Nonlinear Temperature Research Articles

Exploring the mechanical response of functionally graded hollow disks: insights from rotation, gravity and variable heat generation

PurposeThe purpose of the study is to perform elastic stress and deformation analysis of a functionally graded hollow disk under different conditions (rotation, gravity, internal pressure, temperature with variable heat generation) and their combinations.Design/methodology/approachThe classical method of solution, Navier's equation, is used to solve the governing equation. The analysis considers thermal and mechanical boundary conditions and takes into account the variation of material properties according to a power law function of the radius of the disk and grading parameter.FindingsThe findings of the study reveal distinct trends and behaviors based on different grading parameters. The influence of gravity is found to be negligible, resulting in similar patterns to the pure rotation case. Variable heat generation introduces non-linear temperature profiles and higher displacements, with stress values influenced by grading parameters.Practical implicationsThe study provides valuable insights into the behavior of displacement and stresses in hollow disks, offering a deeper understanding of their mechanical response under varying conditions. These insights can be useful in the design and analysis of functionally graded hollow disks in various engineering applications.Originality/valueThe originality and value of this study lies in the consideration of various loading combinations of rotation, gravity, internal pressure and temperature with variable heat generation. Furthermore, the study of effect of various angular rotations, temperatures and pressures expands the understanding of the mechanical behavior of such structures, contributing to the existing body of knowledge in the field.

Research on temperature compensation method for photoelectric sensors

In order to make the temperature error of fiber-optic current sensor (FGB) based on polarization modulation principle meet the requirements of engineering applications, the temperature error characteristics of FGB are analyzed theoretically, and the optimized BP neural network is used for the temperature compensation of FGB, which realizes the nonlinear temperature error correction of the sensor, and compares and analyzes the experimental results with those of other types of temperature compensation algorithms. The results show that the temperature compensation results based on the neural network algorithm are better than other compensation effects. Finally, the repeatability of the FGB was experimentally verified using its full temperature experiment, and the temperature errors of the FGB in the range of 20 ℃~ 100 ℃ were less than 0.5% after the correction of the neural network algorithm.

Nonlinear Temperature Control of Additive Friction Stir Deposition Evaluated on an Echo State Network

Abstract Additive friction stir deposition is a recent innovation in additive manufacturing allowing the deposition of metallic alloys onto a metallic deposit bed, creating a purely mechanical metallic bond. The deposition can be done in a layer-by-layer manner, and the purely mechanical process eliminates the need for high energy consumption and can be deposited at a much higher rate than beam-based welding. The mechanical nature of the process allows the bonding of dissimilar alloys and a reduction in size of the heat-affected zone. The additive friction stir deposition process is difficult to model and existing literature has focused on numerical analysis, which is not amenable to online closed-loop control. In this work, a form of reservoir computing called an echo state network is used to model the additive friction stir deposition process from online process data, and validation is performed on a reserved dataset. Subsequently, a model-free controller using Lyapunov-derived combination of the robust integral of the sign error, and a single hidden layer neural network design is developed to control the additive friction stir deposition process. Control efficacy is given by way of a Lyapunov analysis which shows the system is globally exponentially stable, and simulation results with the echo state networks. Stability proof shows that under one assumption, the controller can be extrapolated to the real system. The mean squared error of the tracking result using the controller and echo state network simulation is 2.05 °C.

