Superposition Model Research Articles

A comparative study on the local structures of the V4+ and Cu2+ centers in WO3

Abstract The local structures and electron paramagnetic resonance (EPR) parameters (the g factors g i and the hyperfine structure constants A i , with i = x, y, z) of the V4+ and Cu2+ centers in WO3 were theoretically investigated based on the perturbation formulas of the EPR parameters for 3d1 and 3d9 ions under rhombically compressed and elongated octahedra, respectively. In these formulas, the adopted crystal-field parameters (CFPs) are obtained from the superposition model which enables connection of the CFPs and hence the EPR parameters to the rhombic distortion. Based on the calculations, the impurity-ligand distances of the studied [VO6]8− (or [CuO6]10−) cluster are found to suffer the axial compression (or elongation) δz of about 0.098 Å (or 0.132 Å) along the z-axis, and the additional planar bond length variation δr (≈0.052 or 0.047 Å) along x- and y-axis, respectively, due to the Jahn–Teller (JT) effect.

Study of cooperative wake control for multiple wind turbines under variable wind speeds/directions

In the wind farm control field, wind turbines are normally manipulated to maximize the individual power production which is named the greedy control. However, this greedy control method can lead to massive losses of total wind farm power production, mainly caused by the wake interference between multiple wind turbines. To this end, the cooperative wake control, which seeks the maximum total power production by coordinating each individual wind turbine at the global optimum operation point, can greatly improve the wind farm output performance. In this paper, we investigate the effectiveness of two different cooperative wake control strategies, i.e., instantaneous control and wind-interval based (WIB) control under variable wind speeds/directions scenario. These two cooperative control strategies are achieved based on the power de-rating operation to the upstream wind turbines. Taking three in-line wind turbines as an example, the control parameters of the two upstream wind turbines are cooperatively optimized while the downstream third wind turbine operates at the maximum power coefficient. To account for the multiple wind turbines wake interference, an artificial neural network (ANN) wake model characterized by the fast computational efficiency and great accuracy, in combination with the best wake superposition model chosen to quantify multiple wake effect, is proposed for the control optimization. By comparing to the baseline greedy control, it shows that both cooperative control strategies are effective in improving the power production of the wind farm. More specifically, the WIB control can maintain the power production at the same level of instantaneous control with a maximum difference less than 3%, while it reduces the operating difficulty to a large extent which greatly facilitates its application under realistic more complex wind scenarios.

Corrosion of Titanium Electrode Used for Solar Saline Electroflotation.

The solar electroflotation (EF) processes using saline electrolytes are today one of the great challenges for the development of electrochemical devices, due to the corrosion problems that are generated during the operation by being in permanent contact with Cl- ions. This manuscript discloses the corrosion behavior of titanium electrodes using a superposition model based on mixed potential theory and the evaluation of the superficial performance of the Ti electrodes operated to 4 V/SHE solar electroflotation in contact with a solution of 0.5 M NaCl. Additionally provided is an electrochemical analysis of Ti electrodes regarding HER, ORR, OER, and CER that occur during the solar saline EF process. The non-linear superposition model by mixed potential theory gives electrochemical and corrosion parameters that complement the information published in scientific journals, the corrosion current density and corrosion potential in these conditions is 0.069 A/m2 and -7.27 mV, respectively. The formation of TiO2 and TiOCl on the anode electrode was visualized, resulting in a reduction of its weight loss of the anode electrode.

