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Thin-walled tubular deployable composite boom (DCB) has gained significant attention due to its lightweight, simple structure and high packaging efficiency. The experimental and numerical simulation methods were employed in this paper to investigate the folding behavior of the DCB. Using T700/epoxy unidirectional reinforced prepreg as raw material, DCB specimens were prepared by the vacuum bag method. To complete the folding experiments of DCB specimens, a folding mechanism was designed and manufactured. Folding experiments of DCB specimens were conducted and folding moment versus rotational displacement curves were measured. In addition, a Finite Element Model (FEM) was established to predict the folding behavior of the DCB. Different failure criteria were considered in the numerical analysis, including the Tsai‐Hill criterion and maximum stress criterion. Prediction results using the FEM were compared with experimental results, and both sets of results were in good agreement. It is shown that the DCB can achieve the folding function without failure. The research results in this paper are of great significance to the practical engineering application of the DCB. [Display omitted] • Six tubular deployable composite boom specimens and a precise folding mechanism were designed and prepared. • Folding experiments were conducted to measure the folding moment and rotational displacement curves. • A finite element model for predicting the folding behavior of the tubular deployable composite boom was established. [ABSTRACT FROM AUTHOR]

The transport properties of gas diffusion layer (GDL) in proton exchange membrane fuel cell are important parameters in fuel cell modelling, and one method to measure them is to simulate the transport of each species at spatial resolutions of a few microns in a microstructure of the GDL. One issue in this method is the size of the microstructure as using an unnecessarily big sample could substantially increase the computational cost. Both carbon-paper and carbon-cloth GDLs are investigated and their microstructures are obtained using numerical generation and X-ray micro-tomography respectively at a resolution of 1.733 µm. For each reconstructed GDL, we use the orthorhombic lattice Boltzmann model to simulate fluid flow through some subsamples taken from it in both the in-plane and the through-plane directions; the results show that the permeability of all subsamples is anisotropic in that their permeability in the in-plane direction is higher than in the through-plane direction. For each GDL, we compare its permeability calculated using samples of different sizes and find its representative elementary volume (REV) – a volume above which the calculated permeability represents the average ability of the GDL to conduct fluids. [ABSTRACT FROM AUTHOR]

• The elastic instability phenomenon in hyperelastic layered materials with the phases exhibiting stiffening behavior is studied • A closed-form expression for the critical stretch of macroscopic instability is derived • An analytical prediction based on Bloch-Floquet analysis for the microscopic instability is exhibited • The critical parameters and transition of instability modes are found to be highly tunable with phase stiffening This paper investigates the elastic instability behavior in soft periodic laminates subjected to finite strains, with a focus on both macroscopic and microscopic instabilities. Considering the deformation-induced phase stiffening, the Gent model with a high bulk-to-shear modulus ratio describes the behavior of incompressible phases. This non-Gaussian statistics-based model captures the non-linear constitutive results from the limited extensibility of polymeric molecular chains. This paper derives an analytical prediction for the onset of macroscopic (or longwave) instability and microscopic instability as functions of material parameters. Moreover, a numerical Bloch-Floquet analysis is imposed on identifying the instability behavior under compression. We consider a wide range of phase combinations and find that the relatively rapid stiffening of the matrix compared to the stiff layer increases the stability of laminates by decreasing the critical stretch ratio. Essentially, properly manipulating the stiffening parameters can produce an absolutely stable region without observed instability. This paper also systematically illustrates the changes in instability and the transition between macro and micro instability in fully Gent laminates, which show higher stability than fully neo-Hookean laminates with larger critical stretch ratios. The critical characteristics of instabilities, such as critical stretch ratios and critical wavenumbers, can be controlled by the choice of stiffening parameters and other material properties, enlarging the tuning of soft laminates for desired buckling patterns in practical applications. [ABSTRACT FROM AUTHOR]

• A model to explore the multiphysics characteristic of semiconductors is presented. • The model determines the thermal and mechanical properties of complex patterns. • Results show a strong correlation between thermal and mechanical properties. • Dielectric bands asymmetrically affect thermal and mechanical behavior. • Machine learning can predict one property from another. As semiconductor performance improves through advanced package designs, it becomes important to consider both thermal and mechanical properties. Better understanding their relationship enhances system design and optimization. This study has introduced a numerical method that takes into account both thermal and mechanical fluxes to construct thermal and mechanical property maps for practical application in semiconductor engineering. Furthermore, this paper investigated the relationship between the two properties using the constructed property maps in commercially available semiconductor packages. Owing to the complexity of packaging design patterns, a coupled isoparametric mapping and machine learning (ML) method was introduced to investigate their effects. The model then determines and investigates the anisotropic equivalent thermal and mechanical properties of the commercialized semiconductor packages with complex pattern designs, according to the package materials, volume fractions of each material, and design patterns. This approach pursues more sophistication and practicality compared to simplified composite structure property evaluation models. Additionally, all processes in the algorithm are automated based on ML methods, making them practically applicable in the semiconductor industry. The study shows that there is a strong correlation between the thermal and mechanical characteristics in the complex package patterns. This relationship was able to form a fairly clear category based on the shape of the dielectric band because the dielectric band had significantly different effects on the thermal and mechanical fluxes. The study discussed the physical implications of the similarities and differences between the two behaviors and validated the results of the equivalent properties through finite element (FE) analysis. Finally, the study cross-validates the relationship by showing that information from one flux behavior can be used to predict the other based on the ML method. Based on the results, this paper can provide a better understanding of thermal and mechanical fluxes in semiconductor package patterns for package design and optimization. [ABSTRACT FROM AUTHOR]

