Experimental Investigation on Dynamic Response of Submarine Pipeline Over Flat Beds in Waves

2007 ◽  
Author(s):  
Yong Sha ◽  
Yongxue Wang ◽  
Lee M. Pearson
Keyword(s):  
Reynolds Numbers ◽  
Order Effect ◽  
Model Tests ◽  
Second Order ◽  
Irregular Waves ◽  
Strain Gauges ◽  
Submarine Pipeline ◽  
Flexible Pipe ◽  
Wave Flume ◽  
Bending Strain

Model tests have been conducted on flexible submarine pipelines over flat beds in both regular and irregular waves and the second order effect induced by waves are concerned within the certain range of Keulegan-Carpenter numbers and Reynolds numbers. The tests were conducted in the wave flume with 55m in length, 4m in width and 2.5m in depth. The pipelines were made by flexible pipe with 60mm in diameter and placed at various distances from a flat bed. Gap to diameter ratio varies from 0.4 to 0.8 when the pipelines are not sagging. The wave period in the model tests is in the range from 0.8 to 2.0 and water depth is 0.4m. The Keulegan-Carpenter numbers are less than 8.0 and the Reynolds numbers are in the subcritical regime. Bending strain was measured by strain gauges bonded on the inner surface of the pipeline. The strain amplitudes and second order effect are analyzed and discussed against various Keulegan-Carpenter numbers and gaps between the pipeline and the flat bed.

Model Tests on the Parametric Resonance of the Deep Draft Semi-Submersible Under Regular and Irregular Waves

2020 ◽  
Author(s):  
Chenglin Li ◽  
Liwei Yu ◽  
Shuqing Wang ◽  
Zhe Tian ◽  
Xujie Wang
Keyword(s):  
Wave Height ◽  
Parametric Resonance ◽  
Model Tests ◽  
Irregular Waves ◽  
Mooring System ◽  
Mooring Lines ◽  
Natural Period ◽  
Beam Wave ◽  
Wave Flume ◽  
Pitch Direction

Abstract Model tests on the parametric resonance of the deep draft semi-submersible (DDS) under regular and irregular waves are conducted in the wave flume of the Ocean University of China (OUC). Model tests with and without mooring lines are conducted under various regular and irregular waves with different wave angles. From the results of the model without mooring lines, it is found that parametric resonance generally occurs when wave period is about the natural period of heave and about half of the natural period of pitch or roll. The steady amplitude of the parameter resonance is larger under larger wave height. In heading waves, parametric resonance occurs in the roll direction, while parametric resonance occurs in both roll and pitch direction for the beam wave. In irregular waves, parametric resonance is practical non-ergodic. For the model without mooring lines, parametric resonance does not occur under the constraints of the mooring system.

Deterministic Reproduction of Nonlinear Waves

2002 ◽  
Author(s):  
Jesper Skourup ◽  
Martin J. Sterndorff
Keyword(s):  
Time Series ◽  
Nonlinear Waves ◽  
Second Order ◽  
Irregular Waves ◽  
Regular Waves ◽  
Order Model ◽  
Wave Flume ◽  
Non Linear ◽  
The Waves ◽  
Second Order Model

A method for deterministic reproduction of non-linear long-crested waves has been implemented. The model is used for non-linear reproduction of measured wave time series from a model test programme in a wave flume. Regular waves, irregular waves and focused waves have been reproduced with the model. Based on measured surface elevation time series at one location in the flume the elevation time series and the kinematics have been reproduced at another location using both linear theory and the second order model. The numerical results have been compared with measurements and it is found that the second order model is able to reproduce the correct shape of the waves as they propagate in the flume — even when the waves are highly non-linear.

Extreme waves, modulational instability and second order theory: wave flume experiments on irregular waves

2006 ◽  
Vol 25 (5) ◽  
pp. 586-601 ◽  
Author(s):  
M. Onorato ◽  
A.R. Osborne ◽  
M. Serio ◽  
L. Cavaleri ◽  
C. Brandini ◽  
...  
Keyword(s):  
Modulational Instability ◽  
Order Theory ◽  
Second Order ◽  
Irregular Waves ◽  
Extreme Waves ◽  
Flume Experiments ◽  
Wave Flume

Amplification of Waves by a Concrete Gravity Sub-Structure: Linear Diffraction Analysis and Estimating the Extreme Crest Height

