Shallow Water Research Articles

Single-hydrophone-based passive localization for vertically moving targets in shallow water

In this article, we consider underwater passive localization for vertically moving targets in shallow water. A method that utilizes parameters derived from interference structures is introduced, which enables the implementation of both range and depth estimations for targets with a single hydrophone. Underwater moving targets radiate broadband continuous spectrum signals by forming multipath signals through interface reflections, resulting in stable interference structures in the time-frequency domain of the received signals. Ray theory is utilized to derive the trajectory equations of the interference fringes. Considering the periodic characteristics of interference structures, a specialized homomorphic filter is designed to effectively restore the peaks of the fringes to reduce localization errors. Furthermore, with a priori information on the target's initial depth, the Hough Transform is used to extract the target's location information within interference fringes formed by direct signal and surface-reflected signal. Addressing the issue of multi-peaks in parameter domain, parameter information across multiple fringes is fused. The effectiveness and robustness of the proposed method have been demonstrated through numerical simulations, lake trial, and error assessments, even when underwater environments information is not precisely known.

Numerical simulation study on ship manoeuvrability in mountainous rivers: Comprehensively considering effects of nonuniform flow, shallow water, narrow banks, winds and waves

Ships navigating inland waterways, especially mountainous waterways, may encounter complex navigation environments. Under these circumstances, the force of the ship is extremely complex, the attitude of the ship may be unstable, and the control performance may decrease, possibly resulting in marine accidents. In this study, a modular-type manoeuvring model (MMG) is used to develop a ship manoeuvring model that comprehensively considers multiple factors. Based on this model, numerical simulations are conducted on the ship Seiun Maru, and Esso Osaka; the simulation results are found to be in good agreement with the results of real ship motions. Then, numerical simulations are conducted on the navigation of a 500-ton ship in a typical mountainous waterway, the Suoluo Rapids in the Lancang River, and the impact of the complex environment in this area on the safety of ship navigation is explored. The results reveal that ignoring the influence of environmental factors may put ships in dangerous situations when navigating mountain waterways. In addition, the model can effectively simulate the manoeuvring motion of a ship in a typical mountain waterway, and the calculation cost is negligible. This study provides valuable suggestions for long-distance ship manoeuvring in complex inland river environments.

Detached eddy simulation of hydrokinetic turbine wake in shallow water depths

Detached eddy simulations (DES) have been performed for flow over a solitary hydrokinetic turbine for two different tip-speed ratios λ = 3.64 and 6.15 and three different tip-clearances (δ = 0.1D, 0.2D, and 0.35D) to elucidate the effect of air-water interface on the turbine performance and wake recovery in shallow water conditions. The power predictions show good agreement with experimental data for λ = 3.64, but a large 12% error for λ = 6.15. The interface introduced unsteadiness in the power predictions, which increased with λ. The interface did not affect the mean power predictions for lower λ significantly, but reduced power for higher λ. The two-phase simulations for λ = 6.15 showed significant improvement in wake deficit and near-wake TKE prediction compared to the single-phase simulations. The improved predictions were identified because the interface causes early tip vortex entanglement and TKE burst. The DES predictions also show turbulence anisotropy maps consistent with the experimental data. Analysis reveals that turbulence is one-dimensional, dominated by streamwise fluctuations behind the blade tip region; two-dimensional, dominated by transverse and spanwise fluctuations in the TKE burst region; and approaches three-dimensional isotropy in the fully developed wake region. Detailed analysis of the vortical structures and wake characteristics reveals that the interface significantly affects the vortex advection, breakdown, and wake evolution. In particular, they enhance the wake deficit, which slows down the advection of the tip vortex filaments, causing an early vortex entanglement. The tip vortices show interaction with vortices generated underneath the interface, but these interactions seem localized. The tip vortex breakdown was identified due to instabilities generated during vortex entanglement and interaction with interface vortices for λ = 6.15 case, and because of tip and root vortex interaction for λ = 3.64. Although the two-phase simulations are encouraging compared to the single-phase case, TKE is still underpredicted in the near-wake region, possibly because of turbulence or rotating interface modeling issues. Two-phase simulations also predict significantly higher swirl, which needs further investigation.