Predictive modeling for the boiling heat transfer coefficient of R1234yf inside a multiport minichannel tube

Existing prediction models of flow boiling heat transfer coefficient, such as the well-known superposition, asymptotic, and flow pattern models, provide an applicable method to attain the closest to the true value of the heat transfer coefficient in specific ranges. In this study, heat transfer coefficient data are collected through an experimental study of R1234yf inside a multiport minichannel tube within a mass flux of 50–500 kg/m2s, heat flux of 3–12 kW/m2, saturation temperature of 6 °C, and vapor quality up to 1. The assessment of the heat transfer coefficient is conducted by comparing the heat transfer coefficient of each model with that of R1234yf. In addition, a machine-learning prediction model is proposed to improve the prediction accuracy of the heat transfer coefficient. A machine-learning method could provide an accurate prediction result for the heat transfer coefficient by feeding the program with a factor from heat transfer coefficient data (e.g., a dimensionless number). Therefore, an alternative prediction method could be applied to predict the heat transfer coefficient with the lowest error by providing the setting parameter that fits the pattern of heat transfer coefficient data. In addition, a heat transfer coefficient correlation is proposed to define the only-value result of the machine-learning model.

Optimized wake-superposition approach for multiturbine wind farms

Optimizing the wind farm layout requires accurately quantifying the wind-turbine wake distribution to minimize interference between wakes. Thus, the accuracy of wind turbine wake superposition models is critical. The sum of squares (SS) model is currently touted as the most accurate, but its application in engineering is hampered by its overestimation of the velocity deficit of the mixed wake. Therefore, previous work relied on approximate power calculations for performing optimization. The physical meaning of the SS model is unclear, which makes optimization difficult. In this study, a univariate linear correction idea is proposed based on the linear increase phenomenon of the SS method error. The unknown coefficients are obtained by fitting experimental data. The results demonstrate that the proposed method can accurately quantify the full-wake two-dimensional distribution of the mixed wake.

Lactoferrin as a carrier of iron: Development and physicochemical characterization

Iron deficiency is the main cause of anemia, one of the most common nutritional deficiencies affecting millions of people worldwide. In addition, iron instability, sensitivity, and intense flavor limit its use in food fortification. In this work, lactoferrin (LF) particles were developed by Nano Spray Dryer (NSD) and its capacity to be used as an iron carrier was evaluated. The effect of NSD temperature (60 °C, 80 °C, and 100 °C) and LF concentrations (10 mg mL−1, 50 mg mL−1, and 100 mg mL−1) was evaluated on the LF structure and on the production and stability of a LF-iron carrier. Results showed that the NSD is suitable for producing LF particles with diameters ranged from 38.8 nm to 4533.6 nm. Although different surface morphologies were obtained, higher protein concentrations (100 mg mL−1) produced round shape and smooth surface particles, but for lower protein concentrations (10 mg mL−1 and 50 mg mL−1) wrinkled particles and doughnut shape particles were obtained. SDS-page electrophoresis and circular dichroism (CD) for secondary structure (185–260 nm) show that the characteristics of the structures were maintained, meaning that NSD does not cause protein degradation. CD for tertiary structure (250 nm–350 nm) and fluorescence tests confirmed the interaction between LF and iron, observed by an intensity decrease and a wavelength shift in fluorescence spectra. The CD tertiary structure analysis showed higher ellipticity for the Trp peak, meaning conformational changes in the neighbor amino acids due to protein-iron interaction. Iron release experiments were performed at different pH values (2.0 and 7.4) at 37 °C aiming to understand the release mechanism in different media. Results showed that at pH 2 the iron release could be described by the linear superposition model (Radj2 = 0.9879) (explained by Fick and relaxation phenomenon) and that at pH 7.4 there is no iron release, showing that particles are stable at neutral pH. NSD is a suitable technology for producing iron-loaded protein-based carriers that could be used in food applications.

A Full-Spectrum Correlated K-distribution Based Interpolation Weighted-Sum-of-Gray-Gases model for CO2-H2O-soot mixture

