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This paper presents a direct 3D numerical simulation of biaxial surface wrinkling of thin metal film on a compliant substrate. The selected compliant substrate is a commercial Scotch tape on which a gold metal thin film has been transferred by using low adhesion between the thin metal film and polyimide substrate. Compared with the previous fabrication of a cylindrical thin-film wrinkling pattern, an undulated wrinkling pattern has been implemented by increasing the width of the thin metal film in order to create biaxial straining in the thin film. To understand the wrinkling behavior due to biaxial loading, a simple direct numerical simulation based on material imperfections defined in the compliant substrate has been conducted. Through modeling and simulation, it was found that the wrinkling mode is determined by the biaxiality ratio (BR), the ratio between transversal strain and longitudinal strain. Depending on the BR, the wrinkling mode belongs to one of the cylindrical, undulated (or herringbone), checkerboard, or labyrinth modes as a function of applied strain. The cylindrical wrinkling is dominant at the input of BR less than 0.5, while the undulated (or herringbone) ones become dominant just after the onset of the wrinkling pattern at BR greater than 0.9. Through the comparison of the wrinkling patterns between simulation and experiment, the applied BR of the fabricated thin film has been successfully estimated. [ABSTRACT FROM AUTHOR]

This paper presents a 3D direct numerical simulation of buckled thin-film packaging based on transferred elastic thin-film wrinkling bonded on a compliant polymer ring. The mode change of the fabricated thin-film cap is found by measuring the thin-film cap shape at different times after Si substrate debonding. The conventional linear and nonlinear buckling simulations are not adequate to understand the behavior of the thin-film buckling mechanism creating such packaging cap mode change. Direct buckling simulation is recently reported as an easy and useful numerical wrinkling simulation method. A novel 3D FEM model of a thin-film package suitable for direct 3D buckling simulation is built to reduce the mode mixture between different buckling modes. Buckling modes of the packaging cap are investigated in terms of elastic moduli of package materials and applied strain due to thermal expansion coefficient difference. Based on the simulation results, it is found that there are two main modes in the fabricated thin-film buckling package determining the shape of the transferred thin-film packaging cover depending on the elasticity ratio between the cap and sealing ring materials. The mode shift from wrinkling cap mode to out-of-plane cap mode due to applied strain along a polymeric sealing ring is found. [ABSTRACT FROM AUTHOR]

This paper presents a direct 3D numerical simulation of biaxial surface wrinkling of thin metal film on a compliant substrate. The selected compliant substrate is a commercial Scotch tape on which a gold metal thin film has been transferred by using low adhesion between the thin metal film and polyimide substrate. Compared with the previous fabrication of a cylindrical thin-film wrinkling pattern, an undulated wrinkling pattern has been implemented by increasing the width of the thin metal film in order to create biaxial straining in the thin film. To understand the wrinkling behavior due to biaxial loading, a simple direct numerical simulation based on material imperfections defined in the compliant substrate has been conducted. Through modeling and simulation, it was found that the wrinkling mode is determined by the biaxiality ratio (BR), the ratio between transversal strain and longitudinal strain. Depending on the BR, the wrinkling mode belongs to one of the cylindrical, undulated (or herringbone), checkerboard, or labyrinth modes as a function of applied strain. The cylindrical wrinkling is dominant at the input of BR less than 0.5, while the undulated (or herringbone) ones become dominant just after the onset of the wrinkling pattern at BR greater than 0.9. Through the comparison of the wrinkling patterns between simulation and experiment, the applied BR of the fabricated thin film has been successfully estimated.

This paper presents a direct numerical simulation for the extraction of material properties based on thin-film wrinkling on scotch tape. Conventional FEM-based buckling simulation sometimes requires complex modeling techniques concerning mesh element manipulation or boundary conditions. The direct numerical simulation differs from FEM (finite element method)-based conventional two-step linear–nonlinear buckling simulation in that mechanical imperfections are directly applied into the elements of the simulation model. Hence, it can be performed in one step to find the wrinkling wavelength and amplitude, which are key parameters to extract the material mechanical properties. Moreover, the direct simulation can reduce simulation time and modeling complexity. Using the direct model, the effect of the number of imperfections on wrinkling characteristics was first studied, and then wrinkling wavelengths depending on the elastic moduli of the associated materials were prepared for the extraction of material properties. Thin-film wrinkling test patterns on scotch tape were fabricated using the transfer technique with low adhesion between metal films and the polyimide substrate. The material properties of the thin metal films were determined by comparing the measured wrinkling wavelengths and the proposed direct simulation results. By consequence, the elastic moduli of 300 nm thick gold film and 300 nm thick aluminum were determined as 250 GPa and 300 GPa, respectively. [ABSTRACT FROM AUTHOR]

