Superposition Model Research Articles

Comparison of individual versus ensemble wind farm parameterizations inclusive of sub‐grid wakes for the WRF model

AbstractWind turbine wakes can be predicted somewhat accurately with mesoscale numerical models, such as the Weather Research and Forecast (WRF) model, via a wind farm parameterization (WFP) that treats the effects of the wakes, which are sub‐grid features, on power production and the environment. A few WFPs have been proposed in the literature, but none has been able to properly account for the individual wakes within a grid cell or the effects of overlapping wakes from multiple turbines. A solution to these two issues is a WFP that includes both a wake model, which is a simplified analytical model of the wind speed (or wind power) deficit caused by a wake, and a wake superposition model, which accounts for overlapping wakes. Several such WFPs are developed here for the WRF model—based on the Jensen, the Geometric, and the Gaussian wake models coupled with two wake superposition methods (based on a squared deficit and a squared velocity superposition)—and tested individually, as well as combined together in an ensemble (EWFP), at two modern offshore wind farms. Most WFPs perform satisfactorily alone, but the EWFP generally outperforms them at both farms. The issue of resolved versus sub‐grid wakes is explored for single‐ and multi‐cell cases and for directions of alignment and non‐alignment between the wind direction and the turbine columns. Although different combinations of wake loss and wake superposition models might be preferred at other wind farms, the general findings and detailed performance statistics given here might provide useful guidance in their selection.

Complex spherical-wave elastic inversion using amplitude and phase reflection information

Unlike the real-valued plane wave reflection coefficient (PRC) at the pre-critical incident angles, the frequency-and depth-dependent spherical-wave reflection coefficient (SRC) is more accurate and always a complex value, which contains more reflection amplitude and phase information. In near field, the imaginary part of complex SRC (phase) cannot be ignored, but it is rarely considered in seismic inversion. To promote the practical application of spherical-wave seismic inversion, a novel spherical-wave inversion strategy is implemented. The complex-valued spherical-wave synthetic seismograms can be obtained by using a simple harmonic superposition model. It is assumed that geophone can only record the real part of complex-valued seismogram. The imaginary part can be further obtained by the Hilbert transform operator. We also propose the concept of complex spherical-wave elastic impedance (EI) and the complex spherical-wave EI equation. Finally, a novel complex spherical-wave EI inversion approach is proposed, which can fully use the reflection information of amplitude, phase, and frequency. With the inverted complex spherical-wave EI, the velocities and density can be further extracted. Synthetic data and field data examples show that the elastic parameters can be reasonably estimated, which illustrate the potential of our spherical-wave inversion approach in practical applications.

Optical Properties of Black Carbon Aerosols with Different Coating Models

Research on the optical properties of black carbon (BC) aerosols is highly important for investigating global climate change. A general inhomogeneous particle superposition model is developed. Inhomogeneous particles with arbitrary shapes can be constructed by this model. BC aerosols with core-shell, spherical, ellipsoid, and irregular coating models are established to explore the impact of coating shape on their optical properties. The optical properties are studied employing the discrete dipole approximation method (DDA). The influences of the morphology of BC aerosols, the coating volume fractions, and the shape of coatings on the optical properties are analyzed. The irregular coating shape causes a higher forward scattering intensity and a lower extinction cross-section. The forward scattering intensity of the core-shell model is lower than other models. The effect of the coating shape on forward scattering intensity becomes smaller as coating volume and fractal dimension increase. Consequently, assuming irregular coating as spherical coating models considered in most studies leads to inaccuracy in the optical properties of BC aerosols. It is necessary to comprehensively consider the effects of aerosol morphology and coating volume for investigating the optical properties of black carbon aerosols.

Study on urban flood early warning system considering flood loss

As an effective way to reduce flood loss, flood early warning system (FEWS) plays an important role in the disaster reduction paradigm. With the frequent occurrence of urban floods, it is of great significance to study urban FEWS. Considering the spatial difference characteristics of flood loss, this paper proposed to build a multi-information early warning system including rainfall information, inundation information and disaster information. First of all, establishing the land use type division and flood simulation superposition model, the rainfall and inundation information of all kinds of building property types can be obtained. Then the disaster information can be obtained through the calculation of submergence depth-damage rate-loss value relationship of different building property types. Finally, dividing the loss threshold through the Iterative Self-Organizing Data Analysis Technique clustering method. Through the comparative analysis of submergence depth early warning and flood loss early warning, it is found that there were differences in the direct loss of building property types under the same submergence depth, in which the residential areas were most affected by floods and the commercial areas had the greatest economic loss. At the same time, due to the high population density in residential and commercial areas, the government and relevant departments should make preparation for waterlogging emergency and rescue in those areas in advance, pay close attention to the rainfall situation and release early warning information in time. It is expected that the research results can provide scientific basis and guidance for disaster prevention and mitigation decision-making and the development of FEWS for flood affected areas in the world.

