Dynamic Response of a Porous Seabed and an Offshore Pile to Linear Water Waves

2008 ◽  
Author(s):  
Jian-Fei Lu ◽  
Dong-Sheng Jeng
Keyword(s):  
Dynamic Response ◽  
Water Waves ◽  
Coupled Model ◽  
Expansion Method ◽  
Wave Theory ◽  
Horizontal Displacement ◽  
Element Model ◽  
Wave Force ◽  
Acoustic Medium ◽  
Linear Wave

In this study, a coupled model is proposed to investigate dynamic response of a porous seabed and an offshore pile to ocean wave loadings. Both the offshore pile and the porous seabed are treated as a saturated poro-elastic medium, while the seawater is considered as a conventional acoustic medium. The coupled boundary element model is established by the continuity conditions along the interfaces between the three media. In the system, wave force is considered as an external load and it is evaluated via the wave function expansion method in the context of a linear wave theory. Numerical results show that the increase of the modulus ratio between the pile and the seabed can reduce the horizontal displacement of the pile and the pore pressures of the seabed around the pile. Furthermore, the maximum pore pressure of the seabed usually occurs at the upper part of the seabed around the pile.

scholarly journals Theoretical Hydrodynamic Analysis of a Surface-Piercing Porous Cylindrical Body

Fluids ◽  
2021 ◽  
Vol 6 (9) ◽  
pp. 320
Author(s):  
Dimitrios N. Konispoliatis ◽  
Ioannis K. Chatjigeorgiou ◽  
Spyridon A. Mavrakos
Keyword(s):  
Water Waves ◽  
Wave Attenuation ◽  
Three Dimensional ◽  
Cylindrical Body ◽  
Expansion Method ◽  
Wave Theory ◽  
Linear Wave ◽  
Wave Loads ◽  
Dimensional Solution ◽  
Eigenfunction Expansion Method

In the present study, the diffraction and the radiation problems of water waves by a surface-piercing porous cylindrical body are considered. The idea conceived is based on the capability of porous structures to dissipate the wave energy and to minimize the environmental impact, developing wave attenuation and protection. In the context of linear wave theory, a three-dimensional solution based on the eigenfunction expansion method is developed for the determination of the velocity potential of the flow field around the cylindrical body. Numerical results are presented and discussed concerning the wave elevation and the hydrodynamic forces on the examined body for various values of porosity coefficients. The results revealed that porosity plays a key role in reducing/controlling the wave loads on the structure and the wave run-up, hence porous barriers can be set up to protect a marine structure against wave attack.

scholarly journals WAVE FORCES ON PILES OF VARIABLE DIAMETER

1982 ◽  
Vol 1 (18) ◽  
pp. 108
Author(s):  
Bernard LeMehaute ◽  
James Walker ◽  
John Headland ◽  
John Wang
Keyword(s):  
Wave Field ◽  
Intertidal Zone ◽  
Wave Theory ◽  
Wave Force ◽  
Wave Forces ◽  
Linear Wave ◽  
Inertial Effects ◽  
Linear Wave Theory ◽  
Variable Diameter ◽  
Wave Induced

A method of calculating nonlinear wave induced forces and moments on piles of variable diameter is presented. The method is based on the Morrison equation and the linear wave theory with correction parameters to account for convective inertial effects in the wave field. These corrections are based on the stream function wave theory by Dean (1974). The method permits one to take into account the added wave force due to marine growth in the intertidal zone or due to a protective jacket, and can also be used to calculate forces on braces and an array of piles.

Calculated Dynamic Response of an Articulated Tower in Waves—Comparison With Model Tests

1987 ◽  
Vol 109 (1) ◽  
pp. 43-51 ◽  
Author(s):  
T. E. Schellin ◽  
T. Koch
Keyword(s):  
Dynamic Response ◽  
Axial Flow ◽  
Wave Theory ◽  
Diffraction Theory ◽  
Model Tests ◽  
Linear Wave ◽  
Vertical Force ◽  
Hydrodynamic Coefficients ◽  
Test Results ◽  
Statistical Measures

Calculated dynamic response of an articulated tower in waves is compared with model tests. The theory used is based on Morison’s equation and linear wave theory and requires specified hydrodynamic force coefficients. Calculations are done with three different sets of coefficients. Firstly, coefficients are assumed not to vary with wave period. Secondly, they are selected from experimental data of oscillating flow past stationary cylinders. Thirdly, they are based on calculations using diffraction theory. Added mass and inertia coefficients have a predominant effect on calculated response, drag coefficients have almost no effect. Calculated tower top motion and horizontal force at the universal joint correlate well for all three sets of coefficients, indicating that hydrodynamic coefficients for normal flow are reasonably well selected and need not be specified with undue precision. In contrast, hydrodynamic coefficients for axial flow need to be chosen carefully. Calculated vertical force at the joint, using initially specified axial flow coefficients, correlates poorly with measurements. Correlation is greatly improved using reduced coefficients for axial flow. Calculated response is reasonably linear with wave height. Spectral analysis techniques are used to determine statistical measures for three irregular seastates. Agreement with corresponding model test results is satisfactory.

