Simcenter Testing Solutions NVH Testing and Data Acquisition
2024-05-16T23:14:57.000-0400
Simcenter SCADAS
Simcenter Testlab
Summary
Details
Need to make noise, vibration, and harshness (NVH) measurements? This article covers what to consider when evaluating an NVH data acquisition system to perform noise and vibration tests. Simcenter Testlab software and Simcenter SCADAS hardware are used as examples.
Article Contents:
1. What is NVH Testing?
1.1 Noise
1.2 Vibration
1.3 Harshness
2. Measurement System Overview
3. Data Acquisition Hardware
3.1 Sampling Rates
3.2 Anti-Aliasing Filters
3.3 Coupling Filters
3.4 Signal Conditioning
4. Noise Capabilities
4.1 Sound Pressure
4.2 Sound Power
4.3 Sound Absorption and Sound Transmission
4.6 Transfer Path Analysis
5. Vibration Capabilities
5.1 Modal Testing and Analysis
5.2 Operational Deflection Shapes
5.3 Rotating Machinery Vibration
6. Harshness Capabilities
6.1 Sound Quality
6.2 Sound Names
7. Other Key Considerations
7.1 Documentation and Active Pictures
7.2 Efficient Processing
7.3 Integration
7.4 Customization and Scripting
7.5 Data Interchange
1. What is NVH Testing?
Noise, Vibration, and Harshness (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 (Figure 1).
Figure 1: Microphone sound measurement on a white good using a Siemens SCADAS XS noise and vibration measurement system.
More information on noise:
1.2 Vibration
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.
Figure 3: Siemens data acquisition system is used to control and monitor vibration on a test subject during a shaker durability test.
1.3 Harshness
Harshness pertains to the subjective impression of sound and/or vibration. Consumers want products to sound as expected (Figure 4). Sounds should not be annoying in nature.
Examples include:
Figure 4: Siemens systems are used in sound quality jury testing to correlate subjective impressions to numerical sound metrics.
More information on harshness:
2. Measurement System Overview
There are three main components to a noise, vibration, and harshness measurement system:
Figure 5: Example Simcenter Testlab software and Simcenter SCADAS hardware test setup with transducers.
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.
3. Data Acquisition Hardware
Noise, vibration, and harshness data acquisition hardware must be capable of simultaneously sampling multiple sensors and converting them from analog signals to digital signals:
3.1 Sampling Rates and Synchronization
The conversion of sensor readings from analog to digital format requires a high sampling rate (i.e., samples per second) to accommodate the human ear's capability of perceiving frequencies up to 20,000 Hz. This conversion needs to occur at a sufficient speed to accurately capture incoming data. Sampling rates of at least 100,000 samples per second are typically required for this purpose.
Furthermore, synchronous conversion of all sensors, ensuring alignment of every sample across each channel of the hardware, is important as shown in Figure 6:
Figure 6: Synchronized sampling across all channel is important for root cause analysis that requires knowing the phase relationship between different measurement channels.
Synchronized sampling enables the correlation of cause and effect, such as linking a ticking noise to the vibration of an injector. It is also important in many measurements that include phase, for example Frequency Response Functions for modal testing.
No “muxing”! Sampling should not be “muxed” when performing noise or vibration measurements. Muxing means that samples are read at different times from different channels and are not aligned in time and/or phase.
More information in the knowledge article: Digital Signal Processing: Sampling Rates, Bandwidth, Spectral Lines, and more….
3.2 Anti-Aliasing Filters
No matter what sampling rate a data acquisition is capable of, it is always possible that the analog signal being measured contains frequency content higher than the sampling rate can adequately measure.
Anti-aliasing filters must be used on measurement signals to remove frequency content that is too high to be sampled properly. An example is shown in Figure 7 below:
Figure 7: Example how inadequate sampling identifies sound or vibration frequency incorrectly. Above is animated gif.
While the amplitude of the vibration or noise is properly recorded in this example, the frequency is not. Without an anti-aliasing filter, an NVH data acquisition system cannot collect data properly.
More information in the knowledge article: Data Acquisition: Anti-Aliasing Filters
3.3 Coupling Filters
NVH data acquisition systems should also have AC and DC coupling filters. AC coupling filters remove offsets from data being collected, while DC coupling includes the offset. This is shown in Figure 8:
Figure 8: A strain gauge measurement with AC coupling (green) and DC coupling (red).
Depending on the measurement situation, AC coupling or DC coupling may be desirable. Some examples include:
Figure 9: Simcenter SCADAS hardware is modular. Signal conditioning cards can be mixed and matched to support any application.
Signal conditioning options include:
Figure 10: Simcenter SCADAS VB8 hardware is used to measure a variety of transducers including ICP accelerometers, strain gauges, potentiometers, microphones, and more...
