Water Content Distribution Research Articles

Modelling Soil Water Infiltration and Wetting Patterns in Variable Working-Head Moistube Irrigation

Moistube irrigation is an efficient method that accurately irrigates and fertilizes agricultural crops. Investigation into the mechanisms of infiltration behaviors under an adjusted working head (WKH) benefits a timely and artificially regulating moisture condition within root zones, as adapted to evapotranspiration. This study explores the laws of Moistube irrigated soil water movement under constant and adjusted working heads. Lysimeter experiments were conducted to measure Moistube irrigation cumulative infiltration, infiltration rate, and to observe wetting front area and water content distribution using digital image processing and time domain reflectometry, respectively. Treatments of constant heads (0, 1, and 2 m), increasing heads (0 to 1, 0 to 2 and 1 to 2 m) and deceasing heads (1 to 0, 2 to 0 and 2 to 1 m) were designed. The results show that (1) under constant heads, the cumulative infiltration increases linearly over time. The infiltration rate and cumulative infiltration are positively correlated with the pressure head. When WKH is increased or decreased, the infiltration rate and cumulative infiltration curves significantly change, followed by a gradual stabilization. The more the head is increased or decreased, the more evident this tendency will be. (2) When WKH is increased, the wetting front migration rate and the wetted soil moisture content marked increase; when WKH is decreased, the wetting front migration rate sharply decelerates, and the water content of the wetted soil slowly grows. They both tend to equilibrium with time. (3) By regarding the same cumulative infiltration of increased WKH and constant WKH treatments as a similar initial condition, we proposed a cumulative infiltration empirical model for Moistube irrigation under variable working head. Additionally, we treat the Moistube as a clayey porous medium and construct a HYDRUS-2D numerical model to predict the infiltration behaviors under variable WKH. The validity of the two models were well proven, with MRE and NRMSE close to 0 and NSE greater than 0.867, indicating good agreements with the experimental results. This model breaks through the limitation of constant boundary of traditional numerical model and applies variable head boundary to the boundary of the Moistube pipe, which can also effectively simulate the response mechanism of Moistube irrigation to variable WKH. The research results further confirmed the feasibility of manually adjusting the WKH to regulate the discharge of the Moistube pipe and soil moisture state. Based on the HYDRUS-2D numerical model simulation results and the root distribution and water demand of typical facility crops, the selection range of placement depth and the adjustable range of WKH of Moistube irrigation were proposed. The research results provide a theoretical reference for manual adjustment or automatic control of Moistube irrigation WKH to adapt to real-time crop water demand in agricultural production.

Effect of soil conditioning on the permeability of coarse-grained soil in mechanized tunnelling

In coarse-grained soils, the reduction of soil permeability via conditioning can effectively prevent groundwater from entering the chamber, thus providing better tunnel face control and ultimately preventing excessive settlements of the surface. In this study, several mixtures of coarse-grained and soil-foam mixtures were utilized in experiments. In which, effects of the foam expansion ratio, foam injection ratio, soil water content, pressure, and grain size distribution on the soil permeability were investigated. In these experiments, two soil types of poorly graded sand (SP) and poorly graded sand with silt and gravel (SP-SM), with different grain sizes were utilized. Based on the experimental results, it has been observed that the soil permeability increases with increasing foam expansion ratio, water pressure, and the coarse-grained portion of the soil. Meanwhile, soil permeability decreases with increasing foam injection ratio and soil water content. Based on the observations, it can be inferred that optimal soil permeability for soil moisture of 15 %, the pressure of 1 bar with a certain grain size occurs at a foam expansion ratio of 7.5 and a foam injection ratio of 52 %.

