Numerical Modelling of Sloshing with VOF Method

Sloshing in tanks carrying LNG, LPG and petroleum is an important phenomenon as dynamic pressure arises from sloshing can destroy the containing tanks. So it is vital to consider this phenomenon in design stages of carriers. The governing equations in fluid flow are conservation of mass and momentum. Modeling of free surface flow in tank needs a suitable tool. One of the most powerful tools to model the free surface is VOF method. Employing additional transport equation together with conservation of mass and momentum enable us to follow the free surface changes. A computer code was developed to evaluate sloshing problem. This code could calculate dynamic pressures exerted on walls of the containers. The model was validated using experimental data

Phasenübergang des Kraftstoff Sprays bei Umgebungsbedingungen des Dieselmotors: Nichtidealität des Phasengleichgewichts

In mixing controlled Diesel combustion concept, mixing processes are a key phenomenon which significantly effects power, efficiency and emissions. A consequence of fuel-air-mixing is the fuel phase change, which its nature in Diesel engine fuel sprays is not clear to this date. There are different stances on the question whether fuel or a fuel-rich phase might get supercritical (one-phase mixing) or not (two-phase mixing). In this study, phase change mechanisms of sprays of different n-alkanes at high temperature and pressure conditions are investigated. Mie scattering imaging is utilized to obtain the maximum liquid penetration of Diesel surrogates (dodecane, decane, heptane and hexane) injected into nitrogen atmosphere in a constant volume chamber at fuel supercritical temperature and ambient pressures ranging from sub- to supercritical with regard to fuel critical point. Two theoretical 1D calculations which are based on an air entrainment model derived from momentum conservation, are utilized to determine local mass ratios of ambient gas and fuel which leads to predict the liquid length based on the required enthalpy for full phase change. On the one hand, the assumption is taken that fuel evaporates without boiling or getting supercritical and on the other hand, evaporation is excluded, assuming that fuel is heated up until boiling or getting supercritical. Both models allow the calculation of values for liquid length of different fuel sprays. In following, these theoretical models are validated against experimental data (around 400 points) to identify phase change regimes for different fuels. Fitting the predicted liquid lengths from both models to the experimental data, the point of switching between those two models is the concept of “transition point”. The observed transition points for different fuels and temperatures are utilized to estimate a transition line. A transition line, at which the change from evaporation to boiling\transcritical phase change occurs, is indicator of “ideal phase equilibrium state” as well. Results indicate that along with ambient conditions, fuel properties remarkably influence the phase change mechanism in a spray. Especially fugacity plays an important role regarding the droplet evaporation rate. An equation is calibrated to the transition lines, as function of fuel fugacity and ambient temperature. The equation can be utilized to estimate the transition line for different fuels at different conditions with satisfactory accuracy.Im Modell der mischungsgesteuerten Verbrennung von Diesel sind Mischvorgänge ein Schlüsselphänomen, welches weitreichende Auswirkungen auf Leistung, Effizienz und Emissionen hat. Eine Folge der Vermischung von Kraftstoff und Luft ist der Kraftstoff-Phasenwechsel, dessen Eigenschaften in Dieselmotor-Kraftstoffsprays bis heute nicht eindeutig geklärt werden konnte. Es bestehen unterschiedliche Standpunkte zu der Frage, ob Kraftstoff oder eine kraftstoffreiche Phase unter Umständen überkritisch werden kann (einphasige Mischung) oder nicht (zweiphasige Mischung). Im Rahmen der vorliegenden Studie sollen Phasenwechselmechanismen von unterschiedlichen Sprühnebeln aus verschiedenen n-Alkanen bei extremen Bedingungen wie hohen Temperaturen oder hohem Druck untersucht werden. Es wird eine Mie-Streuungsbildgebung genutzt, um die maximale Menge von eindringender Flüssigkeit von Diesel-Surrogaten (Dodecane, Decane, Heptane und Hexane) zu erhalten, die in einer Kammer mit konstantem Volumen bei einer überkritischen Umgebungstemperatur und überkritischen Umgebungsdrücken, die im Hinblick auf den kritischen Punkt des Kraftstoffs von unter- bis überkritisch reichen, in eine Stickstoffatmosphäre injiziert werden. Zwei theoretische 1D-Berechnungen, die auf einem aus der Impulserhaltung hergeleiteten Luftporengehaltsmodell basieren, werden genutzt, um lokale Massenverhältnisse des Umgebungsgases und Brennstoffes zu bestimmen. Dies führt zu einer Vorhersage der Flüssigkeitslänge auf Basis der erforderlichen Enthalpie für einen vollständigen Phasenwechsel. Einerseits gilt die Annahme, dass der Brennstoff verdampft, ohne dabei zu sieden oder superkritisch zu werden. Auf der anderen Seite jedoch, ist eine Verdampfung ausgeschlossen, nimmt man an, dass der Brennstoff solange aufgeheizt wird, bis er siedet oder überkritisch wird. Beide Modelle machen die Berechnung von Werten für die Flüssigkeitslänge verschiedener Brennstoffzerstäubungen möglich. Diese theoretischen Modelle sollen in Folgenden auf Basis experimenteller Daten (ca. 400 Punkte) validiert werden, um Phasenwechselschemata verschiedener Brennstoffe zu identifizieren. Werden die vorhergesagten Flüssigkeitslängen beider Modelle an die experimentellen Daten angepasst, so ergibt sich im Punkt des Wechsels zwischen diesen beiden Modellen das Konzept des „Übergangspunktes“. Die so beobachteten Übergangspunkte verschiedener Brennstoffe und Temperaturen dienen dazu, eine Übergangslinie abzuschätzen - eine Übergangslinie, an der der Wechsel von Verdampfung zum Sieden bzw. der Wandel zur transkritischen Phase stattfindet, kann gleichermaßen als Indikator eines „idealen Phasengleichgewichtszustandes“ gesehen werden. Die Ergebnisse zeigen, dass zusätzlich zu den Umgebungsbedingungen die Brennstoffeigenschaften den Phasenänderungsmechanismus in einem Sprühnebel beachtlich beeinflussen. Vor allem Flüchtigkeit spielt hinsichtlich der Verdampfungsrate von Tropfen eine wichtige Rolle. So soll eine Gleichung für die Übergangslinien kalibriert werden, die als Funktion der Brennstoffflüchtigkeit und der Umgebungstemperatur dient. Diese kann genutzt werden, um die Übergangslinie für verschiedene Brennstoffe unter verschiedenen Bedingungen mit ausreichender Genauigkeit abzuschätzen

