Low-velocity Zone Research Articles

Feeding system beneath active volcanoes in central part of Iturup Island (Kuril Arc) inferred from local earthquake tomography

Iturup is the largest island of the Kuril Arc with more than 20 Holocene volcanoes of which 9 considered active. Here we investigate the central part of the island where we deployed in 2022–2023 a portable network of 12 seismic stations. The data of this network together with several permanent stations in surrounding islands were used to identify almost 300 events and to perform seismic tomography based on the picked arrival times of the P and S seismic waves. A challenging problem was that most of the events were located outside the network, and we performed careful analysis to examine the actual capacity of inversion with such data to recover seismic velocity structures below the network. In the resulting model, we found a dominating high-velocity anomaly below the central part of the study area, which is bounded by zones of low velocities and high Vp/Vs ratio collocated with two active volcano complexes (Chirip to the north and Ivan Grozny to the south). Below the third volcano, Baransky, we observe a change of the Vp/Vs ratio from high at large depths to low at shallow depth, indicating the process of degassing, which is supported by strong fumarolic activity and hydrothermal manifestations around this volcano. At depths of more than 20 km, the feeding paths from Baransky and Ivan Grozny volcanoes seem to be connected in one anomaly representing a common magma source below the center of the island. This seems to be a common feature observed below several volcanic islands, such as Tenerife and El Hierro, where the high-velocity rigid core in a central part is surrounded by low-velocity flows associated with recent volcanic manifestations.

Magnetotelluric image of the Patagonian slab window: Constraints on upper mantle physical properties and sources of intraplate magmatism

The Patagonian slab window (PSW) is a region of the Southamerican subduction zone where the absence of subducted slabs is interpreted, due to the subduction of the Chile Mid-Ocean Ridge at the Chile Triple Junction. Here we report the results of a long-period magnetotelluric (MT) study conducted in two 300 km-long trench-parallel transects crossing the northern boundary of the PSW in the proximal backarc. We modeled the MT data using 3-D inversion, obtaining an electrical resistivity model of the continental crust and upper mantle up to a depth of ∼150 km. Our model shows a heterogeneous resistivity structure in the uppermost mantle, dominated by resistivities >300 Ωm below the array of sites even within the PSW, and some low-resistivity zones (LRZs, <10 Ωm) mainly at the edge of the array. Using petrophysical models, we estimated the mantle temperature, water content, melt fraction, and viscosity based on obtained resistivity values and a preexistent model of P-wave velocity (Vp) at 50 km and 100 km depth. These estimates suggest that the uppermost mantle within the PSW region is heterogeneous and dominated by high-viscosity blocks, compatible with the continental mantle lithosphere or even subducted slabs. Based on relatively hot and low-viscosity zones estimated in the periphery of LRZs, we interpret the presence of asthenospheric mantle in areas where LRZs coincide with relatively low Vp. According to this interpretation, asthenospheric upwelling in the study area at depths ≤150 km would be localized rather than ubiquitous over the interpreted extent for the PSW. Such localized asthenosphere upwelling processes in the past could explain the scattered distribution of Neogene basaltic lavas in the southern Patagonia backarc. The continental crust exhibits LRZs in the upper and lower crust. Remarkably, ensembles of LRZs at different crustal depths within the presumable area of the PSW were found below the General Carrera Lake, and towards the North Patagonian Icefield, likely indicating the presence of hidden intraplate magmatic and/or hydrothermal systems.

