varunr14/newsummary huggingface dataset:
The development of a finite element model for time dependent analysis of bonded prestressed concrete girders at service conditions is presented . The effects of creep and shrinkage of concrete and relaxation of steel tendons are taken into account . The concrete creep is modeled based on the Dirichlet series creep compliance with efficiency in simulating the stress history . In addition the interaction between different time dependent effects is fully considered in the numerical procedure . The numerical method is formulated based on the layered Euler Bernoulli beam theory . In the constructed incremental equilibrium equations the equivalent nodal load increments consist of four components contributed by external loads concrete creep concrete shrinkage and tendon relaxation while the stiffness matrix is composed of the material and geometric stiffness matrices . Numerical examples show that the proposed model can well predict the long term behavior of prestressed concrete beams and that the time dependent effects have important influence on the structural behavior . 


Highlights:
A method for time dependent analysis of prestressed concrete girders is developed. The effects of creep shrinkage of concrete and tendon relaxation are considered. The interaction between different time dependent effects is considered.
A robust reduced integration solid shell finite element in irreducible variational formulation is demonstrated in this paper . To enable shell element like performance using a single through shell thickness element layer we apply element technologies isotropically introducing local tri quadratic hierarchical displacement modes thereafter systematically projected to the global coordinate frame . We also enforce uniform bilinear and linear ANS interpolations to all local normal and shear strains respectively imposing identical in plane and out of plane element response for robust 3D thin shell deformation behaviour in non regular trapezoidal shaped meshes . The hierarchical strains realised improve the element performance by complementing the locking alleviating actions of the ANS modified membrane and shear strain fields in reduced numerical integration scheme performed along the designated shell thickness . We restrict our initial numerical investigations to geometrically linear beams plates and shell problems solely for preliminary assessment of the element s in plane and out of plane behaviour in response to the uniform modification of strains and hierarchical displacement modes introduced . To this end the results indicate robust behaviour and comparable accuracy in comparison to mixed variational enhanced assumed strain elements in full and in reduced integration in all structural problem classes undertaken . 


Highlights:
A reduced integration displacement degree of freedom only solid shell is presented. Three hierarchical freedoms compliment the 8 node element trilinear displacement field. ANS enforcement on shear and normal strains improves mesh distortion tolerance. A single element layer through the shell thickness was used with full constitutive laws. The displacement variational element was comparable in accuracy to EAS elements.
A hybrid finite element formulation is used to model temperature evolutions in concrete structures at early ages taking into account the thermo chemical process of cement hydration . The most relevant fields in the application problem namely the temperature and the hydration degree fields are selected for direct and independent approximation . The Galerkin formulation used qualifies as hybrid because the heat flux is also approximated on the boundary of the element . The temperature and hydration degree bases are used to enforce the thermal equilibrium condition and the hydration law respectively and the heat flux basis is used to enforce the thermal continuity conditions . The resulting nonlinear transient hybrid formulation leads to high degree naturally hierarchical elements . They can be implemented on coarse meshes eventually unstructured and involving high aspect ratio elements to reduce the dimension of the solving system while preserving adequate levels of accuracy . The system is symmetric sparse and well suited to adaptive refinement and parallelization . Modelling of boundary conditions and thermo chemical properties of concrete is designed to accommodate experimentally defined properties and code of practice recommendations as well as other research results reported in the literature . The quality of the model is assessed using a set of testing problems supported by experimental data and results obtained with conventional finite elements . 


Highlights:
A hybrid FE formulation is applied to the modelling of cement hydration in concrete. The accuracy of conventional FE is recovered with simpler meshes and fewer variables. Unstructured meshes and uncoupled FE bases simplify the modelling of staged construction. The hybrid FE formulation is well suited to adaptive p refinement and parallelization. Performance is assessed using experimental monitoring data and conform FE solutions.
A finite element formulation for a non local particle method is proposed in this paper for elasticity and fracture analysis of 2D solids . The model is based on a new particle method which incorporates a non local multi body particle interaction into the conventional pair wise particle interactions . The non local particle method is capable of modeling solids with arbitrary Poisson s ratio . Finite element formulation is proposed for the implicit solution of elasticity and fracture problems under static quasi static conditions which is very efficient compared to the direct explicit solution in particle dynamics . Energy minimization principle is used to develop a new finite element with both local pair wise and non local multi body particle interactions . The developed finite element formulation is verified with classical finite element simulation of some benchmark problems . Fracture simulation using the proposed particle based finite element formulation is demonstrated . Some conclusions and future work is drawn based on the current investigation . 