Numerical-statistical projective estimates for solutions of integral equations are constructed and optimized using Legendre polynomials as motivated by the computational complexity of orthogonal expansions with an adapted weight. By applying analytical and corresponding numerical computations, the mean-square error is minimized as a function of the length of the projection expansion segment, while the sample size for the expansion coefficients is fixed. The proposed technique is successfully verified in a test problem close to the Milne one and is found to be more effective than the regularized expansion in terms of Laguerre polynomials. [ABSTRACT FROM AUTHOR]

This paper presents a 3D direct numerical simulation of buckled thin-film packaging based on transferred elastic thin-film wrinkling bonded on a compliant polymer ring. The mode change of the fabricated thin-film cap is found by measuring the thin-film cap shape at different times after Si substrate debonding. The conventional linear and nonlinear buckling simulations are not adequate to understand the behavior of the thin-film buckling mechanism creating such packaging cap mode change. Direct buckling simulation is recently reported as an easy and useful numerical wrinkling simulation method. A novel 3D FEM model of a thin-film package suitable for direct 3D buckling simulation is built to reduce the mode mixture between different buckling modes. Buckling modes of the packaging cap are investigated in terms of elastic moduli of package materials and applied strain due to thermal expansion coefficient difference. Based on the simulation results, it is found that there are two main modes in the fabricated thin-film buckling package determining the shape of the transferred thin-film packaging cover depending on the elasticity ratio between the cap and sealing ring materials. The mode shift from wrinkling cap mode to out-of-plane cap mode due to applied strain along a polymeric sealing ring is found.

Solute transport in unsaturated porous media is of interest in many engineering and environmental applications. The interplay between small-scale, local forces and the porous microstructure exerts a strong control on the transport of fluids and solutes at the larger, macroscopic scales. Heterogeneity in pore geometry is intrinsic to natural materials across a large range of scales. This multiscale nature, and the intricate links between two-phase flow and solute transport, remain far from well understood, by and large. Here, we use high-resolution direct simulation to quantify solute mixing and dispersion behavior within correlated porous media during drainage under an unfavorable viscosity ratio. Through analysis of flow and transport at multiple realizations, we find that increasing spatial correlations in pore sizes increase the size of the required Representative Elementary Volume (REV). We show that increasing the correlation length enhances solute dispersivity through its impact on the spatial distribution of low-velocity (diffusion-dominated) and high-velocity (advection-dominated) regions. Fluid saturation is shown to directly affect diffusive mass flux among high- and low-velocity zones. Another indirect effect of correlated heterogeneity on solute transport is through its control of the drainage patterns via repeated alteration in the connectivity of flowing pathways. Our findings improve quantitative understanding of solute mixing and dispersion under two-phase conditions, highly relevant to some of our most urgent environmental problems. [Display omitted] • Solute transport in correlated media studied by numerical simulation. • Solute dispersion increases with correlation length in pore sizes. • A lower degree of saturation enhances the contribution of diffusive forces to transport. • High local randomness in pore size distribution can potentially destabilize interface. • Unsaturated transport can be impacted by even a minute pore-scale event. [ABSTRACT FROM AUTHOR]

To solve problems of radiation balance, optical sounding, and tomography, it may be necessary to take into account multiple scattering of radiation in a stochastically inhomogeneous medium. In real radiation models, for this purpose, the numerical-statistical 'majorant cross-section method' (MCM, delta-Woodcock tracking) is used based on the alignment of the optical density field by adding an artificial 'delta scattering' event. However, the computation cost of the corresponding unbiased estimate of the averaged problem solution infinitely increases as the correlation scale (correlation radius L) of standard mosaic models for a random medium density decreases. Previously, we constructed the MCM randomization providing asymptotically (for L → 0) unbiased estimates of the required functionals, in which the value of the physical attenuation coefficient is randomly chosen at the end of the particle free path l under condition l > L. Otherwise the value of the physical attenuation coefficient is the same as at the starting point of the particle (CR algorithm). In a more accurate functional correlative randomized algorithm (FCR algorithm), the coefficient remains the same with a probability determined by the correlation function. These correlative randomized algorithms were implemented for a mixture of homogeneous substance (water) and a Poisson ensemble of 'empty' balls. In the present paper, we construct correlative randomized algorithms for problems related to transfer through a 'thick' layer containing a water and a Poisson ensemble of 'empty' layers. A detailed comparative analysis of the results obtained by exact direct simulation (MCM) and approximate algorithms (CR, FCR) for the problems of gamma radiation transfer through a 'thick' water layer containing a Poisson ensemble of 'empty' layers or balls is presented. [ABSTRACT FROM AUTHOR]