A paper-based channel is a useful platform for the facile development of analytical devices implementing various chemical or biological reactions. To improve the analytical performance for various applications, it was necessary to analyze the detailed mixing characteristics within a paper-based channel. In this paper, we proposed a mathematical model to predict a concentration field created as a result of the imbibition of multiple fluids within a porous material. Interestingly, we found that the model exhibited a constant interdiffusion width within a paper-based channel even though the flow front velocity decreased over time. We were able to verify that our model accurately predicted the concentration field by comparing the experimental and numerical results for mixing in a 2 inlet-channel. Finally, we designed and fabricated paper-based channels to generate two (linear and non-linear) concentration gradients based on predictions made by the model. Both the experimental and numerical results were in good agreement, demonstrating that our model was accurate and useful for developing a paper-based analytical device utilizing the mixing characteristics of a sample and reagent flow system. [ABSTRACT FROM AUTHOR]

This paper employs a numerical approach to investigate the impact of liquidity shocks on European options in modeling markets. To accurately capture the behavior of European options under liquidity shocks, a coupled system of differential equations is employed, consisting of a degenerate parabolic equation and a diffusion-free equation. The primary focus is on developing and analyzing implicit-explicit methods for numerically simulating European option pricing, specifically considering the presence of liquidity shocks while ensuring the positivity of the solution. The paper also includes convergence analysis and establishes the discrete comparison principle for the developed methods. Numerical experiments are conducted using both uniform and nonuniform meshes to validate the theoretical findings, demonstrating the efficiency and accuracy of the proposed methods. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the determinability of time related colour changes in prints made using ink that dries on matte coated paper with the offset printing technique and infrared method, has been investigated with artifical neural networks after analysis of the experimental and numerical methods. In the experimental part a ECI 2002 CMYK test scale is printed on a 135g/m2 matte coated. The prints obtained were measured with a spectrophotometer at certain intervals and by converting the reflection data obtained into the CIELAB colour description spectrum, time related changes in printed colours have been determined. In the empirical study however, colour changes in prints made on matte coated paper using inks that dry with the infrared method are modelled numerically. The average deviation has been found to be 0.4%. As a result, artificial neural networks can be used with the aim to digitally calculate time related colour changes in the offset printing system. [Copyright &y& Elsevier]

The mechanical response of three different structural core sandwich panels in out-of-plane compression and shear has been analyzed. Specific core shapes examined are arc-tangent, wavy trapezoidal and hemispherical. Unit cells consisting of representative elements of the core attached to face sheets were selected for analysis. Both face sheets and core were assumed made from paper. Finite element analysis employing large deformation and rotations and orthotropic elastic–plastic behavior was used. The results show that the arc-tangent and trapezoidal cores are prone to collapse by extensive bending and buckling, whereas the hemispherical core behaved more stably in compression and shear. Core sheets with a hemispherical shape were prepared from copy paper sheets in a specially designed forming machine. Sandwich test specimens were prepared from this core and tested in out-of-plane compression, and the load-displacement response was compared to predictions from finite element simulations. The experimental and finite element results were consistent. [ABSTRACT FROM AUTHOR]

Abstract: The transport of electrons through the gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells has a significant impact on the optimal design and operation of PEM fuel cells and is directly affected by the anisotropic nature of the carbon paper material. In this study, a three-dimensional reconstruction of the GDL is used to numerically estimate the directional dependent effective electrical conductivity of the layer for various porosity values. The distribution of the fibers in the through-plane direction results in high electrical resistivity; hence, decreasing the overall effective electrical conductivity in this direction. This finding is in agreement with measured experimental data. Further, using the numerical results of this study, two mathematical expressions were proposed for the calculation of the effective electrical conductivity of the carbon paper GDL. Finally, the tortuosity factor was evaluated as 1.7 and 3.4 in the in- and through-plane directions, respectively. [Copyright &y& Elsevier]

Identifying the yarn end from the package surface is integral to the textile process. Using the automatic method based on negative pressure adsorption instead of the traditional manual method to capture the yarn end is an excellent solution to the time-consuming and inefficient problems caused by the latter. To clarify the influence of process parameters on the process of the yarn end being adsorbed to break away from the package surface by the suction nozzle, this paper first establishes a kinetic model of the yarn attached to the package surface. Next, the air-yarn interaction is solved using the momentum exchanged-based immersed boundary-lattice Boltzmann method (IB-LBM). Then, the effect of the distance between the suction nozzle and the package, the rotational speed of the package, and the airflow velocity in the suction nozzle duct on the movement of the yarn end with the airflow field are studied. Further, the regression model for the depth of the yarn end sucked into the suction nozzle duct when the package turns through a fixed angle is solved. Finally, with the goal of a high success rate, large distance, high efficiency, and energy saving, a multi-parameter optimization is performed using the Central Composite Design-based response surface methodology. The work has been proven effective through experimental validation and practical production applications. It provides a theoretical basis for the automatic process of yarn-end-capturing from the package in the textile field. • The kinetic model of the yarn end being adsorbed to break away from the package surface by airflow is established. • The air-yarn interaction is solved using the momentum exchanged-based immersed boundary-lattice Boltzmann method (IB-LBM). • The effects of several process parameters on the movement of the yarn end with the airflow field are studied emphatically. • Multi-parameter and multi-objective optimization are performed by the Central Composite Design-based response surface method. [ABSTRACT FROM AUTHOR]

