Vibration Measurement Analysis Research Articles

Investigation of vibrations of a main centrifugal fan used in mine ventilation

Operation of machines in resonance ranges is a great challenge for design engineers. The paper focuses on the analysis of centrifugal fan casing vibrations which during machine operation, particularly in unsteady states, are very strong. Within a series of investigations performed according to the experimental modal analysis natural frequencies of fan casing vibrations were specified. Additional numerical simulations helped to define theoretical values of the natural vibrations frequency and its mode shapes. The results were analyzed and the numerical model was adjusted. The information was later used in the analysis of vibration measurements in real operating conditions. The results achieved for a nine-blade impeller (new type) were compared to results of an old construction eight-blade fan impeller. New solutions, which shall facilitate casing operation beyond resonance frequencies vibrations areas, were proposed.

Evaluation of the spray stability on liquid injection in gas–solid fluidized beds by passive vibrometric methods

AbstractFor some operations, such as fluid coking, gas atomised liquid feed must be injected via spray nozzles into gas–solid fluidized beds. A stable or non‐pulsating spray with a controlled droplet size is desired. The spray stability of various gas–liquid pre‐mixer and nozzle combinations was determined in open air conditions through analysis of vibration measurements on the upstream conduit with an accelerometer correlated to physical downstream spray measurements. The open air vibration measurements did not correspond to vibration measurements while spraying into a fluidized bed due to external vibrations from the fluidisation. The vibration measurements, however, can provide a relative ranking of spray stability of various gas–solid pre‐mixer and nozzle combinations for similar fluidisation conditions. In addition, the gas to liquid ratio (GLR) and the gas properties were all found to affect spray stability.

Structural Damage Detection with Cross Correlation Function of Vibration Observations

A structural damage identification technique based on cross correlation function analysis of vibration measurements is proposed. An 8-storey steel shear building model has been chosen as the case verification. Structural acceleration responses from neighbouring test points are used to establish damage identification parameters. Experimental analysis shows that the method can achieve quite precise results.

외팔보에 대한 가진력수준제어를 통한 피로균열규명기법의 실험적 검증

In this study, a new damage identification method for beam-like structures with a fatigue crack is proposed, which does not require comparative measurement on an intact structure but require several measurements at different level of excitation forces on the cracked structure. The idea comes from the fact that dynamic behavior of a structure with a fatigue crack changes with the level of the excitation force. The 2nd spatial derivatives of frequency response functions along the longitudinal direction of a beam are used as the sensitive indicator of crack existence. Then, weighting function is employed in the averaging process in frequency domain to account for the modal participation of the differences between the dynamic behavior of a beam with a fatigue crack at the low excitation and one at the high excitation. Subsequently, a damage index is defined such that the location and level of the crack may be identified. It is shown from the analysis of vibration measurements in this study that comparison of frequency response characteristics of a beam with a single fatigue crack at different level of excitation forces enables an effective detection of the crack.

Damage Assessment in Concrete Beams Using Non-Linear Analysis of Vibration Measurements

Damage Assessment in Concrete Beams Using Non-Linear Analysis of Vibration Measurements

One-year monitoring of the Z24-Bridge: environmental effects versus damage events

When using the analysis of vibration measurements as a tool for health monitoring of bridges, the problem arises of separating abnormal changes from normal changes in the dynamic behaviour. Normal changes are caused by varying environmental conditions such as humidity, wind and most important, temperature. The temperature may have an impact on the boundary conditions and the material properties. Abnormal changes on the other hand are caused by a loss of stiffness somewhere along the bridge. It is clear that the normal changes should not raise an alarm in the monitoring system (i.e. a false positive), whereas the abnormal changes may be critical for the structure's safety. In the frame of the European SIMCES-project, the Z24-Bridge in Switzerland was monitored during almost one year before it was artificially damaged. Black-box models are determined from the healthy-bridge data. These models describe the variations of eigenfrequencies as a function of temperature. New data are compared with the models. If an eigenfrequency exceeds certain confidence intervals of the model, there is probably another cause than the temperature that drives the eigenfrequency variations, for instance damage. Copyright © 2001 John Wiley & Sons, Ltd.