Semi-empirical Prediction Model Research Articles

Mapping Slight and Moderate Saline Soils in Irrigated Agricultural Land Using Advanced Land Imager Sensor (EO-1) Data and Semi-Empirical Models

ABSTRACTAround the world, especially in semi-arid regions, millions of hectares of irrigated agricultural land are abandoned each year because of the adverse effects of irrigation, mainly secondary salinity and sodicity. Accurate information about the extent, magnitude, and spatial distribution of salinity and sodicity will help create the sustainable development of agricultural resources. In Morocco, south of the Mediterranean region, the growth of the vegetation and potential yield are limited by the joint influence of high temperatures and water deficit. Consequently, the overuse of surface and ground water, coupled with agricultural intensification, generates secondary soil salinity. Knowing when, where, and how salinity may occur is very important to the sustainable development of any irrigated production system. Remedial actions require reliable information to help set priorities and to choose the type of action that is most appropriate in each situation. Ground-based electromagnetic measurements of soil electrical conductivity (EC) are generally accepted as the most effective method for quantification of soil salinity. Unfortunately, these methods are expensive, time consuming, and need considerable human resources for land surveying. Moreover, the dynamic nature of soil salinity in space and time makes it more difficult to use conventional methods for comparisons over large areas. A major challenge of remote sensing, as a potential alternative technique, is to detect different levels of soil salinity. The main aim of this research is to assess the potential of the Advanced Land Imager (ALI) sensor on board the Earth Observing-1 (EO-1) satellite, with its rich infrared bands, for the discrimination and mapping of slight and moderate soil salinity in the Tadla’s irrigated agricultural perimeter in Morocco. To achieve this goal, semi-empirical predictive models developed in a previous study using second order regression analysis between the EC of salt-affected soils and different spectral salinity indices were applied to the ALI image. This was atmospherically corrected and the radiometric sensor drift was calibrated. Visual comparisons and statistical validation of these models using ground truth were undertaken in order to identify the best semi-empirical model for slight and moderate salinity mapping. The obtained results show that the model based on the Normalized Difference Salinity Index (NDSI) does not give any results. The model based on the Salinity Index-1 (SI-1) and the SI-Advanced Space-borne Thermal Emission and Reflection Radiometer (SI-ASTER) confuses vegetation with high soil salinity, although the model does bring out areas of lower salinity. Both R2 of 0.67 for the SI-1 and 0.65 for the SI-ASTER further reinforce that these models cause too much confusion to be used with accuracy for salt-affected soil detection. The semi-empirical model based on Soil Salinity and Sodicity Index-1 (SSSI-1) performs better than the two last models. However, there is a relative confusion between the classes in the slight and moderate salinity and in areas that are shown by the validation map; the higher class of salinity does not appear to contain higher levels of salinity. The statistical validation of this model reinforces what is seen on the derived map with only an R2 = 0.68. The model based on the SSSI-2 clearly provides the best results in comparison to the ground truth. Its derived map gives the closest overall visual approximation of the EC map, with a whole range of values. With a statistical validation of R2 = 0.97 to the ground truth, it is by far the best performance of any of the other models, and the different classes are statistically well separated, which further reinforces the accuracy of the visual analysis.

Predicting acid dew point with a semi-empirical model

Decreasing the temperature of exhaust flue gas in boilers is one of the most effective ways to further improve the thermal efficiency, electrostatic precipitator efficiency and to decrease the water consumption of desulfurization tower, while, when this temperature is below the acid dew point, the fouling and corrosion will occur on the heating surfaces in the second pass of boilers. So, the knowledge on accurately predicting the acid dew point is essential. By investigating the previous models on acid dew point prediction, an improved thermodynamic correlation formula between the acid dew point and its influencing factors is derived first. And then, a semi-empirical prediction model is proposed, which is validated with the data both in field test and experiment, and comparing with the previous models.