Highlights • The problem concerns slip flow of carbon–water nanofluid. • Three non-dimensional parameters are wrong. • Some profiles are truncated and wrong. [ABSTRACT FROM AUTHOR]

Abstract: A finite element procedure, developed in order to account for the effect of high anisotropy at folding of coated papers, is presented. The anisotropic behaviour (with very low stiffness in the thickness direction) is modelled using stiff structural elements (trusses and beams). The numerical results indicate that high elastic anisotropy leads to lower strain levels at folding than reported in previous analyses where this effect was not accounted for. High plastic anisotropy, on the other hand, will contradict this result. [Copyright &y& Elsevier]

Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the numerical analysis, the basepaper is modelled as an anisotropic elastic–plastic material (both elastic and plastic anisotropy is accounted for) while the constitutive behaviour of the coating layers are approximated by classical (Mises) elastoplasticity. The numerical results suggest, among other things, that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. It is also shown that delamination buckling, in the present circumstances, will have a very small influence on the strain levels in the coating layer subjected to high tensile loading. [Copyright &y& Elsevier]

In this paper, an improved projection scheme has been constructed for solving the nonstationary magnetohydrodynamic equations, based on the modular grad-div stabilization. Owing to the utilization of the projection scheme and some delicate implicit-explicit approach to the nonlinear coupled terms, the proposed scheme is linear, decoupled and unconditionally energy stable. In addition, the modular grad-div stabilization technique is introduced to improve the conservation of Gauss's law and mass, and reduce the splitting error of the projection method, which is simple to implement with a small intrusion step into existing code. In this way, the developed scheme can prevent the solver from breakdown and enhance computational efficiency with the increasing of grad-div parameters. What's more, we present a rigorous convergence analysis. Finally, several numerical experiments are performed to illustrate the theoretical consequences and their effectiveness. [ABSTRACT FROM AUTHOR]

Efficient finite difference/spectral approximation is proposed for the time-fractional diffusion equation with an inverse square potential on the unit ball in this paper. The efficiency of the method lies in the use of ball functions to mimic the singular behavior of solutions in space and L1 scheme on graded mesh to compensate for the initial weak singularity of solutions in time. The stability and convergence of the fully discrete scheme in both L 2 -norm and H 1 -norm are analyzed. Numerical examples are presented to illustrate the accuracy and efficiency of our proposed discrete scheme. [ABSTRACT FROM AUTHOR]

This paper is devoted to a study of a history-dependent mixed hemivariational-variational inequality arising in contact mechanics. The contact problem concerns the deformation of a viscoelastic body with long memory, subject to a general friction law on one part of the boundary and a frictionless Signorini condition on another part of the boundary. The solution existence and uniqueness of the history-dependent mixed hemivariational-variational inequality based on a Lagrange multiplier approach are proved. Then, a fully discrete scheme is introduced and studied. The trapezoidal rule is used to approximate the integral in the history-dependent operator. For the spatial discretization, the linear finite elements are used to discretize the displacement field, and dual basis functions are used in the approximation of the Lagrange multiplier. Optimal order error estimates are derived for the displacement and the Lagrange multiplier under appropriate solution regularity assumptions. Numerical results are presented to illustrate the theoretical prediction of the convergence orders. [ABSTRACT FROM AUTHOR]

In this paper, Er3+ doped TeO 2 -ZnF 2 -BaF 2 -KF-Ta 2 O 5 tellurite glasses with low hydroxyl content (∼0.03 × 10−19 cm−3) were investigated employing both glass composition and glass melting process optimization. The Raman spectra and physical properties were characterized to analyze the structure of the glasses. Under the pumping of 980 nm LD laser, intense up-conversion fluorescence at 1.5 and 2.7 μm of samples and their lifetimes were detected and analyzed, and the related transition mechanisms with gradient-varying Er3+ doping concentrations were discussed. The maximum absorption and emission cross section at 2.7 μm was calculated to be 6.4 × 10−21 cm2 and 6.8 × 10−21 cm2, correspondingly, which were higher than those of traditional tellurite glasses. Using the calculated and measured spectroscopic parameters of bulk tellurite glass, a dual-wavelength pumping model was established to verify the feasibility of mid-infrared laser output in similar tellurite glass fiber. Experimental results support the assertion that the Er3+ doped tellurite glasses hold promise as a candidate laser gain medium for mid-infrared fiber laser systems. [ABSTRACT FROM AUTHOR]

This paper carried out a high-temperature thermal gradient cycling test of ceramic matrix composites (CMCs), investigating the failure characteristics of CMCs in non-uniform high-temperature environments. The result shows that the damage characteristics of CMCs under thermal gradient environments are significantly different from those under uniform temperature environments. The SiC fiber pull-out lengths at different yarn fractures have obvious differences in the thermal gradient direction. The thermal stress damage propagation pattern of CMCs under the thermal gradient environment is revealed by numerical analysis, and its residual mechanical properties under different thermal gradient environments are predicted. The numerical results could be adopted as a theoretical basis and suggestions for temperature control of CMCs components in practical applications. [ABSTRACT FROM AUTHOR]