Fault-Tolerant Six-Axis FBG Force/Moment Sensing for Robotic Interventions

A fiber Bragg grating (FBG) based six-axis force/moment ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> ) tactile sensor with the capability of nonlinear decoupling, fault-tolerant, and temperature compensation (TC) is developed for robot-assisted minimally invasive surgery. Eight tightly suspended FBGs have been fixed inside a small three-dimensional printed flexure with a diameter of 10 mm to form the force-sensitive unit of the sensor. Considering the suspended FBG fracture risk, an optimized back propagation neural network (BPNN) algorithm has been proposed to eliminate the nonlinear crosstalk effect of the six-axis <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> outputs, diagnose and modify the fault response of the sensor under several FBGs fractures and eliminate the temperature-induce errors. Experimental results indicate that the Type I and Type II errors are within 5% using the BPNN nonlinear decoupling model. The force resolutions can reach 2.73 mN, 2.21 mN, and 28.39 mN within ±4 N, and the moment resolutions can reach 0.36 mN·mm, 0.96 mN·mm, and 47.5 mN·mm within ±20 N·mm. Moreover, the Type I errors in the six-axis can be modified within 8%, the Type II errors can be modified within 10%, even with one and two FBGs fractures. After TC, the maximum temperature-induced errors can be modified within 0.061 N and 0.127 N·mm for force and moment components, respectively. Combining the robot-assisted scanning and the BPNN, the positions of the buried vessels in a phantom can be effectively identified by the designed sensor, even two FBGs fracture. Such merits validate the dependability and robustness of the designed sensor with FBGs fracture.

Pre-trained 1DCNN-BiLSTM Hybrid Network for Temperature Prediction of Wind Turbine Gearboxes

The safety and stability of a wind turbine is determined by the health condition of its gearbox. The temperature variation, compared with other characteristics of the gearbox, can directly and sensitively reflect its health conditions. However, the existing deep learning models (including the single model and the hybrid model) have their limitations in dealing with nonlinear and complex temperature data, making it challenging to achieve high-precision prediction results. In order to tackle this issue, this paper introduces a novel two-phase deep learning network for predicting the temperature of wind turbine gearboxes. In the first phase, a one-dimensional convolutional neural network (1DCNN) and a bidirectional long short-term memory (BiLSTM) network are separately trained using the same dataset. The two pre-trained networks are combined and fine-tuned to form the 1DCNN-BiLSTM model for the accurate prediction of gearbox temperatures in the second phase. The proposed model was trained and validated by measured datasets from gearboxes from an existing wind farm. The effectiveness of the model presented was showcased through a comparative analysis with five traditional models, and the result has clearly shown that the proposed model has a great improvement in its prediction accuracy.

Low-temperature electrical transport in the normal-state of overdoped cuprate superconductors

The low-temperature electrical transport in the normal-state of overdoped cuprate superconductors is investigated based on the t-J model. The momentum relaxation due to the umklapp scattering between electrons by the exchange of the effective spin propagator is employed to evaluate the electrical resistivity within the framework of the Boltzmann transport theory. It is shown that the quadratic temperature dependence of the resistivity develops in the far-lower-temperature region, and is followed by a nonlinear temperature dependence of the resistivity in an extremely-narrow-crossover region and a linear temperature dependence of the resistivity in the low-temperature region. The obtained results also show that the same spin excitation governs both superconductivity and the electron umklapp scattering responsible for the low-temperature linear in temperature resistivity in the overdoped regime.

Mechanical behavior of longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load

Adhesive anchors have been widely used as a post-reinforcement measure to strengthen longitudinally continuous slab tracks. However, the mechanical behavior of the longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load has not been thoroughly investigated. Therefore, this paper was motivated to conduct experimental and numerical investigation on the temperature-induced deformation and damage of the reinforced track. Firstly, experimental tests were carried out to investigate the influence of the borehole conditions on the bond properties of post-installed adhesive anchors. Next, the bond-slip relationships between anchors and concrete were established for anchors in various borehole conditions. Then, a novel finite element model of the reinforced track incorporating a nonlinear cohesive zone model of structural interfaces was developed and validated by filed monitoring data. Finally, the effects of borehole conditions and number of invalid anchors on the deformation and damage behavior of the reinforced track under nonlinear temperature load were systematically studied. Results show: (1) The cubic compressive strength grade of concrete has a significant effect on the bond-slip curves between concrete and anchors of the longitudinally continuous slab track. (2) Wet boreholes and uncleaned boreholes would reduce elastic stiffness and ultimate bond strength between anchors and concrete by 11–37% respectively, compared with dry and cleaned boreholes. (3) The maximum vertical displacement of slabs could increase by 7% and 4% if the boreholes are wet and uncleaned respectively. (4) The interface at the center of slab end near damaged joint will not fail for the track with 1 or 2 invalid anchors when the temperature reaches its highest. However, interface debonding will occur with a temperature rise of 34.6 ℃ if there are 3 invalid anchors.

