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An analytical yawed wake model for wind turbine, which predicts the streamwise velocity distribution within the wake of a yawed wind turbine, is proposed in this study. The model applies mass and momentum conservation and uses a self-similar Gaussian shape to depict the transverse distribution of the streamwise velocity deficit and skew angle. Unlike existing yawed wake models, this model introduces additional equations to predict the transverse locations of maximum velocity deficit at different heights. What's more, a novel formula to calculate the expansion rate of wake width is proposed by the friction velocity, inflow velocity and the thrust coefficient. The measured data of wind tunnel experiment are used to investigate the validity of this model, as well as the other existing models firstly. Then, for validating the velocity distribution in the curled cross-section, the numerical simulations of wake under different yaw angles were carried out to provide the wake data. Comparisons between model predictions, experimental data and numerical results demonstrate that the model can satisfactorily predict the yawed wake deformation, as well as the velocity distribution at different heights. Due to its high accuracy and cost-effectiveness, this yawed wake model is advantageous for the application of yaw angle control. • The Gaussian-shape analytical model is proposed to describe the distribution of wake velocity. • This model considers the curled deformation of yawed wake with height. • A novel formula to compute the expansion rate of wake is introduced through the friction velocity. • The predictions of analytical model give outstanding performance in comparisons with CFD results and experimental data. [ABSTRACT FROM AUTHOR]

The present work is devoted to the hydrodynamic performance prediction of the hybrid contra-rotating shaft pod (HCRSP) propulsors. The HCRSP propulsor is divided into two parts, a single forward propeller and a podded propulsor. For the podded propulsor, an unsteady surface panel method is developed to analyze the open water performance; also the wake model is modified according to wake flow analysis. Then a podded propulsor in uniform flow is simulated by the unsteady surface panel method and the numerical results show a good agreement with experimental data. To improve the computational efficiency and simplify the analysis of HCRSP propulsor, we present a steady surface panel method that treats the propeller and pod unit as a single unit. Numerical results of the steady surface panel method also show good agreement with experimental data. Based on this study, an iterative steady surface panel method program for the HCRSP propulsor is presented and a model test is carried out in a cavitation tunnel to verify the numerical results. [ABSTRACT FROM AUTHOR]

A novel equation of wake model for the wake velocity distribution of a flat plate is proposed and verified in this study. The core of this equation is a special dimensionless method of the velocity deficit and the distance from the trailing edge of the plate along the flow direction, and a dimensionless standard deviation satisfying the law of linear expansion. In this study, it is assumed that the velocity deficit in the wake has a self-similar Gaussian distribution. Moreover, another conservation of momentum and Blasius equation is applied. The velocity distribution expression comprises the near-wake region and the far-wake region in accordance with the standard deviation of the Gaussian distribution. The model is capable of accurately predicting the velocity deficit of the near wake velocity distribution, and the dimensionless standard deviation serves as the only model parameter. The proposed model is compared with the existing research and present water-tunnel measurements, such that they are well consistent with each other. • The wake of flat plate aligned parallel to a uniform flow is studied. • A linear law is adopted to describe the standard deviation of the wake where x < 3 L. • A new analytical model has been suggested to predict the wake of plate aligned parallel to a uniform flow is presented. • The model is verified by the data of water tunnel experiment and existing research. [ABSTRACT FROM AUTHOR]

A reliable load-to-response prediction for flexible risers under drag forces can protect the multiple-riser system from collision and optimize its spatial arrangement. To investigate the drag coefficients for double risers in tandem, a series of experiments for two unequal-diameter flexible cylinders in different initial gap spacings was performed under uniform flows with Reynolds numbers up to 11,328. Based on the reconstructed mean drag displacement from measured strains, a distributed drag force amplified by vortex-induced vibrations can be identified reversely. Meanwhile, a modified wake model was developed to estimate the mean wake velocity for the downstream cylinder. With this mean wake velocity, the drag coefficients of the downstream cylinder were obtained. The features of drag coefficients and vortex/wake-induced vibrations were found to be closer to the corresponding features of an isolated cylinder. Furthermore, an empirical drag coefficient model for double unequal-diameter cylinders in tandem was proposed, which accounts for the drag amplification effect by vibrations, tandem spacing, upstream-to-downstream cylinder diameter ratio, mean wake velocity, etc. The results show that this empirical drag coefficient model can obtain the prediction results with relatively higher precision. • A series of tests were performed to study the drag coefficients of double unequal-diameter flexible cylinders in tandem. • A modified wake model was proposed to predict the wake velocity, considering the VIV of the upstream cylinder. • A new drag coefficient prediction model for double unequal-diameter flexible cylinders in tandem was proposed. [ABSTRACT FROM AUTHOR]

