Bubbles are often present in the natural ocean. Bubbly liquid will have the significant influence the sound propagation, and creates a significant disturbance to under water target's detection. Therefore, it is an important research subject of bubble influence to the sound wave propagation. This study used the sonar training system which developed by British's iTP corporation, through suitable additional design discuss the attenuation of sound propagating through a bubble screen. At first this study collects and infers the formula by the literature review. Secondly, the experimental design of measuring the attenuation of sound wave. The experiment process by using two parallel iron boards to carry on the measurement of gas-volume fraction. Then correlate with the sound pressure from the measurement of hydrophone. After curve fitting, we can clearly know the each other correlation. Finally taking the result compare with the attenuation coefficient formula. The experimental consists of two parts. The first part is to measure the gas-volume fraction of the bubbly liquid contained in the screen; while the second part is to measure the sound attenuation of the bubble screen. The result display that the bubble screen can attenuate about 8 dB per centimeter as the gas-volume fraction stay at 1 percent. At high gas-volume fraction the coefficient of attenuation has increased, and is different from theoretical value. This is because the bubble's correlation has not been considered. In addition, the low frequency sound wave is close to theoretical value, but the high frequency sound wave has big different to theoretical value. Because the high frequency sound wave's wavelength is too small to satisfy the condition. At experiment I suggest to use more appropriate transducers and precise bubble's tube. Thus the experimental result will be better.

Hurricanes are one of the primary threats to the Texas coastal environment and economy. They generate large wave and storm surges that have caused much damage on the Texas coast in the past. Understanding both the hydrodynamic processes that damage coastal habitats and hurricane hazard and risk are critical to preserve coastal vegetation and quantify its benefits to coastal storm protection. The goal of this project is to quantify the impact of wave attenuation and wave refraction as well as the development of coherent structures in marsh fringes and the formation of a rip current system over wetlands on storm protection. The 3D Shallow Water Wave Basin at Texas A&M University hosted a series of large-scale experiments considering an idealized wetland model to pursue this goal. Study of the marsh geometry of the Texas coast was done in order to scale the experiments to the size of the Haynes Laboratory 3D-Water Wave Basin using a Froude and a Reynolds scalings. Particularly, averaged size and idealized shape of marsh segments in the area of Dalehite Cove in Galveston Bay were considered. Three sets of different wave conditions and water levels were tested to approximate different intensities of storm surge. Identical tests with both vegetated and non-vegetated marshes were run to compare the influence of the vegetation in storm conditions, and three different spacings between marsh segments were tested. In the basin, normally incident regular waves were generated at three water circulation structures. Data analysis allows the determination of the impact of discontinuous marsh segments on wave attenuation and wave refraction. Coherent structures such as rip current and the circulation pattern were analyzed to study the change in the flow field during passage of the waves. The experimental measurements were able to describe the wave transformations over the marsh segments. The influence of coastal wetlands was identified to affect the hydrodynamic process and reduce the total wave energy which is dissipated and redistributed by vegetation. The presence of the mounds induced an important decrease in the wave height, in addition to the damping of the waves by the vegetation stems. The variation in spatial coverage of the wetland model has been shown to highly affect the flow dynamics by generating offshore directed flow in the channel and onshore directed flow on the marsh mounds. This experimental approach provides a further understanding of flow dynamics by waves and surge in wetlands, at a large scale.