Numerical simulations of dam-break flows of viscoplastic fluids via shallow water equations

Abstract This paper presents simulations of dam-break flows of Herschel–Bulkley viscoplastic fluids over complex topographies using the shallow water equations (SWE). In particular, this study aims to assess the effects of rheological parameters: power-law index (n), consistency index (K), and yield stress ($$\tau _{c}$$ τ c ), on flow height and velocity over different topographies. Three practical examples of dam-break flow cases are considered: a dam-break on an inclined flat surface, a dam-break over a non-flat topography, and a dam-break over a wet bed (downstream containing an initial fluid level). The effects of bed slope and depth ratios (the ratio between upstream and downstream fluid levels) on flow behaviour are also analyzed. The numerical results are compared with experimental data from the literature and are found to be in good agreement. Results show that for both dry and wet bed conditions, the fluid front position, peak height, and mean velocity decrease when any of the three rheological parameters are increased. However, based on a parametric sensitivity analysis, the power-law index appears to be the dominant factor in dictating fluid behaviour. Moreover, by increasing the bed slope and/or depth ratio, the wave-frontal position moves further downstream. Furthermore, the presence of an obstacle is observed to cause the formation of an upsurge that moves in the upstream direction, which increases by increasing any of the three rheological parameters. This study is useful for an in-depth understanding of the effects of rheology on catastrophic gravity-driven flows of non-Newtonian fluids (like lava or mud flows) for risk assessment and mitigation. Graphical abstract

Rapid seagrass meadow expansion in an Indian Ocean bright spot

The areal extent of seagrass meadows is in rapid global decline, yet they provide highly valuable societal benefits. However, their conservation is hindered by data gaps on current and historic spatial extents. Here, we outline an approach for national-scale seagrass mapping and monitoring using an open-source platform (Google Earth Engine) and freely available satellite data (Landsat, Sentinel-2) that can be readily applied in other countries globally. Specifically, we map contemporary (2021) and historical (2000–2021; n = 10 maps) shallow water seagrass extent across the Maldives. We found contemporary Maldivian seagrass extent was ~ 105 km2 (overall accuracy = 82.04%) and, notably, that seagrass area increased threefold between 2000 and 2021 (linear model, + 4.6 km2 year−1, r2 = 0.93, p < 0.001). There was a strongly significant association between seagrass and anthropogenic activity (p < 0.001) that we hypothesize to be driven by nutrient loading and/or altered sediment dynamics (from large scale land reclamation), which would represent a beneficial anthropogenic influence on Maldivian seagrass meadows. National-scale tropical seagrass expansion is unique against the backdrop of global seagrass decline and we therefore highlight the Maldives as a rare global seagrass ‘bright spot’ highly worthy of increased attention across scientific, commercial, and conservation policy contexts.

Representative High-Temperature Hydrothermal Activities in the Himalaya Geothermal Belt (HGB): A Review and Future Perspectives

