Water Flow Field Research Articles

Modelling study on pedestrian evacuation dynamics considering exit selection behaviour under flood disaster

Flood spreading in metro stations is a dangerous hazard that frequently causes casualties and property losses. However, pedestrian evacuation under flood spreading scenarios has not been fully investigated. To fill this gap,we propose an extend Floor-Field model incorporating flood spreading and exit selection behaviour of individuals. In the model, the dynamic flood spreading process on metro platforms is expressed by using a simulation software named Mike21. The optimal exit selected by pedestrians in each step is decided on three factors, that is pedestrian density around the exit, pedestrian distance to the exit, and water depth at the exit. Meanwhile, the movement speed of pedestrain also changes with the water depth at each time step. Based on this, the transition probability to neighbor cell including static field, dynamic field, height field, and water flow field is calculated. This results in a flood evacuation model considering the pedestrian's behaviour when choosing an exit. The effects of flooding, pedestrian density, different exit selection behaviours, water flow field, and inlet flow on evacuation were thoroughly analysed. The analysis demonstrates that the likelihood of flooding significantly impacts the evacuation of pedestrians from the subway station; the more flooding is taken into account, the more influential the impact. In addition, the effect of inlet flow on evacuation is also noteworthy; considering exit selection behaviour can significantly increase the effectiveness of evacuation. The study's findings can be used to develop evacuation plans for flooded metro stations.

Numerical simulation of the water flow field on subway stairs and evaluation of people safety evacuation

ABSTRACT Stairs in subway stations are vulnerable to floods when rainstorm disasters occur in cities. The stairs, as a critical way for human evacuation, can affect the safe evacuation of people on flood-prone stairs. To evaluate the risk of people evacuating through different slopes and forms of stairs when floods invade subway stations, a numerical model for the water flow on stairs based on the volume of fluid model and the realizable k-ε model was established. The water flow patterns on stairs at the subway station entrance under different slope conditions and with/without rest platforms were simulated. The real-time water flow process on stairs at different inlet depths was obtained, and the escape control index F was used to evaluate the risk of people evacuating through stairs at different slopes and water depths. The results indicate that the presence of a rest platform can cause an increase in water velocity and depth on pedestrian stairs, and people should choose stairs without a rest platform for evacuation during the evacuation process. The research results hope to provide a reference for the people evacuation on stairs, and further improve the theory of safe evacuation of personnel on flood-prone stairs.

(Invited) Comparison of Catalyst-Coated Electrodes vs. Catalyst-Coated Membranes in PEM Water Electrolysis Cells

The PEM (Proton-Exchange Membrane or Polymer Electrolyte Membrane) cell concept [1] is used in fuel cells and water electrolysis cells. PEM water electrolysis is a compact, efficient and flexible technology for the production of “green-hydrogen” from renewable (intermittent) energy sources. The unit cell (Figure 1) is made of several adjacent functional layers: (i) the proton-conducting polymer membrane (1); (ii) two catalysts layers (CLs) for hydrogen/oxygen evolution containing platinum group metals or PGMs (2;2’); (iii) a porous transport layer used for mass transport of reactants/products and electricity distribution (3;3’); (iv) water flow fields for water circulation (4;4’); bipolar plates (5;5’). From a practical viewpoint, the CLs can be deposited on either side of the interfaces formed between the polymer membrane and the porous transport layer: (i) on the supporting porous transport layers to form catalyst-coated electrodes which are then hot pressed against the bare membrane to form membrane – electrode assemblies; (ii) directly onto the membrane to form catalyst-coated membranes (CCM).The aim of this paper is to evaluate the efficiency and durability of both concepts, drawing on recent advances in manufacturing techniques to reduce the loading of PGM catalysts.[1] W.T. Grubb Jr., Batteries with Solid Ion-Exchange Electrolytes. Journal of the Electrochemical Society. 106 (1959) 275-279.[2] C. Rozain, P. Millet, Electrochemical characterization of Polymer Electrolyte Membrane Water Electrolysis Cells, Electrochimica Acta, 131 (2014) 160-167. Figure 1. Schematic diagram showing the cross-section of a PEM water electrolysis cell [2]. Figure 1

