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Keeping Passengers Comfortable with Simulation

The use of digital modeling tools can facilitate the development of comfortable cabins for vehicles

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As automakers drive towards global vehicle platforms, they fight an uphill battle to design vehicles that can be safe and comfortable in all climates – from extreme hot to extreme cold. Summer sun, for instance, can heat car interiors well beyond the unpleasant range. Cold, snowy days, on the other hand, often lead to iced-up windshields that are not only annoying but present the risk that an impatient driver might hit the road without waiting for complete visibility.

Engineering Cabins for Today’s Consumer

Vehicle interiors are becoming more multifunctional and luxurious. With features such as multi-zone climate control, temperature-controlled seats, cupholders, and steering wheels, advanced lighting features, and even air fragrance systems, it’s clear that each new model year raises the comfort bar a little higher.

As a result, drivers have begun to expect these conveniences when shopping for their next car, truck, or SUV. No matter how great the gas mileage or reliable the drivetrain, it’s the vehicle’s interior amenities and climate control system that often seal the deal.

Interior modeling with CAx

Digital modeling tools can facilitate interior design and engineering. (Image: Dassault Systemes)

Advanced climate control impacts more than driver comfort, however. All that blowing air tends to kill the joy of today’s high-fidelity automotive sound and infotainment systems, requiring automotive designers to make fans, ductwork, compressors, and drive motors ever more-efficient.

These heating and cooling systems also consume more electricity. This isn't such a big deal when cars have internal combustion engines under the hood, where perhaps 5% of the fuel usage goes to heating, ventilation, and air conditioning (HVAC) requirements. In electric vehicles, however, HVAC systems can represent 30% or more of a vehicle’s total energy consumption. Because of this, automotive design engineers must continually up their climate control game as electric vehicles gain market share.

Meeting Legacy Challenges Head On

Unfortunately, meeting these demands isn’t easy, or cheap. Traditional design and physical testing methodologies require hugely complex testing tracks, wind tunnels, and climatic chambers to ascertain vehicle performance across the broadest range of environmental conditions possible. Though impressive, these tools replicate only a snapshot of what the vehicle owner can expect in the real world.

With traditional testing there’s the need for prototypes. These are typically limited to individual components and subassemblies during the development phase, followed by complete vehicles during final testing. Either way, they're time-consuming and expensive to produce, with additional expense and lost time when a change is needed. All of it hinders the vehicle development process and simply cannot replicate all the details and factors (for example, engine cooling needs) that a vehicle on the road would encounter.

There is an alternative: simulation. This is doing for the automotive design process what crash test dummies did for vehicle safety. With finite element analysis (FEA), computational fluid dynamics (CFD), and other forms of advanced computer modeling, vehicle development costs plummet, product quality improves, and design and testing times shrink. Vehicles are designed, tested and optimized very early in the product development process — without ever needing a physical prototype.

Addressing Climate Concerns

Consider climate testing. Conventional testing methods call for lengthy solar soaks and deep freeze cycles. These are often performed in environmental test facilities owned by automotive OEMs and their Tier suppliers, or via field testing in extreme hot or cold locations. Both require the shipment of vehicles, components and testing teams to these remote sites for extended stays.

Similar requirements exist for wind tunnel testing, where vehicles are evaluated for their aerodynamic characteristics, as well as the level of cabin noise due to wind, rain, and road conditions. Whatever the test, it's not unusual for vehicles to fail multiple times, each requiring design and prototype modifications, followed by additional testing, over and over again.

Such iterations are far more cost-effective and, arguably, more accurate when simulation software is used to model these and other real-world conditions. Solutions such as SIMULIA PowerFLOW from Dassault Systèmes, for example, capture the full range of physical phenomena experienced by an automobile and its occupants. The entire vehicle and even each individual component can be evaluated for performance and wear characteristics. Using simulation, multiple design iterations can be tested in minutes and hours rather than the weeks or even months necessary with conventional methods.

Safe, Secure, and Streamlined

Yet comfort goes beyond climate and noise control. 3D CAD modeling and simulation software allows engineers to test vehicle ergonomics, using digital models of occupants of all ages, shapes, and sizes. Designers can place virtual but realistic passengers into seats made of various materials. They can test and optimize their designs without the need for physical prototypes. Using simulation pressure points and construction weaknesses become visible, while lumbar and neck support can be evaluated and optimized, increasing rider safety. Where seats are heated, cooled, or ventilated, corresponding thermal characteristics are easily determined. Simulation can even detect how much a particular person will sweat in a given environment and how that will impact the cabin.

As mentioned earlier, power consumption is another concern in vehicle design, especially as the automotive world races towards electrification. Here, too, simulation plays an important role. Digital testing allows designers to optimize electrical systems to meet increasing HVAC and infotainment requirements. They can simulate different battery designs and understand what impact even small changes have on battery life, range, and cost. And here again, designers and engineers are able to perform these and other analyses in a virtual environment, with quantifiable results, significantly reducing development time and cost.

Such systems also make design and engineering tasks easier. The use of advanced simulation tools means critical information and product data is more easily shared between teams. Departmental silos are eliminated, knowledge becomes less tribal, overall efficiency is improved. Nothing is left to chance, since Design Verification Methods (DVM) assure that performance metrics are met at all stages of the project. Simply put, simulation is the easiest, most cost-effective, and efficient way to design vehicles today, whatever their climate control needs. Forget the chambers and wind tunnels – in today’s environment, simulation is an automaker’s best friend.   

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Ales Alajbegovic received his Ph.D. in Engineering Physics at Rensselaer Polytechnic Institute. He started at Exa Corporation as the Applications Manager responsible for the development of external aerodynamics applications using Lattice-Boltzmann Method. His next appointment was at AVL where he was a Team Leader responsible for the development of the multiphase flow CFD capabilities in FIRE code. After AVL, he joined General Dynamics as a Senior Research Scientist. He returned to Exa Corporation where his last role was Vice President responsible for the Ground Transportation Applications. He is currently Vice President for SIMULIA Industry Process Success & Services at Dassault Systèmes.

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