scholarly journals Pressure Sensing Technique for Observing Seabed Deformation Caused by Submarine Sand Wave Migration

2020 ◽  
Vol 8 (5) ◽  
pp. 315 ◽  
Author(s):  
Xiaolei Liu ◽  
Xiaoquan Zheng ◽  
Zhuangcai Tian ◽  
Hong Zhang ◽  
Tian Chen
Keyword(s):  
Wave Height ◽  
Water Pressure ◽  
Sand Wave ◽  
In Situ Observation ◽  
Bottom Pressure ◽  
Flume Experiments ◽  
Pressure Sensing ◽  
And Migration ◽  
Wave Migration ◽  
Sandy Sediments

Long-term, continuous in-situ observation of seabed deformation plays an important role in studying the mechanisms of sand wave migration and engineering early warning methods. Research on pressure sensing techniques has examined the possibility of using the temporal characteristics of the vertical deformation of the seafloor to identify important factors (e.g., wave height and migration rate) of submarine sand wave migration. Two pressure sensing tools were developed in this study to observe the seabed deformation caused by submarine sand wave migration (a fixed-depth total pressure recorder (TPRFD) and a surface synchronous bottom pressure recorder (BPRSS)), based on the principle that as a sand wave migrates under hydrodynamic forcing, the near-bottom water pressure, bottom pressure and total fixed pressure synchronously change with time. Laboratory flume experiments were performed, using natural sandy sediments taken from the beach of Qingdao, China, to better present and discuss the feasibility and limitations of using these two pressure sensing methods to acquire continuous observations of seabed deformation. The results illustrate that the proposed pressure sensor techniques can be effectively applied in reflecting elevation caused by submarine sand wave migration (the accuracy of the two methods in observing the experimental bed morphology was more than 90%). However, an unexpected step-like process of the change in sand wave height observed by BPRSS is presented to show that the sensor states can be easily disturbed by submarine environments, and thus throw the validity of BPRSS into question. Therefore, the TPRFD technique is more worthy of further study for observing submarine sand wave migration continuously and in real-time.

Sand Wave Migration and its Factors on Giant Sand Ridge in Taiwan Strait

2020 ◽  
Author(s):  
Yin-Hsuan Liao ◽  
Ho-Han Hsu ◽  
Jyun-Nai Wu ◽  
Tzu-Ting Chen ◽  
Eason Yi-Cheng Yang ◽  
...  
Keyword(s):  
High Resolution ◽  
Taiwan Strait ◽  
Sand Wave ◽  
Sand Ridge ◽  
Elevation Change ◽  
Seismic Profiles ◽  
Migration Patterns ◽  
Sand Waves ◽  
And Migration ◽  
Wave Migration

<p>        Submarine sand waves are known to be induced by tidal currents and their migration has become an important issue since it may affect seafloor installations. In Taiwan Strait, widely spreading sand waves have been recognized on the Changyun Ridge, a tide-dominated giant sand ridge offshore western Taiwan. However, due to lacking of high-resolution and repeated geophysical surveys before, detailed characteristics and migrating features of the sand waves in Taiwan Strait were poorly understood. As new multibeam bathymetric and seismic data were collected repeatedly during 2016 - 2018 for offshore wind farm projects, we can now advance the understanding of sand wave characteristics and migration patterns in the study area. We apply a geostatistical analysis method on bathymetry data to reveal distribution and spatial characteristics of the sand waves, and estimate its migration pattern by using an updated spatial cross-correlation method. Then, sedimentary features, internal structures and thicknesses of sand waves are observed and estimated on high-resolution seismic profiles. Our results show that the study area is mostly superimposed by multi-scaled sandy rhythmic bed forms. However, the geomorphological and migrating characteristics of the sand waves are complicated. Their wavelengths range from 80 to 200 m, heights range from 1.5 to 8 m, and crests are generally oriented in the WNW-ESE direction. Obvious sand wave migration was detected from repeated high-resolution multi-beam data between 2016 and 2018, and migration distances can be up to ~150 m in 15 months. The average elevation change of the seafloor over the whole survey area is ~3.0 m, with a maximum value of 6.9 m. Moreover, the sand waves can migrate over 30 m with ~2.5 m elevation change in 2 months and migrate over 5 m with ~1 m elevation change in 15 days. The results also show that the orientation of wave movement can be reversed even within a small distance. By identifying the base of sand wave on seismic profiles, the thicknesses of sand waves are found ranging from 1 to 10 meters. The base of wave structure become slightly deeper from nearshore to offshore. Our results indicate that the thickness of sand waves increases with degree of asymmetry and migration rate. By bathymetric and reflection seismic data analyses, systematic spatial information of sand waves in the study area are established, and we suggest that not only tidal currents can affect sand wave migration patterns, but also wave structures and thicknesses play important roles in sand wave migrating processes and related geomorphological changes.</p>