Effect of harvesting frequency and maturity stage of Jerusalem artichoke forage on yield, chemical composition and in vitro fermentation of the tubers and forage

Aim of study: To evaluate the effect of maturity stage and harvesting frequency of Jerusalem artichoke (JA) forage on the nutritional quality of the tubers and forages.Area of study: The plant cultivation and laboratory experiments were carried out in Karaj (Alborz, Iran) and Tehran (Tehran, Iran), respectively.Material and methods: Forages were harvested every 60, 90 and 120 days during the growing season (four, three and two harvests per year, respectively). Tubers were harvested just once, at the end of the growing season, from plots with four, three and two forage cuts per year. Biomass production, chemical composition and in vitro ruminal fermentation of the forages and tubers were assessed.Main results: Compared to 90 and 120 days, the forages harvested every 60 days contained the highest (p<0.05) yearly dry matter (DM) biomass (27.16 t/ha), crude protein (98.6 to 145 g/kg DM), organic matter digestibility (0.607 to 0.691) and microbial biomass production (350 to 369 g/kg DM). Compared to 60 and 90 days, harvesting JA forage every 120 days caused the tubers with the higher (p<0.05) water-soluble carbohydrates (WSC), in vitro digestibility and DM yield (7.63 t/ha). Jerusalem artichoke forages and tubers contained the low phenolics (4.93 to 13.2 g/kg DM) and nitrate (1.12 to 3.19 g/kg DM). Overall, the best harvesting interval of JA forage to achieve tubers with the highest yearly yield, WSC and digestibility was every 120 days, while the highest nutritive value and yield of the forages were observed with harvesting JA every 60 days.Research highlights: The best harvesting interval of JA forage to obtain the highest yearly DM, protein and energy biomass from both tubers and forage was every 60 days

Delineation of within-site terroir effects using soil and vine water measurement. Investigation of Cabernet Franc

. The influence of vine water status was studied in commercial vineyard blocks of Vilis vinifera L. cv. Cabernet Franc in Niagara Peninsula, Ontario from 2005 to 2007. Vine performance, fruit composition and vine size of non-irrigated grapevines were compared within ten vineyard blocks containing different soil and vine water status. Results showed that within each vineyard block water status zones could be identified on GIS-generated maps using leaf water potential and soil moisture measurements. Some yield and fruit composition variables correlated with the intensity of vine water status. Chemical and descriptive sensory analysis was performed on nine (2005) and eight (2006) pairs of experimental wines to illustrate differences between wines made from high and low water status winegrapes at each vineyard block. Twelve trained judges evaluated six aroma and flavor (red fruit, black cherry, black current, black pepper, bell pepper, and green bean), thr~e mouthfeel (astringency, bitterness and acidity) sensory attributes as well as color intensity. Each pair of high and low water status wine was compared using t-test. In 2005, low water status (L WS) wines from Buis, Harbour Estate, Henry of Pelham (HOP), and Vieni had higher color intensity; those form Chateau des Charmes (CDC) had high black cherry flavor; those at RiefEstates were high in red fruit flavor and at those from George site was high in red fruit aroma. In 2006, low water status (L WS) wines from George, Cave Spring and Morrison sites were high in color intensity. L WS wines from CDC, George and Morrison were more intense in black cherry aroma; LWS wines from Hernder site were high in red fruit aroma and flavor. No significant differences were found from one year to the next between the wines produced from the same vineyard, indicating that the attributes of these wines were maintained almost constant despite markedly different conditions in 2005 and 2006 vintages. Partial ii Least Square (PLS) analysis showed that leaf \}' was associated with red fruit aroma and flavor, berry and wine color intensity, total phenols, Brix and anthocyanins while soil moisture was explained with acidity, green bean aroma and flavor as well as bell pepper aroma and flavor. In another study chemical and descriptive sensory analysis was conducted on nine (2005) and eight (2006) medium water status (MWS) experimental wines to illustrate differences that might support the sub-appellation system in Niagara. The judges evaluated the same aroma, flavor, and mouthfeel sensory attributes as well as color intensity. Data were analyzed using analysis of variance (ANOVA), principal component analysis (PCA) and discriminate analysis (DA). ANOV A of sensory data showed regional differences for all sensory attributes. In 2005, wines from CDC, HOP, and Hemder sites showed highest. r ed fruit aroma and flavor. Lakeshore and Niagara River sites (Harbour, Reif, George, and Buis) wines showed higher bell pepper and green bean aroma and flavor due to proximity to the large bodies of water and less heat unit accumulation. In 2006, all sensory attributes except black pepper aroma were different. PCA revealed that wines from HOP and CDC sites were higher in red fruit, black currant and black cherry aroma and flavor as well as black pepper flavor, while wines from Hemder, Morrison and George sites were high in green bean aroma and flavor. ANOV A of chemical data in 2005 indicated that hue, color intensity, and titratable acidity (TA) were different across the sites, while in 2006, hue, color intensity and ethanol were different across the sites. These data indicate that there is the likelihood of substantial chemical and sensory differences between clusters of sub-appellations within the Niagara Peninsula ii

