Meco Control Parameters

Control parameters allow dynamic control of system behavior during simulation. They enable time-varying inputs, operational control, and system optimization of rocket engine performance.

Overview

The Meco Rocket Simulator supports 2 control parameter types:

Parameter Type	Behavior	Applications	Key Features
ControlParameter	Constant value	Fixed operating points	Simple constant control
ControlParameterTransition	Time-varying	Startup, throttling, shutdown	Smooth transitions

Control Target Categories

Control parameters can target different component categories:

Category	ID	Target Components	Available Ports
NODE	1	All node types	"cr" (O/F ratio), "cp"/"c" (pressure)
BRANCH	2	Valve branches	Valve position/opening
MACHINERY	3	All machinery	Speed, power, efficiency modifiers

ControlParameter

Overview

• Type: ControlParameter
• Purpose: Constant control value throughout simulation
• Applications: Fixed operating conditions, design point analysis

Parameters

• Basic Parameters:
  • name - Parameter name (string)
  • value - Control value (double)

• Target Parameters:
  • component_category - Target category: 1=NODE, 2=BRANCH, 3=MACHINERY (integer)
  • component - Target component name (string)
  • component_port - Target port identifier (string, NODE category only)

Node Control Ports

For component_category = 1 (NODE):

• cr - Oxidizer/Fuel ratio control (for gas generators)
• cp or c - Pressure control (for boundary conditions)

Example JSON

{
  "name": "GG O/F Ratio",
  "category": 6,
  "type": "ControlParameter",
  "value": 2.5,
  "component_category": 1,
  "component": "Gas Generator",
  "component_port": "cr"
}

{
  "name": "Main Valve Position",
  "category": 6,
  "type": "ControlParameter",
  "value": 0.85,
  "component_category": 2,
  "component": "Main Control Valve"
}

ControlParameterTransition

Overview

• Type: ControlParameterTransition
• Purpose: Time-varying control with smooth transitions between values
• Applications: Engine startup, throttling sequences, shutdown procedures

Parameters

• Basic Parameters:
  • name - Parameter name (string)
  • startValue - Initial value (double)
  • endValue - Final value (double)
  • midpoint - Transition midpoint time (double)
  • width - Transition width/duration (double)

• Target Parameters:
  • component_category - Target category: 1=NODE, 2=BRANCH, 3=MACHINERY (integer)
  • component - Target component name (string)
  • component_port - Target port identifier (string, NODE category only)

Transition Behavior

The parameter value smoothly transitions from startValue to endValue:

• Before Transition: Value = startValue
• During Transition: Smooth interpolation over width period centered on midpoint
• After Transition: Value = endValue

Timing Guidelines

• Midpoint: Center time of transition (simulation time units)
• Width: Total duration of transition
• Start Time: midpoint - width/2
• End Time: midpoint + width/2

Example JSON

{
  "name": "Startup Throttle",
  "category": 6,
  "type": "ControlParameterTransition",
  "startValue": 0.0,
  "endValue": 1.0,
  "midpoint": 2.0,
  "width": 1.0,
  "component_category": 3,
  "component": "Main Turbine"
}

Control Applications

Gas Generator Control

Oxidizer/Fuel ratio control for combustion optimization:

O/F Ratio Control

• Target: Gas generator nodes
• Port: "cr" (combustion ratio)
• Range: Typically 1.0-4.0 for O2/H2 systems
• Impact: Affects gas temperature and turbine performance

Example:

{
  "name": "GG O/F Control",
  "type": "ControlParameterTransition",
  "startValue": 1.5,
  "endValue": 2.8,
  "midpoint": 1.0,
  "width": 0.5,
  "component_category": 1,
  "component": "Gas Generator Head",
  "component_port": "cr"
}

Valve Control

Dynamic valve positioning for flow control:

Valve Position

• Target: BranchValve or BranchGasValve components
• Range: 0.0 (closed) to 1.0 (fully open)
• Impact: Controls flow rate and pressure drop

Example:

