Nonlinear Newmark-beta integration combines Newmark time-discretization kinematics with Newton-Raphson iteration to solve nonlinear finite element dynamic equilibrium at each time step.
How It Works
The study notes start from dynamic equilibrium with mass, stiffness, and external load terms. At the new time step, the residual depends on displacement, velocity, and acceleration. Newmark-beta relations express velocity and acceleration increments in terms of the unknown displacement increment, so the Newton system can be written as an effective tangent equation for that displacement increment.
Why It Matters
For nonlinear structural dynamics, a time step is not just a matrix update. Internal force and tangent stiffness depend on the current trial displacement, so each step requires repeated residual evaluation, tangent assembly, displacement correction, and velocity/acceleration update until convergence.
Iteration Skeleton
Predict or initialize the new-step displacement, velocity, and acceleration.
Assemble residual from external load, inertia, and internal force.
Form the effective tangent with mass and nonlinear tangent contributions.
Solve for the displacement correction.
Update displacement, velocity, and acceleration using Newmark-beta formulas.
Repeat until the residual and/or correction satisfies convergence criteria.
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