The Effectiveness of Coping Strategies Training with Irrational Beliefs (Cognitive Approach) on Test Anxiety of Students

AbstractThe purpose of this study was to investigate the effectiveness of coping strategies training the irrational beliefs (cognitive approach) on test anxiety of students in one graders of high school. The sample includes 60 students who were selected randomly, according to a multistage sampling method. They were then randomly assigned to experimental and control groups. The design of the study was of pretest-posttest control group type. Instrument used in this study was Ahvaz Test Anxiety Inventory and after and before intervention administrated to both groups. After 8 treatment sessions for experimental group and follow-up test, the result of Repeated Measure analysis revealed that the effects of coping strategies training process on decreasing test anxiety remained significant (p<0.05) for 4 weeks

Geodesic spanners for points on a polyhedral terrain

Let S be a set S of n points on a polyhedral terrain T in R3, and let " > 0 be a xed constant. We prove that S admits a (2 + ")-spanner with O(n log n) edges with respect to the geodesic distance. This is the rst spanner with constant spanning ratio and a near-linear number of edges for points on a terrain. On our way to this result, we prove that any set of n weighted points in Rd admits an additively weighted (2 + ")-spanner with O(n) edges; this improves the previously best known bound on the spanning ratio (which was 5 + "), and almost matches the lower bound

The liquid penetration of diesel substitutes

[EN] Diesel fuel consist of several hundreds of substances on organic basis. Experimental and numerical investigations of this multicomponent fuel are hard to interpret in detail, since the behavior of the multicomponent mixture is complex. Physical and chemical data of this system is not available under engine relevant conditions. Instead, fundamental research substitutes diesel with pure substances, where a big database exists. Prior work already showed, that overall spray propagation (including vapor phase) is nearly independent on the injected fuel. This is due to the high air entrainment at present diesel engine conditions (very high injection pressure and dense ambient atmosphere). The high air entrainment shortly behind the nozzle exit (within the first 5 mm penetration) creates a situation where properties of the ambient gas dominate the spray propagation resulting in similar mass and momentum distributions even for different fuels, if the injection conditions are kept constant. On the other hand, the liquid length is clearly different for different fuels, so that location and time of the phase change differ with consequences on the time available for mixture formation in the gas phase. The paper describes the liquid length as a function of the enthalpy necessary for the phase transition (given by the fuel and fuel temperature at injection) and the injection conditions (ambient gas properties, injector design and injection pressure). We compare two different models describing the enthalpy balance. Siebers et al. presented “Model I”, where mass transfer dominates the enthalpy transfer and evaporation takes place. In our own “Model II” evaporation is suppressed, resulting in a heat transfer driven enthalpy transfer without mass transport. The calculations are validated with experimental data. The liquid length is optically accessible by Mie-Scattering imaging techniques, the complete spray evolution by Schlieren technique. The experimental study was carried out in the high-pressure combustion vessel “OptiVeP” at FAU. The data shown in this paper derived from measurements with dodecane injected at 1200 bar into 613 K ambient. The ambient pressure varies from 1 – 10 MPa. A Continental research injector with a 115 µm hole and L/D of 6.5 was used. Nitrogen atmosphere suppressed ignition. Increasing the ambient pressure leads to a change in the mechanism in phase transition. It switches from a mass transfer dominated regime to a heat transfer dominated regime at high ambient pressures.Riess, S.; Weiss, L.; Rezaei, J.; Peter, A.; Wensing, M. (2017). The liquid penetration of diesel substitutes. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1060-113. https://doi.org/10.4995/ILASS2017.2017.4764OCS106011