Error Band Research Articles

An improved life prediction strategy at elevated temperature based on pure creep and fatigue data: Classical strain controlled and hybrid stress–strain controlled creep-fatigue test

Creep-fatigue (CF) interaction is an important issue for designing the next generation power plants. Thus, strain-controlled CF tests (SCCFTs) and hybrid stress–strain controlled CF tests (HCCFTs) of 9Cr3Co3W1CuVNbB steel were conducted. The cyclic responses and creep behaviors in SCCFTs and HCCFTs were investigated. In addition, an improved CF life prediction method was proposed, and only pure creep and fatigue data were needed. Then, the relaxed stress in SCCFTs and the accumulated creep strain in HCCFTs were predicted. Moreover, the oxidation damage was incorporated into the non-linear interactions. The optimally predictive results of the studied material, Grade 91 steel, and 304 stainless steel were in ±3 error band with strain energy density exhaustion model.

Experimental investigation and dynamic modelling of an upright freezer under periodic door opening conditions

This paper performs a comprehensive experimental and modelling study to examine the dynamic behaviour of an upright freezer with adjustable shelving under periodic door opening conditions with different temperature, pressure and relative humidity values. An uncertainty analysis is carried out for the experimentally measured data. Additionally, the dynamic model is developed with crucial sub-components, such as discretized upright cabinet, frosted evaporator and semi-empirical door opening mechanism using an object-orientated programming language called Modelica. The present model is the validated with experimental data employing the values of the airflow from ambient into the cabinet along with the average cabinet air flowrate and back wall temperatures, transient evaporation and condensation pressures, cabinet average relative humidity change, compressor operation time and power consumption, and finally total energy consumption of refrigerator for both 85%RH and 65% RH conditions at 32 °C ambient. The results show that the model predictions have a similar trendline with the experimental findings within ±3 K error bands regarding average cabinet air and back wall temperature. In contrast, the dynamic cyclic trend before and after door opening is closer to the experiments within ±1 K. The current model predictions for the low and high pressures are found to be within ±3% and ±5% error bands, respectively, whereas the average relative humidity level of the cabinet is captured within ±10% deviation. Furthermore, transient compressor power is well predicted with deviations, but not exceeding 4.5%, and the total energy consumption level is compatible with 6% error bands during the entire experimental period.

Prediction of heat transfer coefficients for steam condensation in the presence of air based on ANN method

Artificial neural network (ANN) methods have been gradually used in the field of nuclear reactor thermal-hydraulics as new methods to improve accuracy or fast prediction. This study establishes a back propagation (BP) neural network model based on the ANN methods to predict the steam condensation heat transfer coefficient outside a heat tube in the presence of air. The main factors affecting condensing heat transfer, such as pressure, air mass fraction, subcooling, and tube diameter, are used as input quantities, and the condensation heat transfer coefficient is used as output quantity. A complete set of neural networks for predicting the heat transfer coefficient for steam condensation in the presence of air is established based on the relevant experimental data collected over the world. The results predicted by the ANN model are compared with the experimental data and those of traditional correlation methods. The data from 2276 experiments are distributed within a ±10% error band at the 95% confidence level. This means that the prediction accuracy of the ANN model is higher than that of the traditional experimental correlation. Therefore, the neural network model developed in this study can be used for the prediction of the heat transfer coefficient for steam condensation in the presence of air.

Testing of Variable-Speed Scroll Compressors and their inverters for the evaluation of compact energy consumption models

Prediction models for energy consumption in heat pumps are critical for design, selection, control and fault detection. However, nowadays, the methodology for characterizing variable-speed compressors has not been standardized, and typically the pair compressor-inverter is studied as a whole. In this study, disaggregated energy consumption results of compressor and inverter are provided by using a double-wattmeter scheme. These results are used to compare the performance of existing models and to establish guidelines to define testsmatrixes as compact as possible to characterize this type of compressors. The widely used 20-coefficient correlation can overfit the compressor behaviour when fitted with an small dataset, introducing significant deviations when extrapolating. Optimal Design methodologies to create rating test matrixes gave excellent results compared with classical clustering techniques. Regarding inverter results, a compact empirical model was proposed to model inverter power losses depending on total consumption and compressor speed. The proposed model used only five fitting coefficients, and most predictions are inside a 5% error band for all tested inverters. Finally, the tested compressors and inverters suffered a significant efficiency loss at very low speeds, which could make cycling more profitable under certain circumstances.

