Thermoelastic Analysis

Providing Temperature Results for Structural and Stress Analyses

C&R Thermal Desktop® allows a thermal engineer and structural engineer to work side by side sharing the same CAD information or design drawings, while both engineers build distinct models that are each honed for their individual needs: even when detailed thermoelastic deformation analysis is needed. In other words, Thermal Desktop's unique model mapping methods means that the thermal model need not be the same as, nor derived from, the structural model.

While Thermal Desktop can directly import all or part of structural FEM models, that step is not necessary to accomplish the accurate export of temperatures and other thermal data back to a structural code for thermal/structural analysis. Pitfalls of competing approaches are avoided, including requirements for "one-to-one" thermal-structural model correspondence and the errors associated with using the structural model to do the mapping.

Thermal Desktop allows an appropriate thermal model to be built using geometric surfaces and solids that are not faceted, and hence do not lose surface area needed for accurate thermal radiation, convection, and contact conductance calculations. It also allows a thermally appropriate mesh that avoids unnecessary details. Thermal Desktop users can create their thermal/fluid models using whatever combinations of finite elements, finite differences, and lumped parameters suit their needs.

When the time comes to produce temperatures for structural analyzers such as NASTRAN or ANSYS, those temperatures are produced at the desired structural element points using the most accurate representation possible: the shape functions and interpolation methods used to produce the temperatures in the first place. 

  Thermal Model Structural Model
Telescope Shell Thermal model of telescope shell Structural model of telescope shell with mapped temperatures
Mirror Support Thermal model of mirror support Structural model of mirror support with mapped temperatures

For example, the thermal models at the left were built independently from the corresponding structural models at the right. All models were generated from the same CAD information. The thermal model for the telescope shell uses mostly finite differences, while the thermal model for the mirror support uses mostly finite elements. In both cases, temperatures can be mapped to the independent structural model with a single command.

In fact, using the Dynamic Mode in Thermal Desktop, such mappings can be made "on the fly" as part of the analysis procedure during a transient analysis (e.g., "estimate deflections or thermal stresses every time slice") or as part a parametric sweep ("estimate thermoelastic responses of each design"). This is possible even if the structural model itself changes between each mapping. This "hands off" automated thermal/structural analysis enables design optimization, statistical design, worst case seeking, etc.

dispersed vs. coalesced front

Tuesday, June 26, 2018, 1-2pm PT, 4-5pm ET

This webinar describes flat-front modeling, including where it is useful and how it works. A flat-front assumption is a specialized two-phase flow method that is particularly useful in the priming (filling or re-filling with liquid) of gas-filled or evacuated lines. It also finds use in simulating the gas purging of liquid-filled lines, and in modeling vertical large-diameter piping.

Prerequisites: It is helpful to have a background in two-phase flow, and to have some previous experience with FloCAD Pipes.

Register here for this webinar

FloCAD model of a loop heat pipe

Since a significant portion of LHPs consists of simple tubing, they are more flexible and easier to integrate into thermal structures than their traditional linear cousins: constant conductance and variable conductance heat pipes (CCHPs, VCHPs). LHPs are also less constrained by orientation and able to transport more power. LHPs have been used successfully in many applications, and have become a proven tool for spacecraft thermal control systems.

However, LHPs are not simple, neither in the details of their evaporator and compensation chamber (CC) structures nor in their surprising range of behaviors. Furthermore, there are uncertainties in their performance that must be treated with safety factors and bracketing methods for design verification.

Fortunately, some of the authors of CRTech fluid analysis tools also happened to have been involved in the early days of LHP technology development, so it is no accident that Thermal Desktop ("TD") and FloCAD have the unique capabilities necessary to model LHPs. Some features are useful at a system level analysis (including preliminary design), and others are necessary to achieve a detailed level of simulation (transients, off-design, condenser gradients).

CRTech is offering a four-part webinar series on LHPs and approaches to modeling them. Each webinar is designed to be attended in the order they were presented. While the first webinar presumes little knowledge of LHPs or their analysis, for the last three webinars you are presumed to have a basic knowledge TD/FloCAD two-phase modeling.

Part 1 provides an overview of LHP operation and unique characteristics
Part 2 introduces system-level modeling of LHPs using TD/FloCAD.
Part 3 covers an important aspect of getting the right answers: back-conduction and core state variability.
Part 4 covers detailed modeling of LHPs in TD/FloCAD such that transient operations such as start-up, gravity assist, and thermostatic control can be simulated.