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Fix rotational mechanics initialization and torque balance #486

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Merged
ChrisRackauckas merged 2 commits into from
Jul 13, 2026
Merged

Fix rotational mechanics initialization and torque balance #486

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55bc880
Define the piston test independent variable
ChrisRackauckas Jul 13, 2026
93ebf68
Fix rotational mechanics initialization and balance
ChrisRackauckas Jul 13, 2026
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1 change: 1 addition & 0 deletions src/Mechanical/Rotational/sensors.jl
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Expand Up @@ -83,6 +83,7 @@ Ideal sensor to measure the torque between two flanges (`= flange_a.tau`)
end

equations = Equation[
0 ~ flange_a.tau + flange_b.tau,
flange_a.phi ~ flange_b.phi,
tau.u ~ flange_a.tau,
]
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3 changes: 3 additions & 0 deletions test/piston.jl
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@@ -1,9 +1,12 @@
using ModelingToolkit, Test
using ModelingToolkitBase: @independent_variables
using SciCompDSL
using SciMLBase
using ModelingToolkitStandardLibrary.Thermal
using ModelingToolkitStandardLibrary.Blocks

@independent_variables t

# Tests ConvectiveResistor and includes FixedTemperature and ThermalResistor

@testset "Piston cylinder wall" begin
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12 changes: 9 additions & 3 deletions test/rotational.jl
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Expand Up @@ -104,7 +104,13 @@ end
@test SciMLBase.successful_retcode(sol)

prob = ODEProblem(
sys, [D(D(sys.inertia2.phi)) => 0.0, sys.spring.flange_b.phi => 0.0], (0, 1.0)
sys,
[
sys.inertia1.w => 0.0,
sys.inertia2.w => 0.0,
sys.spring.flange_b.phi => 0.0,
],
(0, 1.0)
)
sol = solve(prob, Rodas4())
@test SciMLBase.successful_retcode(sol)
Expand Down Expand Up @@ -287,7 +293,7 @@ end
@test all(sol[sys.inertia1.w] .== sol[sys.speed_sensor.w.u])
@test sol[sys.inertia2.w][end] ≈ 0 atol = 1.0e-3 # all energy has dissipated
@test all(sol[sys.rel_speed_sensor.w_rel.u] .== sol[sys.speed_sensor.w.u])
@test all(sol[sys.torque_sensor.tau.u] .== -sol[sys.inertia1.flange_b.tau])
@test all(sol[sys.torque_sensor.tau.u] .== -sol[sys.fixed.flange.tau])

prob = DAEProblem(
sys, D.(unknowns(sys)) .=> prob.f(sol.u[1], prob.p, 0.0), (0, 10.0)
Expand All @@ -298,7 +304,7 @@ end
@test all(sol[sys.inertia1.w] .== sol[sys.speed_sensor.w.u])
@test sol[sys.inertia2.w][end] ≈ 0 atol = 1.0e-3 # all energy has dissipated
@test all(sol[sys.rel_speed_sensor.w_rel.u] .== sol[sys.speed_sensor.w.u])
@test all(sol[sys.torque_sensor.tau.u] .== -sol[sys.inertia1.flange_b.tau])
@test all(sol[sys.torque_sensor.tau.u] .== -sol[sys.fixed.flange.tau])

# Plots.plot(sol; vars=[inertia1.w, inertia2.w])
end
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