Computer Simulation Analysis
Computer simulation analysis also known as finite element analysis has become an important tool in the development and assessment of crash barrier systems. Recent advances in computer hardware and finite element methodologies have given developers of crash barriers the ability to investigate complex dynamic problems involving vehicular impacts into safety barrier systems. Finite element analysis has been used extensively to evaluate both vehicle components and crashworthiness of safety barriers and hardware.
Most computer simulation models use the LS-DYNA finite element code. LS-DYNA is a general purpose, explicit finite element code and is widely used to solve nonlinear, dynamic response of three-dimensional problems and is capable of capturing complex interactions and dynamic load-time history responses that occur when a vehicle impacts a barrier system.
To ensure confidence in the simulation results, the model needs to be appropriately verified with known full-scale crash test results.
The Verification & Validation Process
NCHRP Report 179 provides a process of numerical verification and validation of computer simulation models as follows:
- Identify the baseline experiment.
- Build the computational model of the baseline experiment.
- Use the model to simulate the baseline experiment.
- Validate the model by comparing the simulation results to the physical test results.
- Modify the model to represent incremental improvements.
- Use the model to predict the performance of the incremental improvement, and
- Evaluate the performance of the incrementally modified device.
Frequently Asked Questions
When is it appropriate to undertake computer simulation analysis?
Computer simulation analysis may be used during the development phase of a safety barrier system prior to undertaking full-scale crash testing. Once the system has been crash tested, simulations may be performed on installation variants to assess vehicle and barrier behaviour.
Can computer simulation analysis be used to substitute crash tests?
No. Compliance of a road safety barrier system to a crash test standard should be undertaken using full-scale crash testing.
Does ASBAP accept computer simulation analysis?
Yes. ASBAP will consider simulations as a method of engineering justification, as long as the simulation model is not being used to extrapolate significantly beyond the full-scale crash test data, and that accurate validation and verification of the model has been undertaken in accordance with NCHRP Report 179.
What are the benefits of using computer simulation analysis?
Simulation analysis allows the researcher to evaluate vehicle behaviour and barrier performance during the vehicle impact. Software has the capability of evaluating occupant risk, measuring ride down decelerations and impact velocities. The components of the safety barrier system can be closely analysed, measuring plastic strain and identifying the yielding behaviour of the system. Â Â Â
What are some examples of computer simulation analysis performed by Safe Direction?
Safe Direction undertakes simulation analysis to evaluate modifications to the safety barrier system as follows:
- Reduced post spacing.
- Dynamic deflections at varying vehicle speeds and impact angles.
- Sizing of concrete footings for the installation of posts with baseplates.
- Barrier behaviour with an omitted post.
How does Safe Direction present the results of computer simulation analysis?
Prior to undertaking computer simulation analysis, the model is verified and validated in accordance with NCHRP report 179. Safe Direction computer simulation results are presented in a Technical Directorate providing sequence images of the vehicle impact and recorded measurements.
