Problem Description

This example uses a single degree of freedom structure to test the behavior of a frequency dependent link element. A steady state analysis is performed for various loading frequencies. The resulting link deformations obtained for the various loading frequencies are compared with independent hand calculated results based on theory presented in Chopra 1995.

This model consists of a single joint, labeled joint 1, and one link element. The model is created in the XZ plane. Only the Uz degree of freedom is active for the analysis. The frequency dependent link element is modeled as a single-joint link element at joint 1. This means that one end of the link element is connected to the ground and the other end is connected to joint 1. The link element is oriented such that its positive local 1 axis is parallel to the positive global Z axis. This is the default orientation of single joint link elements. Only U1 degree of freedom properties are defined for the link element.

The link stiffness varies linearly from 80 k/in at a frequency of 0 Hz to 200 k/in at a frequency of 1 Hz. The link hysteretic damping property varies linearly from 0 k/in at a frequency of 0 Hz to 5 k/in at a frequency of 1 Hz.

A 0.03 kip-sec2/in translational mass in the Uz direction is assigned to joint 1. Also a 100 kip point load is assigned to joint 1 in the positive Uz direction.

A single steady state load case named SS1 is created. Results are obtained at loading frequencies, fL, of 0.12, 0.39 and 0.77 Hz.

The following table defines the frequency dependent link properties as they are input into this model.

Tested Features

Frequency dependent links
Steady state analysis

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