---

name: orcaflex-extreme-analysis description: Extract extreme response values with linked statistics from OrcaFlex simulations. Use for design load identification, max/min extraction with associated values, and extreme event characterization. version: 1.0.0 updated: 2026-01-17 category: offshore-engineering triggers:

• extreme analysis
• max tension
• linked statistics
• extreme values
• design loads
• maximum response
• associated values
• peak extraction

---

OrcaFlex Extreme Analysis Skill

Extract extreme response values with linked statistics for design load identification and extreme event characterization.

Version Metadata

version: 1.0.0
python_min_version: '3.10'
dependencies:
  orcaflex-modeling: '>=2.0.0,<3.0.0'
  orcaflex-post-processing: '>=1.0.0,<2.0.0'
orcaflex_version: '>=11.0'
compatibility:
  tested_python:
  - '3.10'
  - '3.11'
  - '3.12'
  - '3.13'
  os:
  - Windows
  - Linux
  - macOS

Changelog

[1.0.0] - 2026-01-17

Added:

• Initial release with linked statistics extraction
• Max/min value extraction with timestamps
• Associated variable extraction at extremes
• Batch processing across multiple simulations

When to Use

• Extracting maximum/minimum values from simulations
• Identifying design loads for structural analysis
• Finding associated values at extreme events
• Characterizing vessel motions at peak tensions
• Riser curvature at maximum tension conditions
• Wave conditions at extreme responses
• Multi-variable correlation at extremes

Prerequisites

• OrcaFlex simulation results (.sim files)
• Python environment with digitalmodel package installed
• Knowledge of variables to extract (object names, variable names)

Key Concepts

Linked Statistics

Linked statistics capture what other variables were doing when a primary variable reached its extreme:

At time T_max when Line1.Tension = MAX:
  - Vessel.Heave = ?
  - Vessel.Pitch = ?
  - Line1.Curvature = ?
  - Wave.Elevation = ?

This enables understanding of the physical conditions that caused the extreme.

Extreme Types

Statistic	Description
Max	Maximum value during simulation
Min	Minimum value during simulation
TimeOfMax	Time when maximum occurred
TimeOfMin	Time when minimum occurred
ValueAtMax	Primary variable's max value
ValueAtMin	Primary variable's min value
LinkedValueAtMax	Secondary variable value at primary's max time
LinkedValueAtMin	Secondary variable value at primary's min time

Configuration

Basic Extreme Extraction

# configs/extreme_analysis.yml

orcaflex:
  postprocess:
    linked_statistics:
      flag: true

      # Primary variable (extremes will be found for this)
      primary:
        object: "Mooring_Line_1"
        variable: "Effective Tension"

      # Linked variables (values at primary's extremes)
      linked:
        - object: "Vessel"
          variable: "Heave"
        - object: "Vessel"
          variable: "Pitch"
        - object: "Vessel"
          variable: "Roll"
        - object: "Vessel"
          variable: "X"

      # Statistics to extract
      statistics:
        - "Max"
        - "Min"
        - "TimeOfMax"
        - "TimeOfMin"
        - "LinkedValueAtMax"
        - "LinkedValueAtMin"

      output:
        format: csv
        directory: "results/extremes/"

Multi-Object Analysis

# configs/extreme_multi_object.yml

orcaflex:
  postprocess:
    linked_statistics:
      flag: true

      # Analyze multiple primary objects
      groups:
        - name: "mooring_tensions"
          primaries:
            - object: "Leg_1"
              variable: "Effective Tension"
            - object: "Leg_2"
              variable: "Effective Tension"
            - object: "Leg_3"
              variable: "Effective Tension"
          linked:
            - object: "CALM_Buoy"
              variable: "X"
            - object: "CALM_Buoy"
              variable: "Y"

        - name: "vessel_motions"
          primaries:
            - object: "Tanker"
              variable: "Heave"
            - object: "Tanker"
              variable: "Pitch"
          linked:
            - object: "Hawser"
              variable: "Effective Tension"

      output:
        format: csv
        directory: "results/extremes/"
        separate_files: true

Python API

Basic Linked Statistics

from digitalmodel.modules.orcaflex.opp_linkedstatistics import OPPLinkedStatistics

