Dynamic Analysis of Deep Water Tension Leg Platforms Under Random Waves

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
R. Jayalekshmi ◽  
R. Sundaravadivelu ◽  
V. G. Idichandy
Keyword(s):  
Deep Water ◽  
Wave Theory ◽  
Iterative Solution ◽  
Integration Scheme ◽  
Wave Forces ◽  
Linear Wave ◽  
Random Waves ◽  
Element Analysis ◽  
Response Characteristics ◽  
Water Tension

The effect of tether-riser dynamics on the response characteristics of deep water tension leg platforms in water depths 900 m and 1800 m under random waves is investigated using a developed nonlinear finite element analysis program in the time-domain. Updated Lagrangian coordinates and incremental iterative solution based on Newmark’s integration scheme are adopted. Linear wave theory is used. Relative velocity form of Morison’s equation is used for estimating the wave forces. Current forces are also included in the analysis. Results are reported in the form of statistical values of responses. The statistical values of responses are found to increase with water depth and significant increase is observed when risers are included.

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.

scholarly journals Spatial Variation of Wave Force Acting on a Vertical Detached Breakwater Considering Diffraction

2021 ◽  
Vol 33 (6) ◽  
pp. 275-286
Author(s):  
Jae-Sang Jung ◽  
Changhoon Lee
Keyword(s):  
Standing Waves ◽  
Wave Theory ◽  
Wave Force ◽  
Wave Forces ◽  
Linear Wave ◽  
Random Waves ◽  
Linear Wave Theory ◽  
Incident Wave Angle ◽  
Wave Angle ◽  
Incident Waves

In this study, the analytical solution for diffraction near a vertical detached breakwater was suggested by superposing the solutions of diffraction near a semi-infinite breakwater suggested previously using linear wave theory. The solutions of wave forces acting on front, lee and composed wave forces on both side were also derived. Relative wave amplitude changed periodically in space owing to the interactions between diffracting waves and standing waves on front side and the interactions between diffracting waves from both tips of a detached breakwater on lee side. The wave forces on a vertical detached breakwater were investigated with monochromatic, uni-directional random and multi-directional random waves. The maximum composed wave force considering the forces on front and lee side reached maximum 1.6 times of wave forces which doesn’t consider diffraction. This value is larger than the maximum composed wave force of semi-infinite breakwater considering diffraction, 1.34 times, which was suggested by Jung et al. (2021). The maximum composed wave forces were calculated in the order of monochromatic, uni-directional random and multi-directional random waves in terms of intensity. It was also found that the maximum wave force of obliquely incident waves was sometimes larger than that of normally incident waves. It can be known that the considerations of diffraction, the composed wave force on both front and lee side and incident wave angle are important from this study.

scholarly journals Comparison of Extreme Surface Elevation for Linear and Nonlinear Random Wave Theory for Offshore Structures

2018 ◽  
Vol 203 ◽  
pp. 01021
Author(s):  
Nurul 'Azizah Mukhlas ◽  
Noor Irza Mohd Zaki ◽  
Mohd Khairi Abu Husain ◽  
Gholamhossein Najafian
Keyword(s):  
Probabilistic Approach ◽  
Wave Theory ◽  
Offshore Structures ◽  
Random Wave ◽  
Linear Wave ◽  
Random Waves ◽  
Sea State ◽  
Higher Order Terms ◽  
Structural Responses ◽  
Nonlinear Random Wave

For offshore structural design, the load due to wind-generated random waves is usually the most important source of loading. While these structures can be designed by exposing them to extreme regular waves (100-year design wave), it is much more satisfactory to use a probabilistic approach to account for the inherent randomness of the wave loading. This method allows the statistical properties of the loads and structural responses to be determined, which is essential for the risk-based assessment of these structures. It has been recognized that the simplest wave generation is by using linear random wave theory. However, there is some limitation on its application as some of the nonlinearities cannot be explained when higher order terms are excluded and lead to underestimating of 100-year wave height. In this paper, the contribution of nonlinearities based on the second order wave theory was considered and being tested at a variety of sea state condition from low, moderate to high. Hence, it was proven that the contribution of nonlinearities gives significant impact the prediction of 100-year wave's design as it provides a higher prediction compared to linear wave theory.

Numerical Simulation of Flows Past Partially-Submerged Horizontal Circular Cylinders in Free Surface Waves

2013 ◽  
Author(s):  
Hans Bihs ◽  
Muk Chen Ong
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Wave Theory ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Wave Forces ◽  
Linear Wave ◽  
Numerical Wave Tank ◽  
Linear Wave Theory ◽  
Free Surface Waves

Two-dimensional (2D) numerical simulations are performed to investigate the flows past partially-submerged circular cylinders in free surface waves. The 2D simulations are carried out by solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω turbulence model. The level set method is employed to model the free-surface waves. Validation studies of a numerical wave tank have been performed by comparing the numerical results with the analytical results obtained from the linear-wave theory. Wave forces on the partially-submerged cylinders have been calculated numerically and compared with the published theoretical and experimental data under regular-wave conditions. The free-surface elevations around the cylinders have been investigated and discussed.