The present paper studies Love-type wave propagation in a fluid-saturated fractured poro-viscoelastic layer sandwich between a coated elastic layer and a non-homogeneous anisotropic Voigt-type viscoelastic half-space. The interfaces between the layers and the half-space are considered as sliding contacts with two different sliding parameters. An impulsive point source is located at a varying depth in the intermediate poro-viscoelastic layer in the form of the Dirac-delta function. The vertical non-homogeneity in the half-space is assumed to be a combination of linear and exponential functions that vary with depth in the medium. Using the Fourier transforms and Green's functions, the equations of motion, in the form of partial differential equations, are solved analytically. An appropriate boundary condition is used to accomplish this. The closed form of the complex dispersion equation has been obtained by assuming that the wavenumber is in the form of a complex quantity. The validity of our model has been examined using several specific cases and compared to the classical Love wave equation. Numerical and graphical analyses of dispersion and displacement were performed using MATLAB software. It has been found that a single porous medium has a higher Love-type phase velocity than a double porous medium. Additionally, the sliding parameters increase the range of wavenumber when there is no phase velocity. An inverse relationship was found between the depth of the point source and the particle displacement in the coated layer. In addition to contributing to our understanding of geophysical phenomena and subsurface explosions, these findings may provide insight into the inner structure of the planet. • Layered media with sliding contacts are introduced. • The coupled Green's function approach is used for Love-type dispersion. • Wavenumbers for non-existence of phase velocity increase with sliding parameters. • An inverse relationship is found between the depth of the point source and the particle displacement in the coated layer. [ABSTRACT FROM AUTHOR]

This paper presents globally numerical properties of a new numerical scheme for a reaction-diffusion advection susceptible-infected-susceptible (SIS) model. A new numerical treatment technique is introduced in spatial discretization of advection-diffusion equation, which enables the numerical solutions to preserve the stability and positivity with less stepsize restrictions. The convergence, biological significance and globally stability of numerical solutions is explored in the paper. A threshold value, named by numerical basic reproduction number and denoted by R 0 Δ x , is introduced in the numerical stability analysis of the model. It is proved the numerical disease free equilibrium (DFE) is globally asymptotically stable if R 0 Δ x < 1 and unstable if R 0 Δ x > 1. It is shown the numerical basic number R 0 Δ x replicates the asymptotic behaviors of the basic reproduction number R 0 for the model. Some numerical experiments are given in the end to confirm the conclusions. [ABSTRACT FROM AUTHOR]

Abstract: Strains, computed by the finite element method, are evaluated and compared to an experimentally determined strain field. The analyzed low-density paper has been designed to ensure bond–breakage as the dominating damage mechanism and the paper material is approximately in-plane isotropic. An optical non-contact displacement measuring system has been used in fracture tests to determine the strain field in the crack-tip region of a pre-fabricated crack. Additionally, acoustic emission monitored tensile tests have been conducted to determine onset and evolution of damage processes and thereby enabling calibration of required constitutive parameters. The results suggest that the investigated paper material can tolerate significantly higher strains than what is predicted by a classic elastic–plastic J 2-flow theory. Immediately before onset of the final fracture (i.e., localization), the experimental measured normal strain in the near-tip region is around 60% higher than the computed strain when using exclusively an elastic–plastic theory for the corresponding load while the strain computed utilizing a non-local damage theory is of the same order of magnitude as the experimentally measured strain. Hence, it seems essential to include a non-local continuum theory to describe strains in the near-tip region quantitatively correct for paper materials. It is demonstrated that path independence of the well-known J-integral does not prevail for this class of material models. Only for the special situation of a homogenous damage field in the crack-tip region may the stress and strain fields be described by the well-known HRR-solutions. [Copyright &y& Elsevier]

Abstract: The high fidelity generalized method of cells (HFGMC) has been originally developed by as a micromechanical method for periodic multi-phase composite media. A computational implementation of the HFGMC equations has been proposed by to enhance numerical efficiency, still with direct reference to the HFGMC formulation. Later, the same computational implementation is recast as a new method called “finite volume direct averaging micromechanics” (FVDAM), starting by . The current discussion paper has two aims. The first is to show that the FVDAM is not a new method and that it has the same assumptions and identical governing equations as those originally derived by the HFGMC. The only difference is in the solution procedure where intermediate dependent variables, in the form of average displacements at the interfaces, are used instead of directly solving for the unknown micro-variables; the coefficients of the displacement polynomials. Thus, renaming the HFGMC micromodel to FVDAM has not been justified. In fact, () have shown that the same reduction of variables can be achieved by a simple static condensation carried out at the global system of equations instead of introducing intermediate variables. The second aim of this paper is to address misrepresentations in a recent discussion paper by the FVDAM authors claiming, in part, that the HFGMC method using parametric geometry of the subcells should follow their formulation (termed parametric FVDAM). We show that the latter is limited to an incomplete quadratic expansion of the displacement and an approximation in the form of a priori constant Jacobian of the parametric mapping. However, the HFGMC with arbitrary cell geometry, (), has been formulated in a direct and general manner, i.e. retaining the full quadratic expansion of the displacement together with the complete Jacobian. Thus, the parametric FVDAM is a special case of the parametric HFGMC, i.e. when the Jacobian is sampled and evaluated only at one point, namely the origin of the parametric coordinate system. The intended new contribution of to refined micromechanics and progressive damage has been completely ignored by the FVDAM-discussion paper. Therefore, in order to maintain scientific clarity, it is strongly advocated to preserve the original name of the HFGMC method, regardless of the different computational implementations used for solving the governing equations for both orthogonal and parametric geometries of the subcells. [Copyright &y& Elsevier]