Wave attenuation by vegetation is a highly dynamic process and its quantification is important for accurately understanding and predicting coastal hydrodynamics. However, the influence of vegetation on wave dissipation is not yet fully established nor implemented in current hydrodynamic models. A series of laboratory experiments were conducted at the Haynes Coastal Engineering Laboratory and in a two-dimensional flume at Texas A and M University to investigate the influence of relative vegetation height, stem density, and stem spacing uniformity on wave attenuation. Vegetation fields were represented as random cylinder arrays where the stem density and spatial variation were based on collected field specimens. Experimental results indicate wave attenuation is dependent on relative vegetation height, stem density, and stem spacing standard deviation. As stems occupy more of the water column, an increase in attenuation occurred given that the highest wave particle velocities are being impeded. Sparse vegetation fields dissipated less wave energy than the intermediate density; however, the extremely dense fields dissipated very little, if any, wave energy and sometimes wave growth was observed. This is possibly due to the highest density exceeding some threshold where maximum wave attenuation capabilities are exceeded and lowering of damping ensues. Additionally, wave attenuation increased with higher stem spatial variation due to less wake sheltering. A one-dimensional model with an analytical vegetation dissipation term was developed and calibrated to these experimental results to capture the wave transformation over the vegetation beds and to investigate the behavior of the vegetation field bulk drag coefficient. The best fit between predicted and measured wave heights was obtained using the least squares method considering the bulk drag coefficient as the single calibration parameter. The model was able to realistically capture the wave transformations over vegetation. Upon inspection, the bulk drag coefficient shared many of the dependencies of the total wave dissipation. The bulk drag coefficient increased with larger relative vegetation heights as well as with higher stem spacing standard deviation. Higher densities resulted in a lowering of the bulk drag coefficient but generally an increase in wave attenuation. These parameters and their influences help in identifying the important parameters for numerical studies to further our understanding of wave attenuation by wetlands.

It is well known that surface water waves interact with fluid mud on the sea bed. Wave mud interaction results in high wave energy dissipation and mud mass transport. This kind of wave energy dissipation, which generally is much more significant than wave dissipation due to bottom friction, should be considered in the simulation of wave evolution and transformation in muddy coastal environments. In this research, a two-dimensional horizontal wave propagation and morphodynamic model for muddy coasts was developed. The model can be applied on a general three dimensional bathymetry of a soft muddy coast to calculate wave damping, fluid mud transport and resulting bathymetry change under wave action. In addition to the effect of wave-mud interaction on wave propagation, the dissipation due to wave-mud interaction was also implemented in SWAN (a third generation numerical model for Simulating WAves Nearshore) using a multilayered wave mud interaction model. These two models combined can be used for generation and propagation of waves in muddy coastal areas. The nonlinear constitutive equations of the visco-elastic-plastic model are adopted for the rheological behavior of fluid mud in this research. The results of the numerical model are compared against a series of wave-basin experiments, wave flume experiments and field observations. Comparisons between the simulated results with the both field and laboratory data reveal the capability of the proposed model to predict the wave transformation and mud mass transport. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-07-24 11:18:18.622

Yes / When ocean waves propagate over porous seabed, they cause variations of the pore pressure within seabed, leading to the possible wave attenuation and soil liquefaction. In order to advance and improve our understanding of the process of wave-induced seabed liquefaction and its impact on wave propagation, systematical experiments are carried out in a wave flume with a soil basin filled with silt. Both the pore pressures and water surface elevations are measured simultaneously, while the seabed liquefaction is videotaped using a high-speed camera. Laboratory measurements show that the pore pressure in surface layer mainly oscillates over time, while the wave period averaged pore pressure has little change. In the deep layer, however, the wave period averaged value of the pore pressure builds up dramatically. The results show that the wave height decreases rapidly along the direction of wave propagation when seabed liquefaction occurs. Such a wave attenuation is greatly enhanced when the liquefaction depth further increases. The experiments also demonstrate that the conditions (wave height and wave period) of incident waves have significant impacts on the wave-induced pore pressures, liquefaction depth and wave attenuation in a silt bed. / National Natural Science Foundation of China (Grant No. 51479053), the 111 Project (Grant No. B12032), the marine renewable energy research project of State Oceanic Administration (GHME2015GC01), the Fundamental Research Funds for the Central University, China (Grant No. 2013B31614), the Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation (Grant No. B1504708), and Open Foundation of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University (Grant No: 2016491011).

