Browsing by Author "Cui, Lin"

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    Flexible multibody dynamics modelling of point-absorber wave energy converters
    (Elsevier, 2018-05-07) Wang, Lin; Kolios, Athanasios; Cui, Lin; Sheng, Qihu
    As an inexhaustible and environmentally-friendly energy resource, ocean wave power, which is extracted from ocean waves through WECs (wave energy converters), is highly valued by coastal countries. Compared to other types of WECs, point-absorber WECs, the main body of which can be fixed on a platform (e.g. ship), save on installation costs and therefore have concentrated significant interest among researchers and technology developers. In the development of point-absorber WECs, it is crucial to develop a reliable structural model to accurately predict the structural dynamic responses of WECs subjected to wave loadings. In this work, a FMBD (flexible multibody dynamics) model, which is a combination of MBD (multibody dynamics) and FEA (finite element analysis), has been developed for point-absorber WECs. The FMBD model has been applied to the structural modelling of the NOTC (National Ocean Technology Centre) 10 kW multiple-point-absorber WEC. The floater arm tip displacement and velocity obtained from the FMBD model are validated against the values obtained from an analytical model, which is also developed in this work. The results from the FMBD model show reasonable agreement with those from the analytical model, with a relative difference of 10.1% at the maximum value of the floater arm tip displacement. The FMBD model is further used to calculate the stress distributions, fatigue life, deformations, modal frequencies and modal shapes of the structure. The results indicate that WECs are prone to experience fatigue failure, with the shortest fatigue life (2 years) observed in the floater arm. The FMBD model developed in this work is demonstrated to be capable of accurately modelling point-absorber WECs, providing valuable information for designers to further optimise the structure and assess the reliability of WECs.
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    Multi-criteria risk assessment approach for components risk ranking - The case study of an offshore wave energy converter
    (Elsevier, 2016-12-02) Okoro, Uzoma; Kolios, Athanasios; Cui, Lin
    Experts’ judgement is employed in offshore risk assessment because reliable failure data for quantitative risk analysis are scarce. The challenges with this practice lies with knowledge-based uncertainties which renders risk expression and estimation, hence components’ risk-based prioritisation, subjective to the assessor – even for the same case study. In this paper, a new risk assessment framework is developed to improve the fidelity and consistency of prioritisation of components of complex offshore engineering systems based on expert judgement. Unlike other frameworks, such as the Failure Mode and Effect Criticality Analysis, it introduces two additional dimensions: variables and parameters, to allow more effective scoring. These additional dimensions provide the much needed and uniform information that will assist experts with the estimation of probability of occurrence, severity of consequence and safeguards, herein referred to as 3-D methodology. In so doing, it achieves a more systematic approach to risk description and estimation compared to the conventional Risk Priority Number (RPN) of FMECA. Finally, the framework is demonstrated on a real case study of a wave energy converter (WEC) and conclusions of the assessment proved well in comparison and prioritisation.
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    Reliability assessment of point-absorber wave energy converters
    (Elsevier, 2018-06-04) Kolios, Athanasios; Di Maio, Loris Francesco; Wang, Lin; Cui, Lin; Sheng, Qihu
    Ocean wave energy is a clean and inexhaustible energy resource, capable of providing more than 2 TW of energy supply worldwide. Among all the technologies available to convert wave energy, the point-absorber is one of the most promising solutions today, due to its ease of both fabrication and installation. The floaters of point-absorber WECs (wave energy converters) are generally exposed to harsh marine environments with great uncertainties in environmental loads, which make their reliability assessment quite challenging. In this work, a reliability assessment framework, which combines parametric finite element analysis (FEA) modelling, response surface modelling and reliability analysis, has been developed specifically for the floater of point-absorber WECs. An analytical model of point-absorber WECs is also developed in this work to calculate wave loads and to validate the developed FEA model. After the validation through a series of simulations, the reliability assessment framework has been applied to the NOTC (National Ocean Technology Centre) 10 kW multiple-point-absorber WEC to assess the reliability of the floater, considering the fatigue limit state (FLS). Optimisation of key design components is also performed based on reliability assessment in order to achieve target reliability. The results show that for the considered conditions, the WEC floater is prone to experience fatigue failure before the end of their nominal service life. It is demonstrated that the reliability assessment framework developed in this work is capable of accurately assessing the reliability of WECs and optimising the structure on the basis of reliability.