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Modia.jl

Stable The MIT License

The Modia Tutorial provides an introduction to Modia. The Modia3D Tutorial provides an introduction to use 3D components in Modia. Modia is part of ModiaSim.

Modia is an environment in form of a Julia package to model and simulate physical systems (electrical, mechanical, thermo-dynamical, etc.) described by differential and algebraic equations. A user defines a model on a high level with model components (like a mechanical body, an electrical resistance, or a pipe) that are physically connected together. A model component is constructed by expression = expression equations or by Julia structs/functions, such as the pre-defined Modia 3D-mechanical components. The defined model is symbolically processed (for example, equations might be analytically differentiated) with algorithms from package ModiaBase.jl. From the transformed model a Julia function is generated that is used to simulate the model with integrators from DifferentialEquations.jl. The basic type of the floating point variables is usually Float64, but can be set to any type FloatType<:AbstractFloat via @instantiateModel(..., FloatType = xxx), for example it can be set to Float32, DoubleFloat, Measurement{Float64}, StaticParticles{Float64,100}.

Modia includes a multibody program and 3D shapes for visualization and collision handling. It is then, for example, possible to model the 3D mechanical part of a robot with Modia multibody components and the electrical motors and gearboxes that are driving the joints with equation-based Modia components. Collision handling with elastic response calculation is performed for shapes that are defined with a contact material and have a convex geometry or are approximated by the convex hull of a concave geometry. The multibody program supports currently tree-structured multibody systems, but does not (yet) support kinematic loops.

Example videos:

Installation

The package is registered and is installed with (Julia >= 1.5 is required):

julia> ]add ModiaBase, ModiaLang, Modia

Modia exports all exported symbols of ModiaLang, DifferentialEquations and of Unitful and the essential exported symbols fo Modia3D.

Furthermore, one or more of the following packages should be installed in order to be able to generate plots:

julia> ]add ModiaPlot_PyPlot      # if plotting with PyPlot desired
        add ModiaPlot_GLMakie     # if plotting with GLMakie desired
        add ModiaPlot_WGLMakie    # if plotting with WGLMakie desired
        add ModiaPlot_CairoMakie  # if plotting with CairoMakie desired

It is recommended to also add the following packages, in order that all tests and examples can be executed in your standard environment:

julia> ]add Measurements, MonteCarloMeasurements, Distributions

Examples

The following equations describe a damped pendulum:

Pendulum-Equations

where phi is the rotation angle, omega the angular velocity, m the mass, L the rod length, d a damping constant, g the gravity constant and r the vector from the origin of the world system to the tip of the pendulum. These equations can be defined, simulated and plotted with (note, you can define models also without units, or remove units before the model is processed):

using Modia
@usingModiaPlot  # Use plot package defined with 
                 # ENV["MODIA_PLOT"] or Modia.usePlotPackage(..)

Pendulum = Model(
   L = 0.8u"m",
   m = 1.0u"kg",
   d = 0.5u"N*m*s/rad",
   g = 9.81u"m/s^2",
   phi = Var(init = 1.57*u"rad"),
   w   = Var(init = 0u"rad/s"),
   equations = :[
          w = der(phi)
        0.0 = m*L^2*der(w) + d*w + m*g*L*sin(phi)
          r = [L*cos(phi), -L*sin(phi)]
   ]
)

pendulum1 = @instantiateModel(Pendulum)
simulate!(pendulum1, Tsit5(), stopTime = 10.0u"s", log=true)
plot(pendulum1, [("phi", "w"); "r"], figure = 1)

The result is the following plot:

Pendulum-Figure

Simulation and plotting of the pendulum with normally distributed uncertainty added to some parameters is performed in the following way:

using Measurements

PendulumWithUncertainties = Pendulum | Map(L = (0.8 ± 0.2)u"m",
                                           m = (1.0 ± 0.2)u"kg",
                                           d = (0.5 ± 0.2)u"N*m*s/rad")

pendulum2 =  @instantiateModel(PendulumWithUncertainties,
                               FloatType = Measurement{Float64})

simulate!(pendulum2, Tsit5(), stopTime = 10.0u"s")
plot(pendulum2, [("phi", "w"); "r"], figure = 2)

resulting in the following plot where mean values are shown with thick lines and standard deviations as area around the mean values.

PendulumWithUncertainty

Main Developers

ModiaLang, ModiaBase

Modia3D

Andrea Neumayr, Martin Otter and Gerhard Hippmann,
DLR - Institute of System Dynamics and Control

License: MIT (expat)