Enlighten™ Lightweighting Optimisation
Introduction
Enlighten™ is a solver based on topometry for lightweighting, designed to tackle complex non-linear dynamic challenges like automotive crashworthiness.
Topometry has established itself as a robust tool in both linear and non-linear statics. Our contribution has been to adapt these methods to the non-linear dynamic realm through the creation of a bespoke optimisation solver. Topometry, which involves adjusting shell thicknesses, is particularly well-suited for designing thin-walled structures like body-in-white (BIW).
The solver can be used as a generative design tool to create new and novel design solutions, as a refining tool on more mature designs or anywhere in-between.
The challenge of converting optimisation outcomes into practical design solutions is well-known. Therefore, we have dedicated considerable effort to integrating geometric constraints that accommodate standard manufacturing processes.
Enlighten™ uses LS-Dyna and Radioss crash solvers.
Case-Study: Nissan Rogue Body-In-White
Background:
To benchmark, highlight and develop Enlighten’s optimisation capabilities Vortex-CAE created the following case-study. The aim was to benchmark a modern vehicle for multiple crash and performance attributes, extract the performance metrics, use these performance metrics to design a body-in-white through generative design that either met or exceeded those metrics. The results will be critiqued for mass-saving potential and design feasibility.
As a benchmark vehicle an LS-Dyna Nissan Rogue model provided by https://www.ccsa.gmu.edu/models/2020-nissan-rogue/ was selected. It should be noted that the baseline results are not validated but are expected to be suitably accurate for the purposes of this study.
Loadcases:
The following loadcases were chosen to cover a broad range of vehicle safety and performance attributes:
Frontal Impacts
Full Frontal Barrier 0 Degrees (FFB 0)
Full Frontal Barrier 30 Degress (FFB 30)
Offset Deformable Barrier (ODB)
Small Offset Rigid Barrier (SORB)
Frontal Centre Pole (FCP)
Side Impacts
Front Door Deformable Barrier (FDDB)
Rear Door Deformable Barrier (RDDB)
Rear Impact
Rear Deformable Barrier (RDB)
Durability and Abuse
Kerb Strike Rear Wheel
Kerb Strike Front Wheel
Additional
Roof Crush
Seatbelt Anchorage (SBA)
Torsional Stiffness and Strength
Assessment Criteria
Frontal Impacts:
Energy absorbing zone is optimised to ensure correct crush as measured at front seat rails
Safety cell is optimised to ensure intrusions and deformations are kept below baseline
Side Impacts:
Barrier intrusion into vehicle is kept below baseline
Safety cell deformations are below baseline
Rear Impacts:
Energy absorbing zone is optimised to ensure correct intrusion between barrier and rear seats
Safety cell is optimised to ensure all intrusions and general deformations are kept below baseline
Durability and Abuse
Subframes and suspension remain firmly attached to Body-In-White
Additional
Roof Crush, the peak roof strength should meet or exceed baseline
Seatbelt Anchorage (SBA), the deflections at all seatbelt anchorage points should be kept below baseline
Torsional Stiffness and Strength, the peak reaction forces at all suspension mounts should meet or exceed baseline
Design Volumes
The primary structures were removed from the baseline model and replaced with optimisation design volumes. The optimisation model uses two design volumes. One design volume is used to A-surface components such as body panels, design volume erosion is therefore disabled. The second design volume is a space-filling scaffold that is used to generate new and novel structures, design volume erosion is enabled.
Geometric constraints
The design volume for the A-surface has gauge limits between 0.5mm and 10.5mm with discrete steps of 2mm. Erosion disabled.
The design volume for the generative design has gauge limits between 0.5mm and 10.5mm with discrete steps of 2mm. Erosion enabled.
Materials
While Enlighten can used multiple materials in it’s analysis, for simplicity a 800MPa UTS steel model was applied to both design volumes
The remaining vehicle components did not have their material definitions modified.
Design Volume 1
Design Volume 2
Iteration 0
Additional Modules
Results in progress
To solve OpenRadioss was used as the CAE solver. A total of 448 CPU’s on Vortex CAE’s HPC were allocated to this problem. This section will be updated when the optimisation is complete in a couple of weeks (19/05/24). It is possible however to share the results of iteration 9 as early indication for where structure would be created. The heatmap demonstrates thick sections (pink) and thin sections (blue). Design volume 2 has started to erode. We expect that approximately 50 iterations will be required for full convergence.
Iteration 9/50 - Work in Progress
Observations
By iteration 9, clear and familiar primary structures are notably forming. Specifically:
Upper and lower load paths are visible in the frontal crush zone, accompanied by the development of a bumper beam.
A significant amount of material is being allocated to the rocker region.
The CANT rail is starting to take shape, providing additional strength at the top of the A-Pillar.
Floor cross-members are emerging for SBA attachment, complemented by B and C-Pillar reinforcements.
Reinforcement of the upper B-Pillar is underway to satisfy Roof Crush requirements.
Brackets for subframe and suspension attachments are beginning to form.
The rear crash zone is materializing, along with the rear bumper beam.
Current Conclusion
The baseline mass was recorded at 1400kg, while the current mass for iteration 9 stands at approximately 750kg. However, this figure is expected to fluctuate by plus or minus 100kg, suggesting a considerable potential for mass reduction.
Although the selected load cases typically account for a significant portion of a vehicle's total mass, it's crucial to acknowledge that the vehicle will possess other structural features that will necessitate additional mass to comply with requirements. Furthermore, there will be efficiency losses when the structure is subjected to Design for Manufacture and Assembly (DFMA) processes.
Updates will be made to this page in the coming days with the most recent iterations (19/05/24).