scholarly journals Mooring Drag Effects in Interaction Problems of Waves and Moored Underwater Floating Structures

2020 ◽  
Vol 8 (3) ◽  
pp. 146
Author(s):  
Cheng-Tsung Chen ◽  
Jaw-Fang Lee ◽  
Chun-Han Lo
Keyword(s):  
Water Waves ◽  
Degrees Of Freedom ◽  
Wave Force ◽  
Wave Forces ◽  
Linear Potential ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Fields ◽  
Present Solution ◽  
Scattering And Radiation

In contrast to either considering structures with full degrees of freedom but with wave force on mooring lines neglected or with wave scattering and radiation neglected, in this paper, a new analytic solution is presented for wave interaction with moored structures of full degrees of freedom and with wave forces acting on mooring lines considered. The linear potential wave theory is applied to solve the wave problem. The wave fields are expressed as superposition of scattering and radiation waves. Wave forces acting on the mooring lines are calculated using the Morison equation with relative motions. A coupling formulation among water waves, underwater floating structure, and mooring lines are presented. The principle of energy conservation, as well as numerical results, are used to verify the present solution. With complete considerations of interactions among waves and moored structures, the characteristics of motions of the structure, the wave fields, and the wave forces acting on the mooring lines are investigated.

Hydrodynamic coefficients of a floater near a partially reflecting seawall in the presence of an array of caisson blocks

2021 ◽  
pp. 1-23
Author(s):  
K G Vijay ◽  
Santanu Koley ◽  
Kshma Trivedi ◽  
Chandra Shekhar Nishad
Keyword(s):  
Wave Scattering ◽  
Structural Parameters ◽  
Wave Force ◽  
Vertical Force ◽  
Hydrodynamic Coefficients ◽  
Floating Structure ◽  
Surface Gravity Wave ◽  
Damping Coefficients ◽  
Half Wavelength ◽  
Scattering And Radiation

Abstract In the present study, surface gravity wave scattering and radiation by a freely floating rectangular buoy placed near a partially reflecting seawall and in the presence of an array of caisson blocks are analyzed. Various hydrodynamic parameters related to the wave scattering and radiation, such as the added mass and radiation damping coefficients, correspond to sway, heave and roll motions of the floating buoy, horizontal force, vertical force and moment acting on the floating structure, and horizontal wave force acting on the partially reflecting seawall are studied for a variety of wave and structural parameters. The study reveals that the resonating pattern in various hydrodynamic coefficients occurs for moderate values of the wavenumber. Further, when the distance between the floater and the sidewall is an integral time of half wavelength, the resonating behavior in the sway, heave and roll added masses, and associated damping coefficients appears, and the aforementioned hydrodynamic coefficients change rapidly around this zone. These resonance phenomena can be diminished significantly with appropriate positioning of the floater with respect to the sidewall and in the presence of partially reflecting seawall.

A Study on Predictions of Fully Nonlinear Motion Aircushion Type Floating Structures Using 2D MPS Method

2008 ◽  
Author(s):  
Mitsuhiro Masuda ◽  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hisaaki Maeda
Keyword(s):  
Water Waves ◽  
Theoretical Calculations ◽  
Numerical Technique ◽  
Ocean Waves ◽  
Nonlinear Phenomena ◽  
Linear Potential ◽  
Floating Structure ◽  
Fully Nonlinear ◽  
Floating Structures ◽  
Mps Method

Very large floating structures (VLFSs) have been proposed for new ocean space utilization and many researches have been carried out. VLFSs are elastically deformed due to ocean waves because the rigidity of the structure decreases relatively. The authors examine the aircushion type floating structure in order to reduce hydroelastic motion. An aircushion type floating structure to which air-chambers are installed can reduce the wave drifting force and hydroelastic motion at the same time. Most theoretical calculations of motion of aircushion type floating structures in water waves have been done based on a linear potential theory so far. As a result, the utility of the aircushion has been proved. However fully nonlinear phenomena such as deck wetness, slamming and air-leakage cannot be investigated by using existing calculations based on the linear theory. In this study, a computer program code of the two-dimensional MPS method that can consider fully nonlinear influence is developed and then the air layer inside an aircushion is expressed with particles of the MPS. Moreover, the numerical technique for introducing directly the mooring force into the motion equation of the particle is developed. Motion response of aircushion type floating structures in a billow is computed. As a result, the usefulness of this numerical calculation method is confirmed.

