The latest release of Simcenter STAR-CCM+ (2502) introduces Stages support for Moving Reference Frame (MRF) and Rigid Body Motion (RBM). This enhancement automates the transition between steady-state and unsteady simulations, streamlining workflows for applications like marine propeller design, where both types of simulations are essential for performance analysis.
In the context of marine simulations, steady-state MRF simulations are typically used to evaluate propeller thrust and torque under fixed operating conditions, while unsteady RBM simulations enable the capture of transient effects such as tip vortex interactions and wake dynamics. By automating the transition from MRF to RBM, the new Stages feature saves significant time and effort while ensuring consistency across projects.
The Process of Staging Motions
Motion specifications are suitable for complex scenarios requiring precise control over how motion interacts with solver physics. Simcenter STAR-CCM+ offers two primary methods for defining motion on a region basis:
1. Motion Specifications: A versatile approach that allows users to define various types of motion, including:
- Morphing
- Rigid Rotations and Translations
- DFBI Motions
- Solver-Specific Motions like solid displacement or harmonic balance flutter
2.Direct Rotation: A simpler and more localized approach that directly defines rotational motion within a region. This option enables part subgrouping, where users can assign independent rotation values to different geometry parts of the same region.
For example, in a full-vehicle simulation, direct rotation motions allow you to assign rotation motion or reference frame directly from the region level. No need to define sperate motion in Tools > Motion.
However, only Direct Rotating option can stage a switch between reference frame and rigid body motion.
How Staging works with Direct Rotation Motions
To stage the transition between MRF and RBM, follow these steps:
- Activate Stages by creating two new stages: MRF and RBM.
- Stage the Motion Specification Option to define the appropriate motion settings for each stage.
- Select Motion Values:
- Use Direct Rotating Reference Frame Values for the MRF stage.
- Use Direct Rotating Motion Values for the RBM stage.
- Define Rotation Properties in the Physics values for each corresponding motion.
- Set Up a Simulation Operation to switch between the stages. This operation also enables effortless time scale adjustments after several revolutions, improving transient modeling accuracy.
For instance, steady-state simulations are often used to assess the impact of design changes on a vehicle’s drag, while unsteady simulations enable high-fidelity analysis to capture complex phenomena, such as impact of rotating rims on unsteady drag. In such workflows, the results from steady simulations are typically used to initialize unsteady simulations, significantly reducing convergence time.
A Marine Example: Propeller Simulation
Consider a marine application involving a propeller, using Stages and Direct Rotation Motions, we can now:
- Set up an initial stage for a steady-state MRF simulation to evaluate propeller performance metrics like thrust and torque. And quickly develop the flow field.
- Transition to an unsteady RBM stage where transient phenomena, such as wake interactions are captured.
- Define the final time step to achieve the desired temporal discretization to investigate tip vortex dynamics
This staged approach ensures seamless transitions and accurate physics throughout the simulation process.
What´s the catch? Incompatibility with DFBI Motion
Despite these advancements, the direct rotation of a region—a key feature of the MRF-to-RBM workflow—is incompatible with Dynamic Fluid Body Interaction (DFBI) motion. This limitation affects scenarios where DFBI is necessary to simulate ship dynamics, such as trim and heave or wave-induced motion.
Conclusion: Enhanced Automation, Balanced by Limitations
The new Stages and Direct Rotation Motions in Simcenter STAR-CCM+ significantly enhance automation and streamline workflows for steady-to-unsteady simulations. This would be invaluable for self-propulsion simulations, allowing us to manage complex transition with ease and precision.
However, the incompatibility of direct region rotation with DFBI motion highlights an important limitation for scenarios involving ship dynamics. By understanding these constraints the functionality is ideal for propeller simulation, fan simulation or other rotating but not floating objects.
As Simcenter STAR-CCM+ continues to evolve, addressing these limitations will further expand its utility, enabling you to tackle an even broader range of marine applications.
The Author
Florian Vesting, PhD
Contact: support@volupe.com
+46 768 51 23 46
