Rectangular Plate Bending Frequencies and Mode Shapes, Finite Element Method, GUI version

mm1

I have added a feature for rectangular plate bending modes to the Matlab GUI package.

Matlab script: Vibrationdata Signal Analysis Package

The script allows for the addition of point masses and point constraints.  This is a work-in-progress.  The next step will be to add base excitation options.

The new feature can be accessed via:

vibrationdata > Miscellaneous > Structural Dynamics > Plates, Rectangular & Circular > Rectangular Plate, Finite Element Method

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Here is a reference paper: FEA_plate_bending.pdf

See also:  Dynamic Response to Enforced Motion

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– Tom Irvine

Two-degree-of-freedom System Subjected to an Applied Force

twodof

I have added a feature for a two-degree-of-freedom system subjected to an applied force to the Matlab GUI package. The applied force options are steady-state sine, arbitrary time history and PSD.

Matlab script: Vibrationdata Signal Analysis Package

The new feature can be accessed via:

Vibrationdata > Miscellaneous > Structural Dynamics > Spring-Mass Systems > Two-DOF System Applied Force

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Here are some related papers:

Calculating Transfer Functions from Normal Modes
An Introduction to Frequency Response Functions
Semidefinite System Force
General Coordinate Method
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– Tom Irvine

Correcting Acceleration, Velocity & Displacement Time Histories

There is a need in certain analysis problems to correct an acceleration signal so that its integrated velocity and double integrated displacement each oscillates about its respective zero baseline.  This may require using high pass filtering, trend removal and tapering throughout the integration process.  Trial-and-error is required to select the optimum combination of steps.

The steps are needed in part because the initial velocity and displacement are undefined.  Also, the acceleration may have a spurious offset or trend for the case of measured data.

Furthermore, the resulting displacement should be such that it can be recovered if it is then double differentiated to acceleration and the acceleration is then double integrated back to displacement.  This requirement is for rigor.  It yields a consistent set of acceleration, velocity and displacement time histories where each oscillates about its respective zero baseline.

This feature is now included in:

Matlab script: Vibrationdata Signal Analysis Package

Time History > Integrate or Differentiate > Correct Acceleration, Velocity, Displacement

Sides: acceleration_correction.pptx

– Tom Irvine

Boeing 717-200

1024px-AirtranJet

I recently flew as a passenger on a Boeing 717-200 aircraft similar to the one shown in the image.  This aircraft has two Rolls-Royce BR700 engines, with the following specifications:

Maximum Engine Rotational Speeds (Both Engines)

N1 Low Pressure Turbine = 6,195 RPM (103 Hz)
N2 High Pressure Turbine = 15,898 RPM (265 Hz)

I made an audio recording from inside the cabin during take-off and climb-out.

data_plot

The sound file Fourier transform for a 10-second segment is shown in the image.

The first peak is at 88 Hz, which is 85% of the maximum N1 speed.

The second peak is at 129 Hz and is unidentified.

Most of the higher frequency peaks are integer multiples of 88 Hz.

Complete audio file:  Boeing_717_200.mp3

The Fourier transform was taken from 40 to 50 seconds into the recording.

A “buzz saw” sound occurs due to shock waves at the turbofan blade tips which have a supersonic tangential velocity.

– Tom Irvine

Digitizing Plots

Gallery

Here is audio/visual file:  Digitizing Plots Here are slides, Matlab scripts and data samples:  Unit_33_PP.zip Here is another script:  digitize_plots.m This is vintage presentation.  I need to add the Matlab scripts to the Vibrationdata GUI package. – Tom Irvine

Notes on Fatigue for Pure Compression Stress

Fatigue is usually associated with tensile stresses.

Engineering knowledge of compressive fatigue is very limited. Compression stresses do not cause cracks, but plastic compressive strain can cause tension stresses when the load is returned to zero and the resulting tension stress causes cracks.

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R = min stress/max stress

But R ->   – infinity   for pure compression stress and with max stress->0

MIL-HBBK-5J S/N curves are typically given for a family of R values starting at a lower limit of R=-1.

So MIL-HBBK-5J is not useful for pure compression.

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Compressive residual stresses can be introduced in the surface by shot peening to increase fatigue life.

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More later…

 

– Tom Irvine

Webinar 48 – Rainflow Cycle Counting for Multiaxial Stress

Slides: To be added before 4/4/2015

This unit gives a method for converting a time-varying stress tensor into a weighted-average equivalent uniaxial stress. The weights are chosen to maximize the fatigue damage.

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Matlab script: Vibrationdata Signal Analysis Package

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Reference Paper:  Tools for Multiaxial Fatigue

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– Tom Irvine

Webinar 47 – Shock Response Spectrum Synthesis, Special Topics

Slides & Video:

webinar_47_SRS_synthesis_special_topics.pptx

A high-range Cummins Generator in a Seismic Shaker Test.mp4

Topics:

1. Shaker Table Seismic Testing of Equipment using Historical Strong Motion Data Scaled to Satisfy a Shock Response Spectrum

2. Temporal Moments

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Matlab script: Vibrationdata Signal Analysis Package

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Reference Papers:

quake_syn.pdf

From SRS to Temporal Moments

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– Tom Irvine