Active Simulation Control
Active Simulation Control Highlights
- Defines logical triggers (conditions) that monitor flow quantities such as pressure, velocity, temperature, and fluid depth, then initiate actions when thresholds are met
- Control moving objects, boundary conditions, valves, squeeze pins, heat sources, droplet sources, and output frequency, all within a single uninterrupted simulation run
- Supports up to 10 conditions per event with AND/OR logic; global conditions can be shared across multiple events
- Applies across industries including metal casting, additive manufacturing, water and environmental engineering, and aerospace
How It Works
Active Simulation Control is built around two concepts: conditions and actions, grouped into events.
Conditions
Conditions monitor quantities from history probes, sampling volumes, flux surfaces, or general history outputs and evaluate whether a logical threshold has been crossed. For example: fluid depth at a probe exceeds 3.25 m, pressure at a probe drops below 1 atmosphere, or average velocity on a flux plane rises above a target value. Allowing conditions based on flow information from sampling volumes and flux surfaces, in addition to point probes, provides more robust control based on spatially averaged quantities rather than single-point measurements; for example, triggering fast shot when the average metal velocity across a flux plane at the gates exceeds a threshold, rather than relying on a single probe that could be affected by local flow variability. Up to 10 conditions can be grouped into a single event, with AND or OR logic controlling whether all conditions or any condition must be met to trigger the event.
Actions
Actions define what changes when an event fires. An action can modify virtually any controllable parameter in the simulation: the velocity of a moving object, the flow rate at a boundary, the output frequency, the state of a valve or vent, or the activation of a squeeze pin. Multiple actions can be assigned to a single event, and multiple events can be defined for a single object.
Conditions can be defined locally for each event, or as global conditions that are shared across multiple events, simplifying setup in complex multi-stage simulations.
What Active Simulation Control Can Control
Active Simulation Control events can be applied to:
- General Moving Objects: translational and angular velocity
- Boundary conditions: pressure, temperature, velocity, volume flow rate, thermal power, density, and scalar concentrations
- Mass and mass/momentum sources: flow rate, velocity, temperature, and scalar concentrations
- Droplet sources: velocity, temperature, pressure, density, radius, and emission interval
- Heat sources and sinks at geometry components
- Cooling channels: on/off control
- Phantom components (solidified fluid velocity): velocity control for continuous casting and additive manufacturing applications
- Squeeze pins: activation based on fluid temperature or solid fraction
- Valves and vents: on/off status, external pressure, and temperature
- Output control: restart, history, and selected data output intervals
- Simulation termination: end a run when a condition is met rather than at a fixed time
Applications
High Pressure Die Casting
In high pressure die casting (HPDC), the injection plunger must transition from slow shot to fast shot at precisely the right moment. Too early and air is entrained in the shot sleeve; too late and the metal front arrives cold. Active Simulation Control can monitor when metal reaches the gates using flux surfaces or sampling volumes and trigger the plunger velocity change automatically. Similarly, deceleration at end of fill to prevent impact pressure spikes can be triggered by metal reaching a specified position in the overflow system.
The PQ2 analysis model can also be applied to control velocity boundary conditions and mass inputs, making it possible to approximate the shot sleeve and plunger with simplified boundary conditions while still tracking whether the HPDC machine is operating within its performance envelope. This significantly reduces simulation time for large and complex castings, including giga-castings, while maintaining filling accuracy.
Gravity and Tilt Pour Casting
Gravity casting often uses a pouring basin to maintain a constant pressure head over the sprue. Active Simulation Control can monitor the fluid height in the basin and control the pour rate to keep it at a target level, preventing premature sprue exposure or overflow.
Continuous Casting
In continuous casting, Active Simulation Control manages the withdrawal velocity of the solidifying billet or slab, adjusting it based on solidified fraction measurements from sampling volumes placed at key positions in the mold. This allows the simulation to replicate the closed-loop control used in real continuous casting machines without prescribing a fixed withdrawal profile.
Active simulation control functionalities have been extended to include phantom objects, commonly used for continuous casting and additive manufacturing applications, as well as for cooling channels, used in casting and in many other thermal management applications.
Additive Manufacturing
In directed energy deposition and other additive manufacturing processes, phantom components represent the substrate or the build volume being deposited layer by layer. Active Simulation Control manages the velocity of these phantom components dynamically, allowing the simulation to track the advancing build front in response to process conditions rather than following a fixed motion profile.
Water and Environmental Engineering
Control gates in fish passages and hydraulic structures must respond to flow velocity measurements to maintain acceptable conditions for passage. Active Simulation Control can move gates or adjust boundary conditions based on velocity readings at probes located in fish resting areas or downstream monitoring points. In reservoir and dam simulations, Active Simulation Control can control spillway gates based on water surface elevation probes.
Aerospace and Cryogenics
Cryogenic propellant tanks must maintain ullage pressure within tight bounds throughout operation. Active Simulation Control can trigger pressurization when ullage pressure drops below a threshold and shut it off when the target is reached, accurately simulating the on/off cycling of pressurization systems without manual intervention between runs.
In this example, a pump (dark grey rectangle) in a cryogenic tank feed pipe pulls liquid oxygen from a propellant tank at a constant flow rate. As the liquid oxygen drains, a mass/momentum source (grey bar at top) is triggered by Active Simulation Control when the pressure in the ullage drops below a specified value. Pressurization is turned off when the ullage pressure rises above a specified value.
Filling and Mixing
In filling and mixing applications, Active Simulation Control can sequence multi-stage operations: detecting when a fill level is reached, retracting the filler tube, lowering the mixer, and starting rotation, all within a single simulation run. Probe variables attached to moving objects track their position and trigger the next stage automatically.
Active Simulation Control sequences a filling and mixing operation in FLOW-3D. The filler tube (pink) retracts when the fill level is reached, the mixing impeller (yellow) lowers into the fluid, and rotation begins when the impeller reaches its target depth. Marker dye concentration shows the mixing progress.