Vibrationdata Matlab Signal Analysis & Structural Dynamics Package

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Please send me an Email if you are going to use this package.

Thank you,
Tom Irvine
Email: tom@irvinemail.org

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Here is a Matlab GUI multi-function signal analysis package:
Vibrationdata Signal Analysis Package

Alternate Link for Package

The main script is: vibrationdata.m

The remaining scripts are supporting functions.

This is a work-in-progress. Some features are not yet installed but will be in a future revision. Please check back for updates.

The download and extraction process should be straightforward, but here are some slides for those who need instruction:  Vibrationdata_download.pptx

See also:  An Introduction to Shock & Vibration Response Spectra eBook

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Here are some webinar and slide presentations which demonstrate the use of the GUI package in exercises:

Webinar Index

Structural Dynamics Webinars

Fatigue Webinars

Seismic Test & Analysis Webinars

Circuit Board Shock & Vibration Analysis

Nastran Modal Transient & Response Spectrum Analysis for Base Excitation

Launch Vehicle Vibroacoustics

Vibroacoustics/Statistical Energy Analysis

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Currently installed features include:

autocorrelation & cross-correlation
Bessel, Butterworth & mean filters
Fourier transform, FFT, waterfall FFT, spectrogram
FFT for Machine Vibration ISO 10816
PSD, cross power spectral density & energy spectral density
PSD time history synthesis
SRS & SRS Tripartite
SRS time history synthesis
SDOF response to base input and applied force
SPL
cepstrum & auto-cepstrum
integration & differentiation
trend removal
rainflow cycle counting
fatigue damage spectrum
ISO Generic Vibration Criteria
modal frequency response functions including H1, H2 & coherence
half-power bandwidth method for damping estimation
generate sine, white noise and other time history waveforms
Helmholtz resonator
spring surge natural frequencies
Davenport-King wind spectrum
Dryden & von Karman gust spectra
Pierson-Moskowitz Ocean wave spectrum
rectangular plate analysis using both classical and finite element methods
spherical bearing stress
unit conversion

Future revisions will have additional functions.

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Please contact me if you have suggestions for added features or if you find bugs.

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See also: Python Signal Analysis Package

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Tom Irvine

Hot Fire Test of an Upper Stage Rocket Engine

rocket4

Liquid fuel rocket engines undergo hot fire testing before flight in order to verify their performance, design integrity, etc.  The engines are mounted to heavy-duty, immovable stands for this purpose.   These tests are also referred to as static fire tests.

Furthermore, the tests are almost always performed at ground ambient air conditions, which is appropriate for first stage engines.  Similar tests are performed for solid rocket motors.

Upper stage engines are also subjected to ground ambient air static fire tests.  But the test data is skewed by the atmospheric pressure effects.  These engines can and should also be fired in altitude simulation chambers, although these more realistic tests are more expensive and time-consuming than open air tests.  An example is the NASA Glenn In-Space Propulsion Facility.

Rocket engine designs often incorporate high expansion ratio nozzles for increased performance.

The flow in the nozzle will separate from the nozzle wall, with a resultant reduction in thrust when these nozzles are operated in an ambient pressure significantly higher than what they were designed for.

Separated flow can also cause nozzle burning due to the shock wave that exists at the separation point, nozzle damage due to unsymmetrical pressure distribution, and excessive vibration as the separation point moves erratically around the nozzle.

The following paper shows that the rocket engine overall vibration level may be as much as 18 dB higher at ground ambient air versus altitude simulation:   Influence study of flow separation on the nozzle vibration response

– Tom Irvine

Blue Origin Employment Opportunities

New_Shepard_Launch_June_19_2016.0.0

New Shepard Launch

I have been working at Blue Origin in Kent, WA since February 2019.  This is an excellent work environment with engaging technical opportunities.

Blue Origin is hiring engineers including some for vibroacoustics.

Please see:  https://www.blueorigin.com/careers

Applicants must be a U.S. citizen or permanent resident (current Green Card holder), or lawfully admitted into the U.S. as a refugee or granted asylum.

You are welcome to apply via the above link.  Please also send your resume to me if you are interested in vibroacoustics.

Thank you,
Tom Irvine
Email:  tom@irvinemail.org

Launch Vehicle Separation Source Shock Scaling Hypothesis

Consider the case where flight or test pyrotechnic source shock data has been measured on a launch vehicle with a 1-meter diameter aluminum cylindrical shell.  Assume that the source device is frangible joint with a certain number of grains per length.  Now the same device will be used on a new 5-meter diameter vehicle with all other variables remaining the same. The question arises as to how the 1-meter data source shock data can be extrapolated to the 5-meter diameter vehicle prior to any testing of the new vehicle’s structure.

