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The bond-based peridynamics and its extended forms are widely used for crack predicting in many materials like concrete. In peridynamics, as for the bond failure, the tensile failure criterion or tensile-compression failure criterion are commonly applied, the combined tensile-shear or compression-shear failure are rarely considered. In this paper, a Cosserat peridynamic model with a novel bond failure criterion (CPD-BP) is proposed for concrete fracture simulation. The peridynamic bond failure criterion is derived from the Bresler–Pister criterion, with which the composite bond failure can be considered properly. Besides, the Cosserat parameters which relate to microstructures of concrete are introduced. Three benchmarks are designed: simple tensile, direct shear, and compression tests. Results show that the CPD-BP can simulate the combined tensile-shear and compressive-shear concrete failure. Crack patterns predicted by CPD-BP generally follow particle flow code in two dimensions results and physical experiments. The larger Cosserat shear modulus will enhance the shear effects. [ABSTRACT FROM AUTHOR]

In this paper, a novel locking-free finite beam element is proposed utilizing the absolute nodal coordinate formulation. By incorporating a gradient vector along the transverse direction at the boundary points, the linear interpolation of the gradient vector field within this element is achieved. Consequently, the problem of constant transverse strain distribution, which is observed in the Omar–Shabana beam element, is effectively addressed. Building upon this concept, this study further extends the proposed element from two dimensions to three dimensions. Additionally, it analyzes and compares the locking alleviation mechanism of the newly developed element and Patel–Shabana beam element. The analysis aims to provide insights into the factors contributing to the locking alleviation of different absolute nodal coordinate formulation (ANCF) elements. Furthermore, to demonstrate the effectiveness of the new element, six numerical simulation examples are designed, comprising three and three dynamic examples. These examples encompass small deformation statics, large deformation statics, small-scale motion, large-scale motion, and rotational motion problems. Finally, the results indicate that the proposed ANCF beam element can effectively alleviate the locking problem. The element exhibits robust adaptability, rationality, and effectiveness when subjected to complex mechanical characteristics by comparing the numerical results of this element with the classical Omar–Shabana, high-order Shen, and Patel–Shabana elements. [ABSTRACT FROM AUTHOR]

The mechanism of drag reduction via polymer additives is long debated in the literature. This journal published a paper (Volokh in Acta Mech 229(10):4295–4301, 2018), in which the drag reduction was explained based on the Navier–Stokes model enhanced with the viscous strength. This explanation was limited by a qualitative consideration of the onset of material instability in the laminar pipe flow. In the present work, we use the theoretical setting of Volokh (2018) in 3D numerical simulations of the realistic pipe flow where material instabilities develop into turbulence. We observe in the simulations that the addition of the polymer solute suppresses the chaotic turbulent motion, indeed, in accordance with the experimental observations of the phenomenon. [ABSTRACT FROM AUTHOR]

In this paper, a rectangular bistable composite laminated plate is studied through dynamic modeling, numerical simulation and experiment. A theoretical model is elucidated, elaborating the dynamic snap-through and nonlinear dynamics of the rectangular bistable composite laminated plate. The potential energy curve, the restoring force curve and the stiffness curve are graphically presented, exhibiting differences from those of square bistable plates. The two potential wells and the negative stiffness region are asymmetric. The dynamic snap-through elucidated by curvature and displacement is graphically presented in phase diagrams and time history diagrams. Due to the asymmetry of the double potential wells, the dynamic snap-through may be unidirectional rather than repeated, and the nonlinear dynamic responses around the two potential wells are asymmetric, which depends on initial positions. In frequency sweep, the frequency-amplitude response curves are characterized by the softening nonlinear stiffness effect and the hysteresis, where there are multiple peaks displaying the first several modes of the rectangular bistable plate around one stable state. The nonlinear dynamic responses are characterized by the periodic and chaotic vibrations, the 1/2 subharmonic resonance, the unidirectional dynamic snap-through and the repeated dynamic snap-through. When the excitation frequency is equal to the first mode frequency for the lower stable state or the third mode frequency for the upper stable state, the dynamic snap-through is found to occur. Linear mode frequencies can show the mechanism of the snap-through to a certain extent. At mode frequencies, sufficient energy is gathered to actuate the snap-through. Unlike square bistable plates, rectangular bistable plates may only be characterized by the unidirectional snap-through under the specific energy input, which depends on initial positions. For rectangular bistable plates, two opportune excitation frequencies that have to be selected can lead to the repeated snap-through. This research is beneficial to the development of aerospace structures, bistable energy harvesters and vehicle vibration isolation devices. Compared to the old work, this work is more in line with the actual situation, where a high aspect ratio morphing wing can adjust its airfoil according to different tasks based on rectangular bistable plates which are more suitable for potential applications in the future. [ABSTRACT FROM AUTHOR]

This paper presents a novel framework combining the state-based peridynamics (SBPD) with the extended finite element method (XFEM) for crack propagation in two-dimensional solids. Numerical examination is conducted fulfilling both the quasi-static and time-dependent loading conditions. The computational domain is partitioned into two regions: (a) SPBD region: the vicinity of crack tips and potential region where the crack is likely to propagate, and (b) XFEM region: the area behind the crack tip and the rest of the body. The salient features of the developed framework include: (a) avoiding requirement of a priori knowledge of enrichment functions like the conventional XFEM; (b) without fracture criteria for crack propagation; (c) no restriction on the value of Poisson's ratio like the bond-based peridynamics; and (d) higher computational efficiency than the pure peridynamics. The efficiency and accuracy of the proposed framework are systematically demonstrated through benchmark examples involving quasi-static crack growth and dynamic crack branching problems. [ABSTRACT FROM AUTHOR]

