TwoFluidPipe Reporting and Validation

This page describes how to extract engineering results from neqsim.process.equipment.pipeline.TwoFluidPipe for long multiphase flowlines and how to compare those results with external simulator or field data.

Current reporting status

TwoFluidPipe exposes detailed profile and summary APIs. The convenience class neqsim.process.equipment.pipeline.twophasepipe.reporting.TwoFluidPipeReport builds standard CSV, text, JSON, event, and benchmark comparison outputs from those APIs.

The recommended production workflow is:

Build and run the TwoFluidPipe model.
Extract spatial profiles from the pipe, or call TwoFluidPipeReport helper methods.
Add summary metrics and flow-assurance indicators.
Export to CSV/JSON for plotting, review, or comparison.
If available, compare against OLGA, LedaFlow, or field data using the benchmark harness.

Steady-state profile reporting

After pipe.run(), the following methods provide one value per pipe section:

API	Unit	Description
`getPositionProfile()`	m	Section midpoint positions
`getPressureProfile()`	Pa	Pressure profile
`getTemperatureProfile()`	K	Fluid temperature profile
`getTemperatureProfile("C")`	degC	Fluid temperature profile in Celsius
`getLiquidHoldupProfile()`	fraction	Total liquid holdup
`getWaterCutProfile()`	fraction	Water fraction of liquid
`getOilHoldupProfile()`	fraction	Oil holdup
`getWaterHoldupProfile()`	fraction	Water holdup
`getGasVelocityProfile()`	m/s	Gas velocity
`getLiquidVelocityProfile()`	m/s	Liquid velocity
`getOilVelocityProfile()`	m/s	Oil velocity when oil-water slip is active
`getWaterVelocityProfile()`	m/s	Water velocity when oil-water slip is active
`getOilWaterSlipProfile()`	m/s	Oil velocity minus water velocity
`getFlowRegimeProfile()`	enum	Gas-liquid flow regime by section
`getHeatTransferProfile()`	W/(m2 K)	Heat-transfer coefficient profile, when configured
`getSurfaceTemperatureProfile()`	K	Ambient/surface temperature profile, when configured

Example Java extraction:

pipe.run();

double[] x = pipe.getPositionProfile();
double[] pressureBara = pipe.getPressureProfile();
double[] temperatureC = pipe.getTemperatureProfile("C");
double[] liquidHoldup = pipe.getLiquidHoldupProfile();
double[] waterCut = pipe.getWaterCutProfile();
double[] gasVelocity = pipe.getGasVelocityProfile();
double[] liquidVelocity = pipe.getLiquidVelocityProfile();
PipeSection.FlowRegime[] regimes = pipe.getFlowRegimeProfile();

for (int i = 0; i < x.length; i++) {
  double pBara = pressureBara[i] * 1.0e-5;
  System.out.printf("%8.1f,%10.4f,%8.3f,%8.5f,%8.5f,%8.3f,%8.3f,%s%n",
      x[i], pBara, temperatureC[i], liquidHoldup[i], waterCut[i],
      gasVelocity[i], liquidVelocity[i], regimes[i]);
}

The same steady-state results can be exported directly:

String profileCsv = TwoFluidPipeReport.toSteadyStateProfileCsv(pipe);
String summaryText = TwoFluidPipeReport.toSummaryText(pipe);
String summaryJson = TwoFluidPipeReport.toSummaryJson(pipe);
String eventsCsv = TwoFluidPipeReport.toSlugAndFlowAssuranceCsv(pipe);

Transient reporting

For transient cases, call runTransient(dt, id) repeatedly and store a snapshot at the reporting interval required by the study. Do not store every internal sub-step for long pipelines unless high-frequency pressure waves or slug arrivals are being investigated.

