Identification of temporal consistency in rating curve data : Bidirectional Reach (BReach)

In this paper, a methodology is developed to identify consistency of rating curve data based on a quality analysis of model results. This methodology, called Bidirectional Reach (BReach), evaluates results of a rating curve model with randomly sampled parameter sets in each observation. The combination of a parameter set and an observation is classified as nonacceptable if the deviation between the accompanying model result and the measurement exceeds observational uncertainty. Based on this classification, conditions for satisfactory behavior of a model in a sequence of observations are defined. Subsequently, a parameter set is evaluated in a data point by assessing the span for which it behaves satisfactory in the direction of the previous (or following) chronologically sorted observations. This is repeated for all sampled parameter sets and results are aggregated by indicating the endpoint of the largest span, called the maximum left (right) reach. This temporal reach should not be confused with a spatial reach (indicating a part of a river). The same procedure is followed for each data point and for different definitions of satisfactory behavior. Results of this analysis enable the detection of changes in data consistency. The methodology is validated with observed data and various synthetic stage-discharge data sets and proves to be a robust technique to investigate temporal consistency of rating curve data. It provides satisfying results despite of low data availability, errors in the estimated observational uncertainty, and a rating curve model that is known to cover only a limited part of the observations

A Comparison of Methods for Streamflow Uncertainty Estimation

International audienceStreamflow time series are commonly derived from stage-discharge rating curves, but the uncertainty of the rating curve and resulting streamflow series are poorly understood. While different methods to quantify uncertainty in the stage-discharge relationship exist, there is limited understanding of how uncertainty estimates differ between methods due to different assumptions and methodological choices. We compared uncertainty estimates and stage-discharge rating curves from seven methods at three river locations of varying hydraulic complexity. Comparison of the estimated uncertainties revealed a wide range of estimates, particularly for high and low flows. At the simplest site on the Isère River (France), full width 95% uncertainties for the different methods ranged from 3 to 17% for median flows. In contrast, uncertainties were much higher and ranged from 41 to 200% for high flows in an extrapolated section of the rating curve at the Mahurangi River (New Zealand) and 28 to 101% for low flows at the Taf River (United Kingdom), where the hydraulic control is unstable at low flows. Differences between methods result from differences in the sources of uncertainty considered, differences in the handling of the time-varying nature of rating curves, differences in the extent of hydraulic knowledge assumed, and differences in assumptions when extrapolating rating curves above or below the observed gaugings. Ultimately, the selection of an uncertainty method requires a match between user requirements and the assumptions made by the uncertainty method. Given the significant differences in uncertainty estimates between methods, we suggest that a clear statement of uncertainty assumptions be presented alongside streamflow uncertainty estimates

Effect of 3D printing on the microstructure and mechanical properties of an Inconel 718 Nickel-alloy (UNS N07718)

Master's thesis in Mechanical engineeringFlow measuring instruments are important for the oil and gas industry. These instruments are exposed to hostile environments during operation. These hostile environments demands high quality materials with excellent properties, such as superalloys. Inconel 718 is a superalloy which can be manufactured by additive manufacturing. Additive manufacturing is threedimensional printing of metals. The technology uses laser or electron beam to melt thin layers of powder material. The method allows manufacturing of complex shapes that are hard or impossible to manufacture with conventional methods. The objective of this thesis is to investigate how the additive manufacturing process affects the microstructure and mechanical properties of an additive manufactured Inconel 718 superalloy. Additive manufacturing produces useful mechanical properties. However, yield and tensile strength is considerably lower than for commercially produced material. Therefore, heat treatments are necessary to obtain the mechanical properties achievable by the alloy composition. The heat treatment conducted in this experiment provided hardness values and tensile properties exceeding those of commercially produced material. However, this was at the cost of properties associated with ductility, elongation at break and contraction at fracture. These properties were considerably reduced and comparatively lower than with commercially produced material. Tensile tests show that the building direction of the additive manufactured material in the asprinted condition parallel to the pull direction of the tensile test, horizontally built, is stronger than the building direction normal to the pull direction, vertically built. EBSD analysis of the additive manufactured material in the as-printed condition shows grain size differences in the various planes of the specimens. Grains are smaller in the direction of laser motion than in the direction normal to it. This means that the horizontally built material has smaller grains than the other building directions in the pull direction. This is believed to be the main contribution to the tensile property differences. The EBSD analysis also shows tendencies of grains orientating in specific directions. The additive manufactured specimen in the as-printed condition built horizontally seems to have grains orientating in preferred directions, while the vertically built seem to have grains randomly orientated, with no preferred direction. This may also contribute to the differences in tensile properties of the various build direction

Estimating the discharge rating curve by nonlinear regression - The frequentist approach

This report provides a discussion about the fundamentals of the frequentist approach to the classical nonlinear least squares head - discharge power-law rating curve model, which is a vital procedure in practical hydrology. It is shown that the multivariate minimization problem of the classical nonlinear least squares rating curve model is equivalent to the maximization of a single argument function. We propose four general criteria which the discharge measurements should meet if a trustable frequentist least squares rating curve estimate should exist. The proposed criteria are applied to a large number of real-life discharge measurements, which suggest that the criteria are particularly useful in practice. We also show that the breakdown of one of the criteria implies an exponential law relationship between the head and the discharge. Numerical maximization of the single argument function and inference are discussed

