### 9.3.1. User Interface

An Analytical Blast boundary condition can be defined and applied to parts in the same manner in which a stress boundary would be. The blast boundary condition parameters that need to be specified are as shown below.

The numerical inputs are as follows:

Parameter | Description | Notes
--- | --- | ---
Charge weight (kg) | Weight of charge in equivalent weight of TNT (in kg) | Must be greater than 0.
X-coordinate of blast | X-coordinate of blast center in model units |
Y-coordinate of blast | Y-coordinate of blast center in model units |
Z-coordinate of blast (3D only) | Z-coordinate of blast center in model units |
Blast start time | Detonation time in model time units |
Ambient Pressure (kPa) | Ambient pressure in kPa | Must be greater than or equal to 0.
Ambient Temp (K) | Ambient temperature in Kelvin | Must be greater than or equal to 0.

Additionally, the following options can be specified:

- Blast Type: options are Air Burst or Surface Burst.

- Pressure Load: options are Automatic, Always Facing, or Never Facing. If Automatic is chosen, the solver determines whether the surface faces the blast in the following manner: if the face normal points away from the blast, then the surface faces the blast (NB for volumes the face normal is assumed to point into the volume). Therefore when applying a blast boundary condition to shells it is necessary to ensure that the shell normals are oriented as required. If Always Facing or Never Facing are chosen, the surfaces to which the blast boundary condition is applied are assumed to be always or never facing the blast, respectively, irrespective of the direction of the face normals. Faces determined to be facing the blast receive the reflected pressure load, while those that are determined not to face the blast receive the incident side on overpressure. The default is Automatic.

- Clearing: can be set to be On or Off. The default is Off. Please read the information regarding clearing in Limitations.

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