Recent advances in approximation concepts for optimum structural design

The basic approximation concepts used in structural optimization are reviewed. Some of the most recent developments in that area since the introduction of the concept in the mid-seventies are discussed. The paper distinguishes between local, medium-range, and global approximations; it covers functions approximations and problem approximations. It shows that, although the lack of comparative data established on reference test cases prevents an accurate assessment, there have been significant improvements. The largest number of developments have been in the areas of local function approximations and use of intermediate variable and response quantities. It also appears that some new methodologies are emerging which could greatly benefit from the introduction of new computer architecture

GPU-accelerated discontinuous Galerkin methods on hybrid meshes

We present a time-explicit discontinuous Galerkin (DG) solver for the time-domain acoustic wave equation on hybrid meshes containing vertex-mapped hexahedral, wedge, pyramidal and tetrahedral elements. Discretely energy-stable formulations are presented for both Gauss-Legendre and Gauss-Legendre-Lobatto (Spectral Element) nodal bases for the hexahedron. Stable timestep restrictions for hybrid meshes are derived by bounding the spectral radius of the DG operator using order-dependent constants in trace and Markov inequalities. Computational efficiency is achieved under a combination of element-specific kernels (including new quadrature-free operators for the pyramid), multi-rate timestepping, and acceleration using Graphics Processing Units.Comment: Submitted to CMAM

Polynomial regression under shape constraints

Calculating regression under shape constraints is a problem addressed by statisticians since long. This paper shows how to calculate a polynomial regression of any degree and of any number of variables under shape constraints, which include bounds, monotony, concavity constraints. Theoretical explanations are first introduced for monotony constraints and then applied to ad hoc examples to show the behavior of the proposed algorithm. Two real industrial cases are then detailed and worked out

Integrating knowledge accross disciplines. Experiences from the NeWater project

The starting question for this deliverable was how to create a new adaptive management concept that can integrate insights from various disciplines and connect people from different institutional backgrounds. From literature research and empirical research on the NeWater project we identified challenges for cross-disciplinary knowledge integration, we evaluated interventions for connecting multiple knowledge frames, we analyzed the process of group model building with UML and formulated recommendations. Cross-disciplinary research has arisen from a growing number of complex problems for which knowledge of a single scientific discipline or societal field is insufficient, but presents important challenges: (1) collaboration and integration of knowledge requires in depth discussions that are timeconsuming; (2) the recursive process of problem structuring and restructuring is often at odds with the sequential planning of project activities; (3) participation and mutual learning are crucial but need to be carefully structured and sequenced; and (4) management and leadership faces the difficult challenge of balancing in depth exploration with timely delivery of tangible results. We conclude with the following general recommendations for large cross-disciplinary projects: (1) including a preparatory proposal phase for thorough exploration of opportunities of between researchers and stakeholders (2) flexible funding, planning and operational arrangements to allow for a recursive research process; (3) a project size that allows frequent interaction opportunities between researchers and between researchers and stakeholders to allow for mutual learning and in depth exploration; and (4) enhancing learning opportunities from one project to the next

Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study

We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder diffraction experiments and electronic structure calculations. These alloys crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn sites (4c and 4c). The neutron data show that the substituting Fe atoms predominantly occupy the 4c transition metal site and carry a lower magnetic moment than Mn atoms. Four kinds of magnetic structures are encountered as a function of temperature and composition: two simple ferromagnetic structures (with the magnetic moments pointing along the b or c axis) and two canted ferromagnetic arrangements (with the ferromagnetic component pointing along the b or c axis). Electronic structure calculations results agree well with the low-temperature experimental magnetic moments and canting angles throughout the series. Comparisons between collinear and non-collinear computations show that the canted state is stabilized by a band mechanism through the opening of a hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This lowering of symmetry could explain the stabilization of the c-axis canted ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a circumstance that would otherwise require unusually large high-order terms in the spin Hamiltonian.Comment: 11 pages, 13 figure