Microseismic activity, recorded everywhere on Earth, is largely due to ocean waves. Recent progress has clearly identified sources of microseisms in the most energetic band, with periods from 3 to 10 ...s. In contrast, the generation of longer‐period microseisms has been strongly debated. Two mechanisms have been proposed to explain seismic wave generation: a primary mechanism, by which ocean waves propagating over bottom slopes generate seismic waves, and a secondary mechanism which relies on the nonlinear interaction of ocean waves. Here we show that the primary mechanism explains the average power, frequency distribution, and most of the variability in signals recorded by vertical seismometers, for seismic periods ranging from 13 to 300 s. The secondary mechanism only explains seismic motions with periods shorter than 13 s. Our results build on a quantitative numerical model that gives access to time‐varying maps of seismic noise sources.
Key Points
The “hum” is caused by the interaction of ocean waves with the bottom slope
Our model yields maps of seismic sources at all periods from 3 to 300 s
Sources of the hum are strongest along shelf breaks, on the east side of oceans
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Numerical Modeling of Submerged Vane Flow Bestami TAŞAR; Fatih ÜNEŞ; Ercan GEMİCİ ...
Aerul şi Apa: Componente ale Mediului,
03/2023, Volume:
2023, Issue:
1
Conference Proceeding, Journal Article
Peer reviewed
Open access
Scours in rivers occur due to high flow velocities. In order to reduce scour, flow velocities need to be reduced. Submerged vane structures are effective in both reducing the flow rate and directing ...the flow. In this study, numerical modeling was made with submerged vane structures. Models of the measured flow velocities in the channel, where submerged vane experiments were performed before, were compared with the results of the submerged vane experiment by using the 3-dimensional computational fluid dynamics (CFD) method. In the present CFD model, continuity and momentum, turbulence model equations are applied. For the turbulence viscosity, k-ε turbulence model is used. The results of the present model are compared with the previous experimental work.
We review the existing methods for evaluating the hydraulic conductivity of a rock mass. Rock mass permeability may be assessed using empirical, analytical and numerical approaches. Empirical methods ...use data from in situ field tests to derive the relationship between depth and permeability by applying a curve-fitting method and establishing the relationship between hydraulic conductivity and a geological index. Analytical methods rely on Darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets. Analytical equations of the flow rate into underground excavations are also developed by solving the Laplace equation for homogeneous and isotropic aquifers under various boundary conditions. Numerical modeling can evaluate the outcomes of both empirical and analytical approaches (and vice versa) and can provide a sensitivity analysis of the parameters that affect rock mass permeability. The importance of stress and joint set characteristics is often investigated via numerical modeling, as are the scale effect and directional permeability. In this review paper, we provide a comprehensive review of these approaches for studying rock mass permeability. We summarize the advantages and disadvantages of existing methods and highlight potential future research directions.
•Existing methodologies for investigating the hydraulic conductivity of a rock mass are reviewed comprehensively.•Hydraulic conductivity of a rock mass can be assessed by empirical, analytical, and numerical methods.•The advantages and disadvantages of existing methods for rock mass permeability are summarized.•Future directions for assessing the hydraulic conductivity of a rock mass are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Appling ECB to recoil machine of artillery.•The analytical electromagnetic model is established by multilayer theory to derive the heat source of this ECB.•The 2D-numerous model is established by FD ...method and coupled with source method.•The working characteristic of this ECB under intense impact load considering temperature is analyzed.
