Journal of Ocean Engineering and Marine Energy

Smooth, rigid, circular cylinders on elastic support in flow perpendicular to their axis undergo vortex-induced vibrations (VIV) over a broad range of velocities. VIV converts hydrokinetic energy to mechanical in the oscillating cylinder. Tip-flow introduces three dimensional effects reducing the effective length of the cylinder which provides the transverse lift force to induce oscillations and consequently the energy in the oscillator. In this study, we investigate experimentally the effect of the cylinder aspect ratio on hydrokinetic energy harnessing. Experiments are conducted in the Reynolds number range 15,000 < Re < 80,000 falling in two different flow regimes: TrSL2 (Transition Shear Layer 2: 1000 < Re < 40,000) and TrSL3 (40,000 < Re < 300,000). Converted power and maximum system efficiencies are calculated from experiments conducted in the recirculation channel of the Flow Induced Motions Laboratory, Istanbul Technical University (ITU FIMLab). It was found that the end-zones of the cylinder, which do not induce lift due to tip flow, are more dominant in lower aspect ratio cylinders. More power can be captured from TrSL3 flows due to higher shear-flow momentum. Higher efficiency in power conversion is achieved in TrSL2.

This paper explores the camber as a variable to parameterize the airfoil of a 3-blade H-shaped vertical axis offshore wind turbine (VAOWT). The influence of airfoil camber (f) on the aerodynamics of H-type VAOWT is investigated. Selecting $$v=4,8,12$$  m/s as the design conditions, and using NACA0015 airfoil ( $$f=0\%)$$ as the prototype to perform the parametric design of the airfoil. A total of 6 blades with the camber of $$f=[0\%,5\%]$$ are designed. A 2D-computational fluid dynamics (CFD) simulation model is established with ANSYS software. Taking the power coefficient ( $$C_\mathrm{p}$$ ), the high-performance tip speed ratio range ( $$\varDelta \lambda $$ ), and the power(P) of the offshore wind turbine as research objects, the aerodynamic law of VAOWT and the changes in torque, pressure, velocity of the airfoil surface under different azimuth angles are studied. The research results find that the camber has a great influence on the aerodynamic performance of vertical axis wind turbines. Airfoil with smaller camber ( $$f\in [0\%,2\%]$$ ) has a better aerodynamic performance.

In the present paper, a commercial CFD code based on RANS equations is used to assess the aerodynamic behavior of the rotor of NREL’s 5MW turbine. The main objective is to evaluate the changes that happen in the wind flow when the scale of the problem is reduced based on Froude-scale law, a procedure that is used for tests of floating wind turbines in wave basins, such as the ones performed as part of the OC4 program. Therefore, the CFD simulations are performed both for real and model scales, considering a range of tip-speed ratios, and the scale effects involved in the aerodynamics of the blades are presented and discussed. The results are compared to experimental and numerical data of the same rotor available in the literature, especially in terms of thrust and power coefficients. As main conclusions, it is found that the present CFD predictions for the rotor in full scale are generally in accordance with the previous numerical data. More importantly, for the model-scale rotor, it is shown that a very good agreement with the experimental data could be obtained, even for the negative power coefficients that happen for certain tip-speed ratios, something that the previous numerical works have reported to be more difficult to reproduce.

This study proposes a multi-connection cross-flow vertical axis wind turbine, an innovative device to supply electric power in aquaculture farms. The device is a new type floating offshore wind turbine consisting of two independent wind turbine floats and a mooring float set in a straight line. A single-point mooring system with tension is utilized at the mooring float, which allows the wind turbine floats to turn around the moored point. However, there are various challenges to this new concept for its practical application mainly related to turning motion about the moored point. Therefore, the focus of this study is to understand the turning mechanism of the proposed FOWT through dedicated water tank experiments and numerical simulations. As a concept demonstration, two cross-flow wind turbines were mounted on the wind turbine floats and turning motion characteristics about the moored point were observed. A prototype model was built with a model scale of 1/36 using Froude scaling assuming rough weather conditions at the aquaculture farm. Wind speed of 35 m/s, wave height of 0.75 m, and wave period of 5–7.5 s are the assumed environmental conditions in the actual model. Free yawing tests were conducted in only-wind, only-wave and combined wind–wave conditions. Further, a numerical simulation considering the wind loads acting on the turbines is developed. It is found that the wind turbine floats turn to a position where the wind loads acting on the left and right sides of the moored point are balanced. The numerical simulation reproduced the turning motion within an error of 10.

Traditionally, submarine hydrodynamic design has focussed mainly on requirements regarding operational range, powering performance and manoeuvring ability for deeply submerged conditions. To improve the effectiveness of the boat, attention is also paid to operating near or at the surface and fortunately, computational tools and experimental methods are available to analyse the performance of submarines at these conditions. To advance submarine hydrodynamics knowledge and tools, DMO and MARIN have conducted a wide variety of bi-lateral or collaborative studies using potential and viscous flow methods and experiments on several submarine hull forms. In this article, several examples are presented of the development and use of hydrodynamic tools available during the design and assessment process of future submarines. These examples range from experimental and numerical studies into at-surface and periscope-depth resistance and powering, periscope-depth manoeuvring, high-fidelity flow around the boat during straight flight and manoeuvring motions, wakes of surface-piercing masts, to depth keeping under waves. It is demonstrated how state-of-the-art studies help in advancing the knowledge on submarine hydrodynamics and improving the overall design of modern submarines.

The publication of this article unfortunately contained a mistake.

We introduce a new concept that utilizes floating foundations to create an urban community base in man-made inlets and basins—an idea that enables the attainment of a prosperous and sustainable urban and rural environment in the long term. This paper proposes the establishment of secure bases using a floating structure to safeguard from natural disasters, especially from flooding caused by heavy rain, storm surges caused by typhoons, tsunamis, and earthquakes. In addition, we introduce a plan for the reconstruction of an area in northeast Japan destroyed by the Great East Japan Earthquake.

This study is dedicated to the assessment of the current influence on the wind wave height in the Black Sea based on numerical modeling. The research was carried out based on the SWAN wave model driven by NCEP/CFSv2 wind reanalysis. Current data from the Remote Sensing Department's archive of the Marine Hydrophysical Institute of RAS were used. It is shown that the average wave height mainly decreases when sea currents are considered. These changes are insignificant relative to the average values of wave heights. The greatest negative changes are typical for the western, central, and northeast parts of the Black Sea. Here, currents reduce the average annual wave heights down to – 7.5 cm. A slight increase in the average wave height is typical for the southern, southeast parts, and the northwest shelf of the sea. Currents have the greatest influence on the wave parameters during winter and the least during late spring and summer. The validation shows that currents increase the correlation coefficient when wave heights are > 2 m, but this increase is insignificant, over 0.05. In general, the quality of wave simulation in the Black Sea does not improve by supplementing currents in the model used in this study.