Overall, signal conditioning plays a pivotal role in enhancing the accuracy, reliability, and compatibility of sensor data for analog-to-digital conversion, thereby facilitating precise measurement.
More articles on signal conditioning:
4. Noise Capabilities
A NVH data acquisition system must be capable of measuring sound in a variety of ways. Sometimes a general sound level must be measured, other times sound is measured in a specific fashion according to certain standards. Some of these sound testing scenarios are covered in the next sections:
4.1 Sound Pressure
Sound pressure is a key parameter in NVH data acquisition systems. Using a microphone, the sound pressure can be shown as a function of time, frequency, octave, or a single overall level value (Figure 11).
Figure 11: A sound pressure frequency spectrum (magenta) overlaid with a sound pressure octave spectrum (green).
Sound pressure is based on the pressure level recorded by a microphone, usually with an underlying pressure unit of Pascals. Instead of Pascals, sound pressure levels are usually converted into decibels or dB. Conversion to decibels is done with a simple right click on the Y-axis as shown in Figure 12:
Figure 12: Right click on Y-axis to convert from Pascals (Pa) to decibels (dB).
Microphones also have a very linear frequency response, while the human ear does not. The A-weighting curve is one way to introduce the effects of human hearing into a microphone recording. This is also done with a right click in the display (Processing -> A-weighting).
For more information:
4.2 Sound Power
Sound Power offers a quantified measurement of the acoustic strength of an object in an NVH system and is typically reported in decibels referenced to 1 PicoWatt (1 pW). Unlike sound pressure, sound power is independent of distance and location. Sound power can be calculated from an array of sound pressure microphone measurements as shown in Figure 13.
Figure 13: In a sound power test, microphones surround a test object (tractor) to capture all sound emitted.
Sound power is crucial when analyzing a system, as we can gain information into the overall acoustic behavior of a source. This measurement helps in the design process of a product to optimize components to minimize noise where needed, ensuring a quieter user experience.
There are many ISO and ANSI standards for measuring sound power, and the software needs to calculate sound power according to these standards.
For more information:
4.3 Sound Absorption and Transmission Loss
Sound absorption and sound transmission loss are measures of a material’s ability to block or absorb sound as shown in Figure 14 below:
Figure 14: Sound absorption is a measure of a materials (purple) ability to absorb sound waves (green). Transmission Loss measures how much a material (red) blocks sound waves (orange).
Absorption measures how well a material absorbs sound, while transmission loss measures how well a material blocks sound.
Absorption expressed as a value between 0 and 1 as a function of frequency. An absorption value of “1” means all sound is absorbed while a value of “0” indicates no sound is absorbed.
Absorption is measured with material samples which are placed in either an impedance tube or a room. An example of the impedance tube measurement is shown in Figure 15 below:
Figure 15: Impedance tube equipment used to characterize the absorption of a material sample.
Transmission loss, which indicates how well a material blocks sound is expressed in dBs of attenuation. The higher the dB value, the more sound that is blocked. Just like absorption, an impedance tube or room can be used to measure transmission loss.
For more information, see articles:
4.6 Transfer Path Analysis
Transfer Path Analysis (TPA) offers a systematic approach to analyzing and understanding key contributors to noise and vibration issues. These contributors are identified using source loads and transfer functions to the response at a target location (Figure 16).
Figure 16: Acquiring transfer functions on a vehicle body as part of the Transfer Path Analysis process.
TPA helps to identify specific sources contributing to noise and vibration problems in a system in an efficient manner. With the knowledge of how energy is transferred through a system, engineers can optimize design and enhance overall performance in a product.
For more information:
5. Vibration Capabilities
Vibration, just like sound, is often measured as a function of time or frequency. Lowering vibration levels helps ensure that products last longer, perform properly, and do not cause any damage to human health.
Measuring vibration levels is important, but to understand the root cause of vibration, tools like Operational Deflection Shapes and Modal Analysis are also needed.
5.1 Modal Analysis
Modal analysis entails examining the resonant behavior of a component and its reaction to mechanical excitation. This encompasses inducing vibrations in the component and analyzing its modal parameters: natural frequencies, damping, and mode shapes.
An example modal test and its results are shown in Figure 17:
Figure 17: Left – Physical modal test with exciters and transducers attached to airplane, Right – Mode shape result from modal test. above is animated
This process requires the acquisition of vibration data and the computation of Frequency Response Functions (FRFs). Modal analysis holds significance as it sheds light on the intrinsic characteristics of structures. Discerning flexible modes of vibration reveals how components vibrate as cohesive entities, thereby enabling better designs and mitigating objective vibrations.
Modal analysis utilizes different excitation methods such as impact testing and shaker testing to characterize the dynamic behavior of structures as shown in Figure 18.
Figure 18: Impact and shaker testing for modal analysis.