With the increasing requirements for safety and reliability, it is now necessary to analyze the thermal characteristics to the same extent as the electromagnetic design for eddy current brakes(ECB), because the working characteristic will be greatly influenced by temperature. In this paper, the transient thermal-magnetic coupling analysis of permanent magnet cylindrical eddy current brake, which is used as the recoil mechanism in artillery, is presented. First, the structure and working principle of this ECB are described in detail. Second, the analytical electromagnetic model is established by multilayer theory to derive the heat source of this ECB. Thirdly, the thermal-magnetic coupling model is established to calculate the dynamic inhomogeneous temperature field of the ECB. The heat conduction equation is solved in different regions with inhomogeneous internal heat source by Finite Difference method(FDM) in two-dimensional cylindrical coordinate. Finally, the validity of the proposed model is verified by commercial Finite Element software. The thermal characteristic and its effects on braking force is analyzed during working. The maximum value of temperature approximately rises by 16℃ in each firing. The braking force will decline by 8% considering temperature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To investigate the seismic performance of a wind turbine that is influenced by both the ice load and the seismic load, the research proposes a numerical approach for simulating the seismic behavior ...of a wind turbine on a monopile foundation. First, the fluid-solid coupled equation for the water-ice-wind turbine is simplified by assigning reasonable boundary conditions and solving the motion equation, and the seismic motion equation of the wind turbine is developed. Then, on this basis, we propose a simplified 3D numerical model that can simulate the interactions among the wind turbine, water and sea ice. By conducting shaking table tests, the results demonstrate that the established numerical model is effective. Finally, we investigate the effect of the boundary range and ice thickness on the seismic performance of a turbine under near-field and far-field seismic actions. Research results illustrate that ice changes the distribution form of the hydrodynamic pressure. Moreover, the thickness of the ice greatly influences the seismic behavior, while the influence of the ice boundary range is only within a certain range. Additionally, the ice load decreases the energy-dissipating capacity of the wind turbine, so the earthquake resilience of the wind turbine is significantly decreased.
The outer bank slump blocks play a fundamental role in modulating the rate of bank erosion, and consequently, have a profound influence on many geomorphic and ecologic processes in meandering ...streams, e.g., channel evolution and habitat creation. To date, no adequate research has been developed regarding how these blocks, partially strengthened by roots of herbaceous plants, impact the near-bank flow velocity, bank erosion, and migration of streambanks. This paper analyzes 246 slump blocks in a meandering stream on the Marqu Meadow, China. Aerial surveys were conducted once a year from 2018 to 2021 and the lateral migration rates (M) of streambanks are estimated by superimposing the current-year drone imagery onto its previous-year counterpart. When compared to the outer bank segments lacking slumps, our research findings indicate that the bank segments exhibiting slumps demonstrate a reduction of 57 % and 43 % in the maximum and average bank erosion rates, respectively. Overall, the wider blocks provide stronger bank protection; nevertheless, they may also introduce or enhance local scouring in their vicinity, thereby increasing the heterogeneity of bank erosion rates. To elucidate this complex influence mechanism, we simulate the three-dimensional flow velocity field of a ~100 m meandering bend containing three slump blocks using the MIKE-3 model. Furthermore, we compare one-year bank migration distance with and without the blocks by correlating the lateral migration distance of outer banks to the longitudinal gradient of near-bank velocity. The paper provides valuable insights into the complex interplay between flow dynamics and streambank behavior in real-world settings, thereby enhancing the effectiveness of future management and restoration practices.
•246 slump blocks were analyzed in a meander on Marqu Meadow, China.•Slump blocks can persist for years but may be washed away in high flows.•The outer bank slump blocks play a vital role in modulating bank erosion rates.•Slump blocks protect outer banks by redistributing the high flow and secondary flow.•Slump blocks help protect bank overall but it may introduce scour in their vicinity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A novel PCM-PV/T collector with PCM connected in parallel is proposed.•A numerical model for the novel PCM-PV/T system is established and validated.•Sensitivity analysis of key operational and ...structural parameters is conducted.•The start time and duration of phase transition process are revealed and analyzed.•Details of melting ratio and heat gain of PCM are displayed and discussed.
