Point absorber wave energy converters in regular and irregular waves with time domain analysis

A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a point-absorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function.The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results

Multibody interactions of floating bodies with time domain predictions

The applications of the three-dimensional transient panel code ITU-WAVE based on potential theory is further extended to take into account the multibody interactions in an array system using linear and square arrays. The transient wave-body interactions of first-order radiation and diffraction hydrodynamic parameters are solved as the impulsive velocity potential to predict Impulse Response Functions (IRFs) for each mode of motion. It is shown that hydrodynamic interactions are stronger when the bodies in an array system are close proximity and these hydrodynamic interactions are reduced considerably and shifted to larger times when the separation distances are increased. The numerical predictions of radiation (added-mass and damping coefficients) and exciting (diffraction and Froude-Krylov) forces are presented on each floating bodies in an array system and on single structure considering array as single floating body. Furthermore, the numerical experiment shows the hydrodynamic interactions are more pronounced in the resonant frequency region which are of important for fluid forces over bodies, responses and designs of multibody floating systems. The present numerical results of ITU-WAVE are validated against analytical, other numerical and experimental results for single body, linear arrays (two, five and nine floating bodies) and square arrays of four truncated vertical cylinders

Control of Wave Energy Converters for Maximum Power Absorption with Time Domain Analysis

A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a point-absorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function. The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results

Time domain prediction of first- and second-order wave forces on rigid and elastic floating bodies

The application and development of a transient three-dimensional numerical code ITU-WAVE which is based on panel method, potential theory and Neumann-Kelvin linearization is presented for the prediction of hydrodynamics characteristics of mono-hull and multi-hull floating bodies. The time histories of unsteady motions in ambient incident waves are directly presented with regards to impulse response functions (IRFs) in time. The first order steady forces of wave-resistance, sinkage force and trim moment are solved as the steady state limit of surge radiation IRFs. The numerical prediction of the second order mean force which can be computed from quadratic product of first-order quantities is presented using near-field method based on the direct pressure integration over floating body in time domain. The hydrodynamic and structural parts are fully coupled through modal analysis for the solution of hydroelastic problem in which Euler-Bernoulli beam is used for the structural analysis. A stiff structure is then studied assuming that contributions of rigid body modes are much bigger than elastic modes. A discrete control of latching is used to increase the bandwidth of the efficiency of Wave Energy Converters (WEC). ITU-WAVE numerical results for different floating

Maximise absorbed wave power with wave energy converter arrays in time domain

A three-dimensional transient numerical code ITU-WAVE based on potential theory and NeumannKelvin approximation is extended to take into account wave interaction in an array system using two and four truncated vertical cylinder arrays. ITU-WAVE panel code is validated against analytical results before applied to power absorption from ocean waves for different array configurations. The effects of the separation distances between array system and heading angles on energy absorption in both sway and heave modes are studied by the support of numerical simulations which show more power absorbed in sway mode than in heave mode and sway mode has wider bandwidth than heave mode for energy absorption. It is also shown wave interactions are stronger when the array systems are close and these wave interactions are reduced significantly and shifted to larger times when the separation distance is increased. The wave interaction is much stronger at the same separation distance and heading angle in heave mode than in sway mode. Numerical experience shows that more power is absorbed in sway mode than heave mode in both two and four array systems at any separation distances and heading angles when the bodies in array system have the same displacement in both sway and heave mode

Computationally efficient stratified flow wet angle correlation for high resolution simulations

n high resolution two-phase pipe flow simulations, such as slug capturing simulation for liquid-gas pipe flow, explicit calculation of stratified flow wet angle has been proposed to improve computational speed of simulations. Most phenomenological and approximate models for obtaining reliable predictions for stratified flow wet angle employ iterative methods or contain long explicit equations which reduce computational efficiency of these models in high-resolution simulations. Therefore, the aim of this study is to adapt a simple mathematical model for predicting stratified flow wet angle to achieve computationally efficient high-resolution liquid-gas pipe flow simulations

Numerical Investigation of Dynamic Pipe-Soil Interaction on Electrokinetic-Treated Soft Clay Soil

© 2019 American Society of Civil Engineers. Researchers have underscored the importance for a pipeline to safeguard against adverse effects resulting from its displacement in the vertical, axial, and lateral directions because of the low shear strength of the soil. The seabed may sometimes consist of soft or very soft clay soil with high water content and low shear strength. Dissipation of the water content from the soil void increases its effective stress, with a resultant increase in the soil shear strength. The electrokinetic (EK) concept has been applied to increase soil bearing capacity with barely any study conducted on its possible application on pipe-soil interaction. The need to explore more options merits further research. The EK process for the pipe-soil interaction consists of two main stages: the electroosmotic consolidation process and dynamic analyses of the pipe-soil interaction. The present study numerically investigated the impact of EK-treated soil on pipe-soil interaction over the non-EK process. The results of dynamic pipe-soil interaction on EK-treated soil when compared with non-EK-treated soil indicate a significant increase in the force required to displace a pipeline

A Control strategy to improve the efficiency of point absorber wave energy converters in complex sea environments

A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a pointabsorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function. The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results

Simplified Transient Two-Phase Model for Pipe Flow

Two-phase flow analyses are critical to successful design and operations of two-phase and multiphase pipe flow applications found in major industrial fields, such as petroleum, nuclear, chemical, geothermal and space industries. Due to difficulties in obtaining analytical transient solutions, approximate solutions have been applied to two-phase pipe flow. However, these approximate solutions neglect convective terms in two-phase Navier-Stokes equations. The aim of this current study was to develop transient tools to predict transient two-phase pipe flow. The objectives of this study were to develop a simplified transient model and to validate the proposed model with published experimental data. A simplified transient two-phase pipe flow model was obtained in this study by simplifying the two-phase Navier-Stokes equations. The simplified equations include: (i) a transient continuity equation of combined two-phase flow that includes two new dimensionless terms; (ii) transient two-phase momentum equations that account for convective terms only; and, (iii) a steady state pressure gradient

Review of offshore pipeline span creation mechanism

The various span creation mechanisms have been studied in great detail and this work has presented the state of the art in the area of offshore pipeline span creation mechanism analysis. The different span creation mechanisms of a pipeline during operation include residual uplifts, scouring, sandwaves, underwater landslides, strudel scour, etc. With this information a software can be formulated which can incorporate the different characteristics of elements of span creation