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## Main Question or Discussion Point

hi all,

Having those input in hand, mass (

To summarize the inputs:

n = the total DoFs in system

m = number of interested modes (m<n)

M = Mass matrix (n*n)

K = Stiffness matrix (n*n)

[itex]\Phi[/itex]=eigen value matrix (m*m diagonal)

Ω=eigen-vectors (m*m)

How am I supposed to find the that m number of modes are enough for modal analysis for the given case?

Generally in books suggest that, modal particiaption factors are (MPF) = R*[itex]\Phi[/itex]

But we are interested with eigen-solution of the problem, so there is no any external loading and reasonably there is no R spatial vector. So what actually is book refering with that p(t) = R*f (t) description ?

Regards,

Having those input in hand, mass (

**[M]**) n*n matrix , stiffness (**[K]**) n*n matrices and having obtained the eigen-values, eigenvectors for the higher-frequencies with subspace or simlutaneous iteration respectively, eigen-values (**[[itex]\Phi[/itex]]**) as m*m diagonal matrix, and m*m eigen-vectors as (**[Ω]**).To summarize the inputs:

n = the total DoFs in system

m = number of interested modes (m<n)

M = Mass matrix (n*n)

K = Stiffness matrix (n*n)

[itex]\Phi[/itex]=eigen value matrix (m*m diagonal)

Ω=eigen-vectors (m*m)

How am I supposed to find the that m number of modes are enough for modal analysis for the given case?

Generally in books suggest that, modal particiaption factors are (MPF) = R*[itex]\Phi[/itex]

_{n}^{T}/ ( [itex]\Phi[/itex]_{n}^{T}*M*[itex]\Phi[/itex]_{n}) where R is the time independent spatial loading type of external loads( p(t) = R*f (t) ).But we are interested with eigen-solution of the problem, so there is no any external loading and reasonably there is no R spatial vector. So what actually is book refering with that p(t) = R*f (t) description ?

Regards,

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