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In recent years, breakwater design has been governed not only by structural stability, but by cost effectiveness as well. Breakwater designers are constantly trying to find the perfect balance between low-risk design and low-cost design. The combination of a main rubble mound breakwater and a submerged offshore reef, that are designed to function together, is known as a tandem breakwater. The reef structure is responsible for dissipating some of the energy by causing wave breaking. Thereafter, the area between the reef and the main structure - the tranquillity zone - allows for natural energy dissipation. The combination of the effects of the reef and tranquillity zone results in reduced significant wave heights at the main rubble mound structure, which allows it to be designed with lighter armour units. This study investigates the application of a tandem breakwater, based on the conditions at the port of Mossel Bay, by achieving the following set of objectives: (1) to determine the influence of the tandem breakwater‟s submerged reef crest elevation on the damage level of the main rubble mound structure, (2) to determine the relationship between the relative wave attenuation distance and the percentage wave attenuation, and (3) to compare the abovementioned parameters for rock and geotube reefs. A physical model test series was conducted to gain the data required for achieving the objectives. A rubble mound structure that makes use of dolos armour units, resembling the one at Mossel Bay, was constructed inside a concrete flume equipped with a single-paddle wavemaker. Two reef structure types (rock and geotube) were tested at three crest elevations (below-LAT, LAT and ML), against combinations of two significant wave heights (2.5 m and 3 m) and two peak periods (8 s and 12 s), at one water level (ML) and one offshore reef distance (50 m). From the model test results, it is evident that the presence of a reef structure significantly affects the wave conditions that reach the main structure. When comparing significant wave heights measured at a prototype distance of 20 m in front of the main breakwater, a reduction of as high as 42% can be observed for a reef structure made from rocks and 54% for a geotube structure. In all cases, the geotube structure causes more wave attenuation due to its lower permeability, which enables it to reflect more wave energy. However, it should be noted that the stability of the geotube reef was not considered during testing. Generic graphs are presented, that aim to provide guidance in the design process of such a tandem breakwater system. The graphs are produced for a case where dolos armour units are used and might not be exactly the same when a different type of armour unit is used. One graph shows the relationship between the damage reduction at the main breakwater and the relative reef submergence. The other shows the relationship between wave attenuation and the relative wave attenuation distance. Unfortunately, the implementation of geotube reefs of the nature described in this investigation is not likely in the South African context at present. This, however, does not eliminate the possibility of future applications. As geotextile technology develops and greater operational experience and equipment is gained, tandem breakwaters that incorporate geotube reefs could provide an alternative that is both cost-effective and more environmentally friendly with regards to transport emissions. Until then, tandem breakwaters that incorporate rock reefs may be able to provide a desired alternative design for certain scenarios. / AFRIKAANSE OPSOMMING: In die afgelope jare, word breekwater ontwerp nie net beheer deur strukturele stabiliteit nie, maar ook koste effektiwiteit. Ontwerpers poog alewig om die perfekte balans tussen lae-risiko ontwerp en lae-koste ontwerp na te streef. Die kombinasie van 'n hoof ruklipgolfbreker en 'n sekondêre onderwater rif breekwater, wat ontwerp is om as 'n eenheid te funksioneer, staan bekend as „n tandem breekwater. Die rif struktuur is verantwoordelik vir die verlies van 'n gedeelte van die golf energie deur golf breking te veroorsaak. Daarna veroorsaak die area tussen die rif en die hoof struktuur – die kalmeringsone – verdere natuurlike energie verlies. Die gekombineerde effek van die rif en kalmeringsone veroorsaak dat kleiner branders die hoof breekwater bereik, wat toelaat dat dit ontwerp kan word met kleiner pantser eenhede. Dié studie ondersoek die toepassing van 'n tandem breekwater, gebaseer op die kondisies by die Mosselbaai hawe, deur die volgende doelwitte te bewerkstellig: (1) om die invloed van die onderwater rif kruinhoogte op die vlak van skade aan die hoof breekwater te bepaal, (2) om die verhouding tussen die relatiewe golfhoogte-verminderings-afstand en die golfhoogte vermindering te bepaal, en (3) om die bogenoemde parameters vir rots en geo-buis riwwe te vergelyk. 