Tracer Measurements in Growing Sea Ice Support Convective Gravity Drainage Parameterizations

Gravity drainage is the dominant process redistributing solutes in growing sea ice. Modeling gravity drainage is therefore necessary to predict physical and biogeochemical variables in sea ice. We evaluate seven gravity drainage parameterizations, spanning the range of approaches in the literature, using tracer measurements in a sea ice growth experiment. Artificial sea ice is grown to around 17 cm thickness in a new experimental facility, the Roland von Glasow air‐sea‐ice chamber. We use NaCl (present in the water initially) and rhodamine (injected into the water after 10 cm of sea ice growth) as independent tracers of brine dynamics. We measure vertical profiles of bulk salinity in situ, as well as bulk salinity and rhodamine in discrete samples taken at the end of the experiment. Convective parameterizations that diagnose gravity drainage using Rayleigh numbers outperform a simpler convective parameterization and diffusive parameterizations when compared to observations. This study is the first to numerically model solutes decoupled from salinity using convective gravity drainage parameterizations. Our results show that (1) convective, Rayleigh number‐based parameterizations are our most accurate and precise tool for predicting sea ice bulk salinity; and (2) these parameterizations can be generalized to brine dynamics parameterizations, and hence can predict the dynamics of any solute in growing sea ic

An evaluation of the stimulants and impediments to innovation within PFI/PPP projects

This paper identifies the theoretical stimulants and impediments associated with the implementation of PFI/PPP (Private Finance Initiative/Public Private Partnership) projects. A current defect of this procurement approach is the unintentional constraint upon the innovations incorporated into the development of PFI projects. A critical evaluation of the published literature has been utilized to synthesize a theoretical model. The paper proposes a theoretical model for the identification of potential innovation stimulants and impediments within this type of procurement. This theoretical model is then utilised to evaluate four previously completed PFI projects. These project case-studies have been examined in detail. The evaluation demonstrates how ineffective current procedures are. The application of this model before project letting could eliminate unintentional constraints and stimulate improved innovation within the process. The implementation of the model could improve the successful delivery of innovation within the entire PFI/PPP procurement process

Effect of temperature on the high strain-rate fracture characteristics of ductile metals

Un chauffage par induction a été employé pour éléver rapidement la température d'une éprouvette en acier et d'une éprouvette en fer pur, avant de les tester aux vitesses de déformation > 103s-1. Les résultats montrent en général que la ductibilité diminue pour des températures au-delà des limites testées (20 - 400 °C). Basé sur des informations expérimentales et sur les résultats de simulations numérique de l'essai, un modèle empirique a été derivé pour du fer pur et donne la tension de fracture en fonction des contraintes et de la température. Récemment, la technique de chauffage par induction a été étendue aux matériaux non-ferreux. Des tests à fortes tensions sur du cuivre à 99,99% pur n'ont pas révélé les effets de la température sur la ductibilité des matériaux au-dessus des températures employées (20 - 300 °C).Induction heating has been employed to rapidly raise the temperature of ferrous specimens prior to testing at strain-rates > 103s-1. The results show a general tendency for the ductility of a specially-processed pure iron to decrease with temperature over the range tested (20-400 C). Based on the experimental data and the results of numerical simulations of the experiment, an empirical fracture model has been derived for the iron which gives fracture strain as a function of state-of-stress and temperature. Recently, the induction heating technique has been extended to non-ferrous materials. High strain-rate tests on 99.9% pure copper revealed no significant effect of temperature on ductility over the range of start temperatures employed (20-300 C)

Ductile Fracture of Pure Copper : An Experimental and Numerical Study

This paper describes the results of interrupted tensile tests carried out on 99.95% pure copper specimens over a range of stress triaxiality conditions. The tested specimens were sectioned and polished to identify the conditions at which voids nucleate and coalesce before the final fracture takes place. Results show that void nucleation and coalescence both have a very strong dependence on stress triaxiality, but appear to be less sensitive to strain-rate. Based on the combined experimental and numerical results, a new criterion for void nucleation is proposed as a function of stress triaxiality.Cet article présente les résultats d'essais de traction interrompus obtenus sur des échantillons de cuirve à 99.95% pur dans des conditions de contraintes triaxiales. Les échantillons testés ont été sectionnés et polis afin d'identifier les conditions de nucléation et de coalescence des vides avant que n'intervienne la rupture finale. Les résultats montrent que la nucléation et la coalescence des vides sont fortement dépendantes de la triaxialité des contraintes ; mais sont moins sensibles aux taux de cisaillement. Basé sur la combinaison de résultats numériques et expérimentaux, un nouveau critère de nucléation des vides est proposé en tant que fonction de la triaxialité des contraintes

DEFORMATION AND FRACTURE ; MODELLING TECHNIQUES TO TAKE ACCOUNT OF STRAIN-RATE BEHAVIOUR AND STRESS STATE

Numerical simulations of the dynamic deformation and ductile fracture of notched tensile specimens have been carried out using the finite element hydrocode DYNA2D and advanced constitutive relations for both pure copper and Remko iron. The predictions of plastic flow were in good agreement with the observed shape at fracture of specimens tested dynamically in a unique impact test facility known as the 'flying wedge' which is capable of applying strain-rates in the range 102- 104 s-1. The DYNA2D results were used to give accurate predictions of the triaxial state-of-stress (defined as the ratio of mean stress P to effective stress Y) at the fracture initiation site as a function of initial geometry, mean strain and strain-rate. Experimentally-measured failure strains were then plotted against predicted values of P/Y for each material. For copper, failure strains decreased with increasing stress triaxiality P/Y but no significant strain-rate effect was apparent. In the case of iron, the same trend of reducing fracture strain with increase in P/Y was observed, but here increased strain-rate produced a marked effect. In fact, a ductile-brittle transition (confirmed by metallurgical examination) was seen to occur at the highest speed of testing and above a certain value of P/Y. Parameters for simple empirical fracture models were estimated from the plots of failure strain versus P/Y. When combined with the standard damage accumulation fracture criterion in DYNA2D, these models gave reasonable predictions of both the site of fracture initiation (ie the centre of the specimen) and the time-to-fracture when compared with fracture times measured on certain specimens using strain-gauges or high-speed photography. More fundamental ductile fracture models which allow for the statistical nature of void initiation and growth and the effect of voids on the yield surface are currently under investigation

High strain-rate properties of materials R.A.R.D.E. agreement 2062/0111; report to 31st December 1984

SIGLEAvailable from British Library Lending Division - LD:2265.630F(BR--94080) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

High strain-rate properties of materials Progress report to 31st May 1985

SIGLEAvailable from British Library Lending Division - LD:2265.63F(BR--96910) / BLDSC - British Library Document Supply CentreGBUnited Kingdo