Experimental study of swirling flow pneumatic liquid-carrying characteristics in the vortex tool inserted tube under liquid loading conditions

Liquid unloading by vortex tool is one of the most important applications of swirling flow pneumatic conveying. However, due to swirl decay, the evolution of gas–liquid flow patterns and the dynamic characteristics of pressure drop downstream of the vortex tool are much more complex than those in non-swirling flow. In this study, the gas–liquid flow patterns and pressure drop inside the vortex tool inserted tube (ID = 60 mm) under liquid loading conditions were experimentally studied and compared with those of the plain tube. With the superficial gas velocities ranging from 0.5 to 6.0 m/s and superficial liquid velocities of 0.01, 0.02, and 0.04 m/s, the effects of the structural parameters and stages of vortex tools on the pressure drop were discussed. The experimental results reveal that three distinct swirling flow patterns can be identified downstream of the vortex tool, namely swirling gas column flow, swirling churn flow and swirling annular flow. The insertion of vortex tool facilitates an earlier transition of the churn flow to the annular flow, and the induced swirling flow can restrain the liquid from falling back. The helix angle of the corkscrew deflector has a more significant effect on the pressure drop than its length. By reducing the helix angle from 54° to 45°, the total pressure drop and downstream pressure gradient are significantly decreased, even lower than those of the plain tube. But the series combination of 54° and 45° vortex tools results in a significant increase in the downstream pressure gradient. Additionally, at low gas flow rate, negative frictional pressure drop occurs in both plain tube and vortex tool inserted tube. Hence, the new friction factor correlations were established respectively for the positive and negative friction regions in the cases of the tube with and without vortex tool, and most of the frictional pressure gradient predictions are within an error band less than 20%.

Impact of lattice strangeness asymmetry data in the CTEQ-TEA global analysis

We study the impact of lattice data on the determination of the strangeness asymmetry distribution ${s}_{\ensuremath{-}}(x)\ensuremath{\equiv}s(x)\ensuremath{-}\overline{s}(x)$ in the general CTEQ-TEA global analysis of parton distribution functions (PDFs) of the proton. Firstly, we find that allowing a nonvanishing ${s}_{\ensuremath{-}}(x)$, at the initial ${Q}_{0}=1.3\text{ }\text{ }\mathrm{GeV}$ scale, in a global PDF analysis leads to a CT18As fit with similar quality to CT18A. Secondly, including the lattice data in the CT18As_Lat fit greatly reduces the ${s}_{\ensuremath{-}}$-PDF error band size in the large-$x$ region. To further reduce its error would require more precise lattice data, extended to smaller $x$ values. We take ATLAS 7 TeV $W$ and $Z$ production data, SIDIS dimuon production data, ${F}_{3}$ structure function data, E866 NuSea data, and E906 SeaQuest data as examples to illustrate the implication of CT18As and CT18As_Lat fits. The parametrization dependence for PDF ratio $(s+\overline{s})/(\overline{u}+\overline{d})(x)$ is analyzed with CT18As2 and CT18As2_Lat fits as results.

Saturated/subcooled flow boiling heat transfer inside micro/mini-channels: A new prediction correlation and experiment evaluation

In this study, a new general heat transfer correlation was developed for predicting the saturated/subcooled flow boiling heat transfer coefficient in micro/mini-channels. The collected database included 4250 data points, which covered eleven different working fluids. These included deionized water, new electronic fluorinated solutions, and refrigerants, among others. The temperature range of the experimental operation was from 0 to 100 °C with a saturated pressure of 101 to 775 kPa. The hydraulic diameter of micro/mini-channels varied from 0.1 to 3 mm, and the liquid sub-cooling was between 0 and 80 K. The database included various operation conditions, such as mass flux, heat flux, vapor quality, and reduced pressure. The liquid and vapor Reynolds numbers were calculated based on the hydraulic diameter. Six existing flow boiling heat transfer correlations were employed to evaluate the present data points in micro/mini-channels. However, it was observed that these correlations were unable to predict the present data points accurately due to high liquid sub-cooling and heat flux. Therefore, a new prediction correlation based on the present database was developed by dividing flow boiling into three stages, including subcooled boiling, developed nucleate boiling and nucleate boiling deterioration. This new prediction model can predict more than 80% of data points within ±30% error band.

