Shallow Water Conditions Research Articles

Shallow water effect of tandem flapping foils on renewable energy production

ABSTRACTStudies about the flapping foil hydrokinetics turbines, as a new method to extract energy from incoming flow field, have recently increased significantly. Studies on the effect of shallow water conditions on the performance of the turbine have not been seen so far. This study investigates the effect of working environment on the performance of flapping foil hydrokinetic turbine. The unsteady and incompressible flow around two flapping foils in tandem operate in shallow water is simulated using Computational Fluid Dynamic (CFD) method. The results of shallow water conditions are compared with deep-water case. It is observed that the shallow water condition heavily affects the performance of the system and the total efficiency decreases considerably. Particularly, when the kinematic parameters are optimum for performance, the total power extraction efficiency of the system for h0 = 6c, h0 = 3c and h0 = 1.5c has a reduction of 7.24, 8.5, and 10.14%, respectively, compared with deep-water case. The interaction between the boundary layer of the sea floor and the flapping foils was found to be the main factor of efficiency reduction.

Paleoclimate reconstruction and mire development in the Eastern Great Hungarian Plain for the last 20,000 years

We present the reconstruction of mire vegetation changes and fire history recorded in a continuous sediment profile that spans the last 20,000 cal yr BP from the Late Pleniglacial to Holocene in North-eastern Hungary. We also aimed to reveal past climate changes by using ecological requirements of specific aquatic plants as summer temperature indicators. Our results suggest the formation of a mesotrophic mire around 20,000 cal yr BP with brown moss, Betula sp. and Selaginella selaginoides cover beside the occurrence of Phragmites australis, Typha latifolia and T. angustifolia suggesting base-rich fen and tundra-like wet-ground habitats on the lakeshore. This community shifted to reed dominated swamp at c. 18,300 cal yr BP with inferred min. July temperatures of 12–15.7 °C. pinus sp., Betula nana, B. pendula/pubescens, Hippuris vulgaris and P. australis dominated until 16,600 cal yr BP pointing to shallow muddy stagnant water and colder climatic conditions than in the preceding interval. The most warmth-demanding species, T. latifolia and T. angustifolia indicated July mean temperatures >14–15.7 °C soon after the LGM. The formation of biogenic carbonate also started at an early stage; major accumulation occurred between 15,200 and 10,000 cal yr BP. In the Early Holocene, environmental indicator species (e.g., Phragmites australis and T. latifolia) pointed to warmer and shallower conditions, while the late Holocene was characterized by strong eutrophication and reed swamp dominance on the lakeshore. Elevated macrocharcoal concentration, wood fragments and remains of Typha species suggested frequent local fires and dry mire surface conditions during the last 1700 years.

Sedimentology, geochemistry and reservoir potential of the organic-rich Qusaiba Shale, Tabuk Basin, NW Saudi Arabia