The Weighted-Sum-of-Gray-Gases (WSGG) method is extensively employed in laboratorial and industrial radiative calculations due to its simplicity and negligible memory requirement. For a CO2-H2O-soot mixture, the superposition model is usually applied to obtain the radiative property of participating medium, which leads to a substantial increase in computing resources. To improve the computational efficiency of existing WSGG methods without significantly reducing accuracy, a Full-Spectrum Correlated K-distribution based interpolation WSGG (iWSGG) method is proposed here. In this method, a CO2-H2O-soot mixture is represented by 8 gray gases, whose absorption coefficients are obtained by linear interpolation, rather than the superposition method. The accuracy and efficiency of iWSGG are evaluated in 3 1D and 3 2D sooting flames. The results show that iWSGG demonstrates good accuracy as compared to the benchmark line-by-line solution in fuel-oxidizer and dry oxy-fuel sooting flames. The computational time of iWSGG is about 1/12 of that of WSGG with 5, 5, and 4 gray gases representing CO2, H2O and soot, and 2/5 of that of WSGG with 5 and 4 gray gases representing CO2-H2O mixture and soot.

Uncertainty quantification analysis for simulation of wakes in wind-farms using a stochastic RANS solver, compared with a deep learning approach

Quantification of uncertainties in Reynolds–Averaged Navier–Stokes (RANS) simulations has gained a considerable interest in turbulence modeling. We present two different approaches for the quantification and propagation of model-form and operational uncertainties in context of wind turbine RANS simulations. The first approach is based on a stochastic RANS solver in OpenFOAM using intrusive polynomial chaos method (Parekh and Verstappen, 2023). Here the uncertainties are propagated through a single (large) simulation for the coupled coefficients of the polynomial expansion. The second approach is a surrogate based uncertainty quantification (SBUQ) method. The surrogate model comprises of a 3D U-Net neural network (trained over a single wind turbine) combined with a wake superposition model in order to the prediction of flow field in an array of wind turbines. The above-mentioned approaches are applied for uncertainty quantification analysis in RANS simulations of two turbulent engineering flow problems — (i) a wake past a single wind turbine, and (ii) wake interactions and power losses in an array of wind turbines. The results show that the uncertain RANS solutions from the two approaches are able to reasonably capture the reference high-fidelity solution. We also discuss comparisons between the two approaches including computational cost, applicability, generality etc. The two methods can be further explored and applied to engineering applications where it is critical to compute the turbulent RANS solution in presence of various sources of uncertainties.

Linear and nonlinear thermoviscoelastic behavior of polyamide 6

AbstractThermoplastic polyamides are used in many industrial areas due to their potential in lightweight applications. Polyamides serve as matrix material in fiber reinforced thermoplastics, for instance. The mechanical behavior of polyamides is characterized by pronounced viscoelastic effects that are strongly affected by environmental conditions like temperature or humidity. In this work, linear thermoviscoelastic behavior of polyamide 6 is considered. Viscoelastic behavior is modeled by the generalized Maxwell model while extended time‐temperature superposition is used to model temperature dependency. A temperature‐frequency sweep conducted by dynamic mechanical analysis serves as input for the model. By horizontal and vertical shifting, master curves of the loss factor, storage modulus, and loss modulus are obtained. Based on this, limitations of time‐temperature superposition and linear thermoviscoelastic modeling are discussed. Furthermore, it is shown that the horizontal shifts can be well approximated by the Williams‐Landel‐Ferry equation for temperatures above and below the glass transition temperature.

비대면 시대의 참여 중심 예술 활동에 관한 연구 - 예문답(藝問答)과 증강현실을 활용한 프로젝트 [Tea Room:2020]을 중심으로

The artistic activities of art museums in the 21st century are turning toward emphasizing the active participation of museumgoers beyond the dual structure of ‘creation-enjoyment’. Reflecting this trend, in 2020, the SEMA Nam-Seoul Museum of Art planned an exhibition, entitled “Never Ever Artistic, Sloppy Museum,” to bolster the active participation of art fans in the non-face-to-face era. The author was invited as an exhibition artist and presented an art prototype project, “Tea Room:2020,” at the exhibition. The purpose of this study is to envision a ‘superposition model of art creation-enjoyment’ in the non-face-to-face period, the experiment “Tea Room:2020” based on the model, and to discuss its meaning. In this way, the study seeks new relationships, the communication and union of creation and appreciation, and examines the significance of these concepts. To this end, the author proposed ‘Yemundap’, a circular, iterative, and discontinuous communication method into which a tea ceremony and Zen riddles were transformed. ‘Yemundap’ also combines drawing and augmented reality to superpose art creation and enjoyment. To realize this, heuristics were applied when implementing “Tea Room:2020.” In this work, the creator and art fans share artistic dialogues while communicating by drawing messages that are contained in paper cups and combined with augmented reality. Here, the roles of the creator and the art fan are overlapped and reversed, and they create a collaborative creation. This project has emotional significance in that the art fans immerse themselves in the creation and exploration of works by a waiting period created by the discontinuous communication of ‘Yemundap’, experiencing the sense of normalcy that existed before the COVID19 pandemic. Nonetheless, in order to generalize the superposition model of ‘Yemundap’, it is necessary to improve its complex process and to reduce its excessive performative methods.