Quantification of the water exchange in an agroforestry system under the background of film-mulching drip irrigation of farmland

Water availability is the most critical constraint for the healthy and sustainable development of agroforestry systems in arid and semi-arid regions; consequently, it is essential to clarify soil water dynamics and quantify water exchange within agroforestry systems. In this study, a two-year field experiment and a HYDRUS-2D numerical simulation model were used to clarify the characteristics of the two-dimensional distribution of soil water and the horizontal water exchange in an agroforestry system under the background of film-mulching drip irrigation of farmland. The results showed that the HYDRUS-2D for agroforestry systems had high accuracy in calculating the water flow and capturing the dynamic water exchange in various soil layers. The model simulation results showed that there were differences in soil water content between forest belt and farmland, and the two-dimensional distribution of soil water content showed vertical water transport and horizontal water exchange in the agroforestry system. During the growing season, the horizontal water flow exchange was mainly from the forest belt side and the farmland side to the agroforestry transition zone, with inflows of 61.3 mm and 199 mm at depths of 0–100 cm, respectively. A long-term severe "water stress zone" developed at a depth of about 0–40 cm in the forest belt, so the 0–40 cm soil depth was the main area of water competition in the agroforestry system. The results could provide a reference for the long-term healthy development of agroforestry systems and the management of agricultural water resources in oasis-desert systems under film-mulching drip irrigation conditions.

Estimating the spatial distribution of soil volumetric water content in an agricultural field employing remote sensing and other auxiliary data under different tillage management practices

AbstractKnowledge of soil volumetric water content (VWC) on agricultural soils as influenced by different soil management practices is important, but the measurement outputs of frequently used traditional sampling techniques are restricted to point‐based measurements with limited spatial coverage. Remote sensing (RS) techniques are therefore being explored because of their greater spatial and temporal availability as well as their ability to cover large‐scale areas. But a general limitation for RS data is the presence of vegetation cover, cloud cover and the effect of topography. To minimize the effects of these factors during field sampling, the use of spectral indices and terrain attributes have proven successful in the estimation of several soil properties; however, the impact of these approaches for the estimation and mapping of soil VWC, an important factor in crop growth and development, especially where different soil management practices are employed, remains limited. To contribute to the knowledge base of RS under varying soil systems, this study explores the possibility of combining in‐situ measurements with remotely sensed (explanatory variables) data obtained under four different tillage practices to produce an estimated soil VWC that represents the entire study field. The tillage practices used include reduced till (RT), strategic till (ST), no‐till (NT) and conventional till (CT). From these tillage plots, three explanatory datasets, namely Sentinel‐2 (S2), spectral indices (SI) and terrain attributes (TA), were collected as predictors. In addition, each of the explanatory variables was structured into four groups, representing each of the four tillage methods. The eXtreme Gradient Boosting (XGBoost) model was used, and the best results were selected based on the root mean squared error (RMSE), the coefficient of determination (R2) and the mean absolute error (MAE). Prior to soil VWC prediction, the Pearson correlation matrix was used to determine the linear relationship between each of the selected explanatory variables (S2 bands, SI and TA) and soil VWC. Furthermore, spatial distribution maps of soil VWC were constructed using the inverse distance weighting (IDW) interpolation technique. For soil VWC estimation, the TA outperformed the SI and S2 datasets (R2 = 0.84). Similarly, the spatial distribution maps obtained from the TA data show a study area with a large concentration of VWC compared with the other datasets. The study also identified CT as the tillage approach that most impacts soil VWC estimation because all predicted results were poor without the addition of data from the CT plot. According to our findings, using TA data collected from various tillage management systems to estimate soil VWC is very promising because they can be used as predictors to improve soil VWC estimation and mapping. This study demonstrates conclusively that remote sensing data collected from different tillage management systems can be used as predictors to enhance the estimation and mapping of soil VWC, complementing the basis for the development of reliable and consistent precision irrigation management systems.

