The Drop Test Wizard works by creating a rigid target geometry within Mechanical at the automatically detected first point of contact, making the target plane a fixed support and adding a Drop Height initial condition to the system. The analysis begins with the contact point of the geometry just touching the target, with an initial velocity determined from the specified drop height.
You can choose to change the orientation of both the geometry and the automatically generated target plane. The Drop Test Wizard always creates an analysis simulating a dropped object in the -Y direction. The dropped geometry should therefore be oriented accordingly.
The first page of the wizard shows the following input fields:
| Field | Description |
|---|---|
| Target Rotation (X) | Enter the angle at which to rotate the target plane geometry about the global X axis. |
| Drop Rotation (X) | Enter the angle at which to rotate the dropped geometry about its center of mass. |
| Drop Rotation (Y) | Enter the angle at which to rotate the dropped geometry about its center of mass. |
| Drop Rotation (Z) | Enter the angle at which to rotate the dropped geometry about its center of mass. |
| Define By | Define the impact magnitude by Drop Height or by Impact Velocity. |
| Drop Height | If you chose to define the drop test by drop height, enter the drop height value. |
| Impact Velocity | If you chose to define the drop test by impact velocity, enter the velocity value. |
The target plane is automatically created if a non-zero angle is input into Target Rotation (X).
The rotations are immediately updated on the dropped geometry in the graphical window when you enter the values, which allows you to inspect the setup of the model visually. The rotations are always applied in the order X, Y, Z irrespective of the order of entry into the Drop Rotation input fields.
If you entered a drop height value, it is converted into an impact velocity with the relationship as shown below.
With the energy balance:
The impact velocity is derived by:
If you choose to define the drop test by impact velocity, the drop height is calculated as follows:
Note: Air resistance is not taken into account in determining impact velocity, which means the conversion is only valid for drop heights of approximately 5 meters. When going beyond this height, it is recommended that experimental data containing impact velocity be used to define the impact conditions.
Once you have set all of these fields to your desired values, click Next to continue. This will display the second page of the wizard and initiate the creation of the objects associated with the fields on the first page of the wizard:
The rotations are stored in a Part Transform object.
The size of the target geometry is calculated as 2.5 times the longest side of the dropped geometry’s bounding box, which gives the geometry room to deform or exhibit sliding behavior. The target is then added to the Geometry using a Construction Geometry object.
The target geometry is positioned such that no separation exists between the geometry to be dropped and the target geometry. Note that if there are shells in the model the target will be offset by the shell thickness to allow you to use shell thickness in contact.
A Drop Height initial condition is added to the analysis, scoped to the dropped geometry with the fields matching those in the wizard. The Drop Height initial condition is fully parameterizable.
The Analysis Settings Preference Type is set to . This setting is only available in Ansys Explicit and therefore does not appear in LS-DYNA.
Sets the analysis end time to a value equal to the time it would take for the geometry to move 10% of its own length in the -Y direction traveling at the impact velocity. If there is more than one step in the analysis, the End Time of the final step is set to this value.
On the second page of the wizard, the following fields are available:
| Field | Description |
|---|---|
| Frictional Behavior | Specify whether the body interaction will be Frictional or Frictionless in the simulation. |
| Friction Coefficient | Set a value for μ, the coefficient of friction for the body interaction. |
| Dynamic Coefficient | Set the value of the dynamic coefficient of friction for the body interaction. |
These fields are used to specify a global body interaction defining the contact behavior between the dropped geometry and the target.
When you click Finish, the wizard does the following:
Creates the Body Interaction.
Creates the Standard Earth Gravity boundary condition and scopes it to the dropped geometry.
Creates a mesh for all the geometry and performs a check to see if any point on the mesh of the dropped geometry is penetrating the mesh of the target. If this is the case, a new target is created in a corrected location and a new mesh is generated. If mesh penetration occurs, a warning message will be displayed in the Messages panel.
Creates a Fixed Support boundary condition and scopes it to the target.
Adds three result objects to the tree: Total Deformation, Equivalent Plastic Strain, and Total Acceleration. However, the wizard adds only two result objects — and — to the tree in LS-DYNA. As a result, must be added later as a User Defined Result.
Once all of these steps are completed, the wizard will close.
Note: You can return from page 2 of the wizard to page 1 using the button, and also the wizard entirely from both pages, but note that any actions that the wizard has performed such as geometry rotations and object creation will not be undone.