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

Low Frequency Wave Forces and Wave Induced Motions of a FPSO in Shallow Water

2007 ◽  
Author(s):  
Longfei Xiao ◽  
Jianmin Yang ◽  
Zhiqiang Hu
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Wave Force ◽  
Wave Forces ◽  
Frequency Wave ◽  
Wave Basin ◽  
The Difference ◽  
The One ◽  
Wave Induced

The low frequency (LF) response of a soft yoke moored 160kDWT FPSO in shallow water is investigated by conducting frequency domain computations and wave basin model tests. An incident wave with Hs = 4.1m and Tp = 8.9s is applied. An obvious LF part appears in the measured wave spectrum at water depth of 16.7m. As a result, the 1st order LF wave force exists and is much larger than the 2nd one. The difference of the spectrums is about one hundred times. The LF wave drift force increases enormously. Consequently, much larger resonant surge response is induced. The LF surge amplitude at h = 16.7m is about 7 times the one at h = 29.0m and 9 times the one in deep water, although the 2nd order response changes a little. Therefore, in very shallow water, LF part of incident waves should be taken into account carefully and LF wave forces and wave induced motions will be very serious.

Application of a Hybrid Boussinesq-Panel Model for Motion Predictions of a Moored Sevan-Floater in Finite Water Depth

2017 ◽  
Author(s):  
Jikun You ◽  
Einar Bernt Glomnes
Keyword(s):  
Water Depth ◽  
Low Frequency ◽  
Boussinesq Equations ◽  
Wave Force ◽  
Irregular Waves ◽  
Wave Forces ◽  
Rankine Source ◽  
Panel Model ◽  
Finite Water Depth ◽  
Incident Waves

This paper presents the applications of an efficient hybrid time-domain simulation model for predicting moored Sevan-floater motions in irregular waves and finite water depth. The irregular incident waves are modeled by the extended Boussinesq equations, which can capture wave-wave interactions and the low-frequency long waves accurately in finite and shallow water depth. By imposing the incident wave kinematics on the surface of the floater, a panel model based on Rankine source method is applied for the calculation of wave forces and corresponding floater motions. The contributions from low-frequency components in incident waves as well as their diffraction effects are included in the wave force calculations. Validation of the irregular waves simulated by the present numerical model are performed against experimental data. Then, the simulated moored floater motions are compared with model test results and results based on Newman’s approximation. The general good agreements with experimental results demonstrate the present model can be used as an alternative for this problem while Newman’s approximation shows non-conservative results.

scholarly journals Experimental Study on Wave Forces of Circular Cylinder in Crossing Wave Fields

1994 ◽  
Vol 10 ◽  
pp. 283-288
Author(s):  
Yoon-Koo Kang ◽  
Katsuhiko Kurata ◽  
Takashi Tomita ◽  
Masahiro Okata ◽  
Koichiro Iwata
Keyword(s):  
Experimental Study ◽  
Circular Cylinder ◽  
Wave Forces ◽  
Wave Fields

Nonlinear wave forces on a circular cylinder

1989 ◽  
Vol 16 (2) ◽  
pp. 182-187 ◽  
Author(s):  
Michael Isaacson ◽  
Qi-Hua Zuo
Keyword(s):  
Circular Cylinder ◽  
Nonlinear Wave ◽  
Perturbation Methods ◽  
Wave Force ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Time Stepping ◽  
Wave Effects ◽  
Accuracy And Stability

Nonlinear wave forces on a surface-piercing vertical circular cylinder are considered using a time-stepping method previously developed which is based on Green's theorem. Possible improvements in the efficiency, accuracy, and stability of the method are considered. Results based on this method are compared with those obtained previously using perturbation methods as well as with experimental results. It is found that the time-stepping method adopted here is quite reasonable. Wave force coefficients are given as functions of the governing parameters of the problem and the importance of nonlinear wave effects on the forces is assessed. Key words: hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

scholarly journals WAVE FORCE ON A VESSEL TIED AT OFFSHORE DOLPHINS

1972 ◽  
Vol 1 (13) ◽  
pp. 92
Author(s):  
Yoshimi Goda ◽  
Tomotsuka Yoshimura
Keyword(s):  
Wave Scattering ◽  
Maximum Amplitude ◽  
Wave Force ◽  
Elliptical Cylinder ◽  
Wave Forces ◽  
Reference Volume ◽  
Wave Approach ◽  
Directional Wave ◽  
The One ◽  
Incident Waves

The solution of wave scattering by a vertical elliptical cylinder is applied to calculate the wave forces exerted upon it. The wave forces in the directions of long and short axes of ellipsis are shown in nondimensional forms as the functions of the angle of wave approach, the diameter-to-wavelength ratio, and the aspect ratio of ellipsis. The results of wave force computed are also shown in terms of the virtual mass coefficients associated with the reference volume of the circular cylinder the diameter of which is approximately equal to the apparent width of the elliptical cylinder observed from the direction of wave approach. Theory is further applied for the wave forces acting upon a vessel moored tight at offshore dolphins and the forces transmitted to the dolphins through the vessel. The vessel is approximated with the fixed elliptical cylinder having the same width-to-length ratio. The computation with directional wave spectra shows that a tanker of 200,000 D.W.T. may exert the force of about 1,400 tons at the one-third maximum amplitude to each breasting dolphin when the tanker is exposed to the incident waves of H,/„=1.0m and T» / =10 sec from the broadside.

scholarly journals SIMULATION OF WAVE FORCES ON A HORIZONTAL CYLINDER

1988 ◽  
Vol 1 (21) ◽  
pp. 163
Author(s):  
Susumu Tsuzuki ◽  
Kiyoshi Horikawa ◽  
Akira Watanabe
Keyword(s):  
Circular Cylinder ◽  
Laboratory Data ◽  
Vortex Method ◽  
Wave Force ◽  
Horizontal Cylinder ◽  
Wave Forces ◽  
Discrete Vortex ◽  
Discrete Vortex Method ◽  
Experimental Findings ◽  
Horizontal Circular Cylinder

The characteristics of wave forces acting on a horizontal circular cylinder were investigated through numerical calculations as well as experimental findings. The laboratory data on wave forces were analyzed by the concept of wave force path and classified into two types. One is the circular type and the other one is the 8 - shaped type. In order to analyze the above phenomena, the discrete vortex method was applied with appropriate assumptions. The comparison between the numerically calculated results and laboratory data shows that the simulation model proposed in this paper seems to be favorable to predict the wave forces acting on a horizontal circular cylinder within a certain range of conditions.

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 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.

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