Evaluating soil water movement and soil water content uniformity under sprinkler irrigation with different soil texture and irrigation uniformity using numerical simulation

Water movement and its distribution uniformity in the soil are essential for the design of sprinkler irrigation systems. They are both crucial factors influencing nutrient migration and the productivity of crops. In this study, a new numerical simulation method was proposed to investigate the soil water movement in sprinkler irrigation under nonuniform infiltration boundary conditions using COMSOL software. Besides, two soil tank experiments were conducted to test the reliability of the simulation model. Finally, the model was applied to evaluate the effects of sprinkler irrigation uniformity, soil texture, and initial soil water content on soil wetting patterns and soil water content uniformity. The results showed that the COMSOL-2D predictions of the vertical wetting fronts were in good agreement with the experimental data. The soil texture and initial soil water content influenced the soil wetting pattern and the risks of surface runoff and deep percolation in sprinkler irrigation systems. When the water application rate was 11.35 mm h−1 with an irrigation duration of 10 h, it was easy to cause surface runoff in silty clay loam while deep percolation in loamy sand. Additionally, when the initial soil water content is high, it should be better to avoid irrigation or cut down the irrigation duration to prevent percolation. The water within the soil was more uniformly distributed than that applied through a sprinkler irrigation system. The uniformity coefficient of soil water content distribution (CUs) increased from 87.75 % to 95.56 %, as the uniformity coefficient of sprinkler irrigation (CU) increased from 40.74 % to 82.41 %. Although a higher initial soil water content brought a higher soil CUs value, it also led to a higher risk of percolation. The experimental and simulation results indicated that the COMSOL-2D model could be used to accurately simulate soil water movement in sprinkler irrigation and determine the suitable operation mode of low-pressure sprinklers.

Stability analysis of heterogeneous infinite slopes under rainfall-infiltration by means of an improved Green–Ampt model

Rainfall infiltration analysis has a great significance to the mitigation and risk assessment of rainfall-induced landslides. The original Green–Ampt (GA) model ignored the fact that a transitional layer exists in infiltration regions of soils under the rainfall permeation; moreover, it cannot effectively analyze the rainfall-infiltrated heterogeneous slope considering the spatial variability of saturated hydraulic conductivity ( ks ). In this study, an improved GA model is proposed for the rainfall-infiltration analysis of heterogeneous slopes. Four common slope cases are investigated to validate the effectiveness of the proposed model. An infinite slope model is taken as an illustrative example to investigate the distributions of volumetric water content and slope stability under the rainfall infiltration. The results show that the distributions of volumetric water content and factor of safety ( Fs) obtained from the proposed model are in very good agreement with the numerical results of the Richards' equation. In contrast, the modified GA model obtains biased distributions of volumetric water content and smaller Fs for the same cases. The results show that the proposed GA model can accurately identify the location of critical slip surface of the slope, and as such it provides an efficient method for risk analysis and control of slopes susceptible to landslide.

Study on Spatiotemporal Transport Characteristics of Soil Moisture in Layered Heterogeneous Vadose Zone Based on HYDRAS-3D

The heterogeneity of layered soils affects the transport processes of water in the vadose zone. However, the mechanism of soil moisture transport in the vadose zone under heterogeneous media conditions, especially the three-dimensional transport mechanism, is a frontier problem to be studied. In order to reveal the law of soil water transport in the vadose zone under heterogeneous media, this paper constructs a three-dimensional model of water transport using HYDRAS-3D (V 2.x) software through in situ tests of water transport in 3 × 3 × 4 m sample and verifies and analyzes the model. The vertical distribution and variability of soil water content and the temporal and spatial rules of soil water transversal transport at the soil–layer interface were analyzed. The results indicate that after adjusting the parameters in the HYDRAS-3D model using measured values, the simulation results are reasonable, and the model has high reliability. To represent the water content variability characteristics of the test tube profile, water movement in the vadose zone was classified as follows: (I) steady period (April–September, less affected by rainfall), (II) slow change period (January–March), and (III) rainfall rapid change period (June, when the impact of rainfall on the test cylinder was greater). The two largest values of the soil water potential variation gradient, 19.9 and 17.8 cm/d, were observed in the silty clay layer of the test cylinder, and the influence of evaporation and infiltration in the silty clay layer was most notable at the interface. The lateral transport of soil water at the interface was influenced to a certain degree by the layered heterogeneity, wherein the fine sand layer exhibited the most pronounced impact. This was followed by silt and silty clay layers, with the silt layer showing the lowest degree of influence. The research results can provide scientific reference for the rational planning of water resources in the Yinchuan Plain.

