Optimising Passenger Vehicle Design By Building Simulation Apps

Technology COMSOL Mahindra Optimising Passenger Vehicle Design Simulation Apps
Optimising Passenger Vehicle Design By Building Simulation Apps

The Indian automotive industry is growing rapidly, and is one of the largest in the world. Product design for modern-day automotive manufacturers is an iterative process that requires collaboration between Computer-Aided Engineering (CAE) analysts, the design team and the suppliers, among others. To maintain a competitive edge in today’s consumer landscape, automotive manufacturers must make collaboration a top priority. One of the main challenges for a company like Mahindra is to introduce new vehicles at an accelerated pace, while ensuring quality, safety and reliability. The team at Mahindra applied COMSOL Multiphysics software in building simulation apps to accelerate the product design process, and embrace a culture of collaboration.

CHALLENGES FACED DURING THE PRODUCT DESIGN PHASE

 Collaboration can be a time consuming process that requires different teams to offer their expertise in a meaningful and efficient manner. Design engineers demand a quick evaluation of new concepts, which is sometimes not possible due to the complexity of the physics involved, so they must work with the CAE analysts.

The design lead time can run into a couple of months for a particular vehicle component depending upon the number of back-and-forth iterations required to finalise the design. Depending on the design complexity of the proposal submitted, the CAE analysts can take anywhere between a week and a month to revert with their observations.

Based on the simulation results, the design team makes certain modifications and again awaits validation of the design by the CAE team. These iterations, which are crucial to the safety and reliability of the vehicle, continue till a final design is obtained. In addition, the availability of resources in various teams can sometimes lead to further delays.

In addition to adopting various methods to reduce the time-to-market for their vehicles, the Methods team at Mahindra have explored the Application Builder tool available in COMSOL Multiphysics to look at various options for the chassis and stabiliser bar designs via simulation apps, in a significantly shorter duration of time compared to the conventional approach.

REDUCING THE ITERATIONS IN CHASSIS CONCEPT GENERATION & VERIFICATION

(1) Structure of a typical utility vehicle chassis

The chassis is an important load-bearing component of any vehicle that acts as a base for mounting other components such as the engine and transmission, in addition to providing stiffness to the vehicle. One of the common architectures is a ladder frame with two long side members and a number of cross members, (1). The number, size, position and shape of the cross members are important parameters which need to be decided early in the design process.

The load carried by the chassis results in combined bending and torsional loads for which no simple analytical solutions are available. In the conventional approach to address this, a few chassis designs would be evaluated based on the packaging requirements and numerous CAE iterations would then be conducted to finalise the design. Each iteration involved three separate analyses: bending stiffness analysis, torsional stiffness analysis and modal analysis. This approach required three to four full CAE iterations, typically taking two to three weeks per iteration, and multiple smaller iterations.

Using COMSOL Multiphysics, the team has been able to couple the physics of the three ‘separate’ analyses and create a simulation app, reducing number of CAE iterations to arrive at the final design. The simulation app for the chassis design, as seen in (2) (a) features a 1D beam model based on the Timoshenko beam theory, which results in a runtime of seconds even for a complicated chassis design with various cross sections and members. Both torsional as well as bending stiffness are computed. The beam analysis provides fast and reliable results for a wide range of configurations.

(2) (a) The user interface of the chassis app

(2) (b) shows the results obtained from the chassis app for a particular configuration. The simulation app offers the convenience of evaluating various design parameters through simple text fields rather than creating a CAD model for each configuration, which is a time saver for the team as well.

(2) (b) The results obtained from the chassis app for a particular configuration

AN INNOVATIVE APPROACH FOR DESIGNING THE STABILISER BAR

Another critical component of suspension used to limit the roll of a vehicle is the stabiliser bar, (lead image). The design is typically either a hollow or solid beam with multiple bends in 3D space. To accurately model the deflections and stresses in such a component, the design team must collaborate with the CAE analysts, or request validation from their suppliers, to ensure the appropriate stiffness and stress levels are met. To speed up the design verification process, the Mahindra team first created a model of the anti-roll bar in COMSOL. After validation studies were completed on the model, an application has been created.

The simulation app of the stabiliser bar can accommodate a large variety of design iterations with up to 15 bends, with the option of exploring a hollow or solid bar designs (4) (a). The end user, typically a member of the suspension design team, enters the coordinates of the bends to represent the geometry of the stabiliser bar and provides details of bearing location, bushing stiffness and cross section.

(4) (a) The user interface of the stabiliser bar app

The CAE analyst pre-defined the constraints within the app, making it simple and quick for the designer to get the stiffness of the stabiliser bar and the stresses for standard load cases. The typical run time of the application is in minutes, empowering the design team to run plenty of iterations and get immediate feedback on their designs. (4) (b) shows the app results for a particular setup.

Knowing that the simulation app is based on the validated multiphysics model, the design team is confident in the results without requiring additional training in simulation. The team at Mahindra has found that the apps result in significant time saved, and the results are in good agreement with the supplier’s reports. Additionally, the new culture of collaboration has fostered a greater sense of ownership of the end product as the design can be generated in one or two days, reducing the dependency on the supplier.

(4) (b) The results obtained from the stabiliser bar app for a particular configuration

APPS & THE ROAD AHEAD

The uniqueness of these applications lies in their ability to handle not only a wide range of parametric variations but also in the physics and boundary conditions. This enabled the designers to explore various design options early into the product development phase, without the need to rely on the CAE analysts for each iteration, or obtain additional training in numerical modelling. The results of the parametric studies are presented as design guidelines, enabling efficient and cost-effective products.

The simulation apps were developed based on detailed discussions with the CAE analysts before being deployed across various teams at Mahindra via the COMSOL Server ™. Complex design configurations, that were previously under the guard of the CAE analysts, have now become accessible to the designers in a convenient and easy-to-use platform. The multiphysics capabilities of COMSOL are also enabling Mahindra to expand their analysis capabilities into diverse domains such as vibro-acoustics and thermo-structural simulations for concept design verification. The ability of the software to combine 1D and 3D analysis, auto-meshing capabilities, and numerous in-built physics equations and boundary conditions allow a wide variety of problems to be solved with a simple, interactive user interface.

CONCLUSION

The past couple of decades have seen several foreign auto giants enter the market. As more and more auto makers continue to invest in the Indian market each year, their indigenous counterparts need to employ innovative techniques to stay ahead of the pack. Mahindra is pioneering this effort with the use of apps in their design process.

(This is a user study jointly authored by COMSOL and Mahindra)