Tidal stream generators, current state and potential opportunities for condition monitoring

Tidal power industry has made significant progress towards commercialization over the past decade. Significant investments from sector leaders, strong technical progress and positive media coverage have established the credibility of this specific renewable energy source. However, its progress is being retarded by operation and maintenance problems, which results in very low operational availability times, as low as 25 %. This paper presents a literature review of the current state of tidal device operators as well as some commercial tidal turbine condition monitoring solutions. Furthermore, an overview is given of the global tidal activity status (tidal energy market size and geography), the key industry activity and the regulations-standards related with tidal energy industry. Therefore, the main goal of this paper is to provide a bird’s view of the current status of the tidal power industry to serve as a roadmap for the academia regarding the real needs of the tidal power industry

A hybrid finite element analysis and evolutionary computation method for the design of lightweight lattice components with optimized strut diameter

Components incorporating lattice structures have become very popular lately due to their lightweight nature and the flexibility that additive manufacturing offers with respect to their fabrication. However, design optimization of lattice components has been addressed so far either with empirical approaches or with the use of topology optimization methodologies. An optimization approach utilizing multi-purpose optimization algorithms has not been proposed yet. This paper presents a novel user-friendly method for the design optimization of lattice components towards weight minimization, which combines finite element analysis and evolutionary computation. The proposed method utilizes the cell homogenization technique in order to reduce the computational cost of the finite element analysis and a genetic algorithm in order to search for the most lightweight lattice configuration. A bracket consisting of both solid and lattice regions is used as a case study in order to demonstrate the validity and effectiveness of the method, with the results showing that its weight is reduced by 13.5 % when using lattice structures. A discussion about the efficiency and the implications of the proposed approach is presented

Acoustic emission localization on ship hull structures using a deep learning approach

In this paper, deep belief networks were used for localization of acoustic emission events on ship hull structures. In order to avoid complex and time consuming implementations, the proposed approach uses a simple feature extraction module, which significantly reduces the extremely high dimensionality of the raw signals/data. In simulation experiments, where a stiffened plate model was partially sunk into the water, the localization rate of acoustic emission events in a noise-free environment is greater than 94 %, using only a single sensor

Theoretical assessment of different ultrasonic configurations for defects detection in composite components

It is well known that structures’ safety is crucial and of great importance. Part of their maintenance procedure is structural inspection, which is currently performed with the aid of Non Destructive Testing techniques, aiming to detect structural defects in damaged or flawed components and prevent a catastrophic failure by substituting or repairing them. The objective of this work is the theoretical assessment of different ultrasonic configurations that could maximize delamination defect detection in composite components. Modeling study was performed using simulation software, where physical models representative of laminated Carbon Fiber Reinforced Polymer composites, consisting of a variety of artificial delamination defect modes (different sizes and depth), were numerically tested. Different ultrasonic configurations on both the positioning and the firing of the probe's elements including Phased Array delay timings and sampled array techniques were investigated and are presented in this paper. The potential of Full Matrix Capture data acquisition technique, modelled here, along with the post processing Total Focusing Method reconstruction approach is also assessed in terms of their ability to enhance defect detectability and visualization

A new synthetic training environment system based on an ICT-approach for manual ultrasonic testing

Training to qualify as a manual ultrasonic inspector takes a long time and costs a considerable amount of money. We developed a virtual training environment using an innovative dead-reckoning optical sensor that yields translational position which offers additional information to operators and examiners alike. The training environment contains a library of test scenarios, shows surface coverage, measures the time of inspection, indicates detected defects and provides a performance score. Our test-bed trial results using a pool of Ultrasonic Test (UT) qualified and unqualified participants on two virtual training blocks that contain 2 flaws each reveal 100% detection and an accuracy of 5mm in locating defects in more than 50% of the measured defect locations

High temperature shear horizontal electromagnetic acoustic transducer for guided wave inspection

Guided Wave Testing (GWT) using novel Electromagnetic Acoustic Transducers (EMATs) is proposed for the inspection of large structures operating at high temperatures. To date, high temperature EMATs have been developed only for thickness measurements and they are not suitable for GWT. A pair of water-cooled EMATs capable of exciting and receiving Shear Horizontal (SH0) waves for GWT with optimal high temperature properties (up to 500 °C) has been developed. Thermal and Computational Fluid Dynamic (CFD) simulations of the EMAT design have been performed and experimentally validated. The optimal thermal EMAT design, material selection and operating conditions were calculated. The EMAT was successfully tested regarding its thermal and GWT performance from ambient temperature to 500 °C

Inspection and structural health monitoring techniques for concentrated solar power plants

Parabolic trough concentrators are the most widely deployed type of solar thermal power plant. The majority of parabolic trough plants operate up to 400 °C. However, recent technological advances involving molten salts instead of oil as working fluid the maximum operating temperature can exceed 550 °C. CSP plants face several technical problems related to the structural integrity and inspection of critical components such as the solar receivers and insulated piping of the coolant system. The inspection of the absorber tube is very difficult as it is covered by a cermet coating and placed inside a glass envelope under vacuum. Volumetric solar receivers are used in solar tower designs enabling increased operational temperature and plant efficiency. However, volumetric solar receiver designs inherently pose a challenging inspection problem for maintenance engineers due to their very complex geometry and characteristics of the materials employed in their manufacturing. In addition, the rest of the coolant system is insulated to minimise heat losses and therefore it cannot be inspected unless the insulation has been removed beforehand. This paper discusses the non-destructive evaluation techniques that can be employed to inspect solar receivers and insulated pipes as well as relevant research and development work in this field

Modelling and empirical development of an anti/de-icing approach for wind turbine blades through superposition of different types of vibration

The generation of green, safe and inexpensive energy by wind turbines is often decreased or interrupted in severe climate areas during cold weather. When the blades are even partially covered by different types of ice, their efficiency drops suddenly due to degradation of the blade profile from the ideal. The present study presents a new approach using ultrasonic guided waves as an anti/de-icing technique supplemented by low-frequency vibrations to effect shedding of the ice from the turbine blades. The study consists of a series of steps including initial theoretical studies and finite element simulation of representative plates and turbine blades, followed by a number of experimental validations concluded by tests of the complete approach in an icing wind tunnel. The results show the efficacy of the developed approach in tackling the different types of ice which can form on the blades, using very low power compared to available thermal techniques