Motions of Articulated Towers and Moored Floating Structures

1989 ◽  
Vol 111 (3) ◽  
pp. 233-241 ◽  
Author(s):  
S. K. Chakrabarti ◽  
D. C. Cotter
Keyword(s):  
Degrees Of Freedom ◽  
Single Point ◽  
Body Motion ◽  
Single Frequency ◽  
Integration Scheme ◽  
Floating Structure ◽  
Mooring Lines ◽  
Random Seas ◽  
Exciting Forces ◽  
The Time Domain

A versatile and efficient method of analysis has been developed to analyze a mooring system composed of a floating structure, e.g., a ship, mooring lines, fenders, and an articulated tower. The floating structure is assumed to be large, but may have an arbitrary shape, and the tower is assumed to be axisymmetrical. Although the program treats the floating structure and tower as a system, each body may be examined alone in the absence of the other. The analysis is carried out in the time domain assuming rigid body motion, and the solution is generated by a forward integration scheme. This approach permits nonlinear line and fender forces to be incorporated readily into the analysis. The exciting forces in the analysis are wind, current, and waves, which are not necessarily collinear. The waves can be single frequency or composed of multiple frequency components. The vessel is free to respond to the exciting forces in six degrees of freedom—surge, heave, sway, roll, pitch, and yaw. The tower is free to respond in two degrees of freedom—oscillation and precession. The analysis has been extensively verified with several different model tests for different structure configurations in regular and random seas. These include an articulated tower, a single-point mooring tanker system, a floating caisson and an inclined mooring tower.

scholarly journals Homogeneous Wave Load Effects on the Connections of Main Parts of Side-Anchored Straight Floating Bridge

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Meysam Rajabi ◽  
Hassan Ghassemi ◽  
Hamidreza Ghafari
Keyword(s):  
Hydrodynamic Interaction ◽  
Numerical Study ◽  
Wave Force ◽  
Wave Forces ◽  
Mooring System ◽  
Wave Direction ◽  
Wave Load ◽  
Mooring Lines ◽  
Homogeneous Wave ◽  
Floating Bridge

In this paper, a numerical study is presented to investigate wave force on the connections of main parts of a side-anchored straight floating bridge concept for the Bjørnafjorden fjord crossing. The floating bridge is supported by 18 pontoons, and three groups of mooring lines are employed to restrain the bridge against horizontal loads and increase its transverse stiffness. The created wave forces at the connections of pontoon-column and column-girder of the floating bridge considering the effects of short-crested and long-crested waves, varying wave direction, hydrodynamic interaction between pontoons, and mooring system are analyzed. It is found that short-crested and long-crested waves depending on their direction decrease or increase the wave forces on the joints. Considering that the effect of hydrodynamic interaction between pontoons can increase or reduce the wave forces and moments created in the joints, which means the neglect of the hydrodynamic interaction effects between the pontoons to simplify the modeling of this type of floating bridge, may be unacceptable. Moreover, the results showed that the bridge mooring system does not merely reduce the wave forces and moments at joints along the bridge.

