Optional opt_name: stringname of this as a Subject
Private amplitude_amplitude of driving force on anchor to make periodic up/down motion
Private anchordamping applied to anchor
Private damping_damping of pendulum
Private frequency_frequency of driving force on anchor to make periodic up/down motion
Protected initialInitial values.
Private length1_length of pendulum rod 1
Private length2_length of pendulum rod 2
Private mouse_Follows the mouse position while applying spring force to anchor
Private pendulumtrue when dragging pendulum bob
Private potentialpotential energy offset
Private running_Whether the simulation is running; determines whether mouse dragging of anchor results in applying spring force or just moving the anchor directly.
Private springtrue when applying spring force to anchor by mouse drag
Private springstiffness of spring made for dragging anchor
Adds the given Observer to this Subject's list of Observers, so that the Observer
will be notified of changes in this Subject. An Observer may call Subject.addObserver
during its observe method.
the Observer to add
Adds the Parameter to the list of this Subject's available Parameters.
the Parameter to add
if a Parameter with the same name already exists.
Notifies all Observers that this Subject has changed by calling observe on each Observer.
An Observer may call addObserver or removeObserver during its observe
method.
a SubjectEvent with information relating to the change
Notifies all Observers that the Parameter with the given name has changed by calling observe on each Observer.
the language-independent or English name of the Parameter that has changed
if there is no Parameter with the given name
Defines the differential equations of this ODESim; for an input set of variables, returns the current rate of change for each variable (the first derivative of each variable with respect to time).
The timeStep is the time since the state variables were last fully calculated, which
can be and often is zero. The current time can be regarded as getTime() + timeStep.
The input variables correspond to the Simulation state at that time. Note that
timeStep is different from the time step used to advance the Simulation (as in
AdvanceStrategy.advance).
The timeStep is typically used when finding collisions in
CollisionSim.findCollisions.
the current array of state variables (input),
corresponding to the state at getTime() + timeStep
array of change rates for each variable (output), all values are zero on entry.
the current time step (might be zero)
null if the evaluation succeeds, otherwise an object relating to the
error that occurred. The change array contains the output results.
Called at the end of a mouse drag operation, performs whatever action is
appropriate. Only called if startDrag returned true.
the SimObject being dragged, or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position to the mouse location at start of drag.
Protected getReturns whether broadcasting is enabled for this Subject. See setBroadcast.
whether broadcasting is enabled for this Subject
Returns the current EnergyInfo for this system.
an EnergyInfo object representing the current energy of this system.
Returns the ParameterBoolean with the given name.
the language-independent or English name of the ParameterBoolean
the ParameterBoolean with the given name
if there is no ParameterBoolean with the given name
Returns the ParameterNumber with the given name.
the language-independent or English name of the ParameterNumber
the ParameterNumber with the given name
if there is no ParameterNumber with the given name
Returns the ParameterString with the given name.
the language-independent or English name of the ParameterString
the ParameterString with the given name
if there is no ParameterString with the given name
Called when a key is pressed or released, performs whatever action is appropriate for that event.
the KeyboardEvent that happened
true means this is a key-down event; false means a key-up event
the modifier keys down during event
Called at each movement during a mouse drag, performs whatever action is
appropriate. Only called if startDrag returned true.
The SimObject being moved is passed in, along with the current mouse position, in
simulation coordinates, and an offset calculated at the start of the drag.
Setting the SimObject position to (x - offsetX, y - offsetY) will move the SimObject
smoothly along with the mouse movement.
the SimObject being dragged, or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position (from DisplayObject.getPosition) to the mouse location at start of drag.
Private moveRemoves the Observer from this Subject's list of Observers. An Observer may
call removeObserver during its observe method.
the Observer to detach from list of Observers
Removes the Parameter from the list of this Subject's available Parameters.
the Parameter to remove
Sets the Simulation back to its initial conditions, see saveInitialState, and calls modifyObjects. Broadcasts event named 'RESET'.
