Winches¶

Winches in OASIS are mechanical drums that control mooring line lengths and tensions. They work in conjunction with mooring lines and a centralised controller that can position a floating body in the horizontal plane.

Concept¶

Each winch is attached to one end of a mooring line. By rotating its drum, the winch pays out or reels in cable, changing the effective line length. The controller coordinates multiple winches to achieve a target body position (surge, sway, yaw).

graph LR
    C[Controller] -->|torque τ| W1[Winch 1]
    C -->|torque τ| W2[Winch 2]
    C -->|torque τ| WN[Winch N]
    W1 -->|ΔL| L1[Line 1]
    W2 -->|ΔL| L2[Line 2]
    WN -->|ΔL| LN[Line N]
    L1 --- B[Body]
    L2 --- B
    LN --- B
    B -->|position| C

Winch Properties¶

Each winch is defined by 5 parameters:

Parameter	Symbol	Units	Description
Line index	—	—	Which mooring line (1-based)
Line end	—	—	1 = first node, 2 = last node
Moment of inertia	\(I\)	kg·m²	Drum inertia
Drum radius	\(r\)	m	Drum radius
Drag coefficient	\(d\)	N·s/rad	Rotational damping

Dynamics¶

The winch equation of motion balances tension torque, motor torque, and damping:

\[I \cdot \alpha = r \cdot F - \tau - d \cdot \omega\]

where:

\(F\) = line tension at the connected end
\(\tau\) = motor torque (from controller)
\(\omega\) = angular velocity
\(\alpha\) = angular acceleration

The line length change is proportional to drum rotation:

\[\Delta L = \frac{\Delta L_0 \cdot (L + r\theta)}{L}\]

Each winch adds 2 DOFs (\(\theta\), \(\omega\)) to the system state vector.

Controller¶

The WinchieController coordinates all winches to position the body using a state-space control law.

Controller Parameters¶

Parameter	Description
`indBody`	Index of the body being controlled (1-based)
`Ac, Bc, Cc, Dc`	Controller state-space coefficients
`Kc` (3 values)	Lead controller gains (surge, sway, yaw)
`Ki` (3 values)	Integral time gains
`Af, Bf, Cf`	Filter state-space coefficients
`Ar, Br, Cr, Dr`	Reference model state-space coefficients
`ur` (3 values)	Reference position setpoint (x, y, heading)
`Kw`	Winch gain
`t_start`	Time to start controlling [s]

Inversor Block¶

The inversor maps desired body forces (surge, sway, yaw) to individual winch tensions:

Type	Description
1	Straight-line mapping
2	Coefficient-based mapping

Constraints enforce maximum and minimum operational tensions.

Input Configuration¶

dataWinches.dat¶

8               // Number of winches
//////////////////
////////////////// New winchie [1]
//////////////////
1               // Line index (1-based)
2               // Line end (last node)
50.0            // Moment of inertia [kg·m²]
0.25            // Drum radius [m]
0.5             // Drag coefficient [N·s/rad]
//////////////////
////////////////// New winchie [2]
//////////////////
2               // Line index
2               // Line end
50.0            // Moment of inertia
0.25            // Radius
0.5             // Drag

dataWinchesController.dat¶

//////////////////
////////////////// Controller parameters
//////////////////
1                               // Body index (1-based)
0.3679 1 -0.6315 1             // [Ac Bc Cc Dc]
3900 5200 120000                // Kc gains
0.003 0.003 0.002               // Ki gains
0.9842 0.125 0.1263             // [Af Bf Cf]
0.9950 0.0625 0.0798 0.0       // [Ar Br Cr Dr]
4 3 0.08727                     // Reference position (x, y, yaw)
10000.0                         // Winch gain (Kw)
20.0                            // Start time [s]
//////////////////
////////////////// Inversor block inputs
//////////////////
1                               // Inversor type
6.0                             // Max tension [tons]
2.0                             // Min tension [tons]

Activation¶

Winches are automatically activated when any BCP in dataBCPs.dat has a non-zero winchId:

//////////////////
////////////////// New BCP [1] [Anchor] [1]
//////////////////
200.0 0.0 -50.0     // Position
1                    // Winch Id (>0 activates winch system)

This triggers loading of both dataWinches.dat and dataWinchesController.dat.

Output Files¶

File	Content
`WinchesTensions.txt`	Time + tension per winch
`WinchedLinesLengths.txt`	Time + line length per winch
`ControlForce.txt`	Time + 3 control force components
`ReferencePosition.txt`	Time + 3 reference position values

Example	Feature
`winches/horizontal_control`	Surge/sway/yaw positioning with state-space controller