Multifield modeling of concrete with discrete element methods

Bauwerke aus Beton sind im Bauwesen weit verbreitet. Die Bauweise ist vergleichsweise kostengünstig und in der Regel durch eine hohe Dauerhaftigkeit und lange Nutzbarkeit gekennzeichnet. Die Umwelt­bedingungen sind je nach Einsatzzweck sehr variabel und müssen bereits beim Entwurf der Betonrezeptur berücksichtigt werden. Immer wieder kommt es dennoch zu Schäden an Betonbauwerken, die eine erhebliche Verkürzung der Lebensdauer zur Folge haben können. Die Erfassung und Bewertung der Schäden ist für eine Prognose der Restlebensdauer unerlässlich. In dieser Arbeit wird ein numerisches Modellierungskonzept auf Basis diskreter Elemente vorgestellt, welches den Beton auf der Mesoskala beschreibt. Die Prozesse auf dieser und den darunter liegenden Ebenen bestimmen maßgeblich die makroskopischen Eigenschaften. Das heterogene Gefüge wird mit Partikelpackungen unterschiedlicher Korngrößen­verteilungen beschrieben. Zur Reduzierung des numerischen Aufwandes wird der Zementstein über die Kontaktbedingungen berücksichtigt und nur die Gesteinskörnung explizit abgebildet. Neben dem mechanischen Verhalten sind auch thermische und chemische Einflüsse sowie deren Wechselwirkungen im Modell erfasst. Zu den höchsten thermischen Belastungen eines Bauteils zählt der Brandfall, dessen thermo-mechanische Auswirkungen mit dem Modell beschrieben werden können. Mögliche Betonabplatzungen infolge starker Temperaturgradienten werden über Bruchbedingungen erfasst. Der Wärmetransport erfolgt mit Hilfe thermischer Verbindungselemente zwischen einzelnen Partikeln. Die Eigenschaften des erhärteten Betons werden maßgeblich durch die Wahl der Zusammensetzung bestimmt. Die Hydratationsreaktionen der Zementsteinphasen sorgen für die Festigkeit und setzen eine hohe Menge an Wärmeenergie frei. Ein vereinfachendes Hydratationsmodell zeigt die chemisch-thermische Kopplung. Für die Beschreibung von Transportprozessen wird ein Poren-Netzwerk Modell verwendet, das auf der Basis einer radikalen VORONOI-Tesselation erstellt wird. Prozesszonen verknüpfen das Poren-Netzwerk mit dem Festkörpermodell und werden zur Berechnung beliebiger chemischer Reaktionen genutzt. Als Beispiel für die chemo-thermisch-mechani-sche Kopplung wird der Sulfatangriff gezeigt.Concrete structures are widely used in civil engineering. The construction method is comparatively cost-efficient and is generally characterized by high durability and long service life. The environmental conditions are quite variable depending on the intended use and must be taken into account already at the design stage of the concrete mix design. Nevertheless, damage to concrete structures occurs at various times, which can lead to a considerable reduction in service life. The identification and evaluation of the damage are essential to predict the remaining service life. In this thesis, a numerical modeling concept based on discrete elements is presented, which describes concrete on the meso-scale. The processes on this and lower scales determine the macroscopic properties to a large extent. The heterogeneous structure is described by particle packings of different grading curves. To reduce the numerical effort, the cement stone is considered by contact conditions and only the aggregate is explicitly represented. Besides the mechanical behavior, thermal and chemical influences and their interactions are also included in the model. One of the highest thermal loads of a member is the fire case, whose thermo-mechanical effects can be described by the model. Possible concrete spalling due to strong temperature gradients is captured via fracture conditions. The heat transport is realized using thermal link elements between individual particles. The properties of hardened concrete are mainly determined by the choice of composition. The hydration reactions of the hardened cement paste phases ensure strength and release a high amount of thermal energy. A simplified hydration model shows the chemical-thermal coupling. For the description of transport processes a pore network model is used, which is based on a radical VORONOI-tesselation. Process zones link the pore network with the solid structure model and are used to calculate any chemical reaction. As an example for chemo-thermal-mechanical coupling, the sulfate attack is shown

Bis[(2-pyridylmeth­yl)(triisopropyl­silyl)amido]zinc(II)–toluene–tetra­hydro­furan (4/2/1)

