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Multiple groups of triaxial shear tests and creep tests were performed on rockfill materials, stress–strain, volume-strain, volumetric creep-time and axial creep-time curves were obtained under different porosity levels. Based on the analysis of the test results, the improved Shen Zhujiang double yield surface elastic–plastic model and the improved creep model were proposed for deformation prediction with higher accuracy, and they were incorporated into the calculation program for concrete face rockfill dams (CFRDs) by program development. Afterward, the regression models were established between the porosity and the parameters of the improved models, which offer quick derivation of the model parameters by porosity under the condition that lithology and gradation are basically the same. Furthermore, relying on digital construction technology, the spatial distributions of model parameters within the entire dam were estimated. Finally, a set of improved model parameters reflecting actual construction quality was assigned to an element, and the refined finite element method (FEM) numerical simulation of the long-term deformation of the CFRD considering the actual construction quality was realized. The engineering example shows that the proposed method can greatly improve the simulation accuracy of the long-term service behavior of the CFRDs. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle combined ejector expansion refrigeration cycle (ORC-EERC) has significant potential for utilizing low-temperature heat. The study on dynamic response of the ORC-EERC combined system plays a particularly important role in optimizing the control strategy for the system, given the instability of the low-temperature heat source. In this paper, the ORC-EERC dynamic models with single and dual condensers are proposed. The simulation results show that the proposed improved model of EERC subsystem presents more accurate results relevant to the experiment system. The impact of the ORC subsystem on the refrigeration subsystem is more pronounced in the ORC-EERC system with a single condenser than in the system with dual condensers. In addition, the phenomenon of chocking in the ejector throat leads to the degradation of system performance when the heat source is disturbed. Therefore, a multi-device cooperative control strategy is proposed to enhance the safety and performance of the system. In the case study of geothermal water mass flow scheduling disturbance, the control strategy increases the cooling capacity of the system by a maximum of 9.29%. • The Simulation results of the improved model are closer to the experimental values. • The dynamic response of ORC-EERC with single and dual condensers are compared. • A cooperative control strategy is proposed to improve the system performance. • The dynamic response of the system under geothermal water scheduling is analyzed. [ABSTRACT FROM AUTHOR]

Abstract Many complex vacuum systems include edge-welded bellows. Their simulation in the molecular flow regime with a Test Particle Monte Carlo (TPMC) code, such as MolFlow+, can take considerable amounts of computing power and time. Therefore we investigated the change of the transmission probability of a bellow compared to a cylindrical tube in TPMC simulations. The results were used to develop an empirical model to simplify the geometry of a bellow in a TPMC model by replacing it with a cylindrical tube of extended length, consequently compensating the reduced conductance of the bellow. The simulated transmission probabilities of a variety of different bellow lengths have been used to fit the parameters of the model. Each bellow geometry simulated with MolFlow + comprised two cylindrical tubes, one at each end, and the central bellow section. The geometry of each bellow is described by two quantities. The first one is the total length of the geometry model normalized to the inner diameter of the bellow. The second one is the fraction of the bellow section with regard to the total length. Simulating a tube instead of a long bellow reduced the simulation time by a factor of up to 1000, while the error introduced through the replacement of the bellow with a cylindrical tube of modified length was in most cases negligible. Highlights • Simulation of the transmission probability of edge-welded bellows (TPMC model). • Deduce a simplified empirical model to estimate the transmission probability of a bellow. • Apply the model to replace the complex bellow geometry in a TPMC simulation by a cylindrical tube. • Reduce the simulation time by several orders of magnitude. [ABSTRACT FROM AUTHOR]

