RESONANCE TESTING IN THE DETERMINATION OF FIXED BASE NATURAL FREQUENCIES OF SHIPBOARD EQUIPMENT.
Abstract
Examination shows that the results of past shake tests to determine the fixed base natural frequencies of in-place shipboard equipment-foundation systems are not correct. A review of the equations of motion for a five-degree-offreedom system revealed that choosing the driving point on the equipment could not give the desired frequencies. The review showed that the fixed base frequencies could be obtained if the driving point were on or below the base of the equipment-foundation system. Prominent valleys occur in the response of the base at the fixed base frequencies of the system above the base and of the supporting structure below the driving point. Comparison of these valleys with prominent peaks in a plot of the ratio of equipment response to base response will eliminate the extraneous frequencies of the structure below the driving point. Although this method functioned well when applied to systems simulated with an analog computer, it will be difficult in the field to place a shaker having sufficient force below the equipment. A situation involving rotation as well as translation magnifies the difficulties, since additional shakers are necessary which are capable of phase control and a range of force ratios at each frequency. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 15, 1964
- Accession Number
- AD0610153
Entities
People
- Lawrence P. Petak
- Ronald E. Kaplan
Organizations
- United States Naval Research Laboratory