Empirical Correction Factors Research Articles

Using computational fluid dynamics and field experiments to improve vehicle-based wind measurements for environmental monitoring

Abstract. Vehicle-based measurements of wind speed and direction are presently used for a range of applications, including gas plume detection. Many applications use mobile wind measurements without knowledge of the limitations and accuracy of the mobile measurement system. Our research objective for this field-simulation study was to understand how anemometer placement and the vehicle's external airflow field affect measurement accuracy of vehicle-mounted anemometers. Computational fluid dynamic (CFD) simulations were generated in ANSYS Fluent to model the external flow field of a research truck under varying vehicle speed and wind yaw angle. The CFD simulations provided a quantitative description of fluid flow surrounding the vehicle and demonstrated that the change in wind speed magnitude from the inlet increased as the wind yaw angle between the inlet and the vehicle's longitudinal axis increased. The CFD results were used to develop empirical speed correction factors at specified yaw angles and to derive an aerodynamics-based correction function calibrated for wind yaw angle and anemometer placement. For comparison with CFD, we designed field tests on a square, 12.8 km route in flat, treeless terrain with stationary sonic anemometers positioned at each corner. The route was driven in replicate under varying wind conditions and vehicle speeds. The vehicle-based anemometer measurements were corrected to remove the vehicle speed and course vector. From the field trials, we observed that vehicle-based wind speed measurements differed in average magnitude in each of the upwind, downwind, and crosswind directions. The difference from stationary anemometers increased as the yaw angle between the wind direction and the truck's longitudinal axis increased, confirming the vehicle's impact on the surrounding flow field and validating the trends in CFD. To further explore the accuracy of CFD, we applied the function derived from the simulations to the field data and again compared these with stationary measurements. From this study, we were able to make recommendations for anemometer placement, demonstrate the importance of applying aerodynamics-based correction factors to vehicle-based wind measurements, and identify ways to improve the empirical aerodynamic-based correction factors.

Time evolution of energy use intensities and energy gap of existing Hellenic non-residential buildings

This work exploits data from the energy performance certificates (EPCs) of the national electronic repository, to characterize the energy use intensity (EUI) of non-residential (NR) buildings in Greece and investigate the gap between the nominal needs and the actual energy use. Over the past eight years, a total of about 1,500,000 EPCs have been issued for various building types, out of which 17.5% for NR buildings. As the national EPC database is progressively enriched with more data, the work considers the time evolution of the average EUI and analyse the available data in order to determine whether they can be regarded as typical and representative for the Hellenic building stock. When available, data on actual energy use of the buildings is used in an attempt to close the gap between calculated (asset) and actual (operational) energy use. The data is organized in terms of different end uses and used to generate empirical correction factors that relate the normative calculated heating energy consumption with the actual energy use. These factors can be used to make more realistic estimates of the energy performance of buildings that undergo different refurbishments at national level.

The Nonaberrational Width of the Angular Spectrum of a Field Probing a Layered Object in Confocal Microscopy

The influence of the numerical aperture of a light beam that probes a layered object on the magnitude of the quantity measured with a confocal interference microscope upon determining the object thickness has been studied theoretically and experimentally for the case in which the signal is significantly affected by the spherical aberration arising in the probing beam as it passes through the object. The dependence of the quantity to be measured on the numerical aperture is obtained taking into account the influence of the spherical aberration on the signal. The criterion of the “nonaberrational” propagation of the beam probing the object is determined and the condition under which the influence of the spherical aberration on the signal of the confocal microscope can be neglected is found. An approximate analytical expression is obtained, which makes it possible to determine the “nonaberrational” width of the angular spectrum of the light beam probing the object, taking into account an empirical correction factor. The applicability limits of the analytical dependence of the quantity to be measured on the numerical aperture, which has been previously obtained for the case of a negligibly weak influence of the spherical aberration on the signal from the confocal microscope, have been determined.