# Initialize extractor
extractor = OPPLinkedStatistics()

# Configure extraction
config = {
    "primary": {
        "object": "Mooring_Line_1",
        "variable": "Effective Tension"
    },
    "linked": [
        {"object": "Vessel", "variable": "Heave"},
        {"object": "Vessel", "variable": "Pitch"},
        {"object": "Vessel", "variable": "Roll"}
    ]
}

# Extract from simulation
results = extractor.extract_linked_statistics(
    sim_file="results/mooring_analysis.sim",
    config=config
)

# Access results
print(f"Max Tension: {results['Max']:.1f} kN")
print(f"Time of Max: {results['TimeOfMax']:.2f} s")
print(f"Heave at Max Tension: {results['LinkedValueAtMax']['Heave']:.2f} m")
print(f"Pitch at Max Tension: {results['LinkedValueAtMax']['Pitch']:.2f} deg")

Direct OrcFxAPI Usage

import OrcFxAPI
from pathlib import Path

def extract_extremes_with_linked(sim_file: str, config: dict) -> dict:
    """
    Extract extreme values with linked statistics.

    Args:
        sim_file: Path to .sim file
        config: Configuration dictionary

    Returns:
        Dictionary with extreme values and linked values
    """
    model = OrcFxAPI.Model(sim_file)

    # Get primary object
    primary_obj = model[config["primary"]["object"]]
    primary_var = config["primary"]["variable"]

    # Get time history
    time_history = primary_obj.TimeHistory(primary_var, period=None)
    times = primary_obj.SampleTimes(period=None)

    # Find extremes
    max_idx = time_history.argmax()
    min_idx = time_history.argmin()

    results = {
        "Max": float(time_history[max_idx]),
        "Min": float(time_history[min_idx]),
        "TimeOfMax": float(times[max_idx]),
        "TimeOfMin": float(times[min_idx]),
        "LinkedValueAtMax": {},
        "LinkedValueAtMin": {}
    }

    # Extract linked values at extreme times
    for linked_config in config["linked"]:
        linked_obj = model[linked_config["object"]]
        linked_var = linked_config["variable"]

        linked_history = linked_obj.TimeHistory(linked_var, period=None)

        results["LinkedValueAtMax"][linked_var] = float(linked_history[max_idx])
        results["LinkedValueAtMin"][linked_var] = float(linked_history[min_idx])

    return results

# Example usage
config = {
    "primary": {"object": "Line1", "variable": "Effective Tension"},
    "linked": [
        {"object": "Vessel", "variable": "Heave"},
        {"object": "Vessel", "variable": "Pitch"}
    ]
}

results = extract_extremes_with_linked("simulation.sim", config)

Batch Extreme Analysis

from digitalmodel.modules.orcaflex.opp_linkedstatistics import OPPLinkedStatistics
from pathlib import Path
import pandas as pd

def batch_extreme_analysis(sim_directory: str, config: dict) -> pd.DataFrame:
    """
    Extract extremes from multiple simulations.
    """
    extractor = OPPLinkedStatistics()

    sim_files = list(Path(sim_directory).glob("*.sim"))
    all_results = []

    for sim_file in sim_files:
        try:
            results = extractor.extract_linked_statistics(
                sim_file=str(sim_file),
                config=config
            )

            results["file"] = sim_file.stem
            all_results.append(results)

        except Exception as e:
            print(f"Error processing {sim_file}: {e}")

    # Convert to DataFrame
    df = pd.DataFrame(all_results)

    # Find overall extremes
    overall_max = df.loc[df["Max"].idxmax()]
    overall_min = df.loc[df["Min"].idxmin()]

    print(f"Overall Max: {overall_max['Max']:.1f} kN in {overall_max['file']}")
    print(f"Overall Min: {overall_min['Min']:.1f} kN in {overall_min['file']}")

    return df

# Run batch analysis
results_df = batch_extreme_analysis(
    sim_directory="results/.sim/",
    config=config
)
results_df.to_csv("extreme_summary.csv", index=False)

Range Graph Extremes

from digitalmodel.modules.orcaflex.opp_range_graph import OPPRangeGraph

# Extract range graph (min/max/mean along arc length)
range_extractor = OPPRangeGraph()

config = {
    "object": "Riser",
    "variables": ["Effective Tension", "Curvature", "Bend Moment"],
    "arc_length_range": [0, 1500]  # meters
}

range_data = range_extractor.extract_range_graph(
    sim_file="riser_analysis.sim",
    config=config
)

