prob = ODEProblem(sys, [], (0, 5))
sol = solve(prob) #ERROR: UndefVarError: `vol2₊rho` not defined

The current versions used are...

(Issue953) pkg> st
Status `C:\Work\Packages\Issue953\Project.toml`

  [961ee093] ModelingToolkit v9.60.0
  [16a59e39] ModelingToolkitStandardLibrary v2.19.0

  [1dea7af3] OrdinaryDiffEq v6.90.1
  [91a5bcdd] Plots v1.40.9

[ChrisRackauckas]

@AayushSabharwal was this covered by the hash consing fixes?

[AayushSabharwal]

It doesn't seem so. I'm yet to figure out if it's hashconsing related or not, but it does seem like it could be.

[AayushSabharwal]

This is an SCCNonlinearProblem issue. Passing use_scc=false to ODEProblem is a workaround.