scholarly journals Effect of land boundary on low-frequency wave-induced motion of a large floating structure

1998 ◽  
Vol 1998 (184) ◽  
pp. 297-302
Author(s):  
Mitsuru Tsuchida ◽  
Takumi Ohyama
Keyword(s):  
Low Frequency ◽  
Floating Structure ◽  
Frequency Wave ◽  
Induced Motion ◽  
Wave Induced

An Improved SPH Model for Simulating Hydrodynamic Consequences Induced by Reef Degradation

2020 ◽  
Author(s):  
Yinlin Zhao ◽  
Hongjie Wen ◽  
Bing Ren ◽  
Guoyu Wang ◽  
Yongxue Wang
Keyword(s):  
Anthropogenic Activities ◽  
Low Frequency ◽  
Mixture Theory ◽  
Natural Disturbance ◽  
Two Phase ◽  
Frequency Wave ◽  
Reef Degradation ◽  
Sph Model ◽  
Smoothed Particle ◽  
Wave Induced

Abstract Coral reefs degradation accelerates in recent decades due to the natural disturbance and anthropogenic activities. It is important to predict and evaluate reasonably the hydrodynamic consequences of reef degradation. An improved weakly compressible smoothed particle hydrodynamic (WCSPH) porous model is developed based on the standard two-phase mixture theory. The developed WCSPH mixture model is validated by comparing the predicted results with the corresponding available data. The model is then adopted to predict the effects of reef degradation on the spatial distributions of wave setup, wave-induced current and low frequency wave energy over the reef-flat under the reef resonance conditions.

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.

Side-by-side FLNG and shuttle tanker linear and second order low frequency wave induced dynamics

2016 ◽  
Vol 111 ◽  
pp. 234-253 ◽  
Author(s):  
João Pessoa ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Frequency Wave ◽  
Wave Induced

scholarly journals Research on the Hydrodynamic Performance of a Vertical Axis Current Turbine with Forced Oscillation

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3349 ◽  
Author(s):  
Yong Ma ◽  
Chao Hu ◽  
Yulong Li ◽  
Rui Deng
Keyword(s):  
High Frequency ◽  
Forced Oscillation ◽  
Oscillation Amplitude ◽  
Low Frequency ◽  
Vertical Axis ◽  
Wake Flow ◽  
Hydrodynamic Performance ◽  
Induced Motion ◽  
Wave Induced ◽  
Current Turbine

For a current turbine fixed on a floating platform, the wave-induced motion responses of the platform change the hydrodynamic performance of the current turbine. In this paper, a numerical simulation method based on commercial computational fluid dynamics software-CFX is established to systematically analyze the turbine loads condition and power output efficiency of the turbine subject to the wave-induced motion. This method works well in terms of 2D hydrodynamic performance analysis and is verified by an experiment. In addition, the method is applied to investigate the hydrodynamic performance of a vertical axis current turbine under forced oscillation by a combining sliding mesh with moving mesh technique. This research mainly focusses on the effects of oscillation frequency and oscillation amplitude on the hydrodynamic performance and the flow field. It is found that a wake flow similar to the Von Karman Vortex Street appears under sway oscillation. Spacing between vortex in the wake flow changes under surge oscillation. The fluctuations of the blade load coefficients can be decomposed into a low frequency part and a high frequency part. The low frequency part is related to the frequency of the forced oscillation, while the high frequency part is a consequence of the rotational frequency of the turbine. The oscillation amplitudes of the turbine load coefficients increase linearly with the growth of oscillation frequency and oscillation amplitude. This paper can provide a useful reference for similar research on the turbine loads condition and power out efficiency of the turbine subject to wave-induced motion. This paper can also provide a reference on the structural design or electronic control of vertical axis current turbines.

