Soil Moisture Transfer Research Articles

Identification of temperature and moisture content fields using a combined neural network and clustering method approach

Studies on the dynamics of temperature and moisture content distributions in porous soils have provided important insight on their effect on the building hygrothermal behavior, where the interaction between both building and soil can contribute to reduce building thermal gains or looses. Hygrothermal aspects can be related to many attributes such as energy consumption, occupants' thermal comfort and health, and material deterioration. Recently, a great variety of mathematical models to predict thermal and moisture content profiles in porous media have been presented in the literature. Most of those models are based on analysis of multilayer measurements or on Fourier analysis. The development and validation of such mathematical models facilitate the understanding of heat and moisture flows at different soil depths. In this research, a radial basis function neural network (RBF-NN) approach, combined with Gath–Geva clustering method in order to predict the temperature and moisture content profiles in soils, has been presented. A set of data obtained from the computation of the coupled heat and moisture transfer in porous soils for the Curitiba city (Paraná State, Brazil) weather data file has been used by the RBF-NN modeling method. Simulation results indicate the potentialities of the RBF-NNs to learn, for the one step ahead identification, the behavior of temperature and moisture content profiles in the media at various depths.

A fundamental solution to the Cauchy problem for a fourth-order pseudoparabolic equation

The Cauchy problem for a fourth-order pseudoparabolic equation describing liquid filtration problems in fissured media, moisture transfer in soil, etc., is studied. Under certain summability and boundedness conditions imposed on the coefficients, the operator of this problem and its adjoint operator are proved to be homeomorphism between certain pairs of Banach spaces. Introduced under the same conditions, the concept of a θ-fundamental solution is introduced, which naturally generalizes the concept of the Riemann function to the equations with discontinuous coefficients; the new concept makes it possible to find an integral form of the solution to a nonhomogeneous problem.

Simultaneous measurement of water flux density vectors and thermal properties under drainage conditions in soils

River water and groundwater are used to irrigate paddy fields and are also principal sources of drinking water for humans. It is important to understand the transport characteristics of water (e.g., direction and intensity of water flow), when grasping a pollution situation in the soil. Endo and Hara (Soc Inst Contr Eng Trans Ind App 2:88–95, 2003) developed the Quintuple-Probe Heat-Pulse (QPHP) sensor to identify water flux density vectors and thermal properties under saturated and steady state conditions. However, there has not yet been any investigation of moisture transfer under transient conditions such as during internal drainage and mid-summer drainage of paddy fields. Only Sand has been used in previous experiments, and examinations with Loamy and Clayey soils have not yet led to done. Simultaneous measurements of the water flux density vectors and thermal properties of soil texture of three types under drainage conditions as well as the soil moisture transfer analysis with Finite Element Method (FEM), were done. The representative drainage flow was indicated as downward, except in the Sandy-Clayey Loam, in which the rightward flux exceeded the downward flux owing to anisotropy of the soil-pore structure and hydraulic conductivity. The apparent horizontal/vertical advanced distance was introduced in order to know about how water moved through the soil column. The estimated volumetric water content was in good agreement with the measured value. Thus, this measurement method was shown to be valid under transient water flow conditions.

광릉수목원 내 산지사면에서의 토양수분 시계열 자료의 단변량 분석

Soil moisture is one of the essential components in determining surface hydrological processes such as infiltration, surface runoff as well as meteorological, ecological and water quality responses at watershed scale. This paper discusses soil moisture transfer processes measured at hillslope scale in the Gwangneung forest catchment to understand and provide the basis of stochastic structures of soil moisture variation. Measured soil moisture series were modelled based upon the developed univariate model platform. The modeling consists of a series of procedures: pre-treatment of data, model structure investigation, selection of candidate models, parameter estimation and diagnostic checking. The spatial distribution of model is associated with topographic characteristics of the hillslope. The upslope area computed by the multiple flow direction algorithm and the local slope are found to be effective parameters to explain the distribution of the model structure. This study enables us to identify the key factors affecting the soil moisture distribution and to ultimately construct a realistic soil moisture map in a complex landscape such as the Gwangneung Supersite.

