Search Results (43)

This study investigates the behavior of spark discharges under various environmental conditions to simulate aspects of early-stage lightning dynamics, with a focus on their spectral characteristics, propagation, and ionization behavior. In a laboratory setting, spark discharges generated by a Tesla coil operating with high-frequency alternating current (AC) were analyzed under varying air humidity and water surface conductivity. Spectral analysis revealed that the discharges are dominated by the second positive system of molecular nitrogen N₂ (2P) and also exhibit the first negative system of molecular nitrogen ions N₂⁺ (1N). Notably, the N₂ (2P) emissions show strong peaks in the 350–450 nm range, closely matching spectral features typically associated with corona and streamer discharges in natural lightning. Environmental factors significantly influenced discharge morphology: in dry air, sparks exhibited longer and more branched paths, while in moist air, the discharges were shorter and more confined. Over water surfaces, the sparks spread radially, forming star-shaped patterns. Deionized (DI) water, with low conductivity, supported wider lateral propagation, whereas higher conductivity in tap water and saltwater suppressed discharge spread. The gap between the electrode tip and the surface also affected discharge extent and brightness. These findings demonstrate that Tesla coil discharges reproduce key features of early lightning processes and offer insights into how environmental factors influence discharge development. Full article

The decommissioning and dismantling of nuclear research reactors can lead to a large amount of low- and intermediate-level radioactive waste. For repositories, the materials must be kept confined and safety must be ensured for extended time spans. Waste is encapsulated in concrete, which leads to alkaline conditions with pH values of 12 and higher. This can be advantageous for some radionuclides due to their precipitation at high pH. For other materials, such as reactive metals, however, it can be disadvantageous because it might foster their corrosion. The Studsvik R2 research reactor contained an AlMg3.5 alloy with a composition close to that of commercial Al5154 for its core internals and the reactor tank. Aluminum corrosion is known to start rapidly due to the formation of an oxidation layer, which later functions as natural protection for the surface. The corrosion can lead to pressure build-up through the accompanied production of hydrogen gas. This can lead to cracks in the concrete, which can be pathways for radioactive nuclides to migrate and must therefore be prevented. In this study, unirradiated rod-shaped samples were cut from the same material as the original reactor tank manufacture. They were embedded in concrete with elevated water–cement ratios of 0.7 compared to regular commercial concrete (ca. 0.45) to ensure water availability throughout all of the experiments. The sample containers were stored in pressure vessels with attached high-definition pressure gauges to read the hydrogen-induced pressure build-up. A second set of samples were exposed in simplified artificial cement–water to study similarities in corrosion characteristics between concrete and cement–water. Additionally, the samples were exposed to concrete and cement–water in free-standing sample containers for deconstructive examinations. In concrete, the corrosion rates started extremely high, with values of more than 10,000 µm/y, and slowed down to less than 500 µm/y after 2000 h, which resulted in visible channels inside the concrete. In the cement–water, the samples showed similar behavior after early fluctuations, most likely caused by the surface coverage of hydrogen bubbles. These trends were further supported by mass loss evaluations. Full article

To ensure safe navigation, ship operators must not only meet the criteria defined in the International Maritime Organization (IMO) maneuverability standards but also understand maneuvering characteristics in restricted waters. This study numerically analyzed the hydrodynamic lateral forces and yaw moments acting on a stern trawler, a container ship, and a very large crude carrier (VLCC) with different hull forms as they navigated near a semi-circular bank wall. The effects of varying bank radius, lateral clearance, and water depth were examined. The results showed that the VLCC experienced the strongest attractive lateral force, while the stern trawler exhibited the most significant yaw moment. The hydrodynamic interaction patterns of the stern trawler and container ship were similar, whereas the VLCC displayed distinct behavior due to its fuller hull and greater inertia. These findings demonstrate that hull geometry significantly influences hydrodynamic interactions near boundaries, and the degree of response varies by ship type. The results provide valuable reference data for improving navigation safety in confined waters and preventing marine accidents such as collisions and groundings. This study contributes to a better understanding of ship–bank interaction and offers a theoretical basis for maneuvering assessments of various ship types in restricted maritime environments. Full article