The transamination reaction of (2-pyridylmeth­yl)(triiso­propyl­silyl)amine with bis­{bis­(trimethyl­silyl)amido}zinc(II) yields the colorless title solvate, [Zn(C15H27N2Si)2]·0.5C7H8·0.25C4H8O. The title compound was crystallized from toluene and tetra­hydro­furan. There are two independent mol­ecules in the asymmetric unit. In each mol­ecule, the Zn atom is tetra­hedrally coordinated by four N atoms. The two mol­ecules differ in the orientation of the isopropyl groups. The mol­ecules show large N—Zn—N angles [143.0 (2) and 145.7 (2)° between the amide groups]

Poly[tetra­kis­(seleno­cyanato-κN)bis­(methanol-κO)tris­(μ-pyrimidine-κ2 N:N′)dicobalt(II)]

In the title compound, [Co2(NCSe)4(C4H4N2)3(CH3OH)2]n, the CoII ion is coordinated by three N-bonded pyrimidine ligands, two N-bonded seleno­cyanate anions and one O-bonded methanol mol­ecule in an octa­hedral coordination mode. The asymmetric unit consists of one CoII ion, one pyrimidine ligand, two seleno­cyanate anions and one methanol mol­ecule in general positions as well as one pyrimidine ligand located around a twofold rotation axis. In the crystal structure, the pyrimidine ligands bridge [Co(CNSe)2(CH3OH)] units into zigzag-like chains, which are further connected by pyrimidine ligands into layers parallel to (010)

Hydrodynamic coefficients of mussel dropper lines derived from large-scale experiments and structural dynamics

The expansion of marine aquaculture production is driven by a high market demand for marine proteins and a stagnation of wild catch of fish. Bivalve farming, i.e., the cultivation of oysters, mussels and scallops, is an important part of the ongoing market dynamics and production expansion. As marine spatial planning is considering various use purposes, available space for near-shore aquaculture is already becoming scarce; this has fueled research and development initiatives to enable production installations further offshore. The highly energetic conditions at more exposed offshore marine sites lead to increased loads on aquaculture systems and their components and it is still not sufficiently understood how the load transfer from oceanic environmental conditions onto shellfish-encrusted surfaces attached to elastic ropes may be appropriately quantified. This study data gathered large-scale data sets in a wave tank facility, which are used to validate a novel, numerical model, building on the dynamics of rope structures which allows for the determination of the hydrodynamic loads transferred to the dropper lines. The forces and hydrodynamic parameters are measured and numerically analyzed. Based on the results, drag and inertia coefficients are determined. A drag coefficient of CD= 1.1 and an inertia coefficient of CM= 1.7 are recommended to model shellfish-encrusted dropper lines exposed to oscillatory flows with KC = 40–90. The numerical model for the determination of wave-induced forces on mussel dropper lines is developed and validated using the experimental data. It employs a modified Morison equation, which takes into account the displacement of the mussel dropper line. The influence of varying aquaculture-related parameters is discussed by applying the numerical model. Based on the gathered insights, recommendations can be given from an engineering point of view concerning the optimal placement of mussel aquaculture within the water column

catena-Poly[[μ3-hydroxido-tetra-μ2-pyrid­azine-1:2κ4 N:N′;1:3κ2 N:N′;2:3κ2 N:N′-tetrakis(selenocyanato)-1κN,2κN,3κ2 N-trizinc(II)]-μ-cyanido-1:2′κ2 C:N]

In the crystal structure of the title compound, [Zn3(NCSe)4(OH)(CN)(C4H4N2)4]n one of the two crystallograph­ically independent zinc(II) cations is coordinated by two terminal N-bonded seleno­cyanato anions and two N atoms of two symmetry-related pyridazine ligands in a trigonal-bipyramidal geometry, while the other zinc(II) cation is coordinated by one terminal N-bonded seleno­cyanato anion, one μ-1,2-cyanido anion and three N atoms of three crystallographically independent pyridazine ligands in a slightly distorted octa­hedral coordination geometry. The zinc(II) atoms are further connected via a μ3-hydroxido anion into trinuclear building blocks. The formula unit consists of three zinc cations, four seleno­cyanato anions, one μ3-hydroxido anion, four pyridazine mol­ecules as well as one cyanido anion. The asymmetric unit contains half of a formula unit. One of the zinc atoms, two seleno­cyanato anions, two pyridazine ligands and the μ3-hydroxido anion are located on a crystallographic mirror plane, whereas the cyanido anion is located on a twofold rotation axis. Therefore, this anion is disordered due to symmetry. The cyanido anions connect the metal centres into polymeric zigzag chains propagating along the a axis

