scholarly journals A Numerical Study on Hydrodynamic Energy Conversions of OWC-WEC with the Linear Decomposition Method under Irregular Waves

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1522
Author(s):  
Jeong-Seok Kim ◽  
Kyong-Hwan Kim ◽  
Jiyong Park ◽  
Sewan Park ◽  
Seung Ho Shin
Keyword(s):  
Energy Conversion ◽  
Decomposition Method ◽  
Numerical Study ◽  
Response Spectrum ◽  
Direct Interaction ◽  
Irregular Waves ◽  
Linear Potential ◽  
Irregular Wave ◽  
The Time Domain ◽  
Hydrodynamic Energy

A numerical study was performed to investigate the applicability of the linear decomposition method for the hydrodynamic energy conversion of an oscillating-water-column type wave energy converter (OWC-WEC). Hydrodynamic problems of the OWC chamber were decomposed into the excitation and radiation problems with the time-domain numerical method based on the linear potential theory. A finite element method was applied to solve the potential flow in the entire fluid domain including OWC chamber structure. The validity of the linear decomposition method was examined by comparing with the direct interaction method for the turbine–chamber interaction based on the linear pressure drop characteristics. In order to estimate the hydrodynamic energy conversion performance under the irregular waves, the response spectrum method was applied with the transfer function based on the linear decomposition method. Under the various irregular wave conditions, the pneumatic power of OWC-WEC calculated by the response spectrum based on the linear decomposition method agreed well with the direct irregular wave simulation results.

Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

2016 ◽  
Author(s):  
Shaowu Ou ◽  
Shixiao Fu ◽  
Wei Wei ◽  
Tao Peng ◽  
Xuefeng Wang
Keyword(s):  
Numerical Study ◽  
Low Frequency ◽  
Optimal Operation ◽  
Hydrodynamic Interactions ◽  
Irregular Waves ◽  
Mooring System ◽  
Time Varying ◽  
Body System ◽  
The Time Domain ◽  
Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

scholarly journals Free Surface Reconstruction for Phase Accurate Irregular Wave Generation

2018 ◽  
Vol 6 (3) ◽  
pp. 105 ◽  
Author(s):  
Ankit Aggarwal ◽  
Csaba Pákozdi ◽  
Hans Bihs ◽  
Dag Myrhaug ◽  
Mayilvahanan Alagan Chella
Keyword(s):  
Free Surface ◽  
Surface Reconstruction ◽  
Deep Water ◽  
Time Domain ◽  
Present Approach ◽  
Surface Elevation ◽  
Irregular Waves ◽  
Free Surface Elevation ◽  
Irregular Wave ◽  
The Time Domain

The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a computational fluid dynamics (CFD) based model to validate and investigate a non-iterative free surface reconstruction technique for irregular waves. In the current approach, the free surface is reconstructed by spectrally composing the irregular wave train as a summation of the harmonic components coupled with the Dirichlet inlet boundary condition. The verification is performed by comparing the numerically reconstructed free surface elevation with theoretical input waves. The applicability of the present approach to generate irregular waves by reconstructing the free surface is investigated for different coastal and marine engineering problems. A numerical analysis is performed to validate the free surface reconstruction approach to generate breaking irregular waves over a submerged bar. The wave amplitudes, wave frequencies and wave phases are modelled with good accuracy in the time-domain during the higher-order energy transfers and complex processes like wave shoaling, wave breaking and wave decomposition. The present approach to generate irregular waves is also employed to model steep irregular waves in deep water. The free surface reconstruction method is able to simulate the irregular free surface profiles in deep water with low root mean square errors and high correlation coefficients. Furthermore, the irregular wave forces on a monopile are investigated in the time-domain. The amplitudes and phases of the force signal under irregular waves generated by using the current technique are modelled accurately in the time-domain. The proposed approach to numerically reproduce the free surface elevation in the time-domain provides promising and accurate results for all the benchmark cases.

