NVH — the study of noise, vibration, and harshness in vehicles — is a special discipline, supported by software and simulation tools. As the automotive industry transitions from combustion engine to electric and hybrid cars, the NVH tools also evolve to address new issues.
National Electric Vehicle Sweden, the new owner of what used to be Saab Automobile AB, is currently using Altair’s Squeak and Rattle Director, described as “a comprehensive set of software automations that rapidly identify and analyze design alternatives to eliminate the root causes of squeak and rattle in assemblies.” DE recently talked to NVH experts from Altair.
Pros and Cons of Losing the Combustion Engine
Jianmin Guan, Director, Vibration and Acoustic Solutions: In a traditional car, the combustion engine — to use industry vernacular — “masks” a lot of the NVH problems, like extraneous noises from accessories and components. In a fully electric vehicle, the engine is no longer there, so these issues become much more prominent to the driver and the passengers. For example, wind and road noises become more prominent.
And all cars have cooling systems, which use pumps. Their sound is not very loud, but can be fairly disturbing if the engine noise is no longer masking it. And even though you no longer have the engine, you still have the gear, so the gear noise becomes more prominent. Usually, engineers have to solve these problems by adding dampening, stiffing, or absorption materials.
Unlike a combustion-engine car, the electric vehicle produces very little external noise, so the pedestrians might not easily recognize its approach. So, by requirement, electric vehicles must make some noise to alert the pedestrians.
Altair’s solutions like OptiStruct and HyperMesh are general tools, all part of the HyperWorks suite. People from many verticals can use them. But the automotive vertical also has distinct disciplines and focuses, like crash safety, durability, ride comfort, and NVH. Altair has specific solutions targeting these areas.
Simulation vs. Human Perception
Jianmin Guan: People generally perceive a car that vibrates too much as a low-quality product. Without the engine, the car has lost one source of vibration. At the same time, without the engine’s vibration, road-induced vibration becomes more prominent. So it can accentuate the perception of low quality.
Andrew Burke, Product Design Team Manager: With NVH, the driver or the customer is the sensor, if you’d like. The diver is the one making the assessment and measurement, whether consciously or subconsciously. So we have to take into account the human perception. With our tools, you can link the simulated noises to a [physical vehicle] simulator, so you can “experience” what it sounds like to be the driver. In some companies, using AR-VR (augmented reality & virtual reality) hardware to experience the simulation is now standard procedure.
Based on research data, you could understand how a human would perceive noise or vibration by looking at a plot [in simulation results]. But there are also subjective reactions you won’t get by just looking at a plot. So, now that we have the technology, it’s really important to feed these simulated data into a simulator so you can experience it. That in turn helps you make better design changes.
Jianmin Guan: When you do a full-vehicle NVH simulation, you’re looking at how all the individual components are coming together and matching one another. So compatibility of components is one issue to look at.
If you turn on the engine and you feel the steering column shaking too much, you’d consider that car not too refined. The problem might even contribute to breakage and failure. But that shake is not the result of a single component but the design issue of the entire structure. It has to do with how the steering column is fastened to the body. To solve such a problem, you really need to look at the full vehicle.
For more on Altair’s NVH solutions, go to http://nvh.altair.com.