A method for eliminating local modes caused by isolated structures in dynamic topology optimization

In the dynamic topology optimization of structures with single-phase material, isolated structures, often appear, resulting in the occurrence of local modes. Each isolated structure has three or six zero eigenvalues for 2D or 3D problems, but are meaningless and harmful to the topology optimization. Furthermore, these zero eigenvalues will cause extra unneeded huge computational cost, especially for large-scale problems. To tackle this issue, this paper proposes a novel method for eliminating local modes caused by isolated structures. Firstly, the Nonlinear Virtual Temperature Method (N-VTM) is introduced to identify isolated structures. Subsequently, a new mass interpolation is developed to eliminate the local modes caused by the isolated structures. Since the developed method has an explicit and simple formulation, and the sensitivity of eigenfrequencies with respect to the design variables can be derived. Typical application examples, including vibrating structures and phononic crystals, are used to validate the effectiveness of the proposed method. The results indicate that the proposed method can effectively identify and eliminate isolated structures in the optimization process, avoiding local mode problems, and ensures stable convergence of the optimization iterations.

Tunable Harmonics Generation from Low Average Power Mode-Locked Er-Fiber Laser Using Periodic Poled Nonlinear Crystals

Abstract: Sufficient second, third, and fourth harmonic generation of mode-locked Er-doped fiber laser (ML - EDFL) was experimentally demonstrated. This was achieved by using periodically poled KTiOPO4 (PPKTP) and PP LiNbO3 (PPLN) PPLN nonlinear crystals. Harmonic generation in both crystals depended on the direction of polarization. The highest conversion efficiency was obtained by using a half-wave plate to rotate the polarization before the crystals. When using the PPKTP nonlinear crystal, conversion efficiencies of 4.88%, 0.02%, and 0.002% were obtained for second, third, and fourth harmonics generation at wavelengths of 980, 520, and 390 nm, respectively. For the PPLN nonlinear crystal, temperature and polarization direction were optimized for each harmonic generation wavelength. As a result, conversion efficiencies of 8.6%, 0.1%, and 0.007% were obtained for second, third, and fourth harmonic generation at the same respective wavelengths. Tunable wavelength ranges and their SHGs, as well as the multi-wavelength output and their corresponding SHG wavelengths, were also reported. Keywords: Er-fiber laser, Passive mode-locked fiber laser, Nonlinear polarization rotation, PPKTP, PPLN, SHG, THG, FHG. PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.

Characterization of multiple debris cloud impacts-induced pitting damage evolution in spacecraft structures using temperature-dependent ultrasonic nonlinearity

Facing the harsh cryogenic-elevated temperature condition, evaluation of the debris cloud-induced pervasive but highly complex pitting damage in manned spacecraft structures, featuring multitudinous small-scale craters and cracks disorderedly scattered over a wide region, accompanied by a diversity of micro-damages, is hitherto still a challenging task. In line with the fact that the use of ultrasonic nonlinearity is restricted by its intrinsic vulnerability to measurement contamination, in particular temperature fluctuations. With this motivation, an insight into the modulation mechanism of typical elastic parameters of material at macroscopic under varying temperatures, as well as microscopic interatomic potential, is achieved via theoretical analysis. Based on this, temperature sensitivity coefficients (TSCs) of these elastic parameters are obtained, and a nonlinear temperature sensitivity index (TSI) is established. On this basis, an active TSI-based evaluation method is proposed to improve the accuracy and reliability of pitting damage evaluation by controlling detection temperature (i.e., exploitation of the benign aspects of the temperature sensitivity of ultrasonic nonlinearity), rather than eliminating or compensating for its adverse effect, when other nonlinear sources interference. This method is experimentally corroborated, in which the multiple debris cloud impacts-induced accumulated pitting damage are accurately and intuitively characterized through temperature control, in terms of its severity and distribution characteristics, which is consistent with the actual results. These findings provide an active structural health monitoring (SHM) strategy for promoting the practical application of this proposed approach for characterizing pitting damage evolution in manned spacecraft in qualitative and semi-quantitative manners.