A ring mesh is a large-scale manufacturable structure with versatile applications in architecture and for protective systems. However, the static and dynamic numerical simulation of a large-scale ring mesh is a resource-intensive task due to the many nonlinear contact points between the individual rings. To characterize the rigid body behavior of the ring mesh, in this paper, a representative volume element is loaded under different in-plane directions. The Green-Lagrangian strain tensor components are obtained as a result. An implicit one-step algorithm is used for this dynamic relaxation issue, modified by the use of stiff springs. Static convergence positions of a representative volume element are determined in several multiaxial tensile directions. The obtained deformation parameters can be used to simulate large deformations of large-scaled ring meshes. [ABSTRACT FROM AUTHOR]

The effects of cracks on the dynamic behavior of engineering structures affect the structure safety. In this paper, a generalized multi-symplectic approach is developed to investigate the effects of crack on a dynamic behavior of a simply supported beam in detail. First, the effect of the crack on the bending stiffness of the simply supported beam is expressed by an equivalent bending stiffness and the dynamic model with variable coefficients is established to describe the transverse vibration of the cracked beam. Then, the approximate symmetric form of the dynamic model is constructed and its dynamic symmetry breaking factors are discussed. The Preissmann scheme of the approximate symmetric form is constructed based on the generalized multi-symplectic theory. In numerical simulations, the structure-preserving properties of the Preissmann scheme are illustrated and the validity of the dynamic model is verified. Then, the effects of the crack on the vibration of the beam are investigated by using the generalized multi-symplectic method in detail. The numerical results presented prove that the proposed generalized multi-symplectic method is an effective approach to investigate the dynamic behavior of cracked structures. [ABSTRACT FROM AUTHOR]

Accurate control of mixing between two fluids is a fundamental aspect in many applications and generally implies the use of small devices operating at low velocities. This is often achieved using micromixers which, due to the combination of small dimensions and low velocities, work in the laminar regime and generally process very limited flow rates. The flow rates can be increased using more mixers at the same time. In this respect it is appealing to use several micromixers connected in a unique device. In this paper we propose and characterize a simple strategy to connect several T-mixers together by aligning them in a row and feeding them by shared inlet channels. Since engulfment is the preferred flow regime for mixing, we investigate the proposed devices specifically focusing on the onset and on the properties of the engulfment regime. This investigation is carried out by a combined use of numerical simulation and linear stability analysis. The results reported here show that the proposed strategy can lead to compact devices in which the single mixers manifest engulfment, although some important differences in comparison with isolated T-mixers may exist depending on the spacing between the inlet/outlet channels in the device. [ABSTRACT FROM AUTHOR]

The natural processes involved in the scouring of submerged sediments are crucially relevant in geomorphology along with environmental, fluvial, and oceanographic engineering. Despite their relevance, the phenomena involved are far from being completely understood, in particular for what concerns cohesive or stony substrates with brittle bulk mechanical properties. In this frame, we address the investigation of the mechanisms that govern the scouring and pattern formation on an initially flattened bed of homogenous and brittle material in a turbulent channel flow, employing direct numerical simulation. The problem is numerically tackled in the frame of peridynamic theory, which has intrinsic capabilities of reliably reproducing crack formation, coupled with the Navier–Stokes equations by the immersed boundary method. The numerical approach is reported in detail here and in the references, where extensive and fully coupled benchmarks are provided. The present paper focuses on the role of turbulence in promoting the brittle fragmentation of a solid, brittle streambed. A detailed characterization of the bedforms that originate on the brittle substrate is provided, alongside an analysis of the correlation between bed shape and the turbulent structures of the flow. We find that turbulent fluctuations locally increase the intensity of the wall-stresses producing localized damages. The accumulation of damage drives the scouring of the solid bed via a turbulence-driven fatigue mechanism. The formation, propagation, and coalescence of scouring structures are observed. In turn, these affect both the small- and large-scale structures of the turbulent flow, producing an enhancement of turbulence intensity and wall-stresses. At the small length scales, this phenomenology is put in relation to the formation of vortical cells that persist over the peaks of the channel bed. Similarly, large-scale irregularities are found to promote the formation of stationary turbulent stripes and large-scale vortices that enhance the widening and deepening of scour holes. As a result, we observe a quadratic increment of the volumetric erosion rate of the streambed, as well as a widening of the probability density of high-intensity wall stress on the channel bed. [ABSTRACT FROM AUTHOR]

The article describes the simulation results of an unbalanced rotary machine with an automatic ball balancer with a deep chamber (ABB-DC) based on a mathematical model of such a system. The ABB chamber has a cylindrical shape and is filled with balls that can move freely in general motion. The model takes into account mutual collisions between the balls, as well as between the balls and the chamber. The model also includes friction forces and rolling resistance. The comparison of simulation results performed with two different construction types of the chamber, classic single-layer drum (ABB-SC) and ABB-DC, confirmed the better efficiency of the ABB-DC in the optimal range of the number of balls. The machine body movement was limited to planar motion. The correctness of such a limitation has been verified by analyzing waveforms of reaction forces of constraints and their moments. Waveforms were divided into transient and steady states. The results of the analysis indicate the additional constraints do not significantly affect machine body movements. However, this might affect the ball arranging process in the ABB chamber. The paper also presents details of performing numerical simulations based on the developed mathematical model and numerical tests to determine the optimal integration time-step. [ABSTRACT FROM AUTHOR]

