Simulation to satisfy safety standards

Robert Roe finds that divergent safety regulations are forcing car manufacturers to turn to integrated simulation

Legislation on car safety, performance and emissions varies across the world, with very little coordination between different regions. Although it may seem paradoxical, one response has been for the providers of engineering simulation software to link the different components of their software more tightly together.

Because the requirements in terms of energy, emissions, and fuel efficiency have not been globally standardised, vehicle manufacturers are making use of increasingly sophisticated simulation to get new vehicles developed as quickly and cheaply as possible while making sure their newest models meet these standards.

Crash testing

Maurice Linscott, UK country manager at ESI said: ‘Automotive engineers in particular tend to do a lot of simulation because of the legislative requirements. The legal requirements for vehicles have become very onerous. Simulating against these requirements gives manufacturers a fast track to overcoming that problem.’ ESI produces software solutions ranging from CFD, vibro-acoustic and composite, to electromagnetic simulation tools and even virtual reality visualisation technology. Linscott stated ESI is focusing on linking these systems together providing a more in-depth analysis than was previously possible.

Linscott explained that, in the company’s Virtual Performance Solution (VPS), ‘you can link together the deformation of a vehicle when it crashes; how the body of the dummy behaves; how the airbag deploys when an impact occurs; and how the seatbelt system works, for example. We can link many different aspects to create a model that represents the body-in-white and all the trim, with the engine, gearbox and other major assemblies – every assembly if you wish – and crash it, and then evaluate that crash. We are able to link together different simulations, not just within the crash environment but also within the manufacturing environment as well.’

Optimising designs

Esteco has also embraced this philosophy of linking systems together. However, its approach is to provide a system that links third party simulation tools, running many or even hundreds of design iterations within a given set of parameters, to optimise the design, in a process referred to as multidisciplinary design optimisation’ (MDO).

Carlo Poloni, president of Esteco said: ‘Automotive engineers need to do a lot of simulations, for design but also to fulfil regulations for the safety of a car, as well as the performance of the car. In order to develop the product as quickly as possible, there needs to be a degree of information sharing between different design teams so that optimisation can take place quickly, with the best models available. This is what our software allows you to do.’

‘We automate the process of integrating different models of a car from the manoeuvrability, crash testing, aerodynamics, and performance for example. Building and automating the design process allows the decision-maker to search for the best solutions that they are looking for.’

Designers in control

Both strategies for optimising design give designers greater control as they can simulate the interaction between various systems, not just in a crash environment, but also during design and manufacturing. Esteco software focuses on automating the analysis of each design so many more iterations can be created and evaluated – reducing the uncertainty and time in developing complex systems but often requiring significant compute power.

Although legislation drives many of the requirements behind automotive simulation, other pressures include strict development times and the need to control the cost of the project effectively. Linscott said: ‘To build a very crude body-in-white for crash is incredibly expensive. It takes a long time, because you have got all of the low-volume tooling, you have to assemble it, and then all you do is run it down a line and crash it. That is one example, but there are a number of examples where previously you would be building physical assets in the industry. If you can replace these physical assets with a digital or simulation approach, you cut vast amounts of money out of the project and you cut vast amounts of time.’

It is for these reasons, Linscott said, that simulation ‘has become such a powerful proposition, and used so aggressively. It has enabled car developers to cut their development times down to less than three years.’

Mass-manufactured vehicles are complex systems and this means that there is a constant compromise between various parameters, such as weight and fuel efficiency. Esteco software focuses on this multi-design approach to optimisation, which helps users to decide on the best solution to a given problem by large numbers of designs based on a pre-described set of parameters.

Poloni said: ‘Typically you will have a goal, such as fuel consumption – which is related to the engine but it is also related to the mass of the car which, of course, has to be minimised. On the other side, some mass has to exist to protect the passengers. So that is a clear compromise that has to be found. It is the interaction between these design parameters that we enable with our software.’

Poloni continued: ‘Suppose that you have a car that has to follow different regulations for different countries – for example the NCAP in Europe for the safety of the car – this is something that is a must-have ,it is not something that you can do without. But you want to reduce the weight of the car, less kilograms means less cost at the end, and then you need to identify the areas where you can relax the design to fulfil the constraints. One way you can do this is the small modifications that you can do to pass through all the prescribed regulations. So satisfying constraints is another important issue – that is not necessarily optimising the car, but it just trying to get the vehicle within the design constraints.’