Hydroelastic Response of Floating Fuel Storage Modules Placed Side-by-Side

2008 ◽  
Author(s):  
Z. Y. Tay ◽  
C. M. Wang
Keyword(s):  
Numerical Model ◽  
Water Waves ◽  
Plate Theory ◽  
Experimental Tests ◽  
Wave Theory ◽  
Mindlin Plate ◽  
Linear Wave ◽  
Plate Element ◽  
Fuel Storage ◽  
Hydroelastic Response

Presented herein are the hydroelastic responses of two large box-like floating modules that are placed adjacent to each other. These two floating modules form the floating fuel storage facility (FFSF). Owing to the small draft when compared to the length dimensions, the zero-draft assumption is commonly adopted in the modeling of very large floating structures (VLFS) as plates for hydroelastic analysis. However, such an assumption is not applicable to the considered floating modules since the effect of draft on the hydroelastic response is significant when the modules are loaded with fuel. A numerical model taking into account the draft effect is hence developed in order to predict correctly the hydroelastic response and hydrodynamic interactions of floating storage modules placed side-by-side. The floating storage modules are modeled as plates where an improved Mindlin plate element, developed by coupling the reduced integration method and the additional non-conforming modes, is used. Such a plate element does not exhibit spurious modes and shear locking phenomena, thereby making it applicable to both thin and thick plate models. Furthermore, the Mindlin plate theory predicts better stress resultants as compared with its Kirchhoff plate counterpart. The linear wave theory is used to model the water waves. The wave-induced deflections obtained from the numerical model are validated by experimental tests.

A Finite Element Model for Efficiency of a Moored Floating OWC Device in Regular Waves

2011 ◽  
Author(s):  
Jean-Roch Nader ◽  
Song-Ping Zhu ◽  
Paul Cooper ◽  
Brad Stappenbelt
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Wave Theory ◽  
Element Model ◽  
Energy Output ◽  
Chamber Pressure ◽  
Hydrodynamic Characteristics ◽  
Linear Wave ◽  
Regular Waves ◽  
Restoring Force

Hydrodynamic characteristics of floating OWC can be quite difficult to predict especially when a strong coupling is present between the chamber pressure and the device movements. Mooring properties, and air pressure inside the chamber can also considerably influence the motion of the device and therefore the energy output. A newly developed 3D finite element model based on the linear wave theory has been applied to a cylindrical type OWC device. The study focused principally on the effects of the mooring restoring force and pressure pneumatic damping in the chamber total volume flux and energy conversion of the device. Results show that properly chosen parameters could effectively increase the efficiency band width of such devices.

A direct method for Bloch wave excitation by scattering at the edge of a lattice. Part II: Finite size effects

2019 ◽  
Vol 72 (3) ◽  
pp. 387-414
Author(s):  
R I Brougham ◽  
I Thompson
Keyword(s):  
Size Effects ◽  
Water Waves ◽  
Direct Method ◽  
Finite Size ◽  
Wave Theory ◽  
Bloch Wave ◽  
General Context ◽  
Linear Wave ◽  
Finite Size Effects ◽  
Scatterer Size

Summary A method for determining the reflection and transmission properties of a periodic structure occupying a half-space, previously developed for lattices formed from point scatterers, is generalized to allow for finite size effects. This facilitates the consideration of much higher frequencies (or more precisely, much higher scatterer size to wavelength ratios), and also a wider range of boundary conditions. The method is presented in a general context of linear wave theory, and physical interpretations are given for acoustics, elasticity, electromagnetism and water waves.

Mitigation of wave force on a circular flexible plate by a surface-piercing flexible porous barrier

2020 ◽  
pp. 147509022096399
Author(s):  
R Gayathri ◽  
Harekrushna Behera
Keyword(s):  
Separation Of Variables ◽  
Flow Distribution ◽  
Expansion Method ◽  
Wave Theory ◽  
Wave Force ◽  
Porous Membrane ◽  
Vertical Surface ◽  
Physical Parameters ◽  
Flexible Plate ◽  
Wave Load

Wave force acting on a circular flexible plate in the presence of a vertical surface-piercing flexible porous membrane is examined under the hypothesis of linear water wave theory. A semi-analytic solution is developed employing the Fourier-Bessel series expansion method along with the methods of separation of variables and least-squares approximation. To keep the outer flexible membrane at a desired position, clamped-moored condition is used. Appropriate orthogonal mode-coupling relationship for the eigenfunctions of the plate covered region is exploited in the expansion formulas together with the continuity of velocity and pressure for achieving the system of equations and to determine the unknowns. The effects of various physical parameters are analyzed by computing wave load on the structures, plate deflection and flow distribution. It is found that due to the presence of vertical flexible porous membrane, a significant amount of wave force on the plate is reduced. Thus, a cylindrical flexible porous membrane can be implemented to protect the inner circular flexible plate.