Applying PCM to the photovoltaic/thermal (PV/T) system can adjust the operating temperature of the photovoltaic cell and further enhance system efficiency. Hence, in the present study, a novel PV/T-PCM collector by connecting the PCM with the heat-absorbing plate in parallel is first proposed. Then, the dynamic model of the PV/T-PCM system is established and verified. Finally, the sensitivity analysis is performed on key parameters, including the water mass flow rate, water tank volume, PCM thickness, and phase transition temperature. The results show that raising the water mass flow rate improves electrical gain, total heat gain, and total system efficiency; however, their change gradient is all inconspicuous as the water mass flow rate is greater than 0.02 L/s. As the water tank volume expands from 75 L to 105 L, electrical gain, total heat gain, and total system efficiency are improved. Thickening the PCM can promote the electrical gain, while the total system efficiency and total heat gain will increase slightly at first and then decrease. The best thickness is 0.015 m. When the phase transition temperature increases from 40 ℃ to 50 ℃, the total system efficiency and total heat gain decline, but the electrical gain decreases insignificantly. The changes of the above four parameters all affect the complete melting ratio of PCM as well as the phase transition start time on the entrance side and exit side of the collector.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Subsurface dams are rather effective and used for the prevention of saltwater intrusion in coastal regions around the world. We carried out the laboratory experiments to investigate the elevation of ...saltwater wedge after the construction of subsurface dams. The elevation of saltwater wedge refers to the upward movement of the downstream saltwater wedge because the subsurface dams obstruct the regional groundwater flow and reduce the freshwater discharge. Consequently, the saltwater wedge cannot further extend in the longitudinal direction but rises in the vertical profile resulting in significant downstream aquifer salinization. In order to quantitatively address this issue, field‐scale numerical simulations were conducted to explore the influence of various dam heights, distances, and hydraulic gradients on the elevation of saltwater wedge. Our investigation shows that the upward movement of the saltwater wedge and its areal extension in the vertical domain of the downstream aquifer become more severe with a higher dam and performed a great dependence on the freshwater discharge. Furthermore, the increase of the hydraulic gradient and the dam distance from the sea boundary leads to a more pronounced wedge elevation. This phenomenon comes from the variation of the freshwater discharge due to the modification of dam height, location, and hydraulic gradient. Large freshwater discharge can generate greater repulsive force to restrain the elevation of saltwater wedge. These conclusions provide theoretical references for the behaviour of the freshwater–seawater interface after the construction of subsurface dams and help optimize the design strategy to better utilize the coastal groundwater resources.
The elevation of saltwater wedge refers to the upward movement of the downstream saltwater wedge after the construction of subsurface dams. The subsurface dams obstruct the regional groundwater flow and decrease the freshwater discharge. Then the saltwater wedge cannot advance in the longitudinal direction due to the block of the dam but rises in the vertical profile because of the reduced freshwater discharge, which eventually increases the saltwater contaminated area in the downstream aquifer.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The physical properties of gas hydrate‐bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase. The host sediment grain size and the state of effective stress ...determine the hydrate morphology in sediments; this information can be used to significantly constrain estimates of the physical properties of hydrate‐bearing sediments, including the coarse‐grained sands subjected to high effective stress that are of interest as potential energy resources. Reported data and physical analyses suggest hydrate‐bearing sands contain a heterogeneous, patchy hydrate distribution, whereby zones with 100% pore‐space hydrate saturation are embedded in hydrate‐free sand. Accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate‐bearing sands and captures observed physical‐property dependencies on hydrate saturation. For example, numerical modeling results of sands with patchy saturation agree with experimental observation, showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations. The hydrate‐patch size itself impacts the physical properties of hydrate‐bearing sediments; for example, at constant hydrate saturation, we find that conductivity (electrical, hydraulic and thermal) increases as the number of hydrate‐saturated patches increases. This increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate‐saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross‐section of the specimen.
Key Points
Controls on hydrate morphology in natural sediments
Accounting for patchy hydrate yields tighter estimates of physical properties
Models to characterize stiffness and conductivities of sands with patchy hydrate
Seismic cycles emerge in a broad range of rupture styles, from slow-slip events to pulse-like earthquake sequences. Meanwhile, large earthquakes in paleoseismic and instrumental catalogues exhibit ...various recurrence patterns going from periodic to chaotic cycles with characteristic or dissimilar ruptures. The potential connection between these observations is still poorly known. Here, we investigate the link between rupture styles and recurrence patterns in quasi-dynamic models of seismicity in two-dimensional faults embedded in a compliant zone, exploring a wide range of frictional and fault zone properties. The recurrence patterns evolve from purely periodic to multiple-periodic time- and slip-predictable cycles, to chaotic sequences of super-cycles with full and partial ruptures with an increasing number of aftershocks. This transition is accompanied by changes of rupture styles from crack-like to pulse-like ruptures. These behaviors can be obtained either by a more compliant fault zone or a reduced characteristic weakening distance of friction. The effects of the compliant zone and other physical characteristics can be conflated into a single non-dimensional number, such that seismic cycles with similar behaviors can be obtained with or without a compliant fault zone in quasi-dynamic simulations. The connection between recurrence patterns and rupture styles implies that the paleoseismic record can bring useful constraints to rupture characteristics and fault zone properties.
•Rupture styles and recurrence patterns of earthquakes are linked.•The nucleation size and fault zone fabric control the rupture style.•Recurrence patterns evolve from periodic to chaotic with varying rupture style.•The paleoseismic record may help constrain rupture characteristics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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