MarineSystemsSim.jl

MarineSystemsSim.jl is a small, Fossen-inspired library for 3-DOF surface vessel models in Julia. The goals are:

• a clean 3-DOF surge–sway–yaw model in standard Fossen form,
• high performance (StaticArrays, cached mass matrix and inverse),
• easy integration with DifferentialEquations.jl and automatic differentiation.

What the package provides

Parameter types

• RigidBody3DOF: mass, yaw inertia, and CG position.
• QuadraticDamping3DOF: quadratic manoeuvring derivatives.
• HydroParams3DOF: added mass and damping matrices.
• VesselParams3DOF: rigid body + hydrodynamics in one bundle.
• Vessel3DOF: cached 3-DOF vessel model (implements AbstractVesselModel).

Kinematics and frames

• rotation_body_to_earth: body → Earth rotation matrix in the horizontal plane.
• kinematics: computes $\dot{\eta}$ from $\eta$ and $\nu$.

Core dynamics and interface

• AbstractVesselModel: DOF-agnostic vessel model interface.
• mass_matrix: builds $\mathbf{M} = \mathbf{M}_{RB} + \mathbf{M}_A$.
• damping_forces: evaluates $\mathbf{D}(\nu)\,\nu$.
• coriolis_forces: evaluates $\mathbf{C}(\nu)\,\nu$.
• body_dynamics: computes $\dot{\nu}$ from $\nu$, model, and $\tau$.
• vessel_dynamics: computes the full $[\,\dot{\eta}\;\dot{\nu}\,]$ state derivative.
• vessel_rhs!: in-place ODE right-hand side for use with DifferentialEquations.jl.

Fossen-style helpers

• hydroparams_fossen3dof: build HydroParams3DOF from manoeuvring derivatives.
• vesselparams_fossen3dof: assemble VesselParams3DOF from rigid-body + manoeuvring data.
• build_vessel3dof_fossen: convenience constructor for a cached 3-DOF model.

See:

• Getting started for a complete end-to-end example with an ODE solver.
• 3-DOF model for the equations and how they map to code.
• API reference for a grouped list of types and functions.

A tiny taste of the API

Here is a minimal sketch of how the pieces fit together. For a full runnable example (including an ODE solver), see Getting started.

using MarineSystemsSim
using StaticArrays

# 1. Rigid body
rb = RigidBody3DOF(m, Iz, xG)

# 2. Hydrodynamics (Fossen-style derivatives)
hydro = hydroparams_fossen3dof(
    Xudot, Yvdot, Yrdot, Nrdot,   # added mass
    Xu,    Yv,    Yr,    Nv,  Nr, # linear damping
    Xuu,   Yvv,   Nrr;            # quadratic damping
    Xv = Xv, Xr = Xr, Yu = Yu, Nu = Nu,
)

# 3. Bundle parameters and build cached model
params = VesselParams3DOF(rb, hydro)
model  = Vessel3DOF(params)  # cached M, M⁻¹ and D_lin

# 4. Evaluate state derivative once
X = @SVector [x, y, ψ, u, v, r]   # 6×1 state: [η; ν]
τ = @SVector [τx, τy, τψ]         # 3×1 generalised forces

Xdot = vessel_dynamics(X, model, τ)

This is the same structure you use inside an ODE right-hand side; the Getting started page shows the full workflow with OrdinaryDiffEq.jl and concrete numbers.