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There is a constant struggle in today¡¯s automotive landscape to predict a vehicle¡¯s behavior under all road and driving conditions as it relates to vehicle safety and durability. Even more so, this type of testing is usually limited in many countries, with only a few shared facilities with endless wait times, making physical tests nearly impossible. In this blog post, we introduce a range of water flow management simulations to help manufacturers optimize vehicle driveability, negating the need for environmentally-unfriendly physical testing.

An estimated 10% of traffic fatalities are a direct result of wet roadways, according to research from the National Highway Traffic Safety Administration (NHTSA) in the United States. Hydroplaning, for example, occurs when a driver loses control in wet road conditions, putting motorists and other road users in great danger. Autonomous vehicle systems must make the right decisions in real-time to avoid crashing, while at the same time mitigating the risk of hydroplaning. And as electric vehicles gain popularity, how do you ensure your vehicle¡¯s critical components won¡¯t become damaged by water?

To test these potentially hazardous scenarios, in the hopes of better understanding our customers¡¯ challenges, we simulated a range of different driving conditions to test the vehicle¡¯s response without relying on any physical prototypes. These situations included normal rainy-day driving, deep flooding for vehicles encountering waters depths of up to 30cm, and soiling.

Water impact has a destructive force that is more powerful than expected. In the worst-case scenario, if the strength of the underside of the vehicle body is inadequate and the quantity of splashed water is large, the impact could cause parts on the underside to fail.

Honda Engineer

Tackling drivability on an ordinary rainy day

Most of the time spent behind the wheel is under normal driving conditions. On a rainy day, we are most likely to encounter shallow puddles of water at average speeds. What does that scenario yield with respect to drivability and will it incur any damage to the vehicle? To get answers, we used simulation to analyze the displacement of a volume of water as it was pushed away by a car to predict whether critical areas like the vehicle¡¯s electrical components need protection from the water or if other special countermeasures, such as changes to the vehicle¡¯s geometry, are required.

We started by simulating the effects of shallow water spray patterns repeatedly hitting the underside of a vehicle. The scene was a car driving at an average speed of 60km/h speed on a wet road with 3cm of water. Then, we investigated three important areas to ensure the short- and long-term drivability of the car under these circumstances.

First, we simulated the effects of high-velocity water splashes on the plastic undercover parts of the car to ensure they were not at risk of rupturing. Second, we completed a salty water splash projection to simulate what areas were susceptible to corrosion during the winter months and how to mitigate that. Last, we verified the appropriate locations of thermal shields to prevent thermal shocks in the exhaust pipes.

One very important thing to note is that if you want to accurately predict water splash patterns and their effect on the vehicle, it¡¯s not enough to simply perform CFD simulation. You must concurrently simulate the tread of the tire, meaning the tire deformation and suspension, as well as the tire pressure. This is also important when it comes to dynamic effects, like potholes or bumps in the road, as they will definitely have an impact on the splash pattern.

All these realistic physics-based simulations are critical in obtaining the most accurate results, which you can get via a single model using simulation.

Predicting soiling and keeping your drivers safe

Rainwater can also adversely affect a driver¡¯s visibility as it makes contact with the driver¡¯s side window, side view mirror, and windshield. One of our very own ESI engineers took to the roads of a French motorway on a rainy day and recorded his findings to show the effects rain has on driving visibility. In this video (below), you can see that, depending on his speed and the wind velocity, the water flow changes. Soiling of the side windows can become a safety issue as it hinders the driver¡¯s vision of the side view mirror.

Testing typically requires physical testing on the road or in a wind tunnel with the exact external makeup of the vehicle. This means that as soon as even one body component is changed (e.g. side view mirror, spoiler, etc.), the test would have to be repeated. These issues arise late in the development cycle when it is usually too late to make the change.

Virtual Prototyping makes it easy to simulate the water trajectory across the vehicle at various speeds. As a result, you can optimize the position of rainwater drainage systems and the vehicle¡¯s shape to improve the flow of rainwater and, most importantly, driver visibility, early in your design cycle and without the need for a physical prototype.

In deep water

If you drive towards a flooded road, is it safe to cross? Will the car remain operational when it comes out on the other side or will the engine flood? Of course, the answer depends on a range of factors, including the water depth, your speed, and your vehicle type. Again, as we did in our ¡®rainy day¡¯ scenario, we analyzed the shape of a volume of water as it was pushed away by a car. This is necessary for predicting possible damage to critical areas, specifically electrical components, and creating a plan to rectify those flaws.

Making any changes late in the car¡¯s development cycle can be a disaster in terms of delays and cost. Automakers face the tough decision of risking a major setback in getting their car to market or omitting changes to the design that remains essential to the vehicle¡¯s performance.

Amend your problem before it¡¯s a problem

Virtual Prototyping allows car manufacturers to certify a vehicle across a broad range of domains, including crash, safety, NVH, durability, and, of course, water flow management. Users gain access to all these domains, with one single core model, avoiding model conversion, simplifying variants evaluation, and at the end saving a vast amount of modeling time.

Using a standard structural model, they set up the driving conditions with minimal effort on model preparation, as no CFD-specific mesh is needed. This saves a minimum of 50% in model preparation time.

Thanks to the combination of this unique approach and predictive physics-based simulation, manufacturers can predict early in the development phase, the drivability of today¡¯s vehicles, whatever the weather.

Read more on how Honda Motor Reduced Trial and Development Time Thanks to the Accuracy of Water Impact Simulation Testing.

Watch our Water Crossing webinar ON-DEMAND on how to Ensure drivability in Realistic Conditions with Water crossing Simulation.