Highlights:
A new finite element implementation scheme for non local particle methods is proposed. 10 particles element is developed to describe both local pair wise and non local multi body particle interactions. The new scheme is verified to be accurate efficient and robust in simulating elastic and fracture problems.
The objectives of this paper are to examine the use of volumetric strain rate and pressure enhancement strategies for low order finite elements and to present a stable matrix free algorithm for solving steady state flow problems . Algorithms based on the method of successive approximation and low order finite elements are examined for determining the steady state flow field of a boundary valued problem consisting of an incompressible material . It is shown that both volumetric strain rate and pressure enhancement are required to mitigate pathological locking and nonphysical pressure variations . Care must however be taken when introducing pressure enhancement which helps mitigate the pressure from drifting as the stress field is perturbed from equilibrium . An algorithm based on dynamic relaxation and radial return stress calculations is presented for matrix free calculations dealing with stress dependent creep . 


Highlights:
Modelling of ice creep with low order elements. Use of volumetric strain rate and pressure enhancement strategies for low order finite elements. Application of the method of successive approximation. Stable matrix free algorithm for solving steady state flow problems.
Transient structural dynamic analyses often exhibit different phases which enable one to use an adaptive modeling . Thus a 3D model is required for a better understanding of local or non linear effects whereas a simplified beam model is sufficient for simulating the linear phenomena occurring for a long period of time . This paper proposes a method which enables one to switch from a beam to a 3D model during a transient dynamic analysis and thus allows one to reduce the computational cost while preserving a good accuracy . The method is validated through comparisons with a 3D reference solution computed during all the simulation . 


Highlights:
Use of a 3D model and a beam model at two different stages of the same computation. For dynamic problems with non linearities restricted in space and time. The switch reduces considerably the computational cost with preserved accuracy. Two different initialization techniques are investigated. The energy consistency of the switch is demonstrated.
The paper proposes a mixed finite element model and experiments its capability in the analysis of elastic and plastic collapse plane problems . The model is easy to formulate and implement because it is based on simple assumptions for the unknown fields . A composite triangular mesh is assumed over the domain . Within each triangular element the displacement field is described by a quadratic interpolation while the stress field is represented by a piece wise constant description by introducing a subdivision of the element into three triangular regions . The elastic solution is constructed through the stationarity condition of the mixed Hellinger Reissner functional . The plastic collapse analysis is formulated as a mathematical programming problem and is accomplished by an Interior Point algorithm which furnishes both the collapse multiplier and the collapse mechanism . A series of numerical experiments shows that the proposed model performs well in elastic problems and achieves the favorite context in plastic analysis where it takes advantage of the absence of volumetric locking and the piecewise constant interpolation of the stress field within the element . 


Highlights:
The model is particularly simple and easy to implement. Nevertheless the element proves to be accurate and robust in the analysis of both elastic and plastic problems. The choice of the displacement and stress interpolations produces an isostatic element which keeps out zero energy modes. The element is locking free. The assumed piece wise constant description of the stress field allows the discontinuities inherent in the plastic solution. The numerical experiments which refer to the analysis of elastic problems and plastic collapse states show that the element furnishes stable results for both regular and irregular meshes also with marked distortions. The element can be extended saving the relevant features to the context of three dimensional analysis.
The objective of this work is to obtain an a posteriori estimate of the discretization error of a reference problem . This reference problem is a mechanical problem solved using a finite element analysis in linear elasticity . We use the constitutive relation error based estimator . The construction of admissible fields which is a pillar of the constitutive relation error method is revisited using a domain decomposition method . The originality of the present work is the introduction of a simplifying hypothesis that leads to an approximation of the discretization error . The construction of admissible fields which is global is then replaced by resolution of several local problems that conduce to lower CPU costs . The key point of this domain decomposition based error estimation is the fact that no inter subdomain communication is needed . We present and illustrate this strategy and evaluate its benefits . 


