A Method of Determing Dynamic Stability Critical Length of Construction Member

Based on the theory of elastic stability of structure,the calculating formula for dynamic stability critical length of construction member being in lateral resonance under the axial dynamic load is derived in this paper. The influence of different parameters, such as end conditions; rod size; damp force and excitation frequency, natural frequency, rod material, on dynamic stability critical length of rod is analyzed. The paper puts forward some related measures for reducing vibration of rod, and may provide reference values for the design and analysis of engineering.

Dynamic Properties of Fine-Scale 1-3 PZT/Epoxy Piezoelectric Composites

Fine-scale 1-3 PZT/epoxy piezoelectric composites were prepared by a dice-fill process, and their resonance characteristics and dynamic piezoelectric properties were investigated. The resonance characteristic was deeply influenced by PZT volume fraction and the thickness of 1-3 PZT/epoxy composite. The experiments proved that reducing the distance between PZT rods and/or increasing the height/width ratio could weaken the additional coupling effect of lateral resonance mode on thickness mode. The PZT/epoxy composites displayed only thickness-mode resonance when the distance between PZT rods was reduced to 220μm and its aspect ratio was increased up to 10.

Mechanical Vibration Problems With Variable Frequency Drives

Variable frequency drives are now frequently used to power large horsepower pipeline pumps to eliminate power costs wasted by throttling, to reduce inrush current on motor start, and to provide greater operating flexibility. This variable speed operation, however, can cause vibration problems in the pump and motor bearings, and in the couplings that are not normally experienced with fixed speed pumps. Enbridge Pipe Line has installed a number of variable frequency drives on units ranging from 2500 to 5000 hp in size and discovered unexpected torsional and lateral resonance vibration in the equipment at certain operating speeds. This presentation discusses the tests that were conducted to determine the source of the vibration, the theoretical analysis of the vibration modes and equipment responses, and the solutions that were implemented to reduce or eliminate the vibration. Recommendations are given for design principles that could be incorporated into the initial pump station design in order to avoid vibration problems with variable speed operation.