Southern Tibet and western Yunnan are areas with an intensive distribution of high-temperature geothermal systems in China, as an important part of the Himalayan Geothermal Belt (HGB). In recent decades, China has conducted systematic research on high-temperature geothermal fields such as Yangbajing, Gudui, and Rehai. However, a comprehensive understanding has not yet been formed. The objective of this study was to enhance comprehension of the high-temperature geothermal system in the HGB and to elucidate the hydrogeochemical characteristics of geothermal fluids. This will facilitate the subsequent sustainable development and exploitation of domestic high-temperature hydrothermal geothermal resources. To this end, this study analysed geothermal spring and borehole data from the Yangbajing, Gudui, and Rehai geothermal fields. Based on previous research results, the source, evolution, and reservoir temperature characteristics of geothermal fluids are compared and summarised. The main high-temperature geothermal water in the geothermal field is derived from the deep Cl-Na geothermal fluid. Yangbajing’s and Gudui’s geothermal waters are primarily recharged by snow-melt water, while Rehai’s geothermal water is mainly recharged by local meteoric water. The average mixing ratios of magmatic water in the Yangbajing, Gudui, and Rehai geothermal fields are 17%, 21%, and 22%, respectively. The Yangbajing and Gudui geothermal fields have a relatively closed geological environment, resulting in a stronger water–rock interaction compared to the Rehai geothermal field. As geothermal water rises, it mixes with shallow cold water infiltration. The mixing ratios of cold water in the Yangbajing, Gudui, and Rehai geothermal fields are 60–70%, 40–50%, and 20–40%, respectively. Based on the solute geothermometer calculations, the maximum geothermal reservoir temperatures for Yangbajing, Gudui, and Rehai are 237 °C, 266 °C, and 282 °C, respectively. This study summarises and compares the hydrogeochemical characteristics of three typical high-temperature geothermal fields. The findings provide an important theoretical basis for the development of high-temperature geothermal resources in the Himalayan Geothermal Belt.

Lump Kink interactional and breather-type waves solutions of (3+1)-dimensional shallow water wave dynamical model and its stability with applications

The shallow water equations are used to describe the behavior of water waves in various shallow regions such as coastal areas, lakes, rivers, etc. These equations are derived by making simplifying assumptions about the water depth relative to the wavelength of the waves. In this paper, the generalized exponential rational function method (gERFM) is used to construct novel wave solutions of the (3+1)-dimensional shallow water wave ((3+1)-dSWW) dynamical model. These solutions encompass distinct kinds of waves, such as solitary waves, solitons, Kink and anti-kink solitons, lump Kink interactional waves, traveling breathers-type waves and multi-peak solitons. The dynamical behavior of these wave solutions is discussed, examining the influence of free parameters on the resulting wave shapes. Furthermore, to provide a scientific elucidation of the obtained results, the solutions are presented graphically, making it easy to distinguish the dynamical features, which have practical implications in different areas of applied sciences and engineering. The stability of this dynamical model is revealed via modulational instability analysis, signifying that all analytical results are stable. The obtained results show that the given technique is universal and efficient. Through comparing the projected technique with the existing techniques, the obtained results demonstrate that the given technique is universal, pithy and efficient.

Vertical variations and environmental heterogeneity drove the symphony of periphytic protozoan fauna in marine ecosystems

Periphytic protozoa are esteemed icons of microbial fauna, renowned for their sensitivity and role as robust bioindicators, pivotal for assessing ecosystem stress and anthropogenic impacts on water quality. Despite their significance, research exploring the community dynamics of protozoan fauna across diverse water columns and depths in shallow waters has been notably lacking. This is the first study that examines the symphony of protozoan fauna in different water columns at varying depths (1, 2, 3.5 and 5 m), in South China Sea. Our findings reveal that vertical changes and environmental heterogeneity plays pivotal role in shaping the protozoan community structure, with distinct preferences observed in spirotrichea and phyllopharyngea classes at specific depths. Briefly, diversity metrics (i.e., both alpha and beta) showed significantly steady patterns at 2 m and 3.5 m depths as well as high homogeneity in most of the indices was observed. Co-associations between environmental parameters and protozoan communities demonstrated temperature, dissolved oxygen, salinity, and pH, are significant drivers discriminating species richness and evenness across all water columns. Noteworthy variations of the other environmental parameters such as SiO3–Si, PO4−-P, and NO2––N at 1 m and NO3−–N, and NH4+–N, at greater depths, signal the crucial role of nutrient dynamics in shaping the protozoan communities. Moreover, highly sensitive species like Anteholosticha pulchara, Apokeronopsis crassa, and Aspidisca steini in varying environmental conditions among vertical columns may serve as eco- indicators of water quality. Collectively, this study contributes a thorough comprehension of the fine-scale structure and dynamics of protozoan fauna within marine ecosystems, providing insightful perspectives for ecological and water quality assessment in ever-changing marine environments.