Ambient Noise Tomography of Northern Borneo Reveals Evidence of Subduction and Post‐Subduction Processes

AbstractThe region of northern Borneo in South East Asia sits within a post‐subduction setting formed by the recent termination of two sequential but opposed subduction systems. In this study we use seismic data from a recent temporary array deployment to image the crustal velocity structure beneath northern Borneo using a two‐stage Bayesian trans‐dimensional tomography scheme, in which period dependent phase velocity maps are first generated, and then used to build a 3‐D shear wave model through a series of 1‐D inversions. In the second stage, we also apply an Artificial Neural Network to solve the 1D inverse problem, which results in a smoother 3‐D model compared to the TransD approach without sacrificing data fit. Our shear wave velocity model reveals a complex crustal structure. Under the Crocker Range, a heterogeneous velocity structure likely represents remnants of early Miocene subduction, including underthrust continental crust from subsequent continent‐continent collision. In the east we observe high velocities that are interpreted to be igneous rocks in the crust generated by melting due to mid Miocene Celebes Sea subduction and later decompression melting as well as a low velocity zone that could represent underthrust sediment or duplexes from Celebes Sea subduction. A low velocity zone in the lower crust is present in a region of apparent crustal thinning. Our preferred explanation for this anomaly is remnant thermal upwelling within a failed rift that represents the on‐shore continuation of the extension of the Sulu Sea, most likely caused by rollback of the Celebes Sea slab.

Experimental Study on Scale Effects of Kerosene Combustion in Scramjet Combustors

The combustion characteristics in two geometrically similar kerosene-fueled scramjet combustors with mass flow rates of 0.69 and 1.41 kg/s are experimentally investigated to explore the scale effects of flame stabilization at Mach 2.52 condition. As the equivalence ratio increases, the combustion usually changes from weak to intensive to blow-out mode. The weak combustion has little effect on the flow field, whereas the intensive combustion has the opposite effect. The transition combustion tends to occur between different modes. When the single injector is used, compared with the small-scale combustor, intensive combustion cannot occur in the large-scale combustor, and the flame stability range is also narrower. One probable reason is that as the combustor scale increases, the boundary layer becomes relatively thinner, resulting in a smaller low-velocity zone and a faster mainstream velocity at the downstream wall of the cavity, which is not conducive to the flame propagation upstream to form the intensive combustion. After shortening the isolator, all cases with intensive combustion in the small-scale combustor are transformed into weak combustion, further confirming the speculation. Compared to the single injector, the dual injector is required in the large-scale combustor to achieve intensive combustion and a wider flame stability range.

Impacts of jet inflow on hydrodynamic performance and waste removal efficiency in recirculating aquaculture system aquaculture tanks based on prototype experiments

Although scaled physical models and numerical simulations have been employed to study the hydrodynamic performance of recirculating aquaculture system (RAS) aquaculture tanks, there remains a paucity of prototype experiments that fully reflect the actual hydrodynamic performance. In this study, a prototype experiment was conducted on RAS aquaculture tanks, utilizing advanced image processing techniques specifically adapted to the prototype scale. This study focused on impacts of various jet inflow parameters, including jet inflow angle (0°, 10°, 20°, 30°, 40°, 45°, 50°, 60°, and 70°), jet inflow rate (150, 180, 210, and 240 l·min−1), jet inflow area (942 and 1884 mm2), and jet inflow location (curved wall and straight wall), on the hydrodynamic performance and waste removal efficiency of RAS aquaculture tanks. The results demonstrated the hydrodynamic performance—specifically average flow velocity, flow field uniformity, and the extent of low-velocity zones conjointly determining waste removal efficiency. The curved wall proved to be the optimal location for inflow pipe placement, while a 45° jet angle yielded the best balance between hydrodynamic performance optimization and waste removal efficiency. Furthermore, reducing the inlet area significantly improved average flow velocity and flow uniformity, whereas variations in inlet flow rate had minimal impact on these factors. Supported by these compelling findings, this study offers theoretical insight and practical guidance for achieving efficient aquaculture in RAS, thereby contributing to the advancement of sustainable aquaculture practices.