Large net structures used in engineering can easily get into vibration under external excitations; however, the corresponding vibration control strategy still remains challenging. In this paper, a wave boundary control (WBC) strategy is proposed for the vibration suppression of large net structures. The stability of the controlled structures is confirmed by using inverse Fourier transform, transfer function analysis, and numerical simulation. When WBC controllers are set at all boundaries and excitations come from the boundaries, dynamic responses for all the strings of the net structures can quickly reduce to zero without any residual vibration. The effects of different observations, controls, and distributions of sensors on the control laws are discussed. As an application, a method for reducing the number of controllers for large net structures is finally proposed. The research provides theoretical guidance for vibration control of large net structures. [ABSTRACT FROM AUTHOR]

In this paper, it is shown that when a flow undergoes a steady bifurcation breaking one reflection symmetry, the mean flow obtained by averaging the two possible asymmetric flow fields resulting from the instability remains marginally stable in the postcritical regime. This property is demonstrated rigorously through an asymptotic analysis which closely follows that proposed in Sipp and Lebedev (J Fluid Mech 792:620–657, 2007) for a Hopf bifurcation with focus on wakes. In the case of wakes, the marginal stability of the mean flow is well known and had several consequences documented in the literature. To the authors' knowledge, the marginal stability of mean flows after a symmetry-breaking pitchfork bifurcation is demonstrated here for the first time. As an example of possible consequences of marginal stability, the self-consistent model proposed for wakes in Mantič-Lugo et al. (Phys Rev Lett 113:084501, 2014) and relying on marginal stability is also applied here to the symmetry-breaking instability of the flow in a channel with a sudden expansion. For this specific case, the marginal stability of the mean flow is first demonstrated by dedicated direct numerical simulations; successively, it is shown that the resulting self-consistent model predicts the nonlinear saturation of the instability with remarkable accuracy. [ABSTRACT FROM AUTHOR]

Kevlar KM2 600 denier yarn is often twisted to improve yarn load at failure. It is noted in ASTM-D-7269 that twisting KM2 past five twists per inch can cause a lower load at failure. Understanding the physics that govern the load decrease at higher twist ratios can lead to improved yarn designs, possibly stronger than the peak values currently seen at three turns per inch. Increasing yarn strength would enable enhanced usage of Kevlar yarn, improving chord and fabric structures. This paper describes the testing and finite element analysis methods used to probe yarn tenacity as a function of twist per inch. The performed tests indicate that strength decreases as the yarn is twisted past three twists per inch and are in agreement with previously conducted trials. The finite element model results were compared to test data performed in this study and ones reported in literature. Employing the validated simulation data, yarn damage and failure pictorials were produced. The frames showing the yarn at varying displacements illustrate the yarn failure propagation at varying twist-per-turn values. It is suggested that yarn softening as a function of twist per turn is attributed to higher strains of the outer filaments, at large amounts of twist, than of the core filaments. Previous work has shown a dependency of local filament strength to its yarn radius. The focus of this paper is to derive a comprehensive filament model, using finite element analysis, that incorporates the yarn strain gradient and is experimentally verified. [ABSTRACT FROM AUTHOR]

The phase field method has emerged as a powerful tool for the simulation of multiphase flow. The method has great potential for further developments and applications: it has a sound physical basis, and when associated with a highly refined grid, physics is accurately rendered. However, in many cases, especially when dealing with turbulent flows, the available computational resources do not allow for a complete resolution of the interfacial phenomena and some undesired effects such as shrinkage, coarsening and misrepresentation of surface tension forces and thermo-physical properties can affect the accuracy of the simulations. In this paper, we present two improved phase field method formulations (profile-corrected and flux-corrected), specifically developed to overcome the previously mentioned drawbacks, and we benchmark their performance versus the classic one. The formulations are first tested considering the rise of a bubble in a quiescent fluid and the interaction of two droplets in laminar shear flow; then, their performances are compared in the simulation of a droplet-laden turbulent flow. The aim of this work is to review and benchmark the different phase field method formulations, with the final goal of laying down useful guidelines for the accurate simulation of turbulent multiphase flow with the phase field method. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the dynamics of flexible fibers in turbulent channel flow. Fibers are longer than the Kolmogorov length scale of the carrier flow, and their velocity relative to the surrounding fluid is non-negligible. Our aim is to examine the effect of local shear and turbulence anisotropy on the translational and rotational behavior of the fibers, considering different elongation (parameterized by the aspect ratio, λ) and inertia (parameterized by the Stokes number, St). To these aims, we use a Eulerian-Lagrangian approach based on direct numerical simulation of turbulence in the dilute regime. Fibers are modeled as chains of sub-Kolmogorov rods (referred to as elements hereinafter) connected through ball-and-socket joints that enable bending and twisting under the action of the local fluid velocity gradients. Velocity, orientation, and concentration statistics, extracted from simulations at shear Reynolds number Reτ=150 (based on the channel half height), are presented to give insights into the complex fiber-turbulence interactions that arise when non-sphericity and deformability add to inertial bias. These statistical observables are examined at varying aspect ratios (namely λr=lr/a=2 and 5, with lr the semi-length of each rod-like element r composing the fiber and a its cross-sectional radius) and varying fiber inertia (considering values of the element Stokes number, Str=1, 5, 30). To highlight the effect of flexibility, statistics are compared with those obtained for fibers of equal mass that translate and rotate as rigid bodies relative to the surrounding fluid. Flexible fibers exhibit a stronger tendency to accumulate in the very-near-wall region, where they appear to be trapped by the same inertia-driven mechanisms that govern the preferential concentration of spherical particles and rigid fibers in bounded flows. In such region, the bending of flexible fibers increases as inertia decreases, and fiber deformation appears to be controlled by mean shear and turbulent Reynolds stresses. Preferential segregation into low-speed streaks and preferential orientation in the mean flow direction is also observed. [ABSTRACT FROM AUTHOR]