To investigate the excavation characteristics and mechanisms of a deep foundation under lateral confined water pressure, a model test was conducted with real-time monitoring of the stress and deformation of the foundation strut system. The results indicate that in stages 1 and 3 (the process of raising the lateral confined water level, O and F), the rise in lateral confined water levels caused the diaphragm wall to shift inward. However, the reduction in earth pressure due to the inward shift of the diaphragm wall exceeded the increase in water pressure from the raised confined water level, resulting in an overall decrease in lateral pressure on the diaphragm wall. During stage 2 (the excavation and supporting process, K1–Z4), as excavation and strut installation progressed, the lateral pressure on the diaphragm wall decreased, while both bending moment and horizontal displacement increased, with the most pronounced changes occurring when excavation reached the depth of the lateral confined aquifer. Upon reaching the soil layers within the depth of the lateral confined aquifer, the axial force of struts increased significantly, with the second level of strut experiencing the greatest axial force. In deep foundation design, it is essential to account for the maximum bending moment and horizontal displacement of the diaphragm wall within the depth range of the lateral confined aquifer, as well as the maximum vertical displacement in the range of 0.50%D–0.83%D outside the pit. Due to the rapid transmission of lateral confined water pressure changes in fine sand, and the delayed transmission in clay due to their low permeability, the diaphragm wall response is most pronounced within the depth range of the lateral confined aquifer. Full article

The Ross Sea I glaciation, marked by the northward advance of the Ross Ice Sheet (RIS) in the Ross Sea, east Antarctica, corresponds with the last major expansion of the West Antarctic Ice Sheet during the last glacial period. During its advance, the RIS was grounded along the southern Victoria Land coast, completely blocking the mouths of several of the McMurdo Dry Valleys (MDVs). Several authors have proposed that very large paleolakes, proglacial to the RIS, existed in many of the MDVs. Studies of these large paleolakes have been key in the interpretation of the regional landscape, climate, hydrology, and glacier and ice sheet movements. By far the most studied of these large paleolakes is Glacial Lake Washburn (GLW) in Taylor Valley. Here, we present a comprehensive review of literature related to GLW, focusing on the waters supplying the paleolake, signatures of the paleolake itself, and signatures of past glacial movements that controlled the spatial extent of GLW. We find that while a valley-wide proglacial lake likely did exist in Taylor Valley during the early stages of the Ross Sea I glaciation, during later stages two isolated lakes occupied the eastern and western sections of the valley, confined by an expansion of local alpine glaciers. Lake levels above ~140 m asl were confined to western Taylor Valley, and major lake level changes were likely driven by RIS movements, with climate variables playing a more minor role. These results may have major implications for our understanding of the MDVs and the RIS during the Ross Sea I glaciation. Full article

In mid-March 2022, a Siberian High brought intense cold air masses, leading to severe weather conditions across southern Europe, including the Black Sea region. This study investigates the spatial and temporal evolution of cold intermediate water (CIW) masses in the Black Sea, with a particular focus on the successive anomalously cold episodes that occurred in March 2022. The research underscores the significance of the northwestern continental slope and cyclonic gyres, especially as the only cold-water mass observations during the warm winters of 2020 and 2021 were concentrated in these areas. Following two warm winters, the cold episodes of March 2022 revealed notable convection and simultaneous cooling, particularly in the cyclonic interior and the Rim Current periphery, excluding the northeastern periphery. Subsequently, cold waters spreading isopycnally throughout the summer months were transported laterally and reached these regions. Argo float measurements provided clear evidence of widespread replenishment of the CIW, indicating that it is not confined to specific areas. The study also highlights regional variability in the characteristics of CIW formation, which is influenced by local dynamics and preconditioning temperatures. The temperatures of CIW increased from west to east, in line with the sea surface temperature gradient. Notably, thicker and colder CIW was found in the western cyclonic gyre compared to the eastern cyclonic area. Furthermore, the study confirms that the warming trend in CIW, identified in previous research, not only continues but has intensified during the recent period analyzed. These findings, observed under the extreme conditions analyzed in this research, offer valuable insights into the widespread occurrence of CIW formation in the Black Sea. Additionally, the study confirms that the warming trend in CIW, identified in previous studies, continued in the region throughout the warm winter period and after the cold spell in 2022. These insights contribute to a deeper understanding of CIW dynamics and their response to extreme weather events in the Black Sea. Full article