The characteristics of steam chamber expanding and the EOR mechanisms of tridimensional steam flooding (TSF) in thick heavy oil reservoirs

Aiming at the shortcoming of conventional steam flooding (CSF), tridimensional steam flooding (TSF) was proposed to expand the limited steam chamber and to enhance the low oil recovery in thick heavy oil reservoirs. In this paper, based on mechanisms of thermal recovery, two 3D experimental models were designed to investigate the evolution of steam chambers and production performance. A new method was proposed to utilize inflection point temperature and remaining oil saturation to identify utilizable ranges, hot water zones, and steam chambers. Then, based on the parameters of the indoor experiments, three numerical models were built to further study advantages of TSF. The results show that: i) Compared to CSF, TSF possesses a plumper steam chamber, a higher steam quality and a more stable displacement front; ii) The oil recovery of TSF can reach 52.85%, while it is only 43.31% for CSF at the same time; iii) At the end of TSF, the volume of steam chamber, low oil saturation zone, low pressure zone, and low viscosity zone is 3.08 times, 3.31 times, 1.61 times, and 1.55 times, respectively, compared to CSF, which demonstrates that TSF is effective. As a result, TSF can effectively expand steam chamber and enhance oil recovery in thick heavy oil reservoirs.

Performance improvement of a centrifugal compressor for cogeneration

This work presents the performance improvement of a centrifugal compressor designed for cogeneration applications. The study involves modifications to geometric parameters, including impeller and diffuser configurations, to enhance pressure ratio, temperature ratio, and overall efficiency using computational fluid dynamics to verify the improvement of those parameters. The study has examined the compressor’s behaviour under surge, design, and choke conditions, showcasing improved homogeneity, reduced low-velocity zones, and an extended operating range. The compressor maps are presented to graphically observe the impact of each proposed modification, facilitating the analysis of each of these and evaluating the performance under various operating conditions. The final compressor configuration exhibits notable improvements in key performance metrics, with pressure ratio, temperature ratio, and efficiency showing increases of 1.753%, 1.640%, and 1.760%, respectively.

Crustal melting and continent uplift by mafic underplating at convergent boundaries.

The thick crust of the southern Tibetan and central Andean plateaus includes high-conductivity, low-velocity zones ascribed to partial melt. The melt origin and effect on plateau uplift remain speculative, in particular if plateau uplift happens before continental collision. The East Anatolian Plateau (EAP) has experienced similar, more recent uplift but its structure is largely unknown. Here we present an 80 km deep geophysical model across EAP, constrained by seismic receiver functions integrated with interpretation of gravity data and seismic tomographic, magnetotelluric, geothermal, and geochemical models. The results indicate a 20 km thick lower crustal layer and a 10 km thick mid-crustal layer, which both contain pockets of partial melt. We explain plateau uplift by isostatic equilibration following magmatism associated with roll-back and break-off of the Neo-Tethys slab. Our results suggest that crustal thickening by felsic melt and mafic underplate are important for plateau uplift in the EAP, Andes and Tibet.

New insight into the velocity and anisotropy structures of the subduction zone in northern Sumatra

In this study, we conducted seismic tomographic inversions to investigate the velocity and anisotropy structures of northern Sumatra, using 9774 P-wave and 8405 S-wave arrivals from regional earthquakes. Isotropic P-wave velocity, isotropic S-wave velocity, P-wave azimuthal anisotropy, and P-wave radial anisotropy models were generated using eikonal equation-based traveltime tomography methods. The study identified low-velocity zones beneath the Toba and Sinabung volcanoes, potentially indicating the presence of magma reservoirs. Furthermore, low-velocity anomalies above the subduction slab were detected, which were likely caused by the dehydration of the slab and interpreted as channels of upwelling flow. The tomographic results revealed a trench-parallel high-velocity belt in the uppermost mantle, representing the subducting slab of the India-Australian plate. The trench-parallel fast velocity directions in the slab suggested that the subducted oceanic slab retains its frozen-in anisotropy formed at the mid-ocean ridge, or that the anisotropy is induced by the lattice-preferred orientation of the B-type olivine. Negative radial anisotropy in the mantle wedge was observed, reflecting hot upwelling flows and transitions of olivine fabrics in the presence of water due to slab dehydration. The results also indicated a multilevel magma plumbing system beneath the Toba Caldera. In summary, the results of this study provided new insights into the structure and dynamic processes of the northern Sumatra subduction zone.