Poly[bis­(acetonitrile-κN)di-μ-thio­cyanato-κ2 N,S;κ2 S,N-nickel(II)]

In the title compound, [Ni(NCS)2(CH3CN)2]n, the NiII cation is coordinated by two N-bonded and two S-bonded thio­cyanate anions, as well as two acetonitrile mol­ecules in an octa­hedral NiN4S2 coordination mode. The asymmetric unit comprises one nickel cation, two thio­cyanate anions and two actonitrile mol­ecules. In the crystal, the NiII cations are connected by bridging thio­cyanate anions into a three-dimensional coordination network

Poly[bis­(methanol-κO)tris­(μ-pyrimidine-κ2 N:N′)tetra­kis(thio­cyanato-κN)dinickel(II)]

In the crystal structure of the title compound, [Ni2(NCS)4(C4H4N2)3(CH3OH)2]n, each nickel(II) cation is coordinated by three N-bonded pyrimidine ligands, two N-bonded thio­cyanate anions and one O-bonded methanol mol­ecule in a distorted octa­hedral environment. The asymmetric unit consists of one nickel cation, two thio­cyanate anions and one methanol mol­ecule in general positions, as well as one pyrimidine ligand located around a twofold rotation axis. The crystal structure consists of μ-N:N′ pyrimidine-bridged zigzag-like nickel thio­cyanate chains; these are further linked by μ-N:N-bridging pyrimidine ligands into layers which are stacked perpendicular to the b axis. The layers are connected via weak O—H⋯S hydrogen bonding

Chloridotetra­pyridine­copper(II) dicyanamidate pyridine disolvate

In the crystal structure of the title compound, [CuCl(C5H5N)4][N(CN)2]·2C6H5N, the copper(II) cations are coordinated by one chloride anion and four N-bonded pyridine ligands into discrete complexes. The copper(II) cation shows a square-pyramidal coordination environment, with the chloride anion in the apical position. However, there is one additional chloride anion at 3.0065 (9) Å, leading to a disorted octa­hedral coordination mode for copper. The copper(II) cation, the chloride ligand and the central N atom of the dicyanamide anion are located on twofold rotation axes. Two pyridine solvent molecules are observed in general positions

cis-Dichlorido(1,3-dimesitylimidazolidin-2-yl­idene)(2-formyl­benzyl­idene-κ2 C,O)ruthenium diethyl ether solvate

The title compound, [RuCl2(C8H6O)(C21H26N2)]·C4H10O, contains a catalytically active ruthenium carbene complex of the ‘second-generation Grubbs/Hoveyda’ type with Ru in a square-pyramidal coordination, the apex of which is formed by the benzyl­idene carbene atom with Ru=C 1.827 (2) Å. The complex shows the uncommon cis, rather than the usual trans, arrangement of the two chloride ligands, with Ru—Cl bond lengths of 2.3548 (6) and 2.3600 (6) Å, and a Cl—Ru—Cl angle of 89.76 (2)°. This cis configuration is desirable for certain applications of ring-opening metathesis polymerization (ROMP) of strained cyclic olefins. The crystalline solid is a diethyl ether solvate, which is built up from a porous framework of Ru complexes held together by π–π stacking and C—H⋯Cl and C—H⋯O inter­actions. The disordered diethyl ether solvent mol­ecules are contained in two independent infinite channels, which extend parallel to the c axis at x,y = 0,0 and x,y = , and have solvent-accessible void volumes of 695 and 464 Å3 per unit cell

(S)-1,2-Dimethyl-1,1,2-triphenyl-2-(4-piperidiniometh­yl)disilane chloride

The title compound, C26H34NSi2 +·Cl−, shows chirality at silicon. Because of its highly selective synthesis with an e.r. of >99:1 by means of a racemic resolution with mandelic acid, the free disilane is of great importance to the chemistry of highly enanti­omerically enriched lithio­silanes and their trapping products. N—H⋯Cl hydrogen bonding is present between the protonated nitro­gen atom of the piperidino group and the chloride counter-anion. The silicon–silicon distance as well as silicon–carbon and carbon–nitro­gen bond lengths are in the same ranges as in other quaternary, functionalized di- and tetra­silanes