Density stratification plays a crucial role in estuarine hydrodynamics and material transport. In this study, we utilized a well-calibrated numerical model to investigate the stratification processes and underlying mechanisms in the dynamically wide Pearl River Estuary (PRE). In the upper estuary, longitudinal straining governs stratification, enhancing it during ebb tide and reducing it during flood tide. The Coriolis force becomes significant in the lower estuary due to the increased basin width, causing seaward freshwater to be confined to the West Shoal, where a pronounced transverse salinity gradient forms. Interacting with lateral current shear, density stratification is most pronounced in this region. The prevailing northeasterly wind creates a mixed layer near the surface, shifting stratification to the middle layer of the water column in the upper estuary. Wind stirring reduces stratification throughout the estuary. Under the wind’s influence, the seaward outflow is confined to a narrower region and shifts westward, resulting in the most apparent stratification occurring on the West Shoal of the PRE due to lateral straining. These findings on the evolution of freshwater pathways and their role in modulating density stratification have significant implications for other wide estuaries, such as Delaware Bay and the La Plata-Parana estuary. Full article

It is necessary to maintain maneuverability for ship navigation in shallow water, such as channels, ports and other confined waters. In this study, a turning circle maneuver with 35° rudder deflection and a 20/5 zigzag maneuver for KVLCC2 in shallow waters are tested numerically to directly predict the maneuverability of the ship in shallow water. A viscous in-house CFD solver is applied with the dynamic overset grid approach. The impacts of the water depth on the ship’s maneuverability in terms of turning and zigzag competence are evaluated, and the underlying mechanism is analyzed. The numerical method is validated by comparing it with experimental data on the turning indices, which shows good agreement. It is demonstrated that the turning capability become worse with a smaller depth–draft ratio, thus resulting in a lower yaw rate and a greater steady turning diameter. However, the drift angle and lateral speed are reduced with a smaller depth–draft ratio for zigzag maneuvers, but the overshoot angle and turn lag vary with the water depth non-monotonically. Full article

The Atlantic blue crab Callinectes sapidus, which is native to the western Atlantic coast and listed among the 100 most invasive alien species in the Mediterranean Sea, is attracting a great deal of interest because of its rapid colonisation of new areas, the significant increase in its population, and the impacts it may have on ecosystems and ecosystem services. Outside its natural distribution range, the species was first found on European Atlantic coasts in the early 1900s and was introduced into the Mediterranean Sea a few decades later, probably through ballast water. Currently, it is found in almost the entire Mediterranean Basin and is also expanding into the Black Sea and along the north African and Iberian Atlantic coasts. Based on a systematic review of C. sapidus occurrences, this study describes its distribution, aggregation patterns, and spatial structure in Northwest Europe, the Mediterranean Sea, and adjacent waters through a series of ecological indicators elaborated using GIS spatial–temporal statistics. The main results highlight that the species is expanding in the Mediterranean and adjacent waters, while in northern Europe, the population remains confined in some areas. Furthermore, the main species detection methods are analysed, finding that traps and nets are the most frequently used methods, and management suggestions are provided. Full article