Abstract: We present a model for the laminated composite plate problem based on the Reissner–Mindlin model and first-order lamination theory. The weak problem based on this model is solved with the finite element method using stabilized MITC (mixed interpolation of tensorial components) finite elements. Detailed a priori estimates are given for the mixed finite element formulation of the problem. Explicit bounds for the continuity and coercivity constants of the coupling terms are presented, thus refining earlier results. Furthermore, we present an application of the theory to the paper cockling problem and investigate the effect of boundary conditions on the small-scale deformation of the solution numerically. [Copyright &y& Elsevier]

Abstract: A model, using the finite element method (FEM), was developed for the analysis of the time and humidity-dependent stresses of paper webs at offset printing press conditions. The offset press was simplified to a flat thin moving web and its unit process steps were described by combinations of prescribed displacements, tractions and moisture ratios. Based on previous modelling and experimental findings, a convective hygro-viscoelastic model of the paper web was derived. The constitutive law and some of the boundary conditions were implemented as user-defined subroutines into commercial FEM software in a displacement-based framework. Some simulation examples were used to study the applicability of the proposed formulation in the analysis of web-fed offset printing at stationary conditions. The numerical stationary solutions converged rapidly and the model was robust for the investigated conditions. Incorporating effects from moisture, the numerical results show web tension profiles along the analysed model press comparable to those found by others from full-scale newsprint printing press trials. Effects of altered levels of the peripheral velocities of rollers, friction, web velocity, moisture and web properties on in-plane stresses and strains are presented. In order to exemplify the practical use of the model for runnability investigations, different analysed quantities obtained from the numerical solutions were related to web tension, web widening, misregister in multi-colour printing, sheet size analysis, conditions for web stability and traction conditions at drag rollers. [Copyright &y& Elsevier]

Abstract: The fundamentals of a new radiation model are described in this paper. The spatial and angular dependence of the radiation intensity are split in such a way that the radiation intensity is approximated by a linear combination of basis functions dependent only on the angular direction. The coefficients of the approximation are functions of the spatial coordinates. The spatial discretization is performed using the finite volume method and the angular discretization is based on the finite element method. This means that the basis functions are defined according to the criteria used in the finite element method. The step scheme was employed in the spatial discretization and bilinear basis functions were chosen for the angular discretization. The method may be applied to both grey and non-grey media, non-scattering and scattering media, simple and complex geometries. However, it is still in an early stage of development, and therefore it is applied in this paper to simple one-dimensional problems of radiative transfer in enclosures with grey, emitting-absorbing and scattering media. The results obtained show that the method gives good results for several benchmark problems with available analytical solutions, and converges to the exact solution as the grid is refined and the number of terms in the approximation increases. [Copyright &y& Elsevier]

Abstract: In a recent paper (Computer Aided Geometric Design 23 (3), 243–260), Yang presented a novel kind of nonlinear and geometry driven subdivision scheme for curve interpolation. The author declared that this scheme was shape preserving when all free parameters were explicitly selected by some specific rules. In this note, we demonstrate that the author (a) ignored the consistency of the definition to straight edges, and also (b) did not give a perfect scheme and proof for the shape preserving subdivision. [Copyright &y& Elsevier]

Abstract: A generalization of two sharp inequalities in a recent paper by N. Ujević is established. Applications in numerical integration are also given and the results of N. Ujević are revised and improved. [Copyright &y& Elsevier]

Abstract: In this paper we study the heat transfer and fluid flow in a step-down 3-phase power transformer. In order to simplify the study we choose an element composed of two windings wound around a core. The Joule effect and the Foucault currents produce an undesirable heat in the different components of the transformer. From an economical and security point of view, there is a need to cool the transformer to preserve it from destruction. Our main objective is the cooling optimization of the power transformer. In order to attain this goal, a numerical study has been conducted for six different geometric configurations with six different flow rates of the cooling oil at the entrance. The physical properties of the fluid are supposed to be function of the temperature. The control volume method has been used to resolve the continuity, the momentum and the energy equations in the steady state. The obtained results show that the structure of the flow is somehow complex and according to the case some rolls appear at the top and the bottom of the windings, these rolls contribute to a good mixing of the fluid leading to a nearly homogeneous temperature. [Copyright &y& Elsevier]

Folding of coated papers is examined numerically using the finite element method. The analysis is focused on the influence from dynamic effects on the folding process. In particular, the behaviour of field variables relevant for cracking of the coating layers are studied in some detail. The results presented indicate that dynamic effects are of little importance as regards maximum strain levels in the coating but will influence the stress and strain distributions. Accordingly, a quasi-static analysis of the problem will be sufficient in order to describe many of the important features related to cracking. [Copyright &y& Elsevier]