Two parallel strings in a deepwater dual-derrick drilling system are likely to interfere with each other. The mechanical interference properties of the two parallel strings have not been systematically studied. A mechanical interference model for parallel strings considering current, wave, platform motion, and the interference effect between two strings is established on the basis of Bernoulli beam theory and wake models. An interference analysis method is also proposed on the basis of the finite element method, Newton's method, and Newmark- β method. Lastly, a mechanical interference analysis program is developed in MATLAB and applied in the static and dynamic interference property analysis of two parallel strings. It turns out that the wake effect of the riser is significant and adsorbs the drill pipe around the riser. The adsorption effect may cause a collision between two parallel strings. The collision risk of parallel strings exists at the end of the hanging string and increases with the hanging water depth. It is also found that the collision between two strings in dynamic analysis decreases when the drill pipe is in upstream due to combined wave and current loads but increases when the drill pipe is in downstream due to the adsorption effect. • A mechanical interference model for parallel strings is established. • An interference analysis method for parallel strings is proposed. • A mechanical interference analysis program is developed in MATLAB. • The interference properties of two parallel strings are disclosed. [ABSTRACT FROM AUTHOR]

Oscillating wave surge converters (OWSCs) have been extensively used to exploit wave energy. To maximize the energy output from an OWSC array, layout optimizations must be conducted; therefore, an analytical wake model of OWSC is needed for fast optimization iterations. However, no wake model of OWSC and no wake-model-based array optimization approach have been developed. To this end, this study proposed a novel analytical wake model of OWSC. Based on the proposed wake model and differential evolution algorithm, layout optimizations of OWSCs in wave energy farms were performed. To establish a database for deriving the analytical wake model, OWSCs were numerically simulated using the smoothed particle hydrodynamics (SPH) method, where the incoming wave height, damping of the power take-off system, and flap width were varied. The attained analytical wake model could predict the wave height changes in wake regions of OWSCs with an accuracy of 90.0% compared with the numerical SPH results. The optimized OWSC layouts demonstrated that staggered layouts with narrow and wide OWSCs placed in the front and back of wave energy farms, respectively, were economical and appropriate. Furthermore, a simplified guideline was proposed to determine OWSC layouts. Finally, all the codes implemented in this study were open-sourced. • Novel analytical wake model of OWSC wave energy converter is proposed. • Wave energy farm with OWSCs is optimized based on the proposed analytical wake model. • Simple guideline for determining layouts of OWSC arrays is proposed. • Staggered layouts with narrow OWSCs placed in the front of the farm are recommended. • Self-compiled DE code for OWSC wave energy converter array optimizations is opened. [ABSTRACT FROM AUTHOR]

CFD simulation with DES-SA turbulence model are conducted to investigate the wake velocity characteristics. The turbine wake velocity distribution of axial, tangential and radial component is analysed by comparing numerical results with previous the experimental and theoretical results. The axial velocity component is continuously recovered along the axial direction. Based on the position of minimum axial velocity, turbine wake can be divided into two zones: zone of flow establishment and zone of established flow. In the zone of flow establishment, two-dipped velocity valleys of the axial velocity distribution appear along the radial direction. These two valleys are combined to one valley at the rotation axis in the zone of established flow. The tangential velocity component is the second largest and the radial velocity component accounts for only a small proportion. Both of tangential and radial velocity decreases along the axial direction. Two velocity peaks of both tangential and radial velocity appear along the radial direction. Several empirical equations of turbine wake are proposed to describe the velocity distribution. • CFD numerical simulation method for tidal current turbine with DES-SA model. • Zone of flow establishment and zone of established flow are divided by the position of minimum axial velocity. • The axial and radial distribution of axial, tangential and radial velocity component are studied based on CFD results. • Empirical equations are proposed to describe the velocity distribution of turbine wake. [ABSTRACT FROM AUTHOR]