There is a need in certain structural dynamics finite element analysis problems to perform a response analysis in the time domain. This would be the case, for example, if the stiffness was non-linear. Loss-of-clearance or contact between two adjacent vibrating parts is another analysis example.… Read more
Consider a single-degree-of-freedom system subjected to base excitation where the input is an arbitrary time history. The response of the system can be calculated via a digital recursive filtering relationship, which is the numerical engine embedded in the SRS calculation. This is done for… Read more
Finding the the natural frequencies of a continuous beam, plate, membrane or even an acoustical volume requires solving for the eigenvalue roots of a characteristic equation, which may contain trigonometric or Bessel functions. Matlab provides an fzero function which can be used for this purpose.… Read more
The Transamerica Pyramind has a Fundamental Frequency of 0.3 Hz * * * Here are some papers which give natural frequencies and damping values for sample tall buildings: Damping in Tall Buildings and Towers: tall_building_damping.pdf The Damping Characteristics of Bolted and Welded Joints: bolted_joint_damping.pdf Transamerica… Read more
I will be teaching two tutorial sessions at: 84th Shock & Vibration Symposium November 3-7, 2013 Atlanta, GA The sessions are: Shock Response Spectra and Time History Synthesis Rainflow Cycle Counting for Random Vibration Fatigue Analysis You are invited to participate. Further information is given… Read more
A colleague recently wrote to me regarding the merits of using statistical energy analysis to predict the vibration levels in a NASA launch vehicle. Here is my reply: I use “old-school” empirical scaling techniques. These work reasonably well for deriving component-level maximum predicted environments. I… Read more
Modal Transient Analysis of a Multi-degree-of-freedom System with Enforced Motion: modal_enforced_motion.pdf Matlab scripts: enforced_displacement.zip enforced_acceleration.zip * * * Frequency Response Function Analysis of a Multi-degree-of-freedom System with Enforced Motion: FRF_enforced_motion.pdf Matlab scripts: enforced_acceleration_frf.zip enforced_displacement_frf.zip * * * Multi-Degree-of-Freedom System Response to Multipoint Base Excitation Modal… Read more
Consider a single-degree-of-freedom system subject to base excitation. Assume a case where the base input is a sine tone which must be converted to an “equivalent” narrowband PSD. The narrowband PSD must be greater than or equal to the sine tone in terms of peak… Read more
Dear brothers, unless we train ministers capable of warming people’s hearts, of walking with them in the night, of dialoguing with their hopes and disappointments, of mending their brokenness, what hope can we have for our present and future journey? It isn’t true that God’s… Read more
Here is a Matlab GUI script to calculate displacement, velocity, and acceleration at a given frequency for a steady-state sine function. sine_amplitude.zip This module is also included in: Vibrationdata Matlab Signal Analysis Package – Tom Irvine