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Soil salinization is one of the major forms of land degradation processes from all over the world. The dielectric constant plays an important role in the process of soil salinity retrieval by using microwave remote sensing. The Dobson model has been widely used to simulate the dielectric constant of nonsaline soil, but the estimated result of the Dobson model did not perform well for saline soil. Moreover, the ions' concentration is related to soil salinity, and the electrical conductance is a critical factor that influences the imaginary part of the dielectric constant. Therefore, the relationship between them needs to further explore. In addition, saturation is neglected in the current dielectric model of saline soil. In this letter, the relationship between the electrical conductance and ions' concentration was analyzed based on the experimental data. The saturation as a new parameter was introduced into the Dobson model to improve the estimated accuracy of the dielectric constant of saline soil in the C-band. The comparison between the revised model, the Dobson model, the Hu Qingrong (HQR) model, and the Wu Yueru (WYR) model was presented. The results indicate that there is a significant linear relationship between the electrical conductance and ions' concentration, with R² of 0.996, a slope of 0.1456, and an intercept of 0.0252. Once the new parameter is implemented, the improved dielectric model based on the C-band reproduces the dielectric constant of saline soil satisfactorily in each soil sample. The simulated results of the improved model are consistent with the laboratory measurement results, with an RMSE of 0.97 and R² of 0.953. Compared with other commonly used three dielectric models of the saline soil, the improved dielectric model performs well in simulating the imaginary part of the dielectric constant. The improved agreements between the simulations and the measurements indicate that the revised dielectric model is appropriate for simulating the dielectric constant of saline soil. The revised dielectric model of saline soil will provide a scientific foundation for the soil salinity retrieval from the microwave remote sensing technology.

An experimental study has been carried out on the characteristics of the fouling process from Water-CaSO4 solutions to the heat transfer surface with and without bulk precipitation. Effects of rotational bulk solution Reynolds number (Re) and surface temperature ( T S ) on the fouling mechanism, fouling behaviour and fouling rate, under surface crystallization (SC) and bulk precipitation (BP) conditions, are investigated. It is found that fouling can enhance the overall heat transfer when Re is high enough in the lack of BP. Under SC conditions, the fouling resistance ( R f ) and the fouling rate ( d R f / d t ) decrease with an increase in Re. The effects of T S on R f and d R f / d t depend on Re, with exponential increases with Re under low Re of 16000, and negligible influence under high Re of 80000. The presence of BP markedly increases d R f / d t by 3.6 times, while decreases the length of the initial period by 4.5 times. The presence of BP alters the overall precipitation fouling mechanisms. A critical Re of 57600 is found separating two distinct fouling mechanisms under the same T S . When Re CaS O 4 solutions, which could provide a benchmark for fouling model development and help develop an effective fouling mitigation strategy.

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives the lateral displacement of the wire, which is determined by minimizing the energy functional that consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is verified with a finite element (FE) simulation. Comparisons between the model predictions and the FE results in terms of the change in helical angle and transverse bending stress show good correlations. The verified model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear, and friction could significantly increase the stress at the end fitting compared with the frictionless case.

An analytical model is given to investigate the behavior of unbonded flexible pipes under biaxial dynamic bending. The stick-slip conditions of each wire are studied in the framework of incremental analysis by an operator splitting of the time step into a stick-state prediction and a slip-state correction step. The tension gradient is calculated using the classical return-mapping algorithm and the obtained tension gradients are integrated numerically to find the axial tension by imposing appropriate boundary conditions. From the axial tension the bending moments with respect to the principal bending axes of the pipe are obtained. Poisson's effect, bending induced tension in the wire, shear deformations of the supporting plastic layer and the changes of the effective torsion and curvature increments of the wire after slip occurs are taken into account in the model. The results of bending moment–curvature relationship from this model are compared with the test data from simple bending and good correlations are found. The comparison of the biaxial bending moment results between this model and the available model also shows good agreement.

Rigorous analytical formulations are given to describe the gross slip initiation and progression in tensile armor layers of unbonded flexible pipes. Then two mechanisms are thought to contribute to the decrease of layer stiffness before gross slip begins. The first one considers the micro-slip occurred at the interlayer contact interfaces. The relative displacement between an armor wire and the underlying layer is determined according to the theory of contact mechanics. Shear deformations of the supporting plastic layer are taken into account in the other mechanism where plane sections no longer remain plane. The results of bending moment-curvature relationship from the presented models are compared with the available test data and good correlations are found. The shear model is seen to describe the slip transition better than other models do.

An evaluation method of the crack tip reverse plastic zone size (CTRPZS) for the center cracked steel plate under tension–compression cyclic loading is proposed. In this method, the variable quantity of maximum crack opening displacement (VMCOD) is used to study the effect of compressive loads on CTRPZS. In the compressive loading stage, CTRPSZ increases linearly with increasing of the compressive load on basis of the existing CTRPZS after the tensile loading and tensile unloading processes. The maximum CTRPZS can be expressed with respect to VMCOD. This expression is suitable for center cracked finite plates with different materials under tension–compression cyclic loading.

The high stress region around weld joints accelerates corrosion and may induce non-uniform corrosion. In this study, the effect of loading on corrosion behavior of the steel in NaCl solution was investigated. The relationship between the corrosion rate and applied loading was deduced based on the electrochemical theory. Electrochemical experiments were carried out to investigate the interaction between loading and corrosion rate on Q235 steel. A butt weld joint of ship deck structure was selected as a case study. Time-dependent stress concentration factor of welded joint as a function of the corrosion deterioration was analyzed, and the iterative process of stress and corrosion degeneration of plate thickness was used to simulate the coupling effect based on results of the experiment. The hot spot stress approach was adopted to calculate the fatigue damage.

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives lateral displacement of the wire, which is determined by minimization of the energy functional consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is validated with a finite element simulation. Comparisons between the model predictions and the finite element results in terms of the change in helical angle and transverse bending stress show good correlations. The validated model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear and friction could significantly increase the stress at the end fitting compared with the frictionless case.

Analytical formulations are presented to determine the bending moment-curvature relationship of a helical layer in unbonded flexible pipes. Explicit expressions describing the variation of both bending stiffness and moment as a function of the applied curvature are given. The approach takes into account the nonlinearity of the response caused by the interlayer slip. The contribution of local bending and torsion of individual helical elements to the bending behavior of helical layers is included. Theoretical results for a typical unbonded flexible pipe using the nonlinear formulation for helical layers are compared with experimental data from the available literature. Encouraging correlations are found and the importance of the initial interlayer pressures is seen. The influence of local bending and torsion of individual helical elements on the bending behavior of the entire pipe is also evaluated. The results show that the inclusion of this local behavior significantly influences the full-slip bending stiffness.

The aim of this paper is to demonstrate that a simple stirred batch cell can be used to study the effects of surface shear stress (among other process parameters) on fouling from saturated calcium salt solutions. For otherwise identical operating conditions, the overall fouling rate on a smooth mild steel surface was found to be reduced either when fine wires were attached to it or when helical threads were incorporated into the surface, either in the form of a continuous helical groove or in the form of a raised helix. The raised helical surface was more effective in reducing fouling than the helical groove. The results confirm the general effect that fouling rates can be reduced by increasing the surface shear stress through surface enhancement. A simple mathematical model has been developed to take into account the dynamic change in bulk concentration as crystallization fouling occurs. In all cases, the overall fouling resistance increased asymptotically toward a constant value and could easily and accurately be described quantitatively by the new analytical model. The variations of shear stresses on the various surfaces were determined from computational fluid dynamics simulations using the commercial package Comsol 4.2.