Stochastic analysis of soil moisture to understand spatial and temporal variations of soil wetness at a steep hillside

Systematic analysis procedures for point scaled data are required to explain spatial and temporal distributions of soil moisture during storm flows and subsequent low flow periods. In this study, field and simulated data of soil wetness were used to improve the understanding of hydrological processes at the hillslope scale. Using multiple TDR sensors on a steep hillside, soil moisture responses to sequential rainfall events were obtained as multiple time series data. Mathematical descriptions of the soil moisture transfer processes can provide the hydrological basis for time series analysis with measured soil moisture at the hillslope scale. The spatial distribution of the models selected for monitoring points of the study area was obtained by applying time series modeling procedures to the measured data. The variation of soil moisture can be characterized using the final model structures in conjunction with terrain attributes such as topographic wetness indices or the distances between monitoring points and the outlet.

Experimental investigation on heat, moisture and salt transfer in soil

In this paper, experiments on coupled heat, moisture and salt transfer in yellow vegetable soil are conducted. A remarkable thermal permeant region in the soil column is found, along with moisture releasing, transition and absorbing zones in the soil column. The capillary flow is the dominant mechanism that governs the moisture transfer. With the moisture transfer, the salt moves from the groundwater and accumulates at the top of the column. However, with the salt accumulation, there will be a gradient of salt content and, as a result, the salt will also diffuse due to this gradient.

Simultaneous heat and moisture transfer in soils combined with building simulation

In order to precisely predict ground heat transfer, room air temperature and humidity, a combined model has been developed and conceived to calculate both the coupled heat and moisture transfer in soil and floor and the psychrometrics condition of indoor air. The present methodology for the soil is based on the theory of Philip and De Vries, using variable thermophysical properties for different materials. The governing equations were discretized using the finite-volume method and a three-dimensional model for describing the physical phenomena of heat and mass transfer in unsaturated moist porous soils and floor. Additionally, a lumped transient approach for a building room and a finite-volume multi-layer model for the building envelope have been developed to integrate with the soil model. Results are presented in terms of temperature, humidity and heat flux at the interface between room air and the floor, showing the importance of the approach presented and the model robustness for long-term simulations with a high time step.

Study of heat and moisture transfer in soil with a dry surface layer

Mathematical model for describing simultaneous heat and moisture transfer in the porous soil with a dry surface layer was developed by using the volume-averaging method. Numerical simulation was conducted to investigate water evaporation, transient distributions of temperature and moisture in the porous soil at environmental conditions, which might be useful for agricultural application. In order to validate the mathematical model and numerical method, an experiment was conducted under natural environmental conditions. An additional experiment was conducted in a closed-loop wind tunnel to investigate the temperature effect on soil moisture transport. Theoretical and experimental results indicate that the dry surface layer has an important effect on heat and moisture migration in soil and the influence of temperature on moisture transport in unsaturated soil is significant.

Inner heat source model with heat and moisture transfer in soil around the underground heat exchanger

This paper presents an inner heat source model of underground heat exchanger based on the heat and mass transfer theory in soil. A number of factors such as moisture movement in soil, soil type, and soil property were taken into account in the model. The underground heat exchanger was simplified as the equivalent inner heat source term in the model. The software of Autough2 was used to conduct the numerical simulations. And the paper presents the analyses on the influences of different soil properties and different operation modes on the underground temperature field around the single U-vertical underground heat exchanger.