The immersed boundary method (IBM) is a well-suited tool for the direct numerical simulation of flows with dense particle suspensions, which feature strong and complex flow-particle and particle-particle interactions. With the aim to model such flows, this paper proposes to extend the Regularised Discrete Momentum Forcing (RDMF-) IBM of Abdol Azis et al. (2018) to immersed boundaries (IBs) whose motion is coupled to the flow. A modification to the direct-forcing formulation, resulting in an offset of the imposed no-slip boundary from a moving immersed boundary, is proposed. This offset is exploited in an iterative strong flow-particle coupling scheme, where the boundary forces are applied at the location of the IB known from the previous time level, while correctly enforcing the no-slip condition at the new location of the IB. This avoids having to reconstruct the interpolation and spreading stencils for every linear iteration of the flow-particle coupling, therefore reducing the computational load of the method. A technique to ensure the stable modelling of flows involving light particles is also presented and is shown to stably cope with a wide range of particle-fluid density ratios. The framework is validated by comparing the results of the simulation of a single sedimenting sphere with published experimental results. Simulations of the fluidisation of heavy rigid particles, as well as of the ascent of closely packed light particles, are also presented. Use of the radius retraction procedure, to compensate for the diffuse representation of the smooth-interface IBM, is demonstrated to consistently yield significant improvements for moving IB cases with low to intermediate Reynolds numbers. The present framework shows good stability properties for a wide range of flow regimes with concentrated particle suspensions. [ABSTRACT FROM AUTHOR]

In this paper, turbulent pipe flows laden with finite-size particles are investigated, using the direct numerical simulations based on the lattice Boltzmann method. Our focus is on the modulation of turbulence statistics in the pipe due to the presence of finite-size neutrally buoyant particles, and the question if the characteristics of modulation differ from those in a turbulent channel flow under comparable system parameters in order to reveal the effect of curved walls in the pipe. The mechanisms responsible for modulations of the turbulent intensity in the pipe flow are clarified through a quantitative budget analysis of the turbulent kinetic energy. [ABSTRACT FROM AUTHOR]

The paper studies the response of a cluster of bubbles to osmotic pressure, and steady and oscillatory shearing by detailed numerical simulations. In contrast to other investigations, the movement of the interstitial fluid is fully resolved. To that end, an immersed-boundary method is employed, yielding the trajectory of each bubble and the flow and pressure field of the fluid. Additionally, a physically motivated collision model ensures realistic bubble interactions. Furthermore, a suitable numerical configuration is proposed which allows imposing osmotic pressure and shear in a way that integrates well into the simulation without generating artefacts. This method allows for the realistic investigation of the compression of bubbles across the jamming limit, demonstrating the influence of the inertia of the interstitial fluid. Applying oscillatory shearing with varying osmotic pressure, shear stress and frequency, the occurrence of shear bands is demonstrated and the influence on rheometric measurements is discussed. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical investigation of the dynamic response of electrostatically coupled microcantilever beams under the combined effect of squeeze-film damping and mechanical shock for MEMS applications. We consider two different microsystem designs, namely single and dual beams, operating at varying conditions to explore their possible use based on the application of interest. The single-beam system is actuated via a fixed electrode (uncoupled actuation), while the electric actuation of the dual-beam system, comprising two movable microbeams, is achieved by applying a DC voltage among them (coupled actuation). We develop a multi-physics model to simulate the dynamic response of single and dual microbeams while accounting for the fringing field effect, the squeeze-film damping resulting from the interactions between the vibrating microbeams and the surrounding fluid, and the mechanical shock. The squeeze-film damping is incorporated using a nonlinear analytical expression rather than solving the fully coupled fluid-structure problem. Numerous studies have shown the validity of this analytical approach under the assumption of long beams and neglecting the fluid compressibility. Some benchmark cases are considered to verify the predictive capability of the numerical model. The simulation results are in good qualitative and quantitative agreements with those reported in the literature. A parametric study is then conducted to investigate the effects of the initial gap distance, the fluid viscosity, and the beam geometry on the shock response of the microsystem. The squeeze-film damping enables the protection of the vibrating microbeams from hitting the substrate under mechanical shock and can be exploited to enhance the reliability of MEMS devices. However, this protection can be significantly reduced by increasing the gap distance or decreasing the operating pressure. The numerical study shows that the dual-beam systems withstand better to a mechanical shock. Breaking the symmetry of the dual-beam system in terms of the beams’ geometry is found to reduce significantly the resistance to shocks. On the other hand, given their high sensitivity to a mechanical shock, single-beam systems are observed to be more attractive for deployment as microswitches. [ABSTRACT FROM AUTHOR]

