Speed-power test with reference model


Quantifying measurement uncertainty


Recently, MARIN has carried out an internal research programme to quantify the measurement uncertainty of three commonly performed types of tests. Here we explain the approach, findings and next steps in the integration of


the uncertainty analysis in the measurement chain. Jorrit-Jan Serraris, j.w.serraris@marin.nl


With each measurement we attempt to obtain the “true value”. However, the first funda- mental step is to realise that a measurement result is only an approximation of the “true value”. Therefore, each time we have to question ourselves: how good is this approximation? It is very important to perform a well-controlled measurement with calibrated devices to guarantee that the measurements are precise and accurate.


The next step is to quantify the quality in terms of measurement uncertainty. A first step to ensure a good quality measurement is to have procedures and in-line Quality Assessment checks in place in order to perform the measurement exactly as intended. Once the measurement is performed, the combined measurement uncertainty can be determined by means of uncertainty analysis. Various sources contribute to the uncertainty of each measured and reported result such


22 report


as model, test setup, sensors, basin effects, measurement system and analysis. The contributions of these very different sources are combined following the ISO/IEC guide 98-3:2008 (Guide to the expression of Uncertainty in Measurement (GUM)). This method results in the measurement uncer- tainty U95, resulting in a bandwidth for the measurement results, in which there is a 95% confidence level.


In the internal research programme, uncertainty analyses have been performed for three types of regularly performed tests: propulsion measurement, current load measurements and seakeeping tests with an Anti Roll Tank. These analyses have resulted in a measure- ment uncertainty for the test results. Further- more, the analyses have revealed detailed insight into the relative contributions of uncertainty sources.


Future speed-power diagram with ‘U95’ for the measurement uncertainty and ‘Stat’ for expected range based on regression analysis of historical data


The present developments need to mature and be further integrated into the measure- ment process. Our final goal is to have the uncertainty analysis integrated in the measurement process. This will result in the reporting of the measurement uncertainty directly after each measurement (see figure).


In this way we aim to contribute to the trust and applicability of measurement results in the design, engineering and decision making process of our clients.


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