Calculation of Wave Forces Acting on a Cylinder With a Porous Plate Fixed Inside

2009 ◽  
Author(s):  
Weiguang Bao ◽  
Fenfang Zhao ◽  
Takeshi Kinoshita
Keyword(s):  
Body Surface ◽  
Porous Body ◽  
Porous Plate ◽  
Wave Theory ◽  
Wave Forces ◽  
Linear Wave ◽  
Normal Velocity ◽  
Wave Loads ◽  
Eigen Values ◽  
Eigen Function

To evaluate wave forces and to estimate the motion of breakwater, a circular cylinder is investigated based on the linear wave theory in the present work. The cylinder possesses a porous sidewall, an impermeable bottom and a horizontal porous plate inside that is fixed in the cylinder to work as obstruct and make wave dissipation more effectively. To simplify the problem, the Darcy’s fine-pore model is applied to the boundary condition on the porous body surface. The boundary value problem is solved by means of the eigen-function expansion approach. The fluid domain is divided into three regions and different eigen-function series are used. The so-called dispersion relation for the region inside the cylinder is quite different from a conventional one due to the existence of the porous plate. It leads to eigen values of complex number. To obtain solutions for the radiation problems, particular solution should be constructed to take account of the normal velocity appearing on the porous boundary. The wave loads are evaluated by integrating the pressure difference on two sides of the wetted body surface. The theoretical works are in good consistence with the experimental results. The Haskind relations are examined for the porous body. It is found that the damping coefficient consists of two parts. In addition to the component of conventional wave-radiating damping, exists a second component caused by the porous effects.

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.

Scattering of Waves by Two-Dimensional Circular Obstacles in Finite Water Depths

1979 ◽  
Vol 23 (01) ◽  
pp. 32-42 ◽  
Author(s):  
Robert A. Naftzger ◽  
Subrata K. Chakrabarti
Keyword(s):  
Wave Interaction ◽  
Wave Theory ◽  
Finite Depth ◽  
Wave Forces ◽  
Linear Wave ◽  
Two Dimensional ◽  
Linear Wave Theory ◽  
Dimensional Object ◽  
Limiting Case ◽  
Water Depths

The wave forces on a fixed two-dimensional object submerged in water of finite depth are obtained under the assumptions of linear wave theory. The far-field characteristics of the wave interaction with the object are also examined. The boundary-value problem for the wave potential is formulated in terms of Green's theorem, and the resulting integral equation is solved numerically. Results for a submerged and half-submerged circular cylinder and a bottom-seated half cylinder are presented. In the limiting case of infinite depth the numerical results compare quite well with known solutions.

Viscous Damping of Floating Bodies in Waves

2015 ◽  
Author(s):  
J. Michael R. Graham ◽  
Martin J. Downie
Keyword(s):  
Prediction Method ◽  
Wave Theory ◽  
Arbitrary Cross Section ◽  
Whole Body ◽  
Floating Body ◽  
Linear Wave ◽  
Viscous Damping ◽  
Random Waves ◽  
Outer Flow ◽  
Velocity Parameter

A numerical method developed from earlier work [1, 2] of predicting damping due to eddy shedding from sharp or rounded bilges of a hull of arbitrary cross-section in beam waves is presented. The method matches an inner solution which simulates the local bilge section separated flow numerically to an outer wave potential flow solution. The latter can be any standard 3-dimensional panel or other method for the whole body which provides the local values of the matching velocity parameter at all bilge sections which shed eddies. Scaling by the matching parameter provides a physically based sectional damping coefficient for a response computation. In the case of free response of a floating body feed-back from the viscous damping to the bilge velocity parameter through the response mode amplitudes necessitates iteration which generally converges very quickly. Computational predictions carried out in the frequency domain using this prediction method assuming linear wave theory for the outer flow are presented and compared with laboratory wave tank measurements for roll response of two floating hulls in regular and random waves. Application of the method to viscous damping of more complex geometries is also possible.

scholarly journals NEW FRAMEWORK FOR PREDICTION OF LONGSHORE CURRENTS

1982 ◽  
Vol 1 (18) ◽  
pp. 99 ◽  
Author(s):  
C.A. Fleming ◽  
D.H. Swart
Keyword(s):  
Wave Theory ◽  
Data Sets ◽  
Linear Wave ◽  
Random Waves ◽  
Longshore Currents ◽  
Longshore Sediment Transport ◽  
Longshore Transport ◽  
Bed Roughness ◽  
Accuracy Of Prediction ◽  
New Framework

The accuracy of prediction of longshore sediment transport depends largely on the accuracy with which the wave-driven longshore currents within the breaker zone can be predicted. Longuet-Higgins (1970) developed a formulation for longshore transport which is widely used today. In the present paper the basic theory of Longuet-Higgins is reexamined. The effect of bed roughness on the magnitude of the longshore current is quantified with the aid of over 350 individual data sets and the theory is theoretically extended to include the effect of random waves, in a similar way to Battjes (1974), and higher-order waves. For this latter purpose the Vocoidal water wave theory of Swart (1978) is used. It is shown that the use of Vocoidal theory leads to a velocity distribution which is in closer correspondence to measured data than that predicted by using linear wave theory.

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