In-Line Forces on Vertical Cylinders in Deepwater Waves

1985 ◽  
Vol 107 (1) ◽  
pp. 18-23
Author(s):  
T. H. Dawson
Keyword(s):  
Deep Water ◽  
Water Waves ◽  
Wave Theory ◽  
Stokes Wave ◽  
Wave Forces ◽  
Linear Wave ◽  
Random Waves ◽  
Morison Equation ◽  
Circular Particle ◽  
Wave Cycle

Laboratory measurements of the total in-line forces on a fixed vertical 2-in-dia cylinder in deep-water regular and random waves are given and compared with predictions from the Morison equation. Results show, for regular waves with heights ranging from 2 to 22 in. and frequencies ranging from 0.4 to 0.9 Hz that the Morison equation, with Stokes wave theory and constant drag and inertia coefficients of 1.2 and 1.8, respectively, provides good agreement with the measured maximum wave forces. The force variation over the entire wave cycle is also well represented. The linearized Morison equation, with linear wave theory and the same coefficients likewise provides close agreement with the measured rms wave forces for irregular random waves having approximate Bretschneider spectra and significant wave heights from 5 to 14 in. The success of the constant-coefficient approximation is attributed to a decreased dependence of the coefficients on dimensionless flow parameters as a result of the circular particle motions and large kinematic gradients of the deep-water waves.

Effect of Applying 2nd Order Wave Theory on Pipeline Dynamic Response

2010 ◽  
Author(s):  
Hammam Zeitoun ◽  
Knut To̸rnes ◽  
Stuart Oldfield ◽  
Gary Cumming ◽  
Andrew Pearce ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wave Theory ◽  
Higher Order ◽  
Cost Driver ◽  
Design Solution ◽  
Linear Wave ◽  
Finite Elements Analysis ◽  
Linear Wave Theory ◽  
Wave Kinematics ◽  
Subsea Pipelines

Ensuring subsea pipelines on-bottom stability by determining the stabilisation requirements which will limit pipelines movement under extreme waves and currents is an essential aspect of subsea pipelines design. These requirements can be a major project cost driver in some locations around the world, where the designer is faced with severe metocean conditions. This is particularly the case when the selected design solution is associated with costly stabilisation requirements such as trenching, anchoring [14], rock dumping, or mattressing. An appreciation of the pipeline structural response, when exposed to waves and steady currents kinematics is fundamental to optimise the stabilisation solution. An advanced approach used to optimise stabilisation requirements is to use transient dynamic finite element analysis. The analysis is used to simulate the dynamic response of subsea pipelines exposed to near-seabed kinematics, due to a combination of steady currents and waves. Wave kinematics at the seabed are therefore an essential input to the analysis and will significantly affect both the hydrodynamic loads on the pipeline and the pipeline response. The typical method for generating the wave kinematics in a dynamic analysis has been based on calculating the near-bed velocities corresponding to a randomly generated seastate, using linear wave theory. It has been acknowledged that this calculation is likely to produce a conservative estimate of the positive wave velocities. An improved prediction of seabed kinematics can be achieved by using higher order wave theories. Application of higher order wave theories, results in changing the velocity magnitude under wave crests and troughs. This change in kinematics may result in a change of pipeline response. This paper investigates the effect of using 2nd order wave theory for predicting the kinematics on the pipeline dynamic response. Dynamic finite elements analysis is used for determining the pipeline response and to compare the pipeline response when using 2nd order wave theory and linear wave theory. The work presented in this paper was commissioned by Woodside and performed by J P Kenny Pty Ltd.

scholarly journals A Theoretical Study of the Hydrodynamic Performance of an Asymmetric Fixed-Detached OWC Device

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2637
Author(s):  
Ayrton Alfonso Medina Rodríguez ◽  
Rodolfo Silva Casarín ◽  
Jesús María Blanco Ilzarbe
Keyword(s):  
Vertical Wall ◽  
Expansion Method ◽  
Wave Theory ◽  
Hydrodynamic Performance ◽  
Linear Wave ◽  
Low Frequencies ◽  
Linear Wave Theory ◽  
Hydrodynamic Efficiency ◽  
Eigenfunction Expansion Method ◽  
Good Agreement

The chamber configuration of an asymmetric, fixed-detached Oscillating Water Column (OWC) device was investigated theoretically to analyze its effects on hydrodynamic performance. Two-dimensional linear wave theory was used, and the solutions for the associated radiation and scattering boundary value problems (BVPs) were derived through the matched eigenfunction expansion method (EEM) and the boundary element method (BEM). The results for the hydrodynamic efficiency and other important hydrodynamic properties were computed and analyzed for various cases. Parameters, such as the length of the chamber and the thickness and submergence of the rear and front walls, were varied. The effects on device performance of adding a step under the OWC chamber and reflecting wall in the downstream region were also investigated. A good agreement between the analytical and numerical results was found. Thinner walls and low submergence of the chamber were seen to increase the efficiency bandwidth. The inclusion of a step slightly reduced the frequency at which resonance occurs, and when a downstream reflecting wall is included, the hydrodynamic efficiency is noticeably reduced at low frequencies due to the near trapped waves in the gap between the OWC device and the rigid vertical wall.

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