The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Oliver Junge - One of the best experts on this subject based on the ideXlab platform.
-
Higher Order finite Element approximation of the dynamic laplacian
Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Nathanael Schilling, Gary Froyland, Oliver JungeAbstract:The dynamic Laplace operator arises from extending problems of isoperimetry from fixed manifolds to manifolds evolved by general nonlinear dynamics. Eigenfunctions of this operator are used to identify and track finite-time coherent sets, which physically manifest in fluid flows as jets, vortices, and more complicated structures. Two robust and efficient finite-Element discretisation schemes for numerically computing the dynamic Laplacian were proposed in Froyland and Junge [SIAM J. Appl. Dyn. Syst. 17 (2018) 1891–1924]. In this work we consider Higher-Order versions of these two numerical schemes and analyse them experimentally. We also prove the numerically computed eigenvalues and eigenvectors converge to the true objects for both schemes under certain assumptions. We provide an efficient implementation of the Higher-Order Element schemes in an accompanying Julia package.
Nathanael Schilling - One of the best experts on this subject based on the ideXlab platform.
-
Higher Order finite Element approximation of the dynamic laplacian
Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Nathanael Schilling, Gary Froyland, Oliver JungeAbstract:The dynamic Laplace operator arises from extending problems of isoperimetry from fixed manifolds to manifolds evolved by general nonlinear dynamics. Eigenfunctions of this operator are used to identify and track finite-time coherent sets, which physically manifest in fluid flows as jets, vortices, and more complicated structures. Two robust and efficient finite-Element discretisation schemes for numerically computing the dynamic Laplacian were proposed in Froyland and Junge [SIAM J. Appl. Dyn. Syst. 17 (2018) 1891–1924]. In this work we consider Higher-Order versions of these two numerical schemes and analyse them experimentally. We also prove the numerically computed eigenvalues and eigenvectors converge to the true objects for both schemes under certain assumptions. We provide an efficient implementation of the Higher-Order Element schemes in an accompanying Julia package.
Hong Zheng - One of the best experts on this subject based on the ideXlab platform.
-
a mixed three node triangular Element with continuous nodal stress for fully dynamic consolidation of porous media
Engineering Analysis With Boundary Elements, 2020Co-Authors: Yongtao Yang, Hong ZhengAbstract:Abstract A mixed three-node triangular Element with continuous nodal stresses (mixed T3-MINI-CNS) is presented for dynamics of porous media based on the three-variable u-w-p Biot model and the numerical manifold method (NMM). The displacement and velocity approximations are derived using the constrained and orthonormalized least-square (CO-LS) scheme, which possess continuous derivatives and Delta property at nodes. The pressure approximation takes linear piecewise interpolation. Relative to Higher-Order Element, the mixed quadratic six-node triangle, mixed T3-MINI-CNS can model dynamic response of porous media more precisely with fewer unknowns, especially the short-term transient response. Moreover, mixed T3-MINI-CNS is immune from locking in both undrained and rigid skeleton limits and achieves more accurate pressure results than other characteristic locking-free Elements. Based on NMM and u-w-p formulation, the most versatile three-node triangular mesh can always be used, avoiding difficulties in mesh generation. As fluid acceleration is involved, mixed T3-MINI-CNS is capable of totally predicting dynamic response of porous mixture, especially under rapid loading condition. In addition, reliability and precision of the time integration are assessed in terms of the energy balance condition. Through calculating benchmark problems, convergence, accuracy, and reliability of the mixed T3-MINI-CNS are thoroughly investigated and validated.
Gary Froyland - One of the best experts on this subject based on the ideXlab platform.
-
Higher Order finite Element approximation of the dynamic laplacian
Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Nathanael Schilling, Gary Froyland, Oliver JungeAbstract:The dynamic Laplace operator arises from extending problems of isoperimetry from fixed manifolds to manifolds evolved by general nonlinear dynamics. Eigenfunctions of this operator are used to identify and track finite-time coherent sets, which physically manifest in fluid flows as jets, vortices, and more complicated structures. Two robust and efficient finite-Element discretisation schemes for numerically computing the dynamic Laplacian were proposed in Froyland and Junge [SIAM J. Appl. Dyn. Syst. 17 (2018) 1891–1924]. In this work we consider Higher-Order versions of these two numerical schemes and analyse them experimentally. We also prove the numerically computed eigenvalues and eigenvectors converge to the true objects for both schemes under certain assumptions. We provide an efficient implementation of the Higher-Order Element schemes in an accompanying Julia package.