Highlights:
We study finite element quality in linear elasticity. We use constitutive relation error estimator. We consider an original construction of admissible field using domain decomposition. We illustrate the strategy.
This paper presents a novel finite element model for the fully material and geometrical nonlinear analysis of shear deformable two layer composite planar beam column members with interlayer slips . We adopt the co rotational approach where the motion of the element is decomposed into two parts a rigid body motion which defines a local co ordinate system and a small deformational motion of the element relative to this local co ordinate system . The main advantage of this approach is that the transformation matrices relating local and global quantities are independent from the choice of the geometrical linear local element . The effect of transverse shear deformation of the layers is taken into account by assuming that each layer behaves as a Timoshenko beam element . The layers are assumed to be continuously connected and partial interaction is considered by adopting a continuous relationship between the interface shear flow and the corresponding slip . In order to avoid curvature and the shear locking phenomena the local linear element is derived from the force based formulation . The present model provides an efficient tool for the elastoplastic buckling analysis of two layer shear deformable beam column with arbitrary support and loading conditions . Finally two numerical applications are presented in order to assess the performance of the proposed formulation . 


Highlights:
Shear deformable plastic composite beams in partial interaction. Geometrically nonlinear analysis of Timoshenko layered beams using the co rotational framework. Local element formulation based on the flexibility approach. Effects of the interlayer slip on the nonlinear behavior of composite beams. Materially and geometrically nonlinear buckling of two layer shear deformable beams with arbitrary support loading conditions.
In this paper an Interior Penalty Discontinuous Galerkin finite element method is analyzed for approximating quasilinear parabolic equations . The equations can be characterized as perturbed parabolic p Laplacian equations . The fully discrete scheme is obtained by applying s stage Diagonally Implicit Runge Kutta methods for the time integration . The nonlinear systems of the algebraic equations appearing in s DIRK cycles are solved by developing two low storage Picard iterative processes . A stability bound is shown for the semi discrete IPDG solution in the broken DG norm . Continuous in time a priori error estimates are proved in case of when linear approximation space is used . A numerical test is performed in order to compare the performance of the two Picard iterative processes . Also the results presented in the theoretical analysis are confirmed by numerical examples . 


Highlights:
In this work we present an Interior Penalty Discontinuous Galerkin finite element method for solving quasilinear parabolic problems. In these problems where the diffusion coefficient has a p exponent form. The natural formulation of the problem is in Lp space For the IPDG method stability bounds and a priori error estimates are shown. Two low computational cost Picard block iterative methods are proposed.
A new structure preserving algorithm for simulating the nonlinear dynamics of geometrically exact rods is developed . The method is based on the simultaneous discretization in space and time of Hamilton s variational principle . The resulting variational integrator is explicit second order accurate and can be identified with a Lie group symplectic partitioned Runge Kutta method for finite element discretizations of rods involving large rotations and displacements . Numerical examples allow to verify that the algorithm presents an excellent long term energy behavior along with the exact conservation of the momenta associated to the symmetries of the system . 


Highlights:
Author Highlights An explicit variational integrator for the dynamics of rods is developed. The method is explicit symplectic and momentum conserving. The method is second order accurate with the time step and the mesh size. The energy drift remains bounded over exponentially long times.
The direct time domain analysis of five layered damped sandwich beams subject to impulse load using the discrete Hilbert transform may lead to the unstable growth in damped time responses owing to the incorrectness of Hilbert transformed imaginary impulse force and the insufficient time duration of applied impulse force . To resolve this problem a time domain analysis method making use of the Hilbert transform superposition and the time duration extension is introduced in this paper . The incorrect imaginary impulse force near the end of time period which is caused by the fact that the discrete Hilbert transform using Fourier transform considers the impulse force as a periodic function is resolved by dividing the external impulse force into a finite number of rectangular impulses . And the sufficient time duration of applied impulse force is estimated by a Newton Raphson based iterative residual method . The validity of the present method is justified from the numerical experiment for analyzing the time response of five layered damped sandwich beam . 


