Integrator

The integrator decides how the solution advances from one step to the next — how much load to add in a static analysis, or how to march through time in a transient one.

🔧 Grasshopper component

IntegratorAlpaca4d ▸ 07_Analysis

Inputs

For static analysis. Adds a fixed increment of load factor at each step.

LambdaNumber1Load factor increment per step.

NumIterInteger(empty)Iterations per step to aim for.

Left empty, every step adds Lambda. Given, together with MinLambda and MaxLambda, it turns on adaptive stepping — see below.

MinLambdaNumber(empty)Smallest increment adaptive stepping may take.

MaxLambdaNumber(empty)Largest increment adaptive stepping may take.

NumIter, MinLambda and MaxLambda have no defaults on purpose: they are one switch, not three settings. Given, OpenSees stops stepping by Lambda and adapts each step to take about NumIter iterations, anywhere between MinLambda and MaxLambda. The load factor the model ends up under is then not Lambda times the number of steps, and nothing reports that it changed. Leave them empty for a model under exactly Lambda × the Analysis Step's steps.

For transient analysis. The standard implicit time-stepping scheme.

GammaNumber0.5Newmark γ.

BetaNumber0.25Newmark β.

γ = 0.5, β = 0.25 is the average acceleration method: unconditionally stable and free of numerical damping. γ > 0.5 introduces numerical damping, which can help a noisy non-linear run at the cost of some accuracy.

For transient analysis. Explicit, no inputs.

Conditionally stable: the time step must be below the critical step of the smallest, stiffest element in the model, or the solution diverges. Suits short, sharp events on models where a small step is wanted anyway.

Outputs

IntegratorIntegratorFor Analysis Settings.

A switcher component: pick the unit in the drop-down under it, or right-click it ▸ Units. The drop-down shows CentralDifference as CentralDiff.

📈 When to use it

Analysis	Integrator
Linear static	LoadControl, Lambda = 1, one step
Pushover / non-linear static	LoadControl with a small Lambda and many steps
Seismic or general dynamic	Newmark
Impact, blast, wave propagation	CentralDifference, with a small Dt

Warning

The integrator and the analysis type have to agree. LoadControl with Transient, or Newmark with Static, will not do what you want.

🔗 Relation to OpenSees

integrator LoadControl       $lambda $numIter $minLambda $maxLambda   ;# the last three only when given
integrator Newmark           $gamma $beta
integrator CentralDifference