Abstract The Qusaiba Shale Formation of the Qalibah Group is the most prolific source rock for the Paleozoic petroleum system in Saudi Arabia and is recently considered as a potential unconventional shale gas reservoir. Detailed sedimentological, petrographical, and geochemical analyses were undertaken on an ~31 m thick outcrop of this organic-rich shale exposed in the northwest of Tayma City, NW of Saudi Arabia to provide a better understanding of the vertical and lateral lithofacies variations and the effects of such variations on reservoir properties. X-ray diffraction analysis reveals that clay minerals (average: 50%) and quartz (average: 28%) dominate the bulk mineralogical composition while K-feldspar, plagioclase, and pyrite occur as common to minor components in the analyzed samples. An integration of the sedimentological description, petrography and mineralogical composition allows the subdivision of the investigated outcrop section into six lithofacies. These are: Laminated organic-rich shale, Graptolitic concretion, Massive organic-rich shale, Organic-lean shale, Siltstone-shale interbedded, and Cross-stratified siltstone/sandstone lithofacies. TOC content in the laminated and massive organic-rich shale lithofacies ranges between 0.5 and 6.1 wt% (average 2.52 wt%) then it decreases upward (0.04–0.35 wt%, average 0.18 wt%) in the overlying organic-lean shale and siltstone lithofacies. Trace elements (Cu, Mo, As, Ni, Co, U and V) show positive excursions in the lowermost 20 m of the organic-rich, dark-grey shale interval and display abrupt depletions at the contact with overlying organic-lean shale. The enrichment factors of these trace elements are characterized by similar distribution patterns as their measured concentrations. Like the elements, these factors also exhibit a significant depletion at the contact between the organic-rich shale and the overlying organic-lean shale. Out of all the redox indices, V/(V + Cr), V/(V + Ni), Th/U and [Mo]s/TOC were found to best distinguish between the organic-rich and the overlying organic-lean intervals. The laminated organic-rich shale lithofacies indicate deposition of hemipelagic sediments by a relatively low energy quiet anoxic bottom water, most likely in a sulfidic conditions that were associated with a strongly restricted bottom water mass circulation at the time of its deposition. This restricted hydrographic condition was likely enhanced in the study area due to the paleotopography that was created by the deglaciation of the Early Silurian time. The TOC richness, common occurrence of pyrite and high enrichment of redox elements Mo, U and V in the organic-rich shale intervals support the existence of anoxic bottom water at the time of deposition. The abrupt decrease of the TOC and the redox sensitive elements and their associated indices from the underlying organic-rich lithofacies to the overlying organic-lean shale lithofacies is likely due to a gradual increase in oxygen level. This improved bottom water oxygenation condition might have led to a reduction in organic productivity and limited organic matter preservation in the organic-lean shale lithofacies. The graptolitic concretion lithofacies found in the sequence, refers to an in-situ, syngenetic to early diagenetic origin formed close to the sediment-water layer when there was little or no deposition or at periods characterized by low sedimentation rates. The siltstone - fine sandstone lithofacies in the topmost part of the studied section, is interpreted to indicate the dominance of high energy and highly oxygenated shallow bottom water conditions during deposition, probably in a middle to inner shelf depositional settings. The kerogen in QS is a mixture of type III (gas prone) and type IV (inert kerogen), Tmax values with an average of 430 °C, and VRo values (average 0.58) calculated from the Tmax, assigned the studied section as immature. Qualitative evaluation of porosity allows the identification of three different types of porosity including inorganic porosity, organic porosity and natural fracture porosity. Although the ductile clay minerals are the most abundant minerals in the lower part of the studied QS (average 56%), the brittle minerals (Quartz, Feldspar, and Pyrite) form an average of 42% and exhibit a uniform distribution of brittleness in the organic-rich interval.

Increasing flooding tolerance in rice: combining tolerance of submergence and of stagnant flooding.

Rice ecosystems in the tropical coastal areas are subject to two types of flooding stress: transient complete submergence and long-term water stagnation (stagnant flooding). Here, we aimed to dissect the mechanisms for stagnant flooding tolerance of rice genotypes carrying SUB1, a quantitative trait locus for submergence tolerance. We screened 80 elite genotypes under stagnant flooding stress in the lowland rice fields in the wet and dry seasons, and examined the tolerance mechanisms of promising genotypes for the two following seasons. Yield reduction under stagnant flooding averaged 48 % in the dry season and 89 % in the wet season. Elite genotypes carrying SUB1 showed 49 % lower yield than those without SUB1 under stagnant flooding, with no differences under shallow water conditions. However, we identified a few high-yielding Sub1 genotypes that were as tolerant of stagnant flooding as a reference genotype that lacked SUB1. These genotypes had intermediate stature with more shoot elongation in response to rising water than a moderately tolerant Sub1 reference variety, resulting in greater canopy expansion and higher yield. It was important to increase lodging resistance, since plant height >140 cm increased lodging under stagnant flooding. The culm diameter was closely associated with culm strength; reduced aerenchyma formation and increased lignin accumulation in the culm should increase lodging resistance. The study demonstrated a successful combination of submergence and stagnant flooding tolerance in a rice breeding programme, and identified elite Sub1 genotypes that also tolerate stagnant flooding. Our results will support genetic improvement of Sub1 varieties for stagnant flooding tolerance.