Filtered actuator disks: Theory and application to wind turbine models in large eddy simulation

SummaryThe actuator disk model (ADM) continues to be a popular wind turbine representation in large eddy simulations (LES) of large wind farms. Computational restrictions typically limit the number of grid points across the rotor of each actuator disk and require spatial filtering to smoothly distribute the applied force distribution on discrete grid points. At typical grid resolutions, simulations cannot capture all of the vorticity shed behind the disk and subsequently overpredict power by upwards of 10%. To correct these modeling errors, we propose a vortex cylinder model to quantify the shed vorticity when a filtered force distribution is applied at the actuator disk. This model is then used to derive a correction factor for numerical simulations that collapses the power curve for simulations at various filter widths and grid resolutions onto the curve obtained using axial momentum theory. The proposed correction, which is analytically derived from first principles, facilitates accurate power measurements in LES without resorting to highly refined numerical grids or empirical correction factors.

Modeling transport of colloidal particles through polydisperse fibrous membrane filters under unfavorable chemical and physical conditions

Numerical simulations of filters with polydisperse fibers under chemically and physically unfavorable conditions were conducted to predict particle retentions on polypropylene fibrous filters. The fibrous filters were analyzed by a scanning electron microscopy to obtain fiber size distributions, and on the basis of a randomized algorithm, 2-D calculation domains were generated, and flow field calculations were conducted. For tracking particles, the standard Lagrangian tracking method in ANSYS Fluent software was modified by user-defined functions to incorporate particle deposition via interception and interaction energy calculations. Particle release from collector surfaces was considered by performing torque analysis for particles attached to the surfaces. Numerical retention efficiencies of fibrous filters showed very good agreement with experimental data without any free parameters or empirical correction factors. The parametric studies of polydisperse fibrous filters were conducted, and the retention efficiency was varied from 0 to 100% depending on chemical and physical conditions.

Determination of the Effective Viscosity of Non-newtonian Fluids Flowing Through Porous Media

When non-Newtonian fluids flow through porous media, the topology of the pore space leads to a broad range of flow velocities and shear rates. Consequently, the local viscosity of the fluid also varies in space with a non-linear dependence on the Darcy velocity. Therefore, an effective viscosity is usually used to describe the flow at the Darcy scale. For most non-Newtonian flows the rheology of the fluid can be described by a (non linear) function of the shear rate. Current approaches estimate the effective viscosity by first calculating an effective shear rate mainly by adopting a power-law model for the rheology and including an empirical correction factor. In a second step this averaged shear rate is used together with the rheology of the fluid to calculate. In this work, we derive a semi-analytical expression for the local viscosity profile using a Carreau type fluid, which is a more broadly applicable model than the power-law model. By solving the flow equations in a circular cross section of a capillary we are able to calculate the average viscous resistance directly as a spatial average of the local viscosity. This approach circumvents the use of classical capillary bundle models and allows to upscale the viscosity distribution in a pore with a mean pore size to the Darcy scale. Different from commonly used capillary bundle models, the presented approach does neither require tortuosity nor permeability as input parameters. Consequently, our model only uses the characteristic length scale of the porous media and does not require empirical coefficients. The comparison of the proposed model with flow cell experiments conducted in a packed bed of monodisperse spherical beads shows, that our approach performs well by only using the physical rheology of the fluid, the porosity and the estimated mean pore size, without the need to determine an effective shear rate. The good agreement of our model with flow experiments and existing models suggests that mean viscosity is a good estimate for the effective Darcy viscosity providing physical insight into upscaling of non-Newtonian flows in porous media.

Empirical corrections for predicting the sound insulation of double leaf cavity stud building elements with stiffer studs.

