Nonlinear Coupled Loads Analysis

ASD engineers have pioneered various nonlinear coupled loads analysis (CLA) capabilities, specifically, sliding component interface friction with stick and slip transients, component “deadband” interface transients and launch vehicle/launch mount separation transients. (see ASD Advanced Methods)

In 2005, a NASA risk mitigation initiative kicked off a Space Shuttle/payloads nonlinear transient CLA effort to simulate/investigate the impact of complex component interfaces involving deadbands. The initial nonlinear CLA, Shuttle mission 1E, which involved just a few deadbands, was executed with commercially available heritage tools and had resulted in what was deemed as “unrealistic” time-histories, i.e., time histories dominated by high frequency “numerical noise/chatter”.

NASA and its Cargo Mission Contractor, Lockheed Martin, began an investigation into ASD’s nonlinear CLA capability. For the same Space Shuttle mission 1E, ASD’s nonlinear CLA time-histories were shown to be highly realistic and free of any numerical noise/chatter. The solution conformed to the physical parameters and constraints defined in the analysis. After a rigorous verification process, ASD was selected by NASA and Lockheed Martin to perform all Space Shuttle/payloads nonlinear CLAs. Subsequent comparison of ASD nonlinear time-histories to test results further confirmed the validity of the ASD solution.

With the deadband sizes in these systems proving to be a significant contributor to component transient launch and landing environments, Space Shuttle/payloads nonlinear CLA quickly became a required mission critical analysis for flight hardware certification.

ASD’s nonlinear CLA capability represents a significant improvement over the existing commercial tool nonlinear capabilities. All ASD nonlinear analyses are performed with particular attention to system level modal accuracy, i.e., preserving accurate system level modal properties throughout all of the component interface transitions that are possible in a nonlinear system. In addition, the salient properties of particular nonlinearities are enforced throughout all transient simulations. For example, in a component interface “deadband” simulation, the components’ relative motion never exceeds the analyst’s specified limits and the interface forces are always compatible with the “deadband” state. The ASD nonlinear analysis methods result in numerically stable and physically realizable time histories, totally mitigating the need for time history post processing practices such as “frequency filtering”.

ASD’s nonlinear CLA experience and expertise has been incorporated into our commercially available ASD/CLAS software tool and includes nonlinearities such as friction, deadbands, one-sided deadbands (snubbers, bumpers), nonlinear springs, straps, and nonlinear dampers. The ASD/CLAS nonlinear module, ASD/NCLA, is licensed by industry leaders such as Lockheed Martin which have utilized it to conduct dozens of design and mission critical nonlinear CLAs to certify flight hardware and reduce mission risk. In fact, one of the most complex Space Shuttle/payloads nonlinear CLAs ever conducted was by Lockheed Martin utilizing ASD/CLAS (see
Customer Success Story).