Impact testing involves striking the structure with an impulsive excitation, typically using an instrumented hammer. Shaker testing employs a controlled mechanical vibration from either a coupled electromechanical or hydrodynamic device to force the structure to respond to a certain profile across a range of frequencies.
Impact testing can be quickly applied to a wide range of structures and does not require complex setup or instrumentation. The exact excitation frequency range can only be controlled via selection of hammer tip stiffness and mass.
Shaker testing offers precise control over the excitation force and frequency, allowing for repeatable and consistent results. Shaker testing also enables the excitation of structures at multiple input points simultaneously, facilitating more comprehensive modal analysis. However, shaker testing typically requires more elaborate setup and instrumentation.
For more information:
5.2 Operational Deflection Shapes
Operational Deflection Shape (ODS) analysis plays a crucial role in understanding the dynamic behavior of structures and machinery during operation by visualizing the underlying patterns or shapes exhibited by a structure while in operation as shown in Figure 19.
Figure 19: Operational deflection shape of the “tramp” mode of a front axle in a truck.
Siemens Simcenter Testlab enables engineers to visualize and interpret complex vibration data under real-world operating conditions, which can help identify potential sources of vibration, resonance phenomena, or structural weaknesses.
For more information:
Specialized tools allow the quick analysis of rotating vibration issues which include order analysis, colormaps or spectrograms, angle domain visualization, and more.
For more information:
6. Harshness Capabilities
Traditionally, harshness was a term used in the automotive industry during the transition from wooden to all-metal body structures. It was commonly perceived at that time that all-metal bodies sounded “harsher” than their wooden counterparts. Technically speaking though, harshness refers to the perceived discomfort or annoyance as indicated by NVH measurements in a given environment.
Engineers can utilize Simcenter Testlab to precisely measure vibration levels and acoustic signatures. By correlating these measurements with human perception data, such as subjective rating scales, engineers can accurately assess the degree of harshness experienced by occupants or users. This holistic approach ensures products meet the desired comfort and quality standards.
6.1 Sound Quality
Sound quality in NVH data acquisition differs from other aspects due to its’ subjective nature. For example, two different people may come to a disagreement on whether a sound is pleasant or not. Commonly available sound metrics such as tonality, loudness, sharpness, and fluctuation strength can be calculated and combined to quantify sound quality subjectively. This can be achieved through Jury Testing. Modeling sound quality in this way enables engineers and design teams to evaluate and implement comfortability into their products, thereby tailoring them to the targeted end users.
A subjective rating scale for NVH measurements enables us to link human perception and response to environmental factors. While objective measurements provide valuable quantitative data, subjective scales offer insights into the qualitative aspects of NVH, such as sound qualities like annoyance or discomfort. By incorporating subjective assessments, engineers and researchers can better understand the impact of NVH on individuals and communities, leading to more informed and value-added decisions. A sound quality jury test is shown in Figure 21.
Figure 21: In a sound quality jury test, different sound combinations are played for participants and there subjective ratings are recorded.
For instance, "buzz" imitates the sound of a bee, while "squeak" echoes the noise of a mouse. For more information on sound names, please read the following article.
For more information: Describing Sounds with Words
7. Other Considerations
There are many other aspects of performing NVH tests that should be considered. These range from documentation to traceability to time efficient data analysis.
7.1 Documentation and Active Pictures
Good documentation is crucial in NVH data acquisition systems for multiple reasons:
Figure 23: Placeholder image showing that documents, etc can be stored in Documentation area of Simcenter Testlab.
Simcenter Testlab also offers Active Pictures for reports (Word, Powerpoint, etc) as shown in Figure 24:
Figure 24: From a Active Picture in a PowerPoint report, all data properties are available including calibration sensitivity of the transducer and more.
Active pictures contain much of the test documentation. From an active picture, data properties include important items like:
7.2 Efficient Processing
Efficient processing is integral to productive NVH data analysis. Simcenter Testlab can process data during and/or immediately after measurement as shown in Figure 25:
Figure 25: While the data acquisition is in progress, Simcenter Testlab analyzes the data live.
The rapid processing capability offered by Simcenter Testlab allows engineers to rapidly identify and resolve issues within systems as they emerge. This real-time processing ability not only furnishes engineers with timely insights into NVH characteristics but also aids in the early detection of anomalies or other issues so that testing does not have to be done again at a later date.
7.3 Integration with the Digital Twin
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 (Figure 26).
Figure 26: Simcenter Testlab Neo can view and analyze Simcenter Amesim 1D simulation models directly.
Some examples of integration features include:
7.4 Customization and Scripting
Simcenter Testlab's support for Windows automation empowers end-users with unprecedented control and customization options within the software environment. By harnessing the power of automation, users can tap into the extensive internal libraries of Simcenter Testlab, crafting unique processes tailored to their specific needs and workflows. This capability not only enhances efficiency but also fosters innovation by enabling users to leverage the full potential of Simcenter Testlab's feature set.