PERFORMANCE OF PRESSURE TUBES IN CANDU REACTORS

The pressure tubes in CANDU reactors typically operate for times up to about 30 years prior to refurbishment. The in-reactor performance of Zr-2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behavior and discusses the factors controlling the behaviour of these components. The Zr–2.5Nb pressure tubes are nominally extruded at 815 °C, cold worked nominally 27%, and stress relieved at 400 °C for 24 hours, resulting in a structure consisting of elongated grains of hexagonal close-packed alpha-Zr, partially surrounded by a thin network of filaments of body-centred-cubic beta-Zr. These beta-Zr filaments are meta-stable and contain about 20% Nb after extrusion. The stress-relief treatment results in partial decomposition of the beta-Zr filaments with the formation of hexagonal close-packed alpha-phase particles that are low in Nb, surrounded by a Nb-enriched beta-Zr matrix. The material properties of pressure tubes are determined by variations in alpha-phase texture, alpha-phase grain structure, network dislocation density, beta-phase decomposition, and impurity concentration that are a function of manufacturing variables. The pressure tubes operate at temperatures between 250 °C and 310 °C with coolant pressures up to about 11 MPa in fast neutron fluxes up to 4 × 1017 n·m−2·s−1 (E > 1 MeV) and the properties are modified by these conditions. The properties of the pressure tubes in an operating reactor are therefore a function of both manufacturing and operating condition variables. The ultimate tensile strength, fracture toughness, and delayed hydride-cracking properties (velocity (V) and threshold stress intensity factor (KIH)) change with irradiation, but all reach a nearly limiting value at a fluence of less than 1025 n·m−2 (E > 1 MeV). At this point the ultimate tensile strength is raised about 200 MPa, toughness is reduced by about 50%, V increases by about a factor of 6, while KIH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation, diametral expansion, and sag. The deformation behaviour is a function of operating conditions and the material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. The effect of material variability on corrosion behaviour is less well defined compared with other properties but there are instances where tube orientation and ingot source can be identified as factors that have an effect on hydrogen pick-up.

A semi-empirical model for peak strain prediction of buried X80 steel pipelines under compression and bending at strike-slip fault crossings

The strike-slip fault is a main type of permanent ground deformation (PGD) faced by long distance gas pipelines. Based on the non-linear finite element method, a numerical model for buried pipelines at strike-slip fault crossings under compression combined with bending was proposed at first. The model, with the advantages of reduced time consumption and high precision, was proven to be reasonable by comparing the numerical results with previous researchers' experiments and numerical results. The peak compressive strain of X80 steel pipelines subjected to strike-slip fault displacement under compression combined with bending was studied using the FE model. According to the investigation of the Second West to East Gas Pipeline Project, suitable ranges of all parameters, including the pipe diameter, wall thickness, soil properties, fault displacement and crossing angle, were obtained. The influence of these parameters on the peak compressive strain was discussed in detail. A regression equation for predicting the peak compressive strain of X80 steel pipelines was derived based on approximately 800 numerical results and regression analysis, and the applicable range of the formula was given. 15 true design cases of the Second West to East Pipeline Project in China were investigated to demonstrate the accuracy and applicability of the proposed methodology by comparing the predicted peak compressive strain results with the FEM results. It was shown that the proposed semi-empirical model predicts the peak compressive strain with good accuracy much less time consumption. It is thus applicable for the strain-based and reliability-based design of X80 steel pipelines subjected to strike-slip fault displacement.

Effect of gas—phase carbon depletion by sooting on the structure of methane/air flamelets

The paper describes an approach to model soot formation/oxidation in non premixed turbulent flames, which in particular accounts for the effect of gas-phase carbon depletion due to sooting. The effect is relevant to combustion chambers fed with oxygen (rather than air), operating at high pressure and overall rich, such as rocket chambers. A scaled gas-phase elemental carbon mass fraction is introduced to this end and, in the framework of a laminar flamelet approach, a library is developed for use in turbulent combustion models. Due to the lack of reference data for rocket chambers conditions, the library is limited for the time being to nonpremixed methane/air flames at two values of pressure, 1 atm and 3 atm, for which experimental data are available. Results indicate a signicant effect of carbon depletion on the concentration of soot precursor acetylene in particular, and on the ensuing soot nucleation rate. The model is shown to correctly capture the decrease of the latter rate with gas-phase carbon depletion, thereby potentially enabling to extend the range of applicability of semi-empirical soot prediction models for nonpremixed turbulent combustion.