The experimentally determined normal incident mass-air-mass resonance frequency for a double leaf cavity stud building element is significantly greater than the theoretically predicted frequency for wood studs and steel studs manufactured from thicker sheet steel. This paper gives a method for calculating the effective mass-air-mass resonance frequency as the root mean square sum of the mass-air-mass resonance frequency and the resonance frequency of the first bending wave mode of the leaves between the studs. This calculation should use the isothermal mass-air-mass resonance frequency if the building element cavity contains porous sound absorbing material. If the cavity does not contain porous sound absorbing material, the usual adiabatic mass-air-mass resonance frequency should be used in the calculation. Because the exact boundary conditions of the building element leaves at the studs and the effective in situ damping are unknown, the paper gives empirical correction factors to determine the actual resonance frequency and the depth of the dip in the predicted sound insulation. This paper also gives empirically derived formulae for the line and point equivalent translational compliances of steel studs manufactured from different sheet steel gauges and compares them with formulae derived by other authors for the case of 25 gauge steel studs.

A Holistic Review on Biomass Gasification Modified Equilibrium Models

Biomass gasification is realized as a settled process to produce energy in a sustainable form, between all the biomass-based energy generation routes. Consequently, there are a renewed interest in biomass gasification promoting the research of different mathematical models to enlighten and comprehend gasification process complexities. This review is focused on the thermodynamic equilibrium models, which is the class of models that seems to be more developed. It is verified that the review articles available in the literature do not address non-stoichiometric methods, as well as an ambiguous categorization of stoichiometric and non-stoichiometric methods. Therefore, the main purpose of this article is to review the non-stoichiometric equilibrium models and categorize them, and review the different stoichiometric equilibrium model’s categorization available in the literature. The modeling procedures adopted for the different modeling categories are compared. Conclusion can be drawn that almost all equilibrium models are modified by the inclusion of empirical correction factors that improves the model prediction capabilities but with loss of generality.

A Formula to Determine Energy Band Gap in Semiconducting Carbon Nanotubes

In this paper we propose a new formula to evaluate in semiconducting Carbon Nanotubes the energy bandgap, i.e. the electronic transition energy from the first valence band to the first conduction band, which is fundamental for electronic applications of CNTs as channel in field effect transistors. The proposed formula is based on empirical correction factors, gained by an optimization procedure aimed at matching experimental data, which results in negligible errors. Moreover the proposed formula shows a new dependence on CNT symmetry indexes (n-m), which has been never observed in literature.

Безаберрационная ширина углового спектра зондирующего слоистый объект поля в конфокальной микроскопии

The effect of the numerical aperture of a light beam probing an object on the value measured by a confocal interference microscope when determining the thickness of a layered object for the case of a significant effect on the signal of the spherical aberration arising in the probe beam at its propagation through an object has been theoretically and experimentally investigated. Taking into account the influence of spherical aberration on the signal the dependence of the measured value on the numerical aperture has been obtained. The criterion of the “aberration-free” propagation of the beam probing an object has been established and the condition under which the effect of spherical aberration on the signal of a confocal microscope can be neglected has been determined. An approximate analytical expression which allows to determine the “aberration-free” width of angular spectrum of the probing light beam taking into account the empirical correction factor has been obtained. The limits of applicability of the analytical dependence of the measured value on the numerical aperture, which was obtained earlier for the case of negligible influence of spherical aberration on the signal of a confocal microscope, have been determined.

