# CG-Motion Macro, UDF, Reciprocating Motion CFD Simulation

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• The problem numerically simulates the moving object using ANSYS Fluent software.
• We design the 3-D model with the Design Modeler software.
• We mesh the model with ANSYS Meshing software, and the element number equals 143,423.
• We performed the simulation in an unsteady (Transient) state.
• We use the Dynamic Mesh model to define the moving object.
• We use the User-Defined Function (UDF) to define a transitional reciprocating motion.
• We use the CG-MOTION Macro for UDF.

## Description

In this project, we performed a numerical simulation using ANSYS Fluent software’s User-Defined Function (UDF). For this CFD product, we used CG-MOTION Macro to write UDF programming. We considered a simple computational zone. Inside this zone, there is a moving cubic object. We assume that the movement is transitional and reciprocating. This means that the moving object moves forward in a straight path and then returns to this path backward. So, we need to define a function that describes the horizontal movement in reciprocating mode.

First, we modeled the geometry in 3D with Design Modeler software. Then, we meshed the model with ANSYS Meshing software. Meshing is unstructured, and 143,423 cells are created. Finally, we numerically simulated the current model based on the CFD method by ANSYS Fluent software.

## Methodology (UDF)

In this project, we want an object to move within a domain. When an object inside the domain moves, the model mesh is deformed. Therefore, we use the Dynamic Mesh model.

We define the moving object as a Rigid Body in dynamic zones. When we use a rigid object, we need to define a motion (translational or rotational) for it. So, we define a User-Defined Function (UDF) to apply a translational movement to the object. We need to use the CG-Motion Macro (DEFINE_CG_MOTION macro) for this UDF.

In this UDF, we define the function according to the velocity value. Our body has one degree of freedom in movement. So, we set the rotational velocity equal to zero in all three directions and consider the value of the translational velocity equal to zero in two directions. We define the function of the velocity value in the x-axis direction as follows. ## Conclusion (UDF)

After completing the calculation, we will review the results. Since the dynamic mesh model is time-dependent, the simulation is performed with an unsteady (Transient) solver. So, we obtain the image of the model geometry at different simulation times. The images show that the object moves straight over time and returns to the same path again.We conclude that we performed the current numerical simulation correctly, and our UDF worked correctly.

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