The problem of minimizing the root-mean-square error of the numerical-statistical projection estimation of the solution to an integral equation is solved. It is shown that the optimal estimator in this sense can be obtained by equalizing deterministic and stochastic components of the error in the case when the norm of the remainder of the utilized decomposition decreases inversely proportional to its length. As a test, the Milne problem of radiation transfer in a semi-infinite layer of matter is solved using Laguerre polynomials. To solve such a problem in the case of a finite layer, a special regularized projection algorithm is used. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes an extension of the finite cell method (FCM) to V-rep models, a novel geometric framework for volumetric representations. This combination of an embedded domain approach (FCM) and a new modeling framework (V-rep) forms the basis for an efficient and accurate simulation of mechanical artifacts, which are not only characterized by complex shapes but also by their non-standard interior structure. These types of objects gain more and more interest in the context of the new design opportunities opened by additive manufacturing, in particular when graded or micro-structured material is applied. Two different types of functionally graded materials (FGM) are considered: The first one, multi-material FGM is described using the inherent property of V-rep models to assign different properties throughout the interior of a domain. The second, single-material FGM—which is heterogeneously micro-structured—characterizes the effective material behavior of representative volume elements by homogenization and performs large-scale simulations using the embedded domain approach.

This paper presents a direct numerical simulation for the extraction of material properties based on thin-film wrinkling on scotch tape. Conventional FEM-based buckling simulation sometimes requires complex modeling techniques concerning mesh element manipulation or boundary conditions. The direct numerical simulation differs from FEM (finite element method)-based conventional two-step linear–nonlinear buckling simulation in that mechanical imperfections are directly applied into the elements of the simulation model. Hence, it can be performed in one step to find the wrinkling wavelength and amplitude, which are key parameters to extract the material mechanical properties. Moreover, the direct simulation can reduce simulation time and modeling complexity. Using the direct model, the effect of the number of imperfections on wrinkling characteristics was first studied, and then wrinkling wavelengths depending on the elastic moduli of the associated materials were prepared for the extraction of material properties. Thin-film wrinkling test patterns on scotch tape were fabricated using the transfer technique with low adhesion between metal films and the polyimide substrate. The material properties of the thin metal films were determined by comparing the measured wrinkling wavelengths and the proposed direct simulation results. By consequence, the elastic moduli of 300 nm thick gold film and 300 nm thick aluminum were determined as 250 GPa and 300 GPa, respectively.

A comparative analysis of various projection Monte Carlo algorithms as applied to estimating the particle flow through a layer of medium with scattering of the Henyey–Greenstein type is carried out. The possibility of minimizing the mean-square error by equalizing the corresponding stochastic and deterministic terms is investigated. [ABSTRACT FROM AUTHOR]

We propose a novel discrete method of constructing Gaussian Random Fields based on a combination of modified spectral representations, Fourier and Blob. The method is intended for Direct Numerical Simulations of the V-Langevin equations. The latter are stereotypical descriptions of anomalous stochastic transport in various physical systems. From an Eulerian perspective, our method is designed to exhibit improved convergence rates. From a Lagrangian perspective, our method offers a pertinent description of particle trajectories in turbulent velocity fields: the exact Lagrangian invariant laws are well reproduced. From a computational perspective, the computing time is reduced by a factor of two in comparison with Fourier-like or Blob-like methods and an order of magnitude in comparison with FFT algorithms. [ABSTRACT FROM AUTHOR]

A three-dimensional direct simulation was carried out to examine the natural convective fluid flow and heat transfer characteristics in a long enclosure with a twisted cylinder. The effects of the Rayleigh number, dimensionless mean radius, and wavelength (or wavenumber) for a twisted cylinder were investigated. In addition to the heat transfer characteristics at cylinder and enclosure, the distributions of temperature and fluid flow are also presented by the iso-surfaces of temperature and vortical structure formed inside the enclosure. An artificial neural network was applied to predict the characteristics of natural convective flow and heat transfer by considering various simulation parameters for the elliptical and twisted cylinders. The input parameters considered in this study significantly affect on the heat transfer characteristics at cylinder and enclosure. [ABSTRACT FROM AUTHOR]

This paper proposes an extension of the finite cell method (FCM) to V-rep models, a novel geometric framework for volumetric representations. This combination of an embedded domain approach (FCM) and a new modeling framework (V-rep) forms the basis for an efficient and accurate simulation of mechanical artifacts, which are not only characterized by complex shapes but also by their non-standard interior structure. These types of objects gain more and more interest in the context of the new design opportunities opened by additive manufacturing, in particular when graded or micro-structured material is applied. Two different types of functionally graded materials (FGM) are considered: The first one, multi-material FGM is described using the inherent property of V-rep models to assign different properties throughout the interior of a domain. The second, single-material FGM—which is heterogeneously micro-structured—characterizes the effective material behavior of representative volume elements by homogenization and performs large-scale simulations using the embedded domain approach. [ABSTRACT FROM AUTHOR]