Theoretical analysis of crystal field parameters and zero field splitting parameters for Mn2+ ions in tetramethylammonium tetrachlorozincate (TMATC-Zn)

Superposition model (SPM) analysis is employed for modeling the crystal field parameters (CFPs) as well as the zero field splitting (ZFS) parameters (ZFSPs) for Mn2+ ions doped into tetramethylammonium tetrachlorozincate, [N(CH3)4]2ZnCl4 crystal (denoted TMATC-Zn). SPM analysis utilizes structural data to predict CFPs and ZFSPs determined for the dopant ions by optical and EMR spectroscopy, respectively. We report model calculations aimed at investigating the two structural options for dopant Mn2+ ions in TMATC-Zn: substitutional and interstitial sites. SPM is employed to predict CFPs, which serve as input for the perturbation theory expressions to calculate the 2nd-rank orthorhombic ZFSPs and to re-analyze optical spectra. Independently SPM is employed to predict the 2nd- and 4th-rank ZFSPs. Correlation of optical and EMR spectroscopy data increases modeling reliability. Comparison of the predicted 2nd-rank ZFSPs with the available experimental ones and consideration of the magnitudes of distortions required to achieve good matching enables discriminating between the substitutional and interstitial sites as location of doped Mn2+ ions. Our study indicates that interstitial sites are more plausible than substitutional sites for Mn2+ ions in TMATC-Zn, in agreement with the experimental prediction. The results reveal the importance of combining two separate methods to determine more reliably the most likely site for substitution of paramagnetic ions. This study also tests the range of applicability of CF theory and SPM analysis for Mn2+ ions in TMATC-Zn crystals and prepares grounds for consideration of the properties of molecular nanomagnets containing Mn2+ ions.

A novel damage index integrating piezoelectric impedance and ultrasonic guided wave for damage monitoring of bolted joints

The structural safety of bolted joints, one of the typical connection techniques utilized in engineering applications, is threatened by the harsh service environment. Herein, a novel damage index (DI) integrating piezoelectric impedance and ultrasonic guided wave is proposed for satisfying the damage monitoring needs of bolted joints. By integrating the two sensing techniques, the shortcomings of a single sensing technique in terms of signal interpretation, stability, and structural adaptability are eliminated. The novel damage severity factor DIZ-V is formed by fusing the damage indices DIZ and DIV weighted by multi-class DIs of the two sensing techniques. Thanks to DIZ-V and a damage mode identification factor presented in this paper, the damage modes and damage severity of early-stage bolt loosening and crack damage are identified. Furthermore, a novel dynamic superposition model (DSM) based on a dynamic-update baseline is developed to address the deficiency that the static baseline method (SBM) has. SBM utilizes the undamaged state signal as the baseline and has the problem of being prone to failure in the later-stage of monitoring. Thus, the phenomenon of nonlinear variation of DIZ-V caused by damage deterioration was avoided via DSM optimization. The feasibility and effectiveness of the proposed method were verified by conducting a series of practical damage identification tests on aluminum bolted joints. And the results demonstrated that the proposed technique could not only identify the severity and mode of damage, but also has excellent reliability. Therefore, the novel damage monitoring technique for bolted joints is a good complement to the existing techniques, which can provide a new strategy for damage monitoring.