# Find critical location
max_curvature_idx = range_data["Curvature"]["Max"].argmax()
critical_arc_length = range_data["arc_length"][max_curvature_idx]

print(f"Maximum curvature at arc length: {critical_arc_length:.1f} m")
print(f"Curvature value: {range_data['Curvature']['Max'][max_curvature_idx]:.6f} 1/m")

Output Formats

Linked Statistics CSV

File,Primary_Object,Primary_Variable,Max,Min,TimeOfMax,TimeOfMin,Heave_AtMax,Pitch_AtMax,Roll_AtMax,Heave_AtMin,Pitch_AtMin,Roll_AtMin
case_001,Mooring_Line_1,Effective Tension,2450.5,320.1,1823.4,2156.7,3.2,-1.5,0.8,-2.1,0.9,-0.3
case_002,Mooring_Line_1,Effective Tension,2380.2,345.6,1567.2,1890.3,2.8,-1.2,0.5,-1.8,0.7,-0.2

Extreme Summary Report

{
  "simulation": "mooring_100yr.sim",
  "primary": {
    "object": "Mooring_Line_1",
    "variable": "Effective Tension",
    "units": "kN"
  },
  "extremes": {
    "maximum": {
      "value": 2450.5,
      "time": 1823.4,
      "linked_values": {
        "Vessel.Heave": 3.2,
        "Vessel.Pitch": -1.5,
        "Vessel.Roll": 0.8
      }
    },
    "minimum": {
      "value": 320.1,
      "time": 2156.7,
      "linked_values": {
        "Vessel.Heave": -2.1,
        "Vessel.Pitch": 0.9,
        "Vessel.Roll": -0.3
      }
    }
  }
}

Common Use Cases

1. Design Load Identification

# Find maximum tension for structural design
config = {
    "primary": {"object": "Riser", "variable": "Wall Tension"},
    "linked": [
        {"object": "Riser", "variable": "Curvature"},
        {"object": "Riser", "variable": "Bend Moment"}
    ]
}

results = extractor.extract_linked_statistics(sim_file, config)
design_tension = results["Max"] * 1.1  # Add 10% margin

2. VIV Characterization

# Characterize conditions at maximum amplitude
config = {
    "primary": {"object": "Riser", "variable": "Max Amplitude"},
    "linked": [
        {"object": "Environment", "variable": "Current Velocity"},
        {"object": "Riser", "variable": "Inline Frequency"}
    ]
}

3. Mooring Load Case

# Extract design load case for mooring
config = {
    "primary": {"object": "Hawser", "variable": "Effective Tension"},
    "linked": [
        {"object": "Tanker", "variable": "X"},
        {"object": "Tanker", "variable": "Y"},
        {"object": "Tanker", "variable": "Heading"}
    ]
}

# Results define the design load case

Best Practices

Variable Selection

1. Primary variable - Choose the most critical response
2. Linked variables - Include relevant causative factors
3. Physical correlation - Select variables that explain the extreme

Time Range

1. Exclude ramp-up - Skip initial transient period
2. Statistical period - Use 3-hour simulation for design
3. Multiple seeds - Consider seed variability

Reporting

1. Context - Include simulation parameters
2. Units - Always specify units
3. Uncertainty - Note seed sensitivity if applicable

Error Handling

try:
    results = extractor.extract_linked_statistics(sim_file, config)
except OrcFxAPI.OrcaFlexError as e:
    print(f"OrcaFlex error: {e}")
    print("Check object names and variable specifications")

except FileNotFoundError:
    print("Simulation file not found")

Related Skills

• orcaflex-post-processing - General post-processing
• orcaflex-operability - Multi-sea-state analysis
• orcaflex-results-comparison - Compare multiple results
• fatigue-analysis - Fatigue from time histories

References

• OrcaFlex Results: Linked Statistics
• OrcFxAPI Documentation
• Source: src/digitalmodel/modules/orcaflex/opp_linkedstatistics.py
• Source: src/digitalmodel/modules/orcaflex/opp_range_graph.py