2004 ◽  
Author(s):  
E. J. van Iperen ◽  
G. Z. Forristall ◽  
J. A. Battjes ◽  
J. A. Pinkster
Keyword(s):  
Wave Model ◽  
Diffraction Theory ◽  
Peak Frequency ◽  
Model Tests ◽  
Second Order ◽  
Irregular Waves ◽  
Regular Wave ◽  
Experimental Surface ◽  
Elevation Data ◽  
Using Data

Diffraction of both regular and irregular waves by a Concrete Gravity Sub-structure (CGS) was investigated using experimental surface elevation data and computational results of the linear diffraction code DELFRAC. The influence of the box-shaped base that supports the four vertical columns was studied independently from the columns, using data from regular wave model tests of the Malampaya CGS. DELFRAC was shown to give accurate results for the focusing of waves over the submerged structure. Results from regular wave data analysis of model tests of the complete Sakhalin II project Lunskoye CGS were compared to the predictions by the linear diffraction code. For the wave cases tested, the first-order amplitudes were accurately predicted. Diffraction of irregular waves at the Lunskoye CGS was studied in a similar way and linear diffraction theory for random seas gave an excellent prediction of incident wave spectral diffraction, including the peaks in the diffracted spectrum near twice the peak frequency in the input spectrum. The results obtained for the Lunksoye CGS in the present study were consistent with results found in similar studies on less complex structures. An attempt to predict the extreme crest heights from the diffracted spectrum was made using a Weibull distribution, and a second-order expansion of the sea surface that captures the effects of wave steepness, water depth and directional spreading with no other approximation than the truncation of the expansion at second order. Depth induced breaking appeared to be an important phenomenon limiting the crest heights. The crest heights in a 100-year sea state at the Lunskoye CGS were accurately predicted.

APPLICATION OF ACOUSTIC METHODS IN RESEARCHES OF THE BOTTOM SEDIMENT DYNAMICS

2018 ◽  
Author(s):  
Б. Дивинский ◽  
B. Divinskiy ◽  
И. Грюне ◽  
I. Gryune ◽  
Р. Косьян ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
Sediment Concentration ◽  
Irregular Waves ◽  
Single Frequency ◽  
Contactless Measurement ◽  
Measurement Means ◽  
Uniform Field ◽  
Wave Flume ◽  
Acoustic Methods ◽  
Back Scattering

Acoustic methods belong to contactless measurement means, possess high spatial and time resolution. Thus, the use of multifrequency allows directly profile both concentration and granulometric structure of the suspended substances. In 2008 in the Big Wave Flume (Hanover, Germany) by efforts of the Russian and German scientists there have been carried out the experiment on studying the bottom material suspension laws under the influence of irregular waves. The Aquascat 1000 acoustic back scattering sensor (ABS) manufactured by British company Aquatec (www.aquatecsubsea.com), equipped by a three-frequency transmitter with frequencies 1,0, 2,0 and 3,84 MHz, has been set on distance of 0,75 m from the bottom and 111 m from wave generator at the total depth of 3,2 m. Several dozen series of measurements at various parameters of surface waves have been carried out. The general picture of suspension is so that the external dynamic influence (currents, wave movements, turbulence, gravitation forces) creates a non-uniform field (gradient) of the suspended particles and in most cases due to this the average size of particles undergoes to the spatial-time variations. For this reason while defining the mass concentration of suspended sediment, using the single frequency transmitter there is necessity for numerous definition of the suspension granulometric structure what by isn’t always possible. If two and more frequencies are used the observed results comparison can give the information on average diameters of particles and on that basis the calculation of suspended sediment concentration is possibleLet's emphasize the basic advantages of back scattering acoustic gauges usage: – Obtaining the particles sizes and concentration distribution profiles is possible; – The initial granulometric structure of bottom sediments can be unknown (at use of several frequencies). The following can be referred to some lacks of the device: – The system should be calibrated in laboratory conditions; – In a positive feedback conditions the iterative computing process can converge to zero or to infinity. In this case experiments with a variation of carrier frequencies chosen for the analysis allow partially solve the problem (say experiments with different frequencies pairs, as 2/1 of MHz or 4/2 MHz).