Effects of vegetation on the spatiotemporal distribution of soil water content in re-vegetated slopes using temporal stability analysis

The temporal stability of soil water is a critical state variable affecting hydrological process and structural stability of slopes. In this study, the effect of vegetation on the spatiotemporal characteristics of soil water content (SWC) was assessed via temporal stability analysis. Three types of re-vegetated slopes (grass, shrub, and grass-shrub) were constructed to explore the spatiotemporal distribution of the SWC at depths of 0–100 cm. Then, the effects of different vegetation covers on the SWC were explored. The coefficient of variation, the Spearman rank correlation coefficient, the mean relative difference, and the index of temporal stability were utilized to demonstrate the temporal stability of the SWC. Finally, a method of estimating the soil water status of re-vegetated slopes based on representative locations was developed. The results revealed that soil water dynamics were considerably governed by vegetation and rainfall. The vegetation cover considerably reduced the similarity of the spatial distribution pattern of the soil water, which tended to be more stable under grass cover. The weight-based prediction method developed in this study can more accurately estimate the overall soil water state of re-vegetated slopes. It provides a theoretical basis for the reasonable layout of SWC monitoring points and guidance for the ecological restoration of engineering slopes.

Numerical study on effect of anisotropic permeability of porous electrodes on PEM fuel cell performance

ABSTRACT The permeability of porous medium characterizes the ability of fluid flowing in the porous medium. The porous electrode of proton exchange membrane fuel cell consists of gas diffusion layer and catalytic layer, with the gas diffusion layer carrying the transport of the reaction gas and the catalytic layer being the main site of chemical reactions within the PEM fuel cell, both of which play a key role in the PEM fuel cell. In this paper, the effect of permeability in different directions within the porous electrode on the performance of PEM fuel cell was investigated in terms of polarization curves, oxygen distribution, and membrane water content distribution. It is found that under the same working conditions, the permeability in X-direction has the greatest influence on the PEM fuel cell performance and the PEM fuel cell performance is proportional to the magnitude of the permeability in X-direction, when the permeability in X-direction change to 0.1 and 0.2 of the original value, the PEM fuel cell performance decreases by 11.36% and 8.01%, and when the permeability in X-direction change to 5 and 10 of the original value, the PEM fuel cell performance increases by 10.18% and 13.79%. The effect of permeability in the Y-direction of porous electrodes on the performance of PEM fuel cells can be neglected. In porous electrodes, the PEM fuel cell performance reaches a peak when the permeability in the Z-direction of the gas diffusion layer is 1.18e-11 m2 and the permeability in the Z-direction of the catalytic layer is 2.36e-12 m2, therefore, increasing or decreasing the permeability in this direction leads to a decrease in the performance of the PEM fuel cell.

Numerical Study of Coupled Water and Vapor Flow, Heat Transfer, and Solute Transport in Variably‐Saturated Deformable Soil During Freeze‐Thaw Cycles

