neqsim-dynamic-simulation

Dynamic Simulation Guidance

Guide for transient/dynamic process simulation in NeqSim.

When to Use Dynamic Simulation

• Startup and shutdown sequences
• Controller tuning and loop analysis
• Pressure relief / blowdown scenarios
• Level and pressure dynamics
• Compressor surge analysis
• Pipeline transients (slug flow)
• Emergency depressurization (EDP/ESD)
• P&ID-derived valve actions where pressure, level, controller response, or inventory release changes with time

For valve-action studies that start from P&ID symbols and plant data, also load neqsim-pid-process-operations to define the process graph, valve semantics, historian tag mapping, and event schedule before running runTransient.

Dynamic Simulation Architecture

NeqSim dynamic simulation advances a ProcessSystem with runTransient() (using the configured timestep) or runTransient(double dt, UUID id) (using an explicit timestep and calculation identifier). Pass a finite, positive timestep. Process and model entry points reject zero, negative, NaN, and infinite values before any area or equipment state changes. Adaptive stepping rejects invalid requests rather than clamping them.

Each timestep:

1. Flowsheet-wide settings are applied. Each setter unit receives exactly one transient call, applying its specification and advancing its own clock once.
2. Simulation time advances, then due events and field inputs are applied.
3. Equipment updates, including its thermodynamic calculations, run in insertion order or dependency-aware graph levels when parallel transient execution is enabled. Setter units are excluded from these explicit, semi-implicit, and parallel equipment passes. Steady-state algebraic equipment still evaluates on every requested pass, but its local clock advances once per non-null timestep calculation identifier. Reusing an identifier may refine a recycle without advancing physical time; use a new identifier for the next physical timestep.
4. Standalone controllers run; controllers actually executed inside equipment retain their equipment-specific timing for compatibility. Execution is coalesced by object identity and the timestep calculation identifier. Merely attaching a controller to equipment that does not execute it must not suppress the standalone update; repeated standalone registration runs once per step. ControllerDeviceBaseClass also makes repeated calls with one identifier idempotent, including semi-implicit equipment passes. Custom controllers integrated by equipment must implement the same identifier contract through hasRunTransient(UUID).
5. Measurement devices are sampled, alarms are evaluated, and history is stored.