Midas NFX Linear Dynamics and Buckling Analyses

Definition

The NFX linear dynamics and buckling thread covers normal modes, linear buckling, effective mass, mode superposition, transient response, frequency response, random response, and response spectrum analysis.

Normal mode analysis uses mass-normalized modes, generalized mass, generalized stiffness, participation factors, and modal effective mass. Buckling uses the same generalized eigenproblem structure but replaces the dynamic mass-like matrix with geometric stiffness and normalizes buckling vectors by maximum displacement component rather than modal mass.

Mode Superposition

The manual presents mode superposition as a reduction of the physical dynamic equation

M u_ddot(t) + C u_dot(t) + K u(t) = f(t)

into modal coordinates. It also documents residual vectors for improving truncated modal bases and enforced-motion handling through constrained/free DOF partitioning.

Linear Response Families

NFX covers direct and modal transient response, direct and modal frequency response, random response, and response spectrum analysis. The manual includes damping treatment, frequency-domain response, random response statistical values, RMS and zero crossing, modal combination, and spectrum correction.

Solver Development Use

For a custom solver, this page defines output checks that should be testable against reference solvers: natural frequencies, periods, mode shapes, modal mass, effective mass ratios, buckling load factors, transient displacement histories, frequency-response amplitudes/phases, response-spectrum modal combinations, and random-response statistics.

Connections

Finite Element Eigenproblem Solvers gives the common eigen extraction context.
Direct Time Integration Methods gives the time-domain integration frame.
Geometric Stiffness Matrix connects linear buckling to stress stiffness.
Midas Civil Dynamic and Seismic Analysis and Midas FEA Linear Dynamics and Buckling Analyses are sibling MIDAS references.

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