orcaflex-static-debug-1-line-catenary-diverged

name	orcaflex-static-debug-1-line-catenary-diverged
description	Sub-skill of orcaflex-static-debug: 1. Line Catenary Diverged (+4).
version	1.0.0
category	engineering
type	reference
scripts_exempt	true

1. Line Catenary Diverged (+4)

1. Line Catenary Diverged

Symptoms:

• Error mentions "catenary" or "line diverged"
• Specific line name in error message

Causes:

• Line too short for connection points
• Incorrect end positions
• Incompatible line type properties

Solutions:

# Check line geometry
line = model["Failing_Line"]

# Get end positions
end_a_x, end_a_y, end_a_z = line.EndAX, line.EndAY, line.EndAZ
end_b_x, end_b_y, end_b_z = line.EndBX, line.EndBY, line.EndBZ

# Calculate required length (straight line minimum)
import math
min_length = math.sqrt(
    (end_b_x - end_a_x)**2 +
    (end_b_y - end_a_y)**2 +
    (end_b_z - end_a_z)**2
)

total_length = sum(line.Length)
print(f"Minimum length required: {min_length:.1f}m")
print(f"Total line length: {total_length:.1f}m")

if total_length < min_length * 1.1:
    print("Line is too short! Increase length by at least 10%")

2. Vessel Not in Equilibrium

Symptoms:

• "Vessel not in equilibrium"
• Large forces/moments on vessel

Causes:

• Mooring forces don't balance
• Incorrect initial position
• Missing or misconfigured lines

Solutions:

# Option 1: Let OrcaFlex find equilibrium position
vessel:
  IncludedInStatics: "Included"
  CalculatedPosition: "Yes"  # Let OrcaFlex calculate position

# Option 2: Fix vessel position
vessel:
  IncludedInStatics: "Included"
  InitialX: 0.0
  InitialY: 0.0
  InitialZ: 0.0  # At draft

3. Anchor Not at Seabed

Symptoms:

• "End not at seabed"
• Anchor position mismatch

Solutions:

# Ensure anchor is at seabed
water_depth = model.environment.WaterDepth

for line in lines:
    if line.EndAConnection == "Anchored":
        # Set anchor at seabed
        line.EndAZ = -water_depth

    if line.EndBConnection == "Anchored":
        line.EndBZ = -water_depth

4. Buoy/Structure Instability

Symptoms:

• 6D Buoy convergence failure
• Unrealistic rotations

Solutions:

# Add constraints during statics
6DBuoy:
  Name: "CALM_Buoy"
  # Fix orientation during statics
  Constraint1: "Fixed"    # Fix X rotation
  Constraint2: "Fixed"    # Fix Y rotation
  Constraint3: "Free"     # Allow Z rotation (yaw)

5. Zero-Tension Lines

Symptoms:

• Singular stiffness matrix
• Lines with zero or negative tension

Solutions:

# Check initial tensions
for line in lines:
    try:
        # Estimate initial tension from catenary
        weight_in_water = line.MassPerUnitLength * 9.81 * (1 - 1025/7850)
        length = sum(line.Length)

        # Very rough tension estimate
        estimated_tension = weight_in_water * length / 2

        if estimated_tension < 100:  # Very low tension
            print(f"Warning: {line.name} may have low tension")
            print("Consider:")
            print("  - Increasing line length")
            print("  - Adjusting end positions")
            print("  - Adding buoyancy")
    except:
        pass