Irradiance and cloud optical properties from solar photovoltaic systems

Abstract. Solar photovoltaic power output is modulated by atmospheric aerosols and clouds and thus contains valuable information on the optical properties of the atmosphere. As a ground-based data source with high spatiotemporal resolution it has great potential to complement other ground-based solar irradiance measurements as well as those of weather models and satellites, thus leading to an improved characterisation of global horizontal irradiance. In this work several algorithms are presented that can retrieve global tilted and horizontal irradiance and atmospheric optical properties from solar photovoltaic data and/or pyranometer measurements. The method is tested on data from two measurement campaigns that took place in the Allgäu region in Germany in autumn 2018 and summer 2019, and the results are compared with local pyranometer measurements as well as satellite and weather model data. Using power data measured at 1 Hz and averaged to 1 min resolution along with a non-linear photovoltaic module temperature model, global horizontal irradiance is extracted with a mean bias error compared to concurrent pyranometer measurements of 5.79 W m−2 (7.35 W m−2) under clear (cloudy) skies, averaged over the two campaigns, whereas for the retrieval using coarser 15 min power data with a linear temperature model the mean bias error is 5.88 and 41.87 W m−2 under clear and cloudy skies, respectively. During completely overcast periods the cloud optical depth is extracted from photovoltaic power using a lookup table method based on a 1D radiative transfer simulation, and the results are compared to both satellite retrievals and data from the Consortium for Small-scale Modelling (COSMO) weather model. Potential applications of this approach for extracting cloud optical properties are discussed, as well as certain limitations, such as the representation of 3D radiative effects that occur under broken-cloud conditions. In principle this method could provide an unprecedented amount of ground-based data on both irradiance and optical properties of the atmosphere, as long as the required photovoltaic power data are available and properly pre-screened to remove unwanted artefacts in the signal. Possible solutions to this problem are discussed in the context of future work.

Analysis of temperature-dependent thermal conductivity and fin efficiency: Direct Akbari-Ganji method

The vast majority of engineering issues, particularly heat transport equations, have a non-linear form. The analytical solution of temperature distribution, fin effectiveness, and fin efficiency of straight convective fins that transport heat with temperature-dependent thermal conductivity convection is derived in this work using the Direct Akbari-Ganji method (DAGM). DAGM is an effective methodology that is very simple and takes less time to solve non-linear temperature distribution fin problems. In the present investigation, Direct Akbari-Ganji technique offers desirable solutions to heat transfer problems. The round-off error is smaller compared to other methods. For the purpose of calibrating the error accuracy of the suggested direct technique, this result is compared with the numerical and earlier solution. The outcomes show that the DAGM for heat transfer equations in engineering situations has excellent validity and considerable promise. Finally, it is clear that when the thermo-geometric fin parameter increases, so does the fin efficiency. The homogeneity of the fin is due to the variable thermal conductivity. Four convection conditions with constant coefficients, growing and decaying convection coefficient with fin temperature are discussed.

Nonlinear Approximation for Natural Convection Flow Past A Vertical Moving Plate With Nonlinear Thermal Radiation Effect

This piece of work contains significant insight associated with the analysis of fluid transport in the vicinity of a constantly moving vertical plate with nonlinear thermal radiation. The heat transport at the wall surface is assumed to be influenced by convective boundary conditions. Furthermore, thermal transport is considered to be enhanced by nonlinear temperature variation with temperature (NDT). The boundary layer approximation equations are simplified through suitable alteration known as the similarity transformation. The resulting ODEs are translated into the IVP via shooting techniques and then integrated using the RKF45 algorithm in Maple. The impact of the dimensionless parameters dictating the fluid behaviour is demonstrated via graphs and tables. In the cause of the analysis, it is observed that the heat transfer enhances when the fluid flow in the direction +ve x-axis whereas the plate moves in the direction of the -ve x-axis but decreases when the plate and fluid move in the same direction. The skin friction coefficient decreases when the fluid flow is directed toward the +ve x-axis whereas the plate moves toward the -ve x-axis but is enhanced when the plate and the fluid move in the same orientation. The temperature and velocity profiles appreciate with the nonlinear thermal radiation when the motion of the plate and the fluid are on the same axis. The temperature gradient near the wall depreciated gradually due to nonlinear thermal radiation growth but appreciate in the free stream.