Micromechanical analysis of contact erosion under cyclic loads using the coupled CFD‒DEM method

Different layers of soil often have distinct particle sizes. When exposed to the natural environment, soil is easily affected by natural rainfall, rising groundwater levels, and human activities, leading to particle contact erosion, which reduces the safety and service performance of the soil structure. In this paper, a coupled computational fluid dynamics–discrete element method (CFD–DEM) model was employed to investigate the particle migration phenomena, mechanical response of contact interfaces, variations in flow fields, and macroscopic deformation during the contact erosion process under cyclic loads at different frequencies and amplitudes. The conclusions are presented as follows: (1) Within one cycle of cyclic loading, both compression during loading and stress relaxation during unloading are the main factors triggering the migration of fine particles. (2) The migration and loss of fine particles mainly occur in the early stages of cyclic loading, where strong contact force chains are formed within the fine particle layer, leading to significant plastic deformation of the soil at the macroscopic level. (3) Under cyclic loading, changes in the soil pore structure cause an upwards hydraulic gradient in the initial quiescent water flow field. This hydraulic gradient can rupture weak contact force chains and cause particle pumping. (4) Increasing the frequency and amplitude of cyclic loading intensifies the erosion of fine particles, causing greater axial deformation of the soil. Compared to cyclic loading frequency, the amplitude of cyclic loading has a greater impact on contact erosion.

Critical hydrodynamic force levels for efficient removal of oral biofilms in simulated interdental spaces

ObjectivesSonic toothbrushes generate hydrodynamic shear forces for oral biofilm removal on tooth surfaces, but the effective thresholds for biofilm removal remain unexplored. This in vitro study aimed to investigate various threshold values for hydrodynamic biofilm removal in vitro.Materials and methodsA specialized test bench was designed with a known water flow field within a gap, ensuring that hydrodynamic shear forces on the wall were solely dependent on the volume flow, which was quantifiable using an integrated flow meter and proven by a computational fluid dynamics simulation. A young 20 h supragingival six-species biofilm was developed on hydroxyapatite disks (∅ 5 mm) and applied into the test bench, subjecting them to ascending force levels ranging from 0 to 135 Pa. The remaining biofilms were quantified using colony forming units (CFU) and subjected to statistical analysis through one-way ANOVA.ResultsVolume flow measures < 0.1 l/s: Error 1% of reading were established with the test bench. Untreated biofilms (0 Pa, no hydrodynamic shear forces) reached 7.7E7 CFU/harvest and differed significantly from all treated biofilm groups. CFU reductions of up to 2.3E6 were detected using 20 Pa, and reductions of two orders of magnitude were reached above wall shear forces of 45 Pa (6.9E5).ConclusionsCritical hydrodynamic force levels of at least 20 Pa appear to be necessary to have a discernible impact on initial biofilm removal.Clinical relevancePure hydrodynamic forces alone are insufficient for adequate biofilm removal. The addition of antiseptics is essential to penetrate and disrupt hydrodynamically loosened biofilm structures effectively.

Design and Study of a Sediment Erosion Test Device for a Single-Flow Channel in the Guide Apparatus of a Reaction Hydraulic Turbine

