Doppler Shift
Here is a Matlab script for Doppler shift calculations: doppler.mHere is a related Newsletter article and sound files: June2003_NL.pdfK5LA.wavcno_wav* * *See also: Vibrationdata Acoustics Page* * *- Tom Irvine
Matlab
Curve-fitting One or More Sine Functions in the Time Domain
Here is a Matlab script and its supporting function for identifying the frequencies and amplitudes for one or more sine functions. sinefind.zip Trial-and-error curve-fitting is used with some convergence techniques. Here is measured accelerometer data from a channel beam excited by an impulse force. channel.txt… Read more
Fun with Sound Files
Making sound recordings is easy these days given that iPods, iPads and Android cell phones have this capability. Here is a freeware program that can be used to process the sound data: Audacity This program can also convert the sound file from one format to… Read more
Simply-Supported Plate, Bending Modes
The Vibrationdata Signal Analysis Package has a function for calculating the natural frequencies of a plate simply-supported about all edges. The package also has options for calculating the response to base excitation. Vibrationdata > Structural Dynamics > Plates, Rectangular & Circular > Rectangular Plate, Simply Supported The… Read more
Mean Filter of a Time History
The mean filter is a simple sliding-window filter that replaces the center value in the window with the average (mean) of all the values in the window. The mean filter is intended as a lowpass filter which smooths the data. It may also be used… Read more
Integrating Accelerometer Time History Signals
The scripts in integrate_th.zip integrate an acceleration time history to a velocity time history and/or a velocity time history to a displacement time history. The main script is: integrate_th.m The remaining scripts are supporting functions. Integrating acceleration to velocity typically causes a spurious offset in… Read more
SDOF Steady-State Response to a Sine Force or Base Excitation
These Matlab scripts calculate the steady-state response of a single-degree-of-freedom (SDOF) system to a sinusoidal force or base excitation: steady.zip – Tom Irvine
FFT for Machine and Pump Diagnostics & Acceptance Evaluation
This Matlab script calculates the one-sided, full amplitude FFT of an acceleration time history: FFT_VD.zip It gives the output FFTs in acceleration, velocity and displacement formats. It is useful for evaluating machine and pump vibration where there are distinct sine tones and harmonics. The main… Read more
Half-Power Bandwidth Method
Please see the following update: MDOF Frequency Response Function Natural Frequency & Damping Extraction including Modal Overlap. Post Link The half-power bandwidth method can be used to estimate the damping ratio and corresponding Q value from the frequency response function of a structure which has… Read more
Miner’s Cumulative Fatigue via Rainflow Cycle Counting
This blog entry is a work-in-progress. Fatigue analysis can be performed in the time domain using rainflow cycle counting. This is an elegant, brute-force approach. One advantage of the time domain approach is that it tends to highlight the occurrences of peaks above 3-sigma for… Read more