The heterogeneity of mudflat erodibility

The prediction of the erosion of mudflats is hampered by inaccurate estimates of the erodibility distribution of the sediment bed. To investigate how erodibility varies in space and what the vertical distribution over the sediment depth is, comprehensive observations of the sediment properties, hydrodynamics and bed-level changes were conducted on an intertidal flat in the Western Scheldt Estuary, the Netherlands. The erosion potential on a mudflat is determined by the critical shear stress for erosion (τe), erosion rate coefficient (M) and local hydrodynamic conditions. A clear difference in hydrodynamic forcing was observed, leading to significant bed level variations at the low water line, where erosion often occurs during very shallow water condition, and a nearly constant bed level at the upper part. The erosion parameters τe and M could be determined over a sediment bed of 12 cm at the low water line. The erosion coefficient M can be considered constant with depth, although there is a large spreading. A clear vertical variation of τe was found: τe increased significantly downward from 0.10 Pa at the sediment surface to 1.13 Pa at 12 cm below the surface. Additionally, there was a strong indication that the presence of diatoms enhanced τe in the upper 2 mm of sediment by five times of the abiotic τe (from 0.09 Pa to 0.46 Pa). These findings lead to the following improvement for predicting morphological changes of tidal mudflats: (1) very shallow conditions should be better simulated, (2) the vertical distribution of τe should be considered. Otherwise, erosion rates can be overestimated, especially during extreme events, because exposure of the deeper well-consolidated layer likely occurs; and (3) an appropriate description of the effect of diatoms should be considered as part of the bottom boundary condition.

Rapid Intensification of Typhoon Hato (2017) over Shallow Water

On 23 August, 2017, Typhoon Hato rapidly intensified by 10 kt within 3 h just prior to landfall in the city of Macau along the South China coast. Hato’s surface winds in excess of 50 m s−1 devastated the city, causing unprecedented damage and social impact. This study reveals that anomalously warm ocean conditions in the nearshore shallow water (depth < 30 m) likely played a key role in Hato’s fast intensification. In particular, cooling of the sea surface temperature (SST) generated by Hato at the critical landfall point was estimated to be only 0.1–0.5 °C. The results from both a simple ocean mixing scheme and full dynamical ocean model indicate that SST cooling was minimized in the shallow coastal waters due to a lack of cool water at depth. Given the nearly invariant SST in the coastal waters, we estimate a large amount of heat flux, i.e., 1.9k W m−2, during the landfall period. Experiments indicate that in the absence of shallow bathymetry, and thus, if nominal cool water had been available for vertical mixing, the SST cooling would have been enhanced from 0.1 °C to 1.4 °C, and sea to air heat flux reduced by about a quarter. Numerical simulations with an atmospheric model suggest that the intensity of Hato was very sensitive to air-sea heat flux in the coastal region, indicating the critical importance of coastal ocean hydrography.

Depositional environment and organic matter enrichment of the lower Cambrian Niutitang shale in western Hubei Province, South China

