Testování NVH

NVH testing requires measuring sound and vibration that a product produces. Typically, this means measuring at key locations where customers would perceive the noise or vibration of the product. To diagnose a noise and vibration issue, it is not enough just to record a few key operator interface locations. Other detailed measurements would also be acquired to diagnose the root cause. For example, recording the noise of washing machine alone is not enough, measuring vibration on several key internal components (motor, vents, fans, etc) is also needed to understand the problem fully.

Noise is another word for the sound or acoustic properties emitted by a product. Noise measurements are often performed for:

• Regulation: Products often must be below legislated noise limits to be sold.
• Damage: Sound waves (like from a rocket on the satellite payload) can be of such a high level they cause damage.
• Detection: In some military applications, sound can give away a position to an enemy. For example, a submarine must be very quiet so as not to be detected when under water.
• Characterized by frequency, level and quality. The human ear perceives sounds between 20 Hz and 20,000 Hz. Measurements performed with microphones.

Excessive vibration is irritating to the users of products. It can also be helpful to understand the vibration of a product to trouble shoot the sound. Vibrating surfaces act like speakers which produce sound.

• Motion sensed by the body mainly in the 0.5 Hz – 50 Hz frequency range.
• Vibration levels should be low and not disturbing. High vibration causes parts to fail over time (Figure 3).
• Vibration levels that are too high can cause health concerns when exposed for too long. Example: Prolonged usage of a jack hammer causes “white finger” syndrome.
• Vibration levels are often amplified by resonant behavior of a structure.
• Vibration is used to understand the underlying cause of unwanted sound.
• Characterized by frequency, level and direction. Measurements performed with accelerometers.

Harshness pertains to the subjective impression of sound and/or vibration. Consumers want products to sound as expected. Sounds should not be annoying in nature. Examples include:

• Pleasing background hum of a dishwasher
• Refined interior noise of an automobile
• Solid door closing sound at a dealership
• Sporty sound of motorcycle
• Rough, grating or discordant sensations associated with the combined effect of noise and vibration should be avoided
• Humans can hear from 20 to 20000 Hz. Audible disturbances mainly occur in the 20 Hz – 5000 Hz frequency range

There are three main components to a noise, vibration, and harshness measurement system:

• Transducers: Sensing devices that when exposed to dynamic excitation react to physical phenomena (such as

  sound pressure or acceleration vibrations) and convert to analog voltage.

• Analog to Digital Hardware: Provides sensor signal conditioning and conversion from analog signals to digital for viewing on computers. The Siemens solution to this is in the signal conditioning and data acquisition system (SCADAS) line of hardware.
• Visualization and analysis software: For visualizing and further processing of acquired signals. Such as

  Simcenter Testlab or Simcenter Testlab Neo software.

The transducers are placed on or near the object making noise or vibration. The analog signals they collect are digitized in the hardware so they can be viewed and analyzed in the software.

Efficient product develop requires modelling product performance with the "digital twin". Simcenter Testlab is fully integrated with computer based simulation modelling, supporting both correlation and verification.

Some examples of integration features include:

• Correlation of dynamic mode shapes (via Modal Assurance Criterion)
• Overlay of simulation and test data in the same engineering units
• Use of Functional Mockup Interfaces in data analysis

If you have a more technical question about NVH testing and data acquisition, then please take a look at the Simcenter Community which contains technical knowledgebase articles as well as visit the Simcenter community for NVH testing.