Restores the Simulation state that was saved with saveState.
Saves the current variables and time as the initial state, so that this initial state can be restored with reset. Broadcasts event named 'INITIAL_STATE_SAVED'.
Saves the current state of the Simulation, so that we can back up to this state later on. The state is defined mainly by the set of Simulation variables, see getVarsList, but can include other data. This state is typically used for collision detection as the before collision state, see CollisionSim.findCollisions.
Private setCalculates anchor Y velocity, so that the anchor stays visible, as though in a 'steady state'. Otherwise the anchor tends to quickly wander off screen.
Derivation:
y'' = a sin(frequency t)
y' = integral(y'' dt) = -(a/frequency) cos(frequency t) + C
y = integral(y' dt) = -(a/frequency^2) sin(frequency t) + C t + C_2
To avoid the anchor wandering need C = 0 therefore
at time t = 0, this gives y' = -(a/frequency)
Protected setSets whether this Subject will broadcast events, typically used to temporarily disable broadcasting. Intended to be used in situations where a subclass overrides a method that broadcasts an event. This allows the subclass to prevent the superclass broadcasting that event, so that the subclass can broadcast the event when the method is completed.
whether this Subject should broadcast events
the previous value
Sets the Terminal object that this simulation can print data into.
the Terminal object that this simulation can print data into.
Protected setSets the VarsList for this simulation.
the VarsList to use in this simulation
Called at the start of a mouse drag. The nearest dragable SimObject is passed in,
along with mouse position in simulation coordinates. If no dragable SimObject was
found, null is passed for the first argument. If the EventHandler does not recognize
the SimObject then it should return false.
the SimObject that is nearest to the mouse drag coordinates,
or null if no SimObject was found
the location of the mouse in
simulation coordinates of the SimView where simObject was found, or in the
focus view
if simObject is null.
distance from the initial object position (from DisplayObject.getPosition) to the mouse location at start of drag
location of 'drag point' on the
SimObject in body coordinates of the SimObject; this is where for example a spring
will be attached on the SimObject when dragging; or null when no SimObject
was found
the modifier keys down during event
true if the EventHandler will handle dragging the SimObject
Returns a minimal string representation of this object, usually giving just identity information like the class name and name of the object.
For an object whose main purpose is to represent another Printable object, it is
recommended to include the result of calling toStringShort on that other object.
For example, calling toStringShort() on a DisplayShape might return something like
this:
DisplayShape{polygon:Polygon{'chain3'}}
a minimal string representation of this object.
Generated using TypeDoc
Simulation of a double pendulum hanging from a moveable anchor point.
The anchor point or 'cart' position can be given any program of motion, it is not affected by the pendulum movement at all. So you could regard the cart as a having infinite mass in comparison to the pendulums. Or that some outside entity is applying whatever forces are needed on the cart to keep it to the fixed program of motion.
The cart is both dragable by the mouse and/or can have a periodic up/down motion. With the periodic motion, this becomes a demonstration of an 'inverted pendulum': if the periodic motion is rapid enough, the pendulum position pointing straight up becomes stable.
There is a parallel but independent simulation for the movement of the cart. The cart is regarded as a point mass that is dragable by a spring force controlled by the user's mouse. Optionally, the periodic force moves the cart up and down.
Note that when changing the anchor amplitude or frequency, that we set the anchor vertical velocity such that the anchor stays centered at its current position. Otherwise, the anchor tends to move rapidly out of view.
Derivation of equations of motion is shown at https://www.myphysicslab.com/Moveable-pendulum.html.
Variables Array
The variables are stored in the VarsList as follows
To Do
Make a Parameter for whether to limit angles to +/- Pi. For some graphs you want this, but for other graphs you don't want it.
The energy values are not correct. When the anchor is moving then energy is being added to the pendulum. The potential energy should change from moving up and down in gravitational field. The kinetic energy should include the motion added by the anchor.
TO DO add ParameterBoolean specifying whether to limit angles to +/-Pi.