Magazine Articles
Modal Space: Back to Basics
- Could you explain modal analysis for me?
- Could you explain the difference between the time domain, frequency domain and modal space?
- Is there any difference between a modal test with a shaker excitation or impact excitation?
- Is there any difference between a roving hammer and a roving accelerometer?
- Should I always use a hard tip for impact testing so the input spectrum is flat over all frequencies?
- Which shaker excitation is best? Is there any difference?
- Curve fitting is so confusing to me! What do all the different techniques mean?
- I still don't understand curve fitting. How do I get mode shapes from FRFs?
- What's the difference between operating deflection shapes and mode shapes?
- Are you sure you can get mode shapes from one row or column of H?
- I heard someone say "Pete doesn't do windows!" What's the scoop?
- I'm still overwhelmed by all this modal stuff - give me the big picture!
- I showed some mode shapes to someone; they asked if the structural design was OK?
- Can I use an oblique angle to run a modal test?
- How many points are enough when running a modal test?
- Someone told me SDM will never work since I don't have all of the modes
- Why is mass loading and data consistency so important for modal parameter estimation?
- I hear about SVD all the time; could you explain it simply to me?
- Does it make any sense to use actual loads when doing a modal test?
- When impact testing, can the use of the exponential window cause any problems?
- Is there any benefit to using multiple references? I thought only one reference was needed?
- What are some of the most important things to consider when impact testing?
- Should I use all measurements when estimating modal parameters?
- Can the test setup have an effect on the measured modal data?
- Which window is most appropriate for the various types of modal tests performed?
- What is the difference between a complex mode and a real normal mode?
- Could you please explain the basic steps to acquire data for modal testing?
- Is there any real advantage to MIMO testing? Why not just collect SISO and then move the shaker?
- What are some of the major mistakes that people make in modal tests so I don't make the same ones?
- Is it better to collect averaged FRF data for a modal test? or collect time data and process it afterwards?
- Why is calibration and mode shape scaling important and does it make a difference?
- Is it really necessary to reject a double impact? Are they really a problem?
- Someone told me that you must have multiple references to identify pseudo repeated roots
- I ran a modal test on a portion of a structure of concern and many modes look the same! What did I do wrong?
- Why do some measurements have anti-resonances and others do not?
- What's the difference between local and global curvefitting ??
- We talked about the number of points needed for a modal test before. Someone told me that the entire shape may not need to be completely defined.
- Do I need to have an accelerometer mounted in the X, Y and Z directions to do a modal test?
- Mode shape scaling requires a drive point measurement. Is there any way to scale shapes without this?
S&V Questions and Answers
- Transducer Signal Conditioning Overload Effects
- The Exponential Window
- Microphone Selection
- The Relationship Between % of Critical and Actual Damping in a Structure
- Dynamic Range
- Accelerometer Dynamic Range
- How to Check Condenser Microphones for Damage
- Checking Piezoelectric Accelerometers for Damage
- How do we Define 'Overall' and 'Broadband'
- Do Mode Shapes Determined from Two Different Impact Testing Techniques Contain the Same Information
- Is it Important to Hit the Same Point in the Same Direction When Making Impact FRF Measurements
- What is the Coherence Function and How Can It Be Used to Find Measurement and Test Setup Problems
- What are the Sources of Variation in Frequency Response Measurements
- Differences in Measurement and Studio Microphones
- Excitation Direction in Modal Testing - Is It Important?
- Measurement of Leq Using an Integrating SLM
- Choosing a Spectral Measurement for Data Analysis