INSIGHTS INTO THE MOHO DEPTH VARIATIONS AND CRUSTAL CHARACTERISTICS IN THE GUELMA–CONSTANTINE BASIN, NORTHEASTERN ALGERIA: A SHORT-PERIOD SEISMIC-RECEIVER-FUNCTION PERSPECTIVE

Teleseismic receiver functions (RF) were extracted from data collected at eight short-period, three-component seismic recording stations over the Guelma–Constantine Basin, northeastern Algeria, to improve the understanding of crustal structure and geodynamic processes. The H-κ stacking method was used to determine the Moho depths and average vP/vS ratios at each station. Careful linear inversion of RF was performed to determine the most appropriate average shear-wave and P-wave velocity profiles at each site. Both methods have yielded highly congruent results, with Moho depths showing robust correlations with previous seismological and geophysical studies. The previously observed pattern of the increasing Moho depth from north to south in the Tell Atlas has been confirmed. Furthermore, the identified transitional nature of the Moho in the Constantine Basin is consistent with a recent study. In addition, we identify a low-velocity zone (LVZ) at approximately 20 km depth within the southern Guelma Basin, confirming previous results in the Constantine Basin and suggesting an eastward elongation of the LVZ, at least into the southern periphery of the Guelma Basin. Examination of data from the northern tip of the Hammam Debbagh–Roknia NW–SE fault, the western boundary of the Guelma pull-apart basin, revealed a shallow Moho depth (22 km), less than the basin average depth of 25 km. The LVZ observed in the lower crust (12 km) suggests the presence of partial melts, consistent with gravimetric and chemical analyses of hydrothermal sources in the area. The extensional tectonic activity along this boundary, coupled with the low-viscosity zone and low average vP/vS ratio, is potentially associated with delamination processes. The effectiveness of our approach underscores its potential as a viable alternative or complementary method for investigating variations in the Moho depth.

The magmatic plumbing beneath the Wudalianchi volcanic region, northeast China, is recharged by magma reservoirs under Keluo volcano

The intraplate magmatic systems of the Wudalianchi potassic volcanic region in northeast China have historically exhibited eruption activity, and there is evidence that they retain the potential for future eruptions. However, the characteristics of this complex volcanic region remain debated and poorly understood due to the relatively low resolution of existing crustal tomography. Here we present a high-resolution shear-wave velocity model of the crust and uppermost mantle obtained by applying full-waveform ambient noise tomography to data recorded at 106 recently deployed broadband seismic stations. Our results reveal two vertical low-velocity anomalies discovered beneath the Nuominhe and Keluo volcanoes, which appear to be magma ascending pathways connecting a mantle source and crustal reservoirs. A horizontally interconnected low-velocity zone in the middle-lower crust indicates a magmatic migration pathway transporting potassium-rich melts directly among the potassic volcanic units. In addition, the Wudalianchi volcano is likely recharged by deeper and larger crustal magma reservoirs under the Keluo volcano. The unique geometries of the magmatic plumbing systems provide valuable seismic evidence for the volcanic eruption dynamics and potential volcanic hazards.

Stability of hydrous basaltic melts at low water fugacity: evidence for widespread melting at the lithosphere-asthenosphere boundary