A Parametric Study on Relative Wave Height of Ships in Short Crested Irregular Sea With Forward Speed

2005 ◽  
Author(s):  
Yoshiyuki Inoue ◽  
N. M. Golam Zakaria ◽  
Ryoji Nakai
Keyword(s):  
Time Domain ◽  
Parametric Study ◽  
Fluid Motion ◽  
Irregular Waves ◽  
Linear Potential ◽  
Forward Speed ◽  
Sea Waves ◽  
Wave Heights ◽  
The Time Domain ◽  
General Cargo

This paper deals with the parametric study of relative wave heights of ships in short crested irregular seas. Here linear potential theory has been used to describe the fluid motion and 3-D sink-source technique with forward speed has been used to determine hydrodynamic forces for surface ship advancing in waves at constant speed. The time domain simulations of relative wave heights of typical container ship, bulk carrier, pure car carrier (PCC) and general cargo ships in short crested irregular waves have been carried out for three different sea states and for the parametric study of these vessels, different sizes of ships have been considered. Empirical roll damping has been taken into account in time domain analyses of motion responses of sea going ships in rough seas and for ensuring longer time simulation of the random sea waves, unequal frequency spacing has been used. Finally, the numerical results of the maximum and the significant values of irregular relative wave heights are discussed by comparing with some requirements by a classification society of shipping for the different sizes of ships which might provide some important information for the designer of ocean going vessel to assess possible deck load or bottom impact force on future regulation of designing ship.

scholarly journals Hydrodynamic Performance of a Pitching Float Wave Energy Converter

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1801
Author(s):  
Yong Ma ◽  
Shan Ai ◽  
Lele Yang ◽  
Aiming Zhang ◽  
Sen Liu ◽  
...  
Keyword(s):  
Energy Conversion ◽  
Frequency Domain ◽  
Wave Energy ◽  
Center Of Mass ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Wave Energy Conversion ◽  
Wave Direction ◽  
Improved Stability ◽  
The Time Domain

This study analyzes the hydrodynamic performance and application of a pitching float-type wave energy conversion device under complex sea conditions in the South China Sea. Potential flow theory and ANSYS-AQWA software are used to establish a method for analyzing hydrodynamic performance in both time and frequency domains, as well as the various factors that influence hydrodynamic performance. The frequency domain characteristics of the conversion device are explored, as well as the time-domain characteristics when exposed to regular and irregular waves. The results show that the frequency domain of hydrodynamic performance conforms to the requirements of an offshore mobile platform. A mooring point that is closer to the center of mass leads to improved stability of the conversion device. The angle arrangement of the anchor-chain mooring method fully conforms to safety requirements. When the wave direction is 45°, the conversion device is highly stressed and its movement is the most strenuous; however, the device can operate safely and stably under all working conditions. These results provide a significant reference for expanding the wave-energy capture range and the hydrodynamic performance of floating wave-energy conversion devices.

scholarly journals CFD Research on the Hydrodynamic Performance of Submarine Sailing near the Free Surface with Long-Crested Waves

2022 ◽  
Vol 10 (1) ◽  
pp. 90
Author(s):  
Kai Dong ◽  
Xianzhou Wang ◽  
Donglei Zhang ◽  
Liwei Liu ◽  
Dakui Feng
Keyword(s):  
Free Surface ◽  
High Frequency ◽  
Control Strategies ◽  
Response Spectrum ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
High Frequency Region ◽  
Irregular Wave ◽  
Grid Approach ◽  
Calm Water

