Eatec Engineering Analysis

Modal Analysis Examples

Eatec Engineering Analysis has undertaken many dynamic analysis projects to calculate the natural frequencies of structures and assemblies for a range of industries, including defence, processing, oil & gas and automotive.

Brief details of some projects are given below.

Dynamic analyses of quarry screens

Screens are used in quarries to grade crushed stone into different size ranges. The screens are vibrated such that the material travels across it, with the smaller pieces passing through the mats and being collected separately from the larger pieces.

A number of dynamic analysis projects have been performed to determine the natural frequencies and mode shapes of screens and identify whether the frequencies are sufficiently different from the operating frequencies to ensure resonance would not occur. Some projects have been undertaken while the screen was still at the design stage, and others have been undertaken following in-service issues.

A common problem is that the screens have torsional modes which are too close to the forcing frequencies, leading to premature fatigue failures. Producing design which have relatively high vertical and lateral bending stiffnesses is normally not too difficult, but due to the operational requirements it is more difficult to achieve high torsional stiffness.

Modal analysis of a casting

A client had designed an assembly which is to be bolted to a diesel engine, and consists of an aluminum casting with a solenoid valve and various pipe connections.

It is important that any natural frequency of the assembly is not excited byCasting engine vibrations , and hence an assessment was required to confirm that the natural frequencies of the assembly were higher than 250 Hz.

A dynamic finite element analysis was performed to determine the natural frequencies and corresponding mode shapes. The mass and stiffening effects of the solenoid and the pipe connections were represented in the assessment in order to improve the accuracy of the results.

The analysis showed the first natural frequency was well in excess of 250Hz, and hence the design met the dynamic requirements.