Fuel Valve Buildup Error Model

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Description

The Fuel Valve Buildup Error Model is a model that simulates Fuel Valve degradation due to impurity buildup over time. As fuel flows through the valve, contaminants accumulate in the mechanism, gradually reducing actuation speed and range of motion. When impurity reaches a threshold, the valve becomes fully seized. The model supports valve cycling operations to clear buildup, allowing operators to mitigate degradation through maintenance procedures.

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Example Use Cases

• Long-Duration Mission Simulation: Model gradual valve degradation over months or years of propellant flow.
• Maintenance Planning: Evaluate cycling frequency needed to keep valves operational.
• Failure Mode Analysis: Simulate stuck-valve scenarios for contingency planning.
• Training Scenarios: Force valves stuck at specific positions to train operators on anomaly response.

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Module Implementation

Impurity Accumulation

Impurity builds up proportionally to the fuel mass passing through the valve:

$$L_{\text{imp}}=m_{\text{total}}\cdot r_{\text{buildup}}$$

where $m_{\text{total}}$ is the cumulative fuel mass (kg) and $r_{\text{buildup}}$ is the impurity buildup rate. Each simulation tick when the valve is open:

$$m_{\text{total}}\leftarrow m_{\text{total}}+|\dot{m}|\cdot \Delta t$$

Degradation Effects

The degradation factor determines how severely the valve is affected:

$$d=\min \left(\frac{L_{\text{imp}}}{L_{\text{threshold}}},1.0\right)$$

where $L_{\text{threshold}}$ is the impurity threshold at which the valve seizes completely.

Actuation Speed: Reduced proportionally to degradation:

$$\omega ={\omega }_{\max }\cdot (1-d)$$

Range of Motion: Shrinks toward the current position as degradation increases. At full degradation ($d=1$), the valve is locked at its current position.

Cycling Recovery

During cycling operations, valve movement reduces impurity buildup:

$$L_{\text{imp}}\leftarrow \max \left(0,L_{\text{imp}}-|\Delta x|\cdot r_{\text{cycle}}\right)$$

where $|\Delta x|$ is the magnitude of position change and $r_{\text{cycle}}$ is the cycle reduction rate. This models the mechanical action of cycling dislodging accumulated contaminants.

Parameters

Parameter	Description	Default
ImpurityBuildupRate	Impurity accumulated per kg of fuel	0.001
ImpurityThreshold	Impurity level at which valve seizes	1.0
ImpurityCycleReductionRate	Impurity reduction per unit of movement	0.1
ImpurityLevel	Current impurity level (read-only)	0.0
TotalFuelPassed	Cumulative fuel mass in kg (read-only)	0.0
ForceStuck	Manual override to immediately seize valve	false

Force Stuck Override

When ForceStuck is enabled, the valve immediately locks at its current position regardless of impurity level. This sets actuation velocity to zero and clamps the range of motion to the current position, useful for simulating sudden mechanical failures or testing stuck-valve scenarios.

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Assumptions/Limitations

• Impurity accumulates only when the valve is open and fuel is flowing.
• Cycling is only effective while IsCycling is true on the parent valve.
• The model does not distinguish between different propellant types or contamination sources.
• Degradation affects both actuation speed and range of motion symmetrically.
• Recovery through cycling is instantaneous within each time step; there is no settling time modeled.