Highlights:
A time domain analysis method using Hilbert transform superposition and the time duration extension is introduced. An arbitrary input signal is divided into several rectangular impulses and their Hilbert transforms are superposed. An appropriate time duration is estimated by a residual based Newton Raphson iteration algorithm.
Geometric designs for the controlled fragmentation of metal cylindrical shells have been considered via CTH hydrocode simulations . Fragmentation is controlled by engineering notches on the interior of the shells . Design parameters considered include the shell radius thickness and the depth and spacing of interior notches . A large number of shell designs were analyzed and their effectiveness on the controlled fragmentation categorized . The best overall controlled fragmentation designs exhibit full and complete fragment breakup as prescribed along the system of interior notches without any of the individual fragments naturally fragmenting throughout their thicknesses . For the combination of the Composition C 4 explosive and the 4340 steel the best performing designs were shown to commonly possess the following characteristics they each have notch or groove depths greater than half of the shell thickness they each have notch or groove spacing within a range that is approximately the same as the shell thickness and they each have shell thicknesses many times smaller than the shell radius . 


Highlights:
We consider designs for the controlled fragmentation of metal cylindrical shells. The best performing designs were shown to commonly possess the following features They each have notch or groove depths greater than half of the shell thickness. They each have notch spacing within a range approximately the shell thickness. They each have shell thicknesses many times smaller than the shell radius.
A mixed finite element model has been derived for the acoustic analysis of perforated dissipative silencers including several effects simultaneously High temperature and thermal gradients in the central duct and the outer absorbent material a perforated passage carrying non uniform axial mean flow . For such a combination the properties of sound propagation media and flow are inhomogeneous and vary with position . The material of the outer chamber can be modelled by its complex equivalent acoustic properties which completely determine the propagation of sound waves in the air contained in the absorbent medium . Temperature gradients introduce variations in these properties that can be evaluated through a heterogeneous temperature dependent resistivity in combination with material models obtained at room temperature . A pressure based wave equation for stationary medium is then used with the equivalent density and speed of sound of the absorbent material varying as functions of the spatial coordinates . Regarding the central air passage a wave equation in terms of acoustic velocity potential can be used to model the non uniform moving medium since the presence of temperature variations introduce not only heterogeneous acoustic properties of the air but also a gradient in the mean flow velocity . The acoustic connection between the central passage and the outer chamber is given by the acoustic impedance of the perforated duct . This impedance depends on the heterogeneous properties of the absorbent material and the non uniform mean flow leading to a spatial variation of the acoustic coupling and also to additional convective terms in the governing equations . The results presented show the influence of temperature thermal gradients and mean flow on the transmission loss of automotive silencers . It has been found that high temperature and thermal induced heterogeneity can have a significant influence on the acoustic attenuation of an automotive silencer and so should be included in theoretical models . In some particular configurations it may be relatively accurate to approximate the temperature field by using a uniform profile with an average value specially for low resistivity materials . It has been shown however that this is not always possible and attenuation overestimation is likely to be predicted mainly for high radial thermal gradients and high material flow resistivities if the temperature distribution is not taken into account . 


Highlights:
Dissipative silencers including high temperature and thermal gradients are analysed. A mixed finite element model combining velocity potential and acoustic pressure is derived. Temperature gradients lead to spatial variations of absorbent material properties mean flow and perforated duct impedance. Attenuation overestimation is likely to be predicted if the temperature distribution is not taken into account.
Triaxial compression of elastoplastic particles was studied with numerical and analytical methods in order to develop a mechanistic model for their interactions at high relative densities . The introduction of an equivalent particle radius that accounted for the elastic volumetric deformation enabled an almost perfect reduction of the results obtained for elastoplastic particles to those obtained for rigid perfectly plastic ones . This in turn made possible a simplified yet mechanistic analytical analysis of the particle response in terms of the contact area pressure and force . The developed model exhibited a good agreement with the numerical results especially for intermediate and large strains and hence laid the foundations for the development of mechanistic contact models suitable for simulations of granular materials at high relative densities with the Discrete Element Method . 


Highlights:
Hydrostatic compression of elastoplastic particles was studied. A combination of numerical and analytical methods was used. The elastoplastic response could be reduced to a rigid perfectly plastic one. A mechanistic model was derived that adequately captured the numerical results. The model can be generalised to other loading conditions.