Simple example of a cantilever beam simulation where the displacement vector is saved into a mesh file at every steps.

displacement_exporter.py

import Sofa, SofaRuntime
import meshio, numpy as np

class Exporter (Sofa.Core.Controller):
    def __init__(self, *args, **kwargs):
        Sofa.Core.Controller.__init__(self, *args, **kwargs)
        self.step_id = 0
        
    def onAnimateEndEvent(self, e):
        x  = self.getContext().mo.position.array()
        x0 = self.getContext().mo.rest_position.array()
        u  = x - x0
        
        cells = self.getContext().topology.tetrahedra.array()
        von_mises = self.getContext().ff.vonMisesPerNode.array()
        filename = f'beam_step_{self.step_id}.vtu'
        meshio.write(filename, meshio.Mesh(points=x0, cells={'tetra':cells}, point_data={'u':u, 'von_mises':von_mises}))
        print(f'Mesh exported at {filename}')
        self.step_id += 1
        

def createScene(root):
    root.addObject(Exporter(name='exporter'))
    root.addObject('RequiredPlugin', pluginName=['SofaBaseMechanics', 'SofaBoundaryCondition', 'SofaEngine', 'SofaImplicitOdeSolver', 'SofaSimpleFem', 'SofaSparseSolver'])
    root.addObject('VisualStyle', displayFlags='showBehaviorModels showForceFields')
    root.addObject('RegularGridTopology', name='grid', min=[-7.5, -7.5, 0], max=[7.5, 7.5, 80], n=[9, 9, 21])
    root.addObject('StaticSolver', newton_iterations=10, absolute_residual_tolerance_threshold=1e-10, printLog=True)
    root.addObject('SparseLDLSolver', template="CompressedRowSparseMatrixMat3x3d")
    root.addObject('MechanicalObject', name='mo', position='@grid.position')
    root.addObject('TetrahedronSetGeometryAlgorithms')
    root.addObject('TetrahedronSetTopologyModifier')
    root.addObject('TetrahedronSetTopologyContainer', name='topology')
    root.addObject('Hexa2TetraTopologicalMapping', input='@grid', output='@topology')
    root.addObject('TetrahedronFEMForceField', name='ff', poissonRatio=0.45, youngModulus=5000, method='large', computeVonMisesStress=1, listening=True)
    root.addObject('BoxROI', name='dirichlet_roi', box=[-7.5, -7.5, -0.9, 7.5, 7.5, 0.1])
    root.addObject('FixedConstraint', indices='@dirichlet_roi.indices')
    root.addObject('BoxROI', name='neumann_roi', box=[-7.5, -7.5, 79.9, 7.5, 7.5, 80.1])
    root.addObject('TriangleSetGeometryAlgorithms')
    root.addObject('TrianglePressureForceField', pressure=[0, -50, 0], triangleList='@neumann_roi.trianglesInROI')