How to Use the GUI
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 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 Toolbar to learn more.
The Forward Dynamics Tool is controlled by a window with three tabbed panes (figure below).
Figure: Window for the Forward Dynamics Tool, Saving and Loading Settings
The Control Panel
At the bottom of all the Tool dialog windows are four buttons, located in what we call the Control Panel.
Note that the Close button can be clicked immediately after execution has begun; the execution will complete even though the window has been closed.
Main Settings Pane
The Main Settings pane is used to specify parameters relating to the subject data, the generic model, and how the model is to be scaled. The pane is organized into four main sections entitled Current Model, Input, Time, and Output.
Actuators and External Loads Pane
The Actuators and External Loads pane is used to specify parameters relating to the actuators appended to the model and the external loads applied to the model during the forward dynamic simulation. The pane is organized into two main sections entitled Actuators and External Loads.
Analyses can be performed while running forward simulation by including them on the Analysis pane. The main purpose for the forward dynamics step, besides validating the CMC results in a basic open-loop forward dynamics system, is to record additional simulation data. Getting additional output data from the Forward Dynamics Tool is done through the use of analyses. These are not unique to the Forward Dyanamics Tool and in fact, analyses can be added to RRA and CMC as well. But since forward runs are significantly faster than CMC, it is more practical to tweak and re-run forward simulations to obtain new data rather than re-run CMC.
The basic analyses of interest are:
- 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.
See the section on Analyses for more information and different types of analyses.
Integrator Settings Pane
The Integrator Settings pane is used to specify parameters of the numerical integrator used during the simulation.
If using controls from Computed Muscle Control, It is recommended that you use the same integration time steps. To do so:
The Forward Dynamics Tool is run using the command forward -S <setup file name>, for example,