Sensitivity of Wake Modelling Setups

Engineering wake modelling with single turbine wake models and wake superposition models (SupModel) requires the choice of two crucial settings: the type of wake superposition and the wake expansion rate parameter. Based on offshore wind farm measurements, the appropriate tuning of such wake modelling setups with respect to wind farm efficiency and their sensitivity to this tuning is investigated. For this purpose, universal and inflow-individual wake expansion rate parameters are optimised for different SupModels via minimising the deviation between simulated and measured power and to compare the results to simulations using a literature value. The work reveals a logarithmic, SupModel-independent sensitivity of the farm efficiency to the wake expansion rate, sufficient to allow equally accurate modelling performance for all setups if a matching parameter is chosen. The choice of the SupModel only matters in case of an unadapted wake expansion rate parameter. Beyond that, the results indicate a systematic flaw of wake models in reproducing farm power measurements for both weak and full wake situations with the same model tuning. Inflow-individual parameters obtained by this work mitigate this with a systematic pattern over wind speed and wind direction and can significantly decrease the modelling uncertainty over varying inflow conditions.

A material point method based investigation on crack classification and transformation induced by grit geometry during scratching silicon carbide

The microcracks and residual stress are commonly regarded as non-negligible obstacles while realizing non-damage surfaces in the grinding of brittle materials. In this paper, with the combination of stress field analysis, material point method simulation and high-speed scratch experiment, a variety of cracks in the classical indentation-induced crack system were decoupled to determine the inducing conditions and coupling modes of different cracks. The tests on pressureless sintered silicon carbide (S–SiC) exhibited that the grit geometry was crucial in inducing different cracks. The Hertzian and lateral crack systems were mainly determined by the rake angle of scratching grit and can transform from one to another near the critical value of −60°. Further, a two-point stress field model was proposed to prove that large contact width is the key factor to induce radial cracks. By contrast, large contact depth is related to the appearance of bottom debris. Furthermore, Raman spectroscopy was used to investigate the velocity effect of grit on cumulative damage. Besides the stacking disorder and residual stress, even chemical disorders such as the fracture of the Si–C bond and the formation of the homonuclear bond were found to be variable at the bottom of the scratch under different contact speeds and depths. Based on the above findings, a multi-layer superposition model was proposed to re-couple the effect of different cracks and predict the workpiece's damage/force state scratched by spherical grits. It proved that blunt grit could also realize low damage machining under specific conditions.

The Influencing Mechanism of a Mid‐Latitude Westerly Trough on Stratospheric Gravity Waves Generated by Typhoon Lekima (2019)

AbstractThe mechanism by which a mid‐latitude trough influenced the gravity waves (GWs) generated by Typhoon Lekima (2019) was studied by changing the initial fields in a series of model experiments. A peak in GW intensity (GWI) develops as typhoons weaken. The vertical speed shows the patterns of GWs generated by the typhoon and trough are the same during this peak GWI period. The typhoon generates the main part of the GWs and the trough enhances their intensity. The phase speed spectra show intense GWs occur when the GWs generated by the typhoon and trough propagate at the same phase speed. The GWI generated by the trough and typhoon were calculated separately in the control experiment, and their sum shows the peak GWI was caused mainly by in‐phase superposition. Finally, the model of the GWs superposition was proposed to quantitatively verify the existence of waves liner positive superposition.