• New curvature Euler-Bernoulli and Timoshenko beams based on the couple stress and its flexoelectric theory are presented. • Analytical solutions for bending and free vibration of Euler-Bernoulli and Timoshenko nanobeam are derived. • An IGA is developed for extending the applicability of the curvature-based flexoelectric nanobeam. • The accuracy of analytical solution is verified through IGA numerical solutions. • The flexoelectric effects, microstructure effects and boundary conditions on mechanical behavior of nanobeams are studied. In this paper, new curvature-based flexoelectric Euler-Bernoulli and Timoshenko beam models are derived based on the couple stress and its flexoelectric theory. These models consider both the microstructure and flexoelectric effects. The governing equations and boundary conditions are obtained using the variational formula of Hamilton's principle. Analytical solutions for the static bending and free vibration problems of Euler-Bernoulli and Timoshenko beam models with a simply supported nanobeam are presented. To extend the applicability of the curvature-based flexoelectric beam models, an isogeometric analysis (IGA) numerical approach which satisfy the needs of C 1 continuity is developed. Numerical results are provided to verify the accuracy of the analytical and IGA numerical solutions, and the influence of flexoelectric effects, microstructure effects and boundary conditions on the mechanical behavior of nanobeams is analyzed. [ABSTRACT FROM AUTHOR]

This paper investigates the attitude coordination control issue for spacecraft formation flying in the presence of actuator saturation and external disturbances with unknown boundaries. Firstly, a super-twisting integral terminal sliding mode surface is developed, which ensures that the sliding mode surface and its first-time derivative converge to zero in finite time. Then, based on the developed sliding mode surface and adaptive technique, a robust anti-saturation distributed attitude coordination controller that enables the attitude and angular velocity to precisely track the desired time-varying command in finite time is devised under the undirected communication topology. Finally, stability analysis and numerical simulations validate the effectiveness and feasibility of the devised control approach. [ABSTRACT FROM AUTHOR]

• The compaction of paperboard is analyzed through finite element simulations of the industrial process. • The mechanisms governing the process are clarified within the rolling contact mechanics framework. • The parameters controlling the final product outcome are identified for industrial optimization. With the goal of partial or complete replacement of plastic components with paper-based products, 3D paper structures have seen a growing interest in industrial applications: from packaging to more complex daily life objects. However, the extensibility of paper has become a key issue within this context and is the main factor determining the formability of these products and determining the depth of the achievable shapes. The most effective way to increase paper's stretch potential is by subjecting the moist paper web to a compaction process, which can be achieved through an extensible unit that is located in the drying section of a paper machine, where the network experiences in-plane compression in the machine direction (MD), under out-of-plane lateral constraints. The objective of this work is to clarify the mechanisms governing the compression process and to evaluate the influence of various parameters on the final material properties to optimize the industrial production of extensible paper. The system operation has been simulated realistically and shows that paper experiences a compressive state passing through the nip, with plastic strains in MD direction being of the same order of the applied speed difference, which was expected experimentally in optimal conditions of compaction. Starting from an initial reference case, a sensitivity study has been performed to identify and address the following factors that may affect the compression state: (a) friction coefficients; (b) indentation level; (c) speed difference; and (d) rubber properties. The analysis of the numerical results gives an insight into the mechanisms governing the compaction operations and allows a better comprehension of the features controlling the process outcome. [ABSTRACT FROM AUTHOR]

• The proposed method (P-SuS) generalises subset simulation from, to the capability of handling distributional responses. • P-SuS can be used in reliability analyses with partially-converged simulations, probabilistic and surrogate models. • The algorithm can be used in lieu of subset simulation in reliability analysis, optimisation, and pre-calibration. Reliability analysis can be performed efficiently through subset simulation. Through Markov chain Monte Carlo, subset simulation progressively samples from the input domain of a performance function (typically a computer model) to find the failure domain, that is, the set of input configurations that result in an output higher than a prescribed threshold. Recently, a probabilistic framework for numerical analysis was proposed, whereby computation is treated as a statistical inference problem. The framework, called probabilistic numerics, treats the output of a computer code as a random variable. This paper presents a generalisation of subset simulation, which enables reliability analysis for probabilistic numerical models. The advantages and challenges of the method are discussed, and an example with industrial application is presented. [ABSTRACT FROM AUTHOR]

This paper introduces two improved variants of the least squares progressive-iterative approximation (LSPIA) by leveraging momentum techniques. Specifically, based on the Polyak's and Nesterov's momentum techniques, the proposed methods utilize the previous iteration information to update the control points. We name these two methods PmLSPIA and NmLSPIA, respectively. The introduction of momentum enhances the determination of the search directions, leading to a significant improvement in convergence rate. The geometric interpretations of PmLSPIA and NmLSPIA are elucidated, providing insights into the underlying principles of these accelerated algorithms. Rigorous convergence analyses are conducted, revealing that both PmLSPIA and NmLSPIA exhibit faster convergence than LSPIA. Numerical results further validate the efficacy of the proposed algorithms. • This paper proposes two refined versions of LSPIA by incorporating Polyak's heavy ball and Nesterov's momentum techniques. • Geometric interpretation of our methods provides insight into the underlying acceleration principles. • Rigorous convergence analyses and numerical results demonstrate that our methods have a superior convergence than LSPIA. [ABSTRACT FROM AUTHOR]