A mesoscopic damage model for the low-cycle fatigue of an extruded magnesium alloy

This paper presents a novel mesoscopic damage model to characterize the low-cycle fatigue damage evolution of an extruded AZ31 magnesium (Mg) alloy, taking into account the effect of twinning. The damage caused by the slip bands (SBs)–twin boundaries (TBs) and SBs–grain boundaries (GBs) interactions is treated based on the Tanaka–Mura model and the Eshelby inclusion theory. Strain energy values at the TBs and GBs are defined as the TB and GB damage variables, respectively. Explicit formulae for the TB and GB damage evolution are derived from the characteristics of the {101¯2} extension twin and the basal texture. A fracture energy-based crack initiation criterion is established, and the proposed damage model is validated against the existing experimental results. The model demonstrates its ability to reproduce the damage evolution processes, and the predictions of the crack initiation life are within the twice error band.

Numerical and experimental investigation of a novel liquid upper-feeding micro-channel flat loop thermosyphon cooling and heat recovery system

ABSTRACT A novel liquid upper-feeding micro-channel flat loop thermosyphon (LUF-MCFLTS) system was developed, to eliminate the drying phenomenon of the upper surface in the traditional LTS and provide a highly efficient solution for DC cooling and heat recovery. The effects of cooling capacity (cooling water flow rate and temperature), heat load, and filling ratio on the heat transfer performance of the LUF-MCFLTS system are investigated experimentally. The results indicated that with the increase in cooling water flow, the decrease in cooling water temperature, and the increase in heat load, the heat transfer performance of the LUF-MCFLTS system was better. Under a heat load of 500 W, a cooling water flow rate of 600 L/h, and a cooling water temperature of 15°C, the heat recovery efficiency could reach 86.28%. Compared with the MCFTS and MCFLTS systems in literature, the recovery efficiency of the LUF-MCFLTS system could be increased by 31.6% and 2.64%, respectively. In addition, an effective numerical model to predict the heat recovery efficiency of the LUF-MCFLTS system with the experimental data in the 2.07% error band has been established. This work provides a new idea and theoretical basis for the design of DC cooling and heat recovery system.

Creep-fatigue damage mechanisms and life prediction based on crystal plasticity combined with grain boundary cavity model in a nickel-based superalloy at 650°C

In this study, a dual-scale numerical procedure is developed to reveal the creep-fatigue damage mechanisms and estimate the crack initiation life for notched structures made of Inconel 718 superalloy at 650 °C. The macro-scale simulation solves the creep-fatigue deformation behavior with viscoplastic constitutive models, and the local deformation histories are supplied to the micro-scale simulation as boundary conditions. In the micro-scale simulation, the local damage evolutions are solved based on crystal plasticity combined with grain boundary cavity model. The creep damage is calculated by a special formulation in the form of cavity nucleation, growth and coalescence. The fatigue damage is represented by accumulated energy dissipation originated from crystal plasticity finite element simulation. Experimentally, the creep-fatigue tests of notched structures are carried out for Inconel 718 superalloy at 650 °C to validate the feasibility and robustness of the proposed numerical procedure. Moreover, the crack initiation behavior, including transgranular cracks under fatigue loading and intergranular cracks under creep-fatigue loading, is explained through different types of microstructure observations together with a dual-scale numerical procedure. In detail, the crack initiation sites transferred from the grain interior at notched surface to the grain boundaries at notched subsurface with an increase in hold times can be well predicted by the proposed numerical procedure. In addition, the simulated life based on the developed life prediction approach agrees well with the experimental data within an error band of ±2. Parametric studies show that the creep damage is more sensitive to grain boundary diffusion than to the external conditions of strain level and hold time.