More information:
7.5 Data Interchange
Simcenter Testlab is an open software platform, and exports/imports and reads a wide variety of file formats. Users can simply browse to an external file via the Navigator (see Figure 27 below), and the software will automatically interpret the file format for you; there is no need to translate files to the Testlab native format (*.ldsf, etc.).
Figure 27: File format export menu in Simcenter Testlab.
Hope this document gives some guidance on key features of a NVH data acquisition system.
Questions? Email peter.schaldenbrand@siemens.com.
Article Contents:
1. What is NVH Testing?
1.1 Noise
1.2 Vibration
1.3 Harshness
2. Measurement System Overview
3. Data Acquisition Hardware
3.1 Sampling Rates
3.2 Anti-Aliasing Filters
3.3 Coupling Filters
3.4 Signal Conditioning
4. Noise Capabilities
4.1 Sound Pressure
4.2 Sound Power
4.3 Sound Absorption and Sound Transmission
4.6 Transfer Path Analysis
5. Vibration Capabilities
5.1 Modal Testing and Analysis
5.2 Operational Deflection Shapes
5.3 Rotating Machinery Vibration
6. Harshness Capabilities
6.1 Sound Quality
6.2 Sound Names
7. Other Key Considerations
7.1 Documentation and Active Pictures
7.2 Efficient Processing
7.3 Integration
7.4 Customization and Scripting
7.5 Data Interchange
1. What is NVH Testing?
Noise, Vibration, and Harshness (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 (Figure 1).
Figure 1: Microphone sound measurement on a white good using a Siemens SCADAS XS noise and vibration measurement system.
To diagnose a noise and vibration issue, it is not enough just to record a few key operator interface locations. Oher 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.
Some further information about each part of the acronym NVH:
1.1 Noise
Noise is another word for the sound or acoustic properties emitted by a product. Noise measurements are often performed for:
Some further information about each part of the acronym NVH:
1.1 Noise
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 (Figure 2).
- 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.
Figure 2: Siemens NVH data acquisition system for pass-by noise regulation testing.
More information on noise:
- Sound Pressure
- Basics: What is a decibel (dB) anyway? Why is it used?
- Noise level certification, how to select the right standard?
- Octaves in Human Hearing
1.2 Vibration
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.
Figure 3: Siemens data acquisition system is used to control and monitor vibration on a test subject during a shaker durability test.
More information on vibration:
- Human Body Vibration
- What is Vibration Control Testing?
- Natural Frequency and Resonance
- Modal Testing Seminar
1.3 Harshness
Harshness pertains to the subjective impression of sound and/or vibration. Consumers want products to sound as expected (Figure 4). 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.
Figure 4: Siemens systems are used in sound quality jury testing to correlate subjective impressions to numerical sound metrics.
More information on harshness:
2. Measurement System Overview
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 & Data Acquisition System (SCADAS) line of hardware.
- Visualization & Analysis Software: For visualizing and further processing of acquired signals. Such as Simcenter Testlab or Simcenter Testlab Neo software.
Figure 5: Example Simcenter Testlab software and Simcenter SCADAS hardware test setup with transducers.
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.
3. Data Acquisition Hardware
Noise, vibration, and harshness data acquisition hardware must be capable of simultaneously sampling multiple sensors and converting them from analog signals to digital signals:
3.1 Sampling Rates and Synchronization
The conversion of sensor readings from analog to digital format requires a high sampling rate (i.e., samples per second) to accommodate the human ear's capability of perceiving frequencies up to 20,000 Hz. This conversion needs to occur at a sufficient speed to accurately capture incoming data. Sampling rates of at least 100,000 samples per second are typically required for this purpose.
Furthermore, synchronous conversion of all sensors, ensuring alignment of every sample across each channel of the hardware, is important as shown in Figure 6:
Figure 6: Synchronized sampling across all channel is important for root cause analysis that requires knowing the phase relationship between different measurement channels.
Synchronized sampling enables the correlation of cause and effect, such as linking a ticking noise to the vibration of an injector. It is also important in many measurements that include phase, for example Frequency Response Functions for modal testing.
No “muxing”! Sampling should not be “muxed” when performing noise or vibration measurements. Muxing means that samples are read at different times from different channels and are not aligned in time and/or phase.
More information in the knowledge article: Digital Signal Processing: Sampling Rates, Bandwidth, Spectral Lines, and more….
3.2 Anti-Aliasing Filters
No matter what sampling rate a data acquisition is capable of, it is always possible that the analog signal being measured contains frequency content higher than the sampling rate can adequately measure.
Anti-aliasing filters must be used on measurement signals to remove frequency content that is too high to be sampled properly. An example is shown in Figure 7 below:
Figure 7: Example how inadequate sampling identifies sound or vibration frequency incorrectly. Above is animated gif.