This paper uses a classical one-dimensional single-DOF model of the falling U-chain as an analytical paradigm for the assessment of a recursive modular modeling methodology, in which constraints can be enforced a posteriori. A two-dimensional nonlinear FEM model for the falling of an inextensible folded string is derived, and a numerical simulation is compared with the adopted paradigm. The proposed model not only reproduces with great accuracy the results obtained from the analytical paradigm, but also shows interesting features of this strongly nonlinear problem that might not be revealed by classical single-DOF models. [ABSTRACT FROM AUTHOR]

This paper investigates the propagation of acceleration waves on a nonlinear, externally damped string. Using the singular perturbation method, the hyperbolic system of quasilinear partial differential equations of a string is analyzed. Employing this method provides an opportunity to acquire further physical insights into acceleration wave propagation by extracting the interactions between damping and nonlinearity and their effects on the system behavior as the wave propagates along the string. Considerable agreement is observed between the analytical model of this paper and numerical simulations. [ABSTRACT FROM AUTHOR]

The present paper deals with the computational simulation of a pile of thin sheets. The sheets are not laminated or glued, but they interact by frictional contact. In general, it is not possible to perform a full-scale finite element contact computation for piles containing thousands of sheets; the problem size becomes too large, and numerical solution methods suffer from severe convergence problems due to the large number of strongly coupled contact conditions. In this paper, a macroscopic material model is presented for the two-dimensional case. The pile of sheets is homogenized by introducing an effective anisotropic constitutive law, which is motivated by formulations of the theory of elasto-plasticity. This macroscopic material law models the behavior of a pile of sheets, allowing for no tensile stresses in the direction normal to the sheets and obeying Coulomb's law of friction in the tangential contact plane. Applying this macroscopic material model, an equivalent homogeneous body can be treated using much coarser discretizations. Computational results for the problems are provided, and a comparison with simplified contact computations is done. [ABSTRACT FROM AUTHOR]

In this paper, we study the propagation of the Rayleigh surface waves in a half-space filled by an exponentially functionally graded thermoviscoelastic material with voids. We take into consideration the dissipative character of the porous thermoviscoelastic models upon the propagation waves and study the damped in time wave solutions. The propagation condition is established in the form of an algebraic equation of tenth degree whose coefficients are complex numbers. The eigensolutions of the dynamical system are explicitly obtained in terms of the characteristic solutions. The concerned solution of the Rayleigh surface wave problem is expressed as a linear combination of the five analytical solutions, while the secular equation is established in an implicit form. The explicit secular equation is obtained for an isotropic and homogeneous thermoviscoelastic porous half-space, and some numerical simulations are given for a specific material. [ABSTRACT FROM AUTHOR]

This paper discusses the role of coupling effects between transfer processes, chemical reactions and deformations in the evolution of phase composition of a growing coating and in the formation of a transition zone between coating and substrate. The proposed model of the coating growth is based on the equations of irreversible thermodynamics and accounts for coupling physical and chemical phenomena: diffusion, thermal diffusion, chemical reactions, elastic fields in the diffusion zone and stresses induced by diffusion. The transfer coefficients and kinetic parameters are calculated using classical theories or identified from experiments. As a result, we developed a theory that has direct practical applications and can be specified for a variety of technological and experimental situations. The formulated problem is solved numerically. The phase composition of the coating and residual stresses in the diffusion zone are obtained as a function of time under various technological conditions. The results can be used for prognosis and technology optimization. [ABSTRACT FROM AUTHOR]

Modeling Kevlar yarn response as a function of twist requires creating a model at the filament level that incorporates capturing the mechanical interaction of numerous fibers. The inherent complexity of building a multiscale interwoven fibrous structure manually is prohibitive for such an endeavor; therefore, computer-aided simulations are preferred. In this study, a random walk methodology was employed to generate a fibrous structure along the axis of a yarn. Since the directionality of the fibers is randomly oriented along the axis, the fibers can wind around each other and tangle or terminate on demand. The resultant geometry can represent the tortuous path that yarn filaments experience. Yarn twist can be introduced through imposing a rotation matrix to the geometry or conducting an initial analysis that applies the preload. The analysis method employed in this paper captures the correct prestress of the twisted yarns at zero, three, and ten twists per inch. The analysis then loaded the yarn until filament fracture occurred. The predicted ultimate load was within 5% for all three twists per inch analyzed. The zero twists per inch linear response matched test results to within 5%. [ABSTRACT FROM AUTHOR]

In this paper, four important subgrid-scale (SGS) stress models are investigated in order to assess their predictive performance on modeling of the SGS physics. The analysis is conducted using the a priori method based on a comprehensive direct numerical simulation (DNS) data set of a transitional boundary layer flow over a flat plate. The study includes examination of the correlations between the modeled SGS stress tensor and that directly computed from the DNS data, investigation of the effects of filter sizes on modeled SGS stresses, and evaluation of forward and backward scatter of the kinetic energy of the flow in the transitional and turbulent regions. [ABSTRACT FROM AUTHOR]