J H J Floor - One of the best experts on this subject based on the ideXlab platform.
-
structural adhesive bonded steel to steel connections an introduction for structural engineering
2014Co-Authors: J H J FloorAbstract:Today, there are only a few types of structural engineering applications where structural adhesives play a role, in contrast to other engineering sectors. The possibilities and difficulties of structural adhesive bonding in structural engineering, especially for steel-to-steel connections, are investigated. Practically all structural adhesives are polymers. The cohesive properties mainly depend on their polymer structure and eventual additives. Specific adhesion covers all adhesion types through intermolecular forces (chemical, adsorptive, diffusive and electrostatic). For specific adhesion, good wetting is important. Mechanical adhesion is characterised by interlocking. The mechanical behaviour of most structural adhesives is best described by the Drucker Prager (or related) model. Therefore the tension strength is limited, hence connections should be designed for shear and compression. Lap connections are prone to shear lag which causes a low effectiveness of long laps. Shear lag is mainly influenced by the axial stiffness of the adherents, and shear stiffness and thickness of the adhesive. Lap connections are also prone to peel, due to eccentricity of the lines of action (externally and/or internally). Peel is mainly influenced by adhesive and adherent thicknesses, bending stiffness of the adherents and axial stiffness of the adhesive. The material properties of adhesive are strongly influenced by time-and-environmental effects, especially temperature, moister and creep are important. The mechanical properties of adhesive bonds provide potential for lengthening of steel beams, structures with thin Elements, small tolerances or HSS, and fatigue sensitive, composite, hybrid and laminated structures. Due to the relative low weight, adhesive bonds have potential for light weight structures. Due to the appearance, aesthetics may allow the choice for adhesive bonding. For structural engineering there are four specific points of attention. Firstly, the strength of adhesive bonds depend on the adhesive thickness. An optimal thickness exists which is relatively small. The tolerances used in structural engineering make the application of a thin bondline difficult. Secondly, the service life of structural engineering applications is usually 50 years. At such time spans the time-and-environmental effect may lower the design strength drastically. Thirdly, for adhesive bonding a clean working environment is needed, which is difficult to achieve on a construction site. Finally, there is a lack in knowledge, products and code/directives for structural engineering. For adhesive bonded beam-to-column connections a continuous beam instead of a continuous column is beneficial with respect to tension. Nevertheless, tension is hard to avoid in T- or X-shaped beam-to-column connections. An L-shaped roof connection is the most suitable beam-to-column connection for adhesive bonding. The connection can be achieved by two adhesive bonded L-shape plates to the flanges of the beam and column at the inner and outer corner. Linear elastic FEM calculations with linear Elements show that, due to shear lag, the effective length of these plates is limited. Due to the large differences of axial stiffness over the width of an H-shaped profile, load transfer mainly takes place near the web. Calculations with Higher Order Element or non-linear material behaviour are not possible with commercial computers. To increase the efficiency of load transfer at the middle of a lap, stepped adherents can be used. The change of axial stiffness at the steps causes an uplift of the shear stress distribution. FEM and practice tests are executed for an adhesive bonded stepped double strap connection. The connection exists of two 15mm thick steel plates (S235) which are bonded (Sikadur-30) by two bonded (Sikadur-30) steel stepped straps. The straps exists of three 3mm thick, steel plates (S235) of 200mm, 400mm and 600mm length. FEM calculations predict a nearly linear load-displacement curve and a failure load of at least 400kN. The load-displacement curves of the practice tests are similar to the FEM curves up to 300kN, afterwards the curve slowly flattens. A mean failure load of 561kN, a sample standard deviation of 12.85kN and a 5th percentile failure load of 549kN have been achieved. Failure was imposed by adhesion failure; all connections show delamination near nearly all lap ends.