The aim of this study is to investigate the dynamic response of axially moving two-layer laminated plates on the Winkler and Pasternak foundations. The upper and lower layers are formed from a bidirectional functional...The aim of this study is to investigate the dynamic response of axially moving two-layer laminated plates on the Winkler and Pasternak foundations. The upper and lower layers are formed from a bidirectional functionally graded(FG) layer and a graphene platelet(GPL) reinforced porous layer, respectively. Henceforth, the combined layers will be referred to as a two-dimensional(2D) FG/GPL plate. Two types of porosity and three graphene dispersion patterns, each of which is distributed through the plate thickness,are investigated. The mechanical properties of the closed-cell layers are used to define the variation of Poisson’s ratio and the relationship between the porosity coefficients and the mass density. For the GPL reinforced layer, the effective Young’s modulus is derived with the Halpin-Tsai micro-system model, and the rule of mixtures is used to calculate the effective mass density and Poisson’s ratio. The material of the upper 2D-FG layer is graded in two directions, and its effective mechanical properties are also derived with the rule of mixtures. The dynamic governing equations are derived with a first-order shear deformation theory(FSDT) and the von Kármán nonlinear theory. A combination of the dynamic relaxation(DR) and Newmark’s direct integration methods is used to solve the governing equations in both time and space. A parametric study is carried out to explore the effects of the porosity coefficients, porosity and GPL distributions, material gradients, damping ratios, boundary conditions, and elastic foundation stiffnesses on the plate response. It is shown that both the distributions of the porosity and graphene nanofillers significantly affect the dynamic behaviors of the plates. It is also shown that the reduction in the dynamic deflection of the bilayer composite plates is maximized when the porosity and GPL distributions are symmetric.展开更多
Subsea pipelines passing through the shallow area are physically protected against the environmental,accidental,and operational loads by trenching and backfilling.Depending on construction methodology,environmental lo...Subsea pipelines passing through the shallow area are physically protected against the environmental,accidental,and operational loads by trenching and backfilling.Depending on construction methodology,environmental loads,and seabed soil properties,the stiffness of backfilling material may become largely different from the native ground(softer than native ground in most of the cases).The different stiffness between the backfill and native ground affects the soil failure mechanisms and lateral soil resistance against large pipeline displacements that may happen due to ground movement,landslides,ice gouging,and drag embedment anchors.This important aspect is not considered by current design codes.In this paper,the effect of trench-backfill stiffness difference on lateral pipeline-backfill-trench interaction was investigated by performing centrifuge tests.The soil deformations and failure mechanisms were obtained by particle image velocimetry(PIV)analysis.Three experiments were conducted by using three different backfills including loose sand,slurry,and chunky clay that represent the purchased,natural in-fill,and preexcavated materials,respectively.The study shows that the current design codes underestimate the lateral soil resistance for small to moderate pipe displacements inside the trench and overestimate it for large lateral displacement,where the pipeline is penetrating into the trench wall.展开更多
文摘The aim of this study is to investigate the dynamic response of axially moving two-layer laminated plates on the Winkler and Pasternak foundations. The upper and lower layers are formed from a bidirectional functionally graded(FG) layer and a graphene platelet(GPL) reinforced porous layer, respectively. Henceforth, the combined layers will be referred to as a two-dimensional(2D) FG/GPL plate. Two types of porosity and three graphene dispersion patterns, each of which is distributed through the plate thickness,are investigated. The mechanical properties of the closed-cell layers are used to define the variation of Poisson’s ratio and the relationship between the porosity coefficients and the mass density. For the GPL reinforced layer, the effective Young’s modulus is derived with the Halpin-Tsai micro-system model, and the rule of mixtures is used to calculate the effective mass density and Poisson’s ratio. The material of the upper 2D-FG layer is graded in two directions, and its effective mechanical properties are also derived with the rule of mixtures. The dynamic governing equations are derived with a first-order shear deformation theory(FSDT) and the von Kármán nonlinear theory. A combination of the dynamic relaxation(DR) and Newmark’s direct integration methods is used to solve the governing equations in both time and space. A parametric study is carried out to explore the effects of the porosity coefficients, porosity and GPL distributions, material gradients, damping ratios, boundary conditions, and elastic foundation stiffnesses on the plate response. It is shown that both the distributions of the porosity and graphene nanofillers significantly affect the dynamic behaviors of the plates. It is also shown that the reduction in the dynamic deflection of the bilayer composite plates is maximized when the porosity and GPL distributions are symmetric.
文摘Subsea pipelines passing through the shallow area are physically protected against the environmental,accidental,and operational loads by trenching and backfilling.Depending on construction methodology,environmental loads,and seabed soil properties,the stiffness of backfilling material may become largely different from the native ground(softer than native ground in most of the cases).The different stiffness between the backfill and native ground affects the soil failure mechanisms and lateral soil resistance against large pipeline displacements that may happen due to ground movement,landslides,ice gouging,and drag embedment anchors.This important aspect is not considered by current design codes.In this paper,the effect of trench-backfill stiffness difference on lateral pipeline-backfill-trench interaction was investigated by performing centrifuge tests.The soil deformations and failure mechanisms were obtained by particle image velocimetry(PIV)analysis.Three experiments were conducted by using three different backfills including loose sand,slurry,and chunky clay that represent the purchased,natural in-fill,and preexcavated materials,respectively.The study shows that the current design codes underestimate the lateral soil resistance for small to moderate pipe displacements inside the trench and overestimate it for large lateral displacement,where the pipeline is penetrating into the trench wall.