Although solving inverse dynamics problems is performed a lot in literature, none of the previous references addressed the general unrestricted solution of three dimensional (3D) trajectories of guided gliders. This glider could be any subsonic flying body such as guided ammunitions. Inverse dynamics could be one of the key techniques of solving similar problems. In this paper, 3D trajectory generation and following are performed. The trajectory generation is divided into three phases: heading correction, glide and terminal phases. The solution of the inverse problem is performed analytically, using the Mu-Pad tool. Next, a special formulation of the general dynamics equations enables the solution of such a problem and the calculation of the required deflection angles. Finally, a six degrees of freedom (6DoF) direct simulation is performed using the obtained deflection angles in order to compare its trajectory with the generated one. This comparison yields fairly good results and validates the quality of the proposed inverse dynamics solution. [ABSTRACT FROM AUTHOR]

This paper presents a simulation of the movement of an aircraft that has an engine malfunction. The nonlinear equations of motion are formulated taking into account the yawing moment which is generated and occurs due to the asymmetry of the thrust line. For this simulation the equations are solved directly to find the trajectory of the aircraft and the variations of angles, angular rates, and velocities with time. An initial conditions is required for the simulation as (𝑉,𝛽,𝛿𝑟,𝛿𝑎,𝑇,𝑝,𝑞,𝑟,𝜙,𝜓,𝛾) and a trim condition is calculated to get the angle of attack. The derivatives of angular, linear velocities, angles, moments and position derivatives are calculated. The derivatives calculated are solved using ordinary differential equations solution 4th order Rung Kutta method to get the yawing, pitching, rolling moments, velocity, angle of attack, side slip angle and trajectory of the aircraft according to control surfaces deflections and thrust as inputs.

The problem relating to the formation of solid particles enabled by hypersonic re-entry in methane-containing atmospheres (such as that of Titan) has been tackled in the framework of a combined experimental–numerical approach implemented via a three-level analysis hierarchy. First experimental tests have been conducted using a wind tunnel driven by an industrial arc-heated facility operating with nitrogen as working gas (the SPES, i.e., the Small Planetary Entry Simulator). The formation of solid phases as a result of the complex chemical reactions established in such conditions has been detected and quantitatively measured with high accuracy. In a second stage of the study, insights into the related formation process have been obtained by using multispecies models relying on the NASA CEA code and the Direct Simulation Monte Carlo (DSMC) method. Through this approach the range of flow enthalpies in which carbonaceous deposits can be formed has been identified, obtaining good agreement with the experimental findings. Finally, the deposited substance has been analyzed by means of a set of complementary diagnostic techniques, i.e., SEM, spectroscopy (Raman, FTIR, UV–visible absorption and fluorescence), GC–MS and TGA. It has been found that carbon produced by the interaction of the simulated Titan atmosphere with a solid probe at very high temperatures can be separated into two chemically different fractions, which also include “tholins”.

Highlights • An improved model for direct simulation of fibers in viscous flow is developed. • Fiber motions in simple shear flow are compared between the proposed and conventional model. • Fiber motions in injection molding are also simulated. • The improved model well reproduces the results of the conventional one. • The model also provides higher computational efficiency than the conventional one. Abstract This paper proposes an efficient model for simulating fiber motion in viscous flow, especially during molding of fiber-reinforced thermoplastics. To increase the computational efficiency, the proposed model discretizes fibers as chains of fewer spheres than in the bead-chain model previously proposed by the authors, which is called the Simplified Bead-Chain Model (SBCM). In addition, in order to make the proposed model reproduce the results of the SBCM, correction factors applied to forces exerted on each sphere are newly derived so that the equation of motion of a fiber for the proposed model can be equivalent to that of the conventional model. Simulations of rigid and flexible fibers in simple shear flow are first performed to compare the fiber motions between the two models. The proposed model reproduces the results of the SBCM closely for cases of both a single fiber and suspensions containing multiple fibers. Finally, fiber orientation behavior during injection molding in a simple-shaped plaque is simulated. The results obtained with the proposed model shows good agreement with those of the SBCM but at lower computational cost. [ABSTRACT FROM AUTHOR]

A new finite strain elastoplastic J2-flow model with thermo-coupled effects is proposed for the purpose of simulating cyclic and non-cyclic thermo-coupled fatigue failure behavior of metals. Novelties in four respects are incorporated in the proposed model: (i) the usual notion of yielding is rendered irrelevant with a smooth transition from the elastic to the plastic state; (ii) the thermodynamic consistency stipulated by the second law is identically ensured; (iii) asymptotic loss of the strength in cyclic and non-cyclic thermomechanical processes is incorporated as inherent constitutive features; and, accordingly, (iv) the fatigue failure behavior may be derived as direct consequences of the proposed model, without involving any additional failure criteria and any additional variables. Thermo-coupled responses of a metal bar with two fixed ends under cyclic heating and cooling over various temperature ranges are studied based on a simple case of the proposed model. Results are obtained for the maximum tensile and compressive stresses changing with the cycle number and, in particular, for the thermal fatigue life versus the temperature amplitude. Model predictions compare well with test data. [ABSTRACT FROM AUTHOR]