The electromagnetic Sigma-to-Lambda transition form factors with coupled-channel effects in the space-like region

Using dispersion theory, the electromagnetic Sigma-to-Lambda transition form factors are expressed as the product of the pion electromagnetic form factor and the Sigma {bar{varLambda }}rightarrow pi pi scattering amplitudes with the latter estimated from SU(3) chiral perturbation theory including the baryon decuplet as explicit degrees of freedom. The contribution of the K{bar{K}} channel is also taken into account and the pi pi –K{bar{K}} coupled-channel effect is included by means of a two-channel Muskhelishvili–Omnès representation. It is found that the electric transition form factor shows a significant shift after the inclusion of the K{bar{K}} channel, while the magnetic transition form factor is only weakly affected. However, the K{bar{K}} effect on the electric form factor is obscured by the undetermined coupling h_A in the three-flavor chiral Lagrangian. The error bands of the Sigma-to-Lambda transition form factors from the uncertainties of the couplings and low-energy constant in three-flavor chiral perturbation theory are estimated by a bootstrap sampling method.

Experimental study and fretting fatigue life prediction in dovetail assembly considering stress–temperature nonlinear coupling effect

AbstractAs a paramount failure form of dovetail assembly, high‐temperature fretting fatigue seriously restricts the actual service life. Aiming at the problem of fretting fatigue life prediction of dovetail assembly of the aero‐engine compressor under the coexistence of stress and high temperature, based on D‐M contact theory and continuum damage mechanics theory, a fretting fatigue life prediction model considering stress–temperature nonlinear coupling effect is proposed in this paper by, respectively, introducing the fretting fatigue stress σfretting and the high‐temperature influence factor λ. Meanwhile, the judgment criterion of fretting fatigue crack initiation and failure is raised based on the strain–displacement method, and the fretting fatigue test is designed and carried out for experimental verification. The results show that the proposed fretting fatigue life prediction model has high life prediction ability, whose life prediction results are within ±1.7 times the error band, which can provide a theoretical reference for the structural design optimization and damage tolerance design of dovetail assembly.

A universal correlation development for film-wise condensation in the presence of non-condensable gases on vertical walls under turbulent free convection

Accurate prediction of steam condensation in the presence of non-condensable gases is essential for accident analysis in nuclear reactor containments. This study uses the steam–air mixture to illustrate the effect of the mixture's compressibility in analyzing steam condensation. Then, a consolidated database of steam condensation on vertical walls was established, and seven typical empirical and semi-empirical correlations were evaluated. Based on heat and mass transfer analogy and curve fitting, a new universal correlation for predicting steam condensation on vertical walls in the presence of non-condensable gases, including binary and ternary mixtures, under turbulent free convection is established, and this correlation can well handle the transition from binary to ternary mixtures using the same formula. More than 90% of predicted results compared with 1027 data points are within the ± 25% error band, and the mean absolute error is 10.6%. The similarity of helium and hydrogen in analyzing steam condensation is discussed.

Impact of vapour bubble movement on the process of two-phase heat transfer phenomena over hybrid elliptical tubes

The use of modified surface to improve the performance of two-phase heat exchanger in terms of pressure drop and heat transfer rate is one of the current need of industries. In light of this, the current analysis compares the diabatic two-phase heat transfer performance of hybrid elliptical tubes with that of traditional circular tubes at atmospheric pressure using distilled water as a quiescent test fluid. For the purpose of this investigation, a circular tube made of AISI 304 with a diameter of 25 mm and a heating length of 130 mm is used. In order to maintain the same surface area and heating length as a circular tube, the hybrid elliptical tubes are fabricated with varying aspect ratios of 1.17, 1.31, and 1.47. The heat flux varies between 14.87 and 94.82 kW/m2. For two orientation angles, i.e. 0ᵒ and 90ᵒ, the heat transfer performance of hybrid elliptical tubes are investigated. The analysis of results confirmed that both the tubes exhibit boiling characteristics. However, hybrid elliptical tubes outperform circular tubes in terms of heat transfer rate. It is also found that the hybrid elliptical tube with 0ᵒ orientation resulted in higher heat transfer coefficient about 20.61%, 36.74% and 20.69% than that of 90ᵒ orientation for aspect ratio of 1.17, 1.31 and 1.47 respectively. Regardless of orientation angle, the hybrid elliptical tube with aspect ratio of 1.31 demonstrated the highest heat transfer coefficient of all aspect ratios. Also, a non-dimensional correlation is developed which is found to predict the heat transfer coefficient of circular as we as hybrid elliptical tubes within an error band of ±12%.