Sediment erosion damage is one of the main causes of structural failure in reaction turbine units. To study the mechanism through which sediment erosion affects the water-guiding mechanism of a reaction turbine unit, this study obtained the average concentration and particle size of sediment during the flood season based on the statistics of the measured sediment data from the power station. Additionally, the characteristics of the solid–liquid two-phase flow of the diversion components of the reaction hydraulic turbine were numerically calculated. Based on the velocity triangle change in the guide apparatus and the flow similarity principle, a flow-around wear test device for the guide apparatus of the reaction turbine was designed. Furthermore, the similarity of the sand–water flow field between the guide apparatus of the prototype unit and the test device was compared and analyzed. The results demonstrated that the sand–water flow field of the diversion components of the prototype unit was axisymmetric and exhibited a potential flow distribution. Additionally, uniform sand–water flow occurred within the guide apparatus, with a small sand–water velocity gradient near the wall of the stay vanes (SV) and the guide vanes (GV). The maximum volume fraction of sediment particles was observed in the tailing area of the spiral casing, indicating an enrichment phenomenon of sediment particles. The velocity of the sediment particles on the surface of the guide vane in the single-channel sediment wear test device and prototype unit ranged from 6.2 to 7.8 m/s, and the velocity of the sediment particles on the surface of the stay vane ranged from 5.1 to 14.6 m/s, and the difference of the sediment particles’ velocity near the wall was 1 to 3 m/s. The trailing vorticity of the guide vane reached a maximum of 120 s−1. Consequently, the single-channel sediment erosion test device can unveil the sediment erosion mechanism of the guide apparatus of a reaction turbine.

Comparison of microstructure and thermal-fluid coupling heat transfer behavior of strip-cast Nd-Fe-B flakes at different cooling roller speeds

Strip-casting is a key step among processes for manufacturing the Nd-Fe-B permanent magnets. Current research on the process parameters of the strip casting process mostly relies on the trial-and-error method. In this paper, the influence of the cooling roller speed on the strip-cast Nd-Fe-B flakes is investigated by a combination of simulation and experiment. The microstructures of the strip-cast flakes prepared at different roller speeds are observed and analyzed. The simulation is further performed by using the thermal-fluid coupling method. The temperature field and cooling water flow field of the cooling rollers at different roller speeds are obtained to explain the principle of the microstructural evolution. The temperature field distribution affects the uniformity of the columnar grains on both sides of the strip-cast flake. Higher or lower temperature can also lead to the formation of α-Fe, cluster rare earth (RE) rich phases, or ultra-fine equiaxed grains. An increase in cooling water flow rate is helpful to obtain the columnar grain with even thickness. The simulation results are consistent with the microstructural results. Furthermore, the simulated results and microstructural analyses are combined to indirectly evaluate the trend of magnetic properties of final sintered magnets from the tested strip-cast flakes. By verifying the performance of magnets prepared under the condition of only changing the roller speed during the entire process flow, the measurement results are consistent with the evaluation results, proving that the combined analysis proposed in this paper can reasonably predict the trend of magnetic properties of sintered Nd-Fe-B permanent magnet materials from the strip-cast flakes prepared at different roller speeds. This paper can provide a transferable idea and method for using numerical simulation to assist in the design and production of Nd-Fe-B flakes and sintered magnets.

Three-dimensional Response Characteristics of Self-potential Field for Dam Leakage Hidden Danger

In order to improve the application of self-potential field monitoring in detecting the potential reservoir dam leakage, we deduced the coupling equation of the self-potential field with water flow field and ions diffusion field, based on the formation mechanism of the self-potential field. We realized the three-dimensional numerical simulation of the self-potential field of reservoir dam by coupling finite and infinite elements by analyzing the response characteristics of the self-potential field with different water levels, different levels of danger, and different periods of typical dam leakage models. The results show that the magnitude of the self-potential field is proportional to the size of the leakage channel and the magnitude of water level difference. Thus, the distribution characteristics of the self-potential field could indicate the development period of a leakage to some extent, and the leakage location and early warning could be realized by monitoring self-potential fields.

