OS-E: 0605 One Step Thermal Transient Stress Analysis

Demonstrates One Step Thermal Transient Stress Analysis using an exhaust manifold.



Figure 1. FE Model

Model Files

Refer to Access the Model Files to download the required model file(s).

The model file used in this example includes:

OSTTS_MANIFOLD.fem

Model Description

An engine exhaust manifold with conjugate heat transfer and structural deformation, constructed of gray cast iron, initially at 300 K. The manifold outer surface has a convective heat transfer coefficient of h = 6 W/m2 K at 300 K. The four inlets to the manifold are held at 500 K with air as the fluid at 5 m/s.

Temperature history is available after linear transient heat transfer analysis. In order to apply temperatures at multiple time steps to a structural analysis, one step transient thermal stress analysis should be used. It provides displacement and stress history for the duration of transient heat transfer.

In order to perform one step transient thermal stress analysis, you can define a linear transient heat transfer subcase and a static subcase. TEMPERATURE case control cards with HTIME keyword can be used in static subcase to choose selected or all time steps to perform stress analysis.
Tip: One step transient thermal stress analysis is to perform static analysis at all output time steps of transient heat transfer analysis. Transient heat transfer analysis outputs temperature results for every time step by default. This can result in a long simulation time and create large result files. It is recommended to use the skip factor on TSTEP card to write temperature results for a limited number of time steps, with which one step transient thermal stress analysis can still capture the stress history without added computational cost. When one step transient thermal stress analysis is a nonlinear static subcase, the number of time steps should be further limited. DLOAD is not supported.
FE Model
Element Types
CTETRA
The linear material properties are:
Property
Value
Young’s Modulus
1.38E11 PA
Poisson's Ratio
0.283
Initial Density
7817 Kg/m3

Stress versus Strain curve defined for MATS1 (for NLSTAT analysis only).

Results

From OSTTS (One Step Thermal Transient Stress) results, you can see the thermal results from the subcase 1 (Thermal Transient) as in Figure 2 and the Stress results from subcase 2 (NLSTAT) as in Figure 3.


Figure 2. Grid Temperature Contour from Subcase 1


Figure 3. Element Stress and Plastic Strain form Subcase 2


Figure 4. Stress and Temperature versus Time (Stress scaled to 1e-6)