Abstract It is important to consider the influences of depositional environment on lithofacies characteristics, lithofacies distribution patterns, and organic matter enrichment when defining reservoir properties and predicting “favorable reservoirs” and “sweet spots”. In this study, we examined the Niutitang shale of the early Cambrian Niutitang Formation in western Hubei Province, middle Yangtze Block, to understand how depositional environment controlled organic matter accumulation in the Niutitang shale. Through a combination of detailed sedimentologic investigations with geochemical analyses, we identified four primary lithofacies, siliceous shale, siliceous-clay mixed shale, calcareous shale, and argillaceous shale, from the Y1 drill core. The sedimentological analyses, including systematic observations of the color of fresh rocks, grain size, sedimentary textures and structures, biogenic and diagenetic (e.g., veins and pyrite) characteristics in cores and thin sections with mineralogical analyses by X-ray diffraction (XRD), and changes in geochemical proxies, including TOC (wt.%), Mo EF , U EF , Ni/Al and Zn/Al, suggest that siliceous shale and siliceous-clay mixed shale were deposited in euxinic and anoxic deep water with high surficial paleoproductivity which primarily controlled by long term global sea level changes, and that the calcareous shale and argillaceous shale were deposited in shallow and oxygen-rich water conditions with low energy and low paleoproductivity in the surface water. The Niutitang shale changed from the siliceous shale-dominated lithofacies association (LA1), to the argillaceous shale-dominated lithofacies association (LA2), and then back to the siliceous shale-dominated lithofacies association (LA1), suggesting a variation of sedimentary environment from euxinic–anoxic deep-water environment (highstand), to relatively oxic and shallow water environment (lowstand), and then back to euxinic–anoxic deep-water environment (highstand). This may reflect changes in sea level and mechanisms of organic matter enrichment during sea level highstand and lowstand. The low Mo/TOC values of the siliceous shale and siliceous-clay mixed shale lithofacies are similar to the Mo/TOC values of marine sediments in Framvaren Fjord, suggesting that the study area was located in a moderately restricted basin during deposition of the Niutitang shale. The Fe/Ti and Al/(Al + Fe) ratios and the Al–Fe–Mn diagram combined with our detailed petrographic studies and the good correlation between TOC and quartz contents are indicative of a mainly biogenic origin with a minor detrital source for the silica in the Niutitang shale. TOC is well correlated to Mo EF , U EF , Ni/Al and Zn/Al values in LA1, but it is only moderately correlated to Mo EF and U EF values and weakly correlated to Ni/Al and Zn/Al values in LA2. The correlation relationships suggest that good preservation in euxinic–anoxic water conditions and high primary paleoproductivity were the major controlling factors of organic matter enrichment, whereas organic matter accumulation during sea level lowstand was mainly controlled by water redox conditions because primary paleoproductivity remained persistently low in the more restricted basin with shallow water and limited nutrient upwelling. The correlations between TOC content and clay minerals within the different lithofacies associations suggest that adsorption of carbon components by clay minerals promoted the accumulation of organic matter to various extents in LA2 but probably did not impact organic matter enrichment in LA1.

An Autonomous Combined Receiving Acoustic System Based on a Three-Component Vector Receiver and a Hydrophone

A hydroacoustic autonomous receiving system that uses a combined receiver has been developed for carrying out investigations of the vector−scalar structure of acoustic fields under shallow water conditions with a submersion depth as large as 100 m. The acoustic fields are investigated by measuring the acoustic pressure and three orthogonal components of oscillatory acceleration using sensors with a sensitivity of 150−180 μV/Pa. In addition, data on the spatial position of the system from the orientation and depth sensors are synchronously recorded and, together with the data from acoustic channels, are saved to an SD card.

Productivity controls on the redox variation in the southeastern Arabian Sea sediments during the past 18 kyr

Redox-sensitive elements (uranium, molybdenum and cadmium) and productivity proxies (total organic carbon, calcium carbonate and phosphorous) were analysed to assess the importance of productivity on redox variation for the last ∼18 kyr in a sediment core off Cochin at a water depth of 280 m in the southeastern Arabian Sea. These proxies document a combination of higher productivity and intense suboxic conditions during the last deglaciation (∼18–13 kyr) and late Holocene (5.5 kyr to Present) versus lower productivity and less suboxic conditions between these intervals (∼13–5.5 kyr). The productivity and redox proxies behave similar to one another suggesting that the variations in productivity controlled the redox conditions. This relationship is supported by patterns during the last deglaciation, when a decrease in productivity at ∼16 kyr preceded improved deep water oxygenation by ∼14 kyr. Therefore, productivity changes were responsible for the development of reducing conditions in shallow waters in the southeastern Arabian Sea.

