Learning Forum

[Yahya Balouchi]

Hello everyone

I am writing to seek your expertise and guidance in conducting a Computational Fluid Dynamics (CFD) simulation using Fluent software. The project at hand involves simulating the behavior of a pressurized Liquid inside the tank during sloshing caused by the six degrees of freedom (6DOF) motion of a ship.

The fluid in this scenario should be considered a multicomponent and multiphase system, as it consists of multiple components and can exist in both liquid and vapor phases. Tracking the interface and phase change for such a complex system poses significant challenges, and I require your valuable consultation or mentoring to navigate this intricate simulation successfully.

Specifically, I would appreciate guidance on the following aspects:

1. Multicomponent and multiphase modeling: Recommendations on the appropriate models and techniques to accurately represent the multicomponent nature of the fluid and capture the liquid-vapor phase transitions during sloshing.
2. Interface tracking: Strategies and best practices for tracking the interface between the liquid and vapor phases, which can be particularly challenging in a sloshing scenario with multiple components.
3. Coupling with 6DOF motion: Approaches to coupling the CFD simulation with the 6DOF motion of the ship, ensuring accurate representation of the sloshing dynamics.

[Rob]

That looks very detailed for a student project, depending on how long you have you may want to discuss reducing some of the complexity. 

Have a look at the various tutorials. You really only need 1DOF as you are moving the object rather than the flow influencing where it goes, you also need the motion path, if you don't know AQWA may be an option to find out what it is. 

Interface tracking would be the VOF model, but the mesh requirements if you're expecting breaking waves in the tank may become prohibitive on the Student licences (you have a cell count limit). 

Leave the phase change until you've got the above working. What drives the phase change? 

[Yahya Balouchi]

Really appreciate your response.

I want to make this simulation as close as possible to real conditions, where the liquid sloshes due to 6 degrees of freedom (6DOF) ship motion caused by sea waves, so considering only 1 degree of freedom (1DOF) motion is an oversimplification.

Additionally, I am aware that I need a motion path, and I considered AQWA for capturing the sloshing pattern of the fluid, but there is no Fluent-AQWA co-simulation since I want to analyze the thermodynamic behavior during sloshing. Also, AQWA cannot calculate fluid velocity to import to Fluent. So I have to move on from AQWA to a User-Defined Function (UDF) to simulate the sloshing pattern.

You have mentioned the Volume of Fluid (VOF) model to track the interface. Isn't the VOF model too simple to track multicomponent systems?

I cannot ignore phase change because there is a cryogenic fluid inside the tank. Despite the high insulation system, there is heat leakage from the environment into the system. Furthermore, violent sloshing affects the exchange of components between the two phases.

[Rob]

Sorry, I meant one way 6DOF - ie the motion of the tank is dependent on the vessel, the tank sloshing doesn't alter the vessel motion. So you just need a motion profile from AQWA. Note, most FPSOs and bulk carriers don't pitch, heave or yaw that much unless in a storm, when we did a test case for a webinar I think we finished up with the equivalent to a rowing boat in a hurricane! That content is most likely lost now, but look for sloshing on ansys.com

VOF is good to track a coherent free surface. You can also have multispecies for each phase if needed. If you're expecting the free surface to break review multifluid VOF. 

[Yahya Balouchi]

Thank you. Your response was very insightful.