Net emission coefficient of complex thermal plasmas used in SWNT synthesis

The calculation of net emission coefficient NEC is done for mixtures He–Ar/N2–[C100−x−y−z,Bz,Nix/Cox,Yy] used in the synthesis of single-wall carbon nanotubes SWNTs by arc discharge technique, at pressure of 60 kPa and at temperature interval going from 1 kK to 30 kK. These mixtures contain helium–argon as a gaseous atmosphere, nitrogen–boron as a doping atoms and a carbon anode filled with yttrium–nickel/cobalt as catalysis. Different proportions of metallic catalysts are considered going from 0.01 atomic% (at%) to 5 at%. Whereas for doping atoms the concentration amounts are much higher and do not exceed 8 at% for boron and 50% for nitrogen. The results of NECs are obtained by summing over all wavelengths, the contributions of atomic and molecular continuum, results of free–free and free–bound transitions, and line and molecular bands emissions corresponding to bound–bound transitions. Doppler broadening, resonance, van der Waals, electron and ion Stark broadening are taken into account for the calculation of the lines widths. As Stark broadening is the most important broadening mechanism at intermediate and high temperature, an empirical correction factors determined for some resonance lines, are added to the semi-empirical Stark formulas for a best reproducing of the experimental Stark widths. The comparisons of the NECs of the pure plasmas of argon, helium, nitrogen and carbon to those given in literature present an acceptable agreement. For the studied mixtures containing He–Ar/N2–[C100−x−y−z,zBz, Nix/Cox,Yy], the obtained results show that the addition of boron or the nitrogen induces a few little changes in the NEC, in contrary to the metal catalysts where we noted a considerable increase in the plasma emission especially at low temperatures. The effect of the addition of yttrium in carbon anode even in a small amount (<0.1 at%) affects strongly the NEC compared to that of cobalt or nickel which have given similar results.

Prediction of modulus of elasticity of poplar wood using ultrasonic technique by applying empirical correction factors

In this research, dynamic modulus of elasticity (MOE) of poplar wood was predicted under two different levels of moisture content, two different specimen dimensions, and three different transducer directions by ultrasonic technique. The main goal of this research was evaluate five correlations for the prediction of MOE and finding the best model based on a correction factor. Ultrasonic velocity in the wood was measured using Sylvatest Duo 9906-015 device. Dynamic MOE was calculated using measured ultrasonic wave velocity and density in different transducer directions and compared to static MOE. Static MOE was directly measured using Instron-4486 universal testing machine. Results generally showed that only two correlations had acceptable errors in the range of 5.8%–10.4% for all levels of moisture content. The results also showed that the ultrasonic technique is a suitable and accurate method for the prediction of MOE of poplar wood using models 2 and 3 (with around 7% relative error), especially in lower level of MC. Transducer direction B give the best outcomes along with minimum relative error (6.7%) among the other transducer directions. The empirical correction factors have an impressive effect on the reduction of relative error.

Molecular Dynamic Simulations of Fibrous Distillation Membranes

The rate of heat and mass transfer through distillation membranes is typically estimated using an over-simplified, straight-cylindrical-pore approach coupled with several empirical correction factors that are included to compensate for the simplicity of the approach. In the present work, we have calculated for the first time the rate of transport of heat and mass through three-dimensional virtual membranes from first principles without the need for any empirical correction factors. More specifically, molecular dynamic (MD) simulations are conducted in idealized 3-D geometries that resemble the microstructure of a nanofiber membrane. The SPC/E molecular model and coarse-grain Pea model are considered to simulate, respectively, water molecules and air. The fibers, on the other hand, are constructed as simple metal lattice, and their contact angle with water is controlled using a scaling factor from the Lorentz–Berthelot mixing parameters. A proof-of-concept study is presented to demonstrate the capabilities of the new modeling approach in predicting the effects of the membrane's microstructural properties on the desalination performance. While the simulations are conducted at scales 3–4 orders of magnitudes smaller than an actual electrospun membrane, the conclusions can be applied membranes with more practical dimensions.

Diffusion of organic anions in clay-rich media: Retardation and effect of anion exclusion

The transport of emerging organic contaminants through the geosphere is often an environmental issue. The sorption of organic compounds slows their transport in soils and porous rocks and retardation is often assessed by extrapolation of batch experiments. However, transport experiments are preferable to strengthen migration data and modelling. In this context, we evaluated the adsorption of various organic acids by means of through-diffusion experiments in a sedimentary clay-rich rock (Callovo-Oxfordian, East of Paris Basin, France). A low diffusivity of organic anions was quantified with effective diffusion coefficients, De, ranged between 0.5 and 7 10−12 m2 s−1. These values indicated an organic anion exclusion. As for chloride, the porosity accessible to organic anions was lower than that of water: εa(organic anions) < ε(water). The partial exclusion of organic anions from rock porosity was linked to both charge and size effects. A significant retardation was observed for organic anions such as oxalate, citrate or α-isosaccharinate. Yet, retardation measured by diffusion experiments was significantly lower than expected from batch experiments on crushed samples. An empirical correction factor is proposed to account for a possible decrease of retardation with accessible porosity of diffusing solute. This feature has significant implications for the estimation of migration parameters of organic compounds in the environment.