Quantifying daily NOx and CO2 emissions from Wuhan using satellite observations from TROPOMI and OCO-2

Abstract. Quantification and control of NOx and CO2 emissions are essential across the world to limit adverse climate change and improve air quality. We present a new top-down method, an improved superposition column model to estimate day-to-day NOx and CO2 emissions from the large city of Wuhan, China, located in a polluted background. The latest released version 2.3.1 TROPOMI (TROPOspheric Monitoring Instrument) NO2 columns and version 10r of the Orbiting Carbon Observatory-2 (OCO-2)-observed CO2 mixing ratio are employed. We quantified daily NOx and CO2 emissions from Wuhan between September 2019 and October 2020 with an uncertainty of 31 % and 43 %, compared to 39 % and 49 % with the earlier v1.3 TROPOMI data, respectively. Our estimated NOx and CO2 emissions are verified against bottom-up inventories with minor deviations (<3 % for the 2019 mean, ranging from −20 % to 48 % on a daily basis). Based on the estimated CO2 emissions, we also predicted daily CO2 column mixing ratio enhancements, which match well with OCO-2 observations (<5 % bias, within ±0.3 ppm). We capture the day-to-day variation of NOx and CO2 emissions from Wuhan in 2019–2020, which does not reveal a substantial “weekend reduction” but does show a clear “holiday reduction” in the NOx and CO2 emissions. Our method also quantifies the abrupt decrease and slow NOx and CO2 emissions rebound due to the Wuhan lockdown in early 2020. This work demonstrates the improved superposition model to be a promising new tool for the quantification of city NOx and CO2 emissions, allowing policymakers to gain real-time information on spatial–temporal emission patterns and the effectiveness of carbon and nitrogen regulation in urban environments.

Crystal structure and optical absorption spectra of LiCo(SO4)OH and its remarkable relationship to the Zn-Mn-silicate hodgkinsonite

Crystals of the compound LiCo(SO4)OH were synthesised at low-hydrothermal conditions, and the crystal structure was determined and refined from single crystal X-ray diffraction data. LiCo(SO4)OH crystallises monoclinic, space group P21/c, Z = 4, a = 9.586(2), b = 5.425(1), c = 7.317(1) Å, β = 109.65(1)°, V = 358.3 Å3, wR2 = 0.0485 (2215 unique reflections, 78 variables). The structure is built from chains of edge-sharing, quite strongly bond-length and -angle distorted Co(OH)3O3 octahedra (< Co–O > = 2.126 Å), which are further linked by common corners, hydrogen bonds, and by properly shaped SO4 tetrahedra (< S–O > = 1.476 Å) to sheets parallel (100). These sheets are connected to a three-dimensional framework by sharing corners with distorted LiO4 polyhedra (< Li–O > = 1.956 Å). Apart from the isotypic sulfates of Mn2+ and Fe2+, only the molybdate LiCd(MoO4)OH crystallises isostructural with LiCo(SO4)OH. However, a very close structural relationship exists with the rare mineral hodgkinsonite, Zn2Mn(SiO4)(OH)2, yielding crystal chemically very uncommon topological equivalents of Zn2+ ≡ S6+ and Si4+ ≡ Li+, aside from the expectable substitution Mn2+ ≡ Co2+. Polarised optical absorption spectra of LiCo(SO4)OH reveal that the dominating spin-allowed 4T1(P) band system of Co2+ (d7 configuration) is strongly split up and covers a prominent part (~ 15,500–24,500 cm−1) of the visible spectral range, in accordance with the significant distortion of the Co(OH)3O3 polyhedron. The spectra are interpreted in terms of the Superposition Model of crystal fields, yielding a new set of intrinsic and interelectronic repulsion parameters for Co2+.