'n Fisiese model toets reeks is uitgevoer sodat die benodigde data ingesamel kan word om die doelwitte te bereik. „n Rotsvul breekwater wat gebruik maak van dolos pantser eenhede, soortgelyk aan dié by Mosselbaai, is gebou in 'n beton kanaal wat toegerus is met 'n enkel-spaan golfmasjien. Twee tipes riwwe (rots en geo-buis) is getoets met drie kruin hoogtes (onder-LAG, LAG en GV), teen kombinasies van twee beduidende golfhoogtes (2.5 m en 3 m) en twee spitsperiodes (8 s en 12 s), by een watervlak (GV) en een sekondêre breekwater afstand (50 m). Uit die model toets resultate is dit duidelik dat die teenwoordigheid van 'n rif struktuur, die golfkondisies wat die hoof breekwater bereik, beduidend beïnvloed. Wanneer beduidende golfhoogtes, gemeet op 'n prototipe afstand van 20 m voor die hoof breekwater, vergelyk word, word 'n vermindering van so hoog as 42% waargeneem vir 'n rif bestaande uit rots en 54% vir 'n rif bestaande uit geo-buise. In alle gevalle veroorsaak die geo-buis struktuur meer golfhoogte vermindering, as gevolg van sy laer deurlaatbaarheid, wat dit in staat stel om meer golfenergie te reflekteer. Die stabiliteit van die geo-buis struktuur is egter nie in ag geneem tydens die toetse nie. Generiese grafieke word weergegee, met die doel om leiding te gee tydens die ontwerpsproses van só 'n tandem breekwater struktuur. Die grafieke hou verband met die geval waar dolos pantser eenhede gebruik word, en mag verskil vir ander tipes pantser eenhede. Een van die grafieke dui die verhouding tussen skadevermindering aan die hoof breekwater en die relatiewe posisie van die onderwater rif se kruinhoogte aan. Die ander grafiek dui die verhouding tussen die golfhoogte vermindering en die relatiewe golfhoogte-verminderings-afstand aan. Huidiglik is die toepassing van die tipe geo-buis riwwe soos beskryf in hierdie ondersoek, ongelukkig onwaarskynlik in die Suid-Afrikaanse konteks. Dit skakel egter nie die moontlikheid van toekomstige toepassings van dié aard uit nie. Soos geo-tekstiel tegnologie ontwikkel en meer operasionele ervaring en toerusting bekom word, kan die effektiewe implementasie van geo-buis riwwe 'n alternatief bied wat beide koste effektief en omgewingsvriendelik is met betrekking tot die vrystelling van uitlaatgasse tydens die vervoer van materiale. Tot dan, kan tandem breekwaters wat van rots riwwe gebruik maak, moontlik die gewenste alternatiewe ontwerp bied vir sekere situasies.

The attenuation mechanism of shock waves of arbitrary strength propagating in air has been reasonably well understood. On the other hand, very little is known about the precise mechanism of shock wave attenuation and energy dissipation in liquids. The equation of state for shock propagation in water is empirical in nature and considerable differences exist with reference to the exact value of various constants even in the cast of Tait’ s equation of state, which is popularly used by researchers to describe the shock wave propagating through water. In recent times, considerable attention is being focused by researchers on shock wave attenuation and associated features in liquid medium mainly in the backdrop of development of many innovative industrial applications of shock waves. The present study focuses on generating reliable experimental data on shock wave attenuation in liquids of different viscosity. Experiments have been performed in a conventional vertical shock tube and a modified diaphragmless shock tube to understand how shock wave of requisite strength attenuates in liquids. A new vertical shock tube was designed, fabricated and successfully tested in the laboratory as a part of this study. In this new facility shock loading experiments with liquids or any complex fluid medium can be carried out. In the present study five liquids (Water, Castor Oil, Sodium Chloride (10%NaCl aqueous solution), Kerosene and Glycerin) have been subjected to shock wave loading. Exhaustive static pressure measurements in the liquid medium have been carried out to understand the attenuation characteristics of shock waves. The validity of Taits equation state has been experimentally verified for water. Based on the experimental results modified Taits equation of state has been obtained for castor oil, sodium chloride, kerosene and glycerin. Illustrative theoretical study is also carried out to complement the experiments.