The influence of soil moisture transfer on building heat loss via the ground

In this paper, the influence of soil moisture transfer on building heat loss via the ground is investigated by comparing fully coupled simulations with linear thermal simulations. The observed influences of coupling are (1) the larger amplitude of surface temperature, (2) the variation of thermal conductivity with moisture content, and (3) the advection of sensible heat by liquid transfer. In a parameter study, it is shown that these conclusions hold for a variety of climates, soils and foundation constructions. However, given the current accuracy level of standard methods, the integration of coupling effects in these calculation methods cannot be defended.

Application of Satellite-Derived Surface Soil Moisture Data to Simulating Seasonal Precipitation by a Simple Soil Moisture Transfer Method

Abstract A simple algorithm is presented for transferring root-zone soil moisture from surface soil moisture data on a global scale. Analysis of offline soil moisture data shows that the climatological relationship between surface and root-zone soil moisture becomes linear when appropriate time lags are applied. The climatological relationship of root-zone soil moisture among different land surface models (LSMs) is also linear; therefore, the root-zone and surface soil moisture obtained from one LSM can be applied to another. The algorithm is then applied to the surface soil moisture observations made by the precipitation radar on board the Tropical Rainfall Measuring Mission precipitation radar (TRMM/PR), and the transferred root-zone soil moisture is input to a general circulation model (GCM) summer—June, July, August—precipitation simulation as the boundary condition. The approach is computationally efficient, and the simulation using the root-zone soil moisture by the transfer method is much better th...

Tangent linear analysis of the Mosaic land surface model

In this study, a tangent linear eigenanalysis is applied to the Mosaic land surface model (LSM) [Koster and Suarez, 1992] to examine the impacts of the model internal dynamics and physics on the land surface state variability. The tangent linear model (TLM) of the Mosaic LSM is derived numerically for two sets of basic states and two tile types of land condition, grass and bare soil. An additional TLM, for the soil moisture subsystem of this LSM, is derived analytically for the same cases to obtain explicit expressions for the eigenvalues. An eigenvalue of the TLM determines a characteristic timescale, and the corresponding eigenvector, or mode, describes a particular coupling among the perturbed states. The results show that (1) errors in initial conditions tend to decay with e‐folding times given by the characteristic timescales; (2) the LSM exhibits a wide range of internal variability, modes mainly representing surface temperature and surface moisture perturbations exhibit short timescales, whereas modes mainly representing deep soil temperature perturbations and moisture transfer throughout the entire soil column exhibit much longer timescales; (3) the modes of soil moisture tend to be weakly coupled with other perturbed variables, and the mode representing the deep soil temperature perturbation has a consistent e‐folding time across the experiments; (4) the key parameters include soil moisture, soil layer depth, and soil hydraulic parameters. The results agree qualitatively with previous findings. However, tangent linear eigenanalysis provides a new approach to the quantitative substantiation of those findings. Also, it reveals the evolution and the coupling of the perturbed land states that are useful for the development of land surface data assimilation schemes. One must be careful when generalizing the quantitative results since they are obtained with respect to two specific basic states and two simple land conditions. Also, the methodology employed here does not apply directly to an actual time‐varying basic state.

The Influence of Soil Moisture in the Unsaturated Zone on the Heat Loss from Buildings via the Ground

In calculations of building heat loss via the ground, the coupling with soil moisture transfer is generally ignored, an important hypothesis which will be falsified in this paper. Results from coupled simulations – coupled soil heat and moisture transfer equations and complete surface heat and moisture balances – are compared to results from linear simulations. It is shown that the coupled calculations give notably higher heat losses. Surface temperature, the driving force for heat loss via the ground, is identified as a first important source for these deviations: it is shown that while the averages of the surface temperature are almost equal in coupled and linear calculations, the amplitude in the coupled simulation is considerably higher. A further study reveals that variation of the thermal properties with moisture content also contributes partially to the observed differences. Transfer and storage of sensible heat linked to moisture in the liquid phase was shown to be the last important influencing factor.