Thermal-fluctuation effects on small-scale statistics in turbulent gas flow

Kolmogorov's theory of turbulence assumes that the small-scale turbulent structures in the energy cascade are universal and are determined by the energy dissipation rate and the kinematic viscosity alone. However, thermal fluctuations, absent from the continuum description, terminate the energy cascade near the Kolmogorov length scale. Here, we propose a simple superposition model to account for the effects of thermal fluctuations on small-scale turbulence statistics. For compressible Taylor–Green vortex flow, we demonstrate that the superposition model in conjunction with data from direct numerical simulation of the Navier–Stokes equations yields spectra and structure functions that agree with the corresponding quantities computed from the direct simulation Monte Carlo method of molecular gas dynamics, verifying the importance of thermal fluctuations in the dissipation range.

Eu3+ ions as a crystal-field probe for low-symmetry sites in doped phosphors - a case study: Eu3+ at triclinic sites in Li6RE(BO3)3 (RE = Y, Gd), YBO3 and ZnO and at trigonal sites in YAl3(BO3)4.

We present crystal-field (CF) calculations of energy levels (Ei) of Eu3+ ions doped in various hosts aimed at exploring the low-symmetry properties of CF parameters (CFPs) and reliability of CFP modelling with decreasing site symmetry. The hosts studied are: Li6Y(BO3)3, Li6Gd(BO3)3, YBO3, and ZnO with Eu3+ at triclinic sites; YAl3(BO3)4 with Eu3+ ions at trigonal D3 symmetry. Two independent CFP modelling approaches utilizing the hosts' structural data are employed: the exchange charge model (ECM) and the superposition model (SPM). We adopt the Eu3+ actual site symmetry and not the approximated one. The Ei values calculated using CFPs modelled by the ECM and SPM mutually agree with the observed ones. For triclinic symmetry, the ECM/CFPs and SPM/CFPs were numerically distinct, yet turned out to be physically equivalent yielding identical rotational invariants, Sk (k = 2, 4, 6) and Ei. For trigonal symmetry, both CFP sets agree numerically, thus Sk and Ei are identical. This disparity poses a dilemma, since the modified crystallographic axis system was used in both approaches. The standardization of the triclinic CFPs using the 3DD package was performed to solve this dilemma. It has enabled discussing standardization aspects in experimental and computed CFP sets and elucidating intricate low-symmetry aspects inherent in CFP sets. Understanding of low-symmetry aspects in CF studies may bring about a better interpretation of the spectroscopic and magnetic properties of rare-earth ion doped host crystals. Thus, our study could provide more deep insights into the importance of clear definitions of axis systems and adequate treatment of actual site symmetry in the modelling of CFPs for low-symmetry cases which is essential for technological applications and engineering of rare-earth activated phosphor materials.

A Study of Modified Characteristics of Hadronic Interactions

We have implemented ad-hoc modifications to the CORSIKA Monte-Carlo generator which allow us to simultaneously adjust the multiplicity, elasticity and cross-section of hadronic interactions with respect to the predictions of the Sibyll 2.3d interaction model, in order to assess whether a reasonable combination of changes (that is not excluded by current experimental data) could alleviate the observed tension between the model predictions and observed features of extensive air showers induced by ultra-high energy cosmic rays (UHECR). Previously, we have studied the effects of such changes on proton-initiated showers. Because a multitude of experimental data suggest that the primary composition of the UHECR is mixed, we have expanded the modification procedure to include nuclear projectiles in a consistent way based on the superposition model, in a similar manner as was used in the previous studies carried out using one-dimensional simulation methods. As we are using a fully three-dimensional approach, we can quantify the effects of the changes on both longitudinal and lateral features of the showers. With the inclusion of nuclear projectiles, we can study the impact of the changes on observable quantities for realistic primary beams as well as on the determination of the primary composition from data under the assumption of the modified hadronic interactions.

Effects of distortions in ion-host systems on optical spectra, crystal-field and spin-Hamiltonian parameters of Cr3+ ions doped pyrochlores Y2Ti2O7 and Y2Sn2O7: exchange charge model and superposition model calculations.

