Best practice guidelines for tank testing of wave energy converters

Experimental tank testing is a key aspect of wave energy conversion research. The performance of designs can be assessed in an accessible and controlled environment and at a fraction of the cost of sea trials. Wave energy converter (WEC) tank testing is complex and has its own specificities compared with model testing of ships and offshore structures. This largely reflects the fact that the main quantity of interest is wave energy: how much is available and how much is harvested by the model. This paper provides an extensive overview of the various aspects of WEC tank testing. These are divided into three categories: physical model, measurements, and wave generation. For each of them, current best practice guidelines are given

Experimental investigation of lift and drag on the NACA 4412 near the water surface

This thesis deals with hydrofoils, appendages which are a growing trend in yacht design and aimed at alleviating boats (this reduces the wetted area and therefore the drag). This thesis acknowledges the research previously done relating to hydrofoils and the testing of hydrofoils from the 1900's until now, from a military and sailing point of view. It goes through the methodology used to extract lift and drag data from tank testing in Cran field University. It goes through the approach to design a test process to extract consistent results from different foils in later stages. The works also details the manufacturing of the rig to test a hydrofoil in near surface conditions: the pro file studied is the NACA 4412, the submergence ranges from 2.5 chords to 0.1 chords, the angle of attack ranges from 10 to -1 degrees and Reynolds Number ranging from 1500000 to 910000 (0.5 to 3.0 m/s). The resulting data showed that lift decreased as the foil got closer to the free surface. With signifi cant effects being seen from a submergence of 1 chord. This project also points outs the limitations of tank testing and the effects of side struts holding the hydrofoil

Concept design of a fast sail assisted feeder container ship

An environmentally sustainable fast sail-assisted feeder-container ship concept, with a maximum speed of 25 knots, has been developed for the 2020 South East Asian and Caribbean container markets. The use of low-carbon and zero-sulphur fuel (liquefied natural gas) and improvements in operational efficiency (cargo handling and scheduling) mean predicted Green house gas emissions should fall by 42% and 40% in the two selected operational regions. The adoption of a Multi-wing sail system reduces power requirement by up to 6% at the lower ship speed of 15 knots. The predicted daily cost savings are respectively 27% and 33% in South East Asian and the Caribbean regions.Two hull forms with a cargo capacity of 1270TEU utilising different propulsion combinations were initially developed to meet operational requirements. Analysis & tank testing of different hydrodynamic phenomena has enabled identification of efficiency gains for each design. The final propulsion chosen is a contra-rotating podded drive arrangement. Wind tunnel testing improved Multi-wing sail performance by investigating wing spacing, wing stagger and sail-container interactions. The associated lift coefficient was increased by 32%. Whilst savings in sail-assisted power requirement are lower than initially predicted an unexpected identified benefit was motion damping.The fast feeder-container ship is a proposed as a viable future method of container transhipment

Wave Excited Mass-Spring-Damper System for a Self-recharging Autonomous Underwater Vehicle

Autonomous underwater vehicles\u27 (AUVs) endurance is constrained by the lifetime of their batteries and the distance that tether wires can traverse. Solving the endurance problem of AUV using the enormous potential of ocean wave energy is the motivation behind this thesis. The objective of this research is to model a mass-spring-damper system to emulate the permanent magnet linear generator (PMLG) of a self-recharging AUV and identify its energy absorption capability through numerical simulation and experimental testing. The research activities started with modeling and fabricating a 1:5 scale model. The scaling was done by comparing the most common AUV size of 1.5m. The preliminary dry testing result confirmed the inadequate damping of the devised prototype. After detailed wave tank testing with a fixed PTO, the vertical orientation of the converter was chosen for the second stage research. A modified 1:3 large-scale prototype was developed in the next phase. The model showed strong oscillating mass motion in the dry test rig. Comparison with numerical simulation showed that for lower wave frequency, the damping coefficient of the model matches well with the experimental result. But the prototype damping behavior is much more complex for a higher wave frequency. The tank testing confirmed that the prototype pitch amplitude in the wave needs to be enhanced for higher energy absorption

Development of a Fused Deposition 3D Printed Buoy and Method for Quantifying Wave Tank Reflections

Testing model scale prototypes is integral to the development of wave energy converter (WEC) technology. Model scale WECs are tested in wave tanks where they are subjected to repeatable wave fields. Their presence in water creates radiated waves that eventually reflect off tank walls disrupting the intended wave field. Fabrication of model scale WECs is another developing aspect of tank testing. Often model WECs are built of foam. Additive manufacturing is a promising alternative although the most common method, fused deposition modeling (FDM) 3D printing, does not typically produce waterproof parts. The goals of this work were 1) develop a method to characterize tank reflections on a model specific basis and 2) develop an efficient and economic method for creating FDM 3D printed model WECs. A spherical physical model buoy was developed to act as both an actuator and sensor to quantify reflections in a circular tank. In conjunction with a calibrated computational model, it detected and quantified changes in reflections caused by varying damping treatments applied to tank walls. A waterproofing technique for FDM 3D printed buoys was found. This work demonstrates that damping treatments can be tuned on a model specific basis prior to tank testing through the use of WEC model surrogate buoys, and that these surrogate buoys can be efficiently and economically produced using the widely available technology of FDM 3D printing

Experimental study of a TLP offshore floating wind turbine

Tank testing in a wind and wave environment is a key part of the design process for the development of an offshore floating wind turbine. The current paper describes an extensive experiment campaign carried out at the Kelvin Hydrodynamics Laboratory at the University of Strathclyde to determine the hydrodynamic performance of the Iberdrola TLPWIND offshore floating wind turbine with the NREL 5MW reference turbine over a range of environmental conditions. Tests were carried out for 70m water depth and the deployment area selected as off Aberdeen, North Sea. The campaign included free oscillation tests, tests in regular waves and irregular waves, and additionally examined failure and accidental load cases

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