Fatigue life prediction of workpiece with 3D rough surface topography based on surface reconstruction technology

The fatigue performance of a workpiece depends on its surface quality. In traditional fatigue life prediction, the effect of surface quality is commonly accounted for by using empirical correction factors, which is imprecise when safety is of great concern. For surface quality, the surface topography is an important parameter, which introduces stress concentration that reduces the fatigue life. It is not feasible to test the stress concentration of different surface topographies. On the one hand, it is time-consuming and high-cost, and on the other hand, it cannot reflect the general statistical characteristics. With the help of surface reconstruction technology and interpolation method, a more efficient and economic approach is proposed, where FE simulation of workpiece with the reconstructed surface topography is used as a foundation for fatigue life prediction. The relationship between surface roughness (Sa) and fatigue life of the workpiece is studied with the proposed approach.

Micro Electro Discharge Machining of Nonconductive Ceramic: The Issue of Spalling

Nonconductive ceramic materials are used in many engineering applications such as car brake, turbine blade, and hip-bone replacement because of its high dimensional accuracy, corrosion and wear resistant, and biocompatibility. These materials are usually processed with diamond grinding and limited laser applications such as cutting, drilling and scribing. Specific shapes and profiles are still difficult and costly to machine using these processes. Electrical discharge machining (EDM), extensively used for various shapes and profiles on conductive materials having minimum electrical conductivity of 0.10 S.cm-1. It is not directly applicable on nonconductive ceramic materials due to its very low electrical conductivity (&lt;10-10 S.cm-1). However, recently EDM is used on nonconductive materials with the aid of assisting electrode to initiate the spark between conductive tool electrode and nonconductive workpiece. The available material removal models of EDM are based on single spark erosion with uniform melting and vaporization of workpiece materials. However, in EDM of nonconductive ceramics, material removal is not uniform because of random spalling due to alternating thermal stress. In addition, it is difficult to create single spark erosion on a nonconductive ceramic workpiece as initial sparks are occurred between tool electrode and assisting electrode attached to workpiece. This paper presents the empirical factor for the estimation of spalling along with melting and vaporization through experimental study. Model of material removal rate as a function of capacitance and voltage are developed in micromachining of nonconductive zirconium oxide (ZrO2) using (R-C) pulse type micro-EDM. The single spark erosion volume is derived from the fundamental principle of melting and vaporization. An empirical correction factor is introduced to compensate random spalling and multi-spark erosion effect.

Analysis of the semi-empirical Stark broadening methods to improve the line emission accuracy: applications on He, Ar and Fe thermal plasmas

Stark broadening of isolated lines plays a crucial role in the calculation of radiative transfer of thermal plasmas. The most popular methods used are: the simple formula based on the semi-empirical method developed by Griem; the more elaborated method of Dimitijević and Konjević and the well–known Lindholm formula. Their accuracy are investigated through comparisons of obtained Stark widths with previous experimental and theoretical results for HeI, ArI, ArII, ArIII, FeI and FeII lines at different temperatures and electron number density values. An improvement of the calculated Stark results is proposed and discussed by adding an empirical correction factor to the proposed formulas. All the calculated factors are supplied in tables in order to use them in the calculation of radiative properties of thermal plasmas. The influence of the Stark models and of the empirical correction factors in the calculation of the net emission coefficient (NEC) of line are analyzed and discussed for pure helium, argon and iron plasmas, in a temperature range from 0.3 kK to 30 kK, and the atmospheric pressure. The obtained results show that the effect of the empirical correction factor does not exceed 31% but the choice of the proposed Stark broadenings models can induce huge variations in line radiation.