Response of Sea Water Exchange Processes to Monsoons in Jiaozhou Bay, China

The self-purification capacity of semi-closed bays is closely related to the exchange process of open sea water. In recent years, with the enhancement of human development activities, environmental problems such as eutrophication, weak hydrodynamics, and poor water exchange capacity have appeared in the bays. In this paper, the water exchange time and flow field in Jiaozhou Bay (JZB) were investigated using the environmental fluid dynamics code with a coupled dye module. Specifically, Jiaozhou Bay was divided into seven zones to explore the effect mechanism of a monsoon on the water exchange process. A detailed analysis was performed on the current water exchange status in the highly polluted northeastern region of the bay and its influence on the surrounding areas. Based on the definition of the average residence time and considering the effect of the tracer release moment, the distribution of the water exchange time in the bay under three circumstances was obtained. Results showed that the timing of the tracer release exerted minimal influence on the average residence time. The water exchange process was influenced by a combination of astronomical and meteorological factors. The overall exchange capacity of the bay was strongest under the impact of a winter monsoon and tides, followed by a summer monsoon and tides, and the weakest exchange occurred under the influence of tides alone. Moreover, both summer and winter monsoons greatly facilitated water exchange in the heavily polluted northeastern region. However, pollutants from this region had a significant impact on surrounding areas during a summer monsoon. Changes in the structure and intensity of residual flow fields were the primary causes of exchange rate discrepancies.

Numerical Investigations of Heat Transfer and Fluid Flow Characteristics in Microchannels with Bionic Fish-Shaped Ribs

Microchannel cooling technology is an effective method to solve local thermal stacking. In this paper, four innovative microchannels with bionic fish-shaped rib arrangements (CM-O, CM-R, CM-H, and CM-G) are designed by imitating geese and fish clusters. The heat transfer and flow characteristics of the microchannels are simulated numerically at different Reynold’s numbers (Re = 200 − 1600). The liquid water temperature and flow field in the four innovative microchannels with bionic ribs are analyzed. The results show that the ribs’ arrangement has an influence on the thermal performance of microchannels. Compared to the smooth microchannel (CM), the of the Nu microchannels with the bionic fish-shaped ribs increases by 33.00–53.26% while the fave increases by 28.63–34.93% at Re = 1200. The vortices around the ribs are clearly observed which improves the temperature gradient. The performance evaluation criterion (PEC) of CM-H is higher than that of the others. This indicates that the rib arrangement of CM-H is superior for heat dissipation application.

Optimization and numerical simulation of the internal flow field of water–pesticide integrated microsprinklers

AbstractA new type of water–pesticide integrated microsprinkler has been developed in this study. Microsprinklers can irrigate crop roots to meet the irrigation index demand under low‐pressure conditions and apply pesticides on the backs of crop leaves to meet the spraying pesticide index demand under medium‐pressure conditions. In this paper, the structure and working principle of the water–pesticide integrated microsprinkler are discussed, and the key structural parameters are the number and diameter of the small round holes and the number and width of bevel grooves. Computational fluid dynamics (CFD) numerical simulations were performed to analyse the influence and variation in the key structural parameters on the microsprinkler flow field. The optimized structural parameters of the microsprinkler were determined: The outlet nozzle diameter was 3 mm, with three small round holes of 2 mm diameter and three bevel grooves of 0.8 mm width. The hydraulic performance of the optimized sprinkler and original sprinkler (outlet nozzle diameter was 2.5 mm, with two small round holes of 3 mm diameter and four bevel grooves of 1 mm width) were compared under different working pressure conditions. The results showed that the wetted radius and uniformity coefficient of the optimized sprinkler increased by 23% and 16%, respectively.