The existence of structural strength in undisturbed soil results in its distinct characteristics compared to remolded soil. Under the influence of freeze–thaw cycles, this difference may easily cause geotechnical disasters in cold regions. This study aimed to analyze and discuss the expression degree and influencing factors of the structural strength of expansive soil. The unconfined compressive strength (UCS) test, high-pressure consolidation test, and microscopic test were performed on expansive soil retrieved from a seasonally frozen region. Moreover, sensitivity parameters, including stress sensitivity (S_t.qu, S_t.σk) and strain sensitivity (S_t.ɛu, S_t.Cc), were applied to explore the expression degree and influencing factors of structural strength in a seasonally frozen region. The results reveal that the undisturbed samples have better structural connection and particle arrangement than the remolded samples. However, the primary fractures have a certain degrading effect on the strength of the undisturbed soil as influenced by a seasonally frozen region. With the increase in water content and the decrease in density, the expression degree of the structural strength in terms of compressive strength and the ability to resist deformation enhances under the unconfined condition. By contrast, the expression degree increases in strength and decreases in ability under the confined condition. Furthermore, the effect mechanisms of the basic property, particle composition, structural linkage, lateral confinement, and historical role on the structural expression were analyzed. Full article

Given the changing climate, understanding the recent variability in large-scale rainfall patterns is a crucial task in order to better understand the underlying hydrological processes that occur within a watershed. This study aims to investigate how rainfall events in western Japan have changed due to climate change and how these changes have affected runoff–turbidity dynamics during the rainy season. To address the research objectives, we analyzed two decades of precipitation records in the Gōno River watershed and examined the associated runoff–turbidity dynamics during floods using turbidity–discharge (T-Q) loops, quantified using an enhanced hysteresis index. Our findings revealed a kind of intense rainfall event occurring every 3 to 4 years. Additionally, spatial pentad analysis showed varying intensities of accumulated precipitation, indicating that extreme rainfall is not confined to a specific spatial zone. Regarding turbidity–discharge behavior, we found that clockwise hysteresis patterns were caused by sediment sources from near-channel areas, while anticlockwise patterns were caused by soil erosion from nearby areas. Another notable finding was that turbidity peaks during floods may represent the earlier (or later) arrival of turbid water from distant upstream sources due to intense precipitation. One of the key challenges in quantifying hysteresis patterns is that there is no agreed-upon definition for how to determine the start and end of a flood event. This can lead to bias in the quantification of these patterns. Full article

Electrical resistivity and borehole data are applied to delineate lithostratigraphic boundaries and image the geometry of confining-unit breaches in Eocene coastal-plain deposits to evaluate inter-aquifer exchange pathways. Eight dipole–dipole array surveys were carried out, and apparent resistivity was inverted to examine the lateral continuity of lithologic units in different water-saturation and geomorphic settings. In addition, sensitivity analysis of inverted resistivity profiles to electrode spacing was performed. Resistivity profiles from Shelby Farms (SF) highlight the effect of varied electrode spacing (2.5, 5, and 10 m), showing an apparent ~0.63 to 0.75 depth shift in resistivity-layer boundaries when spacing is halved, with the 10 m spacing closely matching borehole stratigraphy. Grays Creek and Presidents Island profiles show clay-rich Eocene Cook Mountain Formation (CMF), with resistivity ranging from 10 to 70 Ω-m, overlying the Eocene Memphis Sand—a prolific water-supply aquifer. Resistivity profiles of SF and Audubon Park reveal sandy Cockfield Formation (CFF) paleochannels inset within and through the CMF, providing hydrogeologic connection between aquifers, and clarifying the sedimentary origin of confining-unit breaches in the region. The results underscore the efficacy of the electrical resistivity method in identifying sand-rich paleochannel discontinuities in a low-resistivity regional confining unit, which may be a common origin of breaches in coastal-plain confining units. Full article

