Determination of structural damping in straight piping sections using modal analysis
Three- and eight-inch diameter pipes, supported rigidly at the ends and at intermediate points by typical piping supports, were excited to assess structural damping. Vibration sources for the 10 m (33-ft) lengths were an overhead crane (for snapback motion), impact hammer, and hydraulic shaker. Responses were measured by accelerometers, strain gauges, and an LVDT. Damping was calculated using complex-exponential curve fit (with commercial software), half-power, and logarithmic decrement methods. The paper details the test setup and steps taken to attain satisfactory coherence for the shaker frequency-response-functions. Additionally, the relative merits of each type of instrumentation and computational technique for this application are discussed. In these tests, damping was related to the support positions relative to each mode. When a mode excited an energy dissipating support, higher damping was induced, whereas supports located at nodal points did not affect damping. Gaps and other geometric nonlinearities produced higher damping levels. Damping behaved nonlinearly with excitation level. At low levels Coulomb friction produced high damping; at intermediate levels damping was relatively low; whereas damping increased linearly with stress level at and above the yield stress. Thus damping measured at one excitation level cannot always be extrapolated to other levels.
- Research Organization:
- EG and G Idaho, Inc., Idaho Falls (USA)
- DOE Contract Number:
- AC07-76ID01570
- OSTI ID:
- 6135613
- Report Number(s):
- EGG-M-09585; CONF-860224-8; ON: TI86005316
- Country of Publication:
- United States
- Language:
- English
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