Enhancement technology of underground water flow field in coal mine to improve energy efficiency of heat pump system in geothermal energy development

In order to solve the problem that the cold/heat released from the underground pipe of coal mine into the soil layer is difficult to dissipate in a short time, the technology of enhancing the underground flow field of coal mine in geothermal energy development to improve the energy efficiency of the heat pump system is proposed. In this paper, based on the ground source heat pump project located in a coal mine, the energy efficiency enhancement technology of the artificial flow field ground source heat pump system is studied and tested. The test results show that when starting work at about 8:00, due to the increase of heating load, the accumulation of cooling capacity around the buried pipe increases gradually, and the return water temperature at the ground source side decreases gradually. At 14:05, the water was pumped for the operation of the artificial groundwater flow field. It can be seen that the temperature of the return water at the ground source side began to rise gradually, indicating that the accumulation of cold water around the buried pipe was relieved to a certain extent. In conclusion, the artificial groundwater flow field can alleviate the accumulation of cold water around the buried pipe heat exchanger to a certain extent, improve the return water temperature of the buried pipe heat exchanger, and improve the energy efficiency of the ground source heat pump system.

Oscillation dynamics of the air-core in a hydrocyclone

Tangential introduction of liquid results in a swirling flow within a cylindro-conical hydrocyclone. Upon continuous feeding with water, the central axial region experiences local low pressure across the height yielding the formation of an air-core, which executes meandering motion similar to the oscillation of an elastic string. We investigated the vortical flow and the induced oscillating behavior of an air column submerged in a water flow field inside a hydrocyclone. Through a series of experiments in a transparent hydrocyclone and subsequent full scale multiphase flow simulations with the Reynolds stress model, we analyzed the morphological characteristics of the air-core (mean and fluctuating properties). Air-core oscillations are characterized in terms of spatial wavelength and frequency. We show that hydrodynamics driven oscillating behavior of the air-core shares an analogy with the vibration of an elastic beam. Following this analogy, we obtain a scaling relationship between the wavelength and air-core radius, which is in good agreement with our experimental data and numerical results.

Analysis of Movements and Behavior of Bighead Carps (Hypophthalmichthys nobilis) Considering Fish Passage Energetics in an Experimental Vertical Slot Fishway.

Simple SummaryHydraulic structures have modified the natural waterways, and they have inevitably blocked fish migration routes and reduced fish habitat. To mitigate the impact on fish, fish passages have been developed as an effective way to restore riverine connectivity. The design of fish passage facilities refers to both hydrodynamics and fish behavior, and the information on the energetic expenditure of fish can be used to identify movement zones that are suitable for fish migration. Thus, this paper intended to identify fish movement behavior in response to water flow field information by means of estimating the energetic expenditure using an IBM approach. The results demonstrated that the fish required more energy in high TKE zones, and they were therefore likely to utilize the low TKE zones. This study provides a reference for optimizing the design of fish passages, and the method can be applied to assess the efficiency of fish passages and other fish bypass structures.An understanding of fish movement behavior in response to flow field variables is important for exploring the hydrodynamic strategies of fish in fish passages. In this paper, bighead carps were taken as an example. The fish movement behavior response to water flow field information by means of estimating the energetic expenditure using an IBM approach in an experimental fishway was investigated. Fish swimming velocity, drag force, and energy expenditure were analyzed in varied flow conditions related to hydraulic variables, including velocity (V), turbulent kinetic energy (TKE), and strain rate (SR). The result indicated that the fish will require more energy in high TKE zones. This study provides a reference for optimizing the design of fish passages and fisheries management. This method can be applied to assess the efficiency of fish bypass structures and conduct fish survival studies.

Study on the influence of contact surface curvature on water jet impingement flow field and initial damage of coal seam

AbstractThe design of the contact surface has a big impact on how well water jets penetrate coal rock. The influence of water jets on contact surfaces with various curvatures is studied using numerical modeling to elucidate the flow field and coal seam damage characteristics. The water jet impingement flow field region can be separated into three areas: velocity concentration, divergent flow, and wall recirculation. As the jet water pressure rises, the flow field's distribution features become more apparent. Water jet impact morphology and flow field properties on contact surfaces of various curvatures are comparable. The peak velocity ratio of the wall and axis falls first, then increase as the curvature radius ratio (n) of the contact surface increases. Near n = 0.8, the peak velocity ratio of the wall and axis reaches a minimum, indicating that the kinetic energy loss in the process of water jet impact to the contact surface is the greatest. When water jets of various pressures impact the contact surface, the peak velocity drops by two‐thirds before and after impact, and nearly 89% of the kinetic energy is lost in the impact process. The range of the initial damage and failure area in the center of the contact surface and the initial damage and failure area on both sides of the wall caused by water jet impact decreases gradually as n increases. When n = 2, the initial damage and failure region on both sides of the wall has virtually vanished; when n = 0.2. The contact surface's center failure depth induced by water jet impact is the deepest. The initial injury is unaffected by changes in jet water pressure.

