Silent Dynamics

Month: February 2022

Exporting STEP files with named surfaces from PTC Creo

When preparing geometry for numerical simulations, it is often required to mark individual surfaces in the model. These surfaces can then be used, for example, as an inlet or for applying forces and pressures in a structural simulation.

The STEP format supports named entities. The question is: how to set the names in the CAD program? And how to achieve that they are actually stored in the STEP file? In the following, these questions are answered for the software PTC Creo.

Name Surfaces

Select “File” > “Prepare” and then “Open Model Properties”, then select “Names” in the model properties dialog:

You can then select faces by clicking on them and enter a name in the dialog box:

Exporting Names in STEP File

If you export an STP file with the default settings, the names will not be stored in the file. You need to change the export setup for them to be kept.

Open the settings dialog via “File” > “Options”. Then navigate to “Configuration Editor”. Here, you need to add the option “intf_out_assign_names” and set it to “user_name”.

Accessing Named Entities in ISCAD

It is now possible to access faces through their assigned names, e.g., in ISCAD. Once the STEP file is imported, its sub-entities can be explored by typing Ctrl-I (see below). The named faces appear as “face_” in the hierarchy:

February 28, 2022
Vector Analysis in the Bash Shell
When performing preparatory operations for CFD or FEM analyses, for example, it is often necessary to specify vector parameters. Vector constants are easy to handle:
```
myMesh --direction "$1 0 0"
```
However, it quickly becomes complicated if the vectors have to be manipulated, e.g. multiplied by scalars or rotated.

A powerful solution is to use the Matlab Octave clone to perform the operations. Two features of Octave are useful in this context:
- the command-line option “--eval” to specify the expression to handle
- The `disp` function outputs results in a plain format on a single line.
Here's the translation: An example:
```
DIR="1 0 0"
VELOCITY=$(octave --eval "disp( 11.*[$DIR] )")

myMesh --direction "$DIR"
mySolver --velocity "$VELOCITY"
```
More complicated operations are possible, though one needs to take care to produce line vectors as results. Rotation is an example:
```
DIR="1 0 0"
ANG=45

DIR_ROT=$(octave --eval "pkg load linear-algebra; disp( (rotv([0 0 1], $ANG*pi/180)*[$DIR]')' )")

myMesh --direction "$DIR_ROT"
```
February 28, 2022
Simulation of Gas Removal from Liquids with OpenFOAM
Lack of space and high cost pressure ultimately lead to increasingly complex and smaller hydraulic tanks. This results in a drastic reduction of air separation in the tank – and thus to an increased amount of free air in the hydraulic system.

In hydraulic systems, free air remains a technical challenge today. As long as the air is dissolved in the oil, it does not alter its properties.

Unresolved air, i.e., air bubbles, cause:

Corrosion on pumps and controls
Reduced efficiency of pumps and hydraulic motors, increased compressibility and thus possible jerky movements in the drive. In addition, there is
- Accelerated oil aging
- Noise increase
- Damage to components (e.g., cavitation)
- etc.
Air enters the system during assembly, through leaks in the negative pressure area, and when oil flows back into the tank. Depending on the separation efficiency of the filter-tank system, the air rises slowly in the tank and is drawn back in by the pump.

Simulation in Air-Liquid Tanks

Silentdynamics uses InsightCAE to perform a series of simulations of dispersed gas bubbles in a degassing tank. The application of the solver twoPhaseEulerFoam enables the unsteady-state tracking of the gas phase, integral values of air at the outlets, and the overall quality of the degassing device.

As an example, a simple degassing example is presented. One inlet and two outlets, including a wear plate in the middle. The oil-gas mixture moves over the wear plate for degassing.

After setting the gas-oil dispersion boundary conditions such as gas bubble size, mixing coefficients, phase properties, etc., the simulation was able to proceed with twoPhaseEulerFoam to be started.

Using the advanced solver settings within InsightCAE allows for large time steps to be taken, enabling simulations to be completed in a reasonable amount of time.

Iso-surfaces of at a gas phase fraction of 1%.

The modification of the degassing tank's geometry using numerical simulation leads to a sufficient degassing process of the hydraulic oil.
February 28, 2022
OpenFOAM Electronic Cooling Simulation

Limited space and high power consumption ultimately lead to an innovative cooling design for a wide range of PCBs. The arrangement of power supplies, the dimensions of heatsinks, and the design of the outer casing are gaining importance. Thermal simulations during the PCB design process help to avoid overheating problems in the later production phase.

Different materials, the combination of heat conduction, convection, and radiation in solids and air result in a rather complex thermal simulation. Setting material properties, boundary conditions, solver settings, and coupling areas often takes a significant amount of time.

As an example, a typical printed circuit board (PCB) with its components is presented.

Thermal simulation

Silentdynamics managed to set up the simulation using OpenFOAM thermal solvers (chtMultiRegionFoam, chtMultiRegionSimpleFoam) to bundle within the InsightCAE framework for rapid preprocessing.

The import of CAD files for each component and the optimized process of parallel meshing of the regions with snappyHexMesh are essential for the conservative thermal coupling of the different regions.

Please note that the use of different Vias, copper wires, thermal interface materials, or other heat-related points must be considered in the simulation model. With the help of region modeling, CellSets, and layer definitions for each component, all necessary thermal properties can be taken into account.

The ability to define special placeholders makes the setup of the CHT simulation nearly automated.

Furthermore, improved treatment of thermal radiation and optimized solver settings form the basis for stable and convergent simulations.

February 25, 2022