Estimation of Extreme Flood Characteristics Using Physically Based Models of Runoff Generation and Stochastic Meteorological Inputs

There are two main schools of estimation of extreme flood characteristics in the world hydrological practice. The first approach is based on fitting a statistical distribution to available measurements of flood peak discharges and extrapolating this distribution to estimate the floods of needed low exceedance probabilities. The second one uses the concept of probable maximum flood. Neither approach practically utilizes available meteorological observations (that contain important information on possible variations of runoff generation) and both are based on implicit assumptions that the physical mechanisms of runoff generation do not depend on the magnitudes of the water inputs and land use changes. To overcome these shortcomings, a new technique based on coupling the Monte Carlo simulation of meteorological inputs with application of the detailed physically-based model of runoff generation processes is suggested. The paper illustrates the implementation of this technique for estimation of the extreme flood characteristics for the Seim River basin (the catchment area is 7,460 km2). The model of runoff generation is based on the finite-element schematization of river basins and includes the description of snow cover formation and snowmelt, freezing and thawing of soil, vertical soil moisture transfer and infiltration, overland, as well as and channel flow. The Monte-Carlo simulation is based on stochastic models of daily precipitation series, daily air temperature and daily air humidity deficit (for continuous simulation during autumn-winter-spring seasons) or distributions of snow water equivalent, depth of frozen soil, and soil moisture content before snowmelt (for simulation during only spring period). The calculated exceedance probabilities of the flood peak discharge have been compared with ones calculated using long-term runoff data. As an example of the application of the developed technique, changes of the Seim River flood runoff characteristics resulting from changes of basin land use are given.

Thermo-hydro-mechanical coupling in clay barriers

A thermo-hydro-mechanical model is presented to tackle the complex coupling problems encountered in clay barriers. A detailed formulation coupling heat, moisture (liquid water and water vapour) and air transfer in a deformable unsaturated soil is given. The formulation of Alonso–Gens' mechanical model for unsaturated soil is also incorporated. Finally, a small-scale wetting–heating test on compacted bentonite is performed for validation; the numerical results are compared to the experimental measurements.

Ground-Coupled Heat and Moisture Transfer from Buildings Part 1–Analysis and Modeling*

Ground-heat transfer is tightly coupled with soil-moisture transfer. The coupling is threefold: heat is transferred by thermal conduction and by moisture transfer; the thermal properties of soil are strong functions of the moisture content; and moisture phase change includes latent heat effects and changes in thermal and hydraulic properties. A heat and moisture transfer model was developed to study the ground-coupled heat and moisture transfer from buildings. The model also includes detailed considerations of the atmospheric boundary conditions, including precipitation. Solutions for the soil temperature distribution are obtained using a finite element procedure. The model compared well with the seasonal variation of measured ground temperatures.

One-dimensional soil moisture profile retrieval by assimilation of near-surface observations: a comparison of retrieval algorithms

This paper investigates the ability to retrieve the true soil moisture and temperature profiles by assimilating near-surface soil moisture and surface temperature data into a soil moisture and heat transfer model. The direct insertion and Kalman filter assimilation schemes have been used most frequently in assimilation studies, but no comparisons of these schemes have been made. This study investigates which of these approaches is able to retrieve the soil moisture and temperature profiles the fastest, over what depth soil moisture observations are required, and the effect of update interval on profile retrieval. These questions are addressed by a desktop study using synthetic data. The study shows that the Kalman filter assimilation scheme is superior to the direct insertion assimilation scheme, with retrieval of the soil moisture profile being achieved in 12 h as compared to 8 days or more, depending on observation depth, for hourly observations. It was also found that profile retrieval could not be realised for direct insertion of the surface node alone, and that observation depth does not have a significant effect on profile retrieval time for the Kalman filter. The observation interval was found to be unimportant for profile retrieval with the Kalman filter when the forcing data is accurate, whilst for direct insertion the continuous Dirichlet boundary condition was required for an increasingly longer period of time. It was also found that the Kalman filter assimilation scheme was less susceptible to unstable updates if volumetric soil moisture was modelled as the dependent state rather than matric head, because the volumetric soil moisture state is more linear in the forecasting model.