Small water channel network for designing wave fields in shallow water

2018 ◽  
Vol 849 ◽  
pp. 90-110 ◽  
Author(s):  
Takahito Iida ◽  
Masashi Kashiwagi
Keyword(s):  
Transmission Line ◽  
Shallow Water ◽  
Water Waves ◽  
Design Method ◽  
Water Channel ◽  
Electric Circuit ◽  
Linear Potential ◽  
Channel Network ◽  
Wave Fields ◽  
Small Water

A small water channel network is proposed for designing shallow water fields, and the network is applied to attain water wave cloaking. The design formula is derived from an analogy between waves in a water channel and in an electric circuit; an approach of a transmission line metamaterial is extended to water waves and the water channel is used as an alternative of the transmission line. The size of the water channel is sufficiently smaller than the wavelength and a number of the channels are periodically connected as a network. This small water channel network makes artificial wave fields, and it works for a wide band of frequencies. First, we make an isotropic network equivalent to a shallow water space with constant depth in order to validate the proposed design method. It shows no wave reflection at the interface due to impedance matching. After that, the proposed theory is applied to designing an anisotropic small water channel network for demonstrating shallow water cloaking. A cylinder is cloaked from waves by the network surrounding the cylinder. Both cases are confirmed with numerical computations by solving the boundary-value problem based on linear potential theory.

A Prediction Method of Hydroelastic Motion of Aircushion Type Floating Structures Considering With Draft Effect Into Hydrodynamic Forces

2008 ◽  
Author(s):  
Tomoki Ikoma ◽  
Masato Kobayashi ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda
Keyword(s):  
Potential Theory ◽  
Water Waves ◽  
Large Scale ◽  
Prediction Method ◽  
Linear Potential ◽  
Wave Loads ◽  
Floating Structure ◽  
Model Experiments ◽  
Very Large Floating Structure ◽  
Linear Potential Theory

An aircushion type floating structure can prevent to enlarge the wave drifting force restraining the hydroelastic response of it in water waves. The floating structure should be large scale to incident waves in order to make the best use of such advantages, i.e. it is a very large floating structure. The linear potential theory is useful to easily handle the wave force etc. on the aircushion type floating structure theoretically because it is predicted that its theory can give good results of behaviors of water elevation within aircushions and pressure and of wave loads on the structure qualitatively. The authors have confirmed from our past model experiments that non-linear effect does not always increase but for some exceptions. A prediction method of hydroelastic responses for the aircushion type very large floating structure by using the three-dimensional linear potential theory is shown in this paper. The validity of the method is proven and the application of the method is investigated by comparing the theoretical results with the results of the past model experiments.

scholarly journals NONLINEAR METHOD FOR REAL-TIME WAVE FORCE RECONSTRUCTION ON A CYLINDER BY USING MEASURED WAVE ELEVATION

2020 ◽  
pp. 6
Author(s):  
Jiabin Liu ◽  
Anxin Guo
Keyword(s):  
Circular Cylinder ◽  
Real Time ◽  
Linear Method ◽  
Wave Force ◽  
Wave Forces ◽  
Frequency Wave ◽  
Wave Fields ◽  
Wave Elevation ◽  
Force Reconstruction ◽  
Incident Waves

For a constructed offshore structure, wave force evaluation on its foundation in an intricate wave field will benefit the load data collection and structural safety monitoring. Then, the collected data can provide valuable references for similar structures constructed in the same ocean region in the future. A real-time wave force prediction can further contribute to the active control of the structural dynamic responses. According to the incident waves known or unknown, the wave force reconstruction issue can be divided into two categories. When the incident waves are known, the wave forces on the cylinder can be achieved by the theoretical methods or numerical methods. When the incident waves are unknown, researchers try to reconstruct the wave force indirectly. For a small-scale cylinder, researchers predicted the wave forces by using the Morison equation in random wave fields with measured data of wave elevation. These studies indicated a shortcut for determining the wave force on the cylinder by using the data of water surface elevation. However, the wave fields are assumed to be undisturbed by the structure in the mentioned studies. For a vertical larger-scale cylinder, Liu et al. (2018) established a prediction method to reconstruct wave force by using the recorded data of wave elevation around the cylinder. A linear method for the circular cylinder is provided that shows an excellent reconstruction of wave force for its dominant frequent components. However, reconstruction results showed that high frequency wave forces are underestimated and low frequency wave forces are overestimated, which means the linear method is incapable to predict the nonlinear wave forces on the structure. An improved method is built for reconstructing wave forces on a circular cylinder in the real-time. Two different algorithms, Fast Fourier Translation (FFT) and Recursive Least Squares (RLS), for real-time reconstruction are conducted. The present method can be applied for the data collection of wave loads on a constructed offshore structure.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/PYOuCNP8pgQ