Computational fluid dynamics based optimal design of hydraulic capsule pipelines transporting cylindrical capsules

Rapid depletion of energy resources has immensely affected the transportation sector, where the cargo transportation prices are rising considerably each year. Efforts have been made to develop newer modes of cargo transportation worldwide that are both economical and efficient for a long time. One such mode is the use of energy contained within fluids that flows in the pipelines for transportation of bulk solids. After appropriate modifications to these pipelines, bulk solids can be transported from one location to another very effectively. Solid material can be stored in cylindrical containers (commonly known as capsules), which can then be transported, either singly or in a train through the pipeline. Both the local flow characteristics and global performance parameters associated with such pipelines need careful investigation for economical and efficient system design. Published literature is severely limited in establishing the effects local flow features on system characteristics of hydraulic capsule pipelines (HCPs). The present study focuses on using a well validated computational fluid dynamics (CFD) tool to numerically simulate the solid–liquid mixture flow in HCPs, installed both on-shore and off-shore, along-with the pipe bends. Local static pressure fields have been discussed in detail for a wide range of geometrical and flow related parameters associated with the capsules and the pipelines. Numerical predictions have been used to develop novel semi-empirical prediction models for pressure drop in HCPs, which have then been embedded into a pipeline optimisation methodology that is based on Least-Cost Principle. This novel optimisation methodology that has been developed for HCPs is both robust and user-friendly.

Prediction of Acid Dew Point in Flue Gas of Boilers Burning Fossil Fuels

The temperature of flue gas should be controlled to be higher than the acid dew point to avoid fouling and corrosion of heating surfaces in the second pass of boilers. Decreasing the temperature of flue gas in boilers is one of the most effective ways to improve thermal efficiency, enhance electrostatic precipitator efficiency, and decrease water consumption of the desulfurization tower. Accurate knowledge in predicting acid dew point is required. Thus, based on previous research achievements, a measuring device is designed based on the principle of conductive dew point meter, and the acid dew points under different flue gas conditions are measured in this work. An improved thermodynamic correlation formula between the acid dew point and its influencing factors is also derived based on previous research achievements. Then, a semiempirical prediction model that considers the functions of H2SO4 and H2O is proposed. The proposed prediction model is validated by field test data, experimental data, and predict...

Study on the Prediction of Troposcatter Transmission Loss

In this article, a novel semiempirical average annual troposcatter transmission loss prediction model is presented. The model is generated by optimizing the correlation coefficients of propagation path conditions utilizing the modern optimization algorithm. The statistical relativities of troposcatter transmission loss as captured by changing frequency, path length, scatter angle, and meteorological condition are each analyzed using the terrestrial trans-horizon propagation loss data banks released by the International Telecommunication Union (ITU). For the percentages of time transmission loss not falling below 50%, the model is combined with the model of anomalous propagation mechanism introduced in the Recommendation ITU-R P.2001. The prediction results of this new troposcatter model are compared with other troposcatter models and with the trans-horizon propagation loss data banks. The comparisons show that the new model has a better estimated accuracy.

A semi-empirical swell prediction model formulated from ‘clay mineralogy and unsaturated soil’ properties

Swell behavior of expansive clays is an inherent property that can be better explained through its hydro mechanical volume change behavior arising from soil attributes like matric suction and clay mineralogy information. Previous swell related modeling studies have not incorporated these attributes for swell behavior, thereby leading to poor to erroneous characterization practices. Both chemical and hydrological attributes of the soils are targeted in this expansive soil modeling. Eight natural expansive soils were collected and their swell strains were measured under different confining pressure conditions. Soil suction properties of expansive soils as well as soil water characteristic curves (SWCC's) were determined using standard measurement procedures including pressure plate and filter paper techniques. Slope of the paths traversed by the soil specimens in a void ratio — soil matric suction framework are determined and used as mechanical input parameters for the heave modeling. A new parameter, Mechanical Hydro Chemical Parameter (MHCP) is used that accounts for both matric suction and clay mineralogy information. This parameter is correlated with swell property measurements and the correlations developed provided reliable and reasonable swell property predictions. Independent validations with other soils are still needed for further enhancement of the MHCP framework for more reliable predictions.