Three‐dimensional coupled heat, moisture, and air transfer in a deformable unsaturated soil

A three-dimensional numerical model is presented for three-phase flow (moisture, air, and heat) in a deformable partly saturated soil with deformation calculated via a non-linear elastic theory. The present work is an extension of a two-dimensional analysis presented by Thomas and He. The objective of this work is the solution of problems of greater geometric complexity. The mathematical formulation of this coupled problem consists of four governing equations, developed from the principles of mass and energy conservations as well as the stress equilibrium equation. Darcy's flow law is used to describe the motion of liquid and air in the porous medium, and a Philip and de Vries type vapour flow approach is employed in the formulation. A Galerkin finite element method coupled with a finite difference recurrence relationship is used to obtain simultaneous solutions to the governing equations where pore liquid, pore air pressures, temperature and displacements are the primary variables. The method allows the non-linear nature of the soil parameters to be modelled. Three-dimensional 20-noded isoparametric elements are used to simulate different types of cases for the verification of the work. Results are presented of the application of the new model to four problems, two of which are isothermal and two heating simulations. The three-dimensional nature of the results achieved is highlighted. Copyright © 1999 John Wiley & Sons, Ltd.

Three-dimensional coupled heat, moisture, and air transfer in a deformable unsaturated soil

A three-dimensional numerical model is presented for three-phase flow (moisture, air, and heat) in a deformable partly saturated soil with deformation calculated via a non-linear elastic theory. The present work is an extension of a two-dimensional analysis presented by Thomas and He. The objective of this work is the solution of problems of greater geometric complexity. The mathematical formulation of this coupled problem consists of four governing equations, developed from the principles of mass and energy conservations as well as the stress equilibrium equation. Darcy's flow law is used to describe the motion of liquid and air in the porous medium, and a Philip and de Vries type vapour flow approach is employed in the formulation. A Galerkin finite element method coupled with a finite difference recurrence relationship is used to obtain simultaneous solutions to the governing equations where pore liquid, pore air pressures, temperature and displacements are the primary variables. The method allows the non-linear nature of the soil parameters to be modelled. Three-dimensional 20-noded isoparametric elements are used to simulate different types of cases for the verification of the work. Results are presented of the application of the new model to four problems, two of which are isothermal and two heating simulations. The three-dimensional nature of the results achieved is highlighted. Copyright © 1999 John Wiley & Sons, Ltd.

Three-dimensional heat, moisture and air transfer in unsaturated soils

A new three-dimensional numerical model of coupled heat, moisture and air transfer in unsaturated soil is presented. In particular, the model accommodates moisture transfer in the form of liquid and vapour flow and heat transfer arising from conduction, convection and latent heat of vaporization. The bulk flow of dry air and the movement of air in a dissolved state are also included. The theoretical basis of the model, the finite element solution of the spatial terms and finite difference solution of the temporal terms are briefly presented. Attention is focused on the verification of the new numerical solution. This is achieved via comparisons with independent solutions of heat, moisture and air transfer in an unsaturated soil. The physical problem considered includes the highly non-linear hydraulic properties of sand. Thermal conductivity is also included as a function of soil moisture content. Excellent correlation of results is shown thus providing confidence in the new model. The new model is also applied to a number of test cases which illustrate the need for the development of a model which can fully include three-dimensional behaviour. In particular, three applications are presented each increasing in complexity. The first application illustrates three-dimensional heat transfer. This particular application is verified against existing commercial finite element software. Subsequent applications serve to illustrate how the coupled processes of heat moisture and air transfer combine to yield three-dimensional problems even within a simple geometric domain. Visualization of three-dimensional results is also addressed. © 1998 by John Wiley & Sons, Ltd.