The upper mantle low velocity zone is often attributed to partial melting at the lithosphere-asthenosphere boundary. This implies that basaltic melts may be stable along plausible geotherms due to the freezing point depression in the presence of water and other incompatible impurities. However, the freezing point depression (ΔT) as a function of water content in the near-solidus basaltic melt (cH2O) cannot be precisely determined from peridotite melting experiments because of difficulties in recovering homogeneous basaltic glasses at high pressures. We therefore used an alternative approach to reinvestigate and accurately constrain the ΔT–cH2O relationship for basaltic melts at the low water fugacities that are expected in the upper mantle. Internally heated pressure vessel (IHPV) experiments were performed at water-saturated conditions in the anorthite-diopside-H2O system at confining pressures of 0.02 to 0.2 GPa and temperatures between 940 and 1450 ℃. We determined the water-saturated solidus, and obtained ΔT by combining our data with reports of dry melting temperatures in the anorthite-diopside system. In another series of experiments, we measured water solubility in haplobasaltic melts and extrapolated cH2O to pressures and temperatures of the water-saturated solidus. By combining the results from these two series of experiments, we showed that the effect of water on ΔT was previously underestimated by at least 50 ℃. The new ΔT–cH2O relationship was then used to revise predictions of melt distribution in the upper mantle. Hydrous melt is almost certainly stable beneath extensive regions of the oceanic lithosphere, and may be present in younger and water-enriched zones of the subcontinental mantle.

3-D P-wave velocity structure of the upper mantle beneath eastern Indonesia from body wave tomography

Eastern Indonesia's tectonic setting is well known for its complexity and intense seismic activity. Controlled by several major and minor plates, including the Eurasian, Australian, and Pacific plates, this region is famous for its U-shaped subduction system beneath the Banda Arc. To better understand the architecture of the underlying structure in this region, we performed body-wave travel time tomography using ten years of catalog data provided by the Indonesian Agency for Meteorology, Climatology, and Geophysics. We utilize 9729 events in total, from which 46,446 P-wave arrival times were extracted. We used a double difference method to relocate the initial event catalog, which produced a pattern of seismicity consistent with a curved subduction system. Our tomographic model reveals a high velocity band between 90 and 240 km depth in the upper mantle, which is interpreted to be a concave dipping lithospheric slab that is parallel to the present-day Banda arc. Our results also show that lithosphere subducting from the north and south starts to collide at a depth of 300–350 km and becomes shallower further east. Apparent discontinuities in the high velocity band and a corresponding lack of seismicity supports the presence of a slab tear to the west of Seram. A dipping high velocity structure that is present from south to north beneath the island of Timor represents a subducting slab that dips more steeply beyond a depth of 150–200 km, which appears consistent with slab roll-back. Our tomographic model also shows evidence of back arc thrusting to the north of Sumbawa and Flores Islands in the form of a south-dipping higher velocity band at shallow depth. Furthermore, our tomographic models also reveal the possible presence of underthrust continental forearc in the form of a thin higher velocity anomaly that connects the backarc thrust and northward dipping lithosphere slab in the Timor area. Finally, a zone of low velocity above the higher velocity slab is clearly seen beneath Seram Island at a depth of ∼100 km and may represent a partial melting zone.

Effects of wind barriers on the aerodynamic forces and driving safety of vehicles on a wide bridge girder at various angles of attack

This paper presents the effects of angles of attack (AOA) on the windproof effect of wind barriers and the driving safety of highway vehicles on a wide bridge girder. The aerodynamic force coefficients of the vehicles were obtained using the force measurement technique. Computational fluid dynamics simulations were employed to investigate the mean wind velocity field on the upper surface of the girder. A comparison was made between the aerodynamic forces on a vehicle at various AOA on a bridge deck with guardrails and a deck with wind barriers. The windproof effect of wind barriers at various AOA was accessed by the safety factor of a vehicle. The results showed that the maximum of the aerodynamic forces of vehicles was not typically observed at a 0° AOA. The windproof effect of wind barriers became more pronounced as the magnitude of the AOA increased. As AOA increases, the height of the low wind velocity zone above the deck shows an upward trend. Compared to the deck with the guardrails, the height of the low wind velocity zone was much higher in the presence of wind barriers. The increase in the height of the low wind velocity zone will result in a decrease in the aerodynamic side force and an increase in the rolling moment acting on vehicles. It is also noteworthy that the installation of wind barriers can cause a reduction of overturning and side-slip safety factors of vehicles at specific AOA. This suggests that the wind barrier may potentially compromise driving safety at specific AOA.

