It is common practice nowadays with critical machinery to measure, either on-line or off-line, the vibration response at a number of suitable locations and to assess the state of health of the equipment based on obser...
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ISBN:
(纸本)0912053534
It is common practice nowadays with critical machinery to measure, either on-line or off-line, the vibration response at a number of suitable locations and to assess the state of health of the equipment based on observed changes in one or more of the response parameters. Early diagnosis of potentially damaging faults or defects can lead to substantial cost savings. Frequently. in practice, interpretation of the vibration data is performed more on a qualitative as opposed to quantitative basis which may be of limited benefit. The work presented here shows that by utilising a simple approach involving the (SVD) Singular Value Decomposition method, changes in measured vibration data can be incorporated into an appropriate rotordynamic model and identification of the cause of the modified vibration response achieved. The technique is intended to be used in conjunction with available information related to the machine's construction and/or operational history. The proposed approach consists of two separate components:- the first used to identify bearing-related problems and the second employed in the diagnosis of rotor balance problems. The effectiveness of the proposed procedure is assessed by recourse to analysis of a real representative rotor system.
The fatigue strength of a generic submersible, enhanced to a FPF, was determined using 1980 design regulations and compared with 1993 guidelines. The fatigue clock on this older semisubmersible was reset using advance...
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ISBN:
(纸本)1880653117
The fatigue strength of a generic submersible, enhanced to a FPF, was determined using 1980 design regulations and compared with 1993 guidelines. The fatigue clock on this older semisubmersible was reset using advances in the fatigue assessment of weld imperfections that were not available at the time this vessel was originally designed. An inspection strategy of critical weld details was established based upon recently available crack growth data and more up-to-date fracture mechanics methods. Examples of this data include crack growth rate and threshold stress intensity factor data. Fracture mechanics analyses were performed that recognized the importance of weld imperfection shape and its evolution throughout life. Recent 3-D finite element analyses of semi-elliptical cracks located at weld toes show that crack shape and proximity of the crack front to the weld toe can significantly affect crack life. S-N fatigue damage analyses that recognize the influence of stress response bandwidth and rainflow stress cycle counting led to reductions in fatigue damage between 15 and 25 percent. Where necessary, fatigue life was improved further by a factor of 2.2 through the use of controlled weld toe grinding. Lastly the fatigue clock was reset to practically zero through the use of a carefully designed weld repair program. This latter strategy was based upon S-N fatigue and crack propagation analyses using latest calculation methods and data, detailed finite element analyses, and in-service inspection records.
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