Unique critical state single-surface anisotropic hyperplasticity

This paper presents the theoretical development and algorithmic implementation of a single surface anisotropic hyperplasticity model. The model extends the isotropic family of models developed by Coombs and Crouch (2011) through (i) intro- ducing anisotropic shearing into the yield surface and (ii) using a more physically realistic pressure sensitive elastic free energy function. This model overcomes the difficulty of determining the constants of the isotropic two-parameter surface by analytically relat- ing them to a single experimentally measurable physical quantity, namely the normalised hydrostatic position of the Critical State. This link results in a unique Critical State surface, invariant of the level of anisotropy inherent in the yield envelope. The model is compared with experimental data on Lower Cromer Till and contrasted against the SANIclay model

The Transformative Effects of Public-Private Partnerships in Cleveland: An Inside View of Good Government under Mayors Voinovich and Jackson

This article focuses on two mayoral-led public-private partnerships designed to renew good government in Cleveland — Mayor George Voinovich’s Operations Improvement Task Force (OITF) (1979-1982) and Mayor Frank Jackson’s Operations Efficiency Task Force (OETF) (2006-2009). The Voinovich OITF public-private partnership enabled Cleveland to “come back” after the city’s 1978 default. The Jackson OETF public-private partnership successfully rightsized Cleveland in relationship to its much smaller population needs during challenging economic times without disruptions in service. The authors use three data sources, including interviews with both mayors and their key partnership managers, to gain a complete inside picture of each mayoral-led public-private partnership. The article concludes with the lessons learned and the governance implications of a mayoral-led public-private partnership in fostering long-term (transformative) administrative change. This article shows how both mayoral-led public-private partnerships quietly transformed Cleveland’s government to meet the demands of fewer resources, greater complexity, more transparency, and more timely decisions in the delivery of public services to citizens

A geometrically-exact Finite Element Method for micropolar continua with finite deformations

Micropolar theory is a weakly non-local higher-order continuum theory based on the inclusion of independent (micro-)rotational degrees of freedom. Subsequent introduction of couple-stresses and an internal length scale mean the micropolar continuum is therefore capable of modelling size effects. This paper proposes a non-linear Finite Element Method based on the spatial micropolar equilibrium equations, but using the classical linear micropolar constitutive laws defined in the reference configuration. The method is verified rigorously with the Method of Manufactured Solutions, and quadratic Newton-Raphson convergence of the minimised residuals is demonstrated

An hp-adaptive discontinuous Galerkin method for phase field fracture

The phase field method is becoming the de facto choice for the numerical analysis of complex problems that involve multiple initiating, propagating, interacting, branching and merging fractures. However, within the context of finite element modelling, the method requires a fine mesh in regions where fractures will propagate, in order to capture sharp variations in the phase field representing the fractured/damaged regions. This means that the method can become computationally expensive when the fracture propagation paths are not known a priori. This paper presents a 2D -adaptive discontinuous Galerkin finite element method for phase field fracture that includes a posteriori error estimators for both the elasticity and phase field equations, which drive mesh adaptivity for static and propagating fractures. This combination means that it is possible to be reliably and efficiently solve phase field fracture problems with arbitrary initial meshes, irrespective of the initial geometry or loading conditions. This ability is demonstrated on several example problems, which are solved using a light-BFGS (Broyden–Fletcher–Goldfarb–Shanno) quasi-Newton algorithm. The examples highlight the importance of driving mesh adaptivity using both the elasticity and phase field errors for physically meaningful, yet computationally tractable, results. They also reveal the importance of including -refinement, which is typically not included in existing phase field literature. The above features provide a powerful and general tool for modelling fracture propagation with controlled errors and degree-of-freedom optimised meshes

Modelling Screwpile Installation Using the MPM

Screwpiles are, as the name suggests, piled foundations which are screwed into the ground. They provide restraint to both upwards and downward loading directions and are commonly used for light structures subject to overturning or wind loading, such as sign gantries at the sides of motorways. An EPSRC-funded project led by University of Dundee has recently started, with Durham and Southampton as partners, in which the use of screwpiles (individual or in groups) for offshore foundations is under investigation. At Durham, a numerical modelling framework based on the material point method (MPM) is being developed for the installation phase of a screwpile. The aim is to use the model to provide an accurate representation of the in situ ground conditions once the pile is installed, as during installation the ground is disturbed and any model that “wishes in place” a screwpile may not provide representative long-term performance predictions. Following modelling of installation, the soil state will be transferred to a standard finite element package for the subsequent modelling of in-service performance (the MPM being considered unnecessary and computationally expensive for this phase of the life of a screwpile). In this preliminary work, we present the development of features of this numerical tool to simulate the screwpile installation. These features include a moving mesh concept (both translation and rotation) and interface elements. The effectiveness of the algorithm is illustrated through simple examples

Physical modelling to demonstrate the feasibility of screw piles for offshore jacket supported wind energy structures

Screw piles potentially offer quieter installation and enhanced axial tensile capacity over straight shafted driven piles. As such, they have been suggested as a possible foundation solution for offshore jacket supported wind turbines in deeper water. To investigate the feasibility of their use in this setting, centrifuge testing of six model screw piles of different designs was conducted to measure the installation requirements and ultimate axial capacity of the piles in very-dense and medium-dense sand. The screw piles were designed to sustain loads generated by an extreme design scenario using published axial capacity and torque prediction formulae. Single and double-helix designs, including an optimised design, intended to minimise installation requirements, with reduced geometry were installed and tested in-flight. Piles in the medium-dense sand for example had significant installation requirements of up to 18.4MNm (torque) and 28.8MN (vertical force) which were accurately predicted using correlations with cone resistance data (CPT). Existing axial capacity design methods did not perform well for these large-scale screw piles, overestimating compressive and tensile capacities. Revised analytical methods for installation and axial capacity estimates are proposed here based on the centrifuge test results