MarkerNodePosition

A node-Marker attached to a position-based node. It can be used for connectors, joints or loads where position is required. If connectors also require orientation information, use a MarkerNodeRigid.

Interface

Provides: Position
Nodes it can be attached to: NodePoint, NodePoint2D, NodeRigidBodyEP, NodeRigidBodyRxyz, NodeRigidBodyRotVecLG, NodeRigidBody2D, NodePoint2DSlope1, NodePointSlope1, NodePointSlope12, NodePointSlope23, NodePointGround
Connectors, constraints and loads that can use it: ObjectConnectorSpringDamper, ObjectConnectorCartesianSpringDamper, ObjectConnectorGravity, ObjectConnectorHydraulicActuatorSimple, ObjectConnectorDistance, ObjectContactSphereSphere, ObjectContactSphereTriangle, ObjectJointSpherical, ObjectJointRevolute2D, LoadForceVector

Parameters

The parameters of the item; in a dictionary, its type is ‘NodePosition’:

name	type	default	description
name	String	‘’	marker’s unique name
nodeNumber	NodeIndex	invalid (-1)	node number to which marker is attached to
visualization	VMarkerNodePosition		parameters for visualization of item

Visualization parameters

The parameters of VMarkerNodePosition, given as visualization:

name	type	size	default	description
show	Bool		True	set true, if item is shown in visualization and false if it is not shown

Drawing

Drawn as all markers.

Detailed description

Marker quantities

quantity	symbol	as computed
position	\(\LU{0}{\pv}_m\)	the position of the node, as its output variable `Position`
velocity	\(\LU{0}{\vv}_m\)	the velocity of the node, as its output variable `Velocity`

Both are global, or in the frame the object reads the node in (see the page of the node).

Jacobians

The position Jacobian of the node, \(\LU{0}{\Jm_{pos}} = \partial \LU{0}{\pv} / \partial \qv\) with respect to the node’s coordinates: the unit matrix for NodePoint, the first three columns for a rigid body node, and for a 2D node the \(x\) and \(y\) rows.

Mini example

#the position of a node: a mass hanging on a spring from a ground node, released at rest
nMass = mbs.AddNode(NodePoint(referenceCoordinates=[0,0,-1]))
mbs.AddObject(ObjectMassPoint(nodeNumber=nMass, mass=1))
mMass = mbs.AddMarker(MarkerNodePosition(nodeNumber=nMass))
mFixed = mbs.AddMarker(MarkerNodePosition(nodeNumber=nGround))
k = (2*np.pi)**2 #1 Hz
mbs.AddObject(ObjectConnectorSpringDamper(markerNumbers=[mFixed, mMass], stiffness=k, referenceLength=1))
mbs.AddLoad(LoadForceVector(markerNumber=mMass, loadVector=[0,0,-9.81]))

mbs.Assemble()
simulationSettings = exu.SimulationSettings()
simulationSettings.timeIntegration.endTime = 0.5 #half a period
mbs.SolveDynamic(simulationSettings)

#lowest point: twice the static deflection, -2*g/k
exu.sys['testResult'] = mbs.GetNodeOutput(nMass, exu.OutputVariableType.Displacement)[2] #-0.497

Examples (Ex) and TestModels (TM) that show this item, with weblink to github: doublePendulum2D.py (Ex), pendulum2Dconstraint.py (Ex), interactiveTutorial.py (Ex), simple4linkPendulumBing.py (Ex), connectorGravityTest.py (TM)