Logical Unit Operations

NeqSim provides several “logical” unit operations that do not represent physical equipment but are used to control the simulation, transfer data, or perform calculations. These include Calculator, Adjuster, SetPoint, and Recycle.

Calculator

The Calculator unit operation allows for custom calculations and data manipulation within a process simulation. It is useful for calculating derived properties or implementing simple control logic. Custom lambdas are the preferred hook for AI-generated logic because they let you keep the same simulator graph while swapping in new behavior at runtime.

Usage

Create: Calculator calc = new Calculator("name");
Add Inputs: calc.addInputVariable(inputUnit);
Set Output: calc.setOutputVariable(outputUnit);
Define Logic: Use setCalculationMethod with a lambda expression.

Example

Calculator energyCalc = new Calculator("Energy Calc");
energyCalc.addInputVariable(inletStream);
energyCalc.setOutputVariable(outletStream);

energyCalc.setCalculationMethod((inputs, output) -> {
    Stream in = (Stream) inputs.get(0);
    Stream out = (Stream) output;
    double energy = in.LCV() * in.getFlowRate("Sm3/hr");
    // Adjust outlet temperature based on energy
    out.setTemperature(300.0 + energy / 1e5, "K");
});

Declarative presets (energy balance, dew point targeting)

For frequently reused logic you can rely on CalculatorLibrary presets instead of hand-written lambdas. This makes it easier to reference calculations declaratively (e.g., from an AI agent or configuration file):

Calculator presetCalc = new Calculator("dew point targeter");
presetCalc.addInputVariable(feedStream);
presetCalc.setOutputVariable(targetStream);

// Apply by enum or by name
presetCalc.setCalculationMethod(CalculatorLibrary.preset(CalculatorLibrary.Preset.DEW_POINT_TARGETING));
// presetCalc.setCalculationMethod(CalculatorLibrary.byName("dewPointTargeting"));

Available presets:

ENERGY_BALANCE – matches the output stream enthalpy to the sum of input enthalpies by flashing at the output pressure.
DEW_POINT_TARGETING – sets the output stream temperature to the source stream dew point at the output pressure (optionally with a temperature margin via CalculatorLibrary.dewPointTargeting(double marginKelvin)).

Adjuster

The Adjuster is used to vary a parameter in one unit operation (the “adjusted variable”) to achieve a specific value in another unit operation (the “target variable”). It is essentially a single-variable solver. Use lambdas for the getters/setters to keep the hook flexible for AI-generated control logic.

Standard Usage

You can specify standard properties like “pressure”, “temperature”, “flow”, etc.

Adjuster adjuster = new Adjuster("Pressure Adjuster");
adjuster.setAdjustedVariable(inletStream, "flow", "kg/hr");
adjuster.setTargetVariable(outletStream, "pressure", 50.0, "bara");

Custom Target Calculation

You can also define a custom function to calculate the target value from the target equipment. This is useful if the variable you want to control is not a standard property.

adjuster.setTargetValueCalculator((equipment) -> {
    Stream s = (Stream) equipment;
    // Control based on a custom metric, e.g., Flow * Temperature
    return s.getFlowRate("kg/hr") * s.getTemperature("K");
});

Custom Adjusted Variable

You can also define custom logic for how to read and write the adjusted variable. This allows you to manipulate parameters that are not standard properties.

// Define how to read the current value of the adjusted variable
adjuster.setAdjustedValueGetter((equipment) -> {
    return ((Stream) equipment).getTemperature("K");
});

// Define how to set the new value of the adjusted variable
adjuster.setAdjustedValueSetter((equipment, val) -> {
    ((Stream) equipment).setTemperature(val, "K");
});

SetPoint

The SetPoint unit operation sets the value of a variable in a target unit operation equal to the value of a variable in a source unit operation. It is used for feed-forward control or copying values between equipment.

Standard Usage

SetPoint setPoint = new SetPoint("Pressure Copy");
setPoint.setSourceVariable(sourceStream, "pressure");
setPoint.setTargetVariable(targetStream, "pressure");

Supported Target Variables

Equipment Type	Supported Variables
`Stream`	`pressure`, `temperature`
`ThrottlingValve`	`pressure` (outlet)
`Compressor`	`pressure` (outlet)
`Pump`	`pressure` (outlet)
`Heater`/`Cooler`	`pressure`, `temperature`

Functional Interface Mode

Use setSourceValueCalculator to define a custom function that calculates the value to set on the target equipment. This provides full flexibility for non-linear relationships, unit conversions, or conditional logic.

Method Signature

Method	Type	Description
`setSourceValueCalculator`	`Function<ProcessEquipmentInterface, Double>`	Custom function to compute the value to set

Basic Example

SetPoint setPoint = new SetPoint("Custom SetPoint");
setPoint.setSourceVariable(sourceStream);
setPoint.setTargetVariable(targetStream, "pressure");

// Set target pressure based on source temperature: P = T / 10.0
setPoint.setSourceValueCalculator((equipment) -> {
    Stream s = (Stream) equipment;
    return s.getTemperature("K") / 10.0;
});

setPoint.run();
// Target pressure is now 30.0 bara (if source temp = 300 K)

Percentage Scaling Example

setPoint.setSourceValueCalculator((equipment) -> {
    Stream s = (Stream) equipment;
    // Set target pressure to be 10% of source pressure
    return s.getPressure("bara") * 0.1;
});

Computed Ratio Example

// Set compressor outlet pressure based on inlet conditions
SetPoint pressureRatio = new SetPoint("Pressure Ratio Control");
pressureRatio.setSourceVariable(compressorInlet);
pressureRatio.setTargetVariable(compressor, "pressure");

pressureRatio.setSourceValueCalculator((equipment) -> {
    Stream inlet = (Stream) equipment;
    double inletP = inlet.getPressure("bara");
    double inletT = inlet.getTemperature("K");
    // Higher inlet temperature = lower pressure ratio
    double ratio = 4.0 - (inletT - 300.0) * 0.01;
    return inletP * Math.max(ratio, 2.0);
});

When to Use Functional Mode

Use Case	Example
Non-linear relationships	Pressure = f(temperature, flow)
Unit conversions	Convert from source units to target units
Computed ratios	Set valve to percentage of max flow
Conditional logic	Different values based on operating mode
Multi-variable calculations	Value depends on multiple stream properties

Recycle

The Recycle unit operation is used to close loops in a process simulation. It compares the inlet and outlet streams of the recycle block and iterates until they converge within a specified tolerance.

Recycle recycle = new Recycle("Recycle");
recycle.addStream(recycleStream);
recycle.setTolerance(1e-6);