UUID id = UUID.randomUUID();
double dt = 1.0;
int reportEvery = 10;

for (int step = 0; step < 3600; step++) {
  pipe.runTransient(dt, id);

  if (step % reportEvery == 0) {
    double time = pipe.getSimulationTime();
    double[] x = pipe.getPositionProfile();
    double[] p = pipe.getPressureProfile();
    double[] hL = pipe.getLiquidHoldupProfile();
    // Write one row per position with this time stamp.
  }
}

Recommended transient CSV columns:

time_s,position_m,pressure_bara,temperature_C,liquid_holdup,water_cut,
gas_velocity_m_s,liquid_velocity_m_s,oil_velocity_m_s,water_velocity_m_s,
flow_regime

Summary metrics

Use these methods for an executive summary or design report:

API	Description
`getInletPressure()`	Inlet pressure in bara
`getOutletPressure()`	Outlet pressure in bara
`getAverageLiquidHoldup()`	Volume-weighted average liquid holdup
`getDominantFlowRegime()`	Most frequent flow regime
`getAverageSuperficialGasVelocity()`	Average superficial gas velocity
`getAverageSuperficialLiquidVelocity()`	Average superficial liquid velocity
`getAverageMixtureDensity()`	Volume-weighted mixture density
`getMaxMixtureVelocity()`	Maximum mixture velocity
`getErosionalVelocity()`	API 14E erosional velocity
`getErosionalVelocityMargin(double)`	Maximum velocity divided by erosional velocity
`getFlowAnalysisSummary()`	Mid-pipe dimensionless flow summary
`getThermalSummary()`	Thermal model summary
`getSlugStatisticsSummary()`	Slug-tracking summary
`getHydrateRiskSections()`	Sections below configured hydrate temperature
`getWaxRiskSections()`	Sections below configured wax appearance temperature

Closure diagnostics

The two-fluid closure pass updates additional section-level diagnostics that are useful for model review and validation:

Section API	Description
`getOilWaterFlowRegime()`	Oil-water flow configuration
`isWaterWetting()`	Water-wetting indicator for corrosion screening
`isWaterDropoutRisk()`	Water dropout / accumulation risk
`getEntrainmentFraction()`	Estimated liquid entrainment fraction in annular/mist flow
`getEntrainedDropletDiameter()`	Characteristic entrained droplet diameter
`getSevereSluggingNumber()`	Riser-base stability indicator
`isSevereSlugPotential()`	Severe slugging risk flag

These values are stored on TwoFluidSection objects. They are not yet exposed as top-level TwoFluidPipe profile arrays, so a future report exporter should add profile accessors for them.

Benchmark comparison format

The validation harness reads external simulator or field data in this CSV format:

case,time_s,position_m,variable,value,abs_tolerance,rel_tolerance,source

Supported captured variables include:

pressure_pa
pressure_bara
temperature_k
liquid_holdup
water_cut
oil_holdup
water_holdup
gas_velocity_m_s
liquid_velocity_m_s
oil_velocity_m_s
water_velocity_m_s

Example use:

Path reference = Path.of("olga_export.csv");
List<TwoFluidBenchmarkHarness.BenchmarkPoint> points =
    TwoFluidBenchmarkHarness.readCsv(reference);

TwoFluidBenchmarkHarness.Snapshot snapshot = TwoFluidBenchmarkHarness.capture(pipe);
TwoFluidBenchmarkHarness.Comparison comparison =
    TwoFluidBenchmarkHarness.compare(snapshot, points);

if (!comparison.isPassed()) {
  throw new AssertionError(comparison.failureSummary());
}

For transient comparisons, capture and pass a list of snapshots. The harness interpolates in both time and position. Comparison results can be exported as CSV:

String comparisonCsv = TwoFluidPipeReport.toComparisonCsv(comparison);

Reporting recommendations for long flowlines

For long oil and gas flowlines, report at least:

Geometry and discretization: length, diameter, roughness, elevation profile, number of sections, mesh refinement strategy.
Boundary conditions: inlet stream, flow rate, outlet pressure, transient changes.
Thermodynamics: fluid model, flash interval, mass-transfer relaxation time, heat-transfer setup.
Pressure and temperature profiles.
Liquid holdup, water cut, phase velocity, and flow-regime profiles.
Slug statistics and terrain low-point liquid accumulation.
Hydrate/wax/thermal risk sections if thresholds are configured.
Erosional velocity margin and maximum mixture velocity.
Benchmark comparison table when OLGA, LedaFlow, or field measurements are available.

Gaps and planned improvements

The current API is adequate for engineering studies and benchmark development. A polished industrial report workflow should still add:

Top-level profile accessors for closure diagnostics such as entrainment fraction, water wetting, and severe slugging number.
Plot templates for pressure, temperature, holdup, water cut, flow regime, and slug events.
Direct import of OLGA/LedaFlow export formats where licensing allows it.