Time Domain Methodology for Vortex-Induced Motion Analysis in Monocolumn Platform

2009 ◽  
Author(s):  
Thiago Aˆngelo Gonc¸alves de Lacerda ◽  
Gilberto Bruno Ellwanger ◽  
Marcos Queija de Siqueira ◽  
Elizabeth Frauches Netto Siqueira
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Low Frequency ◽  
Cylindrical Shape ◽  
Floating Structures ◽  
Induced Motion ◽  
Six Degree Of Freedom ◽  
Offshore Oil ◽  
Wave Induced ◽  
Force Calculation

The offshore oil exploration in Brazil has been, traditionally, made by semi-submersible and moored ship-based units. The need for more restricted wave-induced motions has demanded new conceptions of floating structures, in which the mono-column concept distinguishes itself. Due to its cylindrical shape hull, this floating unit could present a significant low frequency vibratory movement caused by the vortex shedding phenomenon. This kind of phenomenon on huge structures like platforms is usually known as VIM (Vortex Induced Motions). The main objective of this work is to evaluate a time domain methodology applied in VIM problems. This methodology uses a Van der Pol equation to represent the vortex shedding phenomenon. The force calculation schemes presented in this work are applied in physical examples and its results will be compared to model test data. The analyses were performed in a non linear dynamic analysis program, using a six degree of freedom model, developed for this study.

On Combination of Slamming-and Wave-Induced Responses

1994 ◽  
Vol 38 (02) ◽  
pp. 104-114
Author(s):  
P. Friis Hansen
Keyword(s):  
Wave Amplitude ◽  
Low Frequency ◽  
Nonstationary Process ◽  
Frequency Wave ◽  
Induced Stress ◽  
Probability Densities ◽  
Highly Correlated ◽  
The Times ◽  
Non Gaussian ◽  
Wave Induced

Attempts to solve the combination problem of the low-frequency wave-induced bending and the high frequency slamming induced bending moments in ships have so far been based on a Poisson pulse train model for the occurrence of the slamming impacts. Embedded in the Poisson pulse model is the assumption that the time of occurrence and the intensity of a slamming impact are independent of the corresponding quantities of the previous impact. This assumption is not valid because the periodic character of the ship motion tends to concentrate the slamming impacts in clusters. Further, the times of occurrence of the slamming impact and the wave-induced stress peaks are highly correlated. Slamming impact usually generates the first peak of a compressive (sagging) slamming stress in the deck, as the wave-induced stress passes from hogging to sagging. The magnitude of the wave-induced and slamming-induced stress peaks, however, tends to be slightly negatively correlated. The work in the present paper is based on the so-called Slepian model process. This is a non-Gaussian and nonstationary process that gives a complete description of the original ergodic Gaussian process after an arbitrary upcrossing into a critical interval. By use of the Slepian model process, the joint distribution of the wave amplitude and the frequency is established at the occurrence of maximum slamming response within a cluster of slamming impacts. Thereafter the response is calculated for regular sinusoidal waves at selected wave amplitudes and frequencies. Response statistics are obtained by weighing the calculated response by the probability densities of the various pairs of wave amplitude and frequency.

Prediction of Surge Motion Response of Floating Structure Using Kalman Smoother Adaptive Filters Based Time-Domain Volterra Model

2014 ◽  
Vol 660 ◽  
pp. 799-803
Author(s):  
Edwar Yazid ◽  
M.S. Liew ◽  
Setyamartana Parman ◽  
V.J. Kurian ◽  
C.Y. Ng
Keyword(s):  
Time Series ◽  
Transfer Function ◽  
Time Domain ◽  
Adaptive Filters ◽  
Low Frequency ◽  
Volterra Model ◽  
Floating Structure ◽  
Frequency Responses ◽  
Kalman Smoother ◽  
System Output

This work presents an approachto predict the low frequency and wave frequency responses (LFR and WFR) of afloating structure using Kalman smoother adaptive filters based time domain Volterramodel. This method utilized time series of a measured wave height as systeminput and surge motion as system output and used to generate the linear andnonlinear transfer function (TFs). Based on those TFs, predictions of surgemotion in terms of LFR and WFR were carried out in certain frequency ranges ofwave heights. The applicability of the proposed method is then applied in ascaled 1:100 model of a semisubmersible prototype.

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