Stereological correction of perimeter based estimates of exposed grain surface area

Data necessary for liberation and/or exposure analysis is frequently obtained from two-dimensional (2D) polished section images of mineral particles of specified size. This data overestimates the extent of liberation and/or exposure, and in the past an empirical correction (locking) factor has been used to give a better estimate of the extent of dispersed phase liberation and/or exposure. With such 2D data, exposed grain surface area is estimated from perimeter analysis of sectioned particles. Although many researchers have reported 2D mineral liberation analysis in terms of area grade and/or perimeter based grain exposure, comparison of 2D perimeter based liberation with three-dimensional (3D) mineral liberation analysis has not been reported.In this current research, perimeter based estimates of exposed grain surface areas from 2D polished section analysis of feed and products from HydroFloat (HF) flotation of a copper porphyry ore are evaluated from corresponding 3D high resolution X-ray microtomography (HRXMT) data. Results show that for mean dispersed phase grades (sulfide mineral content) greater than 10%, perimeter based polished section analysis provides a good approximation of the exposed grain surface area determined by HRXMT. For mean grades less than 10%, stereological correction of the 2D data is required for satisfactory estimation of the exposed grain surface area. The most significant stereological correction with respect to exposed grain surface area is for the 0% grade class (“liberated” gangue minerals). For example, in the case of the 417 × 212 µm size class, 2D perimeter analysis indicates that about 96% of the particles have 0% grain area exposure whereas 3D analysis shows that in reality about 77% of the particles have 0% grain area exposure.

A theoretical model for predicting the wax breaking force during pipeline pigging

Pipeline pigging is a major conventional wax remediation technique for waxy crude oil transportation. Predicting the wax breaking force, a decisive parameter for pigging arrangements, however still remains an open question, primarily due to the ambiguities in wax removal physics as well as a lack of methods. To address this issue, here we propose a new theoretical wax breaking model to explain the wax removal mechanism and predict the wax breaking force, allowing the no empirical parameters or correction factors. It is met by introducing orthogonal cutting in wax removal explanation and employing slip-line field theory in wax breaking force calculation. Scraping disk deformation is incorporated in this model. An indirect trial method is adopted for the wax-disk frictional angle determination. To check its correctness, we conducted verification experiments with 29-mm-ID and 50-mm-ID pipes. Good agreement between the predicted and measured wax breaking forces has been observed with the maximum and average relative deviations being 21.98% and 8.85% respectively. Moreover, case study suggests this model can potentially enable applications in pig design. Recommendations on pig geometry are accordingly given in detail. On the whole, calculating the wax breaking force, this presented model benefits in optimizing the pig design. In a broader perspective, it further helps to avoid pig stall.

Improved Hardin-Drnevich model for the dynamic modulus and damping ratio of frozen soil

The Hardin-Drnevich model is frequently employed in the seismic ground response analysis, but the original model cannot be directly applied to frozen soils, the dynamic properties of which are functions of the soil temperature. Resonant column tests were carried out and empirical correction factors were proposed to revise the model. The improved model was applied to the seismic ground response analysis of a permafrost site, and the influences of the variations of the correction factors were analyzed. The resonant column test results indicated that soil temperature had large influences on the shear modulus and damping ratio, while in the range investigated in this study, the effect of the degree of saturation was not significant. The proposed correction factors properly fitted the test results in the present and previous studies, but the correction factors varied considerably even for the same category of clayey or silty or sandy soils. Compared with the correction factors for the modulus reduction curve and damping curve, the correction factor for the maximum shear modulus had a larger effect on the seismic ground response of a permafrost site. In the seismic response analyses, the response spectral values at the ground surface were generally larger if the investigated site was assumed to be non-frozen.