Wind-driven natural ventilation for buildings with two openings on the same external wall

This study uses wind tunnel experiments to investigate the wind-driven ventilation for buildings with two openings on a single wall. The exchange rates are measured by the tracer gas decay method under different external wind speeds, directions and opening sizes. The experimental results indicate that the time-averaged pressure difference across the openings is much larger than the fluctuating pressure when the wind direction is θ=22.5–45°, and the ventilation rate can be predicted by the orifice equation. When the wind direction is θ=0° and 67.5–180°, the pressure difference across the openings is insignificant and the fluctuating pressure entrains air across the openings. The exchange rate is proportional to the root-mean-square of the pressure fluctuation. Furthermore, the dimensionless exchange rate of the shear-induced ventilation (wind is parallel to the openings) is found to be independent of the wind speed, opening area and location. The exchange rate for buildings with an internal partition is lower than that without a partition when the wind direction is θ=0–90°. A semi-empirical prediction model is proposed to calculate the exchange rate by incorporating the time-averaged pressure difference and pressure fluctuation. The application of the prediction model to compute the air change rate (ACH) is also discussed.

A semi-empirical ship operational performance prediction model for voyage optimization towards energy efficient shipping

Voyage optimization is a practice to select the optimum route for the ship operators to increase energy efficiency and reduce Green House Gas emission in the shipping industry. An accurate prediction of ship operational performance is the prerequisite to achieve these targets. In this paper, a modified Kwon׳s method was developed to predict the added resistance caused by wave and wind for a specific ship type, and an easy-to-use semi-empirical ship operational performance prediction model is proposed. It can accurately predict the ship׳s operational performance for a specific commercial ship under different drafts, at varying speeds and in varying encounter angles, and then enables the user to investigate the relation between fuel consumption and the various sea states and directions that the ship may encounter during her voyage. Based on the results from the operational performance prediction model and real time climatological information, different options for the ship׳s navigation course can be evaluated according to a number of objectives, including: maximizing safety and minimizing fuel consumption and voyage time. By incorporating this into a decision support tool, the ship׳s crew are able to make an informed decision about what is the best course to navigate.In this study the Energy Efficiency of Operation (EEO) is defined as an indicator to illustrate the ratio of main engine fuel consumption per unit of transport work. Two case studies are carried out to perform the prediction of ship operational performance for Suezmax and Aframax Oil Tankers, and the results indicate that the semi-empirical ship operational performance prediction model provides extremely quick calculation with very reasonable accuracy, particularly considering the uncertainties related to the parameters of interest for the case study data. Within the case studies, the additional fuel consumption caused by the combined hull and propeller fouling and engine degradation is included in the model as a time-dependent correction factor. The factor may assist the ship owner/operator to determine the hull coating selection, and/or the dry-docking and main engine maintenance strategy.

Modeling of oil retention and pressure drop in vertical suction risers

A semi-empirical model for prediction of oil retention and pressure drop in vertical suction lines of an air-conditioning system is presented. The model was developed using experimental data for R134a with polyol ester oil International Organization for Standardization 32 oil in a 10.2-mm-inside-diameter pipe and was supported by data for R410A with polyol ester oil 32 flows in 7.1- and 18.5-mm-inside-diameter pipes. The model predicts 90% of oil retention data within ±20% relative error and pressure drop data within ±30% relative error. A model was also developed for prediction of minimum refrigerant mass flux, which ensures oil returns as annular film in vertical suction lines. The oil return model was used to develop minimum cooling capacity tables versus vertical suction line diameter for R134a.

