Automating Thermal Analysis with Thermal DesktopTM

Thermal analysis is typically executed with multiple tools in a series of separate steps for performing radiation analysis, generating conduction and capacitance data, and for solving temperatures. This multitude of programs often leads to many user files that become unmanageable with their multitude, and the user often looses track as to which files go with which cases. In addition to combining the output from multiple programs, current processes often involve the user inputting various hand calculations into the math model to account for MLI/Insulation and contact conductance between entities. These calculations are not only tedious to make, but users often forget to update them when the geometry is changed. Several new features of Thermal Desktop are designed to automate some of the tedious tasks that thermal engineers now practice. To start with, Thermal Desktop is a single program that does radiation analysis, generates conduction/capacitance data and automates the building of a SINDA/FLUINT model to solve for temperatures. Some of these new features of Thermal Desktop are Radiation Analysis Groups, Property Aliases, MLI/Insulation Objects, Contact Conductance Objects, Model Browser, and the Case Set Manager. This paper describes the application and benefits of Thermal Desktop along with other unique features used to automate the thermal analysis process. INTRODUCTION: THERMAL DESKTOPTM Thermal DesktopTM is a PC/Cad based thermal analyzer. This system, while fully integrated into a neutral, low cost CAD system, and which utilizes both FEM and FD methods, does not compromise the needs of the thermal engineer. Rather, the features needed for concurrent thermal analysis are specifically addressed by combining traditional parametric surface based radiation and FD based conduction modeling with CAD and FEM methods. The use of flexible and familiar temperature solvers such as SINDA/ FLUINT is retained. The Thermal Desktop is implemented as a single application that: 1) Integrates CAD, FEM, FD, radiation (RadCAD®), and procedural modeling into a single low-cost environment. The environment simultaneously supports both "design geometry" used for the exact specification of hardware and "analysis geometry" which may (or may not) be a simplified abstraction of the design geometry used for thermal analysis. 2) Allows analysis geometry to be constructed using CAD operations: booleans, sweeping, blending, ruling, revolving, etc. 3) Allows design geometry to be imported from other CAD systems using IGES and/or DXF formats. 4) Permits design geometry to be used "as is" for analysis geometry, or used as "scaffolding" on which to construct suitable analysis geometry using interactive graphics operations. 5) Provides familiar types of thermal modeling surfaces such as cones, paraboloids, discs, rectangles, and cylinders using true mathematically precise representations (rather than as a collection of facets). These surfaces provide all of the functionality associated with TRASYS type surfaces but are directly integrated within the CAD environment. 6) Imports radiation models from TRASYS, Nevada, and IDEAS. 7) Integrates CAD methods for generating, resizing, and positioning surface types. 8) Integrates conduction/capacitance generation, surface insulation, radiation analysis, and contact conductance calculations. 9) Provides graphical construction of arbitrary nodes and conductors for abstract thermal network modeling. 10) Allows FE models to be created natively, or imported from popular FE programs such as NASTRAN, IDEAS, or FEMAP. 11) Provides efficient radiation analysis for common types of finite elements plus implements new types of curved finite elements for even faster radiation analysis. 12) Implements a new thermal sub node that simplifies a collection of complex nodes/conductors/finite elements into one or more SINDA/FLUINT nodes. 13) Provides graphical construction of procedural thermal model entities such heat loads and thermostats. 14) Outputs data in both SINDA/FLUINT and SINDA/G type formats. RADIATION ANALYSIS GROUPS Consider a model that has enclosures of some kind within it. This model could be a simple satellite that has electronics on the interior of some type of body, such as the satellite shown in Figure 1. Radiation plays an important part in the thermal analysis of this interior body. Radiation also plays an important part on the exterior part of this body, not only for radiation conductors, but also for heating rates from the sun and the planet. For a small model, the user could place all the surfaces in the same model and do radiation analyses. This overloads the analysis by calculating zero values for the heating rates on the interior of the satellite. A better way is to create two separate radiation models. Prior methods using programs such as TRASYS[1] and TSS[2] would require the user to build two completely separate models to analyze the radiation, one for the interior and one for the exterior. Thermal Desktop allows the user to build a single model and to place different sides of surfaces in different radiation analysis groups. This input is shown in Figure 2. The benefits of radiation analysis groups are: • Changes to the geometry such as scaling the body size are only performed once, thus eliminating the need to edit two models which lowers the risk of making an error. • For surfaces with the same node numbers on each side, the management is much simpler for the user because the node id is referenced from only one place. • Allows the program to make calculations more efficiently, thus doing them faster and also using less disk space to store the results. • All of the geometric data is stored in a single place. This not only creates an environment for simpler file management, but it also helps to eliminate modeling errors. • There is no limit to the number of radiation analysis groups in a model. Thus, models with multiple enclosures may easily be analyzed.