AbstractAs climate change intensifies, soil water flow, heat transfer, and solute transport in the active, unfrozen zones within permafrost and seasonally frozen ground exhibit progressively more complex interactions that are difficult to elucidate with measurements alone. For example, frozen conditions impede water flow and solute transport in soil, while heat and mass transfer are significantly affected by high thermal inertia generated from water‐ice phase change during the freeze‐thaw cycle. To assist in understanding these subsurface processes, the current study presents a coupled two‐dimensional model, which examines heat conduction‐convection with water‐ice phase change, soil water (liquid water and vapor) and groundwater flow, advective‐dispersive solute transport with sorption, and soil deformation (frost heave and thaw settlement) in variably saturated soils subjected to freeze‐thaw actions. This coupled multiphysics problem is numerically solved using the finite element method. The model's performance is first verified by comparison to a well‐documented freezing test on unsaturated soil in a laboratory environment obtained from the literature. Then based on the proposed model, we quantify the impacts of freeze‐thaw cycles on the distribution of temperature, water content, displacement history, and solute concentration in three distinct soil types, including sand, silt and clay textures. The influence of fluctuations in the air temperature, groundwater level, hydraulic conductivity, and solute transport parameters was also comparatively studied. The results show that (a) there is a significant bidirectional exchange between groundwater in the saturated zone and soil water in the vadose zone during freeze‐thaw periods, and its magnitude increases with the combined influence of higher hydraulic conductivity and higher capillarity; (b) the rapid dewatering ahead of the freezing front causes local volume shrinkage within the non‐frozen region when the freezing front propagates downward during the freezing stage and this volume shrinkage reduces the impact of frost heave due to ice formation. This gradually recovers when the thawed water replenishes the water loss zone during the thawing stage; and (c) the profiles of soil moisture, temperature, displacement, and solute concentration during freeze‐thaw cycles are sensitive to the changes in amplitude and freeze‐thaw period of the sinusoidal varying air temperature near the ground surface, hydraulic conductivity of soil texture, and the initial groundwater levels. Our modeling framework and simulation results highlight the need to account for coupled thermal‐hydraulic‐mechanical‐chemical behaviors to better understand soil water and groundwater dynamics during freeze‐thaw cycles and further help explain the observed changes in water cycles and landscape evolution in cold regions.

Stochastic Analysis of the Drawdown Time of Infiltration Basins in the Presence of Heterogeneous Soils

AbstractThe drawdown time is important for the design and assessment of infiltration basins. This paper investigates its dependence on soil heterogeneity, and simple analytical solutions for the mean and the variance are given. The solutions are tested through Monte Carlo simulations in various realistic scenarios, using a modified Green Ampt model for layered soils and a model based on the integration of the 1‐D Richards equation. The impact of the employed approximations is assessed, and the leading role of the spatial distribution of the saturated hydraulic conductivity is emphasized. The effects of other relevant design and natural factors, including the initial water level and water content distribution, are also investigated.

Dosimetry Predictors of Late Skin Reactions after Whole Breast Radiotherapy on a Large Mono-Institutional Cohort of Patients

To develop an NTCP model predicting late skin toxicity using dosimetric parameters from the breast dermis to identify possible RT constraints on such a structure. The skin structure was defined as the 5 mm inner isotropic expansion from the outer CT body contour. It was retrospectively segmented on a large mono-Institutional cohort of early-stage breast cancer patients enrolled between 2009 and 2017 (n = 1066). Patients were treated with tangential-field RT, delivering 40 Gy in 15 fractions without a RT boost. Toxicity was reported during FU using SOMA/LENT scoring. The study endpoint was moderate-severe late toxicity consisting of Fibrosis-Atrophy-Telangiectasia-Pain (FATP G2+) developed within 42 months after RT completion. Automatic delineation of skin and DVH extraction were accomplished by scripting using the MIM_assistant software. Also, the impact of changes in the dose calculation algorithms during enrolment time was quantified. A logistic model was created by combining multifactorial variables, considering both clinical factors and the absolute skin DVH (cc). Variance Inflation Factor (VIF) was performed to reduce the multicollinearity. Repeated 5-fold cross-validation with SMOTE approach to overcome the class unbalance was applied for model feature selection. The predictive model was then developed on the entire population due to the limited G2+ events. The FATP G2+ rate was 3.8% with 40/1066 experiencing late toxicity. Among them, a 40% had already developed acute symptoms after RT completion showing a consequential effect. The multicollinearity analysis selected 27 clinical-treatment-dosimetric factors. After repeated (20 times) 5-fold cross-validation, the best-performing model included Post-Surgery Cosmetic alterations, Aromatase Inhibitors (as a protective factor), V20 Gy (50% of the prescribed dose - DVH plateau region) and V42 Gy (105% of the prescribed dose - DVH high-dose tail). Accuracy and f1-score were 0.76 and 0.58 in both training and test sets, providing good reliability for selected variables. AUC for the final model on the entire population was 0.76+/-0.04. We quantified the association between fibrosis and skin DVH when delivering 40 Gy in 15fr. The model suggested an independent role of V20 and V42 Gy and a heavy risk modulation by surgical effects and aromatase inhibitors. This last factor could interfere with adipose tissue and water-content distribution within the breast. For this purpose, a CT-based densitometry characterization of toxicity patients is ongoing.