A hypothetical method is presented in:  source_shock_hypothesis.pdf

This method maintains a constant pseudo velocity at the knee frequency as the frequency is shifted for the new vehicle.  Note that the knee frequency is the same as the respective ring frequency.

Experimental verification is pending, but the method is rational.

See also: pyrotechnic shock 

– Tom Irvine

More Launch Vehicle Vibroacoustics

This is a work-in-progress.

Here are some slide presentation with an emphasis on launch vehicles.

Equivalent Static Loads for Random Vibration & Alternate Link

Damping & Isolation & Alternate Link

Liftoff Vibroacoustics & Alternate Link

Ascent Vibroacoustics & Alternate Link

Launch Vehicle Pogo, Combustion Instability and Thrust Oscillation & Alternate Link

Launch Vehicle Statistical Energy Analysis & Alternate Link

Modal Testing, Part I & Alternate Link

The Matlab GUI package and additional slide presentations may be downloaded at:

Vibrationdata Matlab Signal Analysis & Structural Dynamics Package

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The aerodynamic flow-induced pressure during the transonic and maximum dynamic pressure phases can be calculated using the follow tools:

Prediction of Sound Pressure Levels on Rocket Vehicles During Ascent:
flow.pdf & Alternate Link

See also:

NASA SP-8072 Launch Vehicle Liftoff Acoustics 

Vibroacoustics/Statistical Energy Analysis

Non-Gaussian Acoustic Pressure Amplitudes in High-Intensity Sound Fields

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Miscellaneous

Launch Vehicle Tip Over Analysis

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– Tom Irvine

State-Space Method for Systems with Dashpot Damping

two_dof_system_dashpots

Structural dynamics systems can be represented in terms of mass, damping and stiffness matrices.  Each of these matrices may be coupled depending on the model complexity, degrees-of-freedom, etc.   The mass and stiffness matrices in the assembled equation of motion may be uncoupled using the normal modes for the undamped system.  This approach gives real natural frequencies and real mode shapes.

Damping effects can be included in forced response analyses by implicitly assuming that the damping matrix can be diagonalized into modal damping coefficients by the undamped modes.   But systems with dashpots in general have damping matrices which cannot be uncoupled in this manner.

The state-space method is useful for modal and forced response analysis of systems with discrete dashpot damping.  This approach yields complex natural frequencies and mode shapes, with real and imaginary components.

Here is a paper:

Two-Degree-of-Freedom System, State-Space Method:   two_dof_state_space_revC.pdf

More later…

– Tom Irvine

Damping Identification from Shock Data via Wavelet Responses

three_shocks

Structural system & component damping can measured via modal testing with applied force excitation.  One excitation method is an impulse hammer test.  Another method is a  small shaker attached to structure via a stinger rod.

Damping can also be measured by mounting the test unit on a shaker table and applying base excitation.

There is a need to estimate component damping from pyrotechnic or pyrotechnic simulation shock tests where the source energy measurements are incomplete or unavailable.  This need may arise because modal and shaker table test data is unavailable.  Furthermore, damping is nonlinear and may be higher for a pyrotechnic shock event than for a modal or shaker table test

A source shock waveform can be modeled by a series of wavelets per Ferebee R , Irvine T, Clayton J, Alldredge D,  An Alternative Method Of Specifying Shock Test Criteria,  NASA/TM-2008-215253.   This method was original develop to characterize space shuttle solid rocket booster water impact shock.  This method can be extended for natural frequency and damping measurement for shock data.

The Wavelet Response Curve-fit Methodology is appropriate for mid and far field shock measurements where modal responses appear in the accelerometer time history data.

The method is implement via the following steps:

  • Assume a series of wavelet as the base input
  • Calculate the response of one or more SDOF systems to the assumed wavelet series
  • Subtract the resulting response signal from the measured accelerometer data and calculate error
  • The goal is to repeat this process thousands of times where the to minimize the residual error
  • Each of the following parameter are varied randomly with convergence
  • For each base input wavelet: frequency, amplitude, number of half-sines, delay
  • For each SDOF oscillator response: natural frequency, damping

The method yields natural frequency and damping estimates for the response acceleration.  It also gives an estimate of the assumed base input source shock.

The method is demonstrated in the following slides.

Slides:  shock_wavelet_damping_revC.pptx

Matlab scripts & sample shock data: Vibrationdata Signal Analysis Package

avionics_shock_data.mat

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Reference Papers:

An Alternative Method Of Specifying Shock Test Criteria:
NASA/TM-2008-215253 & PowerPoint slide overview

 

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– Tom Irvine

Damping References

pdtrans

Structural damping depends on materials, joints, boundary conditions, friction, acoustic radiation, etc.  Damping may be nonlinear, increasing as the excitation and response levels rise. The damping for a given structure or component must be measured!  

