Large Scale Simulation with Scaled Boundary Finite Element Method

Nowadays scientific and engineering applications often require wave propagation in infinite or unbounded domains. In order to model such applications we separate our model into near-field and far-field. The near-field is represented by the well-known finite element method (FEM), whereas the far-field is mapped by a scaled boundary finite element (SBFE) approach. This latter approach allows wave propagation in infinite domains and suppresses the reflection of waves at the boundary, thus being a suitable method to model wave propagation to infinity. It is non-local in time and space. From a computational point of view, those characteristics are a drawback because they lead to storage consuming calculations with high computational time-effort. The non-locality in space causes fully populated unit-impulse acceleration influence matrices for each time step, leading to immense storage consumption for problems with a large number of degrees of freedom. Additionally, a different influence matrix has to be assembled for each time step which yields unacceptable storage requirements for long simulation times. For long slender domains, where many nodes are rather far from each other and where the influence of the degrees of freedom of those distant nodes is neglectable, substructuring represents an efficient method to reduce storage requirements and computational effort. The presented simulation with substructuring still yields satisfactory results. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Prediction of energy decay in room impulse responses simulated with an image-source model

A method is proposed that provides an approximation of the acoustic energy decay (energy-time curve) in room impulse responses generated using the image-source technique. A geometrical analysis of the image-source principle leads to a closed-form expression describing the energy decay curve, with the resulting formula being valid for a uniform as well as nonuniform definition of the enclosure's six absorption coefficients. The accuracy of the proposed approximation is demonstrated on the basis of impulse-response simulations involving various room sizes and reverberation levels, with uniform and nonuniform sound absorption coefficients. An application example for the proposed method is illustrated by considering the task of predicting an enclosure's reflection coefficients in order to achieve a specific reverberation level. The technique presented in this work enables designers to undertake a preliminary analysis of a simulated reverberant environment without the need for time-consuming image-method simulations.     

Horizontal capillary flow of a Newtonian liquid in a narrow gap between a plane wall and a sinusoidal wall

An experimental and theoretical study of the capillary flow of a Newtonian liquid (mineral oil) in a Hele-Shaw cell in which the gap varies sinusoidally in one coordinate direction, and flow takes place in the direction of constant channel cross-sectional area is reported. The geometric non-uniformity of the gap is observed to produce interface fingering. Finger length is observed to increase with decreasing spacing between plates of fixed shape, and with increasing gross penetration distance. In the regime of interest, finger length is observed to increase slowly with increasing interface advancement, motivating a quasi-steady model in which gross interface advancement is predicted by a Lucas–Washburn model and interface fingering is predicted by a Hele-Shaw model of steady flow. The steady interface velocity in the Hele-Shaw model is set equal to the instantaneous interface velocity predicted by the Lucas–Washburn model. Fingering predicted by the quasi-steady model matches the experimentally observed trends with regards to plate spacing and gross penetration distance.     

Excess Molar Volumes and Viscosities of Binary Mixtures of Methanol and the Ionic Liquid 4-Methyl-N-butylpyridinium Tetrafluoroborate at 25, 40, and 50°C

Experimental data of densities and viscosities are presented for the system 4-methyl-N-butylpyridinium tetrafluoroborate + methanol at 25, 40, and 50, 323.15 K and ambient pressure using a vibratage-tube densimeter and an Ubbelohde viscometer. Excess molar volumes V ^E and excess logarithm viscosities (ln )^E have been determined. V ^E is negative and (ln )^E positive over the entire mixture composition.     

Saline Water Evaporation and Crystallization-Induced Deformations in Building Stone: Insights from High-Resolution Neutron Radiography

Transport in Porous Media - To assess salt damage risks in building materials and geomaterials, the key components to identify are the accumulation of salts and the damage propagation. Experimental...     

Efficient viscosity contrast calculation for blood flow simulations using the lattice Boltzmann method

The lattice Boltzmann method (LBM) combined with the immersed boundary method is a common tool to simulate the movement of red blood cel ls (RBCs) through blood vessels. With very few exceptions, such simulations neglect the difference in viscosities between the hemoglobin solution inside the cells and the blood plasma outside, although it is well known that this viscosity contrast can severely affect cell deformation. While it is easy to change the local viscosity in LBM, the challenge is to distinguish whether a given lattice point is inside or outside the RBC at each time step. Here, we present a fast algorithm to solve this issue by tracking the membrane motion and computing the scalar product between the local surface normal and the distance vector between the closest LBM lattice point and the surface. This approach is much faster than, for example, the ray-casting method. With the domain tracking applied, we investigate the shape transition of a RBC in a microchannel for different viscosity contrast and validate our method by comparing with boundary-integral simulations.     

Nickel(II) Phosphane- and N-heterocyclic Carbene Complexes with Tridentate,Dianionic [S,N,O]2– Ligands

Square-planar dinuclear nickel(II) complexes containing [S,N,O]^2– ligands formed by condensation of acetyl acetone or benzoyl acetone with cysteamine were prepared. These dimeric nickel(II) compounds undergo bridge-cleavage reactions with the cage phosphine PTA (PTA = 1,3,5-triaza-7-phosphaadamantane) or in situ generated N-heterocyclic carbenes. The resulting diamagnetic, square planar Ni^II complexes were characterized by spectroscopic methods and X-ray diffraction.     

Occurrence of superconductivity in R2-z Ce z CuO4 and related compounds

The facts concerning the occurrence of superconductivity in R_2-z Ce _z CuO₄ and in R_2-z Th _z CuO₄ are studied using a combination of simple tools: a hard-sphere model, the self-consistent bond-valence-sum method and Madelung potential calculations. Doping by isolated substitutional Ce should produce Ce³⁺, and not Ce⁴⁺, causing us to conclude that the dopants are not isolated, but (Ce, O_interstitial) pairs, which make the material p type and not n type. The L = 0 magnetic rare-earth ions Gd and Cm are unsplit pair breakers, unlike the other magnetic rare-earth ions which lead to superconductivity. As the rare-earth ions become smaller, the c-axis length shortens; then the O ions rotate after they come into contact with one another. Eu_1.85Th_0.15CuO₄ does not superconduct because quadrivalent Th is too large to fit at the dopant site, but Eu_1.85Ce_0.15CuO₄ does superconduct because Ce fits.