Creating a random load event

Using the Random Event command, you can create a random load event to perform durability analysis of a model, which is exposed to a random excitation described by power spectral densities (PSD) and cross correlations.

For durability analysis of a random load event, you must define the random data source, the scaling factor, and the durability option. The random data source contains the data required for the dynamic analysis of the solution. The random load event accesses the random data source, and contains the parameters required for the durability analysis. You must also create a Local Stress State simulation object that uses linear projections, for example with critical planes. You can also define the load length and assign a temperature source to the load event.

Data source

Using the Random Data Source command, you can create the random data source, that is used to define a random event, by specifying the mode set, the vibration input, and, optionally, the correlation input and the static loads.

A mode set is a collection of structural modes that are derived from different data sources. The modes are characterized by the natural frequency, modal damping, modal mass, and mode shape vector. You can define the boundary conditions used to compute the modes contained in the mode set, or instruct the solver to extract the modal participation factors from a source file, instead of computing them.

For a vibration input, you define translational and rotational vibration inputs as free, fixed, enforced motion, nodal force, or nodal moment excitation types, and assign them to the selected nodes in specified directions. You can also correlate two vibration inputs using a cross spectral density (CSD) function that defines the similarity and dependency between the two selected vibration inputs.

Durability options

The irregularity factor of a PSD sample is defined as the number of zero crossings, or mean level crossings for a signal with a non-zero mean, divided by the number of peaks. This number falls in the range of 0 to 1. When the value of the sample is 1, it is proximate to a harmonic load, meaning the process is narrow band. When the value for the irregularity factor tends towards 0, the process is broader and additional frequencies are found in the sample.

Specialist Durability uses one of the following options to compute the probability distribution of a random load that is defined by a PSD.

Dirlik

Is recommended for typical durability loads.

Narrow band

Is an analytical method to estimate the stress range distribution. Choose this method only for narrow band loads as it would be too conservative for typical durability loads.

Equivalent sine wave

Is a simple deterministic approach that calculates an equivalent sine wave excitation of the PSD. Use this method for a fast preview analysis.

Where do I find it?

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed part
Command Finder	Random Event Random Data Source
Simulation Navigator	Right-click the Events node→New Event→Random EventRight-click the Random Data Sources node→Random Data Source
Location in dialog box	Random Event dialog box→Data Source group→Create Data Source

How do I

Create a temperature source load for part of the model

Create a temperature source load for the entire model

Automatically create a duty cycle load event

Create a random data source

Create a vibration input

Create a random load event

Create a harmonic data source

Create a harmonic load event

Learn more

Supported solution types for load events

Creating a temperature source load

Creating a block load event

Creating a superposition event

Creating a transient event

Creating a flexible body event

Creating a duty cycle load event

Automatically creating a duty cycle load event

Creating a harmonic load event

Managing specialist durability load events

Look up more details

Modal basis in vibration load events definition

Quick links

Command reference

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Creating a random load event, Simcenter 3D 2021.1 Series

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