But here is some empirical background data…

Papers

Damping Properties of Materials

Damping Cross-Reference

Damping Values in Aerospace Structures and Components

Free Vibration with Coulomb Damping

Damping Identification Rev A

Related Blog Posts

Honeycomb Sandwich Panels

Vibroacoustics/Statistical Energy Analysis  – empirical formulas for loss factors

Wire Rope Cable Damping

Tall Building Natural Frequencies and Damping

Piezoelectric Shunt Damping

Nonlinear Modeling of Bolted Interfaces & Joints

Convert Modal Damping to a Damping Coefficient Matrix

Vibration Absorbers & Tuned Mass Dampers

Half-Power Bandwidth Method

Isolation

Isolator Photo Gallery

Avionics Box Isolation

Transmissibility of a Three-Parameter Isolation System

Webinar 43 – Two-degree-of-freedom System, Two-stage Isolation

– Tom Irvine

Engineering Status Reports

For the past eight years, I have written a required monthly status report to another organization for my NASA contractor work. I have written my accomplishments and planned work in short, concise sentences, usually in numbered list format.

I was then notified by this organization that the writing rules had been changed substantially. The new rules prohibited bullet or numerical list format. Personal pronouns could no longer be used. The sentences must be varied to avoid beginning each with the subject. The writing had to be in paragraph format with three sentences per paragraph, and on and on. There were so many new rules that I did not even read all of them. I wondered if perhaps an English literature major had been given an administrative role and was projecting his or her frustrations by imposing Byzantine writing style rules upon myself and others in this technical community.

So I submitted the following status report, with slight edit changes to avoid disclosing any proprietary information. I refer to myself in third person as the “greybeard.”

The organization responded by instructing me to return to my previous, concise writing style for the status reports, exempting me from the new rules.

And I really did give a presentation to NASA engineers that included a slide about monkeys SLaMS_SCLV201_keynote_revA.ppt

– Tom Irvine

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Significant Accomplishments:

Dynamics Engineering: A Call to Serve! Enlightened were the apprentices as the greybeard mentored them with this presentation at the SLaMS Early Career Community webinar meeting, March 27, calling upon them to share their knowledge and become themselves teachers of the rising generation, underscored with Seneca the Younger’s proverb Docendo discimus – Latin “by teaching, we learn.” Reciprocal altruism of Vervet monkeys! Blind Faults underneath the Los Angeles Basin! Dragons to be launched on towering SpaceX boosters powered by Merlin engines! Thus was the eclectic tutelage of that day.

The raw, ominous Zeus-like power of pyrotechnic shock pulses cutting through rocket joint metal, propagating through modules and threatening sensitive electronic parts mounted on circuit boards – such has been the forlorn of many a NASA engineer. To which challenge did the greybeard prepare shock, structural dynamics, fatigue and statistical energy analysis software and training materials as tools for discerning the energy’s spectral content.

Work Planned:

Gathered will be engineers at the NESC Joint GN&C TDT and L&D TDT F2F Meeting at MSFC – week of April 16, 2018, bringing opportunities of collaboration for the greybeard and his esteemed colleagues. New ideas will arise upon which the greybeard will muse, research and present new papers and methodologies, knowing that if he sees farther than others– it is because he stands on the shoulders of giants.

The response of mechanical components bending and flexing in multi-modes driven by the surging oscillations of pyrotechnic shock waves, the stresses pulling molecules apart, potentially inducing cracks which threaten both component and launch vehicle, for which the greybeard is preparing a presentation for the Aerospace Spacecraft and Launch Vehicle Dynamic Environments Workshop, El Segundo, CA, June 26-28, 2018 – this and more are the planned endeavors for the month of April.

Deliverables:

Matlab scripts, the tools for synthesizing acceleration time histories across a series of wavelets, the greybeard’s quest to numerically replicate the damage potential of powerful undulations which could break launch vehicle components and structure, will be conveyed to NASA engineers. Tutorials and slides with examples using the scripts will be provided, enabling these ladies and gentlemen to perform calculations of their own in service of America’s space program.

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Here is the bullet version, with no literary allusions.

Significant Accomplishments:

1. Gave presentation “Dynamics Engineering: A Call to Serve!” to the NASA SLaMS Early Career Community via webinar meeting, March 27. Presentation included references to reciprocal altruism of Vervet monkeys and blind faults underneath the Los Angeles basin.
2. Writing avionics component FEA shock analysis software and tutorials for NASTRAN implementation.