This paper is devoted to a new approach for the derivation of main thermoelastic Green's functions (MTGFs), based on their new integral representations via Green's functions for Poisson's equation. These integral representations have permitted us to derive in elementary functions new MTGFs and new Poisson-type integral formulas for a thermoelastic octant under mixed mechanical and thermal boundary conditions, which are formulated in a special theorem. Examples of validation of the obtained MTGFs are presented. The effectiveness of the obtained MTGFs and of the Poisson-type integral formula is shown on a solution in elementary functions of a particular BVP of thermoelasticity for octant. The graphical and numerical computer evaluation of the obtained MTGFs and of the thermoelastic displacements of the particular BVP for an octant is also presented. By using the proposed approach, it is possible to derive in elementary functions many new MTGFs and new Poisson-type integral formulas for many canonical Cartesian domains. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the mechanical behavior of a sandwich structure impacted by a steel ball. Sandwich structures are used as protection devices against rock falls and made of a front wall of gabions and an inside layer of sand. Such a structure has been built, instrumented, and experimentally tested using a pendular impact facility. A granular mechanical model of the structure is presented as well as the A-CD 2 (atomized efforts contact dynamics respecting Clausius–Duhem’s inequality) computational method for multi-body dynamics used to compute the impacts on the mechanical model. For four successive impacts with increasing energy level, the measured forces, accelerations, and displacement in different locations of the structure are compared to the data obtained by the numerical simulations. The accuracy of the numerical results obtained in this study is encouraging for the use of this computational method in further simulations of impacts on granular layers with increased number of grains. However, some computational improvements need to be investigated to reduce the computational time. [ABSTRACT FROM AUTHOR]

This paper investigates the behaviour of elongated, axi-symmetric ellipsoidal particles, their interaction with turbulence, and the effects of the ellipsoids on turbulence in a turbulent channel flow with Reτ = 150. The simulations are carried out with full four-way coupling using the point-source approach: the particles are affected by the fluid, the particles affect the fluid, and the particles can collide with each other or the wall using a realistic collision algorithm. The trajectories of the ellipsoids are tracked by solving the translational and rotational equations of motion in a Quaternion framework and are closed with hydrodynamic drag and torque laws. To specifically identify the effect of particle shape, simulations of single phase channel flow are compared to simulations with spherical particles and to simulations with ellipsoids. In all cases, the driving pressure drop, to establish a flow with Reτ = 150, is kept constant. Both the spherical particles and the ellipsoidal particles have a Stokes number of 5. Although the volume fraction is very low, 0.00725 and 0.0219 % for the spheres and ellipsoids, respectively, there is some effect of the particles and the ellipsoids on the turbulence. Although the transport terms in the turbulent kinetic energy equation of the fluid are hardly affected, the turbulence kinetic energy itself decreases by 6.0 % for the flow laden with spherical particles and 4.8 % for the ellipsoidal particles. The homogeneous dissipation of turbulence kinetic energy by the fluid decreases due to the addition of particles, and the production also decreases. The particles dissipate turbulence kinetic energy of the fluid phase, predominantly in the near-wall region. Because there is a high average slip velocity in the stream-wise direction between the particles and the fluid in the near-wall region, the root mean square of the particle velocity is higher than that of the fluid velocity in this direction. In the other directions, the root mean square velocities of the particles are significantly lower than of the fluid. There is, however, a positive slip velocity between the particles and the fluid in the wall-normal direction, indicating that the particles move towards the wall with a higher momentum than that they return to the centre of the channel with. As a result, there is a 4–5 times higher concentration of particles near the wall than in the centre of the channel. As both the spherical and the ellipsoidal particles are very small, there is no major difference in their overall behaviour. However, in the near-wall region, there are some profound differences. The collision mechanism of ellipsoids with the walls is significantly different compared to spheres, the former predominantly inducing rotation resulting from a collision and the latter predominantly moving away from the wall after colliding. This is confirmed by the strong rotation as well as large root mean square of rotation of the ellipsoidal particles in the near-wall region. This results in a slight inward shift of the peak of the root mean square velocities of the fluid and the ellipsoidal particles as well as the peak in slip velocity, driving the momentum transfer, compared to the simulations with the spheres. Finally, the statistics of the orientation show that the ellipsoids align in the stream-wise direction in the near-wall region, because of the fluid boundary layer as well as the particle–wall collisions, but that there is no significant orientation of the ellipsoids outside of the near-wall region. [ABSTRACT FROM AUTHOR]