This paper investigates the applicability of direct simulation considering a stratified atmosphere to an unsteady analysis of a blast wave caused by a meteorite explosion. Axi-symmetric Euler equations with a gravity term that considers a horizontally stratified atmosphere are numerically solved to analyze blast wave propagation from the source of meteorite explosion to the ground. Computations are made to reproduce the blast wave generated by the Chelyabinsk meteorite in 2013, assuming a spherically uniform high-pressure and high-temperature core as the source of explosion. The amount of energy released by the explosion at an altitude of 25 km is assumed to be 500 kt of trinitrotoluene, and the computational domain ranges over a radial distance of 50 km from the center of the explosion. The simulation results in a uniform atmosphere agree well with the results of well-known Brode's empirical formula, and the blast wave obtained from the simulation considering a standard atmosphere is expected to cause serious damage to the ground, as experienced at the time of the Chelyabinsk event. Moreover, the simulation results clarify the characteristics of blast wave propagation through uniform, isothermal, and standard atmospheres. [ABSTRACT FROM AUTHOR]

The evaluation of ship maneuverability characteristics typically involves the mode tests, direct CFD computations, and system-based simulations. The three methods have been widely used in traditional vessels. However, the trimarans, which are appended with the waterjet propulsion systems, have been rarely researched and assessed comprehensively based on the above methods. This paper used a free-running waterjet-propelled trimaran model test to obtain the constant turning and zigzag maneuvering performance in calm water conditions. By embedding the speed and heading controllers in a CFD program, along with the region moving method, a direct free-running maneuvering CFD model was established on a waterjet-propelled trimaran. Compared to the free-running model tests, the simulation results indicated that an empirical hydrodynamic derivative-based Maneuvering Model Group (MMG) method produced the fastest results but lacked accuracy in simulating a constant turning diameter, making it suitable for fast maneuvering estimation and prediction during the design stage. Conversely, a direct force (moment)-based CFD model required more accurate input estimates to acquire acceptable simulated results. Meanwhile, a body force-based CFD model considered more complex nonlinear impacts and was most similar to reality, achieving better agreement with the experimental results. Additionally, the simulations of the direct free-running maneuvering CFD model in calm and wavy water proved advantageous in examining hull-propulsor interaction during physically similar maneuvering processes where the model test was inadequate. • A direct CFD approach for maneuvering of waterjet-propelled trimaran considering hull-propulsor interaction is proposed. • Speed and heading controllers is embedded in the CFD program. • BFM-based direct CFD model shows advantage in trajectory prediction and stern wake details than the DFM-based model. • Accounting for complex geometry and environment, the direct maneuvering CFD approach has the potential to replace model test. [ABSTRACT FROM AUTHOR]

Innovative elastoplastic J 2 − flow models with nonlinear combined hardening are proposed for the purpose of simulating multi-axial thermo-coupled fatigue failure for metals and alloys, in a direct sense without involving any usual damage-like variables and any ad hoc failure criteria. As contrasted with usual models, the yield condition and the loading-unloading conditions need not be imposed as extrinsic coercive conditions but may be automatically incorporated into a free, smooth flow rule in a more realistic sense. Novel results in three respects are available directly from model predictions, namely, (i) complex features of thermo-coupled fatigue failure may be automatically represented by simple asymptotic properties of the hardening functions introduced, (ii) critical failure states may be derived with a criterion in unified form, and, in particular, (iii) direct procedures may be established for determining fatigue lives under either stress cycles or thermal cycles. Simulation results in the simplest cases of the proposed model are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

New elastoplastic J2-flow constitutive equations at finite deformations are proposed for the purpose of simulating the fatigue failure behavior for metal matrix composites. A new, direct approach is established in a two-fold sense of unification. Namely, both low and high cycle fatigue failure effects of metal matrix composites may be simultaneously simulated for various cases of the weight percentage of reinforcing particles. Novel results are presented in four respects. First, both the yield condition and the loading-unloading conditions in a usual sense need not be involved but may be automatically incorporated into inherent features of the proposed constitutive equations; second, low-to-high cycle fatigue failure effects may be directly represented by a simple condition for asymptotic loss of the material strength, without involving any additional damage-like variables; third, both high and low cycle fatigue failure effects need not be separately treated but may be automatically derived as model predictions with a unified criterion for critical failure states, without assuming any ad hoc failure criteria; and, finally, explicit expressions for each incorporated model parameter changing with the weight percentage of reinforcing particles may be obtainable directly from appropriate test data. Numerical examples are presented for medium-to-high cycle fatigue failure effects and for complicated duplex effects from low to high cycle fatigue failure effects. Simulation results are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