In this work, a comprehensive insight into the new passive flow control method, i.e. a two-dimensional streamwise waviness (recently proposed by Dróżdż et al. [1]) is provided using Large Eddy Simulations. This approach was demonstrated to be effective in postponing turbulent boundary layer separation at high Re , which is out of reach for other commonly known passive flow control strategies. Although the effectiveness of the wavy wall in delaying flow separation has been confirmed, the physical mechanisms standing behind the skin friction enhancement are not fully understood which opens a space for future work. Of particular interest is an insight into the fluid flow in the near-wall region just above the waviness and this paper is aimed at doing so. To separate the effect of the global adverse pressure gradient, the results were confronted with the ones obtained under zero pressure gradient conditions for the identical wavy wall geometry and the same R e τ = 2500. Also additional simulations of the turbulent boundary layer building up on the flat wall were conducted to have an additional reference for the flow fields obtained above the wavy wall under zero and adverse pressure gradients respectively. A detailed inspection of the streamwise velocity and its fluctuation profiles indicated that the contribution of the global adverse pressure gradient to the flow statistics begins when the Rotta-Clauser pressure gradient parameter β ≥ 3. The paper confirms an enhancement of the wall shear stress τ w downstream the corrugation, which is the necessary condition to postpone the separation. Interestingly, the effect of increased τ w was not observed for the case with the same waviness and without pressure gradient. [ABSTRACT FROM AUTHOR]

• The failure modes and causes of Cr12Mo1V1 crimping die were clarified. • The life extension measures of the dies were put forward. • The simulation model of multi-body contact deformation is constructed by Deform software. • The structure designs of the electrical connector dies were optimized. A type of Cr12Mo1V1 electric connection die occured brittle fracture after 200 times of service, and its life was much lower than the design life of the die. In this paper, the 5M1E failure analysis method was adopted, combined with the characteristics of Cr12Mo1V1 cold-work die steel, scanning electron microscopy, direct reading spectrometer, Rockwell hardness tester, metallographic microscope and other means were used to analyze and test the macro fracture morphology, material composition, mechanical properties and microstructure of Cr12Mo1V1 electric connection die. The crimping process of the die was simulated by Deform software. The results show that the material composition is not up to standard, the strength is too low, the internal eutectic carbide is not uniform, the size of carbide exceeds the standard and so on are the root causes of the short life and brittle fracture of the die. In addition, the unreasonable designs of the crack slot and round hole of the die lead to excessive stress concentration in the crimping process of the die, which is too the main reason for the brittle fracture failure of the die. In view of the above factors, the paper puts forward some measures to prolong the life of the electric connection die from the aspects of raw materials, heat treatment, forging process and die structure design. [ABSTRACT FROM AUTHOR]

• Granular PCMs are proposed to be used in respirators for breathing air cooling. • Commercially available PCMs can be used to cool the inhaled air in indoor fires. • An increase in the melting temperature worsens the cooling efficiency of the respirator. • Time variations of the outlet air flow rate can considerably affect the device characteristics. • Partial closure of the respirator outlet can decrease the operating time of the device. In this paper, we propose to use granular phase change material (PCM) as a heat accumulating material in a thermal protective respirator also called a heat exchanger to cool the breathing air. Such device is needed to protect human respiratory system from thermal injuries at indoor fires. Using the original solver for OpenFOAM software developed and validated previously, the ability of the commercially available granular PCM in the respirator to cool hot air for breathing during the time required for the human evacuation has been shown numerically: mass of 130 g is enough to cool the air from 177 °C to a temperature of less than 50 °C within 10 min. This result gives hope that such cooling element can be combined with "conventional" gas-and-smoke protective element, resulting in the creation of respirators for the protection of a person from both hot air and toxic combustion products. A parametric study of the performance of the thermal protective respirator is carried out in the paper: effect of PCM melting temperature, time variation of the outlet air flow rate and partial closure of the outlet from the cooling element have been analyzed. It has been shown that an increase in the PCM melting temperature while keeping the other parameters unchanged worsens the thermal performance of the breathing air cooler. The cooling efficiency is also worsened when the cooling element is narrowed or its outlet is partially closed, as this leads to an increase in the maximum temperature of the inhaled air. It has been shown that the time variation of the inhaled air flow rate, which is used in the calculations of the thermal protective respirator, must be close to the parameters of real human breathing, and the use of the assumption of constant air flow rate is unacceptable, since this can significantly affect the output characteristics of the respirator. [ABSTRACT FROM AUTHOR]

Welded tubular joints are integral components in various engineering structures, subject to cyclic loading conditions throughout their operational lifespan. This paper investigates the evolution of welding residual stresses within the CHS X-joint and CHS double K-joint under cyclic loading, shedding light on their intricate behavior and potential implications for structural integrity. The advanced XRD experimental technique enables the characterization and monitoring of residual stress variations over multiple loading cycles. Assisted by the non-destructive XRD measurements, this study validates the optimization-improved thermal-mechanical simulation method for predicting not only the as-welded residual stresses in the tubular joints but also the residual stress evolutions during the cyclic loading tests. The most pronounced relaxation of peak residual stresses in the tubular joints occurs within the first cycle and then maintains a relatively stable magnitude in subsequent cycles. The findings of this research contribute to the enhancement of structural reliability and serve as a foundation for mitigating the adverse effects of welding residual stresses in welded tubular joints under cyclic loading scenarios. • This paper reports the experimentally measured residual stress during cyclic loads. • The residual stresses in both X and DK CHS joints relax significantly within 1st cycle. • Numerical analyses predict closely the evolution of residual stresses under cyclic actions. [ABSTRACT FROM AUTHOR]