The Liao river is one of the seven major rivers in China, and the process of phosphorus (P) cycling and change of water quality in this basin are influenced to a considerable extent human activities. In this work, the traditional net anthropogenic phosphorus inputs (NAPI) model was improved by considering the dynamic change of wastewater treatment capacity and P deposition (PDEP) and reclassifying the sources of phosphorus into human P consumption (PHUM), agriculture P consumption (PAGR), livestock P consumption (PANIM) and PDEP to analyze its dynamic spatio-temporal change in the Liao river basin. The results showed that the annual mean NAPI was 785.53 kg P km−2 yr−1 (2001–2020), the maximum value was 940.49 kg P km−2 yr−1 in 2009, and the minimum value was 586.04 kg P km−2 yr−1 in 2001. The temporal variation of NAPI presented an increasing-fluctuation-increasing trend and was basically in line with that of the water quality throughout the three stages, and the spatial distribution of NAPI gradually increased from upstream to downstream. During the two decades, PANIM was the predominant component of NAPI with a share of 64.32%. PHUM, PAGR, and PDEP accounted for 15.97%, 11.54%, and 8.17%, respectively, and the point source NAPI (NAPIP) contributed to 4.95% of NAPI. Further, the INAPI (Improved NAPI) -MR (Multiple Regression) -SWAT (Soil and Water Assessment Tool) model was developed to predict the spatial distribution of P flux under two scenarios. The results showed that the Liao river basin experienced a reduction in P flux to different degrees due to the improvement of the wastewater treatment system, which was more significant in its downstream area. Long-term water quality monitoring is encouraged to develop refined water quality models in the future. [Display omitted] • Dynamic wastewater phosphorus removal was considered to improve NAPI model. • Spatiotemporal change of NAPI in the Liao river basin was investigated at city level. • INAPI-SWAT-MLR model was developed to describe the P flux across the basin. [ABSTRACT FROM AUTHOR]

As a very important second messenger, Ca 2+ plays the role of adjusting various cellular physiological processes through calcium oscillations. In this paper, a further theoretical study is conducted to explore the kinetic behavior of the calcium signals based on a mathematical model. At first, the causes behind the appearance and disappearance of calcium oscillations are strictly verified from the theoretical level and a comparative analysis between the improved model and the original model is also made. Then, it is found that with the increase of relaxation time, the second bifurcation point of the system moves towards the increasing direction of the stimulus intensity and the oscillation interval displays gradual increase. It is also found that under given stimulus intensity, with the relaxation time getting longer, both the peak value and the period of the calcium oscillations display significant increase. Combining the results from the comparative analysis between the improved model and the original model with the results from the analysis of the relaxation time, it shows that the calcium pump activity exerts a direct impact on the calcium oscillation interval. Finally, the calcium leakage item is introduced into the improved model and it is found that as the calcium leakage increases, the two Hopf bifurcation points of the system both move towards the decreasing direction of the stimulus intensity and the oscillation interval gradually narrows down. The study also shows that under given stimulus intensity, as the calcium leakage increases, the peak value of the calcium oscillations displays slow increase and the oscillation period displays gradual decline. [ABSTRACT FROM AUTHOR]

In this study, we explain the causes and effects of the geometrical impossible result encountered in the widely adopted tetrakaidecahedron model (Boomsma and Poulikakos, 2001; Dai et al., 2010) for the effective thermal conductivities (ETCs) of metal foam. The geometrical impossible result is successfully eliminated by accounting for the size variation of the node with porosity. The improved model provides predictions of ETCs that are more precise than available models. For aluminum foams ( k s = 218 W m - 1 K - 1 ) using water and air as fluid media, the relative root-mean-square (RMS) deviation of the present predictions from the experimental data is about 5.3%; for the reticulated vitreous carbon (RVC) foams ( k s = 8.5 W m - 1 K - 1 ), the relative RMS deviation is about 7.4%. [ABSTRACT FROM AUTHOR]

Abstract: An extension of a simplified model for the effective thermal conductivity (ETC) of open-cell porous foams, that originally contained only one adjustable parameter, is proposed in this article. The present improved model consists of two adjustable parameters those can be calculated directly from detailed numerical predictions of the ETC under vacuum condition and in presence of a reference fluid with known thermal conductivity ratio (of fluid and solid phases). The performance of present simplified model is evaluated by comparing its estimations with results obtained from detailed numerical simulations, those take into account the true morphology of porous media, as well as predictions obtained from the original simplified model, for the complete range of thermal conductivity ratios, lower than unity ( ). Geometries of porous media are either synthetically generated for idealized regular structures or obtained from high resolution three-dimensional computed tomography-scan images for real foams. The present study clearly demonstrates that the proposed simplified model yields extremely accurate estimation of the ETC for all the investigated structures, as long as the reference thermal conductivity ratio of fluid and solid phases is judiciously chosen. [Copyright &y& Elsevier]