Experimental studies of a damaged ship section in forced heave motion

This work documents a detailed series of experiments performed in a wave flume on a thin walled prismatic hull form. The model consists of a rectangular opening located on the side. The length of the model is slightly smaller than the flume breadth to achieve two-dimensional (2D) behavior in the experiments. Forced oscillatory heave tests in calm water have been carried out by varying the model-motion parameters and examining both intact and damaged conditions. Video recordings, measurements of the wave elevation inside the damaged compartment and of the force on the model were performed in all the experiments. The effect of damage opening in the model on hydrodynamic loads is examined by comparing with an intact section. A theoretical analysis is used to explain the behavior of added mass and damping coefficients in heave for a 2D damaged section. The presented results demonstrate occurrence of sloshing and piston mode resonances in the tests and their influence on the hydrodynamics loads of a damaged ship. Detailed physical investigations are presented at these resonance frequencies for the damaged section. Effect of filling level in the damage compartment, damage-opening length and air compressibility in the airtight compartment is examined. Nonlinear effects are documented and appear dominant, especially, for lowest filling level where we have shallow-water depth conditions in the damaged compartment. Resonance phenomena that can lead to significant local loads are identified for the shallow water condition. Air compressibility in the airtight compartment and floodwater act as a coupled system and influence inflow/outflow of floodwater in the compartment. It has a significant effect on local floodwater behavior in the damaged compartment.

Classification of bore patterns induced by storm waves overtopping a dike crest and their impact types on dike mounted vertical walls – a large-scale model study

ABSTRACTShort duration bores in the coastal zone are generated by wave breaking in shallow water and mild foreshore conditions. In storm weather situations and for sea level rise scenarios, these bores approach the dike and interact with previously overtopped or reflected bores. Combined laser scanner and video measurements were used to study the complex and turbulent bore interaction processes. Five bore interaction patterns were distinguished as (1) regular bore pattern; (2) collision bore pattern; (3) plunging breaking bore pattern; (4) sequential overtopping bore pattern, and (5) catch-up bore pattern. Video images of the bore running up the wall and motion tracking of the leading edge were used to obtain a time series of the run-up water at the wall. The impact loads of the bore hitting the wall on the promenade were studied based on the signal of a vertical array of 13 pressure sensors installed over the wall height. Three impact types were distinguished and classified as (1) impulsive impact type; (2) dynamic impact type; and (3) quasi-static impact type. The majority of ~2/3 of the total number of impacts were comprised of the quasi-static impact type.

РЕЗУЛЬТАТЫ ЭКСПЕРИМЕНТАЛЬНЫХ ГИДРОАКУСТИЧЕСКИХ ИССЛЕДОВАНИЙ ПО ОЦЕНКЕ ПРОСТРАНСТВЕННОГО РАСПРЕДЕЛЕНИЯ СЕГОЛЕТОК ОСЕТРОВЫХ РЫБ В МЕЛКОВОДНОЙ ЧАСТИ СЕВЕРНОГО КАСПИЯ В 2017 ГОДУ

Since 2005, in the Russian part of the Northern Caspian, Caspian Research Institute of Fisheries has been conducting trawl-acoustic surveys to solve problems in determining the density, biomass and seasonal dynamics of commercial marine fish species. Recently, special attention has been paid to the estimation of the number of sturgeon fishes and their juveniles due to a sharp decrease in the concentrations of these fish in the areas of traditional trawl-acoustic surveys. Until 2015, sonar studies were carried out with the help of a fishfinder echosounder - a video plotter PEV-K, created in the Design Bureau of Marine Electronics “Vector” (Taganrog, Russia). Taking into account the shallow water of the Northern Caspian (depth 3-10 m), this echo sounder of the vertical location gave an insufficiently qualitative quantitative estimate of marine fish concentrations. According to the latest works in the field of acoustics on shallow water bodies, significant shortcomings in the use of vertical echolocation only have been identified, due to a significant underestimation of fish in the near-surface layer in shallow water conditions. It is proved that the most optimal alternative for conducting trawl-acoustic surveys is the simultaneous use of vertical and horizontal echolocation. Solving the actual problems of obtaining representative acoustic data, Caspian Research Institute of Fisheries acquired EY-60 hydroacoustic complex from “Simrad”, using the complex allows simultaneous horizontal and vertical echolocation. Within 2015-2017, with the help of this complex, a survey considering sturgeon yearlings was regularly conducted in the Northern Caspian.

An investigation into the effects of increasing salinity on photosynthesis in freshwater unicellular cyanobacteria during the late Archaean.