Flow resistance of emergent rigid vegetation in steady flow

Abstract Enhanced understanding of flow resistance in open channels with emergent vegetation is essential for flood management and river ecosystem restoration. The presence of vegetation can significantly alter bed resistance, leading to a challenge in accurately predicting flow discharge, water levels, sediment transport, and bed deformation. Previous studies on vegetated flows have focused on vegetation resistance, on which the impact of vegetation has been ignored or poorly estimated. This study proposes a new analytical model, built upon the momentum conservation law, to predict flow resistance to vegetated zones in a plain bed without bed forms, explicitly quantifying bed resistance and vegetation resistance in a corollary manner. The proposed model is benchmarked against five typical sets of laboratory experiments. It is demonstrated that the present model using a modified logarithmic velocity distribution performs best, whereas that assuming a uniform velocity profile considerably overestimates the vegetation resistance and neglects the effect of vegetation on bed resistance. The ratio of bed resistance to the total resistance is shown to range between 5% and 40%, and it decreases with increasing vegetation density and decreases with water depth. Therefore, bed resistance cannot be ignored when modelling shallow water flow with sparsely distributed vegetation. It is also revealed that vegetation arrangements significantly affect flow resistance, and therefore a model incorporating the effect of vegetation arrangement performs better. Overall, the present model facilitates a viable and promising tool for quantifying flow resistance in emergent vegetated channels.

Application of Laplace Adomian decomposition method for fractional Fokker-Planck equation and time fractional coupled Boussinesq-Burger equations

PurposeFractional Fokker-Planck equation (FFPE) and time fractional coupled Boussinesq-Burger equations (TFCBBEs) play important roles in the fields of solute transport, fluid dynamics, respectively. Although there are many methods for solving the approximate solution, simple and effective methods are more preferred. This paper aims to utilize Laplace Adomian decomposition method (LADM) to construct approximate solutions for these two types of equations and gives some examples of numerical calculations, which can prove the validity of LADM by comparing the error between the calculated results and the exact solution.Design/methodology/approachThis paper analyzes and investigates the time-space fractional partial differential equations based on the LADM method in the sense of Caputo fractional derivative, which is a combination of the Laplace transform and the Adomian decomposition method. LADM method was first proposed by Khuri in 2001. Many partial differential equations which can describe the physical phenomena are solved by applying LADM and it has been used extensively to solve approximate solutions of partial differential and fractional partial differential equations.FindingsThis paper obtained an approximate solution to the FFPE and TFCBBEs by using the LADM. A number of numerical examples and graphs are used to compare the errors between the results and the exact solutions. The results show that LADM is a simple and effective mathematical technique to construct the approximate solutions of nonlinear time-space fractional equations in this work.Originality/valueThis paper verifies the effectiveness of this method by using the LADM to solve the FFPE and TFCBBEs. In addition, these two equations are very meaningful, and this paper will be helpful in the study of atmospheric diffusion, shallow water waves and other areas. And this paper also generalizes the drift and diffusion terms of the FFPE equation to the general form, which provides a great convenience for our future studies.

