Learning Forum

[masud407]

Can anyone please tell me the basic difference between the transient analysis and harmonic response analysis (implying on the result of modal analysis)?

Thanks.

[peteroznewman]

Harmonic response analysis computes the response of the structure to a load that has a sinusoidal time-history. For example, an out-of-balance motor, which generates a force that oscillates with a frequency that depends on the speed of the motor.  Harmonic response is computed for a range of frequencies. The structure will have some natural frequencies of its own, which are computed by a Modal analysis, and when the harmonic load frequency matches the natural frequency, the response will be larger than when the harmonic frequency is higher or lower than the natural frequency.

Transient analysis is just computing the time-history of the structure to a load that can have any amplitude-time history. No periodic frequency assumptions are made in the analysis. 

[masud407]

Thanks Peter for your response. If I have a load that has a sinusoidal time history (for example: f=sin(2*pi*frequency*time)). In that case, which analysis should I do to find the graph for frequency vs deflection (or any other mechanical output parameter) ?

[peteroznewman]

Harmonic Response, but you just enter the amplitude of the force on the structure, the solver assumes that there is a sinusoidal function and varies the frequency over the range you specify while calculating the amplitude of the sinusoidal deflection.