Identifying and Minimising Uncertainty for ExperimentalJournal Bearing Studies

Over the last few decades, different experimentalmethods, with varying forms of data analysis, have been employedon a wide range of journal bearing types. Under thesecircumstances, it is not surprising that the results presented,and their accuracy, are subject to varying scatter. Many of theassessments have been rather imprecise, often using unquantifiedstatements such as “generally good agreement with predictions.”Most authors seem to have accepted that the appreciable scatter ofresults, especially in the dynamic oil film coefficients, wasinevitable. Uncertainty is defined as the estimate of the errors.Note that the estimate may often be too optimisticbecause some sources of error have not been identified. This paperhighlights sources of error for experimental journal studies,including some associated with the measurement system and physicalmisalignment. It is intended that this paper presents a coherentsource of information on best practice in the field ofexperimental bearing research, offering a clearly prescribedmethodology to estimate uncertainty and reduce error. The resultsof calculations of the sensitivity of the dynamicbearing coefficients to experimental errors in some commonly usedrig configurations are presented. It is shown that one of theexcitation schemes gives significantly lower sensitivity, but eventhis scheme has quite high sensitivity to measurement errors,especially phase. In conclusion, some of the critical precautionsin the search for good quality results for experimental journalbearing studies are described