Aerodynamic forces on a tall building in a turbulent boundary layer

The model studies were designed to obtain information concerning wind loads on a tall building by placing the model in a turbulent shear flow simulating expected atmospheric boundary-layer winds. Since current design codes are inadequate for predicting all possible motions of tall buildings, it is important that better knowledge of mean and fluctuating loadings and their distributions becomes available. Experiments were conducted to determine the mean and fluctuating forces and twisting moments at several levels over the surface of a model. By determining the effects at several levels simultaneously, it was possible to correlate forces and moments at five levels with one common level. A single model was tested at varying orientations. Tests were also conducted with an identical model placed upstream so that its wake influenced the flow around the instrumented model. Results are presented in terms of distributions of force and moment coefficients and correlations at different levels. The spectral character of the force and moment components is illustrated for one case. Paper was presented at 1977 SESA Spring Meeting held in Dallas, TX on May 15–20.     

An easy-to-use estimate of the energy-release rate for crack arrays

Formation of crack arrays plays an increasing role in several fields of applied physics. The energy-release rate of the cracks controls the development of the array. Therefore, following the concept of configurational forces, a simplified analytical expression is provided for the energy-release rate, which is based both on numerical studies and on a specially adapted beam model. Comparisons of this easy-to-use estimate of the energy-release rate with established results from the literature as well as detailed numerical results are presented. The provided estimate of the energy-release rate can easily be extended to non-equidistant cracks and an anisotropic material.     

An analysis for the DIIS acceleration method used in quantum chemistry calculations

This work features an analysis for the acceleration technique DIIS that is standardly used in most of the important quantum chemistry codes, e.g. in DFT and Hartree–Fock calculations and in the Coupled Cluster method. Taking up results from Harrison (J Comput Chem 25:328, 2003), we show that for the general nonlinear case, DIIS corresponds to a projected quasi-Newton/secant method. For linear systems, we establish connections to the well-known GMRES solver and transfer according (positive as well as negative) convergence results to DIIS. In particular, we discuss the circumstances under which DIIS exhibits superlinear convergence behaviour. For the general nonlinear case, we then use these results to show that a DIIS step can be interpreted as step of a quasi-Newton method in which the Jacobian used in the Newton step is approximated by finite differences and in which the according linear system is solved by a GMRES procedure, and give according convergence estimates.     

Flow structures and heat transfer characteristics in arrays of submerged laminar impinging jets

This study summarizes the scaling behavior of single laminar submerged jets with circular and planar cross sections. Unified correlations for the stagnation zone heat transfer of both configurations, based on the dominant dimensionless numbers, are presented. In technical applications, impinging jets are often applied in jet array configurations. Compared to single jet impingement, jet-to-jet interaction can have a substantial influence on local heat transfer. A distinct pattern of the heat transfer coefficient was observed experimentally. Numerical simulations revealed two counter-rotating vortices in the interaction zone between two jets to be the causing mechanism of this pattern. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bis[N,N′‐diisopropylbenzamidinato(−)]silicon(II): Lewis Acid/Base Reactions with Triorganylboranes

Reaction of the donor‐stabilized silylene 1 (which is three‐coordinate in the solid state and four‐coordinate in solution) with BEt₃ and BPh₃ leads to the formation of the Lewis acid/base complexes 2 and 3 , respectively, which are the first five‐coordinate silicon compounds with an Si?B bond. These compounds were structurally characterized by crystal structure analyses and by multinuclear NMR spectroscopic studies in the solid state and in solution. Additionally, the bonding situation in 2 and 3 was analyzed by quantum chemical studies.