Abstract: In this paper, a comprehensive modeling and parameters extraction method is proposed to describe the current–voltage and power–voltage characteristic of photovoltaic cells. This method is based on data commonly issued by commercial photovoltaic data sheet. By using Lambert W function, the improved model of solar cells is given. Meanwhile, the current–voltage and power–voltage curves of photovoltaic cells are calculated. To extract the model parameters from only three state points at standard test conditions, an optimized approach using iterative method and approximate method is presented. Compared to the popular R p model and experimental data, the proposed method shows excellent agreement between the current–voltages points. It is found that the proposed modeling and parameters extraction method has less error at the maximum power point state. Moreover, the proposed model is more realistic when subjected to ideality factors variations. [Copyright &y& Elsevier]

Abstract: The traditional GABP model used in complex coal and gas outbursts prediction, which trains the back-propagation neural networks (BPNN) by Genetic Algorithm (GA), is provided with some limitations, such as massive time-consuming, optimal stop condition of GA pretreatment indeterminacy, independency and complex task of great importance. To overcome these problems, a new method of coal and gas outbursts intensity prediction by Incorporate Genetic Algorithm Based Back Propagation Neural Network (IGABP) is applied to determine parameters of BPNN automatically and propose an efficient GA which reduces its iterative computation time for enhancing the training capacity of BPNN. First, improved GA is based on single population model among continuous generation model and used the modified self-adapted crossover rate, crossover strategy, self-adapted stop criterion, as well as special survival condition. Second, BP operator is introduced into the evolution of GA operations, improving the standard GA optimization of random search and self-guiding optimization searching. To show the validity of the proposed method, we compare it with traditional GABP and IGABP using a dataset. The results show that the IGABP model can effectively overcome the inadequacies of the traditional model, its operating efficiency and forecast performance are improved significantly. [Copyright &y& Elsevier]

Abstract: Tailrace tunnel ventilating can be used as a highly efficient and energy saving air conditioning for factory buildings in hydropower station. This paper describes an improved model of heat and moisture transfer for tailrace tunnel ventilating system with the assumption of thermal insulated for the tunnel wall and with the same temperature at any cross section as the wet bulb temperature of that air, and the improved model has been validated against the field test from Yingxiuwan hydropower station and compared with the reference simplified model, the results show that the improved model has a good agreement with the field test data and a better precision than the reference simplified model for the performance prediction of heat and moisture transfer of tailrace tunnel ventilating, especially for the short tunnel system. Moreover, the thermodynamic calculation method of heat and moisture transfer is presented, and the method is intended for use in annual performances prediction or design tools for tailrace tunnel ventilating system in hydropower station. [Copyright &y& Elsevier]

Abstract: Most engineering structures with crack-like defects experience varying crack-tip loading during their service. This variation may result from combinations of varying applied loads and displacements and/or varying body force including residual stress. It is known that crack growth rates differ according to the R-ratios when expressed via a single parameter, stress intensity factor range, ΔK. Many methods have been proposed to incorporate the effect of the R-ratio, including effective stress intensity factor range models based on crack closure and the two-parameter driving force model etc. However there are few clear statements about the choice of material constants for the calculation of crack growth lives under varying amplitude loading. This is a significant omission. In this paper, a simple crack growth rate equation has been proposed, which can condense the crack growth data under different R-ratios to the curve corresponding to R =0. Fatigue crack growth rate data for several materials taken from the literature, were analyzed using a new formulation. These data then cluster around the R =0 crack growth rate curve. The result implies that crack growth rates for fatigue life calculation under different R-ratios may be obtained directly from the constants corresponding to R =0. Thus the most commonly tested crack growth rate constants corresponding to R =0–0.1 are sufficient for fatigue crack growth calculation under different loading conditions. [Copyright &y& Elsevier]

Abstract: In this paper, an improved theoretical interfacial stress analysis is presented for simply supported concrete beam bonded with a FRP plate. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends, while all existing solutions neglect this effect. Remarkable effect of shear deformations of adherends has been noted in the results. Indeed, the resulting interfacial stresses concentrations are considerably smaller than those obtained by other models which neglect adherent shear deformations. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam. This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP–RC hybrid structures. [Copyright &y& Elsevier]