While the amplitude of the vibration or noise is properly recorded in this example, the frequency is not. Without an anti-aliasing filter, an NVH data acquisition system cannot collect data properly.
More information in the knowledge article: Data Acquisition: Anti-Aliasing Filters
3.3 Coupling Filters
NVH data acquisition systems should also have AC and DC coupling filters. AC coupling filters remove offsets from data being collected, while DC coupling includes the offset. This is shown in Figure 8:
Figure 8: A strain gauge measurement with AC coupling (green) and DC coupling (red).
Depending on the measurement situation, AC coupling or DC coupling may be desirable. Some examples include:
- AC Coupling: NVH measurements are interested in dynamic vibration or sound performance. Including a 1 g offset of gravity in a vibration measurement is not desirable. Similarly, measuring the overall atmospheric pressure is not desirable.
- DC Coupling: Understand the permanent deformation or plastic strain of an object can only be done using DC coupling.
More information: AC versus DC Coupling - What's the difference?
3.4 Signal Conditioning
Signal conditioning is a crucial step preceding analog-to-digital conversion, encompassing various processes aimed at optimizing the quality and integrity of raw sensor data. It is very helpful if the data hardware can handle multiple types of signal conditioning in an integrated fashion. The Simcenter SCADAS hardware shown in Figure 9 has built-in signal conditioning so external amplifiers are not needed.
3.4 Signal Conditioning
Signal conditioning is a crucial step preceding analog-to-digital conversion, encompassing various processes aimed at optimizing the quality and integrity of raw sensor data. It is very helpful if the data hardware can handle multiple types of signal conditioning in an integrated fashion. The Simcenter SCADAS hardware shown in Figure 9 has built-in signal conditioning so external amplifiers are not needed.
Figure 9: Simcenter SCADAS hardware is modular. Signal conditioning cards can be mixed and matched to support any application.
Signal conditioning options include:
- ICP/IEPE: ICP (Integrated Circuit Piezoelectric) sensors or IEPE (Integrated Electronics Piezo-Electric) signal conditioning involves providing the necessary constant current excitation to power the sensor and amplifying its low-level output signal to a suitable voltage level for subsequent processing.
- Charge-type sensing accelerometers are often used in high temperature environments. They require specialized signal conditioning to convert the charge output of the sensor into a voltage signal that can be digitized.
- Digital Audio: Signal conditioning extends to digital formatting protocols like SPDIF (Sony/Philips Digital Interface Format), ensuring seamless transmission of digital audio signals without loss of fidelity.
- Strain: In applications involving strain gauge sensors, signal conditioning encompasses supplying precise excitation voltage and amplifying the small resistance changes induced by strain to ensure accurate measurement of mechanical stress. Onboard completion resistors are also needed for quarter bridge measurements.
Figure 10: Simcenter SCADAS VB8 hardware is used to measure a variety of transducers including ICP accelerometers, strain gauges, potentiometers, microphones, and more...
Overall, signal conditioning plays a pivotal role in enhancing the accuracy, reliability, and compatibility of sensor data for analog-to-digital conversion, thereby facilitating precise measurement.
More articles on signal conditioning:
- Simcenter SCADAS Mobile and SCADAS Recorder
- Microphone Basics
- All About Accelerometers
- How to Measure Strain Gauges with Simcenter Testlab?
- Simcenter Testlab: Measuring a String Pot
- Simcenter Testlab: Working with Charge Accelerometers
- Simcenter Testlab Thermocouples
4. Noise Capabilities
A NVH data acquisition system must be capable of measuring sound in a variety of ways. Sometimes a general sound level must be measured, other times sound is measured in a specific fashion according to certain standards. Some of these sound testing scenarios are covered in the next sections:
4.1 Sound Pressure
Sound pressure is a key parameter in NVH data acquisition systems. Using a microphone, the sound pressure can be shown as a function of time, frequency, octave, or a single overall level value (Figure 11).
Figure 11: A sound pressure frequency spectrum (magenta) overlaid with a sound pressure octave spectrum (green).
Sound pressure is based on the pressure level recorded by a microphone, usually with an underlying pressure unit of Pascals. Instead of Pascals, sound pressure levels are usually converted into decibels or dB. Conversion to decibels is done with a simple right click on the Y-axis as shown in Figure 12:
Figure 12: Right click on Y-axis to convert from Pascals (Pa) to decibels (dB).
Microphones also have a very linear frequency response, while the human ear does not. The A-weighting curve is one way to introduce the effects of human hearing into a microphone recording. This is also done with a right click in the display (Processing -> A-weighting).
For more information:
- Sound Pressure
- Basics: What is a decibel (dB) anyway? Why is it used?
- Root Mean Square (RMS) and Overall Level
- What is A-weighting?