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

scholarly journals Flume experiments on vegetated alternate bars

2018 ◽  
Vol 40 ◽  
pp. 02034 ◽  
Author(s):  
Giulio Calvani ◽  
Simona Francalanci ◽  
Luca Solari
Keyword(s):  
Hydrological Regime ◽  
Spatial Arrangement ◽  
Flume Experiments ◽  
Rigid Vegetation ◽  
Hydraulic Conditions ◽  
Laboratory Flume ◽  
Alternate Bars ◽  
River Reach ◽  
Bed Slope ◽  
And Migration

The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In these experiments and also in numerical modelling, vegetation is usually represented by rigid cylinders, although it is widely recognized that this schematization cannot reproduce the effects of root stabilization and binding on riverbed sediment. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments. We performed laboratory experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced alternate bars according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies. Results show the effects of rigid vegetation on the alternate bar configuration on the overall topographic pattern, the main alternate bar characteristics (such as amplitude and wavelength) and migration rate.

Study of sand wave migration over five years as observed in two windfarm development areas, and the implications for building on moving substrates in the North Sea

2014 ◽  
Vol 105 (4) ◽  
pp. 241-249 ◽  
Author(s):  
Ken P. Games ◽  
David I. Gordon
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
Oil And Gas ◽  
Sand Wave ◽  
Sand Waves ◽  
Migration Rates ◽  
The North ◽  
The North Sea ◽  
Wave Migration ◽  
The Impact

ABSTRACTSand waves are well known indicators of a mobile seabed. What do we expect of these features in terms of migration rates and seabed scour? We discuss these effects on seabed structures, both for the Oil and Gas and the Windfarm Industries, and consider how these impact on turbines and buried cables. Two case studies are presented. The first concerns a windfarm with a five-year gap between the planning survey and a subsequent cable route and environmental assessment survey. This revealed large-scale movements of sand waves, with the displacement of an isolated feature of 155 m in five years. Secondly, another windfarm development involved a re-survey, again over a five-year period, but after the turbines had been installed. This showed movements of sand waves of ∼50 m in five years. Observations of the scour effects on the turbines are discussed. Both sites revealed the presence of barchans. Whilst these have been extensively studied on land, there are few examples of how they behave in the marine environment. The two case studies presented show that mass transport is potentially much greater than expected and that this has implications for choosing turbine locations, the effect of scour, and the impact these sediment movements are likely to have on power cables.

scholarly journals RS CVn STARS: Photospheric Phenomena and Rotation

1983 ◽  
Vol 71 ◽  
pp. 343-361
Author(s):  
S. Catalano
Keyword(s):  
Migration Rate ◽  
Orbital Motion ◽  
Rotation Period ◽  
Maximum Amplitude ◽  
Activity Level ◽  
Period 2 ◽  
Rs Cvn Stars ◽  
Activity Cycles ◽  
And Migration ◽  
Wave Migration

ABSTRACTThis review presents a summary of observed photospheric phenomena on RS CVn stars: the amplitude, shape, evolution and migration rate of the photometric wave in relation to the rotational and orbital motion.The main points considered are: 1) the activity level (maximum amplitude, short and long timescale variability) versus rotation period; 2) the activity cycles as inferred from changes in the wave migration rate and direction and from the variation of its amplitude; 3) the detection of differential rotation; 4) the connection between the orbital period variation and activity.