Impact of submerged vegetation, water flow field and season changes on sediment phosphorus distribution in a typical subtropical shallow urban lake: Water nutrients state determines its retention and release mechanism

Sediment phosphorus act as a vital role on eutrophication in shallow lakes. The knowledge about the effect of submerged vegetation types and water flow field on sediment total phosphorus (STP) and the relationship with environmental variables in eutrophic shallow lakes is limited. In this study, temporal and spatial characteristics of water and sediment nutrients in a typical subtropical shallow urban lake Hangzhou West Lake were evaluated, meanwhile, quantitative analyses were investigated to determine the contribution of water nutrients, sediment properties and submerged vegetation on retention and release of sediment total phosphorus. Results illustrated that the water nutrients characteristics are determined by the water flow field and season changes. Additionally, much lower Nitrogen/Phosphorus (N/P) ratio (6.29 ± 3.25–16.82 ± 1.54) of downstream locations compared to that (9.79 ± 1.30–26.33 ± 2.90)of upstream and midstream locations in lake water, which led to the inconsistent characteristics between water nutrients and water chlorophyll a (Chl-a) and trophic state index (TSI). Temporal and spatial distribution of STP determined by season changes, water flow field types, submerged vegetation types, and deposition of aluminium salt (Al-salts) originated from water diversion project. The effect of interception of submerged vegetation and flow velocities reduction induced by water flow field types changed are similar that both accelerate the phosphorus retention in sediments. Results of structural equation modeling illustrated that the main effect on STP is water nutrients including water total nitrogen (TN), Chl-a, and TSI, which implied that the nitrogen limitation is the key factor. Water nutrients significantly and directly affect (coefficient is 0.254) STP while submerged vegetation exhibited indirectly effect induced by water nutrients (coefficient is 0.077) and sediment properties (coefficient is 0.062). The loss of nitrogen and an increase in phosphorus mainly influence the submerged vegetation distribution, higher trophic level index and sediment phosphorus release.

CFD Modelling of Spiral Concentrator- Prediction of Comprehensive Fluid Flow Field and Particle Segregation

A comprehensive numerical analysis of the fluid flow and dilute particulate flow in the LD9 spiral separator is presented in this work. The air–water flow field on a coal spiral is simulated using the volume of fluid (VOF) coupled with RANS turbulence models. Water depth and flow field predictions by RSM show close agreement with experiments. Stability depth, turbulence intensity was analyzed for entire liquid depths. The discrete phase model is used to model the dilute particulates at different flow rates. Turbulent dispersion of particles using dispersion index and Bagnold force analysis indicate that centrifugal force dominates the separation at increased particle size and water depth level, whereas the fines are significantly affected by turbulence dispersion at the outer trough region. The magnitude of the Bagnold to gravitational force increases from the inner to outer trough region and a dip at the outer edge region due to inherent change of shear rate. Coarse particles experience higher lift than the fines and migrate to the top flowing layers.