Deep structural insights into the origin of the Heyuan ms 4.5 revealed by deep seismic sounding profiles in southeast China

This study presents an interpretation of a deep seismic sounding (DSS) profile that carried out along the Cathaysia Block in southeast china, aiming to explore the crustal velocity structure. Data used in the survey were obtained from three controlled-source explosions conducted along the 320 km long Lianping-Heyuan-Shanwei profile. The modeling was based on ray tracing, using the extrapolation of seismic wave arrival times with the help of travel times predicted from a one-dimensional velocity model. The average velocity structure of the middle crust is 6.0–6.4 km/s, while a low velocity anomaly of approximately 0.1–0.2 km/s in the vicinity of the Heyuan-Shaowu fault zone. The resulting 2D velocity model indicates that steeply dipping low-velocity zones that correlate with the projection of two major fault zones. These zones, together with a flat LVZ at a depth of 12 km, define a triangular region that correlates with numerous hypocenters. This tectonic setting is favorable for the accumulation and release of strain in high-velocity media within the triangular region. The unique triangular structure in the upper crust provides necessary shallow medium conditions for seismic activity. This indicates that increased seismicity within this area is partially attributed to heightened stress within higher-velocity material. The triangular annular low-velocity body, situated in the upper crust, is influenced by dynamic environmental factors caused by deep thermal disturbances. The deep-seated fault serves as a conduit for the historical migration of thermal material, likely contributing to the seismogenic conditions for earthquakes in Heyuan’s region through deep-seated thermal disturbances. These findings provide a novel geophysical reference model for the regional seismicity near the Xinfengjang reservoir and significantly contribute to understanding the causal relationship between tectonic setting and seismicity. In comparison with previous studies, our research is dedicated to investigating the causes of shallow earthquakes in the region and exploring the relationship between deep and shallow structures.

Investigation of droplet splashing behavior during oblique jet impact onto a wall

For the issue of jet impingement on the wall in industrial cooling processes, an experimental setup based on high-speed photography for oblique jet impingement onto the wall was constructed. The experimental focus was on the study of liquid droplet splashing behavior after oblique jet impingement on the wall, discussing the liquid droplet splashing behavior under three jet impingement modes: Rayleigh regime, first wind-induced regime, and secondary wind-induced regime. By employing methods such as trajectory imaging and particle image velocity for liquid droplet parameter image measurement, obtaining the particle size, velocity, and distribution of splashed droplets after oblique jet impact on walls under different working conditions. The impact of jet impingement velocity and angle on droplet splashing parameters was analyzed. The results showed that when the impingement point is before the breakup length, with increasing flow velocity, the surface wave of the liquid column, and the spreading liquid film became more pronounced, but the loss of liquid-phase components due to splashing was relatively small. When the impingement point is after the breakup length, the secondary breakup resulting in a “crown”-shaped liquid film after droplet impingement leads to a significant loss of liquid-phase components through splashing. As the inlet velocity of the jet increases, there is a decreasing trend in droplet size and an increasing trend in droplet velocity. With an increase in jet angle, there is a decreasing trend in droplet size and velocity. Based on the concentration, size, and velocity distribution characteristics of splashing droplets, the area after oblique jet impingement on the wall can be divided into the impingement zone, low-concentration low-velocity zone, high-concentration high-velocity zone, and lateral splashing zone. This has significant implications for understanding the splashing mechanism after oblique jet impingement on the wall and optimizing operating conditions.

Aerodynamic optimization design and experimental verification of a high-load axial flow compressor

The performance and stable operating range of compressors are critical to the efficient operation of various turbomachinery systems. This paper proposes a multi-level optimization strategy combining the uni-uniform direct free deformation method, Linux partitioned CPU accelerated parallel computing technology, multi-objective particle swarm optimization algorithm and downhill simplex algorithm, which improves design efficiency. Numerical results show that after optimization design, the average value of peak efficiency and stall margin increases. The flow mechanism of compressor performance improvement after optimization lies in the reduction of a low-velocity separation zone in stator hub region. Moreover, the experiment study confirms the reliability and accuracy of the optimization design method and found that flow instability triggering mode, propagation characteristics of the stall cell, and surge frequency are changed after optimization design. Setting a probability distribution threshold for autocorrelation coefficient and cross-correlation coefficients can be used to predict the arrival of the surge condition.