A statistical modelling algorithm is constructed for solution of the nonlinear kinetic Boltzmann equation based on the projection method. Hermite polynomials are used as an orthonormalized basis. The algorithm was tested on calculations for the problem of one-dimensional relaxation of gas with a known solution. [ABSTRACT FROM AUTHOR]

SLADS (), a parallel code for direct simulations of X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations, is presented. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. Parallelization is achieved in real space for the sake of memory limitation. The system sizes attempted are up to one billion atoms, and particle concentrations in dense systems up to 0.36. Anisotropy is explored in terms of superlattices. One- and two-dimensional small-angle scattering or diffraction patterns are obtained. SLADS is validated self-consistently or against cases with analytical solutions. [ABSTRACT FROM AUTHOR]

The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and alloys over the whole deformation range up to failure. As contrasted with the usual elastoplasticity models, such new models of much simpler structure are totally free, in the sense that both the yield condition and the loading–unloading conditions need not be introduced as extrinsic coercive conditions but are automatically incorporated as inherent constitutive features into the models. Furthermore, the new models are shown to be thermodynamically consistent, in a further sense that both the specific entropy function and the Helmholtz free energy function may be presented in explicit forms, such that the thermodynamic restriction stipulated by Clausius–Duhem inequality for the intrinsic dissipation may be identically satisfied. Secondly, it is then demonstrated that the thermo-coupled fatigue failure behavior under combined cyclic changes of stress and temperature may be derived as direct consequences from the new models. This novel result implies that the new model can directly characterize the thermo-coupled fatigue failure behavior of metals and alloys, without involving any usual damage-like variables as well as any ad hoc additional criteria for failure. In particular, numerical examples show that, under cyclic changes of temperature, the fatigue characteristic curve of fatigue life versus temperature amplitude may be obtained for the first time from model prediction both in the absence and in the presence of stress. Results are in agreement with the salient features of metal fatigue failure. [ABSTRACT FROM AUTHOR]

This paper presents a simulation of the movement of an aircraft that has an engine malfunction. The nonlinear equations of motion are formulated taking into account the yawing moment which is generated and occurs due to the asymmetry of the thrust line. For this simulation the equations are solved directly to find the trajectory of the aircraft and the variations of angles, angular rates, and velocities with time. An initial conditions is required for the simulation as (V, β, δr, δa, T, p, q, r, φ, ψ, γ) and a trim condition is calculated to get the angle of attack. The derivatives of angular, linear velocities, angles, moments and position derivatives are calculated. The derivatives calculated are solved using ordinary differential equations solution 4th order Rung Kutta method to get the yawing, pitching, rolling moments, velocity, angle of attack, side slip angle and trajectory of the aircraft according to control surfaces deflections and thrust as inputs. [ABSTRACT FROM AUTHOR]

We propose a novel approach— direct simulation —for interactive simulation with accuracy control, for CAD models undergoing parametric modifications which leave Dirichlet boundary conditions unchanged. This is achieved by computing offline a generic solution as a function of the design modification parameters . Using this parametric expression, each time the model parameters are edited, the associated simulation solution for this model instance can be cheaply and quickly computed online by evaluating the derived parametric solution for these parameter values. The proposed approach furthermore works for models undergoing topological changes, and does not need any mesh regeneration or mesh mapping. These results are achieved by use of the proper generalized decomposition model reduction technique, in combination with R-functions. We believe this is the first approach that can interactively simulate the physical properties of a CAD model, even undergoing topological change, without expensive re-computation. The approach is demonstrated for linear elasticity analysis; numerical results demonstrate its simulation accuracy and efficiency in comparison with the classic FE method. [ABSTRACT FROM AUTHOR]

The effect of pore-scale heterogeneity on non-Darcy flow behaviour is investigated by means of direct flow simulations on 3-D images of a beadpack, Bentheimer sandstone and Estaillades carbonate. The critical Reynolds number indicating the cessation of the creeping Darcy flow regime in Estaillades carbonate is two orders of magnitude smaller than in Bentheimer sandstone, and is three orders of magnitude smaller than in the beadpack. It is inferred from the examination of flow field features that the emergence of steady eddies in pore space of Estaillades at elevated fluid velocities accounts for the early transition away from the Darcy flow regime. The non-Darcy coefficient β , the onset of non-Darcy flow, and the Darcy permeability for all samples are obtained and compared to available experimental data demonstrating the predictive capability of our approach. X-ray imaging along with direct pore-scale simulation of flow provides a viable alternative to experiments and empirical correlations for predicting non-Darcy flow parameters such as the β factor, and the onset of non-Darcy flow. [ABSTRACT FROM AUTHOR]