This study investigates the steady flow resulting from dewatering by a partially penetrating well in a confined aquifer with a cut-off barrier. By considering flow in both horizontal and vertical directions and incorporating the barrier and pumping well as flow boundary conditions, separate mathematical models are established for the inside and outside of the cut-off barrier. The interaction between these zones is ensured through continuous conditions along the opening of the two zones. A semi-analytical solution is derived for the problem using the finite Fourier cosine transform and boundary transformation methods. The effectiveness of the method is verified by comparing it with the finite element numerical results and pumping test data respectively. Based on the proposed solutions, we proceed to analyze the influence of some relevant factors: the extent to which the cut-off wall is embedded within the confined aquifer, the depth of the partially penetrating well, and the distance to the lateral head boundary. Results indicate that a greater depth of the cut-off wall leads to a reduced pumping rate requirement for achieving a desired drawdown of the confined water level within the excavation. According to the presented solution, placing pumping wells near the top of the confined aquifer in excavation dewatering projects can facilitate a faster reduction of the confined water head at the excavation bottom. Additionally, proximity of lateral head boundary could significantly impact dewatering, with closer boundaries reducing dewatering effectiveness due to improved aquifer recharge. Finally, the use of the Fourier method showcases impressive convergence properties in the approach presented in this study. The computed results maintain a high level of approximation quality, even with extremely coarse discretization. Full article

In the Loess Plateau region, loess, as a widely distributed building material, is often used as a filling material for dams. When the water level reaches a certain height, the body of a dam is prone to shear failure due to the penetration of water. The change in the shear performance of local loess filler can affect the overall strength of loess dams. Therefore, the filler of a loess dam is selected to study the shear performance. The progressive failure process of a loess dam is simulated. The shear failure characteristics of loess filler under the influence of water content, confining pressure, and dry density were explored. The characteristics of the shear failure of a loess dam were analyzed. The remolded loess is prone to shear expansion failure under low confining pressure, low water content, and high dry density, and is prone to shear shrinkage failure under high confining pressure, high water content, and low dry density. When the water content is constant, the cohesion increases with the increase in dry density. When the dry density is constant, the internal friction angle generally increases with the increase in water content. However, when the dry density is high, the permeability of the remolded loess is weakened, resulting in uneven water distribution under a low water content, which affects the test results. The failure process of the loess dam is a progressive shear failure, which is affected by the water level and water pressure, and is destroyed under the action of pore water pressure and water body lateral pressure. Full article

Spalling disease caused by freeze–thaw cycles often occurs on the loess cut-slopes in northern Shaanxi. The deterioration of the pore structure and mechanical strength of loess under a freeze–thaw environment is one of the critical reasons underlying the occurrence of spalling disease in the slopes. In order to explore the effects of freeze–thaw cycles on the pore structure and the mechanical strength of loess, four initial water contents (7%, 9%, 12%, and 14%) and six freeze–thaw cycles (zero, one, three, five, 10, and 20) were considered in this study. Nuclear magnetic resonance (NMR) and triaxial compression tests were carried out to analyze and reveal the mechanisms of effect causing the deterioration of the soil strength that affects the stability of loess cut-slopes. The results showed that the porosity growth increased with the initial water content and continued to increase during the freeze–thaw process until a later stage of the freeze–thaw cycle, when it gradually stabilized. The stress–strain curves were primarily influenced by the number of freeze–thaw cycles, the initial water content of the samples, and the confining pressure. Both the cohesion and the internal friction angle exhibited a decay law that showed a significant decrease, then a slow decrease, and finally stabilization during the freeze–thaw process. Small and micropores were predominant among the pore structures of the loess, while medium pores were the second most common, and large pores were the least common. With the increase in the initial water content, the pores transformed from micropore structures to medium and large pore structures. The soil strength deterioration was primarily driven by the phase changes of the pore water, as well as the water migration during the freeze–thaw process. This study will be beneficial for identifying the characteristics and types of freeze–thaw disease in cut-slope engineering in seasonally frozen loess areas and providing a theoretical reference and design basis for achieving green and sustainable development in slope engineering, management, and maintenance. Full article