In this paper, the rotation of rigid fibers is investigated for the reference case of turbulent channel flow. The aim of the study is to examine the effect of local shear and turbulence anisotropy on the rotational dynamics of fibers with different elongation and inertia. To this aim, statistics of the fiber angular velocity, Ω, are extracted from direct numerical simulation of turbulence at shear Reynolds number Re = 150 coupled with Lagrangian tracking of prolate ellipsoidal fibers with Stokes number, St, ranging from 3 to 100 and aspect ratio, λ, ranging from 1 to 50. Accordingly, the fiber-to-fluid density ratio ranges from $${S \simeq 7}$$ (for St = 1, λ = 50) to $${S \simeq 3, 470}$$ (for St = 100, λ = 1). Statistics are compared one to one with those obtained for spherical particles to highlight effects due to elongation. Results for mean and fluctuating angular velocities show that elongation is important for fibers with small inertia ( St ≤ 5 in the present flow-fiber combination). For fibers with larger inertia, elongation has an impact on fiber rotation only in the streamwise and wall-normal directions, where mean values of Ω are zero. It is also shown that, in the center of the channel, the Lagrangian autocorrelation coefficients of Ω and corresponding rotational turbulent diffusivities match the exponential behavior predicted by the theory of homogeneous dispersion. In this region of the channel, the probability density function of fiber angular velocities is generally close to Gaussian, indicating that particle rotation away from solid walls can be modeled as a diffusion process of the Ornstein-Uhlenbeck type at stationary state. In the strong shear region (comprised within a distance of 50 viscous units from the wall in the present simulations), fiber anisotropy adds to flow anisotropy to induce strong deviations on fiber rotational dynamics with respect to spherical particles. The database produced in this study is available to all interested users at . [ABSTRACT FROM AUTHOR]

Unusual ferroelectricity emerges in nanoscale Perovskite oxides owing to their characteristic structures, and it strongly interacts with mechanical stress/strain, namely, 'multi-physics property'. For systematic understanding, the ferroelectricity and multi-physics property in the nano-components are discussed in terms of their 'macroscopic' component shape (e.g., films, wires, tubes and dots) and 'inner' inhomogeneous structure (e.g., domain walls and grain boundaries), based on the first-principles density-functional theory calculations. Moreover, this paper also presents a remarkable interplayed effect of the macroscopic shape and the inner structure on the property through a theoretical investigation on polydomain PbTiO ultrathin films. [ABSTRACT FROM AUTHOR]

The charged system search as a recently developed meta-heuristic algorithm has been successfully utilized for optimum design of different examples. In addition, the fields of forces model provides a means to enhance the algorithm, and this results in the enhanced charged system search (ECSS). This paper utilizes positive features of the chaos in the ECSS algorithm to optimize engineering design problems. Simulation results and comparisons based on various well-known mechanical and engineering design problems show the efficiency of the present algorithm. [ABSTRACT FROM AUTHOR]

A number of sets of modes, for example eigenmodes, constraint modes, inertia-relief attachment modes, may be used to describe the linear elastic deformation of a flexible body in multibody dynamics. It is always possible to transform modes so that the conditions of the Buckens-frame are fulfilled. The latter frame leads to serious simplifications in the equations of motion, but cannot avoid a coupling between the body's rotational rigid body motion and its elastic deformation. In the present paper the deformation modes will be subdivided into low- and high-frequency modes. It will be shown that the latter-mentioned coupling effect of the second ones can be safely neglected in comparison with the first ones. Consequently, the high-frequency components can be removed from time integration at all, which leads to significant savings of computational effort while the accuracy regarding the body's deformation remains almost the same. In the case of a known frequency content of external excitation, an algorithm is given so that the available modes can be automatically separated into such low- and high-frequency modes. While the number of low-frequency modes remains more or less constant, there is a significant trend to use an increased number of high-frequency modes. Examples are moving loads (e.g., guidance) or distributed loads as they occur in contact problems or when fluid pressure is acting on surfaces. A final numerical example is given in order to demonstrate the potential of the proposed method. [ABSTRACT FROM AUTHOR]

The global bifurcations and multi-pulse chaotic dynamics of a simply supported honeycomb sandwich rectangular plate under combined parametric and transverse excitations are investigated in this paper for the first time. The extended Melnikov method is generalized to investigate the multi-pulse chaotic dynamics of the non-autonomous nonlinear dynamical system. The main theoretical results and the formulas are obtained for the extended Melnikov method of the non-autonomous nonlinear dynamical system. The nonlinear governing equation of the honeycomb sandwich rectangular plate is derived by using the Hamilton's principle and the Galerkin's approach. A two-degree-of-freedom non-autonomous nonlinear equation of motion is obtained. It is known that the less simplification processes on the system will result in a better understanding of the behaviors of the multi-pulse chaotic dynamics for high-dimensional nonlinear systems. Therefore, the extended Melnikov method of the non-autonomous nonlinear dynamical system is directly utilized to analyze the global bifurcations and multi-pulse chaotic dynamics of the two-degree-of-freedom non-autonomous nonlinear system for the honeycomb sandwich rectangular plate. The theoretical results obtained here indicate that multi-pulse chaotic motions can occur in the honeycomb sandwich rectangular plate. Numerical simulation is also employed to find the multi-pulse chaotic motions of the honeycomb sandwich rectangular plate. It also demonstrates the validation of the theoretical prediction. [ABSTRACT FROM AUTHOR]

In this paper, firstly, the acceleration of the temperature and concentration are assumed to need the extra increment of the heat and energy. The inertial entropy and the inertial chemical potential were proposed by Kuang (Acta Mech 203:1-11, , Acta Mech 214:275-289, ). Secondly, the expressions of dissipative energy produced by the variation of the temperature and concentration are derived by using the second law of thermodynamics. Finally, several variational principles for coupled temperature-diffusion-mechanics are established, and their corresponding governing equations and boundary conditions are naturally presented. Meanwhile, some numerical simulations are carried out to describe the coupled reciprocity, which shows concentration diffusion with a finite velocity. [ABSTRACT FROM AUTHOR]