{
  "name": "Throttle Valve",
  "type": "ControlParameterTransition",
  "startValue": 0.1,
  "endValue": 0.9,
  "midpoint": 3.0,
  "width": 2.0,
  "component_category": 2,
  "component": "Main Throttle Valve"
}

Machinery Control

Control of rotating machinery parameters:

Speed Control

• Target: Pump or turbine components
• Applications: Speed governors, power control
• Range: Depends on machinery design limits

Power Control

• Target: Turbine components
• Applications: Power extraction control
• Range: 0.0 (no power) to 1.0 (full power)

Example:

{
  "name": "Turbine Power",
  "type": "ControlParameter",
  "value": 0.95,
  "component_category": 3,
  "component": "Main Turbine"
}

Pressure Control

Boundary condition pressure control:

Inlet Pressure

• Target: Inlet nodes (NodeInlet, NodeGasInlet)
• Port: "cp" or "c"
• Applications: Tank pressure, feed system pressure
• Units: Pascals (Pa)

Example:

{
  "name": "Tank Pressure",
  "type": "ControlParameter",
  "value": 2500000,
  "component_category": 1,
  "component": "LOX Tank Inlet",
  "component_port": "cp"
}

Engine Operation Sequences

Startup Sequence

Typical rocket engine startup control sequence:

1. Pre-ignition: Set initial valve positions and pressures
2. Ignition: Initiate gas generator or igniter
3. Ramp-up: Gradually increase O/F ratio and valve openings
4. Mainstage: Reach nominal operating conditions

Example Control Timeline:

Time 0-1s:    Valve positions: 0.0 → 0.2
Time 1-2s:    O/F ratio: 1.0 → 2.5
Time 2-3s:    Throttle valve: 0.2 → 0.9
Time 3s+:     Steady-state operation

Throttling Control

Dynamic thrust control during flight:

1. Throttle Command: External control input
2. Valve Response: Adjust main valve positions
3. O/F Adjustment: Maintain optimal mixture ratio
4. Pressure Control: Adjust feed system pressures

Shutdown Sequence

Safe engine shutdown procedure:

1. Throttle Down: Reduce valve openings
2. O/F Reduction: Lower gas generator power
3. Valve Closure: Sequential valve closing
4. Cutoff: Complete propellant cutoff

Design Guidelines

Transition Timing

• Smooth Transitions: Use adequate width to avoid abrupt changes
• System Response: Consider system time constants
• Stability: Avoid rapid changes that cause instability
• Physical Limits: Respect actuator speed and authority limits

Control Authority

• Full Range: Ensure control covers full operating range
• Margins: Provide control margin for off-nominal conditions
• Redundancy: Consider backup control methods
• Failure Modes: Design for safe failure positions

Parameter Coordination

• Sequence Coordination: Coordinate multiple parameter changes
• Interdependencies: Consider parameter interactions
• Optimization: Optimize control for performance and safety
• Verification: Validate control sequences through simulation

Integration with Simulation

Time Integration

• Control updates: Applied at each simulation time step
• Interpolation: Smooth interpolation between control points
• Event handling: Discrete events trigger control changes
• Real-time: Support for real-time control applications

Feedback Control

• Sensor Input: Use simulation outputs as control feedback
• Closed Loop: Implement feedback control algorithms
• Stability: Ensure control system stability
• Performance: Optimize control for desired response

Common Control Strategies

Open Loop Control

• Pre-programmed: Fixed control sequences
• Simple: Easy to implement and understand
• Robust: Not sensitive to measurement errors
• Applications: Startup sequences, nominal operations

Closed Loop Control

• Feedback: Uses system response for control decisions
• Adaptive: Responds to off-nominal conditions
• Complex: Requires control system design
• Applications: Thrust control, mixture ratio control

Feed-Forward Control

• Predictive: Anticipates system needs
• Fast Response: No delay from feedback
• Model-Based: Requires accurate system model
• Applications: Disturbance rejection, optimization

See Also

• Main Components Overview
• Node Components
• Branch Components
• Machinery Components
• Control Systems Engineering
• Rocket Engine Control Systems
• Dynamic Simulation Methods