Page Comparison

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The Forward Dynamics Tool is accessed by selecting Tools → Forward Dynamics… from the OpenSim main menu bar. Like all tools, the operations performed by the Forward Dynamics Tool apply to the current model. The name of the current model is shown in bold in the Navigator. See chapters __40__ Opening, Closing, and Using the Navigator Window for information on opening models and making a particular model current.

As of 3.1, you can also use the Simulation Controls in the toolbar to quickly run a simulation. See the section on the __40__ Toolbar to learn more.

The Forward Dynamics Tool is controlled by a window with three tabbed panes (figure below). 

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Figure: Window for the Forward Dynamics Tool, Saving and Loading Settings

Main Settings Pane

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	The section for Current Model displays uneditable information about the current model that is to be used for analysis by the Forward Dynamics Tool.
	The section for Input displays editable information that allows you to specify the controls and states or motion to be used to run the forward simulation, as discussed in __40__ How Forward Dynamics Works.  You may use the folder button to browse for the controls and states or motion files. Both these settings are optional with the default behavior to use zero value for controls if none is specified and to use the inital pose of the model in case no initial states file is specified.  Since most OpenSim muscle models have internal states (e.g. Fiberlength and Activation for many muscle models), the check box to "solve for equilibrium of actuator states" is provided to allow the muscles to initialize to reasonable non-zero fiberlength if the initial states file does not contain values for these muscle states or if an initial states file is not specified altogether. This is done by computing a fiber length for the muscle that is consistent with the muscle's activation level.
	The section for Time displays editable information that allows you to specify the start and end time for the forward simulation.
	The section for Output displays editable information that allows you to specify the prefix appended to all of the resulting output files, the directory to which the files are saved, and the precision of the decimal places used when writing results.  You may use the folder button to browse for and specify a directory in which to save the output files. You may use the  button to open an Explorer window to the specified directory.

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	The section for Actuators displays editable information that allows you to specify additional force set files that specify forces to supplement the muscles of the model, as discussed in __40__ How Forward Dynamics Works.  You may use the  button to edit the list of force set files describing the forces to be appended to or replaced in the model.
	The information in the External Loads section is optional.  If checked, the section displays information so that you can specify the external loads applied to the model.  Please refer to the section on ExternalLoads specification under the __40__ How to Use the Inverse Dynamics Tool for more details.

Analyses

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• Kinematics: Records the generalized coordinates (q's), generalized speeds (u's), and the accelerations (i.e., derivatives of the generalized speeds: du/dt)
• BodyKinematics: Records the configuration (center of mass position and orientation) of each body, as well as their velocities (linear and angular) and accelerations (linear and angular). Additionally, it records the overall center of mass of the model, as well as the velocity and acceleration of this center of mass.
• Actuation: Records the generalized force, speed, and power developed by each actuator of the model. The generalized force can either be a force (with units N) or a torque (with units Nm). The actuator speed is the rate at which the actuator shortens. Depending on the actuator, a speed can be either a translational speed (m/s) or an angular speed (deg/s). An actuator power (Watts) is the rate at which an actuator does work. Positive work means that the actuator is delivering energy to the model; negative power means that the actuator is absorbing energy from the model.

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The Integrator Settings pane is used to specify parameters of the numerical integrator used during the simulation.

If using controls from __40__ Computed Muscle Control, It is recommended that you use the same integration time steps. To do so:

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