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====== Body Loads ======

Body loads comprise forces that are distributed over a solid volume. Probably the most familiar of these is the gravitational force acting on a mass to give it weight. Simple gravitational loads are applied in the Specify tab using the Gravity checkbox. Rotational body loads and general linear acceleration loads are applied by choosing **[Add]** in the **Loads** group. Followed by the **__B__ody** option at the command line.
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===== Gravitational Loads =====
 
Gravitational loads are the simplest to apply. Simply check the **[ ] Gravity** checkbox to apply a gravitational load and simulate the model under its own weight. Gravitational loads applied in this manner act in the -Z direction with a magnitude corresponding to Earth's surface gravitation. More complex gravitation scenarios may be simulated using [[wiki:sns:sns2014:body_loads#Linear Acceleration Body Loads|linear acceleration loads]]. If the **Gravity** box is checked, the gravitational load is **added** to any other loads being applied.

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===== Rotational Body Loads =====
 
Rotational body loads are applied by choosing **[Add]** in the **Loads** group of the **Specify** tab. Choose the the **__B__ody** option at the command line to bring up the **Body Load Creator** dialog.

A rotational body load consists of 2 components: angular velocity and angular acceleration; specified using the following steps:

  - Enable rotational body loads by checking the **[ ] Active** checkbox in the **Rotational Load** group.
  - Click **[Axis]** and choose an axis (a ray) of rotation by specifying an origin for the axis followed by a point on the axis (the ray's direction).
  - Specify the angular velocity and angular acceleration in the entry boxes.
  - Click **[OK]** to dismiss the dialog and apply the load to the model.

The direction of the rotation is determined using the right hand rule: using your right hand, point your thumb in the direction of the axis. A positive angular acceleration would simulate moving the restraints in the direction the fingers of your right hand would wrap around the axis. The body will tend to deflect in the opposite direction. The radial deflection due to angular velocity is independent of rotational direction.

The rotational body load is **added** to the body loads due to gravity and linear acceleration.
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===== Linear Acceleration Body Loads =====
 
Linear acceleration loads are applied by choosing **[Add]** in the **Loads** group of the **Specify** tab. Choose the the **__B__ody** option at the command line to bring up the **Body Load Creator** dialog.


Linear acceleration vector loads are specified by entering the components of a linear acceleration vector in fractions of Earth's **g**. It is **added** to the body loads due to gravity and rotation.

  - Enable linear acceleration vector body loads by checking the **[ ] Active** checkbox in the **Linear Acceleration Vector** group.
  - Specify the x, y, z components in the entry box in the form **A<sub>x</sub>,A<sub>y</sub>,A<sub>z</sub>**.
  - Click **[OK]** to dismiss the dialog and apply the load to the model.

The body's response to the linear acceleration is simulated as if the restraints are accelerated in the specified direction. The distributed mass of the body will tend to deflect in the opposite direction.
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