In this paper, the fluid flow and the diaphragm deflection are studied in the pneumatically actuated diaphragm microvalve by performing finite element and analytical fluid-structure interaction simulations. The results of these approaches are compared and their validity is discussed. An analytical relation is obtained for the critical diaphragm deflection which leads to unstable response of the microvalve. This relation shows that the critical deflection is only a function of the microvalve geometry, namely its inlet height and outlet radius. The phenomenon of the diaphragm deflection jump is justified in the microvalve behavior. The effect of different fluid flow and diaphragm parameters on the microvalve response is investigated that can be used to improve the microvalve design. [ABSTRACT FROM AUTHOR]

In this paper, a gradient crystal plasticity model in a polycrystalline grain structure is investigated. Hereby, the focus is on the influence of the grain boundary conditions. A new type of grain boundary conditions is introduced, the so-called micro-flexible boundary condition. In particular, it is compared to existing grain boundary conditions of plastic slip. Numerical results are given for the stress-strain response as well as for the plastic slip field in the grain structure. [ABSTRACT FROM AUTHOR]

This paper investigates sway, roll and yaw motions of a floating body with the aim to determine coupled motion characteristics based on the order-wise analysis of hydrodynamic coefficients. To compute the hydrodynamic coefficients and wave force exerted on the floating body, we employ speed-dependent strip theory. The governing equations are solved analytically for linear restoring moment. For nonlinear restoring moment which is expressed as an odd-order polynomial of fifth degree in roll angle, we apply the Runge–Kutta–Gill method to solve the coupled equations. To investigate the effect of initial disturbances on sway, roll, yaw and speed of the body, numerical experiments have been carried out for a Panamax Container ship under the action of a sinusoidal wave of periodicity 11.2 s with varying wave height and speed. For the linear restoring moment, we first derive associated motion equations for various cases based on the relative magnitude of the hydrodynamic coefficients. The order-wise analysis leads to the classification of coupled characteristics exhibiting the nature of coupling. For the nonlinear restoring moment, we notice that the initial disturbance plays an important role in the ship’s stability. The effects of forward speed and variation in wave heights are illustrated through typical numerical experiments. [ABSTRACT FROM AUTHOR]

The problem considered in this paper concerns the edge-wave buckling phenomenon commonly encountered in forming processes such as rolling and levelling. Due to the combined action of global tensile forces and residual stresses, the elastic strips involved in these scenarios experience a symmetric short-wave deformation pattern that tends to be confined near their long edges. We use boundary-layer techniques to provide simple estimates for the critical load and the wavelength of the buckling waves. A number of complementary asymptotic features of the marginal stability curves are also reported. [ABSTRACT FROM AUTHOR]

The three-dimensional attitude stabilization of a satellite using fluid rings is proposed in the present paper. The general formulation of the system that comprises a satellite and three fluid rings, one on each axis, is obtained through Euler’s moment equations. The linearized system model is derived and the stability conditions are obtained. Linear control laws and nonlinear control laws based on sliding mode control techniques are developed for fluid control torques. The numerical simulation of the governing nonlinear equations of motion of the system along with stability analysis establishes the feasibility of achieving desired attitude stabilization of the satellite. The fluid controllers are successful in stabilizing the attitude of the satellite in presence of high attitude disturbance torques and intermittent actuators’ failures. In the case of sudden attitude disturbance torques, the nonlinear fluid controllers outperform the linear fluid controllers with virtually no effect on the satellite attitude response. The proposed attitude stabilization method may find applications in future satellite missions. [ABSTRACT FROM AUTHOR]

Modeling and analysis of wave propagation in elastic solids undergoing damage and growth process are reported in this paper. Two types of diagnostic problems, (1) the propagation of waves in the presence of a slow growth process and (2) the propagation of waves in the presence of a fast growth process, are considered. The proposed model employs a slow and a fast time scale and a homogenization technique in the wavelength scale. A detailed analysis of wave dispersion is carried out. A spectral analysis reveals certain low-frequency bands, where the interaction between the wave and the growth process produces acoustic metamaterial-like behavior. Various practical issues in designing an efficient method of acousto-ultrasonic wave based diagnostics of the growth process are discussed. Diagnostics of isotropic damage in a ductile or quasi-brittle solid by using a micro-second pulsating signal is considered for computer simulations, which is to illustrate the practical application of the proposed modeling and analysis. The simulated results explain how an estimate of signal spreading can be effectively employed to detect the presence of a steady-state damage or the saturation of a process. [ABSTRACT FROM AUTHOR]

Welding deformations play an important role in sealing capabilities and service life of welded pipe-flange joints. A numerical procedure for modeling of tack welds in girth butt-welding of such joints is of vital importance for the prediction of transverse shrinkage and flange face deformation, which is directly related to the joint sealing capability. This paper presents a 3-D finite element simulation of a pipe-flange joint to describe the numerical procedure for modeling of tack welds in circumferential joints. Sequentially coupled nonlinear transient thermo-mechanical analysis is performed to simulate Metal Inert Gas (MIG) welding. Single pass butt weld geometry with single “V” for 100 mm nominal diameter pipe with same sized weld neck type ANSI flange of class no. 300 is used. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. The peak temperature of the tack during the butt-welding of the tacked model is concluded a key parameter for numerical prediction of deformations, whereas tack temperature has negligible effect on the residual stresses. [ABSTRACT FROM AUTHOR]