Top > Application Examples > The Story Behind the Development of Cradle scSTREAM Moving Object Function

### Yuki Kanayama (Software Cradle, Software Engineering Dept.)The Story Behind the Development of Cradle scSTREAM Moving Object Function

With the improvement in computer performance, analysts expect to simulate more complex phenomena. One such analysis is moving objects. Most often, moving objects are analyzed using unstructured mesh software. Cradle's SC/Tetra, unstructured grid CFD software is capable of simulating moving objects. However, Cradle also enhanced the capabilities of the moving object function in their scSTREAM structured mesh software. We interviewed Mr. Kanayama, developer of the scSTREAM moving object function, to learn the story behind this development work.

Yuki Kanayama
Software Engineering Dept.

#### Versatility of the Moving Object Function

The moving object function is used to analyze fluid flow around moving objects. Moreover, the moving object function in scSTREAM can analyze both translation and rotation of objects. This also includes the combination of translation and rotation, and the calculation of velocity change. This function can be used as part of temperature, diffusive species, and multi-phase flow analyses. It can be used as part of a thermal environment analysis or to calculate the concentration of diffusive species around moving objects. In addition, a powerful capability is the analysis of thermal conductivity inside the moving object, which enables calculating the time varying temperature within the moving objects themselves.

#### How to Use the Moving Object Function in scSTREAM

1. Allocate moving objects
The attribute of the objects must be a finite element model. The object can be created by hexahedron or conical base elements in scSTREAM. If the object is imported as NASTRAN mesh data from an external file, the  data can be imported without any changes.

2. Generate the mesh
To solve for heat transfer within the moving object, the element material  properties must be set to "moving object." The mesh must be generated so that each moving object element contains one or more fluid element points.

3. Set boundary conditions
Use the Condition Wizard to set velocity and heat boundary conditions. If diffusive species are part of the calculations, their concentrations must also be specified.

4. Continue with regular set-up process
Steps 1-3 must be performed in addition to the regular steps used to solve ordinary thermal fluid problems. The conditions can be set using the Condition Wizard which  makes it simple and easy to set moving object conditions.

Using the moving object function in scSTREAM can enhance the realism and complexity of simulations in a low cost and simple manner. In addition, not only can object motion be simulated, but heat transfer between the contact faces of the moving objects and/or species diffusion can also be simulated.

There are instances where it can be difficult to generate a robust unstructured mesh for a moving object application. Meshing methods to simulate moving objects often use mesh stretching and/or overset mesh. If the object moves significantly, the distorted mesh can lead to unstable calculations and convergence difficulties. In contrast, the scSTREAM moving object function does not involve mesh distortion so movement can be simulated more freely. In addition, the structured mesh can be generated very quickly.

Figure 4. A forklift enters a refrigerated warehouse.

While the scSTREAM structured mesh moving object function has many positive features, there are still some restrictions. The time interval between calculation steps must be reasonable so the object doesn't move too far in one time step. If the time interval is too large, this can lead to unstable calculations. Cradle also recommends setting a base pressure point to improve calculation stability.

When scSTREAM Version 11 is released, it will have the ability to include radiation with the moving object function. This will enable analysis of moving objects influenced by thermal radiation such as a reflow furnace.

#### Closing Remarks

The moving object function in scSTREAM is purposely designed to be simple for the user to implement so that even less-experienced engineers will find it intuitive and easy to use. A user-friendly set-up Condition Wizard helps collect the necessary input data. As long as reasonable time interval is specified, the calculation can be fast and stable. Cradle continues to improve and enhance the moving object function in scSTREAM. With these advances, more difficult problems can be simulated, and realism and accuracy are improved.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of June 1, 2013 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.