Contribution of Various Loads to the Convex Shape of Rock Wool Insulation Slabs during Production.

Rock wool insulation slabs are produced in special curing ovens, where molten rock wool fibres coated with binder are compressed between two slat conveyors and blown with hot air for vitrification. Often, the cross-section of the final slabs is slightly convex, which is undesirable. The degree of convexity depends on the deformation of the steel crossbars of the slat conveyors, which are subjected to combined pressure and nonlinear temperature loadings. Due to this complex loading state, it is difficult to determine the contribution of individual load to the total deformation. The main aim of the study was to determine these contributions. Temperature and stress measurements of the crossbars were performed during rock wool production. Upon collecting these measurements, a finite element (FE) model of a crossbar was established for the identification of the pressure loading acting on the crossbars, and finally for determination of their deformations. As a main result of the study, an inverse problem-based methodology for the identification of the deflection of a structure due to unknown temperature and pressure loadings was established and applied on the specific case. The deviations between the deformations of the FE crossbars and the final shape of the rock wool slabs were below 10%, which validates the novel methodology.

Thermoelastic free vibration analysis of functionally graded conical shell based on trigonometric higher-order shear deformation theory

The fundamental frequency of a rotating cantilevered porous functionally graded (FG) twisted conical shell with varying thickness along the longitudinal direction is calculated using a trigonometric higher-order shear deformation theory under thermal loading. Finite element method is employed for this purpose. The shell is discretized using eight-noded isoparametric shell elements with seven degrees of freedom per node. Using a simple power law across the transverse direction, the temperature-dependent material properties of the FG shell are determined. The nonlinear temperature distribution across the thickness direction is calculated using the one-dimensional Fourier heat conduction equation. The dynamic equation of motion is derived using Lagrange's equation. Finally, a parametric investigation of the effects of taper ratio, porosity, pretwist angle, temperature, and rotational speed on the fundamental frequency of the porous FG rotating conical shell is performed. It is also discussed how such characteristics affect mode shapes.

A thermodynamic analysis of CLC transporter dimerization in lipid bilayers

The CLC-ec1 chloride/proton antiporter is a membrane-embedded homodimer with subunits that can dissociate and associate, but the thermodynamic driving forces favor the assembled dimer at biological densities. Yet, the physical reasons for this stability are confounding as dimerization occurs via the burial of hydrophobic interfaces away from the lipid solvent. For binding of nonpolar surfaces in aqueous solution, the driving force is often attributed to the hydrophobic effect, but this should not apply in the membrane since there is very little water. To investigate this further, we quantified the thermodynamic changes associated with CLC dimerization in membranes by carrying out a van 't Hoff analysis of the temperature dependency of the free energy of dimerization, ΔG°. To ensure that the reaction reached equilibrium at different temperatures, we utilized a Förster resonance energy transfer assay to report on relaxation kinetics of subunit exchange as a function of temperature. Equilibration times were then applied to measure CLC-ec1 dimerization isotherms at different temperatures using the single-molecule subunit-capture photobleaching analysis approach. The results demonstrate that the dimerization free energy of CLC in Escherichia coli-like membranes exhibits a nonlinear temperature dependency corresponding to a large, negative change in heat capacity, a signature of solvent ordering effects such as the hydrophobic effect. Consolidating this with our previous molecular analyses suggests that the nonbilayer defect required to solvate the monomeric state is one source of the observed change in heat capacity and indicates the existence of a generalizable driving force for protein association in membranes.

