Create a drop impact or constant velocity impact simulation

Specify the impact point

1. Define an enforced motion location at the impact point on your model, on a single node. All degrees of freedom for the enforced motion location must be set to Enforced. For the steps to create an enforced motion location, see Specify excitation locations. Note: No other constraints are necessary. The enforced motion location in all six DOFs is sufficient to restrain the model. Also, the enforced motion location cannot be defined on multiple nodes.

2. Create a 1D connection, using rigid or beam elements, from the node on which the enforced motion location is defined to the appropriate nodes near the impact location (see the example below). For the steps to create a 1D connection, see Spider element connections. Example 1D connection (from impact node in center)

3. When defining the output requests for the SOL 103 – Response Dynamics solution, include Displacement and Stress results (in addition to any other results you may be interested in). Also, request a sufficient number of modes or range of modal frequencies to capture the motion you will be analyzing. For example, if you will be analyzing a drop simulation in the -Z direction, you typically should have 80–90% of the effective mass in the Z direction.

4. Solve the model.

Create the excitation

1. Create a new Response Dynamics solution process.

2. Define damping as needed and deactivate any irrelevant modes. Verify your mode shapes and ensure that sufficient effective mass is captured in the direction of interest.Note: In most cases, damping is not necessary with velocity impact excitations. Because the duration of the impact is so short, the structure reaches its peak response before significant energy has time to dissipate.

3. Create a transient event. Make sure the event Duration covers the pre-impact time period (if any) plus the impact duration you intend to use. For example, if you intend to model a drop of 10 feet with an impact duration of 0.0001 seconds, the pre-impact plus the impact will be around 0.75 seconds. To capture the impact, you must ensure your transient event's duration is longer, such as 0.8 seconds.

4. In the Simulation Navigator, right-click the Excitations node (under the current Event node) and choose New Excitation→Velocity Impact.Note: The velocity impact excitation must be the only excitation in the event.

5. Under Impact Method, choose whether to create a Drop Impact or Constant Velocity Impact.

6. Enter a name and description for the excitation as desired.

7. Enter the appropriate Impact Parameters for the type of impact excitation you are creating. You can define:The duration of the impact pulse. This should be a very small number, such as 0.001 or smaller. Whether the impact calculation starts before the impact (such as when the model is dropped) or at the moment of impact. The pre-impact duration is used only to calculate the position of the model at the start of the simulation. After solving for the dynamic response, you can animate the contour plot and visualize the model displacement.The Drop Height (only for Drop Impact excitations) or the Velocity. For drop impact excitations, when you specify the Drop Height, the software calculates the Velocity (alternatively, you can specify the Velocity and let the software calculate the Drop Height). For constant velocity excitations, if you choose Before Impact, the software assumes a starting time point that is 10 times the Pulse Duration and an initial displacement of zero. Note: The software automatically applies the excitation to the node on which your solved enforced motion location is defined.For more information about these parameters, see New Velocity Impact Excitation dialog box.

8. Under Impact Direction, specify the direction of the excitation in terms of nodal direction components (for example, X, Y, Z). If the enforced motion location is enforced in all three translational DOFs, you can choose the User Defined option to define the excitation direction using the standard vector definition options. Note: If you are modeling drop impact, adding a gravity load to the solution is not recommended. However, if you do include a gravity load, the Impact Direction in the excitation should match the direction of the gravity load.

9. A green preview arrow appears in the work coordinate system to indicate the direction of the excitation. To reverse the excitation direction, click Reverse Direction .

10. Click OK to create the excitation.

Perform the response evaluation

Because this is a linear simulation, the solution results are valid only for the moment of impact until the reaction force at the impact point goes below zero. This simulation type does not support the bounce that would occur in reality after the moment of impact (instead, the reaction force goes into tension). Regardless, the post-impact results are irrelevant to your analysis because the highest stress occurs at the moment of impact.

Before generating the contour results, it may be helpful to first plot the displacement or reaction force to determine the moment of impact.

1. Use the Evaluate Nodal Function Response dialog box to generate a displacement or reaction force response function at the impact node in the direction of interest, and plot the function.

2. Use Probing Mode to mark the point of impact in the graph. Displacement response function; impact point marked

3. Make a note of the time of impact and then close the graph.

4. Use the Evaluate Response Results dialog box to generate the response results for the entire model. In the Requested Results group, select Displacement and Stress.In the graphics window, select all nodes in the model.Under Evaluation Domain by Range, in the Output Start Point box, enter the number of seconds after the start of the event to start the impact evaluation. The default starting point is 0 seconds (that is, the start of the event). In the Output End Point box, enter the number of seconds after the start of the event to end the evaluation (the default value is the end of the event). Make sure this value extends the evaluation past the point of impact. For example, if you determined that the time of impact is at 0.05 seconds, you could enter 0.06 seconds as the Output End Point. (Remember that you determined the time of impact earlier using the nodal displacement function.)In the Decimation Order box, enter a value to reduce the number of data points. Reducing the number of data points increases the performance of the solve; however, if you use a decimation order, be careful that you do not miss the point of impact in the evaluation. The calculated number of points is indicated in the dialog box under Number of Points.Click OK.

Post-process and analyze results

1. Open the Post Processing Navigator.

2. Right-click your solution process event and choose Load to load the results.

3. Right-click your solution process event and choose New Postview.

4. Right-click the new post view and choose Edit.

5. In the Post View dialog box, click the Deformation tab.

6. In the list next to Scale, choose Absolute.

7. In the Scale box, enter an appropriate scale value for the displacement results and click OK.

8. In the Post View dialog box, click the Result tab.

9. On the Result page, in the second list, choose Stress – Element-Nodal.

10. In the third list, choose the appropriate stress option and click OK to close the Post View dialog box.Note: Notice that the contour colors are scaled relative to your entire model and not according to the area of the model you are interested in. The remaining steps describe how to scale the contour colors.

11. In the Post Processing Navigator, expand the Post View node and clear the check boxes next to any elements of the model that are not the primary target of your analysis.

12. In the Post Processing Navigator, under your event results node, find the time increment that corresponds to the time of impact. Expand the Stress – Element-Nodal node under that results increment.

13. Double click Von-Mises to display the stress contour plot at the time of impact for the area of interest on your model.

14. Edit the post view again.

15. In the Post View dialog box, click the Legend tab.

16. From the Legend Extremes list, select Specified.

17. The value in the Max box is the maximum stress value for the displayed portion of the model for the time of impact. Adjust this value up slightly to scale the color bar appropriately for the entire model.

18. Click OK.

19. Expand the Post View node (if necessary) and select the check boxes to redisplay the hidden elements of your model, so the entire model is again displayed. Note that the contour colors are now scaled relative to the maximum stress in your area of interest.

20. Choose Results tab→Animation group→Animate .

21. In the Animate list, choose Iterations.

22. Click Play .

Note that the time iteration that contains point of impact may not show stresses in the contour plot; rather, the time iteration directly following the point of impact should begin to show stresses.

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Learn more

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Response Dynamics Function Toolkit

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Velocity Impact excitations

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PSD correlation

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Function requirements by excitation type

Function parameters by event type

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Create a drop impact or constant velocity impact simulation, Simcenter 3D 2021.1 Series

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