Oyster reefs provide valuable ecosystemservices that contribute to coastal resilience. Unfortunately, many reefs have been degraded or removed completely, and there are increased efforts to restore oysters in many coastal areas. In particular, much attention has recently been given to the restoration of shellfish reefs along eroding shorelines to reduce erosion. Such fringing reef approaches, however, often lack empirical data to identify locations where reefs are most effective in reducing marsh erosion, or fully take into account habitat suitability. Using monitoring data from 5 separate fringing reef projects across coastal Louisiana, we quantify shoreline exposure (fetch + wind direction + wind speed) and reef impacts on shoreline retreat. Our results indicate that fringing oyster reefs have a higher impact on shoreline retreat at higher exposure shorelines. At higher exposures, fringing reefs reduced marsh edge erosion an average of 1.0 m y-1. Using these data, we identify ranges of shoreline exposure values where oyster reefs are most effective at reducing marsh edge erosion and apply this knowledge to a case study within one Louisiana estuary. In Breton Sound estuary, we calculate shoreline exposure at 500 random points and then overlay a habitat suitability index for oysters. This method and the resulting visualization show areas most likely to support sustainable oyster populations as well as significantly reduce shoreline erosion. Our results demonstrate how site selection criteria, which include shoreline exposure and habitat suitability, are critical to ensuring greater positive impacts and longevity of oyster reef restoration projects.

A series of small- to moderate-sized earthquakes occurred in Arkansas, Oklahoma and Texas from 2010 to 2012, coinciding with the arrival of the EarthScope Transportable Array (TA). The data the TA recorded from those earthquakes provide a unique opportunity to study attenuation of the Lg phase in the mid-continent and Gulf Coastal region. The TA data reveal previously unrecognized regional variability of ground motion propagation in the central United States. A study of the Fourier amplitude spectra shows the Lg phase exhibiting strong attenuation for ray paths from Arkansas, southwest through the Ouachita Orogenic Belt and into central Texas, and south into the Gulf Coastal region. Less attenuation is seen in central Texas for ray paths extending directly south from Oklahoma, though attenuation remains strong along the Gulf Coast. In contrast, ray paths to the north, regardless of source location, exhibit very little attenuation, especially in northern Missouri and southern Iowa. Regression models that incorporate near-receiver (distance-independent) attenuation due to thick sediments in the Gulf Coastal Plain successfully reduce path-related bias in the regression residuals for stations near the Gulf Coast. Dividing the central United States into three regions (the Gulf Coastal Plain, the Great Plains and the Midwest) further reduced bias, and allowed for the development of Q models in the Gulf Coastal Plain and the Great Plains. In the Gulf Coastal Plain, the Q model for that part of the ray path through the basement, from the earthquake to the base of the sediment deposits below the receiver, was found to be Q=(295±11)*f^(0.645±0.029). The model for attenuation in the sediment section near the receiver in the Gulf Coastal Plain is Q=(72±6.7)*f^(0.32±0.06) (velocity through the sediments is unconfirmed but thought to be approximately 1 km/s). The Q model for the Great Plains is  Q=(692±61.3)*f^(0.43±0.07). The Midwest region exhibited extremely complicated behavior: the data indicate little or no attenuation of amplitudes in the frequency band from approximately 0.7 to 2.0 Hz. As a consequence, Q in the Midwest region in that frequency range could not be realistically determined. / Master of Science