Seismic structure of Iceland revealed by ambient noise Rayleigh wave tomography

As it is an ideal location for studying plume–ridge interactions, a clear image of the Icelandic upper mantle structure is necessary. We collect continuous seismic records from 164 stations and extract Rayleigh wave dispersion curves via the frequency-Bessel (F-J) transform method. Based on ambient noise tomography, we provide a new shear-wave velocity model of the Icelandic crust and uppermost mantle, extending to a depth of 120 km. The model is validated by the waveform simulation method and reveals extensive crustal low-velocity zones (LVZs) across both the neovolcanic and nonvolcanic zones of Iceland. These crustal LVZs may be attributed to elevated temperatures, partial melting, and lithological variations. A distinct LVZ beneath a depth of 60 km, mainly on the North American Plate, may correspond to Icelandic plume material. Additionally, hot plume material may be delivered to the crust through low-velocity conduits beneath the spreading mid-ocean ridge. There is a clear contrast between the uppermost mantle low-velocity zones (UMLVZs) in the western region and the uppermost mantle high-velocity zones in the eastern region, which may indicate asymmetric tectonic plates on both sides of the mid-ocean ridge. This asymmetry may be attributed to the multiple eastward jumps of the ridge systems. The eastern high-velocity body, meaning a cooler uppermost mantle than that of the western region, may act as a barrier to obstruct the eastward plume flow. Under plume–ridge interactions, plume material can affect crustal accretion and feed volcanic activity on the surface along the spreading Mid-Atlantic Ridge.

Numerical investigation and rapid prediction of the erosion rate of gate valve in gas-solid flow

Gate valves are essential control components in pneumatic conveying systems and often experience erosion on their sealing structures due to impacts from solid particles. The erosion leads to a degradation of the sealing effectiveness and, in severe cases, system malfunction. To address this issue, a numerical model based on computational fluid dynamics (CFD) is developed for the simplified two-dimensional gate valve. The two-way Euler-Lagrange method is utilized to investigate the characteristics of gas-solid two-phase flow and erosion rate. The simulation procedure is verified by comparing the simulation results with experimental data. Results show that the sealing surface separates the free shear layer above the cavity and a low-velocity zone is created on the sealing surface. The particles moving at the downstream bottom are the main particles that impact the sealing surface. The erosion results show that the maximum erosion rate occurs near the top of the sealing surface. And the low-velocity zone reduces the erosion rate within that region. Particle diameter, gas velocity, and valve opening have an important effect on erosion on the sealing surface. The erosion rate increases as the valve opening decreases. The value of the maximum erosion rate increases with particle diameter and gas velocity, and its position changes. Finally, based on the established numerical model, a prediction model for the sealing surface erosion rate is constructed using the surrogate model approach.

Geoelectric studies in earthquake hazard assessment: the case of the Kozlodui nuclear power plant, Bulgaria

AbstractThe study presents the results of geoelectric research for seismic risk assessment on the example of the Kozlodui nuclear power plant in Bulgaria. The image of the geoelectric structure in the study area was obtained using one-dimensional inverse electrical resistivity modeling of the full five-component magnetotelluric data and quasi-three-dimensional inverse conductivity modeling of the geomagnetic responses recorded during the summer 2021 field campaign. According to the presented results, the geoelectrically anomalous structure is divided into two levels. The near-surface anomalous structure in the immediate reach of human geotechnical activity corresponds to the electrically conductive sedimentary fill. The mid-crustal layer is coincident with the low seismic velocity zone at the brittle and ductile crust interface, revealed in previous studies. The presented results imply that the geological environment is not affected by large faults capable of transmitting seismic energy from tectonically active areas, however, in further studies, attention should be paid to the strike-slip fault systems adjacent to the study area.