Overview and statistical analysis of boundary layer clouds and precipitation over the western North Atlantic Ocean

Abstract. Due to their fast evolution and large natural variability in macro- and microphysical properties, the accurate representation of boundary layer clouds in current climate models remains a challenge. One of the regions with large intermodel spread in the Coupled Model Intercomparison Project Phase 6 ensemble is the western North Atlantic Ocean. Here, statistically representative in situ measurements can help to develop and constrain the parameterization of clouds in global models. To this end, we performed comprehensive measurements of boundary layer clouds, aerosol, trace gases, and radiation in the western North Atlantic Ocean during the NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) mission. In total, 174 research flights with 574 flight hours for cloud and precipitation measurements were performed with the HU-25 Falcon during three winter (February–March 2020, January–April 2021, and November 2021–March 2022) and three summer seasons (August–September 2020, May–June 2021, and May–June 2022). Here we present a statistical evaluation of 16 140 individual cloud events probed by the fast cloud droplet probe and the two-dimensional stereo cloud probe during 155 research flights in a representative and repetitive flight strategy allowing for robust statistical data analyses. We show that the vertical profiles of distributions of the liquid water content and the cloud droplet effective diameter (ED) increase with altitude in the marine boundary layer. Due to higher updraft speeds, higher cloud droplet number concentrations (Nliquid) were measured in winter compared to summer despite lower cloud condensation nucleus abundance. Flight cloud cover derived from statistical analysis of in situ data is reduced in summer and shows large variability. This seasonal contrast in cloud coverage is consistent with a dominance of a synoptic pattern in winter that favors conditions for the formation of stratiform clouds at the western edge of cyclones (post-cyclonic). In contrast, a dominant summer anticyclone is concomitant with the occurrence of shallow cumulus clouds and lower cloud coverage. The evaluation of boundary layer clouds and precipitation in the Nliquid ED phase space sheds light on liquid, mixed-phase, and ice cloud properties and helps to categorize the cloud data. Ice and liquid precipitation, often masked in cloud statistics by a high abundance of liquid clouds, is often observed throughout the cloud. The ACTIVATE in situ cloud measurements provide a wealth of cloud information useful for assessing airborne and satellite remote-sensing products, for global climate and weather model evaluations, and for dedicated process studies that address precipitation and aerosol–cloud interactions.

Fast-nondestructive measurement of axial slice water content and water distribution with NMR SFG-MSCPMG sequence

Measuring hydraulic conductivity by instantaneous profile method needs to detect the pore water content of soil at different positions, but most of the detecting methods will disturb the soil sample. In the study, the axial slice scanning of soil samples was carried out by using static filed gradient multi-slice Carr-Purcell-Meiboom-Gill (SFG-MSCPMG) sequence of nuclear magnetic resonance (NMR) technology, which can nondestructively determine water content and distribution at different positions of soil column. In this experiment, three clays were used to illustrate the relationship between NMR test results and oven drying results of water content. The results show that there is a good linear relationship between the NMR signal and water content. Combining mercury intrusion porosimetry (MIP) data, the transverse surface relaxivity parameters (ρ2) of clays are obtained. With ρ2 = 41.90 μm/s the T2 distribution curve of pore water in the ordinary clay can be converted into the pore water distribution curve, which is in good agreement with that obtained with MIP. Nevertheless, it is found that the T2 distribution curve of pore water in expansive clay obtained with NMR technique is more suitable for analyzing the average pore water distribution because of the fast exchange of pore water between the interlayers, intra-aggregates and inter-aggregates in expansive clay.