A semi-empirical predictive model for the attenuation properties of fine-grained sediments

It is of interest to be able to predict the acoustic properties (especially the compressional sound speed and attenuation) of sediments that can be classified as mud. An inverse problem is constructed to infer estimates of the surface sediment attenuation, the attenuation gradient, and the frequency exponent and applied to acoustic data in the 10–400 Hz band collected in the Gulf of Oman basin. The results indicate that, unlike a sandy seabed, the surface attenuation is about 0.005 dB/m-kHz and the frequency exponent is close to unity. These estimates are compared to those of an inversion analyses for a shallow-water site in the Gulf of Mexico, which is an environment with similar sediment properties. Further, the inferred attenuation values from both experiments are compared to calculated values from the Buckingham grain-shearing model. The geological histories of the shallow- and deep-water seabeds are compared with the intent of constructing a semi-empirical predictive model for the attenuation properties of fine-grained sediments.

Displacement thickness evaluation for semi-empirical airfoil trailing-edge noise prediction model

This study proposes a criterion for evaluating the turbulent boundary layer displacement thickness when predicting airfoil trailing-edge noise with semi-empirical methods. The boundary layer integral parameter is usually employed as the typical turbulence length-scale in the classic NASA-BPM semi-empirical airfoil self-noise prediction model and its variations. Although the semi-empirical noise prediction methods have been, in theory, superseded by more complex and demanding simplified-theoretical methods, they arguably remain the most suitable methods for noise investigation during the preliminary design phase of airfoils and wind turbine blades. The purpose of the criterion discussed is to limit the adverse impact of the uncertainty associated with the scaling parameter into the overall intrinsic quality of the semi-empirical noise prediction method. The criterion may be then employed, along with computational efficiency, to sort out methods for the task of feeding the popular BPM noise prediction model and its variations. As an illustration of the application of the proposed criterion, the performance of CFD-RANS and XFoil codes are examined and compared with experimental data from turbulent, incompressible flow available from the literature in the range $$5.0 \times 10^{5} < \text{Re}_{\text{C}} < 1.5\, \times 10^{6}$$ .

Frost Depth: General Prediction Model

Accurate frost depth prediction is an important aspect of engineering design for infrastructure including pavement, building and bridge foundations, and utility lines. Actual frost depth is affected by material type, soil thermal properties, and soil water content as well as climatic conditions such as temperature, wind speed, precipitation, and solar radiation. Numerical or analytical modeling techniques could be used to estimate frost depth; however, the required input data are unavailable or expensive to collect. Therefore, the use of numerical and analytical models entails estimating missing data that affect the reliability of the results. The accuracy of three analytical and semiempirical frost depth prediction models (Stefan, modified Berggren, and Chisholm and Phang empirical) were tested with soil temperature data from the Michigan Road Weather Information System. Because none of the models yielded accurate results, revised empirical models developed for different soil types required only daily high and low air temperatures as inputs. The predicted frost depths were more accurate than in previous models. Finally, by using thermal conductivity values for each soil type, the models were combined into one general model that required thermal conductivity and average air temperature as inputs.

INFLUENCE OF REACTOR PRESSURE ON TWIN-FLUID ATOMIZATION: BASIC INVESTIGATIONS ON BURNER DESIGN FOR HIGH-PRESSURE ENTRAINED FLOW GASIFIER

The conversion of low-grade fossil and biogenic energy resources to a high-quality chemical energy carrier (syngas) in a high-pressure entrained flow gasification process opens a wide spectrum for energy efficient fuel conversion. Typically, twin-fluid atomizers are used to generate fuel spray in high-pressure entrained flow gasification. The quality of the syngas produced by entrained flow gasifiers depends strongly on drop size distribution generated by the burner nozzle. In consequence fundamental knowledge concerning the influence of operating parameters, especially ambient pressure on spray quality, is mandatory. Atomization experiments were performed using an external-mixing twin-fluid atomizer and varying reactor pressure up to 21 bar. Radial SMD profiles were measured using a phase Doppler analyzer. Additionally, primary jet breakup was investigated using a highspeed camera. To qualitatively prove the PDA results a photo-optical shadowgraphy system was used to estimate the size range of the droplets. The experiments showed that keeping the We number constant while varying ambient pressure leads to an increase of SMD with increasing ambient pressure. Keeping the gas velocity constant resulted in constant SMD values nearly independent from ambient pressure. The conducted analysis of experimental data shows that the typically used dimensionless parameter, the We number, for prediction of droplet size is not favorable for correlations to be valid in a wide range of reactor pressures. Finally the results were used to generate a semi-empirical model for prediction of SMD, based on a simplified theoretical energy consideration.