Simulating in-car electronics

One of the tools that ESI offers is called the Computational Electromagnetic (CEM) solution for full virtual testing and it allows users to analyse EMC/EMI issues appearing in a wide spectrum of on-board electronics and complex cable networks.

Linscott said: ‘That is the reason that electro-magnetic simulation has become so prevalent within the simulation industry, because cars are becoming packed with lots of different types of electronics, both transmitting and receiving.’

Linscott continued: ‘All of those electronic devices which these days are sitting in your car need to be validated in respect to their compatibility both within the vehicle and when the vehicle is on the road in an environment with many other vehicles. Again, simulation allows manufacturers to short circuit what would have been very difficult to model physically.’

Linscott continued: ‘Our end-to-end solution is about being able to evaluate systems, but also linking it to more.’ He gave the example of the B-pillar in a normal car; this is the pillar on the side of the car that has the seatbelt attached to it and takes the side impact in the event of a crash. It is one of the more challenging components when designing the body-in-white for a car. Linscott explained that the software can simulate different manufacturing processes from traditional cold-steel stamping, through laser-welding and then compare the benefits and trade-offs that occur when using different processes. This kind of simulation early on before manufacturing allows designers to fine-tune the material properties to get the strongest structure for the smallest amount of weight. It is the sort of area where simulation plays a valuable role for companies like VW who use that approach in their simulation and modelling. It was, Linscott concluded, ‘this ability to link things together that creates a much more meaningful simulation.

Cool engines

The transient cooling system of BMW’s six cylinder/225kW diesel engine represents an example of interlinking by Esteco. The team of BMW engineers developed the air side and coolant circuit model using Kuli, supported also by 3D-CFD simulations which were then investigated using ModeFrontier to identify better configurations for the transient cooling system.

The coolant circuit and the air path models represented in the engine model included two clear groups of parameters integral to optimising the design. Five heat transfer coefficients and four heat capacities were identified and modeFRONTIER allowed the engineers to set up an effective optimisation workflow that was capable of automatically interacting with the Kuli engine model and detecting the optimal configuration for the nine parameters.

Günther Pessl, head of simulation at BMW, said: ‘The easy-to-build integration between the two software enabled faster identification of the best heat transfer coefficients and thermal inertia in the engine analysed.’

Esteco has also been successful in the optimisation of components for crash simulation in a project with Volvo. The idea was to optimise material properties of a bumper to reduce failures and develop a better understanding of how the materials responded under varying stresses.

Poloni said: ‘Maybe this is something that relates to high-performance computing, because today one of the most expensive and time consuming simulations is the crash simulation which may take days on several hundred CPUs and we need to run hundreds of these simulations to get to the optimal result. When you are designing the components of a car, like a bumper in this case, then what you want to achieve is to minimise the mass of the components while fulfilling the mission, which is typically a pre-described load or impact energy when the car hits something. In this situation it is fairly straightforward to define the objective which is the minimum weight but the constraints are playing a major role there.’

Material test data was used to perform analysis and curve fitting was performed in modeFRONTIER in order to build and validate models using response surface methods (RSM) of material properties and predict the behaviour of the bumper.

Poloni said: ‘There is a large spectrum of numerical methods under the name RSM, in general it means that you have some data and you want to build an artificial model using only the inputs and the outputs generalising this information to create a model of the behaviour.’

Poloni explained that RSM is a very important tool in two circumstances, the first being you have experimental data but you do not have a model and you want to correlate the inputs and the outputs. The other situation is if you have a very expensive simulation, like crash simulation for example. You would do some sampling, you would execute a number of pre-described simulations and you build responses for these simulations. You want to predict what happened between the values and get a quick answer.’

In this case, RSM reduced the amount of simulation that is done as virtual curves can be produced, which are then verified against experimental data. This reduces the cost of expensive simulation while still providing a realistic model for crash simulation.

Poloni concluded: ‘Response surface methods is a way of sharing information between different application areas where simulations are particularly expensive.

‘You may build responses for each objective that you have and then make decisions on the basis of the response surfaces instead of expensive simulation tasks and then go back and verify that your decision is what you would expect, that the actual response is what is predicted from the RSM.’

With the advent of data-centric computing and the adoption of HPC by smaller companies this type of complex, computationally intensive simulation will become more prevalent as companies innovate in a competitive market.

About the author

Robert Roe is a technical writer for Scientific Computing World, and Fibre Systems.

You can contact him at robert.roe@europascience.com or on +44 (0) 1223 275 464.

Find us on Twitter at @SCWmagazine, @FibreSystemsMag and @ESRobertRoe.

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