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Paper des Monats
- ja (28)
The authors are currently investigating the possibility to apply compaction grouting for offshore pile foundations (Jacket piles as well as monopiles) as a possible retrofitting technique for an optimised foundation concept. In this research project, we are developing a design approach aiming to predict the ideal amount and properties of a grout for a specific soil situation and desired improvement of pile bearing capacity after Installation and during service time. Both numerical and experimental tests have been carried out to investigate the injection process during which a highly viscous grout is injected into the soil under high pressure to displace and compact the surrounding soil without fracturing it. The implicit Material Point Method (MPM) based on a mixed formulation is the numerical technique chosen to deal with the expected large deformations and the arbitrary shape of the developing grout bulb. The usage of MPM prevents both the need of remeshing and the numerical instability induced by extensive mesh distortion. For validation with experimental results, we have constructed a testing chamber with one transparent sidewall. This chamber enables us to observe the injection process directly at the transparent vertical window and to measure the in-plane soil displacements and strains by means of the Digital Image Correlation (DIC) technique.
The results already reveal the interrelation of soil and grout properties for a successful usage of this common ground improvement technique.
Coupling of an isogeometric surface and bulk finite element discretization for contact problems
(2018)
This work aims at combining the advantages of both discretization procedures (IGA and FEM) by coupling an isogeometric contact surface with a bulk FE-discretization. The isogeometric contact interface is represented by a NURBS surface, which is tied to the FE mesh. For the discretization of the bulk parts, higher order spectral elements are used. The contact problem is discretized with the mortar method and a penalty approach is used to enforce the contact constraints. Two different types of coupling of the NURBS surface and the bulk part are considered: mortar and pointwise mesh tying. The mortar mesh tying approach shows accurate results, whereas the pointwise tying leads to large oscillations in the contact stresses. Element-based quadrature is applied for mortar tying, as well as for mortar contact discretizations. Using an isogeometric layer, the related quadrature error can be efficiently reduced by a higher degree interpolation or increased integration order.
IAPR participates in the EMPIR 16SRT02, entitled ‘Certified forensic alcohol reference materials - ALCOREF’ funded by EURAMET as an external funded partner. The Research in this project will address the needs for better enforcement of drink-driving legislation in several European countries, by building up long-term capacities for the production and certification of forensic alcohol reference materials, suitable for the calibration of evidential breath alcohol analyzers. The certification procedure includes characterization of the materials, assessment of homogeneity, stability, and uncertainty estimation. An interlaboratory comparison will be conducted to test the materials and capabilities developed. EMPIR 16SRT02-ALCOREF project is coordinated by BAM (DE).
Chemical composition of the welding seam and HAZ has significant effect on weld quality. Current inspection methods for weld seams measure and investigate post factum and cannot prevent weld defects. Element burn-off may significantly affect solidification leading to embrittlement or cracking Control of weld chemical compositions insures a controlled solidification and resistance to related weld defects.
In the near future, phosphorus (P) recycling will gain importance in terms of decreasing primary resources. Sewage sludge (SSL) is an adequate secondary P-resource for P-fertilizer production but it is also a sink for heavy metals and organic pollutants. The present study is an investigation on thermochemical P-recycling of SSL. Various temperatures and amendments were tested regarding their performance to remove heavy metals and polycyclic aromatic hydrocarbons (PAH) and simultaneous increase of the plant-availability of P. The investigations were carried out on two types of SSL originating from wastewater treatment plants with chemical P-precipitation and enhanced biological P-removal, respectively. The results show that thermochemical treatment with chlorine donors is suitable to remove the majority of heavy metals and that a combination of a gaseous chlorine donor (HCl) and sodium additives leads to both high heavy metal removal and high plant availability of P. Furthermore, plant experiments Show that almost all investigated thermochemical treatments can significantly reduce the bioavailability and plant uptake of heavy metals. Furthermore, PAHs are secondarily formed during low-temperature treatments (400–500 ° ), but can be significantly reduced by using sodium carbonate as an additive.
An improved algorithm for calibration-free laser induced breakdown spectroscopy (CF LIBS) is presented which includes several novel features in comparison with previously proposed similar algorithms. In particular, it allows using spectral lines with arbitrary optical thickness for the construction of Saha-Boltzmann plots, retrieves the absorption path length (plasma diameter) directly from a spectrum, replaces the Lorentzian line profile function by the Voigt function, and allows for self-absorption correction using pre-calculated and tabulated data rather than approximating functions. The tabulated data embody the solutions of the radiative transfer equation for numerous combinations of optical thicknesses and line widths. The algorithm is thoroughly verified with synthetic spectra.
Laser-induced plasmas are widely used in many areas of science and technology; examples include spectrochemical analysis, thin film deposition, material processing, and even jet propulsion. Several topics will be addressed. First, general phenomenology of laser-induced plasmas will be discussed. Then, a chemical model will be presented based on a coupled solution of Navier-Stokes, state, radiative transfer, material transport, and chemical (Guldberg-Waage) equations. Results of computer simulations for several chemical systems will be shown and compared to experimental observations obtained by optical imaging, spectroscopy, and tomography. The latter diagnostic tools will also be briefly discussed. Finally, a prospective application of laser-induced plasma and plasma modeling will be illustrated on the example of calibration-free MC LIBS (Monte Carlo Laser Induced Breakdown Spectroscopy), in which concentrations of elements in materials are found by fitting model-generated and experimental spectra.
Moisture testing and mapping
(2018)
Selected resonance states of the deuterated formyl radical in the electronic ground state X^2A´ are computed using our recently introduced dynamically pruned discrete variable representation [H. R. Larsson, B. Hartke, and D. J. Tannor, J. Chem. Phys. 145, 204108 (2016)]. Their decay and asymptotic distributions are analyzed and, for selected resonances, compared to experimental results obtained by a combination of stimulated emission pumping and velocity-map Imaging of the product D atoms.
The theoretical results show good agreement with the experimental kinetic energy distributions. The intramolecular vibrational energy redistribution is analyzed and compared with previous results from an effective polyad Hamiltonian. Specifically, we analyzed the part of the wavefunction that remains in the interaction region during the decay. The results from the polyad Hamiltonian could mainly be confirmed. The C=O stretch quantum number is typically conserved, while the D-C=O bend quantum number decreases. Differences are due to strong anharmonic coupling such that all resonances have major contributions from several zero-order states. For some of the resonances, the coupling is so strong that no further zero-order states appear during the dynamics in the interaction region, even after propagating for 300 ps.