Electromagnetism as a second order effect

1961 ◽  
Vol 3 (1) ◽  
pp. 28-44 ◽  
Author(s):  
W. G. V. Rosser
Keyword(s):  
Order Effect ◽  
Second Order

Analysis on the Performance of Deckwetness of Sandglass-type and Cylindrical Floating Bodies

2016 ◽  
Vol 60 (03) ◽  
pp. 145-155
Author(s):  
Ya-zhen Du ◽  
Wen-hua Wang ◽  
Lin-lin Wang ◽  
Yu-xin Yao ◽  
Hao Gao ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Linear Response Theory ◽  
Second Order ◽  
Irregular Waves ◽  
Wave Loads ◽  
Floating Bodies ◽  
Drift Motion ◽  
First Order ◽  
Series Of Experiments ◽  
Deck Wetness

In this paper, the influence of the second-order slowly varying loads on the estimation of deck wetness is studied. A series of experiments related to classic cylindrical and new sandglass-type Floating Production, Storage, and Offloading Unit (FPSO) models are conducted. Due to the distinctive configuration design, the sand glass type FPSO model exhibits more excellent deck wetness performance than the cylindrical one in irregular waves. Based on wave potential theory, the first-order wave loads and the full quadratic transfer functions of second-order slowly varying loads are obtained by the frequency-domain numerical boundary element method. On this basis, the traditional spectral analysis only accounting for the first-order wave loads and time-domain numerical simulation considering both the first-order wave loads and nonlinear second-order slowly varying wave loads are employed to predict the numbers of occurrence of deck wetness per hour of the two floating models, respectively. By comparing the results of the two methods with experimental data, the shortcomings of traditional method based on linear response theory emerge and it is of great significance to consider the second-order slowly drift motion response in the analysis of deck wetness of the new sandglass-type FPSO.

Experimental Wave Flume Tests in ROV-Wave Interaction Effects on the Line Tension for a Work Class ROV in Splash Zone

2021 ◽  
Author(s):  
Michael Binsar Lubis ◽  
Mehrdad Kimiaei
Keyword(s):  
Time History ◽  
Wave Interaction ◽  
Line Tension ◽  
Irregular Waves ◽  
Splash Zone ◽  
Remotely Operated Vehicle ◽  
Wave Flume ◽  
Flume Tests ◽  
Tension Time ◽  
Work Class

Abstract Integrity and stability of Remotely Operated Vehicle (ROV) when passing through the splash zone is one of the main concerns in the design of an ROV-umbilical system. Due to the lightweight nature of ROV in water, the umbilical experiences repetitive rapid transitions between slack and taut as the ROV travels through the splash zone. These rapid transitions induce tension spikes in the umbilical, namely snap forces, that can endanger the launch and recovery of an ROV. Therefore, it is important to ensure that the tension spikes do not exceed the safe working load of the umbilical. In this study, launch and recovery of a deep-water work class ROV are experimentally investigated using a 1:10 scaled ROV model through a series of wave flume tests. Different regular and irregular waves are generated in the flume while the ROV model is hung over the flume in four different positions. The tension time-history in the line is measured and recorded using a load cell at the top-end of the line. A simplified numerical model for launch and recovery of the ROV is developed and the numerical results are compared with the experimental ones. It is shown that the presented simplified model can be accurately used for analysis of launch and recovery of the ROV.

Extreme Response of Very Large Floating Structure Considering Second-Order Hydroelastic Effects in Multidirectional Irregular Waves

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Xujun Chen ◽  
Torgeir Moan ◽  
Shixiao Fu
Keyword(s):  
Second Order ◽  
Irregular Waves ◽  
Bending Moments ◽  
Floating Structure ◽  
First Order ◽  
Fluid Forces ◽  
Principal Coordinates ◽  
Vertical Displacements ◽  
Exciting Forces ◽  
Nonlinear Fluid

Hydroelasticity theory, considering the second-order fluid forces induced by the coupling of first-order wave potentials, is introduced briefly in this paper. Based on the numerical results of second-order principal coordinates induced by the difference-frequency and sum-frequency fluid forces in multidirectional irregular waves, the bending moments, as well as the vertical displacements of a floating plate used as a numerical example are obtained in an efficient manner. As the phase angle components of the multidirectional waves are random variables, the principal coordinates, the vertical displacements, and the bending moments are all random variables. Extreme values of bending moments are predicted on the basis of the theory of stationary stochastic processes. The predicted linear and nonlinear results of bending moments show that the influences of nonlinear fluid forces are different not only for the different wave phase angles, but also for the different incident wave angles. In the example very large floating structure (VLFS) considered in this paper, the influence of nonlinear fluid force on the predicted extreme bending moment may be as large as 22% of the linear wave exciting forces. For an elastic body with large rigidity, the influence of nonlinear fluid force on the responses may be larger than the first-order exciting forces and should be considered in the hydroelastic analysis.

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