The paper presents a new composite structure made up of a double-layer microchannel structure, an impinging jet structure, and a turbulent flow structure. In this paper, the combination of these three structures improves the overall thermal performance of the model compared to the basic impingement-jet double-layer nested microchannel heat sinks (IDN-MHS) model. At Reynolds numbers ranging from 138.2 to 580.4 (0.25≤u in ≤1.05), the thermal performance of the model within introduction of bifurcations is enhanced compared to traditional models that only contain double-layer microchannel structures and impact jet structures. Using 3D printers and conducting experiments, it was discovered that numerical simulation and experimental images were generally consistent. Additionally, IDN-MHS with streaming vertical bifurcations, n=6 (IDN-MHS-VB6) performed well in numerical simulations, with a temperature decrease of 1.24K over IDN-MHS when compared to IDN-MHS. In addition, this model performs better than IDN-MHS with streaming vertical bifurcations, n=2, IDN-MHS with streaming vertical bifurcations, n=4, and IDN-MHS with streaming vertical bifurcations, n=8 (IDN-MHS-VB2/4/8). Compared to IDN-MHS, IDN-MHS-VB6 has the outstanding advantage of reducing substrate temperature while maintaining a relatively low pressure drop. • This structure is an innovative combination of double layer microchannel structure and bifurcation structure of impact jet structure. • In the designed composite structure, the highest substrate temperature is 1.23 K lower than IDN-MHS. • The innovative structure designed has an acceptable pressure drop. • The designed bifurcation structure can effectively increase the coolant flow rate and reduce the substrate temperature. • The IDN-MHS-VB6 allows the coolant to come into contact with more high-temperature areas, achieving cooling effect. [ABSTRACT FROM AUTHOR]

In this paper we propose a solution strategy for the Cahn-Larché equations, which is a model for linearized elasticity in a medium with two elastic phases that evolve subject to a Ginzburg-Landau type energy functional. The system can be seen as a combination of the Cahn-Hilliard regularized interface equation and linearized elasticity, and is non-linearly coupled, has a fourth order term that comes from the Cahn-Hilliard subsystem, and is non-convex and nonlinear in both the phase-field and displacement variables. We propose a novel semi-implicit discretization in time that uses a standard convex-concave splitting method of the nonlinear double-well potential, as well as special treatment to the elastic energy. We show that the resulting discrete system is equivalent to a convex minimization problem, and propose and prove the convergence of alternating minimization applied to it. Finally, we present numerical experiments that show the robustness and effectiveness of both alternating minimization and the monolithic Newton method applied to the newly proposed discrete system of equations. We compare it to a system of equations that has been discretized with a standard convex-concave splitting of the double-well potential, and implicit evaluations of the elasticity contributions and show that the newly proposed discrete system is better conditioned for linearization techniques. [ABSTRACT FROM AUTHOR]

This paper studies the effects of liquid oxidizer flow distribution on combustion characteristics and performance of hybrid rocket motor with axial injection through numerical simulations of two-phase flow. Axial injection is widely used in hybrid rocket motor, however, the regression of burning surface may change combustion efficiency of the motor at different moments. Consequently, it is necessary for hybrid rocket motor to design injector patterns that could increase the average combustion efficiency in the whole operating process. The orifice injector plate is divided into three areas, which are recorded as zone I, zone II and zone III, respectively. Oxidizer flow distribution is achieved through changing the diameter of injector holes in various zones, and three-dimensional steady numerical simulations of two-phase flow of hybrid rocket motor with axial injector patterns at different moments are conducted. The motor adopts 98% hydrogen peroxide and hydroxyl-terminated polybutadiene as the propellants. Numerical analysis reveals that oxidizer flow distribution mainly influences the flow field structure in the pre-combustion chamber and front part of fuel grain port. Increasing oxidizer mass flow rate in zone III is beneficial for the chamber head thermal environment. Relative position in the radial direction of fuel grain inner surface and oxidizer distributed in the injector plate affects fuel regression rates, and the influence mainly exists in the front part of solid fuel grain. When the oxidizer mass flow rate in zone I is equal, the average fuel regression rate rises with the increase of oxidizer flow rate in zone II at initial moment, and decreases as the oxidizer in zone II increases at middle moment. The average combustion efficiency increases with the increase of oxidizer mass flow rate in zone II when the oxidizer in zone I remains unchanged. Both the average combustion efficiency and the chamber head thermal protection need to be considered in the design of axial injector patterns. Research results of this paper provide an important reference for the design of high performance injector patterns of hybrid rocket motor. • Effects of oxidizer flow distribution on hybrid rocket motor performance are studied. • Steady two-phase flow simulations for various injector patterns are conducted. • Adding oxidizer in zone III is good for thermal environment of the chamber head. • Relative position of fuel inner surface and oxidizer affects fuel regression rates. • When zone I is fixed, combustion efficiency raises with oxidizer in zone II adding. [ABSTRACT FROM AUTHOR]