Ultra-High-Cycle Fatigue Life Prediction of Metallic Materials Based on Machine Learning

The fatigue life evaluation of metallic materials plays an important role in ensuring the safety and long service life of metal structures. To further improve the accuracy and efficiency of the ultra-high-cycle fatigue life prediction of metallic materials, a new prediction method using machine learning was proposed. The training database contained the ultra-high-cycle fatigue life of different metallic materials obtained from fatigue tests, and two fatigue life prediction models were constructed based on the gradient boosting (GB) and random forest (RF) algorithms. The mean square error and the coefficient of determination were applied to evaluate the performance of the two models, and their advantages and application scenarios were also discussed. The ultra-high-cycle fatigue life of GCr15 bearing steel was predicted by the constructed models. It was found that only one datapoint of the GB model exceeded the triple error band, and the RF model had higher stability. The network model coefficient of determination and mean square error for the GB and RF models were 0.78, 0.79 and 0.69, 3.79, respectively. Both models could predict the ultra-high-cycle fatigue life of metallic materials quickly and effectively.

Design and Metrological Analysis of a Backlit Vision System for Surface Roughness Measurements of Turned Parts.

The focus of this study is to design a backlit vision instrument capable of measuring surface roughness and to discuss its metrological performance compared to traditional measurement instruments. The instrument is a non-contact high-magnification imaging system characterized by short inspection time which opens the perspective of in-line implementation. We combined the use of the modulation transfer function to evaluate the imaging conditions of an electrically tunable lens to obtain an optimally focused image. We prepared a set of turned steel samples with different roughness in the range Ra 2.4 µm to 15.1 µm. The layout of the instrument is presented, including a discussion on how optimal imaging conditions were obtained. The paper describes the comparison performed on measurements collected with the vision system designed in this work and state-of-the-art instruments. A comparison of the results of the backlit system depends on the values of surface roughness considered; while at larger values of roughness the offset increases, the results are compatible with the ones of the stylus at lower values of roughness. In fact, the error bands are superimposed by at least 58% based on the cases analyzed.

Mass flow rate measurement of gas-liquid two-phase flow using acoustic-optical-Venturi mutisensors

The measurement of multiphase flow parameters is essential for the online monitoring of industrial production and energy metering. In this paper, a multi-sensor experimental measurement device is designed based on NIR, acoustic emission sensors, and throated Venturi. The measurement information is decomposed using modal decomposition, and the characteristic variables of the gas volume fraction are extracted by flow noise decoupling and light attenuation analysis. A new gas volume fraction model is proposed based on Gradient Boosting Decision Tree (GBDT) through feature-level fusion, and the Mean Absolute Percentage Error (MAPE) of the gas volume fraction prediction models is within 4% for the three flow patterns. A new flow rate model is established based on the Homogeneous and Collins models. Laboratory results indicate that the MAPE of the flow rate model is 1.56%, and 98.61% relative deviations are within ±20% error band. The study provides a new method for online measurement of multiphase fluid motion and a theoretical basis for sensing mechanism and measurement of multiphase flow.

Curvilinear mask optimization with refined generative adversarial nets

Inverse lithography technology (ILT) can optimize the mask to gain the best process window and image quality when the design dimension shrinks. However, as a pixel level correction method, ILT is very time-consuming. In order to make the ILT method useful in real mask fabrication, the runtime of ILT-based optical proximity correction mask must evidently decrease while keeping the good lithographic metric performance. Our study proposes a framework to obtain the curvilinear ILT mask with generative adversarial network (GAN). It is subsequently refined with the traditional ILT to exclude unexpected outliers generated by the GAN method. We design conditional GAN, reverse GAN (RGAN), and high discretion GAN (HDGAN) to generate curvilinear ILT mask. Their runtime and the performance are compared. Compared with the CILT method, the speed of GAN type methods with the afterward refinement is increased by an order of magnitude. The RGAN has a better performance in edge placement error and process variation band evaluation, and HDGAN has a better performance in the mask error enhancement factor evaluation. The designed RGAN and HDGAN are promising in actual application to generate the curvilinear mask. They can evidently decrease the runtime and have better lithographic metric performance.

