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+---
+type: concept
+title: "Midas NFX Linear Dynamics and Buckling Analyses"
+created: 2026-06-02
+updated: 2026-06-02
+address: c-000178
+aliases:
+  - NFX linear dynamics
+  - NFX buckling analysis
+tags:
+  - concept
+  - finite-element-method
+  - midas-nfx
+  - dynamics
+  - buckling
+status: current
+related:
+  - "[[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]]"
+  - "[[midas NFX]]"
+  - "[[Direct Time Integration Methods]]"
+  - "[[Finite Element Eigenproblem Solvers]]"
+  - "[[Geometric Stiffness Matrix]]"
+  - "[[Midas NFX Equation Solvers and Eigen Extraction]]"
+sources:
+  - "[[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]]"
+---
+
+# 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.
+
+## Modal and Buckling Base
+
+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
+
+```text
+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.