Velocity Impact excitations

Use a Velocity Impact excitation to simulate a drop test or a constant velocity impact test at a single nodal location on your model in a transient event.

This excitation type provides a good approximation of response away from the impact point where the response may still be linear. It is not intended for analyzing localized stress at the impact point (it cannot predict nonlinear response).

To use this excitation type:

• A single, solved enforced motion location must be defined on the node at which impact occurs. The enforced motion cannot be defined on multiple nodes.

• All six rigid-body degrees of freedom must be constrained. Typically, you set all six degrees of freedom for the enforced motion location to Enforced.

• No other excitations can be defined in the event.

• The Initial Conditions for the event must be set to Zero (if initial conditions are defined, they are ignored).

Impact methods

• Drop Impact — Lets you specify either the drop height or the desired velocity at the time of impact. The software calculates the velocity from the drop height or vice versa (using ), depending on which of the two values you specify.

• Constant Velocity Impact — Lets you specify a constant velocity to be used for the impact.

With either impact method, you can also include a pre-impact duration in the impact calculation (see the next section).

Impact start time and duration

You define the duration of the actual impact pulse in the Pulse Duration box. The impact duration is typically very short.

The Start Position option lets you define the starting point for the impact simulation. The simulation can start at the moment of impact or you can add a pre-impact duration.

• At Impact — The calculation starts at the time of impact.

• At Drop — (Available with Drop Impact excitations only) The software adds an additional time duration before the actual impact, during which the model undergoes free fall from acceleration due to gravity. The software uses this equation to calculate the drop duration (t0):Where h is the value you specify for Drop Height and g is the gravitational constant.

       Note: 
      
      It is not necessary to add a gravity load when using a **Drop Impact** excitation.
     The software solves for enforced motion of the applied acceleration from gravity starting at time 0 up to the time of impact.
  

• Before Impact — (Available only for Constant Velocity Impact excitations) The software assumes a starting point 10 times the Pulse Duration. The software assumes the model is moving at the specified Velocity and the initial displacement is zero at the time of impact. The calculated pre-impact duration is noted in the dialog box under the heading Pre-Impact Duration.

Any pre-impact duration is noted in the dialog box under the heading Drop Duration. The pre-impact duration is used only to calculate the position of the model at the start of the simulation. It does not affect the impact calculations, but is useful for animating the pre-impact motion in post-processing.

Impact calculation

The software solves for the impact pulse as follows:

1. Internally creates a haversine acceleration impulse function with amplitude (amax) from time t0 to the Pulse Duration time t0 + Δt.Havsine=amax*0.5(1–cos(2πt/Δt))The software determines amax such that integration of the haversine function is equal to the impact velocity, –v0. For example, for an object falling in the –Z direction that has an impact velocity of –1400 mm/sec, the area under the haversine function must be +1400.

2. Solves for enforced motion of the applied acceleration (uses the time from the excitation definition and solves to the end of the event).

3. Uses v0 as initial velocity at time = t0. Displacement at this time is zero. At time t0 + Δt, the velocity at the enforced motion point should be zero, indicating that impact has completely stopped the initial velocity.

Because this is a linear simulation, the solution results are valid only for the moment of impact until the reaction force 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). The post-impact results are irrelevant to your analysis anyway because the highest stress typically occurs soon after the moment of impact.

Reaction force response function

In the picture, three points are marked:

• — Point of impact. Reaction force at this point is still zero.

• — The peak reaction force.

• — The point when reaction force drops below zero. Data after this point is invalid.

The duration of the impact pulse determines the “sharpness” of impact. A shorter duration indicates a harder contact surface. For example, 0.001 seconds for wood, 0.002 seconds for carpet, or 0.0008 seconds for metal.

Impact direction

You can specify the Impact Direction in terms of the nodal direction components (for example, X, Y, Z) that correspond to the solved DOFs in the enforced motion location on which the excitation is defined. For example, if your enforced motion location is enforced in the Z direction, you can define the velocity impact excitation in the Z direction.

If the enforced motion location is enforced in all three translational DOFs (X, Y, and Z), you can choose the User Defined option to define the excitation direction using the standard vector definition options.

If the solution contains a Gravity load, the Impact Direction for the excitation must be the same as the direction of the Gravity load.

Animating the impact

You can use the Animate command to post-process the impact results, allowing you to visualize the drop or motion before and at the moment impact.

The following example shows the post-processing animation of a drop impact. The handheld electronics device is dropped on the front-right corner (a node on the front-right corner is specified as the enforced motion location). The first animation shows the Von mises stress over the entire model.

Handheld electronics device (von Mises stress)

The second animation shows the stress distributed to the internal circuit board, which is the area of interest. The front and back covers of the device are hidden.

Circuit board inside device (von Mises stress)

Where do I find it?

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed part
Command Finder	Velocity Impact Excitation
Simulation Navigator	Right-click the Excitations node→New Excitation→Velocity Impact

How do I

Convert SRS/PSD/Time functions

Import test data into Response Dynamics

Create nodal and enforced motion excitations

Create distributed load excitations

Create static excitations

Create a drop impact or constant velocity impact simulation

Calculate random RMS functions from PSD input

Using Fast RMS Fitted PSD functions

Create rotating force excitations

Correlate two PSD excitations

Create DDAM excitations

Learn more

Excitation loads

Response Dynamics Function Toolkit

Using pulse functions for shock analysis

Rotating forces and unbalanced masses

PSD correlation

Look up more details

Function requirements by excitation type

Function parameters by event type

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Velocity Impact excitations, Simcenter 3D 2021.1 Series

© 2020 Siemens

window.mainLanguage="en_US"

window.delivId=""

window.projectId=""

MathJax.Hub.Config({ TeX: { extensions: ["autoload-all.js"] }, tex2jax: { displayMath: [ ] }, "SVG": { scale: 125 } });