Conférence invitée : Some challenges in hydrometry

Hydrometry has always been an important branch in hydrology. Even so, the quality of streamflow data might not have evolved in accordance with the advances in hydrological sciences. A too large uncertainty in published data is still a challenge in hydrometry. Hydrometric field work is a diverse profession. Technical equipment and personnel competence are usually in accordance with accepted standards. Hence, there are no technical or practical reasons that should indicate that it is impossible to achieve accurate data for a particular gauging station, given that it is reasonably located in the river channel. This short note argues that two main reasons for a too large uncertainty in published data are too comprehensive hydrometric networks and no criteria for accuracy of published data. It is also argued that the chief uncertainty factor in rating curves is extrapolation uncertainty. A short description of a project in Statkraft that has been launched to minimize extrapolation of rating curves in the network owned by the company is also given.Petersen-Øverleir Asgeir. Conférence invitée : Some challenges in hydrometry. In: 35es journées de l’hydraulique de la Société Hydrotechnique de France. Hydrométrie 2013. Paris, 15-16 mai 2013. 2013

Holomorfe symplektiske avbildninger, Darboux teorem.

Symplektisk teori er i historisk matematisk perspektiv en relativt ny gren innen matematikken. Denne oppgaven viser holomorfe resultater innen symplektisk teori. Den er delt inn i to kapitler, et om symplektisk lineær algebra og et om symplektiske mangfoldigheter. Kapittelet om symplektisk lineær algebra gir en innføring i kompleks symplektisk teori. Et viktig mål med oppgaven har vært å bevise Darboux teorem for komplekse mangfoldigheter. For å få til det er det nødvendig å bevise forskjellige resultater innen holomorfe differensialligninger og holomorf differensialgeometri. Kapitelet om symplektiske mangfoldigheter viser disse resultatene og gir et holomorft bevis for Darboux teorem

Some challenges in hydrometry

Hydrometry has always been an important branch in hydrology. Even so, the quality of streamflow data might not have evolved in accordance with the advances in hydrological sciences. A too large uncertainty in published data is still a challenge in hydrometry. Hydrometric field work is a diverse profession. Technical equipment and personnel competence are usually in accordance with accepted standards. Hence, there are no technical or practical reasons that should indicate that it is impossible to achieve accurate data for a particular gauging station, given that it is reasonably located in the river channel. This short note argues that two main reasons for a too large uncertainty in published data are too comprehensive hydrometric networks and no criteria for accuracy of published data. It is also argued that the chief uncertainty factor in rating curves is extrapolation uncertainty. A short description of a project in Statkraft that has been launched to minimize extrapolation of rating curves in the network owned by the company is also given

Selvbilde til ungdom med et annerledes utseende : en studie av 16-åringer med leppe-kjeve-ganespalte

Bakgrunn: Formålet med denne studien er å studere selvbildet til en gruppe ungdom med annerledes utseende. Tidligere forskning har vist at utseendeavvik i et komplekst samspill med sosiale og individuelle faktorer, kan medføre en økt risiko for negativ selvevaluering. For å bedre forståelsen av hvordan ungdom betrakter seg selv, ønsker vi å belyse betydningen av utseendeavvik, i tillegg til kjønn, og to forhold ved psykososial funksjon, henholdsvis nære vennskap og depressive plager. Metode: Studien baserer seg på et krysseksjonelt design. Utvalget består av 16-åringer med leppe-kjeve-ganespalte, totalt 227. Som mål på selvbilde benyttes Self-Perception Profile for Adolescents (SPPA). Symptoms Checklist (SCL-12) blir benyttet som mål på depressive plager. Tilleggsinformasjon er innhentet fra journal. Resultat: Variabelen som målte selvbilde viste sammenheng med både depressive plager, kjønn og nære vennskap, hvorav depressive plager forklarte mest av variasjonen i selvbilde. Disse sammenhengene viste seg å være uavhengig av spaltetype. Konklusjon: Selvbildet til ungdom med leppe-kjeve-ganespalte er ikke relatert til spaltetype, men nært forbundet med psykososial funksjon. Dette tydeliggjør at selvbilde ikke bestemmes av omfang og alvorlighetsgrad av utseendeavvik, og at psykisk helse og sosial funksjon er viktig for hvordan ungdommen betrakter seg selv. Psykososiale forhold bør derfor stå sentralt i oppfølging og behandling av ungdom med spalte

Stage-discharge uncertainty derived with a non-stationary rating curve in the Choluteca River, Honduras

Uncertainty in discharge data must be critically assessed before data can be used in, e.g. water resources estimation or hydrological modelling. In the alluvial Choluteca River in Honduras, the river-bed characteristics change over time as fill, scour and other processes occur in the channel, leading to a non-stationary stage-discharge relationship and difficulties in deriving consistent rating curves. Few studies have investigated the uncertainties related to non-stationarity in the stage-discharge relationship. We calculated discharge and the associated uncertainty with a weighted fuzzy regression of rating curves applied within a moving time window, based on estimated uncertainties in the observed rating data. An 18-year-long dataset with unusually frequent ratings (1268 in total) was the basis of this study. A large temporal variability in the stage-discharge relationship was found especially for low flows. The time-variable rating curve resulted in discharge estimate differences of − 60 to + 90% for low flows and ± 20% for medium to high flows when compared to a constant rating curve. The final estimated uncertainty in discharge was substantial and the uncertainty limits varied between − 43 to + 73% of the best discharge estimate