A Training-Free Multipath Enhancement (TFME-RTI) Method for Device-Free Multi-Target Localization

Many intelligent perception systems are progressively approaching people’s daily lives. Device-free localization (DFL), as a technology that can achieve positioning without the target being equipped with any equipment, has broad development prospects. RFID-based radio tomographic imaging (RTI) method has attracted much attention because of its low cost, easy deployment, and strong real-time performance. However, RTI, as a real-time imaging method that uses the line-of-sight path information and analyzes the received signal strength behavior, cannot effectively resist multipath interference. As the number of targets increases, the positioning performance using RTI method will be hit. In response to this problem, this paper proves the feasibility of applying static reflection multipath to device-free localization, and proposes a new training-free multipath enhancement (TFME-RTI) method using known spatial information. By analyzing the static multipath superposition model and target interference characteristics, a transformation model is established to take advantage of the multipath effect to enhance the positioning performance. Experiments demonstrate that the TFME-RTI method has better positioning performance and robustness in two typical indoor scenarios.

Structural and Functional Analyses of Type I IFNa Shed Light Into Its Interaction With Multiple Receptors in Fish.

Teleost type I interferons (IFNs) are categorized into group I and II subgroups that bind to distinct receptors to activate antiviral responses. However, the interaction between ifn ligands and receptors has not fully been understood. In this study, the crystal structure of grass carp [Ctenopharyngodon idella (Ci)] IFNa has been solved at 1.58Å and consists of six helices. The CiIFNa displays a typical structure of type I IFNs with a straight helix F and lacks a helix element in the AB loop. Superposition modeling identified several key residues involved in the interaction with receptors. It was found that CiIFNa bound to cytokine receptor family B (CRFB) 1, CRFB2, and CRFB5, and the three receptors could form heterodimeric receptor complexes. Furthermore, mutation of Leu27, Glu103, Lys117, and His165 markedly decreased the phosphorylation of signal transducer and activator of transcription (STAT) 1a induced by CiIFNa in the Epithelioma papulosum cyprini (EPC) cells, and Glu103 was shown to be required for the CiIFNa-activated antiviral activity. Interestingly, wild-type and mutant CiIFNa proteins did not alter the phosphorylation levels of STAT1b. Our results demonstrate that fish type I IFNs, although structurally conserved, interact with the receptors in a manner that may differ from mammalian homologs.

Symmetries in the Superposition Model of Extensive Air Shower Development

According to the superposition principle, an extensive air shower initiated by a nucleus with energy E and mass number A can be approximated as the superposition of A proton-initiated showers each with energy E/A. The superposition principle for interactions of atomic nuclei proposes to describe nucleus-initiated extensive air showers using simulations performed for proton showers. Single detectors and systems working in tight coincidence mainly register events initiated by particles with very low energies, which are affected by major statistical fluctuations, such as those used in high schools for education and outreach purposes. Verifying whether the superposition principle is still a good approximation in the low-energy region is important for the validity of the interpretation of such measurements. We present results of the comparison of results of the superposition model with detailed simulations of showers with the CORSIKA program from the energy of 10 GeV. While the energy dependence of the mean shower parameters satisfies the superposition principle, the higher moments do not. A modification of the superposition model based on the wounded nucleon model, reducing these discrepancies, is proposed. The semi-analytical description of showers in the modified superposition model can give the density spectrum of cosmic ray particles, which is consistent with the measurements. In this paper, we present results both consistent with the superposition model and indicating the need for its modification. This modification is proposed and tested.

A comparable study of the optical spectra and EPR parameters for 3d1 - and 3d9 -doped MgNH4 PO4 ·6H2 O.

VO2+ (3d1 ) and Cu2+ (3d9 ) are the two complementary states that usually show opposite distortions when they are doped in crystals. In this work, the optical absorption spectra (OAS), electron paramagnetic resonance (EPR) parameters, and local structure (LS) for VO2+ (and Cu2+ ) in MgNH4 PO4 ·6H2 O (MPPH) are uniformly investigated on the basis of the high-order perturbation formulas for a 3d1 (and 3d9 ) ion in tetragonally compressed (and elongated) octahedra, respectively. In the calculated formulas, the required crystal-field parameters can be obtained from the superposition model and reasonably linked with the LS distortion for VO2+ and Cu2+ centers. Based on the calculations, the tetragonal compressed [VO(H2 O)5 ]2+ cluster (and tetragonal elongated [Cu(H2 O)6 ]2+ cluster) is found to suffer tetragonal compression ratio of 1.65% and tetragonal elongation ratio of 3.8% along C4 -axis, respectively, due to the Jahn-Teller (JT) effect. The theoretical EPR parameters based on the above lattice distortions agree well with the experimental data, and the LS of the VO2+ and Cu2+ centers in MPPH is discussed.