The simulations of submarine sailing near the free surface with long-crested waves have been conducted in this study using an in-house viscous URANS solver with an overset grid approach. First, the verification and validation procedures were performed to evaluate the reliability, with the results showing that the generation of irregular waves is adequately accurate and the results of total resistance are in good agreement with EFD. Next, three different submerged depths ranging from 1.1D to 3.3D were selected and the corresponding conditions of submarine sailing near calm water were simulated, the results of which were then compared with each other to investigate the influence of irregular waves and submerged depths. The simulations of the model near calm water at different submerged depths demonstrated that the free surface will cause increasing resistance, lift, and bow-up moments of the model, and this influence decreases dramatically with greater submerged depths. The results of the irregular wave simulations showed that irregular waves cause considerable fluctuations of hydrodynamic force and moments, and that this influence remains even at a deeper submerged depth, which can complicate the control strategies of the submarine. The response spectrum of hydrodynamic forces and moments showed slight amplitudes in the high-frequency region, and the model showed less sensitivity to high-frequency excitations.

scholarly journals Study on the Resonant Behaviors of a Bottom-Hinged Oscillating Wave Surge Converter

2021 ◽  
Vol 10 (1) ◽  
pp. 2
Author(s):  
Yao Liu ◽  
Yong-Hwan Cho ◽  
Norimi Mizutani ◽  
Tomoaki Nakamura
Keyword(s):  
Maximum Velocity ◽  
Irregular Waves ◽  
Width Ratio ◽  
Wave Surface ◽  
Regular Waves ◽  
Peak Period ◽  
Natural Period ◽  
Irregular Wave ◽  
Cfd Method ◽  
The Time Domain

This paper studied the resonant behaviors of a bottom-hinged oscillating wave surge converter (OWSC) as well as the relationship of resonance with the response and capture width ratio (CWR). The time-domain dynamic equation of an OWSC in shallow water based on the boundary element method (BEM) was solved by a Python code, considering the corrected wave surface and the nonlinearities of restoring moment, drag, and friction. The unknown factors, such as wave surface corrected factor and drag coefficient, were effectively calibrated with computational fluid dynamics (CFD) method. An intermediate initial angle in free decay is appropriate for use to determine the natural period. Under regular waves, the resonance occurs near the natural period for the uniform wave amplitude, rather than the uniform wave torque amplitude, and can disappear due to the amplification of Power Take-Off (PTO) friction. Under unit-amplitude regular waves, the period of maximum CWR is relatively close to the period of maximum velocity, but far from the resonant period. Under irregular waves, no stable resonance is observed because the maximum equivalent pitch angle appears at different peak periods of wave spectra with the variation in PTO damping. When the period of a regular wave or the peak period of an irregular wave is close to the natural period, a phase hysteresis of velocity relative to wave torque always occurs.

Irregular Wave and Current Loads on a Fish Farm System

2018 ◽  
Author(s):  
Arnt G. Fredriksen ◽  
Basile Bonnemaire ◽  
Øyvind Nilsen ◽  
Leiv Aspelund ◽  
Andreas Ommundsen
Keyword(s):  
Particle Velocity ◽  
Fish Farm ◽  
Fluid Particle ◽  
Irregular Waves ◽  
Engineering Practice ◽  
Irregular Wave ◽  
Environmental Force ◽  
The Mean ◽  
Particle Velocities ◽  
Farm System

Accurate calculation of the design mooring loads on an aquaculture fish farm mooring system is often a difficult task. The fish farm system has a large horizontal extension with variable environmental conditions across the entire structure. In addition, the drag loads on the fish nets are thought to be the governing environmental force. This means that the mean position of the fish farm is a function of the mean of the fluid particle velocity squared, where the fluid particle velocity must be taken as the sum of current and wave induced fluid particle velocities. Additional offsets will be slowly varying, where the response time will depend on the total mooring stiffness. The magnitudes depend on the height and length on wave groups in the irregular sea state. The paper presents simulations of the response of such a system to a set of combined irregular waves and current conditions. The response evolution in time is discussed as well as parameters affecting the maximum responses in the systems (displacements and loads). Finally, the resulting loads on the fish farm in irregular waves are compared to loads obtained in equivalent regular waves, as this is an often used engineering practice when analyzing the response and mooring loads of a fish farm.

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