3D-dimensional Effective Stress Analysis of Wetting and Wetting Trapping Process in Wet-submerged Loess Tunnel Surrounding Rock Based on BP Neural Network

INTRODUCTION: China's loess is vast. Loess has apparent high strength and resistance to deformation once encountered with water immersion and humidification, fusible salts precipitated on the surface of soil particles, the soil's carry alkalization strength is relatively reduced, while the vertical tubular pores in the soil accelerate the infiltration of water, the earth will be in the self-weight or the overlying loads of the additional action of the soil body will produce a significant settlement deformation, which results in the structural damage of the upper building, which is the loss of the wetting of subsidence.
 OBJECTIVES: From China's practical point of view, the humidification and wetting process of wetted loess tunnel peripheral rock is deeply discussed and analyzed, and the water content distribution characteristics of wetted loess tunnel peripheral rock are sought.
 METHODS: Using the particle swarm algorithm, four neural optimization network models, namely, radial basis neural network (RBFNN), generalized regression neural network (GRNN), wavelet neural network (WNN), and fuzzy neural network (FNN), are simulated and created for the analysis of three-dimensional effective stresses in the process of humidity and wetness subsidence in the surrounding rock of loess tunnels of a northwestern city in China and a central city in China.
 RESULTS: By analyzing the comparison graphs between the predicted and actual values of these four models on the test data of two sets of experimental data, the distribution of the proportion of the expected difference to the true value, and the results of the calculation of the three error indexes, it can be found that when using the four neural networks, namely, RBFNN, GRNN, WNN, and FNN, for the analysis of the three-dimensional effective stresses during the process of increasing wetting and wetting of the surrounding rock of the tunnel in the soil-wetted loess, the prediction performance of the WNN is the best.
 CONCLUSION: The soil's unsaturated settlement characteristics differ for different water contents and humidification times. The shorter the period, the more the soil column water content difference. With the continuous increase of water content change in the soil layer, the distribution of water content change in the loess soil column tends to be relatively uniform, and the difference in damage rate between the upper and lower layers tends to be reduced—the amount, time, and pressure of humidification controls wet subsidence.

Experimental and numerical study of tomatoes drying kinetics using solar dryer equipped with PVT air collector

The present work aims to develop a 3D numerical simulation that describes fresh tomatoes' heat- and mass-transfer characteristics using software COMSOL Multiphysics. Besides, a numerical study of the effect of drying parameters (drying temperature, Velocity of air drying and thickness of the slice) on the moisture content elimination from the tomato slice was realized. Also, an experimental study of the effect of the continuity and the discontinuity of the drying process on the water content vaporization is carried out. In contrast, the numerical simulation developed is validated by comparing the experimental data with the numerical results of the temperature distribution and mass transfer inside the tomato slice. The results show that the numerical simulation is agrees with the experimental tests. In addition, the results show that bacteria contamination appears in the tomato slice when the drying temperature decreases under 50 °C. The discontinuity of the drying process harms the quality of the dried product. Furthermore, the results show that the water evaporation rate in the thin slice was faster compared to the thick slice. Consequently, the drying time was reduced by 39 h when the thickness of the product was decreased from 33 mm to 10 mm. Also, the numerical simulation shows that moisture elimination is faster at higher drying air temperatures and increasing the drying air velocity leads to decrease drying time. The results show that the numerical simulation developed in this paper can accurately simulate the drying process characteristics of the agro-food product, especially Tomato, and that it provides a high spatial resolution of the distribution of water content and temperature inside the slice of tomatoes during the drying process.