A novel entrainment wind farm flow model for power prediction

ABSTRACT The wind farm flow (WFF) models, which are enabled to predict the power output of downstream, located turbines within a wind farm. A WFF model consists of two main model components: a single wake model and a superposition model. Two WFF models, the Root Sum Square (RSS) superposition model incorporated into the single wake models (e.g. Bastankah and Porté-Agel wake (BPA) model and Jensen wake model), have been extensively applied in engineering. But the WFF models above-mentioned tend to overestimate the power deficit of the whole wind farm. Hence, a novel entrainment wind farm flow (NEWFF) model is proposed in this paper, which is a combination of a modified linear entrainment wake (MLEW) model and the RSS superposition model. Different from the previous linear entrainment wake (LEW) model, the MLEW model developed in this paper considers the impacts of terrain roughness variables on the wake distribution of downstream wind turbines. The MLEW model significantly improves the accuracy of the wake simulation over the advanced BPAW model and JW model, as well as the LEW model, as shown in two cases from the TNO wind tunnel. Finally, several cases of Horns Rev offshore wind farm and Lillgrund offshore wind farm are utilized to validate the NEWFF model. Compared with the latest advanced Zong and Agel superposition wake (ZASW) model and BPA wind farm flow (BPAWFF) model, it has been demonstrated that the prediction results obtained with the NEWFF model exhibit the best agreements with measured power data under full and partial wake conditions.

A Dynamic Imaging Simulation Method of Infrared Aero-Optical Effect Based on Continuously Varying Gaussian Superposition Model.

Aero-optical effect correction has become a crucial issue in airborne infrared imaging. However, it is impractical to test the correction algorithm using flight tests and numerical simulation because of its high cost. This study proposes a dynamic imaging simulation method for the infrared aero-optical effect based on a continuously varying Gaussian superposition model. The influence of infrared image degradation under different high-speed aerodynamic flow fields was investigated in detail. A continuously varying Gaussian superposition model was established for flight speed, altitude, and attitude. A dynamic infrared scene simulation model was constructed. Experimental results show that the proposed method can realistically simulate actual aero-optical effects of any flight case. Moreover, it can simulate continuous frames of aerodynamically degraded infrared images. The method uses a simpler model than numerical simulation and provides more data for multitype tasks.

The balance effects of momentum deficit and thrust in cumulative wake models

Due to the intricacies of wind wake transition, it is necessary to estimate both the atmospheric boundary layer (ABL) contributions as well as the momentum deficit and thrust balancing. Wake superposition models such as Linear and Katic produce inconsistent wake predictions that are empirically derived. Designing an explicit cumulative model based on the momentum deficit and thrust budget analysis is not feasible. We use the analytical and machine learning approach to predict and correct inconsistencies between momentum deficits and thrust. The Mass Flow Conservation Superposition (MFCS) model is derived using the Linear Momentum equation, and the Mass Flow and Thrust Conservation Superposition (MFTCS) model is derived by fitting the Gaussian Process Regression (GPR) model to Large Eddy Simulation (LES) data. Noticeably from our results, the MFCS underestimates the thrust magnitude and the wake recovery rates. The MFTCS model based on the GPR model fit correctly estimates the momentum deficit and thrust balance. The GPR model assesses the smoothness and differentiability of the LES data to predict wake recovery. The MFTCS outperforms Katic and MFCS results but is more accurate than the LES data based on the goodness of fit criteria.

Testing the superposition model in small CORSIKA shower simulations

The idea of superposition in the high-energy interactions of cosmic ray nuclei and the development of extensive air showers initiated by them has been known for more than half a century. It has been thoroughly and successfully tested in a number of simulations for primary energies around 1015 and above. In this work, we will investigate its applicability to lower energies. At the lowest energies, when the shower contains on average about one charged particle (or even less), deviations from the superposition model can be seen in the simulation results. Fluctuations of higher moments of the main shower parameters are systematically broader than expected. Further studies to confirm superposition in particular in the shower longitudinal profile are in progress. A correct description of the longitudinal development of the small shower, a precise description of its fluctuations on the observational level with a correct implementation of the superposition principle will enable to construct a simple and fast phenomenological algorithm generating small showers indispensable for the interpretation of measurements made using a small local shower array and determination of the flux of single, incoherent, secondary cosmic ray particles.

