Skyscraper design was once governed almost entirely by strength — could the frame carry gravity, wind and seismic loads with adequate margin? For the new generation of ultra-slender “pencil towers,” the governing requirement has shifted to something more subtle: occupant comfort. A building can be… Read more
Internal friction and heat generation cause a deviation from perfect elasticity, resulting in the hysteresis loop in the stress-strain curve. The damping capacity ψ is: ψ = ΔW/W where W is the initial strain energy and ΔW is the energy lost during one cycle of oscillation. Some damping capacities… Read more
Introduction Vibration test fixtures are the mechanical interface between the shaker system and the unit under test (UUT). Their purpose appears simple: hold the test item securely and transmit the specified vibration input. In practice, fixture design is one of the most important and often… Read more
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… Read more
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… Read more
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… Read more
Wire rope damping depends on: 1. Material 2. Diameter 3. Length 4. Number of strands 5. Number of turns per length 6. Initial tension or preload 7. Displacement amplitude The damping can be very nonlinear, particularly depending on displacement amplitude. The flexing of wire rope… Read more
This post is a work-in-progress… Frequency Response Function based substructuring (FBS) predicts the dynamic behavior of a coupled system on the basis of free interface FRFs of the uncoupled components. Here is a tutorial paper: Frequency Response Function Substructuring Modal damping requires special consideration: Notes on… Read more
Here is a method for converting modal damping to a damping coefficient matrix for all modes. It is based on a pseudo inversion of the modal damping matrix. The resulting coefficient matrix will be fully populated. The damping terms will not necessary corresponding to physical dashpots,… Read more
A vibration absorber is a tuned spring-mass system which reduces the vibration of a harmonically excited system. Here is a paper for an applied force: Vibration Absorber Here is a Matlab script and its supporting function: vibration_absorber_trans.m mratio.m * * * Here is a paper… Read more