Work Planned:

1. Preparation of structural dynamics & statistical energy analysis software & webinars.
2. Prepare presentation for the Aerospace Spacecraft and Launch Vehicle Dynamic Environments Workshop, El Segundo, CA, June 26-28, 2018. Presentation title is Avionics Component FEA Shock Analysis.
3. Participate in the NESC Joint GN&C TDT and L&D TDT F2F Meeting at MSFC.

Deliverables:

1. Webinar audio/visual presentation files.
2. Revised Matlab & Python GUI signal analysis packages with enhanced features.
3. Statistical energy analysis, structural dynamics, vibration fatigue software and tutorial papers.

Honeycomb Sandwich Panels

Honeycomb-Sandwich-Panels-Marketimg_20171107_170159_750x750

Honeycomb sandwich structures are designed to have a high stiffness-to-mass ratio.   The stiff, strong face sheets carry the bending loads, while the core resists shear loads.

The face sheets are typically made from aluminum or carbon fiber with epoxy resin.

The honeycomb core material is usually aluminum for aerospace applications.   Other core materials include Nomex aramid or Kevlar para-aramid fiber sheets saturated with a phenolic resin.  In addition, closed cell foams such as Rohacell are substituted for honeycomb in some sandwich panel designs.

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According to Klos, Robinson and Buehrle…

Panels constructed from face sheets laminated to a honeycomb core are being incorporated into the design of modern aircraft fuselage and trim treatments. The mechanical properties of these panels offer a distinct advantage in weight over other commonly used construction materials.

The strength to weight ratio of honeycomb composite panels is high in comparison to rib stiffened aluminum panels used in previous generations of aircraft. However, the high stiffness and low weight can result in supersonic wave propagation at relatively low frequencies, which adversely affects the acoustical performance at these frequencies.

Poor acoustical performance of these types of structures can increase the cabin noise levels to which the passengers and crew are exposed.

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Honeycomb sandwich structures are used in a wide variety of critical structures in Air
Force space systems. These include payload fairings (shrouds) for launch vehicles, adapters for mounting of satellite payloads, solar array substrates, antennas, and equipment platforms.

Since 1964, there have been several known or suspected failures of honeycomb structures. These failures have been attributed to the lack of venting in the panel design manufacture. On the other hand, based on available information, vented honeycomb sandwich panels never have experienced failure during flight. In the cases documented herein, the consequences of the failures have been significant and costly.

Honeycomb sandwich panels that are not vented will contain air (and possibly volatiles,
including moisture) which causes a pressure differential during launch into orbit. If heating also is involved, the internal pressure will rise further. In any case, each individual unvented honeycomb cell acts as a tiny pressure vessel imposing stresses on the skin-to-core bonds. If these stresses are high enough, panel failure (i.e., skin-to-core debonding) will occur. Certain defects introduced during panel manufacture would make failure more likely.

Excerpt from:  SMC-TR-94-02

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Constrained layer damping material consists of a viscoelastic material on the bottom and a stiff constraining layer on top

It uses shear deformation in the viscoelastic layer for energy dissipation

The use of “add-on” constrained layer damping may be difficult to achieve for composite and sandwich-composite structures due to the high stiffness of the base structure. Better damping is achieved by embedding the viscoelastic material either in the skin or in the core.

Reference:  Hambric, Sung, Nefske, Engineering Vibroacoustic Analysis, Wiley, West Sussex, United Kingdom, 2016

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Here are some references:

Natural Frequencies of a Honeycomb Sandwich Plate:  honeyG.pdf

Honeycomb Sandwich Panel Damping:  honeycomb_sandwich_damping.pdf

Honeycomb Sandwich Ring Mode Frequency:  honeycomb_sandwich_ring_frequency.pdf

Hexcel Honeycomb Sandwich technical information:  honeycomb_design.pdf

Sound Transmission through a Curved Honeycomb Composite Panel:  ST_curved_honeycomb_panel.pdf

More later…

– Tom Irvine

An Indirect Method for Converting a Shock Response Spectrum Specification to a New Q Value

  •  Aerospace pyrotechnic shock response spectrum (SRS) specifications are almost always given with an amplification factor Q=10
  • Corresponding time history waveforms for the base input acceleration are almost never given with the specifications
  • Users are allowed to synthesize their own waveforms to satisfy the SRS for analysis & test purposes
  • Some shock analysis methods use the SRS directly without time history synthesis, such as modal combination methods
  • The following method enables an SRS specification to be converted to a new Q value for engineering purposes

Slides:  150_SRS_specification_new_Q.pptx

Software: Matlab Vibrationdata GUI

– Tom Irvine