4.2 Sound Power
Sound Power offers a quantified measurement of the acoustic strength of an object in an NVH system and is typically reported in decibels referenced to 1 PicoWatt (1 pW). Unlike sound pressure, sound power is independent of distance and location. Sound power can be calculated from an array of sound pressure microphone measurements as shown in Figure 13.
Figure 13: In a sound power test, microphones surround a test object (tractor) to capture all sound emitted.
Sound power is crucial when analyzing a system, as we can gain information into the overall acoustic behavior of a source. This measurement helps in the design process of a product to optimize components to minimize noise where needed, ensuring a quieter user experience.
There are many ISO and ANSI standards for measuring sound power, and the software needs to calculate sound power according to these standards.
For more information:
- What is Sound Power?
- Sound Pressure, Sound Power, and Sound Intensity: What’s the difference?
- Simcenter Testlab Pass-by Noise Testing
4.3 Sound Absorption and Transmission Loss
Sound absorption and sound transmission loss are measures of a material’s ability to block or absorb sound as shown in Figure 14 below:
Figure 14: Sound absorption is a measure of a materials (purple) ability to absorb sound waves (green). Transmission Loss measures how much a material (red) blocks sound waves (orange).
Absorption measures how well a material absorbs sound, while transmission loss measures how well a material blocks sound.
Absorption expressed as a value between 0 and 1 as a function of frequency. An absorption value of “1” means all sound is absorbed while a value of “0” indicates no sound is absorbed.
Absorption is measured with material samples which are placed in either an impedance tube or a room. An example of the impedance tube measurement is shown in Figure 15 below:
Figure 15: Impedance tube equipment used to characterize the absorption of a material sample.
Transmission loss, which indicates how well a material blocks sound is expressed in dBs of attenuation. The higher the dB value, the more sound that is blocked. Just like absorption, an impedance tube or room can be used to measure transmission loss.
For more information, see articles:
4.6 Transfer Path Analysis
Transfer Path Analysis (TPA) offers a systematic approach to analyzing and understanding key contributors to noise and vibration issues. These contributors are identified using source loads and transfer functions to the response at a target location (Figure 16).
Figure 16: Acquiring transfer functions on a vehicle body as part of the Transfer Path Analysis process.
TPA helps to identify specific sources contributing to noise and vibration problems in a system in an efficient manner. With the knowledge of how energy is transferred through a system, engineers can optimize design and enhance overall performance in a product.
For more information:
- An Introduction to Transfer Path Analysis
- Blocked Forces versus Contact Forces in Transfer Path Analysis (TPA)
- Time Domain Transfer Path Analysis: Listening to Paths!
5. Vibration Capabilities
Vibration, just like sound, is often measured as a function of time or frequency. Lowering vibration levels helps ensure that products last longer, perform properly, and do not cause any damage to human health.
Measuring vibration levels is important, but to understand the root cause of vibration, tools like Operational Deflection Shapes and Modal Analysis are also needed.
5.1 Modal Analysis
Modal analysis entails examining the resonant behavior of a component and its reaction to mechanical excitation. This encompasses inducing vibrations in the component and analyzing its modal parameters: natural frequencies, damping, and mode shapes.
An example modal test and its results are shown in Figure 17:
Figure 17: Left – Physical modal test with exciters and transducers attached to airplane, Right – Mode shape result from modal test. above is animated
This process requires the acquisition of vibration data and the computation of Frequency Response Functions (FRFs). Modal analysis holds significance as it sheds light on the intrinsic characteristics of structures. Discerning flexible modes of vibration reveals how components vibrate as cohesive entities, thereby enabling better designs and mitigating objective vibrations.
Modal analysis utilizes different excitation methods such as impact testing and shaker testing to characterize the dynamic behavior of structures as shown in Figure 18.
Figure 18: Impact and shaker testing for modal analysis.
Impact testing involves striking the structure with an impulsive excitation, typically using an instrumented hammer. Shaker testing employs a controlled mechanical vibration from either a coupled electromechanical or hydrodynamic device to force the structure to respond to a certain profile across a range of frequencies.
Impact testing can be quickly applied to a wide range of structures and does not require complex setup or instrumentation. The exact excitation frequency range can only be controlled via selection of hammer tip stiffness and mass.
Shaker testing offers precise control over the excitation force and frequency, allowing for repeatable and consistent results. Shaker testing also enables the excitation of structures at multiple input points simultaneously, facilitating more comprehensive modal analysis. However, shaker testing typically requires more elaborate setup and instrumentation.
For more information:
- What is a Frequency Response Function (FRF)?
- Modal Testing: A Practical Guide
- Simcenter Testlab Impact Testing
- Simcenter Testlab MIMO FRF Testing
- Simcenter Testlab MIMO Swept and Stepped Sine
- Using Pseudo-Random for high quality FRF measurements
- Qsources: Acoustic and Structural Exciters
5.2 Operational Deflection Shapes
Operational Deflection Shape (ODS) analysis plays a crucial role in understanding the dynamic behavior of structures and machinery during operation by visualizing the underlying patterns or shapes exhibited by a structure while in operation as shown in Figure 19.