The oldest species of bacteria capable of oxygenic photosynthesis today are the freshwater Cyanobacteria Gloeobacter spp., belonging to the class Oxyphotobacteria. Several modern molecular evolutionary studies support the freshwater origin of cyanobacteria during the Archaean and their subsequent acquisition of salt tolerance mechanisms necessary for their expansion into the marine environment. This study investigated the effect of a sudden washout event from a freshwater location into either a brackish or marine environment on the photosynthetic efficiency of two unicellular freshwater cyanobacteria: the salt-tolerant Chroococcidiopsis thermalis PCC7203 and the cyanobacterial phylogenetic root species, Gloeobacter violaceus PCC7421. Strains were cultured under present atmospheric levels (PAL) of CO2 or an atmosphere containing elevated levels of CO2 and reduced O2 (eCO2 rO2 ) in simulated shallow water or terrestrial environmental conditions. Both strains exhibited a reduction in growth rates and gross photosynthesis, accompanied by significant reductions in chlorophyll a content, in brackish water, with only C.thermalis able to grow at marine salinity levels. While the experimental atmosphere caused a significant increase in gross photosynthesis rates in both strains, it did not increase their growth rates, nor the amount of O2 released. The differences in growth responses to increasing salinities could be attributed to genetic differences, with C.thermalis carrying additional genes for trehalose synthesis. This study demonstrates that, if cyanobacteria did evolve in a freshwater environment, they would have been capable of withstanding a sudden washout into increasingly saline environments. Both C.thermalis and G.violaceus continued to grow and photosynthesise, albeit at diminished rates, in brackish water, thereby providing a route for the evolution of open ocean-dwelling strains, necessary for the oxygenation of the Earth's atmosphere.

Turonian–Coniacian (Upper Cretaceous) of the Babadag Basin (North Dobrogea, Romania): integrated biostratigraphy and microfacies succession

The Upper Turonian to Middle Coniacian (Upper Cretaceous) succession of the Babadag Basin (North Dobrogea, Romania) constitutes an apparently continuous fossiliferous carbonate succession. The presence of moderately rich inoceramid, ammonite and foraminiferal assemblages allows for the application of a precise biostratigraphic subdivision. The palaeoenvironmental conditions and evolution of the Babadag Basin during the Late Turonian–Middle Coniacian are inferred using microfacies analysis and foraminiferal spectra. Together, these suggest the Turonian–Coniacian Badabag Basin reflects relatively shallow-water conditions in a near-shore environment, punctuated by two regression events in the Late Turonian and in the Middle Coniacian.

Validation of a three-dimensional depth-semi-averaged model

The present work completes the validation of the depth-semi-averaged model defined in Antuono et al. [“A depth semi-averaged model for coastal dynamics,” Phys. Fluids 29, 056603 (2017)] providing a numerical implementation in three spatial dimensions. In particular, the model is aimed at describing a wide variety of phenomena typical of the coastal region, as for example nonlinear interaction between waves and the bottom bathymetry (diffraction/refraction phenomena), dispersion effects, and beach inundation. To this purpose, the proposed scheme is tested against benchmark experimental data available in the literature for wave propagation problems in both intermediate and shallow water conditions. A final simulation is carried out by considering a tsunami wave running over a prototype bathymetry resembling a bay-promontory coastline. Different widths of the bay have been considered, describing their influence on the run-up dynamics.

Photoacclimation and induction of light-enhanced calcification in the mesophotic coral Euphyllia paradivisa.

Corals and their photosymbionts experience inherent changes in light along depth gradients, leading them to have evolved several well-investigated photoacclimation strategies. As coral calcification is influenced by light (a process described as LEC—‘light-enhanced calcification’), studies have sought to determine the link between photosynthesis and calcification, but many puzzling aspects still persist. Here, we examine the physiology of Euphyllia paradivisa, a coral species found at a wide range of depths but that is strictly mesophotic in the Red Sea; and also examines the coupling between photosynthesis and LEC by investigating the response of the coral under several controlled light regimes during a long-term experiment. E. paradivisa specimens were collected from 40 to 50 m depth and incubated under three light conditions for a period of 1 year: full-spectrum shallow-water light (approx. 3 m, e.g. shallow-light treatment); blue deep-water light (approx. 40 m, e.g. mesophotic-light treatment) or total darkness (e.g. dark treatment). Net photosynthesis remained similar in the shallow-light-treated corals compared to the mesophotic-light-treated corals, under both low and high light. However, calcification increased dramatically with increasing light intensity in the shallow-light-treated corals, suggesting a decoupling between these processes. Photoacclimation to shallow-water conditions was indicated by enhanced respiration, a higher density of zooxanthellae per polyp and lower chlorophyll a content per cell. The dark-treated corals became completely bleached but did not lower their metabolism below that of the mesophotic-light-treated corals. No Symbiodinium clade shift was found following the year-long light treatments. We conclude that E. paradivisa, and its original symbiont clade, can adapt to various light conditions by controlling its metabolic rate and growth energy investment, and consequently induce LEC.

