scholarly journals Semi-submersible Offshore Coupled Motion in Irregular Waves

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Baoji Zhang ◽  
Ying Wang
Keyword(s):  
Return Period ◽  
Simple Algorithm ◽  
Wave Force ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Offshore Platforms ◽  
Wave Direction ◽  
Motion Response ◽  
Irregular Wave ◽  
Control Equation

In order to predict the hydrodynamic performance of semi-submersible offshore platform accurately, based on CFD theory, continuous equation and N-S equation as the control equation, RNG type k-ε model as turbulence model, using the finite difference method to discretize the control equation，using the Semi-Implicit Method for Pressure Linked Equation (SIMPLE) algorithm to solve the control equation，using the VOF method to capture the free surface. The numerical wave tank of irregular wave is established, and the wave force and motion response of the semi-submersible platform under irregular wave are studied. Based on the Jonswap spectrum density function, for a certain area of two irregular waves (South China sea, a-ten-year return period, a-hundred-year return period) sea condition, five wave direction Angle (0 °, 30 °, 45 °, 60 °, 90 °), a total of 10 kinds of conditions of the motion response of semi-submersible platform are simulated, through analysis and comparison of simulation results, the influence law of wave angle, wave period and wave height on platform motion is obtained. Compared with the experimental values, the results of heave and pitch are close to the experimental data under the sea condition of 2, 0 degree wave angles. The research results in this paper can provide reference for the design and motion response prediction of practical semi-submersible offshore platforms.

scholarly journals Study on determination method of hydrodynamic coefficient of Marine pile foundation

2020 ◽  
Vol 143 ◽  
pp. 01021
Author(s):  
Jiang Zongnan
Keyword(s):  
Fourier Analysis ◽  
Time History ◽  
Least Square Method ◽  
Wave Force ◽  
Least Square ◽  
Irregular Waves ◽  
Hydrodynamic Coefficient ◽  
Irregular Wave ◽  
Advantages And Disadvantages ◽  
The Moment

The irregular waves are simulated by using standard spectrum. Instantaneous value method, Fourier analysis method, least square method and "harbour hydrological code" are used to determine the moment force of coefficient CM and drag coefficient CD. Then CM and CD that linearized by Borgman L.E. equation are substituted into Morison equation. The time history curve of the wave force on the pile is calculated and compared with the measured wave force data under the action of irregular wave to analyze the advantages and disadvantages of several methods to determine CM and CD. The results show that the comparison between CM and CD determined by Fourier analysis and least square method is practical.

Hydrodynamic Performance of a Novel Free Surface Pitching Breakwater

2014 ◽  
Author(s):  
Vengatesan Venugopal ◽  
Stefan Zlatev
Keyword(s):  
Body Shape ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Scale Model ◽  
Reflected Waves ◽  
Irregular Wave ◽  
Wave Flume ◽  
Floating Breakwater ◽  
Wave Heights ◽  
Transmission Ct

A new concept floating breakwater was developed and tested to evaluate its hydrodynamic performance in this paper. This innovative floating breakwater has a rocking body shape which could also be used as a wave power device. A scale model was tested in a wave flume under regular and irregular wave conditions for various combinations of wave frequencies and wave heights. The breakwater has been tested for three immersion depths of 0.05 m, 0.09 m and 0.13 m from still water level. The measured transmitted and reflected waves were used to evaluate the coefficients of transmission (CT), reflection (CR) and dissipation (CL). The results illustrated that the breakwater model performed at its best when submerged at 0.13m, as this immersion depth produced lower coefficients of transmission (CT), lower reflection coefficients (CR) and higher energy dissipation (CL) coefficients. The comparison between regular and irregular waves produced similar ranges of transmission, reflection and energy coefficients.

scholarly journals STUDY OF STATISTICAL CHARACTERISTICS OF IRREGULAR WAVE PRESSURE ON A COMPOSITE BREAKWATER

1986 ◽  
Vol 1 (20) ◽  
pp. 131
Author(s):  
Chien-Kee Chang ◽  
Ching-Her Hwang
Keyword(s):  
Pressure Distribution ◽  
Wave Height ◽  
Wave Force ◽  
Shock Pressure ◽  
Irregular Waves ◽  
Statistical Characteristics ◽  
Wave Forces ◽  
Incoming Wave ◽  
Wave Pressure ◽  
Irregular Wave

Wave pressure is the most important external force for the design of breakwater. During recent years, there has been considerable development in the technology of vertical face breakwater; however, there is no reliable method to compute wave forces induced by irregular waves. The purpose of this study is to obtain statistical characteristics of irregular wave pressure distribution from the data of model tests. The results of this study shown that vertical face breakwater under the action of irregular waves, some waves are reflected, so that the next wave breaks a critical distance resulting in a rapidly rising shock pressure on the breakwater. On the average, the wave pressure increase with incoming wave height, but the maximum wave force does not necessarily occur for the largest wave height. It can be occurred for serval larger wave group in an appropiate phase composition. The irregular wave pressure distribution on the breakwater is quite uniform; the ratio of tested and calculated wave pressures decreases with the reduction of relative crest height of breakwater. Coda formula can predict the total horizontal force of the upper part of breakwater quite well except exetreme shock pressure occurred by non-breaking waves. Wave forces calculated by Miche-Rundgren and Nagai wave force formula are about 10% cummulated exceeding percentage of wave force obtained from model test.

