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AZT has been utilizing the Finite Element Method (FEM) for the
investigation of damages for many years. With the aid of FEM, the stress of
forces on assemblies, components and complete structures can be simulated by
computer.
Parallel to the development of the computer, the corresponding calculation
programs have been further developed tremendously as well. Today's pre- and
post-investigation programs permit the rapid design of models and make
reporting of the results easy. Both the simulation of purely static loads
and of dynamic strains is possible. The resulting stresses can be
ascertained from the calculated temperature distributions. Issues in the
area of flow mechanics or electromechanics (field strength distributions,
electromagnetic forces, etc.) are also covered by FEM.
AZT uses ANSYS Multiphysics, a powerful program system. FEM is utilized
when, for example, it is important to clarify origins and causes of damages
quickly, when the stress relationships are unclear, when solutions for the
repair should be verified, etc. The following examples serve to illustrate
how FEM is applied.
Vibrations in a Penstock
In the penstock (pressurized pipeline) of a hydroelectric power station, an
increase in vibrations appeared after a change to the turbine, which gave
cause for concern. After investigating the natural (inherent) frequencies
and characteristic forms of the pipeline by means of technical measurements,
the corresponding values were determined with the aid of the Finite Element
Method (FEM) and compared with one another. Through targeted
design-engineering changes, which had been simulated in advance by the
computer, the natural frequencies of the penstock could be shifted out of
the critical range of frequencies caused by the turbine.
Fractures in a Forging Press
The second example concerns a large forging press with a printing pressure
of 20,000 tons. In the borehole of the upper crossbeam, several fractures,
the positions of which were partially not explainable, appeared. In the
first step, the positions of the fractures were verified using the Finite
Element Method (FEM). It was shown that some of the fractures must have
developed under unusual loads. Together with the insured party, which
supported the calculations by means of its own measurements of stress on the
crossbeam, different alternative constructions were discussed and calculated
with the aid of FEM. Finally, a solution was chosen; it is now being
completed.
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