Our client is concerned about the vibration of a nuclear plant component known as a Generator Neutral Enclosure (NE). The NE is a hollow horizontal aluminum cylinder, 58″ diameter and 146″ long. The NE shell construction consists of several plates bolted together. The purpose of this analysis was to determine if the NE would resonate with the plant vibrations. Modifications were recommended to alter the neutral enclosure natural frequency.
An FEA model of the neutral enclosure was created that allowed us to perform a modal analysis and determine that two dominant frequencies of the NE fell close to the plant vibration frequency. A harmonic analysis was then performed using ODS measured displacements as inputs into the FEA model. The resulting vibration velocities and deformed shape were very similar to the measured ODS velocities and deformation. We then created a conceptual modification to shift the frequency away from the plants vibration frequency; three circumferential stiffeners were added near the central portion of the structure. With our modifications in place, the natural frequency was successfully shifted away from all forcing frequencies.