Measurement-based carbon intensity of US offshore oil and gas production

Abstract The United States (US) produces oil and gas from six offshore regions: the North Slope of Alaska, Cook Inlet in Alaska, offshore California, and three Gulf of Mexico (GOM) sub-regions: state shallow, federal shallow, and deep waters. Measurement-based assessment of direct greenhouse gas emissions from this production can provide real-world information on carbon emissions to inform decisions on current and future production. In evaluating the climate impact of production, the Carbon Intensity (CI, the ratio of greenhouse gases emitted compared to the energy of fuels produced) is often used, though it is rarely quantified with measurements. Here, we complete an observational evaluation of the US offshore sector and present the largest current set of measurement-based CIs. We collected airborne measurements of methane, carbon dioxide, and nitrogen oxides from the North Slope, Cook Inlet, and California and combined with prior GOM results. For Alaska and California, we found emissions agree with facility-level inventories, however, the inventories miss some facilities. The US offshore CI, on a 100-year GWP basis, is 5.7 gCO2e/MJ[4.5, 6.8, 95% confidence interval]. This is greater than double the CI based on the national US inventory, with the discrepancy attributed primarily to methane emissions from GOM shallow waters, with a methane dominated CI of 16[12, 22] for GOM federal shallow waters and 43[25-65] for state shallow waters. Regional intensities vary, with carbon dioxide emissions largely responsible for CI on the North Slope 11[7.5, 15], in Cook Inlet 22[13, 34], offshore California 7.2[3.2, 13], and in GOM deep waters 1.1[1.0, 1.1]. These observations indicate offshore operations outside of the GOM in the US have modest methane emissions, but the CI can still be elevated due to direct carbon dioxide emissions. Accurate assessment of different offshore basins, with differing characteristics and practices, is important for the climate considerations of expanded production.

The effects of intensive trapping on invasive round goby densities.

The round goby (Neogobius melanostomus) is an invasive benthic fish first introduced to the Laurentian Great Lakes in 1990 that has negatively impacted native fishes through increased competition for food and habitat, aggressive interactions, and egg predation. While complete eradication of the round goby is currently not possible, intensive trapping in designated areas during spawning seasons could potentially protect critical native fish spawning habitats. Baited minnow traps were spaced 10 meters apart in shallow water along a 100-meter stretch of shoreline within the Duluth-Superior Harbor during the round goby breeding period (June to October) with captured round gobies removed from interior traps (N = 10) every 48 hours. These traps were bracketed by two pairs of reference traps deployed weekly for 48 hours, from which round gobies were also tagged and released. The number of round gobies captured in the interior traps declined by 67% compared to reference traps over the course of the study, with extended periods of no captures. The tagged round gobies showed high site affinity, with 82.8% of tagged fish recaptured at the previous release site. The results indicate that even at open water sites, which allow natural migration of round gobies into the area, extensive trapping could reduce local population numbers.

Occupancy, movement, and behaviour of namew (lake sturgeon Acipenser fulvescens) in an intact river in Canada

Most sturgeon populations are imperilled and living in fragmented rivers. Here, we studied namew (lake sturgeon Acipenser fulvescens), fish important to Ililiwak (Moose Cree Peoples), in the North French River: a free-flowing, intact river in Kit Aski Nahnuun (the Moose Cree Homeland) in northern Ontario, Canada. This study was co-created alongside members of Moose Cree First Nation and used acoustic telemetry to passively track 20 tagged namew over 6 yr (2016-2022). Namew occupied the entire monitored river reach: about 45 km. Namew used 2 overwintering areas and occupied more overall river sections during spring and summer (out of 6 total seasons often used by Ililiwak). We did not detect namew moving upstream or downstream during freeze-up and winter. Generally, namew showed the greatest acceleration and travelled the longest distances during spring and summer, and they occupied shallower water during summer at lower water levels and deepest waters during freeze-up. We found an interaction between season and diurnal period, where namew occupied shallower depths and had higher acceleration at dawn and night relative to morning and afternoon in most seasons; dusk behaviour was variable among seasons. However, this pattern was absent in spring, when namew showed no diurnal pattern in acceleration and were in shallower water during morning and afternoon. Diurnal patterns were less pronounced, but detectable, during ice-affected seasons. This river provides year-round habitat for namew, and our data reveal distinct patterns of namew occupancy, movement, and behaviour in a free-flowing, intact river. Our work is an example of successfully co-creating research that addresses both scientific and community priorities.