In situgranulation by thermal stress during subaqueous volcanic eruptions

Some of the most complex volcanic thermodynamic processes occur when erupting magma interacts with water. In shallow water, “Surtseyan” eruptions are spectacular, and they efficiently fragment magma into fine ash particles. The aviation hazard from these eruptions depends the amount of transportable fine ash that is generated and whether it is aggregated into particle coatings or accretions. To investigate both mechanisms, we analyzed ash-encased lapilli from the Surtseyan eruptions of Capelinhos (Azores, 1957–1958) and Hunga Tonga–Hunga Ha’apai (Tonga, 2014–2015) using X-ray computed microtomography and electron microscopy. We discovered pyroclasts that were not coated, sensu stricto, but had enveloping ash produced by in situ granulation of the particle surface. This was caused by thermal stress as pyroclasts briefly traveled through water and were quenched during eruption. In situ granulation is thus an important secondary disruption process in shallow subaqueous eruptions. Our results imply that ash encasement is not always evidence of particle aggregation and accretion, but it may also result from new ash formation. Shallow-water conditions produce the most efficient ash-generation conditions, leading to the greatest hazard to downwind populations and air traffic.

Experimental investigation of free-running ship manoeuvers under extreme shallow water conditions

We present an experimental investigation of a free-running manoeuvring inland waterway ship at extreme shallow water conditions. Physical tests of zig-zag manoeuvres at two different water depths were performed in model scale and investigated with regards to the effects of limited under-keel clearance. Experimental data comprise results from repeatability studies and may serve for validation of manoeuvring simulations.

Energy Consumption in Relay Underwater Acoustic Sensor Networks for NDN

In recent years, a typical representation of the next-generation Internet architecture, named data networking (NDN), and a critical form of the underwater Internet of Things (IoT), underwater acoustic sensor networks (UASNs), have attracted widespread attention in academia. Meanwhile, since the battery energy of the sensor node is limited and the battery is difficult to replace or recharge in underwater environments, extending the networks' lifetime has become a key issue in UASNs. In this paper, we try to deploy a UASN on NDN architecture and explore the energy consumption of the NDN-based UASN under shallow water and deep water conditions based on the relay network topology. A simulation is carried out to compare the delay performance of NDN-based and IP-based UASNs and validate the result. It is believed that the study could provide a theoretical criterion for the selection of the direct or relay path to optimize energy consumption in the future deployment of NDN-based UASNs.

GENERATION OF EXTREME TRANSIENT WAVES IN EXPERIMENTAL MODELS

The transfer of natural waves and sea states into small- and large-scale model teste contributes to the proper design of offshore and coastal structure. Such shallow-water ocean surface waves are highly nonlinear and subject to wave transformation and nonlinear wave-wave interactions. However, the standard methods of wave generation according to conventional wave theories and wave analysis methods are limited to simple regular waves, simple sea states and low-order wave generation without considering the nonlinear wave-wave interactions. The research project Generation of Extreme Transient Waves in Experimental Models (ExTraWaG) aims to accurately generate target transient wave profile at a pre-defined position in the wave flume (transfer point) under shallow water conditions. For this purpose, the KdV-based nonlinear Fourier transform is introduced as a continuative wave analysis method and is applied to investigate the nonlinear spectral character of experimental wave data. Furthermore, the method is applied to generate transient nonlinear waves as specific locations in the wave flume, considering the nonlinear transformation and interactions of the propagating waves.