scholarly journals THE INTERACTION OF OBLIQUE WAVES WITH A PARTIALLY IMMERSED WAVE ABSORBING BREAKWATER

2011 ◽  
Vol 1 (32) ◽  
pp. 56 ◽  
Author(s):  
Yong Liu ◽  
Yucheng Li
Keyword(s):  
Hydrodynamic Performance ◽  
Design Stage ◽  
Wave Forces ◽  
Linear Potential ◽  
Transmission Coefficients ◽  
Present Solution ◽  
Preliminary Design Stage ◽  
Practical Engineering ◽  
Linear Potential Theory ◽  
Incident Waves

By considering obliquely incident waves, the hydrodynamic performance of a partially immersed wave absorbing breakwater is examined in this study. The breakwater consists of a perforated front barrier and a solid rear barrier. The two barriers are both partially immersed with the same draft. An analytical solution based on the linear potential theory is developed to calculate the reflection and transmission coefficients of the breakwater and the wave forces acting on the barriers. Some useful results are presented according to numerical examples. The present solution may be used at a preliminary design stage in practical engineering.

The Concept of the Optimum Alignment of Discharge Pipelines Due to the Minimization of the Wave Forces

1992 ◽  
Vol 25 (9) ◽  
pp. 211-216
Author(s):  
A. Akyarli ◽  
Y. Arisoy
Keyword(s):  
Wave Height ◽  
Wave Force ◽  
Wave Forces ◽  
Wave Direction ◽  
Incoming Wave ◽  
Pipeline Route ◽  
Optimum Alignment ◽  
The Cost ◽  
Resultant Wave

As the wave forces are the function of the wave height, period and the angle between the incoming wave direction and the axis of the discharge pipeline, the resultant wave force is directly related to the alignment of the pipeline. In this paper, a method is explained to determine an optimum pipeline route for which the resultant wave force becomes minimum and hence, the cost of the constructive measures may decrease. Also, the application of this method is submitted through a case study.

scholarly journals Characteristics of Breaking Wave Forces on Piles over a Permeable Seabed

2021 ◽  
Vol 9 (5) ◽  
pp. 520
Author(s):  
Zhenyu Liu ◽  
Zhen Guo ◽  
Yuzhe Dou ◽  
Fanyu Zeng
Keyword(s):  
Wave Breaking ◽  
Stokes Equations ◽  
Slope Angle ◽  
Wave Force ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Secondary Wave ◽  
Wave Forces ◽  
Breaking Wave ◽  
Breaking Wave Forces

Most offshore wind turbines are installed in shallow water and exposed to breaking waves. Previous numerical studies focusing on breaking wave forces generally ignored the seabed permeability. In this paper, a numerical model based on Volume-Averaged Reynolds Averaged Navier–Stokes equations (VARANS) is employed to reveal the process of a solitary wave interacting with a rigid pile over a permeable slope. Through applying the Forchheimer saturated drag equation, effects of seabed permeability on fluid motions are simulated. The reliability of the present model is verified by comparisons between experimentally obtained data and the numerical results. Further, 190 cases are simulated and the effects of different parameters on breaking wave forces on the pile are studied systematically. Results indicate that over a permeable seabed, the maximum breaking wave forces can occur not only when waves break just before the pile, but also when a “secondary wave wall” slams against the pile, after wave breaking. With the initial wave height increasing, breaking wave forces will increase, but the growth can decrease as the slope angle and permeability increase. For inclined piles around the wave breaking point, the maximum breaking wave force usually occurs with an inclination angle of α = −22.5° or 0°.

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