Simulation speeds rollcage design process

The need for speed is what racing is all about. However, before cars even make it onto the tracks, the teams, vehicle fabricators and component manufacturers must ensure that the vehicles are safe – and adhere to the strict regulations set forth by the appropriate governing bodies.

Just ask Brett Longhurst, owner and Managing Director of Bremar Automotion. Based in Carrum Downs, Victoria, his company provides simulation, testing, validation, and design optimisation services to customers across many industries, including automotive and motorsport. In particular, Bremar is accredited by the Fédération Internationale de l’Automobile (FIA) the world governing body for motorsport, to certify vehicles’ rollcages using finite element analysis (FEA). This accreditation enables the company to independently certify rollcages for competition use both here in Australia and internationally. Life savers

Rollcages protect occupants from being injured in roll-overs and other accidents that sometimes occur in the heat of competition. They can vary greatly in design, depending on the level of racing and the type of racecar. For example, a rollcage for the Australian V8 Supercar Series – based around General Motors and Ford production cars – is very different from a rollcage built for off-road racing vehicles. Depending upon the type of vehicle and race category, there are also different requirements on which bars, materials and types of reinforcement are used. “The rollcage regulations that we work to generally depend on the vehicle weight,” says Longhurst. He adds that the grade of material often governs the complexity of rollcage design. For instance, a cage made out of lower-grade steel will usually require thicker material and more tubes, which generally leads to a heavier structure. A higher-grade steel such as chromoly, however, has a much higher strength, so the tubes can be thinner to reduce the overall weight of the rollcage structure, but would come at a greater cost for materials and fabrication time.

Bremar Automotion created this rollcage design concept and CAD overlay for a Side By Side (SxS) off-road race buggy. “Like any engineering design, the factors affecting product development, such as weight, strength and cost, are always playing off each other and have conflicting impacts on the design,” continues Longhurst. Design and certification

When customers approach Bremar Automotion about developing a new rollcage, the first step in product development is often to perform a 3D scan of the vehicle and/or its interior to determine where the rollcage will be placed. The Bremar team then packages specified vehicle sub-systems and components within a CAD model – including information on the driver and steering wheel, among others – and provides an initial rollcage design and tube sizing. In some cases, a mock-up of the rollcage is created with plastic tubing to ensure that the driver can get into and out of the car, that there’s sufficient head clearance, and that the rollcage is not impeding the driver’s ability to steer or reach vehicle controls. It’s often difficult to judge these ergonomic factors in CAD, so a physical mock-up in the vehicle is often the simplest and most accurate way for the driver and team to confirm it meets the requirements. Once the team is satisfied with the design, a drawing of the rollcage is submitted to the governing body for the racing category. “Before we go through the process of doing the analysis and building the rollcage, we want to get confirmation that it is actually compliant with all other aspects of the regulations,” says Longhurst. Once the governing body provides in-principle support for the design, Bremar creates FEA models of the rollcage, applies the various load cases, and assesses the results against the required acceptance criteria. If the rollcage doesn’t initially meet the requirements, the analyst can easily alter the design by thickening a tube or placing a bar in a different location and rerunning the simulation. Once the design has been approved, the rollcage is built by the customer or manufacturer. If there are any changes made during the build process, Bremar updates the simulation models and does another round of FEA to ensure that the final as-built structure is still compliant with all the requirements before issuing a certification report.

Rollcage and test fixtures designed in CAD, and the physical test setup.

Matching simulation to physical testing

To obtain accreditation for the FIA’s “Technical List no.35”, Bremar was required to construct and test a full-size rollcage by applying the FIA’s specified rollcage loads to the structure. Destructive testing was used to confirm the accuracy of the company’s computer modelling methods, and to demonstrate competency to the FIA. Bremar engineers developed a rollcage design for a vehicle weighing approximately 1,200kg and conducted the necessary simulations to ensure it met FIA requirements. They then had the cage constructed ready for physical testing, where it was instrumented with multiple sensors and gauges to measure deflection and strain at various locations during the different tests. Loads were applied as per the FEA simulations, which were in the order of 10 tons. Additional tests were also conducted in excess of the FIA requirements in order to further validate Bremar’s FEA modelling methods, with loads in excess of 20 tons resulting in over 75mm of deflection in the rollcage structure. Bremar correlated the results of the physical testing with its nonlinear FEA simulations, which were performed using Altair RADIOSS. According to Longhurst, there was a close correlation between the physical structure and computer simulations, providing a high level of confidence in Bremar’s FEA methods for rollcages and other similar structures. The efficiency factor

The time and cost required to perform physical testing of any product, component or system can often be prohibitive. However, simulation methods such as those that Bremar utilises for its rollcage certifications enable its customers to optimise and validate their designs before ever making a physical part, providing enormous efficiency gains in terms of development time and costs. Moreover, correlated simulation results demonstrate that the products will perform as predicted. Longhurst says: “That gives us a high level of confidence that we can use simulation to develop and validate designs, and that our analysis methods are providing accurate results.” Pushing the boundaries

After more than 15 years operating in the industry, and staffed by a team with decades of simulation experience in large automotive OEMs, Bremar has seen simulation capabilities advance over the years. “When we started our company, we were performing more basic analysis for our customers,” says Longhurst. “Now, with advancement in the software and greater awareness of computer aided engineering (CAE) in general, I feel we’re really pushing the boundaries of what can be achieved and increasing the reliance on simulation for our clients.” The company, for example, is now conducting virtual wind tunnel testing. It performs external aerodynamic analysis on vehicles and aerodynamic components using HyperWorks Virtual Wind Tunnel, and is using Altair AcuSolve to perform fluid flow analysis on engine manifolds and brake ducts, among other components. Multi Body Dynamics (MBD) simulation is also heavily utilised at Bremar to model complex automotive mechanisms such as seating, suspension and steering systems, and even to simulate the handling of complete vehicles and large truck combinations on rough road surfaces. These MBD analyses are also able to generate loads on components, which can be fed into detailed FEA stress and fatigue analysis models, as is commonly used for Bremar’s work in the aftermarket suspension and GVM (gross vehicle mass) upgrade industries. Many small and medium-sized companies, including racing organisations, don’t have access to leading-edge resources such as this, which is where Bremar fits in, providing the technology and services that bring its customers up to speed in the way they’re designing, developing and manufacturing their products. “We sell software we use,” says Longhurst. “So we can support our clients either through consulting services, or by helping them develop their own in-house capability through software sales, training and mentoring. “I think it’s a real strength, and one of Bremar’s differentiators, that we can bring such a broad range of technology and ‘big company’ experience into these businesses. It enables the use of advanced simulation methods, along with modern design and manufacturing techniques – and allows customers to realise actual time and cost savings on their projects, which is always really rewarding to see.” www.bremarauto.com

Altair Virtual Wind Tunnel enables engineers to analyse a Speads RS10 sportscar to assess downforce and radiator airflow.