Estimating the total organic carbon (TOC) content is crucial in shale reservoir evaluation. Among the available methods for TOC estimation from well logs, the ΔlogR technique is currently the only globally used model that is based on a rigorous petrophysical model. Literature reviews reveal that the overlay-coefficient between the porosity and the resistivity curves in the ΔlogR model has been the focus of many studies. However, the current methods of determining the overlay-coefficient based on the rock minerals or empirical parameters weaken its applicability and accuracy. In this study, we developed a V-ΔlogR model for the prediction of the total organic matter content. The V-ΔlogR model is comprised of three modifications to the ΔlogR model, i.e., replacing the fixed overlay-coefficient with a variable one, removing the maturity, and replacing the baselines with a single one. Among these, a critical improvement is treating the overlay-coefficient (k) as a variable and determining it from the measured TOC values or from well logs. The application of our improved model in the Songliao, Bohai Bay, and Sichuan basins indicates that the V-ΔlogR model can accurately predict the TOC of shale with large lithological and mature variations. Because it uses actual geological data to determine the overlay-coefficient in the model, the V-ΔlogR model offers more reliable results for test wells than other commonly used models (e.g., the modified Schomoker, multiple regression analysis, modified ΔlogR). The V-ΔlogR model eliminates the need for mineral and maturity data constraints and the overlay-coefficient can be determined using only the well logs, which significantly expands the applicability of the ΔlogR method. • An improved method (the V-ΔlogR model) predicts TOC content is proposed. • The method is based on sonic and the resistivity log, and a ratio of k between them. • A easily implemented method for predicting k using the log curves is presented. • The V-ΔlogR model expands the applicability of the ΔlogR method, and can be accurate in TOC predicting. [ABSTRACT FROM AUTHOR]

An effective empirical model for the velocity-field characteristic associated with a semiconductor offers the community of semiconductor device engineers with a tool that will ultimately allow them to relate key features of a semiconductor's velocity-field characteristic with the resultant device performance. Noting the limitations of previously devised empirical models for a semiconductor's velocity-field characteristic, we have developed an alternate approach. In particular, building upon the empirical velocity-field characteristic model of Eastman et al. related to high-field domains (Eastman et al., 1980), we develop an approach wherein the model's internal adjustable parameters may be directly tied with the velocity-field characteristic's observable features. We then apply this approach to the specific case of gallium arsenide, a contrast with results gleaned from Monte Carlo electron transport simulations being used to show that the resultant fits are indeed quite satisfactory. A comparison with other empirical velocity-field characteristic modeling approaches is offered, our approach being shown to be more effective than the other ones in several regards. Finally, within the framework of this empirical model, a means of evaluating the maximum value of the negative differential mobility associated with a given velocity-field characteristic is provided, such a value being of interest to those who wish to draw upon the aforementioned high-field domain effects. • An improved unicameral empirical model for the velocity-field characteristic of a semiconductor that takes into account the negative differential mobility. • Internal adjustable parameters associated with this model are shown to be directly related with the form of the velocity-field characteristics. • Contrasted the fit acquired through the use of this model with that determined from Monte Carlo electron transport simulations for the specific case of gallium arsenide. • The maximum value of the negative differential mobility associated with a given semiconductor's velocity-field characteristic. [ABSTRACT FROM AUTHOR]

• The flame heights are compared with classic Thomas model and Oka et al. model. • The experimental results deviate from calculations of classic models. • The characteristic size ratio λ = d / D is introduced into Thomas' and Oka et al.'s model. • The measured data of flame heights follow well with the improved models. The development of liquid fire depends mainly on fuel evaporation and heat feedback of flame configuration which are both influenced by the ambient winds. In current work, the height of pioneering flame in the process of flame spread above the surface of jet fuel is measured inside a bench-scale air flow tunnel. The longitudinal air flow velocities are 0.45, 0.88, 1.3, 1.73, 2.15 and 2.57 m/s for both concurrent and opposed flame spreads. Five oil pans with the same length of 100 cm but different widths of 4, 8, 12, 16 and 20 cm are utilized. The experimental results of flame heights considerably deviate from the calculations of classic Thomas model and Oka et al. model. Then, the new-proposed non-dimensional parameter, characteristic size ratio of pool λ = d / D is introduced into Thomas' model and Oka et al.'s model respectively. The measured flame heights follow well with the improved models H / d = a m ̇ * η (u ∗) b λ c and H / d = α F r 2 / 3 Q ̇ ∗ β λ γ , regardless of direction of air flow. The values of empirical coefficients and exponents of the correlations a , b , c , η in improved Thomas model and α , β and γ in improved Oka et al. model are derived from the experimental results. [ABSTRACT FROM AUTHOR]