Figure 19: Operational deflection shape of the “tramp” mode of a front axle in a truck.
Siemens Simcenter Testlab enables engineers to visualize and interpret complex vibration data under real-world operating conditions, which can help identify potential sources of vibration, resonance phenomena, or structural weaknesses.
For more information:
5.3 Rotating Machinery Vibration
Rotating machinery creates a variety of vibrations, from imbalance forces to torsional vibration to order driven phenomenon (Figure 20):
Rotating machinery creates a variety of vibrations, from imbalance forces to torsional vibration to order driven phenomenon (Figure 20):
Figure 20: Simcenter SCADAS (right, foreground) used to perform rotating machinery (left, background) analysis.
Specialized tools allow the quick analysis of rotating vibration issues which include order analysis, colormaps or spectrograms, angle domain visualization, and more.
For more information:
- What's an Order?
- Simcenter Testlab Signature
- Balancing: Static, Coupled, and Dynamic
- Torsional Vibration: What is it?
- Angle Domain: What is it?
6. Harshness Capabilities
Traditionally, harshness was a term used in the automotive industry during the transition from wooden to all-metal body structures. It was commonly perceived at that time that all-metal bodies sounded “harsher” than their wooden counterparts. Technically speaking though, harshness refers to the perceived discomfort or annoyance as indicated by NVH measurements in a given environment.
Engineers can utilize Simcenter Testlab to precisely measure vibration levels and acoustic signatures. By correlating these measurements with human perception data, such as subjective rating scales, engineers can accurately assess the degree of harshness experienced by occupants or users. This holistic approach ensures products meet the desired comfort and quality standards.
6.1 Sound Quality
Sound quality in NVH data acquisition differs from other aspects due to its’ subjective nature. For example, two different people may come to a disagreement on whether a sound is pleasant or not. Commonly available sound metrics such as tonality, loudness, sharpness, and fluctuation strength can be calculated and combined to quantify sound quality subjectively. This can be achieved through Jury Testing. Modeling sound quality in this way enables engineers and design teams to evaluate and implement comfortability into their products, thereby tailoring them to the targeted end users.
A subjective rating scale for NVH measurements enables us to link human perception and response to environmental factors. While objective measurements provide valuable quantitative data, subjective scales offer insights into the qualitative aspects of NVH, such as sound qualities like annoyance or discomfort. By incorporating subjective assessments, engineers and researchers can better understand the impact of NVH on individuals and communities, leading to more informed and value-added decisions. A sound quality jury test is shown in Figure 21.
Figure 21: In a sound quality jury test, different sound combinations are played for participants and there subjective ratings are recorded.
These scales enable the characterization of perceived loudness, pitch, and vibrational intensity, helping to tailor mitigation strategies and ensure compliance with regulatory standards. Additionally, subjective ratings facilitate effective communication of findings to stakeholders, fostering greater awareness and engagement in addressing noise and vibration concerns.
6.2 Sound Names
Humans have an innate tendency to associate sounds with familiar phonetic patterns, often resulting in the creation of names for those sounds. This phenomenon stems from our innate need to make sense of our surrounding environment. Onomatopoeic words mimic the sounds they describe, bridging the gap between perception and expression (Figure 22).
For more information:
- Sound Quality Metrics: Loudness and Sones
- Sound Modulation Metrics: Fluctuation Strength and Roughness
- Tone-to-Noise Ratio and Prominence Ratio
- Sharpness in Simcenter Testlab
- Sound Metrics: Speech Interference Level
- Articulation Index
- Sound Quality Jury Testing
6.2 Sound Names
Humans have an innate tendency to associate sounds with familiar phonetic patterns, often resulting in the creation of names for those sounds. This phenomenon stems from our innate need to make sense of our surrounding environment. Onomatopoeic words mimic the sounds they describe, bridging the gap between perception and expression (Figure 22).
Figure 22: Onomatopoeic words mimic the sounds.
For instance, "buzz" imitates the sound of a bee, while "squeak" echoes the noise of a mouse. For more information on sound names, please read the following article.
For more information: Describing Sounds with Words
7. Other Considerations
There are many other aspects of performing NVH tests that should be considered. These range from documentation to traceability to time efficient data analysis.
7.1 Documentation and Active Pictures
Good documentation is crucial in NVH data acquisition systems for multiple reasons:
- Clear documentation also increases accuracy and reliability when collecting data. This can be valuable for use in troubleshooting future projects where similar issues may occur. Documentation can include not only the test object information, like product model, serial number, and configuration, but also the instrumentation serial numbers, locations, etc.