Applicability of Empirical Formulae for the Fatigue Notch Factor to Estimate Riveted Lap Joint Fatigue Strength

A semi-empirical fatigue life prediction model under development by the present authors for riveted lap joints used in aircraft structures is outlined. In contrast to existing models, it will account for the influence of the rivet squeeze force on the fatigue life of riveted joints. To determine the effect of rivet-hole interference on the fatigue behaviour of a riveted joint, a series of fatigue tests on filled hole coupons with different amounts of interference will be carried out under loading conditions representing the bypass load, transfer load and secondary bending. These experiments will allow evaluating of the dependency of the fatigue notch factors on rivet hole expansion. Preliminary results obtained so far are presented in this paper.

Transient Thermal Analysis and Viscoplastic Damage Model for Life Prediction of Turbine Components

This paper reports the process and computer methodology for a physics-based prediction of overall deformation and local failure modes in cooled turbine airfoils, blade outer air seals, and other turbomachinery parts operating in severe high temperature and high stress environments. The computational analysis work incorporated time-accurate, coupled aerothermal computational fluid dynamics (CFD) with nonlinear deformation thermal-structural finite element model (FEM) with a slip-based constitutive model, evaluated at real engine characteristic mission times, and flight points for part life prediction. The methodology utilizes a fully coupled elastic-viscoplastic model that was based on crystal morphology, and a semi-empirical life prediction model introduced the use of dissipated energy to estimate the remaining part life in terms of cycles to failure. The method was effective for use with three-dimensional FEMs of realistic turbine airfoils using commercial finite element applications. The computationally predicted part life was calibrated and verified against test data for deformation and crack growth.

A semi-empirical traction prediction model for an agricultural tyre, based on the super ellipse shape of the contact surface

This study presents a semi-empirical model for predicting the traction force and traction efficiency for a 2WD agricultural tractor, assuming that the shape of the tyre–ground contact area is a super ellipse. The model assumes that, under the vertical load, the wheel sinks into the soil and that the load induces tyre deflection; as a result, the virtual radius of the deformed tyre increases, as it flattens in the tyre–ground contact area. A computer programme was developed in order to solve the equations of the model, using an iterative process. In order to evaluate the maximum traction force it was assumed that it is limited only by the soil shear strength and the Mohr–Coulomb equation was used to calculate the soil maximum shear stress.Because the available literature presents a large range of values for the super ellipse exponent, field tests were performed in order to validate the model; the experimental data were collected during ploughing tests. In order to evaluate the precision of the model the predicted data were compared with the test data by the means of a goodness-of-fit analysis.The results predicted by the model show that the length of the tyre–ground contact surface is not affected by the shape of the contact surface (value of the super ellipse exponent), while increasing the value of the super ellipse exponent results in an increased of the area of the contact surface.The best fit between model data and experimental data was achieved when the value of the super ellipse exponent was set to k=3.5.

Semi-Empirical Model for SEGR Prediction

The underlying physical mechanisms in single event gate rupture (SEGR) are not known precisely. SEGR is expected to occur when the energy deposition due to a heavy ion strike exceeds a certain threshold simultaneously with sufficient electric field across the gate dielectric. Typically the energy deposition is described by using the linear energy transfer (LET) of the given ion. Previously the LET has been demonstrated not to describe the SEGR sufficiently. The work presented here introduces a semi-empirical model for the SEGR prediction based on statistical variations in the energy deposition which are described theoretically.