Dynamic Mesh Training Course in ANSYS Fluent

This session is very deep. It covers every button and rule in the Dynamic Mesh panel. We explain the core theory and how the solver actually works.

• Dynamic Mesh vs. MRF: We learn the golden rule: If the domain volume changes, you MUST use Dynamic Mesh. Sliding Mesh is only for rigid rotation.
• Physics Theory: We study the Arbitrary Lagrangian-Eulerian (ALE) formula and Grid Velocity. We learn the GCL rule: boundaries must not cross a cell center in one step.
• Zone Types: How to correctly assign Rigid Body, Deforming, and Stationary zones. We also cover Passive Zones.
• Smoothing Methods: A deep look at all four models. We cover Spring-Based Smoothing (Spring Constant Factor), Diffusion-Based (Diffusion Parameter), Linearly Elastic Solid, and Radial Basis Function (RBF). We also learn how to protect inflation layers using the Deform Adjacent Boundary Layer tool.
• Dynamic Layering: How to add or remove structured cells. We explain Height-Based vs. Ratio-Based, Ideal Cell Height, Split Factor, and Collapse Factor.
• Remeshing: Rebuilding bad cells. We cover Local Cell, Local Face, Region Face, and 2.5D Remeshing. We explain the rules: Minimum/Maximum Length Scale, Maximum Cell Skewness, and Size Remeshing Interval. We also look at Zone Remeshing for emergencies.
• Modern Tools: How to use Overset Mesh for zero-deformation overlapping grids, and the In-Cylinder model for engine kinematics (Crank Radius, RPM).
• 6DOF Solver Setup: Defining mass, moment of inertia tensor, and 1DOF translation/rotation constraints.
• Advanced Panel Options: We deeply cover Relative Motion (how to set up a Child zone that moves with a Parent zone). We also explain the Exclude Mesh Motion in Boundary Conditions box (when to use it for physical motion vs. numerical sliding).
• Stability & Troubleshooting: Using Implicit Update for light objects, using Events (Crank Angle), and a step-by-step guide to fixing the Negative Cell Volume error.

In this session, you learn how to write a Dynamic Mesh UDF code using Microsoft Visual Studio. We explain every data type and macro simply.

• UDF Basics: Setting up the C Compiler. Understanding udf.h and dynamesh_tools.h.
• Data Types & Macros: Learning Fluent’s special containers (real, Thread, Dynamic_Thread). Using Vector Math (NV_S, NV_MAG), Time macros (CURRENT_TIME), and Looping macros (begin_f_loop).
• DEFINE_CG_MOTION: Prescribed solid motion.
  
  • Example 1: Store separation (bomb drop) with acceleration and rotation.
  • Example 2: Steady-state motion (pseudo-transient).
• DEFINE_GEOM: Keeping nodes on a specific mathematical shape.
  
  • Example 3: Forcing nodes to follow a Parabola curve.
• DEFINE_GRID_MOTION: Deforming individual mesh nodes.
  
  • Example 4: Simulating a pulsing artery using sine wave equations and SET_DEFORMING_THREAD_FLAG.
• DEFINE_DYNAMIC_ZONE_PROPERTY: Changing settings during the run.
  
  • Example 5: Changing layering cell height for a piston near Top Dead Center.
• Contact & 6DOF UDFs:
  
  • Example 6: Store Separation with an ejector spring using DEFINE_SDOF_PROPERTIES.
  • Example 7: A 1-DOF rocket constrained to a rail. We also learn DEFINE_CONTACT to stop negative volumes when valves close.

This is a perfect example to show how solid motion interacts with free-surface liquids. It shows the greatness of combining a simple UDF with multiphase physics.

• What you will do: You will build a 2D water tank with a rotating paddle.
• The Magic: You will write a DEFINE_CG_MOTION code to move the wall back and forth like a sine wave.
• The Result: You will use Dynamic Layering perfectly. You will watch real water waves form using the VOF model. It proves you can control rigid motion precisely while the fluid domain adapts around it.

This is a masterpiece of Fluid-Structure Interaction (FSI). Simulating a closing valve is one of the hardest jobs in CFD because the mesh gap drops to zero, which usually crashes the software. This example shows you how to defeat that crash.

• What you will do: You will simulate a flexible reed valve that is pushed open and closed by water pressure.
• The Magic: You will use the 6DOF solver. You do not tell the valve when to open; the fluid pressure decides!
• The Result: You will combine three UDFs. You will use DEFINE_CONTACT to detect when the valve hits the wall. This stops the mesh from crushing to zero. It is a brilliant example of handling extreme mesh deformation safely.

This final project shows the true, supreme power of the 6DOF solver in ANSYS Fluent. It is a pure, physics-driven simulation with zero prescribed velocity.

• What you will do: You will simulate a complex Pelton turbine wheel with cups. A high-speed water jet will shoot at the cups.
• The Magic: You only define the mass and the Moment of Inertia of the heavy steel wheel using DEFINE_SDOF_PROPERTIES. You lock it to only rotate on one axis (1-DOF Rotation).
• The Result: When you run the simulation, the water hits the wheel. The force of the water makes the wheel spin. Fluent calculates the exact RPM and torque for you. This example proves you can simulate highly advanced, real-world machines perfectly.