- Test templates and test procedures: With new team members joining projects, documentation can increase workflow efficiency by providing past references on testing practices, etc.
- Provides end-to-end traceability of published data: When and how it was acquired, signal conditioning settings, transducer information, processing parameters, and more.
Within Simcenter Testlab, the Documentation worksheet is the first available tab. The Documentation tab allows users to keep track of test details in a particular Simcenter Testlab project, providing an easy, convenient way to keep all the information about a test in a central location as shown in Figure 23.
Figure 23: Placeholder image showing that documents, etc can be stored in Documentation area of Simcenter Testlab.
Simcenter Testlab also offers Active Pictures for reports (Word, Powerpoint, etc) as shown in Figure 24:
Figure 24: From a Active Picture in a PowerPoint report, all data properties are available including calibration sensitivity of the transducer and more.
Active pictures contain much of the test documentation. From an active picture, data properties include important items like:
- Serial number and transducer model
- Calibration sensitivity
- Project file name and creation date
- Processing parameters like sampling rates, spectral resolution.
- Engineering unit information
- Applied windows and correction factors
Active pictures also save time in making reports. Graphs can be altered and changed directly in PowerPoint without having to go back to the original application to change the view.
More information:
More information:
7.2 Efficient Processing
Efficient processing is integral to productive NVH data analysis. Simcenter Testlab can process data during and/or immediately after measurement as shown in Figure 25:
Figure 25: While the data acquisition is in progress, Simcenter Testlab analyzes the data live.
The rapid processing capability offered by Simcenter Testlab allows engineers to rapidly identify and resolve issues within systems as they emerge. This real-time processing ability not only furnishes engineers with timely insights into NVH characteristics but also aids in the early detection of anomalies or other issues so that testing does not have to be done again at a later date.
7.3 Integration with the Digital Twin
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 (Figure 26).
Figure 26: Simcenter Testlab Neo can view and analyze Simcenter Amesim 1D simulation models directly.
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
- Accessing Simcenter3D Motion Results in Simcenter Testlab
- Nastran and Simcenter Testlab: Viewing Mode Shapes and FRFs
- Correlating Simulation & Modal Test Results with Simcenter 3D
- Using Simcenter Testlab Project Files in Simcenter 3D Correlation
- Accessing Simcenter Amesim Models in Simcenter Testlab Neo
- Simcenter Testlab Neo and Functional Mock-Up Interface
- Modal Analysis and FEA-Test Correlation Seminar
- Virtual Prototype Assembly (VPA) Seminar
7.4 Customization and Scripting
Simcenter Testlab's support for Windows automation empowers end-users with unprecedented control and customization options within the software environment. By harnessing the power of automation, users can tap into the extensive internal libraries of Simcenter Testlab, crafting unique processes tailored to their specific needs and workflows. This capability not only enhances efficiency but also fosters innovation by enabling users to leverage the full potential of Simcenter Testlab's feature set.
More information:
- Simcenter Testlab Automation
- Simcenter Testlab Automation Forum
- Simcenter Testlab Automation: Application Objects
- Simcenter Testlab Automation: Parameters
- Simcenter Testlab Automation: Display Example Program
- Simcenter Testlab Automation: Cursor Example Program
- Simcenter Testlab Automation: Excel Export Example Program
- Simcenter Testlab Automation: Measurement Example Program
7.5 Data Interchange
Simcenter Testlab is an open software platform, and exports/imports and reads a wide variety of file formats. Users can simply browse to an external file via the Navigator (see Figure 27 below), and the software will automatically interpret the file format for you; there is no need to translate files to the Testlab native format (*.ldsf, etc.).
Figure 27: File format export menu in Simcenter Testlab.
File types include:
- Simcenter Time Files (*.ldsf)
- Simcenter Testlab Projects (*.lms)
- CADA-X Database (*.idx)
- DSPCON DATX
- Excel, ASCII, CSV (*.xlsx, *.xls, *.csv)
- WAV (*.wav)
- Universal File (*.unv, *.uff)
- RPC3 (*.rsp)
- Standard Data File (*.sdf and *.dat)
- MATLAB (*.mat)
- TEAC TAFFmat (*.hdr)
- NASTRAN (*.pch, *.bdf, *.op2)
- ANSYS (*.rst)
- ABAQUS (*odb)
- Simcenter3D Motion Results Files (*.mres)
- Simcenter Amesim (*.ame)
- I-DEAS (*.ati, *.afu, *.ash)
- ASAM-ODS (*.atfx)
- MDF 3.0 and higher (*.mdf, *.dat)
- GPS (*.nmea and *.kml)
- IST RigSys (*.dmd, *.drv, *.acq, *.tgt)
- And more...
Hope this document gives some guidance on key features of a NVH data acquisition system.
Questions? Email peter.schaldenbrand@siemens.com.