High Cycle Fatigue Life Prediction of Single-Crystal Specimen Based on TCD Method and Crystal Plasticity Theory

This paper performs a comprehensive investigation on the high cycle fatigue (HCF) life prediction of turbine blade with film cooling holes. The modified theory of critical distance (MTCD) method is proposed to estimate the fatigue life of the specimen considering the notch sensitivity coefficient and multiaxial stress effect. Then, two types of specimens were designed with regard to the single-hole and multihole conditions. Afterwards, the dangerous path and fatigue life of the two specimens were achieved implementing the MTCD method. Then, the experiments and failure analysis were carried out. The results show that the stress concentration and multiaxial stress resulting from the film cooling holes are the primary reasons that the cracks originated. Meanwhile, the dangerous path of the single-hole specimen is quite different from the multihole specimen due to the interhole interference. Finally, most of the calculated fatigue life is within the twice error band of the tested life.

Quasi-Steady Simulation of Glaze Ice Accretion and Heat Transfer in the Supercooled Large Droplet Regime in Atmospheric Turbulent Air Flow

Abstract To avoid the use of a computationally intensive full unsteady simulation while providing an accurate solution, a quasi-steady simulation has been performed to study glaze and mixed ice accretion in the supercooled large droplet (SLD) regime in turbulent flow of atmospheric air. We have attempted to find the minimum time-step necessary to adequately simulate the icing process on an airfoil surface. Based on node displacement, a mesh morphing scheme has been adopted in the computations to account for the moving boundaries that are caused by the continuous ice buildup. We have modeled ice accretion on an airfoil surface for a time period of 232 s using several time steps. At each time-step we solved the steady-state conservation equations for the air and droplet phases and then used the results as initial conditions for the next time position. The magnitude of the time-step ranged from a least accurate two-shot simulation (where the time-step is 116 s) to a most accurate 2320-shot simulation (where the time-step is 0.1 s). In-between these two extreme time steps, we have performed a three-shot simulation (where the time-step is 77.33 s), a four-shot simulation (where the time-step is 58 s), a six-shot simulation (where the time-step is 38.67 s), a 46-shot simulation (where the time-step is 5 s), and a 232-shot simulation (where the time-step is 1 s). We have done so to find out the degree of accuracy (or inaccuracy) of the multishot simulation approach and to find out the appropriate time-step needed for a successful and valid quasi-steady simulation. A valid quasi-steady simulation needs to use a time-step that is small enough to reproduce the full time-dependent solution within a very small error band. We have found that both the 1 s and the 0.1 s time steps produce virtually identical results. This is the primary litmus test that proves the validity of the quasi-steady-state assumption. The results adopted in this paper are thus all based on the more conservative 0.1 s time-step. In the process of performing the simulations, remeshing was required in order to maintain the grid density in zones of high curvature to be able to capture the full physics in those zones. After successfully modeling glaze ice accretion over the airfoil surface using the 0.1 s quasi-steady simulation approach, the effects of supercooled large droplets (SLDs) impacting the surface have been examined and presented in terms of the variation of the local collection efficiency, the water film thickness, and the heat transfer rate. Examination of the variation of the angle that the ice horn makes with the airfoil chord line demonstrated a 20% improvement in angle prediction when the time-step is reduced from 116 s to 0.1 s. The analysis also reveals a 12% or 8.5% increase in the maximum collection efficiency, βmax, depending on whether the value of the liquid water content (LWC) has been doubled from 0.5 g/m3 to 1 g/m3, or the value of the freestream velocity has been doubled from 75 m/s to 150 m/s, respectively. Because of the need to monitor the local collection efficiency and convective heat fluxes at each shot (regardless of the number of shots employed), the approach adopted here was found to be effective in successively and successfully reproducing the curvature of the glaze ice horn.