Through mechanical coupling, thermal effects can lead to drifts in circuits׳ electrical performances, as well as integrated circuits reliability issues. It is thus necessary to consider thermal, mechanical and electrical effects all together in a self-consistent manner. This work focuses on the electro-thermo-mechanical simulation of integrated circuits, performed in a unique Computer Aided Design environment, in the target of ICs reliability monitoring from the early design stages. An electro-thermo-mechanical simulation tool was developed using the Cadence® environment and the Spectre® simulator. The simulation principle is based on the direct approach with a mixed compact and finite element modelling. Three networks, i.e. the electrical, the thermal and the mechanical networks are automatically generated, linked together, and then simulated using a single simulator, i.e. Spectre®. The electro-thermal modelling being already developed, this paper is focused on the finite element modelling of the thermo-mechanical effects using the behavioural language Verilog-A. First simulation results on a single silicon cube have been compared with results obtained from COMSOL Multiphysics®, showing a good agreement. Finally a simplified two-material integrated circuit featuring a power device has been simulated in order to show the possibilities of the tool. [ABSTRACT FROM AUTHOR]

Surface science is key to innovations on microfluidics, smart materials, and future non-equilibrium systems. However, challenging issues still exist in this field. In this article, from the viewpoint of the fundamental design, we will briefly review our strategies on improving the micro-fluidic devices using the nonlinear electro- and thermo-kinetic phenomena. In particular, we will review the microfluidic applications using ICEO, the correction based on the ion-conserving Poisson–Boltzmann theory, the direct simulation on ICEO, and the new horizon such as nonlinear thermo-kinetic phenomena and the artificial cilia. [ABSTRACT FROM AUTHOR]

Typically the spreading length-scale in a diffusion process increases in time as [ABSTRACT FROM AUTHOR]

Pore-scale forces have a significant effect on the macroscopic behaviour of multiphase flow through porous media. This paper studies the effect of these forces using a new volume-of-fluid based finite volume method developed for simulating two-phase flow directly on micro-CT images of porous media. An analytical analysis of the relationship between the pore-scale forces and the Darcy-scale pressure drops is presented. We use this analysis to propose unambiguous definitions of Darcy-scale viscous pressure drops as the rate of energy dissipation per unit flow rate of each phase, and then use them to obtain the relative permeability curves. We show that this definition is consistent with conventional laboratory/field measurements by comparing our predictions with experimental relative permeability. We present single and two-phase flow simulations for primary oil injection followed by water injection on a sandpack and a Berea sandstone. The two-phase flow simulations are presented at different capillary numbers which cover the transition from capillary fingering at low capillary numbers to a more viscous fingering displacement pattern at higher capillary numbers, and the effect of capillary number on the relative permeability curves is investigated. Overall, this paper presents a new finite volume-based methodology for the detailed analysis of two-phase flow directly on micro-CT images of porous media and upscaling of the results to the Darcy scale. [ABSTRACT FROM AUTHOR]

A multivariate probability transformation between random variables, known as the Nataf transformation, is shown to be the appropriate transformation for multi-Gaussian kriging. It assumes a diagonal Jacobian matrix for the transformation of the random variables between the original space and the Gaussian space. This allows writing the probability transformation between the local conditional probability density function in the original space and the local conditional Gaussian probability density function in the Gaussian space as a ratio equal to the ratio of their respective marginal distributions. Under stationarity, the marginal distribution in the original space is modeled from the data histogram. The stationary marginal standard Gaussian distribution is obtained from the normal scores of the data and the local conditional Gaussian distribution is modeled from the kriging mean and kriging variance of the normal scores of the data. The equality of ratios of distributions has the same form as the Bayes' rule and the assumption of stationarity of the data histogram can be re-interpreted as the gathering of the prior distribution. Multi-Gaussian kriging can be re-interpreted as an updating of the data histogram by a Gaussian likelihood. The Bayes' rule allows for an even more general interpretation of spatial estimation in terms of equality for the ratio of the conditional distribution over the marginal distribution in the original data uncertainty space with the same ratio for a model of uncertainty with a distribution that can be modeled using the mean and variance from direct kriging of the original data values. It is based on the principle of conservation of probability ratio and no transformation is required. The local conditional distribution has a variance that is data dependent. When used in sequential simulation mode, it reproduces histogram and variogram of the data, thus providing a new approach for direct simulation in the original value space. [ABSTRACT FROM AUTHOR]