Molecular diameters of rarefied gases

Molecular diameters are an important property of gases for numerous scientific and technical disciplines. Different measurement techniques for these diameters exist, each delivering a characteristic value. Their reliability in describing the flow of rarefied gases, however, has not yet been discussed, especially the case for the transitional range between continuum and ballistic flow. Here, we present a method to describe gas flows in straight channels with arbitrary cross sections for the whole Knudsen range by using a superposition model based on molecular diameters. This model allows us to determine a transition diameter from flow measurement data that paves the way for generalized calculations of gas behaviour under rarefied conditions linking continuum and free molecular regime.

Investigations on the optical absorption bands and the EPR parameters of rhombic cu2+ center in bis(L-asparaginato)zinc(II) crystal

In this work, we theoretically study electronic paramagnetic resonance (EPR) parameters (g-factors and A-constants) of the rhombic Cu2 + center in Bis(L-asparaginato)zinc(II) crystal by using the high-order perturbation formulae for these parameters of d9 ion in rhombic octahedral environment from the cluster approach. In these formulae, the contribution to EPR parameters from the ligand orbital and spin–orbit coupling (SO) interactions for the studied Cu2+ center are considered in view of strong covalency. The energy splittings related to the optical absorption spectra are calculated by the superposition model and the local structure of the studied center. On the basis of the studies, the local structure of the center is slightly different from that of the host site due to the Jahn–Teller effect. The calculated results (EPR parameters and optical absorption band positions) are in better agreement with the experimental values than those of previous works.

Blasting Vibration Characteristics Calculation Formula considering Cylindrical Charge Delay Time

The surrounding rock is divided into the elastic zone and the plastic zone according to the motion and deformation characteristics of the medium in rock blasting. The vibration caused by the cylindrical charge blasting is outlined on the basis of previous research concerning the blasting elastic-plastic theory. Meanwhile, a superposition model is used to calculate the vibration of cylindrical charge blasting on the premise of considering the influence of detonation velocity, the number of drug columns, and the time delay between holes. The analysis results show that the blasting causes the uneven spatial distribution of vibration, containing both strong and weak directions. The velocity of the vibration along weak directions decreases slowly with the increase of distance. But generally, the velocity along weak directions is faster. The vibration distribution of a cylindrical charge is closely related to the detonator location. Furthermore, more vibration distributes towards the forward direction of the detonation wave.

Evaluation Method and Application of Ecological Sensitivity of Intercity Railway Network Planning

In the planning stage of the intercity railway network, the ecological sensitivity evaluation of the planning scheme is not only the key content to explore the ecological environmental rationality of the planning scheme but also a scientific means to promote the sustainable development of intercity railway networks. The purpose of this study is to establish an evaluation method that can quantitatively evaluate the ecological sensitivity of intercity railway network planning to put forwards targeted optimization and adjustment suggestions for the planning scheme. Taking the intercity railway network planning of Guizhou Province as an example, its ecological sensitivity is predicted and evaluated. Six types of ecologically sensitive areas were selected as ecological sensitivity evaluation factors, including protected areas, drinking water sources, geological disaster-prone areas, soil erosion areas, cultivated land resource distribution areas and coal resource distribution areas. Based on the GIS overlay method, the quantitative measurement methods of each evaluation factor are established in turn, and the single factor sensitivity evaluation index is obtained. In addition, the weighted superposition model is used to quantitatively calculate the ecological sensitivity of the planned lines of the intercity railway network in Guizhou Province. Finally, the short board factor of each planned line is obtained, and targeted optimization and adjustment suggestions are put forwards. The research content of this paper can provide a theoretical reference for the practical evaluation of the ecological sensitivity of intercity railway network planning.

Event-by-event correlations and fluctuations with strongly intensive quantities in heavy-ion collisions with ALICE

The strongly intensive quantity Σ is a new observable, introduced recently to the domain of heavy-ion physics. In superposition models which assume independent particle production from statistically identical sources, Σ is insensitive to the number of sources and its fluctuations, contrary to the standard forward-backward correlation coefficient (bcorr). Therefore it provides direct information on the multiplicity correlations and fluctuations from a single source. This paper presents new results on forward-backward correlations studied with the quantity Σ, measured by ALICE at the LHC in Xe–Xe collisions at √sNN = 5.44 TeV and in Pb–Pb collisions at √sNN = 2.76 and 5.02 TeV. These results are compared with ALICE measurements in pp collisions at √s = 13 TeV.