In-situ observation of cooperative grain boundary sliding and migration in the nano-twinned nanocrystalline-Au thin-films

2020 ◽  
Vol 180 ◽  
pp. 97-102 ◽  
Author(s):  
Qizhen Li ◽  
Lihua Wang ◽  
Jiao Teng ◽  
Xiaolu Pang ◽  
Xiaodong Han ◽  
...  
Keyword(s):  
Thin Films ◽  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
In Situ Observation ◽  
Boundary Sliding ◽  
Au Thin Films ◽  
And Migration

Using robust correlation matching to estimate sand-wave migration in Monterey Submarine Canyon, California

2016 ◽  
Vol 376 ◽  
pp. 102-108 ◽  
Author(s):  
Kai Zhang ◽  
Fanlin Yang ◽  
Chunxia Zhao ◽  
Chengkai Feng
Keyword(s):  
Submarine Canyon ◽  
Sand Wave ◽  
Wave Migration ◽  
Correlation Matching

scholarly journals The Maximum Height and Attenuation of Impulse Waves Generated by Subaerial Landslides

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Baoliang Wang ◽  
Lingkan Yao ◽  
Haixin Zhao ◽  
Cong Zhang
Keyword(s):  
Influencing Factors ◽  
Wave Height ◽  
Water Waves ◽  
High Speed ◽  
Transient Flow ◽  
Evaluation Criteria ◽  
Maximum Height ◽  
Flume Experiments ◽  
Orthogonal Experiments ◽  
Wave Height Attenuation

High-speed landslides that flow into reservoirs can cause impulsive water waves. To study the characteristics of the maximum impulse wave’s height and its attenuation, 25 sets of flume experiments were conducted using orthogonal theory and 6 main influencing factors were considered. Taking the impulse wave heights as the evaluation criteria and analyzing the 6 influencing factors at 5 different levels, the characteristics of the maximum impulse wave’s height and its attenuations were obtained. Then, statistical relationships between the maximum wave height and the controlling factors were proposed. Then, by combining the continuity equation and the hydrodynamic open channel transient flow movement equation, the process of landslide wave height attenuation was studied, and it was found that the attenuation of the wave is consistent with exponential attenuation. Then, combined with the data obtained from the orthogonal experiments, an attenuation equation for the surge was derived. Finally, the proposed equation was validated by applying it to the landslides that took place along the shore of the Zipingpu reservoir, which were triggered by the Wenchuan earthquake, and the results indicate that the calculated results are very close to the observed results.

scholarly journals RANDOM BREAKING WAVES HORIZONTAL SEABED

1986 ◽  
Vol 1 (20) ◽  
pp. 68 ◽  
Author(s):  
Hans Peter Riedel ◽  
Anthony Paul Byrne
Keyword(s):  
Wave Height ◽  
Water Depth ◽  
Breaking Waves ◽  
Random Wave ◽  
Random Waves ◽  
Flume Experiments ◽  
Depth Ratio ◽  
Wave Trains ◽  
Monochromatic Waves

According to wave theories the depth limited wave height over a horizontal seabed has a wave height to water depth ratio (H/d) of about 0.8. Flume experiments with monochromatic waves over a horizontal seabed have failed to produce H/d ratios greater than 0.55. However designers still tend to use H/d 0.8 for their design waves. Experiments have been carried out using random wave trains in the flume over a horizontal seabed. These experiments have shown that the limiting H/d ratio of 0.55 applies equally well to random waves.

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