Coastal counties make up only 17% of the land area in the continental United States, yet 53% of the nation’s population resides in these locations. With sea level rise, erosion, and human disturbances all effecting coastal areas, researchers are working to find strategies to protect and stabilize current and future shorelines. In order to maintain shoreline stability while maintaining intertidal habitat, multipurpose living shorelines have been developed to mimic natural shoreline assemblages while preventing erosion. This project determined the effectiveness of a living shoreline stabilization containing Crassostrea virginica (eastern oyster) and Spartina alterniflora (smooth cordgrass) in the field and through controlled wave tank experiments. First, fringing oyster reefs constructed of stabilized oyster shell and smooth cordgrass plugs were placed along three eroding shoreline areas (shell middens) within Canaveral National Seashore (CANA), New Smyrna Beach, FL. For each shell midden site, four treatments (bare shoreline control, oyster shell only, S. alterniflora only, and oyster shell + S. alterniflora) were tested in replicate 3.5 x 3.5 meter areas in the lower and middle intertidal zones. Each treatment was replicated five times at each site; erosion stakes within each replicate allowed measurement of changes in sedimentation. After one year in the field, the living shoreline treatments that contained oyster shells (oyster shell only and oyster shell + S. alterniflora) vertically accreted on average 4.9 cm of sediment at two of the sites, and an average of 2.9 cm of sediment at the third, while the controls lost an average of 0.5 cm of sediment. S. alterniflora did not significantly contribute to the accretion at any site due to seagrass wrack covering and killing plants within one month of deployment. Next, the reduction in wave energy caused by these living shoreline stabilization techniques relative to bare sediment (control) was quantified. The energy reduction immediately after deployment, and the change in energy reduction when S. alterniflora had been allowed to grow for one year, and the stabilized shell was able to recruit oysters for one year was tested. Laboratory experiments were conducted in a nine-meter long wave tank using capacitance wave gauges to ultimately measure changes in wave height before and after treatments. Wave energy was calculated for each newly deployed and one-year old shoreline stabilization treatment. Boat wake characteristics from CANA shorelines were measured in the field and used as inputs to drive the physical modeling. Likewise, in the wave tank, the topography adjacent to the shell midden sites was measured and replicated. Oyster shell plus S. alterniflora attenuated significantly more wave energy than either the shells or plants alone. Also, one-year old treatments attenuated significantly more energy than the newly deployed treatments. The combination of one-year old S. alterniflora plus live oysters reduced 67% of the wave energy. With the information gathered from both the field and wave experiments, CANA chose to utilize living shorelines to stabilize three shell middens within the park. Oyster shell, marsh grass and two types of mangroves (Rhizophora mangle, Avicennia germinans) were deployed on the intertidal zones of the eroding middens. Significant accretion occurred at all middens. Two sites (Castle Windy and Garver Island) vertically accreted an average 2.3 cm of sediment after nine months, and six months respectively, and the other site (Hong Kong) received on average 1.6 cm of sediment after six months. All control areas (no stabilization) experienced sediment loss, with erosion up to 5.01 cm at Hong Kong. Plant survival was low ( < 20%) at Castle Windy and Garver Island, while Hong Kong had moderate survival (48-65%). Of the surviving marsh iv grass and mangroves on the three sites, almost all ( > 85%) had documented growth in the form of increased height or the production on new shoots. Landowners facing shoreline erosion issues, including park managers at CANA, can use this information in the future to create effective shoreline stabilization protocols. Even though the techniques will vary from location to location, the overall goal of wave attenuation while maintaining shoreline habitat remains. As the research associated with the effectiveness of living shorelines increases, we hope to see more landowners and land managers utilize this form of soft stabilization to armor shorelines.