A Structural-Thermal-Optical-Performance (STOP) analysis is an interdisciplinary analysis used to verify optical requirements. It is performed to identify and solve design issues early before building hardware. In a traditional STOP analysis, data must flow sequentially from engineer to engineer, requiring multiple data handoffs, which are time-consuming. If the STOP analysis shows that design changes are necessary, trade studies can also be time-consuming.
NASA Langley Research Center engineers used Comet software to develop an abstract, reusable, CAD-based STOP analysis process for analyzing the High Spectral Resolution Lidar (HSRL) Michelson interferometer instrument. The primary goal of the STOP analysis was to reduce warping of the air arm mirror with changes in system temperature.
In the Comet modeling procedure, a STOP analysis process is built, the CAD model is imported, the environment is set, and the analysis process is run to create a thermal model, a structural model, and an optical model.
The Comet software communicates with existing physics tools and provides linkages between the tools. The new approach captures all discipline expertise in one place, and all models are able to use the same inputs and boundary conditions, which can reduce modeling errors. The models run sequentially, and complex geometric changes can be analyzed rapidly. A single engineer can run the entire analysis process, which allows overall analysis/design time to be reduced. This can lead to better design performance than the traditional method.
In the traditional method, changes made to the physical design (geometry) would require the engineers to manually update meshes and models, rerun the individual analyses, and re-do the data exchanges between the models to calculate the final results. Use of Comet automates these steps, and new geometry can be analyzed in a few hours; the traditional method can take up to a few days, depending on complexity of the changes.
Analytical checks were performed against the STOP model, and all results were physically accurate. STOP prediction comparisons to lab testing of an existing interferometer showed excellent agreement. After these checks, the model was then used to compare design changes to the existing interferometer to try and improve performance. The trade studies indicated that 10x better performance could be achieved with simple modifications. All trade studies were completed in about two weeks by one engineer using a single laptop computer.
Use of the Comet software to create automated, reusable processes expanded the design trade space, and reduced overall analysis time. The new method enabled multi-disciplinary understanding of how changes affect the entire system. All engineers can review results of another aspect of the analysis in the same model. For example, an optical engineer can use the model to determine the effects of thermal changes without help from the thermal engineer.
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