Dynamic Mesh

What is Dynamic Mesh?

The dynamic mesh model can model flows where the domain’s shape changes with time due to motion on the domain boundaries. Combined with the six degrees of freedom (6 DOF) solver, dynamic mesh allows the trajectory of a moving object to be determined by the aero or hydrodynamic forces from the surrounding flow field. In ANSYS Fluent, the dynamic mesh capability is used to simulate problems with boundary motion, such as check valves and store separations. The building blocks for dynamic mesh capabilities within ANSYS FLUENT are three dynamic mesh schemes: smoothing, layering, and remeshing. Combining these three schemes is used to tackle the most challenging dynamic mesh problems. In fact, in problems where the specific region of fluid and its boundaries were displaced during the simulation, a moving mesh should be used to transform and move the cells in the mesh momentarily. The mesh Smoothing and Remeshing techniques provide instant mesh deformation capability. Remeshing is used when the mesh is more sensitive to mesh changes, which can be used to manually specify ranges of the maximum and minimum Length Scale for mesh changes. Generally, the dynamic mesh technique simulates models that require a moving mesh area. This model enables the spatial variation of the defined areas for fluid flow and allows the mesh of the region at the same time as the spatial location of the points and boundaries of the region changes compatibility with the place at the present moment. The dynamic mesh technique is composed of three steps: determining dynamic mesh methods, specifying specific modes with dynamic mesh options, and defining the dynamic mesh zone.

 

 

 

 

 

smoothing method

The smoothing method adjusts the mesh of an area by moving or deforming boundaries, but the number of nodes and connections does not change. In this type of mesh switching, the edges between the two mesh nodes are known as a mesh of interconnected springs in the spring-based smoothing method. The initial occupancy of the edges between the two mesh nodes before any boundary movement constitutes an equilibrium state of the meshes. Each displacement at a given boundary point produces a partial force for displacement along all the springs connected to the node, that is, the edges between two nodes, such as a pressure spring or a force pull to displace the node. Therefore, for the settings of this section, one must consider the coefficient of spring constant (denoting the value of the spring stiffness and having a value between zero and one) in the constant spring factor and the number of iterations in a duplicate equation derived from the state of the spring’s equilibrium in the number of iterations. Therefore, the software repeatedly resolves at each time step until the set number of iterations occurs or the solution reaches a convergence step whose convergence criterion is the value of the convergence tolerance.

 

layering method

The dynamic layering method is used when multilayers of cells are added to or subtracted from the cell layer adjacent to the moving boundary. This can be based on the layer height adjacent to the moving surface, meaning that the cell layer adjacent to the moving border is subdivided or merged with its subsequent cell layer and requires an ideal height limit. It is determined by the value of the split factor and the collapse factor, or it can be based on the ratio of the layer height adjacent to the moving boundary to its next layer. In this case, it also has a limit-to-height ratio, which is also dependent on the split ratio and the decay ratio.

 

remeshing method

The remeshing method is used for situations where the boundary displacement is large compared to the size of the local cells, which causes the cell quality to deteriorate; thus, the mesh becomes invalid. For example, a negative cell volume error may occur, eventually leading to a problem-solving divergence at the next step. Therefore, it compresses cells that disrupt the skewness value or critical size limit and locally remeshes the meshed cells or surfaces to address this problem. If the new cells satisfy the critical skewness value, the mesh is updated locally with the new cells; otherwise, the new cells are discarded, and the same old cells remain. Among remeshing methods, the local cell method only affects triangular and tetrahedral cells, the local face method can modify the tetrahedral and wedge cells in the boundary layer meshes, the face method applies to triangular and tetrahedral cells, and the 2.5D method only works on hexagonal meshes or wedge cells given the volume of triangular plane elements. To use these dynamic mesh methods, one must define the maximum and minimum longitudinal scales and the maximum plate and cell density values as the dynamic meshing intervals and the number of meshing times to achieve.

Specific states of motion can be defined in the options section and defined for the selected areas and borders in the dynamic mesh zones section. These specific modes include In-cylinder, 6 DOF, implicit update, and contact detection.

 

Six degrees of freedom (6-DOF)

Six degrees of freedom (6-DOF) are used to calculate external forces and moments (including aerodynamic and gravitational forces and moments) applied to components capable of moving the rigid object. These forces are obtained numerically by integrating the shear stress and pressure around the component surfaces. Extra loading forces such as injectable forces, thrust or propulsion forces, and torques produced by tubular springs can also be added to the degree of freedom. This multi-degree of freedom can be applied to many applications using the ANSYS Fluent software and a dynamic mesh method. In this case, the defined fields are the components of the mass tensors and moment of inertia. To define the 6DOF model, the properties of the multi-degree model must be adjusted.

The following project simulates the movement of a gulf ball movement in the air using the Dynamic Mesh method:

 

 

https://www.mr-cfd.com/shop/movement-of-the-golf-ball-due-to-the-impact-cfd-simulation/

 

MR-CFD, an Expert in the Field of Dynamic Mesh

With several years of experience simulating various problems in various CFD fields using ANSYS Fluent software, the MR-CFD team is ready to offer extensive modeling, meshing, and simulation services. Simulation Services for Dynamic mesh are categorized as follows:

• Six DOF dynamic mesh for modeling variation of location and angle of ship and boat in wavy sea situation
• Simulation of the tidal turbine using six DOF dynamic mesh methods (calculating rotation speed)
• Releasing of food box from airplane using six DOF dynamic method
• Simulation of globe valve movement during the time
• Train movement in the tunnel by variable velocity function in an urban tunnel
• Simulation of flap movement of an airplane wing
• Falling boxes into the water tank
• Modeling the underwater vehicle in Submerged and non-submerged situations
• Solid fuel combustion and modeling solid height level during burning fuel
• Fluid solid interaction of blood flow and vessel
• FSI simulation of blood flow pumping in a human heart
• Fluid solid interaction of airflow around building and finding final deflection and fluctuation (two-way and one-way FSI)
• Two and four-stroke internal combustion engine
• …

You may find the related products in the categories mentioned above in our CFD shop by clicking on the following link:

https://www.mr-cfd.com/product-category/fluent-modules/dynamic-mesh/

Our services are not limited to the mentioned subjects, and the MR-CFD team is ready to undertake different and challenging projects in the dynamic mesh field ordered by our customers. You can consult with our experts freely and without charge and order your project by sending the problem details to us using the following address.

[email protected]

By outsourcing your project to the MR-CFD as a CFD simulation freelancer, you will not only receive the related project’s files (Geometry, Mesh, …), but also you will be provided with an extensive tutorial video demonstrating how you can create the geometry, mesh, and define the needed settings(pre-processing, processing and post-processing) in the ANSYS Fluent software all by yourself. Additionally, post-technical support is available to clarify issues and ambiguities.