Distributions and Influencing Factors of Dissolved Manganese in Kongsfjorden and Ny-Ålesund, Svalbard

The contributions of polar glaciers to the global distribution of trace metals have attracted an increasing amount of attention due to global warming. To better understand the distributions and influencing factors of dissolved manganese (dMn) in the Arctic, samples were collected in Ny-Ålesund and Kongsfjorden in Svalbard in August 2013. dMn concentrations in the drainage basin of the Bayelva River, of which the average value was 216.4 ± 54.2 nM (n = 16) and higher than that in other polar rivers and lakes, showed no significant differences from upstream to downstream in August. dMn varied differently at certain stations in the mainstream of Bayelva River on different days due to complex factors in the polar region, e.g., topography, tributaries, groundwater, organic matter content, and runoff fluxes. It was estimated that the scale length (distance from the initial concentration to 1/e) of dMn in the coastal area of the Bayelva River was 1050 m, indicating that the influence of Bayelva River on the distributions of dMn in Kongsfjorden was insignificant. Affected by high-dMn concentration tidewater glacier meltwater (∼581.1 nM) in the inner fjord, dMn showed an increasing trend from the fjord entrance to the inner zone in the surface layer of Kongsfjorden. Furthermore, the longer scale length (4.25 km) and overlying relatively large discharge suggested a higher incidence of tidewater glaciers in Kongsfjorden. The vertical distributions of dMn presented obvious stratification, with higher dMn at the surface (80.9 ± 53.7 nM, n = 21) and lower dMn below the surface (12.6 ± 2.4 nM, n = 11). Combined with the water mass properties and flow field, the distributions of dMn in Kongsfjorden were mainly controlled by relatively high dMn concentrations, low-salinity surface water, relatively low dMn concentrations, and high-salinity Atlantic water mixing. The dMn concentrations in Ny-Ålesund and Kongsfjorden were significantly higher than those in the North Atlantic Ocean and Arctic Ocean around Svalbard. Tidewater glaciers (Kongsvegen, Kronebreen, and Kongsbreen) and glaciers of Svalbard were estimated to export 0.46 and 74 Mmol/year of dMn, which was comparable to other sources to the Arctic Ocean. The contributions of glaciers to the distributions of dMn in the Arctic and global Ocean were expected to be increasingly significant considering the increasing amount of glacier meltwater in the context of global warming.

Seepage effect on failure mechanisms of the underwater tunnel face via CFD–DEM coupling

Seepage plays a significant role affecting the tunnel face failure process. However, its effect on the stability of the underwater tunnel face remains unclear. To study the seepage effect on the failure mechanism of the underwater tunnel face, this study models the failure process by the Computational Fluid Dynamics-Discrete Element Method (CFD–DEM) approach, in which the seepage force is simulated by fluid–particle interaction between CFD and DEM. The contact parameters of the sand particles in water were obtained by calibrating the results of underwater sand column collapse tests. In this study, three hydraulic conditions including dry, undrained, and seepage are considered for the tunnel face. The simulation results indicate that seepage affects the failure mechanism and the support pressure significantly. Then, a comparison between CFD–DEM results and solutions in previous literature was conducted, which suggests that the tunnel face permeability is the key factor that causes the difference in the support pressure under different hydraulic conditions. Additionally, failure mechanisms with different water depths were analyzed by displacement field, water pressure field, flow field, and support pressure. The results show that under the seepage conditions the failure zone is enlarged as the water depth increases. Besides, the microscopic contact information under the seepage condition in different regions was presented. This work provides evidence for evaluating the support pressure of a stable tunnel face when considering the seepage.

Data Assimilation of Water Elevation in Shallow Water Flow Based on the Extended Kalman Filter FEM Using Measurement Data from Image Analysis

In this paper, we present a data assimilation analysis in a shallow water flow field considering shoreline movement, based on the extended Kalman filter finite element method (extended Kalman filter FEM). It is known that if the combined method of the Kalman filter and the finite element method(FEM) is employed, a solution can be obtained that is closer to the practical observed value than that based on normal FEM. A dam-break problem is targeted in numerical experiments. In this study, the observed values used in the extended Kalman filter FEM are obtained by image analysis, and we investigate the estimation accuracy by changing the governing equation for shallow water flow.