Abstract: X-ray micro computed tomography (μ-CT), originally developed for non-destructive biomedical imaging, is increasingly being employed in areas as diverse as materials characterization and reverse engineering. The technique employs computer processed X-rays to produce tomographic images or slices of specific regions of the object under investigation. This paper presents a numerical analysis of air flow through four different high-porosity ERG copper foams having different pore sizes (5, 10, 20, and 40 pores per inch, PPI), and approximately the same relative density (6.4-6.6% solid fraction). These samples were scanned with a commercial micro computed tomography scanner at a resolution of 20μm, yielding a stack of two- dimensional images. Starting with these two-dimensional images, the real, random structure of the foams was reconstructed and subsequently meshed using the commercial software Simpleware. Meshes thus produced were then exported to FLUENT for simulating the fluid flow through the pore space of the foam samples. The results of μ-CT based CFD computations are compared against experimental measurements of pressure drop that were previously obtained with the same samples. The comparison reveals excellent agreement between the numerical and experimental results, highlighting the accuracy of this novel approach. [Copyright &y& Elsevier]

Sintered porous structures are ubiquitous as heat transport media for thermal manage-ment and other applications. In particular, low-porosity sintered packed beds are used as capillary-wicking and evaporation-enhancement structures in heat pipes. Accurate pre-diction and analysis of their transport characteristics for different microstructure geome-tries is important for improved design. Owing to the random nature and geometric complexity of these materials, development of predictive methods has been the subject of extensive prior research. The present work summarizes and builds upon past studies and recent advances in pore-scale modeling of fluid and thermal transport within such hetero-geneous media. A brief review of various analytical and numerical models for simplified prediction of transport characteristics such as effective thermal conductivity, permeabil-ity, and interfacial heat transfer is presented. More recently, there has been a growing in-terest in direct numerical simulation of transport in realistic representations of the porous medium geometry; for example, by employing nondestructive 3D imaging techni-ques such as X-ray microtomography. Future research directions are identified, looking beyond techniques intended for material characterization alone, and focusing on those targeting the reverse engineering of wick structures via modeling of the physical sintering fabrication processes. This approach may eventually be employed to design intricate sin-tered porous structures with desired properties tailored to specific applications. [ABSTRACT FROM AUTHOR]

We apply an accurate numerical scheme to solve for Stokes flow directly on binarized three-dimensional rock images, such as those obtained by micro-CT imaging. The method imposes no-flow conditions exactly at the solid boundaries and employs an algebraic multigrid method to solve for the resultant set of linear equations. We compute the permeability of a range of consolidated and unconsolidated porous rocks; the results are comparable with those obtained using the lattice Boltzmann method and agree with experimental measurements on larger core samples. We show that the Kozeny-Carman equation can over-estimate permeability by a factor of 10 or more, particularly for the more heterogeneous systems studied. We study the existence and size of the representative elementary volume (REV) at lamina scale. We demonstrate that the REV for permeability is larger than for static properties-porosity and specific surface area-since it needs to account for the tortuosity and connectedness of the flow paths. For the carbonate samples, the REV appeared to be larger than the image size. We also study the anisotropy of permeability at the pore scale. We show that the permeability of sandpacks varies by less than 10 % in different directions. For sandstones, permeability changes by 25 % on average. However, the anisotropy of permeability in carbonates can be up to 50 %, indicating the existence of connected pores in one direction which are not connected in another. [ABSTRACT FROM AUTHOR]

The oro-pharyngeal-laryngeal human airway is a complex geometry; the flow physics within are subjected to and influenced by a variety of different factors that produce jet-like flow, re-circulating flows that are enhanced by curvature, detached and secondary flows. Simulation and experiment are the tools available to the fluid dynamics researcher. Simulation results obtained from direct and large-eddy simulation, and Reynolds-averaged Navier–Stokes and associated models of turbulence are reviewed. Experimental data obtained through the use of flow visualisation, hot-wire anemometry and particle image velocimetry are also reviewed. A comparison of data obtained from the application of these tools reveals many inconsistencies that are explored in this article. While much progress has been made to understand some of the physics of the flow in the human airway, we continue to uncover new and significant fluid dynamic behaviour. Finally, future research directions are suggested. [ABSTRACT FROM AUTHOR]

With coupled weakly-damped periodically driven bistable oscillators subjected to additive and multiplicative noises under concern, the objective of this paper is to check to what extent the resonant point predicted by the Gaussian distribution assumption can approximate the simulated one. The investigation based on the dynamical mean-field approximation and the direct simulation demonstrates that the predicted resonant point and the simulated one are basically coincident for the case of pure additive noise, but for the case including multiplicative noise the situation becomes somewhat complex. Specifically speaking, when stochastic resonance (SR) is observed by changing the additive noise intensity, the predicted resonant point is lower than the simulated one; nevertheless, when SR is observed by changing the multiplicative noise intensity, the predicted resonant point is higher than the simulated one. Our observations imply that the Gaussian distribution assumption can not exactly describe the actual situation, but it is useful to some extent in predicting the low-frequency stochastic resonance of the coupled weakly-damped bistable oscillator. [ABSTRACT FROM AUTHOR]