Analysis of variational autoencoders for imputing missing values from sensor data of marine systems

Velasco-Gallego, Christian and Lazakis, Iraklis (2021) Analysis of variational autoencoders for imputing missing values from sensor data of marine systems. In: Naval Architects and Marine Engineers (SNAME) Maritime Convention (SMC), 2021-10-25 - 2021-10-29, Providence.

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    Of all the causes of accidents to ships, 14% pertains to damage due to ship equipment. Accordingly, the maritime industry is currently considering state-of-the-art maintenance and inspection processes, an example of which is Condition-Based Maintenance (CBM). This is a strategy that hinges on the condition monitoring of assets. Condition Monitoring (CM) has proven to increase efficiency, reliability, profitability, and performance of vessel, and thus facilitate emissions reduction during its operational lifetime. To enable this maintenance strategy, sensors need to be installed along the most critical ship components and around the environment where these assets are operating through the appliance of Internet of Ships (IoS). IoS has demonstrated to be effective for collecting data in real time as well as performing diagnosis and prognosis to assess the current and future health of machinery to assist instant decision-making processes. The employment of IoS presents several challenges, an example of which is the imputation of missing values. Data imputation is a compelling pre-processing step, the aim of this is to estimate identified missing values to avoid under-utilisation of data. This data preparation step has gained popularity over the last few years due to its importance when dealing with Industrial Internet of Things (IIoT) sensor data. Nonetheless, very few publications presently refer to this aspect in the maritime industry. Although some articles presented new methodologies to impute missing values from sensor data of marine machinery based on machine learning methodologies, deep learning models have not yet been considered. For this reason, variational autoencoders for imputing missing values from sensor data of marine systems are analysed in this study. To assess the performance of variational autoencoders as imputation methods, a comparative study is performed with widely implemented imputation techniques. Mean imputation, Forward Fill and Backward Fill, and k-Nearest Neighbors are considered. To that end, a case study on marine machinery system parameters obtained from sensors installed on a diesel generator is performed. Results demonstrate the applicability of variational autoencoders when dealing with missing values from marine machinery systems sensor data, achieving a coefficient of determination of 0.99 when imputing missing values of the diesel generator power parameter.

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