Effects of temperature, inlet gas pressure and humidity on PEM water contents and current density distribution

The liquid water content directly affects the performance of the proton exchange membrane fuel cell (PEMFC). However, the liquid water content is influenced by the temperature, inlet gas pressure and humidity, so this investigation seeks to explore the relationship among the operating parameters, liquid water content and the current density distribution that used to characterize the cell performance. Firstly, a three-dimensional monomer model of PEMFC was established for numerical simulation based the COMSOL software to study the effect of temperature and inlet gas parameters on cell performance. Then the PEMFC reactor performance test used control variable method was carried out on the 15 kW test bench to verify the research. From the simulation and test results, we can acquire that the liquid water content and current density distribution of fuel cell are the maxima under the condition of 0.2 MPa pressure and 100% humidification. Finally, the experiment confirmed that when the temperature is 353 K, the liquid water content is the highest, and when the temperature remains constant, the higher inlet gas pressure and humidity was given, the higher liquid water content will be generated in the proton membrane which can increase the current density on the membrane to a certain extent, hence to improve the cell performance.

Water content imaging during capillary rise within a rammed earth structure

The capillary rise in earthen buildings is a factor of risk since it changes the mechanical properties of rammed earth. A laboratory-scale experiment is performed to see the ability of time-domain induced polarization to non-intrusively monitor the change in the water content during a capillary rise experiment in a rammed earth wall (150 cm in height and 75 cm in width). A total of 64 self-adhesive Ag/AgCl electrodes are placed at the surface of the rammed earth wall. The contact between the electrodes and the wall is insured by a conductive gel. The distance between the electrodes is 4.5 cm. An impedance meter is used to perform time-domain induced polarization measurements at 7 specific dates in July 2022. The raw data (apparent resistivity and chargeability) are inverted to produce tomograms of electrical conductivity and normalized chargeability through the wall. These tomograms are presented along the plane drawn through the position of the electrodes. A petrophysical model recently developed to interpret electrical conductivity and normalized chargeability data is used here to recover the water content distribution over time. The results are compared to local measurements of the water content performed thanks to a TDR (Time Domain Reflectometry) probe placed within the wall. In addition, the wet front associated with the capillary rise is monitored using a camera. The data shows a consistent position of the capillary rise between the various datasets. A methodology is described to obtain the distribution of the water content over space and time in the rammed earth structure.

A numerical simulation of the distribution and the variation law of the liquid water content in icing wind tunnel

To solve the aircraft icing problem, simulation of the high-altitude clouds as the icing environment becomes necessary. Clouds always contain many micro-scale subcooled droplets. The accurate control of the icing environment simulation is challenging. To investigate the distribution and the variation law of the liquid water content in the icing wind tunnel, a simulation model of the icing wind tunnel was developed with the reprogramming software FLUENT. The model was validated with the parameters of ice shape and maximum ice thickness on the model of SC0710 airfoil with a constant cross-section at zero angle of attack. The errors of the maximum ice thickness, the maximum and mean deviation are 5.06%, 0.22 mm and 0.13 mm, respectively. Then, the influences of the parameters of water droplets at the nozzle exit and airflow were simulated and analyzed. The results indicate that increasing the initial velocity or temperature of water droplets at nozzle exit will promote the uniformity of the liquid water content (LWC) distribution and reduce the average LWC in the test section. The average LWC of the test section is significantly reduced due to a large amount of water droplets hitting the wall under the action of inertia once the medium volume diameter (MVD) exceeds 40 μm.

Characterisation of geological thin layer by borehole radar

To investigate a thin layer, we conducted borehole radar measurements at the GPR facility of Tohoku University, Japan. Both zero-offset profiling and tomography measurements were used to obtain water content distributions. Analyzing first arrival times with amplitudes, we found that a borehole radar can detect velocity changes caused by a high-water content, which acts as an electromagnetic waveguide. We conducted a 3D FDTD simulation and confirmed that the EM wave propagates as a guided wave in a thin layer related to antenna frequency. We determined a thin geological layer compared to an antenna frequency that cannot be detected by reflection measurement due to the poor radar resolution. By comparing the simulated data with measurement data, we could determine the geological boundary between host layers and a thin layer with high water content. In contrast, both the amplitude and the travel time of direct waves are affected by antenna positions and electrical parameters, including permittivity and conductivity. A vertical velocity profile was obtained by combining complementary zero-offset profiling and tomography data, which can be used to investigate water content distribution. The low-velocity thin layer was characterised by amplitude attenuation and late arrival time.