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  1. zzy

    How to Calculate Natural Frequenecy of Steel Structure

    For a little complicated parts, it is very hard, if not impossible, to find a closed-form of natural frequency. Finding natural frequency in FEA is very easy. It is probably the easiest type of analysis in FEA. If you need help, let me know.
  2. zzy

    swept sine vibration analysis

    Even a simple structure like a beam will have multiple modes (natural frequencies). Normal modes are NOT equal to degrees of freedom. Basically, these two quantities are measused in two different domains (or reference space). DOF is in physical domain (i.e., X-Y-Z coordinate) while modes are in...
  3. zzy

    Random Vibration Calculations

    Yes. It is possible to calculate ramdom response based on your structural parameters and input PSD chart with SOFTWARE. As an output, you will get responses (displacement, velocity, or acceleration) in terms of PSD (response v.s. frequency^2) or RMS. The procedure involving both theories on...
  4. zzy

    Transient analysis for evaluating dynamic stresses

    long time ago, I used a linearization approach for transient problems with modal data (frequency, mode shape, damping). The concept is very simple. If you have a total time of T over which some nonlinear behavoirs are expected. You first divide T into a set of sub-intervals, T1, T2, ....Tn...
  5. zzy

    Why is stiffer better?

    For the second question regarding excitation at harmonics, it is better to understand it by using Fourier theory. For Example, your narural frequency is f0 and your excitation frequency f1=0.5*f0. If the excitation waveform is purely sine or cosine wave, the resonance with f0 will not be...
  6. zzy

    Tolerance Chains & Tolerance Stack-up

    check out www.ci.com for a software maker named Cognition Corp., which is specialized in a tolerance stackup software -- MECHANICAL ADVANTAGE.
  7. zzy

    Impact damage

    This is a problem involving meterial's permanent deformation (indentation). It has to be solved as such. There are a few FEA (finite element analysis) softwares available to handle this problem. The initial kinetic energy due to impact speed will be converted into strain energy less the loss...

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