Breaking Wave Statistics In Short-Crested Seas

The accurate prediction of loads to allow for a safe yet efficient design of coastal and offshore structures requires a thorough understanding of the distribution of crest heights. Although deep water waves are relatively well understood and accurately modelled by existing wave and crest height models, the same cannot be said for waves in intermediate and shallow waters (Tayfun &amp; Alkhalidi, 2020). This work addresses this gap by analysing long, random records of laboratory-generated short-crested seas. The analysis focuses on the application of a novel method to identify waves that undergo significant nonlinear amplification and breaking. Following their identification, the associated energy transfers and dissipation are calculated per wave and probabilistically approximated. A modelling suite is proposed to describe the probability of wave breaking and associated dissipation in short-crested seas. This is then converted into a mixture model to recover crest height statistics. The success of the proposed approach is demonstrated through comparisons between model predictions and measurements.

A 2D shallow water flow model with 1D internal boundary condition for subgrid-scale topography

In this work, a dynamic internal boundary condition is used as subgrid model in a two-dimensional (2D) model based on the shallow water equations in order to model narrow regions in the domain. In this way, computational savings are sought, since it is not necessary to discretize these regions with cells of reduced size. The new internal boundary condition simplifies other works where 1D–2D coupled models were presented, since the 1D model is a subgrid for the 2D mesh, so the coupling between both models is simple and direct. The coupling is performed using mass conservation, simplifying the calculation in the transfer between both models. Test cases are studied to validate the implemented boundary condition, and a mountain catchment as a realistic case. The results obtained with a fully 2D mesh and a 2D mesh with rills in narrow regions are very similar, with a large reduction in computational cost when using rills, both in test cases and in the realistic case. Thus, the use of the implemented internal boundary condition is an effective tool to study regions with narrow regions by reducing the computational cost with little loss of accuracy in the results.

Distributed acoustic sensing for seismic surface wave data acquisition in an intertidal environment

The application of distributed acoustic sensing (DAS) for shallow marine seismic investigations is assessed, in particular with respect to the collection of seismic surface wave data in an intertidal setting. Appropriate selection and directional sensitivity of fiber-optic cables is considered and the measured data is validated with respect to conventional seismic data acquisition approaches, using geophones and hydrophones, along with independent borehole and seismic cone penetration test (SCPT) data. In terms of cable selection, a reduction in amplitude and frequency response of an armored cable is observed, when compared with an unarmored cable. For seismic surface wave surveys in an offshore environment where the cable would need to withstand significant stresses, the use of the armored variant with limited loss in frequency response may be acceptable from a practical perspective. The DAS approach also has indicated good consistency with conventional means of surface wave data acquisition, and the inverted [Formula: see text] also is very consistent with downhole SCPT data. Observed differences in phase velocity between high tide (Scholte wave propagation) and low tide (Rayleigh wave propagation) are not thought to be related to the particular type of interface wave due to shallow water depth. These differences are more likely to be related to the development of capillary forces in the partially saturated granular medium at low tide. Overall, this study demonstrates that our novel approach of DAS using seabed fiber-optic cables in the intertidal environment is capable of rapidly providing near-surface S-wave velocity data across considerable spatial scales (multikilometer) at high resolution, which is beneficial for the design of subsea cables routes and landfall locations. The associated reduction in deployment and survey duration, when compared with conventional approaches, is particularly important when working in the marine environment due to potentially short weather windows and expensive downtime.

Open‐source stand‐alone version of atmospheric model Aeolus 2.0 software

AbstractIn this discourse, we present the unveiling of an open‐source software package designed to facilitate engagement with the atmospheric model, Aeolus 2.0. This particular iteration stands as a self‐contained model of intermediate complexity. The model's dynamical core is underpinned by a multi‐layer pseudo‐spectral moist‐convective Thermal Rotating Shallow Water (mcTRSW) model. The pseudo‐spectral problem‐solving tasks are handled by the Dedalus algorithm, acknowledged for its spin‐weighted spherical harmonics. The model captures the temporal and spatial evolution of vertically integrated potential temperature, thickness, water vapour, precipitation, and the intricate influence of bottom topography. It comprehensively characterizes velocity fields in both the lower and upper troposphere, employing resolutions spanning a spectrum from the smooth to the coarse, enabling the exploration of a wide range of dynamic phenomena with varying levels of detail and precision.