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 A Theoretical Study on the Hydrodynamics of a Zero-Pressurized Air-Cushion-Assisted Barge Platform

2020 ◽  
Vol 8 (9) ◽  
pp. 664
Author(s):  
Fengmei Jing ◽  
Li Xu ◽  
Zhiqun Guo ◽  
Hengxu Liu
Keyword(s):  
Coupling Effect ◽  
Low Cost ◽  
Engineering Application ◽  
Theoretical Method ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Floating Body ◽  
Motion Response ◽  
Air Cushion ◽  
Heave Motion

Thebarge platform has the advantages of low cost, simple structure, and reliable hydrodynamic performance. In order to further improve the hydrodynamics of the barge platform and to reduce its motion response in waves, a zero-pressurized air cushion is incorporated into the platform in this paper. The pressure of the zero-pressurized air cushion is equal to atmospheric pressure and thus does not provide buoyancy to the platform. As compared to the conventional pressurized air cushion, the zero-pressurized one has advantages of less air leakage risk. However, due to the coupling effect on the interface between water and air cushion, the influence of the gas inside the air cushion on the performance of the floating body has become a difficult problem. Based on the boundary element method, the motion response of the zero-pressurized air-cushion-assisted barge platform under regular and irregular waves is calculated and analyzed in the paper. Compared with the barge platform without air cushion, numerical results from the theoretical method show that in regular waves, the air cushion could significantly reduce the amplitude of heave and pitch (roll) response of the round barge platform in the vicinity of resonance. In irregular waves, the air cushion also observably reduces the pitch (roll) motion, though amplifies the heave motion due to the transfer of heave resonance frequency. Thetheoretical study demonstrates that the zero-pressurized air cushion can reduce the seakeeping motion of barge platforms in high sea states, but might also bring negative effects to heave motion in low sea states. One should carefully design the air cushion for barge platforms according to the operating sea states to achieve satisfactory hydrodynamic performance in engineering application.

Lifting Operation Simulation of a Dynamic-Position Crane Vessel

2013 ◽  
Author(s):  
Shangmao Ai ◽  
Liping Sun ◽  
Chuanyun Cheng
Keyword(s):  
Time Domain ◽  
Pid Control ◽  
Weak Coupling ◽  
Time Sequence ◽  
Irregular Waves ◽  
Dynamic Positioning ◽  
Wave Direction ◽  
Sea State ◽  
Control Equation ◽  
Made In

A time domain method, weakly coupling the block and crane vessel in time sequence, has been developed for lifting operation of the dynamic-position crane vessel. Restoring thrust is distributed by the dynamic positioning PID control system and directly acted on the crane vessel’s control equation as external force; the weak coupling simulation between the block and crane vessel is realized through the sling elastic deformation. Lifting operation simulation of a dynamic-position crane vessel in irregular waves shows that the posture of crane vessel relative to the wave direction in the lifting operation should be adjusted as soon as possible, and had better be made in ahead sea state to improve the security of the suspension stage.

Finite Element Analysis for Structural Performance of Offshore Platforms under Environmental Loads

2013 ◽  
Vol 569-570 ◽  
pp. 159-166 ◽  
Author(s):  
Shehata E. Abdel Raheem ◽  
Elsayed M.A. Abdel Aal
Keyword(s):  
Finite Element ◽  
Return Period ◽  
Wave Force ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Current Increase ◽  
Environmental Loads ◽  
Highly Nonlinear

Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. The structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.

scholarly journals A NEW DESIGN METHOD OF RUBBLE MOUND STRUCTURES

1986 ◽  
Vol 1 (20) ◽  
pp. 161 ◽  
Author(s):  
Cheong-Ro Ryu ◽  
Toru Sawaragi
Keyword(s):  
Design Method ◽  
Wave Train ◽  
Wave Force ◽  
Irregular Waves ◽  
Wave Condition ◽  
Irregular Wave ◽  
The Mean ◽  
Rubble Mound ◽  
Run Up ◽  
Wave Control

A new design method of rubble mound structures with stability and wave control consideration is proposed, by which the reduction of wave reflection and run-up and increase in rubble stability are assured under the given wave conditions. Wave control and stability increasing functions due to change of the slope shape of rubble mound structures are discussed on the basis of the experimental results for regular and irregular waves. The new design formula developed here considered the allowable percentage of damage and the wave grouping effects on rubble stability using a new assumption of the mean run-sum as an index of the irregular wave force. The run-sum is defined as the energy sum of a run satisfying a critical wave condition and the mean run-sum is the mean of run-sum for a irregular wave train.

scholarly journals SIMULATION OF EXTREME WAVE INTERACTION WITH MONOPILE MOUNTS FOR OFFSHORE WIND TURBINES

2012 ◽  
Vol 1 (33) ◽  
pp. 22 ◽  
Author(s):  
Feng Gao ◽  
Clive Mingham ◽  
Derek Causon
Keyword(s):  
Wind Farm ◽  
Wave Interaction ◽  
Wave Force ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Extreme Wave ◽  
Irregular Wave ◽  
Run Up

Extreme wave run-up and impacts on monopile foundations may cause unexpected damage to offshore wind farm facilities and platforms. To assess the forces due to wave run-up, the distribution of run-up around the pile and the maximum wave run-up height need to be known. This paper describes a numerical model AMAZON-3D study of wave run-up and wave forces on offshore wind turbine monopile foundations, including both regular and irregular waves. Numerical results of wave force for regular waves are in good agreement with experimental measurement and theoretical results, while the maximum run-up height are little higher than predicted by linear theory and some empirical formula. Some results for irregular wave simulation are also presented.

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