Model ElementThe Point_Mass is an entity that has mass but no inertia
properties.
Class Name
Point_Mass
Description
Three translational coordinates characterize the position of the
Point_Mass. By default, the orientation of the
Point_Mass is set to be the same as the global coordinate
system. It never changes during simulation. Markers on Point_Mass
may have location and orientation coordinates. The orientation of these Markers does
not change during the simulation.
Attribute Summary
Name
Property
Modifiable by
command?
Designable?
id
Int
()
label
Str
()
qg
Location (Point())
Yes
zg
Location ()
Yes
xg
Location ()
Yes
zv
Location ()
Yes
xv
Location ()
Yes
reuler
Angles ()
Yes
mass
Double ()
Yes
Yes
cm
Reference ("Marker")
Yes
vx
Double (None)
Yes
FD Only
vy
Double (None)
Yes
FD Only
vz
Double (None)
Yes
FD Only
exact
Exact ()
function
Function ("MASS_READ")
routine
Routine ()
Usage
Point_Mass (optional_attributes)
Attributes
id
Integer
Specifies the element identification number. This number must be unique
among all the Point_Mass objects in the model.
This attribute is optional. MotionSolve will
automatically create an ID when one is not specified.
Range of values: id > 0
label
String
Specifies the name of the Point_Mass object.
This attribute is optional. When not specified, MotionSolve will create a label for you.
mass
Double
Specifies the mass of the Point_Mass object.
The attribute mass is optional. If a
Point_Mass is fully constrained and you are not
interested in the constraint forces, then mass needs not to be specified.
When not specified, mass is set to zero.
Valid range of values: mass ≥ 0.0
cm
Reference to a Marker
Specifies the Marker that is located at the
center-of-mass of the PART.
The attribute cm is optional. If a
Point_Mass is fully constrained and you are not
interested in the constraint forces, then mass and inertia need not to be
specified. When these are not specified, you must not specify
cm.
Note: In order to remove circular
references, the body is created in two steps. First the body is defined
without a CM marker. Then the CM attribute is explicitly
defined.
qg
A Location object or a list of three doubles.
Specifies the coordinates of local part reference Marker. This Marker is
used as the reference coordinate system for all Markers defined on this
Point_Mass.
The qg attribute is optional. When not specified, it is
assumed to be coincident with the global origin, (0, 0, 0).
zg
A Location object or a list of three doubles.
Specifies the coordinates of a point on the z-axis of the local part
reference Marker. This Marker is used as the reference coordinate system for
all Markers defined on this Point_Mass.
The zg attribute is optional. When not specified, the
point is assumed to be on the global z-axis.
The zg/xg attribute is exclusive to
zv/xv, reuler,
and function. Only one of them may be specified.
xg
A Location object or a list of three doubles.
Specifies the coordinates of a point on the x-axis of the local part
reference Marker. This Marker is used as the coordinate system for all
Markers defined on this Point_Mass.
The xg attribute is optional. When not specified, the
point is assumed to be on the global x-axis.
The zg/xg attribute is exclusive to
zv/xv, reuler,
and function. Only one of them may be specified.
zv
A Location object or a list of threedoubles.
Specifies the z-axis of the local part reference Marker. This Marker is
used as the reference coordinate system for all Markers defined on this
Part.
The zv attribute is optional. When not specified, the
z-axis is assumed to be the global z-axis.
The zv/xv attribute is exclusive
to zg/xg,
reuler, and function. Only one
of them may be specified.
xv
A Location object or a list of three doubles.
Specifies the x-axis of the local part reference Marker. This Marker is used
as the coordinate system for all Markers defined on this
Part.
The xv attribute is optional. When not specified, the
x-axis is assumed to be the global x-axis.
The
zv/xv attribute is exclusive
to zg/xg,
reuler, and function. Only one
of them may be specified.
reuler
A list of three doubles.
Specifies the body-fixed 3-1-3 Euler angles of the local part reference
Marker with respect to the global coordinate system. This Marker is used as
the reference coordinate system for all Markers defined on this
Point_Mass.
The reuler attribute is optional. When not specified, it
is assumed to be (0,0,0), in other words, the local part reference Marker
has the same orientation as the global coordinate system.
The reuler attribute is exclusive to
function and
zg/xg. Only one of them may be
specified.
function
String
Specifies the list of parameters that are passed from the data file to the
user-written defined.
The attribute function is optional.
The function attribute is exclusive to
reuler and
zg/xg. Only one of them may be
specified.
routine
String or a pointer to a function.
Specifies an alternative name for the user subroutine.
The attribute routine is optional. The default name of
the user subroutine is MASS_READ.
vx
Double
Specifies the initial translational velocity of the PART
along the global x-axis.
The vx attribute is optional.
When not specified, MotionSolve will
perform an internal computation to ensure that all
Point_Mass velocities are consistent with the
first time derivative of the constraints.
When specified, MotionSolve will try to
maintain the value specified as it perform the internal computation
to ensure that all Point_Mass velocities are
consistent with the first time derivative of the constraints.
vy
Double
Specifies the initial translational velocity of the PART
along the global y-axis.
The vy attribute is optional.
When not specified, MotionSolve will
perform an internal computation to ensure that all
Point_Mass velocities are consistent with the
first time derivative of the constraints.
When specified, MotionSolve will try to
maintain the value specified as it perform the internal computation
to ensure that all Point_Mass velocities are
consistent with the first time derivative of the constraints.
vz
Double
Specifies the initial translational velocity of the PART
along the global z-axis.
The vz attribute is optional.
When not specified, MotionSolve will
perform an internal computation to ensure that all
Point_Mass velocities are consistent with the
first time derivative of the constraints.
When specified, MotionSolve will try to
maintain the value specified as it perform the internal computation to
ensure that all Point_Mass velocities are consistent
with the first time derivative of the constraints.
exact
Example
Referring to the 3-body problem in the XML Reference, specify the Sun as a
Point_Mass.
sun = Point_Mass (Label="SUN", mass=3.328e5, vx=0, vy=0, vz=0)
sun.cm = Marker (body=sun, label="Sun’s center") #location defaults to [0,0,0]
Referring to the 3-body problem in the XML Reference, specify the Earth as a
Point_Mass.
