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A ``small'' but interesting riddle from the theory of vibrations

A ``small'' but interesting riddle from the basic theory of vibrations. Haven't run into it in any physics/classical mechanics text/reference.

OVERHEAD ELECTRICAL CONDUCTORS IN BENDING : NEW TEST DATA

A paper by Kubelwa et al. (Statistical Modelling of Bending Stress in ACSR Overhead Transmission Line Conductors subjected to Aeolian Vibrations –I) reports data from vibration tests on 4 ACSR.  under  3 axial loads (20, 25 and 30% UTS). An 84.5 m conductor span is vibrated at various bending amplitudes and strain is measured near a clamped end (distance not given). Clamps are rigid square-faced bushings. Vibration amplitude is measured at 89 mm from bushing. Strain gages are glued on 3 adjacent top layer wires.

How to recover eigenvector components for specified displacements ?

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I have a problem visualising specified displacements from a modal/buckling analysis. 

When solving the algebraic system of equations [K]{u}={f} resulting from FEA discretization, the vector {u} does not have components for the specified displacements, zero or not zero, because the corresponding degrees of freedon (dof) have been eliminated. To visualize all the displacements, even the ones that are specified, we recover them from the input data to create a longer vector {u|u*} where {u} are the active dof and {u*} are the specified dof, zero or not zero. 

Adina Vibrations

Hi,

I´m analizing the modes of a structure but I don´t know how to plot the different modes (I only see the first one). I´m using  Adina 8.7.3.

Thank you very much! 

gap of von mises stress between Ansys and Abqus

Hello ,

 I am doing the correlation between Ansys and Abaqud for a shroud of cooling module (solid 92-C3D10) .I find the coorelation is perfect in frequency , but when i do the powerspectral density analysis, i noticed a gap of 10-20% on the peak value of nodal von mises stress ,  i'd like to know the reason of the diffrence .

 

 

Thank You .


 

Free Vibrations of Nonuniform Timoshenko Beams II

This post contains the equations of nonuniform Timoshenko beam theory, a seconf order finite difference method for the solution of the free vibrations thereof and a Scilab computer program implementation. The implementation also allows for the calculation of static deflection for a user specified load distribution that can also contain point loads. A number of static and free vibration examples are given.

I hope this can be useful to students and others.

Mike Ciavarella's picture

Mechanics of love and happiness

An interesting application of non linear dynamics, including happiness with a simple 1D damped oscillator!

Rotor dynamics

 

 

“Project of automatic balancing system for rigid
rotors”

 

 

ABSTRACT

The paper presents the
conceptual design for the automatic system for balancing rigid rotors.

[LS-DYNA] Attenuating vibrations of shell element after an explosion

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Hello!

The model I'm working on in LS-DYNA is a simple pyramid-shaped shell constrained along the bottom edges with all DOF taken. The material used is MAT_PIECEWISE_LINEAR_PLASTICITY. Above the model there's a LOAD_BLAST (Air burst) placed, which deforms the model after the explosion.
The issue is that the model seems to vibrate ininitely after the explosion, what can be seen on the attached images (first one shows the graph of "Rigid Body Displacement", second one shows close-up of the line within the yellow rectangle).

Andrew Norris's picture

Lord Rayleigh

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