Timescale of Groundwater Recharge in High Percolation Coastal Plain Soils

Understanding and modeling the timing and magnitude of groundwater recharge from rainfall infiltration through vadose-zone percolation is important for many reasons but especially because the flux is being acted on by root-zone evapotranspiration (ET), and very little rainfall infiltration ever becomes water-table recharge. This study elaborates on the considerable time of the wetting front’s arrival and ultimate bulk recharge of rainfall infiltration in the shallow water table with fine-sandy soil typical of coastal plain environments such as Florida. Calibrated Hydrus-1D modeling of Florida (Myakka) soil was evaluated at varying depths of the water table and hydraulic conductivities to bracket the timing of arrival of the wetting front and bulk fluxes. Useful normalized timing parameters are defined. In addition, this research further quantifies the concept of “wet equilibrium”, and the considerable vadose-zone storage potential over and above the hydrostatic pressure equilibrium that must be overcome to achieve any significant water-table recharge in typical seasonal hydrologic timescales. The results indicate recharge timescales for water-table depths of 1 m are approximately 1 day but are considerably longer for 2 m (2 weeks), 3 m (1 month), and 4 m (50 days) conditions. Given that daily vadose-zone potential ET demand can exceed 0.5 cm/day in this environment, estimating recharge from rainfall infiltration is likely unreliable unless this timescale and the plant-root-zone uptake processes are properly modeled in surface-groundwater models.

Numerical Tools For Wave Overtopping At Rubble Mound Breakwaters With Submerged Berms

In the era of climate change, the adaptation of existing coastal structures as a response to potential increasing loads, has become a trending topic in coastal engineering. The combination of sea level rise, storm surge, tides and waves is going to dramatically increase the wave overtopping. In this context, this research is focused on the evaluation of wave overtopping for conventional rubble mound breakwaters, modified by the introduction of a submerged berm. Recent studies illustrated how the introduction of emerged berms on the seaward slope reduces the wave overtopping. The goal then becomes to turn the spotlight on the submerged berms, whose effectiveness has yet to be attested, although it has proven useful in reducing wave loads on the armour layer and seabed pressure under the structure. Therefore, the reliability of two different numerical models in detecting overtopping phenomenon have been assessed. IHFOAM and SWASH have been used (see Figure 1). The first one can solve both Reynolds Averaged Navier Stokes and the Volume Averaged Reynolds Averaged Navier–Stokes equations. The second one solves the non-linear shallow water equations with a non-hydrostatic pressure term, representing a simplified form of the Navier-Stokes equations, with associated limited computational cost. The numerical models have been validated based on experimental tests carried out in a wave flume at the University of L’Aquila.

Experimental Test Bench In A Wave Flume For The Development Of A New Mini Morphable Wells Turbine

The aim of this research study is to perform experimental tests on a new morphable mini Wells turbine designed to operate in presence of waves with limited energy content which presents a high frequency of occurrence along the Mediterranean coasts (Corsini et al., 2010). The strengths of these mini Wells turbines are: i) extremely light rotor; ii) no need of actuators to morph the rotor blades; iii) low construction and maintenance costs; iv) capability to produce energy starting from low wave heights in the order of a few decimetres. Furthermore, the small size and low investment costs of the turbine make it particularly suitable to be installed either in existing structures, such as anti-reflective perforated caissons (often used in the Mediterranean harbors), or in devices for coastal defense from erosive phenomena located on shallow water conditions. The need to carry out experimental tests derives from the difficulty of handling in a virtual Computational Fluid Dynamics environment the huge difference in the time scale of the turbine, which spins at 1500-3000 rpm, and the wave periods, in the order of some seconds (Corsini et al., 2012; Barnabei et al., 2020). Properly designed lab tests, executed in controlled conditions with irregular sea states, are therefore mandatory to fully characterize the behavior of morphable Wells turbines to be employed in the Mediterranean Sea, and in particular to assess their self-start capability.