Modern vehicles; modern challenges
Vehicles are getting ever more complex, with subsystems becoming further interdependent with the wider system dynamics than ever before. Beyond this, modern vehicles now interact with their surroundings, reacting and responding to changes in the immediate environment. This is never truer than in autonomous vehicles. Consideration of the wider system effects on subsystem behaviour and vice-versa is now of paramount importance, along with the environmental interactions between vehicle and surroundings.
Therefore, tools capable of considering the vehicle not only in a holistic total system manner, but also as a function of the environment, are required. Harnessing the modular, acausal and multi-domain nature of Dymola and the Modelica language, the VeSyMA suite of libraries can be deployed with the rFpro real-time virtual test environments to provide such a solution.
Reusable component-oriented models enable engineers to study the behaviour of the same single models in all desired scenarios. This can range from isolated R&D style bench tests to vehicle laboratory tests, controlled dynamic vehicle tests and full-scale open world driving complete with traffic and pedestrian interactions. In the race to bring autonomous vehicles to market, this flexibility of virtual testing environment and elimination of parallel development and maintenance can deliver significant efficiency savings. This is true of both cost and development lead time, versus a discrete approach to simulation tool deployment.
The VeSyMA – rFpro toolchain
Dymola has long been established as a favoured tool for the simulation of vehicles; its component-oriented physical modelling approach can span multiple physical domains, such as mechanical, fluid, control, electrical and thermal in an acausal manner. Coupled with the concept of model reuse, Dymola enables the engineer to focus on the modelling of the components themselves, rather than reformulating and maintaining banks of models for different analysis types.
These concepts underpin the VeSyMA platform of libraries, a modular approach to modelling a full vehicle, comprised of the cornerstone VeSyMA library which has 6 subject specific extension libraries built upon it. The VeSyMA library itself defines vehicle and subsystem level templates along with idealised models capable of conducting longitudinal based studies. Templates included in the VeSyMA library define all subsystem boundaries of models in the subject extension libraries, which means any model from any VeSyMA suite of libraries can be deployed in a VeSyMA vehicle model.Detailed engine models of both mean value and crank angle resolved formats are available in the VeSyMA – Engines library, with the VeSyMA – Powertrain library providing full rotational multibody driveline models. VeSyMA –Suspensions provides high fidelity models focused on vehicle dynamics modelling, specifically driver models, full multibody suspension linkages, anti roll bars, steering systems and tyre models.
On top of these libraries are the VeSyMA – Motorsports, VeSyMA – Driver-in-the-Loop, and VeSyMA – Terrain Server libraries. VeSyMA – Motorsports is an extension of the Suspensions library with models pertaining to specialist Motorsports applications. VeSyMA – Driver-in-the-Loop and VeSyMA – Terrain Server enable the interface between Dymola and rFpro. The Driver-in-the-Loop library contains the models and build functions to compile a full physics vehicle model built using a VeSyMA template into an app capable of running within rFpro; the Terrain Server library enables the use of high fidelity rFpro road models in Dymola. Scalability is also built into the Driver-in-the-Loop library export models, with the ability to compile vehicle models for use in both full motion platforms and small-scale desk based workstations.
The same model can be used both offline and real-time
One key benefit of the VeSyMA suite is the ability to use the same vehicle model in both offline simulations and real-time in rFPro. This means that it is a simple process to evaluate changes determined from offline testing in the full rFpro environment. The export template provided as part of the Driver-in-the-Loop library handles all interfacing between the vehicle model and the rFpro environment, including collision handling, wheel-to-road interface, atmosphere interface and the ground interface. Depending on the rFpro plug in utilised, telemetry data can be streamed to System Monitor, Gredi or other data capture tools; vehicle parameters can also be adjusted without recompilation.
Preparing a vehicle model for real-time
Speed of simulation is, as one would expect, of consideration when developing a model for real-time running. In other words, it has to run quickly enough on the target machine to complete each time step of simulation within the specified time step. Within the DiL library, there are mock simulation environments which enable the user to test the performance of the vehicle model using real time settings; these functions and model also analyse the results to inform the user on how the model performs, indicating which elements and components need to be revised to improve performance. This includes advising the user of what settings should be adjusted within rFpro to accommodate the vehicle model.
With the vehicle model selected in the DiL export template, the process of compilation of the vehicle model into an app to use in rFpro is a simple process. The video below demonstrates this process (for a vTAG app), showing how to export the vehicle model as part of the export template using functions included in the DiL library. As can be seen, there are various options available to the user to customise the exported app, such as solver settings, build method and naming, result file inclusions, code export and compiler settings.
Two tools, one solution
All of this means that through VeSyMA, Claytex can offer an effective unified solution, enabling engineers to be able to fully utilise the power of both the detailed, high fidelity offline vehicle simulation in Dymola and the complex, virtual test environments of rFpro in conjunction. Component oriented model re-use eliminates inefficient model duplication and unnecessary maintenance, enabling engineers to focus on the problem at hand. For more information, please see the Claytex website.
Written by: Theodor Ensbury – Project Engineer
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