Comparative modelling of the crystal-field parameters (CFPs), CF energy levels, and effective spin-Hamiltonian parameters (SHPs), i.e., the g-factors and zero-field splitting parameter (ZFSP), D, of the ground state 4A2g of the Cr3+ dopant ions in Y2Ti2O7 and Y2Sn2O7 is carried out. The CFPs are calculated using XRD structural data by employing two semi-empirical models: the exchange charge model (ECM) and superposition model (SPM). This two-fold approach ensures increased reliability of CFP modelling and thus of the final results. The modelled CFPs serve as the input to the crystal-field analysis/microscopic spin-Hamiltonian (CFA/MSH) program to predict CF energy levels and wave functions, and to extract SHPs. Since the site symmetry of Cr3+ ions in these crystals is trigonal D3d, a symmetry adapted axis system (SAAS) conforming to Watanabe convention is adopted for CFP modelling. The calculated CF energies and SHPs for Y2Ti2O7:Cr3+ are in good agreement with the experimental results. Variations of the Racah parameter B, as well as ECM and SPM parameters for Y2Sn2-xCrxO7 are correlated with the chromium concentration (x), which affects distortions of CrO6 structures. We find that the SHPs originate predominantly from the spin-orbit coupling, though contributions from spin-spin and spin-other-orbit couplings are also appreciable and thus important for analysis of lattice distortions and structural disorder. The uniqueness of the SAAS used for CFP modelling is also discussed. The present study enables exploring the influence of the radial and angular distortions of host clusters (Ti-O6/Sn-O6) introduced by Cr3+ ions on the structural and optical properties as well as the SHPs of Cr3+ ions doped in Y2Ti2O7 and Y2Sn2O7.

Radiative heat transfer calculations using full spectrum k-distribution method for benchmark test cases

In the present work, the full spectrum k-distribution method (FSK) has been adopted to calculate the radiative transfer in the presence of participating gaseous medium within an enclosure. The radiative properties of the medium is obtained from the HITEMP-2010 database. Further, the radiative properties have been assembled into a monotonically increasing function using the FSK. Moreover, a look-up table has been developed for these properties at different thermodynamic states and a multi-dimensional linear interpolation technique for unavailable thermodynamic states of gases. Furthermore, the FSK method is extended for mixture of gases using different mixing models such as superposition, multiplication and hybrid models. The radiation transfer equation (RTE) is solved by finite angle method to calculate the wall heat fluxes and the divergence of radiative heat flux for various test cases in the categories of homogeneous and non-homogeneous medium having different conditions of temperature and mole-fraction. The multiplication mixing model produces most accurate results among the mixture models used here. The results obtained from FSK has been validated against benchmark solution of line by line method (LBL). The FSK method has been also successfully applied to non-homogeneous gaseous medium for single gas or mixture of gases with almost LBL accuracy at extremely less computational cost.

Creep modeling of composite materials based on improved gene expression programming

In this article, a new method for creep modeling and performance prediction of composite materials is presented. Since Findley power-law model is usually suitable for studying one-dimensional time-dependent creep of materials under low stress, an intelligent computing method is utilized to derive three temperature-related sub-functions, the creep model as a function of time and temperature is established. In order to accelerate convergence rate and improve solution accuracy, an improved gene expression programming (IGEP) algorithm is proposed by adopting the probability-based population initialization and semi-elite roulette selection strategy. Based on short-term creep data at seven temperatures, a bivariate creep model with certain physical significance is developed. At fixed temperature, the univariate creep model is acquired. R2, RMSE, MAE, RRSE statistical metrics are used to verify the validity of the developed model by comparison with viscoelastic models. Shift factor is solved by Arrhenius equation. The creep master curve is derived from time–temperature superposition model, and evaluated by Burgers, Findley and HKK models. R-square of IGEP model is above 0.98 that is better than classical models. Moreover, the model is utilized to predict creep values at t = 1000 h. Compared with experimental values, the relative errors are within 5.2%. The results show that the improved algorithm can establish effective models that accurately predict the long-term creep performance of composites.