Thermo-electro-elastic coupled modeling and simulation of functionally graded piezoelectric structures

Compared with the composite materials, the functionally graded materials can not only provide better specific stiffness but also reduce the risk of layered damage. Therefore, the graded distribution forms have become the development trend of advanced structures. An efficient finite element (FE) modeling method and numerical simulation of plate and shell with nonlinear temperature gradient coupling are developed based on the FOSD hypothesis for thermo-electro-elastic coupled functionally graded piezoelectric material (FGPM) integrated with smart structures in this paper. The constitutive model for thermo-electro-elastic coupled FGPM is derived. Assuming that the temperature gradient distribution changes secondarily through the thickness, two nonlinear physical models for temperature change are constructed. Based on the FOSD hypothesis, the multi-field coupled FE equation of plate and shell is derived. The accuracy of the present FE model is verified by the commercial calculation structures. The parametric simulation of FGPM shells is carried out based on the FE model.

The association between temperature and alcohol- and substance-related disorder hospital visits in New York State

BackgroundLimited evidence exists on how temperature increases are associated with hospital visits from alcohol- and substance-related disorders, despite plausible behavioral and physiological pathways.MethodsIn the present study, we implemented a case-crossover design, which controls for seasonal patterns, long-term trends, and non- or slowly-varying confounders, with distributed lag non-linear temperature terms (0–6 days) to estimate associations between daily ZIP Code-level temperature and alcohol- and substance-related disorder hospital visit rates in New York State during 1995–2014. We also examined four substance-related disorder sub-causes (cannabis, cocaine, opioid, sedatives).ResultsHere we show that, for alcohol-related disorders, a daily increase in temperature from the daily minimum (−30.1 °C (−22.2 °F)) to the 75th percentile (18.8 °C (65.8 °F)) across 0–6 lag days is associated with a cumulative 24.6% (95%CI,14.6%–34.6%) increase in hospital visit rates, largely driven by increases on the day of and day before hospital visit, with an association larger outside New York City. For substance-related disorders, we find evidence of a positive association at temperatures from the daily minimum (−30.1 °C (−22.2 °F)) to the 50th percentile (10.4 °C (50.7 °F)) (37.7% (95%CI,27.2%–48.2%), but not at higher temperatures. Findings are consistent across age group, sex, and social vulnerability.ConclusionsOur work highlights how hospital visits from alcohol- and substance-related disorders are currently impacted by elevated temperatures and could be further affected by rising temperatures resulting from climate change. Enhanced social infrastructure and health system interventions could mitigate these impacts.

Free vibration response of rotating pretwisted porous exponential and sigmoid functionally graded conical shells in thermal environment

A finite element method is used to analyze the free vibration of rotating functionally graded (FG) porous conical shell in thermal environment. Exponential and sigmoid laws are used for grading the FG conical shell in the presence of even and uneven porosity distributions. The one-dimensional Fourier heat conduction equation is used to calculate the nonlinear temperature distribution across the thickness of the shell. The parametric studies reveal that the porosity volume fraction has a significant impact on natural frequency. Centrifugal stiffening, which manifests as a geometrical stiffness matrix, causes rotational speed to enhance the natural frequency of the FG shell.

Multistability in a coupled ocean–atmosphere reduced‐order model: Nonlinear temperature equations

AbstractMultistabilities in the ocean–atmosphere flow were found in a reduced‐order ocean–atmosphere coupled model, by solving the nonlinear temperature equations numerically. In this article, we explain how the full nonlinear Stefan–Bolzmann law was implemented numerically and the resulting change to the system dynamics was compared with the original model where these terms were linearised. Multiple stable solutions were found that display distinct ocean–atmosphere flows, as well as different Lyapunov stability properties. In addition, distinct low‐frequency variability (LFV) behaviour was observed in multiple attractors. We investigated the impact on these solutions of changing the magnitude of the ocean–atmospheric coupling, as well as the atmospheric emissivity, to simulate an increasing greenhouse effect. Where multistabilities exist for fixed parameters, the possibility for tipping between solutions was investigated, but tipping did not occur in this version of the model where there is a constant solar forcing. This study was undertaken using a reduced‐order coupled quasigeostrophic ocean–atmosphere model.