MarkerBodyMass

A marker attached to the body mass; use this marker to apply a body-load (e.g. gravitational force).

Interface

Provides: BodyMass
Bodies it can be placed on: ObjectGround, ObjectMassPoint, ObjectMassPoint2D, ObjectMass1D, ObjectRigidBody, ObjectRigidBody2D, ObjectFFRF, ObjectFFRFreducedOrder, ObjectANCFCable, ObjectANCFCable2D, ObjectALEANCFCable2D, ObjectANCFBeam, ObjectBeamGeometricallyExact2D, ObjectBeamGeometricallyExact, ObjectANCFThinPlate
Connectors, constraints and loads that can use it: LoadMassProportional

Parameters

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

name	type	default	description
name	String	‘’	marker’s unique name
bodyNumber	ObjectIndex	invalid (-1)	body number to which marker is attached to
visualization	VMarkerBodyMass		parameters for visualization of item

Visualization parameters

The parameters of VMarkerBodyMass, 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

None that a connector reads: the marker exists to take a load proportional to the mass of the body, LoadMassProportional, and provides only its Jacobian.

Jacobians

The mass-weighted integral of the position Jacobian over the body,

\[ \Jm_{m} = \int_V \rho\, \frac{\partial \LU{0}{\pv}}{\partial \qv}\, dV , \]

which the body computes (its access function DisplacementMassIntegral_q); a load vector \(\LU{0}{\bv}\) per unit mass gives \(\Qm = \Jm_{m}\tp \LU{0}{\bv}\). For a rigid body it is the mass times the position Jacobian of the center of mass.

Mini example

#gravity on a planar rigid body: the load acts on the mass of the whole body
node = mbs.AddNode(NodeRigidBody2D(referenceCoordinates=[0.5,0.2,0]))
body = mbs.AddObject(ObjectRigidBody2D(nodeNumber=node, mass=2, inertia=0.1))
mMass = mbs.AddMarker(MarkerBodyMass(bodyNumber=body))
mbs.AddLoad(LoadMassProportional(markerNumber=mMass, loadVector=[0,-9.81,0]))

mbs.Assemble()
mbs.SolveDynamic()

#free fall: y = -g/2*t^2 at t=1, independent of the mass
exu.sys['testResult'] = mbs.GetNodeOutput(node, exu.OutputVariableType.Displacement)[1] #-4.905

Examples (Ex) and TestModels (TM) that show this item, with weblink to github: basicTutorial2024.py (Ex), tutorialSpringDamperCreate.py (Ex), tutorialRigidBody.py (Ex), tutorialRigidBodyCreate.py (Ex)