1,720,987 research outputs found
Temperature variations and heat flow in coastal soils in the Arctic. Monitoring and modeling the thermic state of soils surrounding the landfall pipeline of Longyearbyen, NO
No full textLAUREA MAGISTRALEOffshore development on the Arctic shelf requires the construction of pipelines providing the transport of hydrocarbons from the shelf on shore. The infrastructure development assumes also the construction and support of pipe-lines crossing water barriers (bays, rivers, lakes). Erosion and ice processes in the coastal zone can influence conditions of the pipeline laying in the coastal zone and representing a possible cause of accidents. Temperature control is necessary to maintain the fluid in the pipeline at the necessary flowing temperature and to prevent excessive warming of the surrounding soil with consequent permafrost thawing.
When pipelines cross the shore they represent a challenge for pipeline management as they are at the border between onshore and offshore conditions.
This study represent the continue of the research project started in 2011and ended in 2013 with the aim of analyzing the thermic state of shore soils surrounding the Longyearbyen power plant landfall pipeline and creating a numerical model to simulate temperature variations in soils. Particular attention was put in investigating how the tide cycle influences the heat transfer in the soils.
Soil temperature data were used to calculate horizontal and vertical heat fluxes inside the shore soils. Soil temperature and heat fluxes series were put in relation with pore pressure measures to see how oscillations of the underground water level, caused by tide cycles, is affecting temperature and heat transfer variations.
Four numerical models were developed with increasing complexity to simulate two years of temperature changings in soils. Comparisons among models were useful in understanding how atmospheric temperature, pipeline temperature and tide cycles concur in defining the temperature field of shore soils.
Models showed, in accordance to field evidences, that tide cycles are responsible of short term, see semidiurnal or diurnal, since weather condition can’t affect so quickly soil temperature especially during winter. Tide cycles increase the absolute value of vertical heat flux between deeper soils and ground surface
Observations and Numerical Simulation of Icebergs in Broken Ice
Get PDFSea ice and icebergs are the major challenges for offshore activities in the Arctic. Design
loads for Arctic offshore structures may be significantly reduced if the drift of sea ice
and icebergs is possible to forecast accurately and perform physical ice management
when required. So far, this has been successfully done solely for sea ice or solely for
icebergs drifting in open water. There is a lack of knowledge about icebergs drifting
together with broken ice, and there is no operational experience of deflecting an iceberg
in broken ice.
An iceberg moving relatively sea ice should experience additional resistance force,
which in general grows as the ice thickness, relative velocity or the ice concentration
increase. It complicates the drift forecasting and potentially threatens iceberg towing
operations in sea ice. This resistance force is hard to estimate: there are only a few
analytical equations, and there is only one model-scale experiment of iceberg towing in
ice. Published information about full-scale trials of towing is almost absent. However,
numerical methods, that have been used to model floaters and ships in broken ice, are
possible to utilize for the modelling of icebergs in broken ice.
This thesis covers observations, tracking and forecasting of icebergs and sea ice in the
Greenland Sea and in the Barents Sea, and numerical modelling of iceberg towing in
broken ice. The tracking has been performed using GPS that provided high temporal
and spatial resolution of the drift trajectories. Statistical data on drift velocities, spectra,
trajectory curvatures are derived. In addition, the relative drift velocity between the
sea ice and icebergs is obtained. Characteristic values and observations are used for
the numerical modelling part. Finally, for the first time, the yawing of real icebergs is
measured and simulated. These data can be used for the design of offshore structures
or when planning offshore operations, especially the ice management.
The numerical modelling of iceberg towing in ice is performed using the non-smooth
discrete element method. A number of important knowledge gaps in material
description and in the numerical method are filled. First of all, it is demonstrated that
the collisions of floating ice floes are almost inelastic, resulting in restitution coefficient
values close to zero. Second, the characteristic feature of the method is a solution
calculated in the form of contact impulses between the bodies, which makes it hard to
estimate the contact forces. A conversion method between the contact impulses and
the contact forces is proposed based on the experiments on a wide range of scales.
Also, a potential flow is introduced in the vicinity of the simulated iceberg leading
to better ice flow representation. Finally, an algorithm generating broken ice fields
for the simulations is developed. The algorithm produces numerical ice fields having
natural ice floe size distribution and target ice concentration.
In the situation when available relevant data are extremely limited, a validation
study is performed on a model-scale experiment in broken ice. The numerical model
reproduces the average towing force magnitude measured in the experiment and the
motion of ice when the ice concentration is below 80%. In addition, the ice resistance
obtained numerically is compared to existing analytical estimates of ice resistance to
drifting icebergs. The estimates appear to give much lower ice resistance mainly due
to no mechanical confinement during the drift.
The numerical model can be further developed in a number of ways: ice floe failure in
different modes might be introduced, the model of iceberg in ice can be coupled with
a ship model, validation against full-scale trials can be performed after they happen,
etc. On the current stage, the model can be used as a numerical towing tank or as an
aid for planning the first towing operations in the broken ice
Observations and Numerical Simulation of Icebergs in Broken Ice
No full textSea ice and icebergs are the major challenges for offshore activities in the Arctic. Design
loads for Arctic offshore structures may be significantly reduced if the drift of sea ice
and icebergs is possible to forecast accurately and perform physical ice management
when required. So far, this has been successfully done solely for sea ice or solely for
icebergs drifting in open water. There is a lack of knowledge about icebergs drifting
together with broken ice, and there is no operational experience of deflecting an iceberg
in broken ice.
An iceberg moving relatively sea ice should experience additional resistance force,
which in general grows as the ice thickness, relative velocity or the ice concentration
increase. It complicates the drift forecasting and potentially threatens iceberg towing
operations in sea ice. This resistance force is hard to estimate: there are only a few
analytical equations, and there is only one model-scale experiment of iceberg towing in
ice. Published information about full-scale trials of towing is almost absent. However,
numerical methods, that have been used to model floaters and ships in broken ice, are
possible to utilize for the modelling of icebergs in broken ice.
This thesis covers observations, tracking and forecasting of icebergs and sea ice in the
Greenland Sea and in the Barents Sea, and numerical modelling of iceberg towing in
broken ice. The tracking has been performed using GPS that provided high temporal
and spatial resolution of the drift trajectories. Statistical data on drift velocities, spectra,
trajectory curvatures are derived. In addition, the relative drift velocity between the
sea ice and icebergs is obtained. Characteristic values and observations are used for
the numerical modelling part. Finally, for the first time, the yawing of real icebergs is
measured and simulated. These data can be used for the design of offshore structures
or when planning offshore operations, especially the ice management.
The numerical modelling of iceberg towing in ice is performed using the non-smooth
discrete element method. A number of important knowledge gaps in material
description and in the numerical method are filled. First of all, it is demonstrated that
the collisions of floating ice floes are almost inelastic, resulting in restitution coefficient
values close to zero. Second, the characteristic feature of the method is a solution
calculated in the form of contact impulses between the bodies, which makes it hard to
estimate the contact forces. A conversion method between the contact impulses and
the contact forces is proposed based on the experiments on a wide range of scales.
Also, a potential flow is introduced in the vicinity of the simulated iceberg leading
to better ice flow representation. Finally, an algorithm generating broken ice fields
for the simulations is developed. The algorithm produces numerical ice fields having
natural ice floe size distribution and target ice concentration.
In the situation when available relevant data are extremely limited, a validation
study is performed on a model-scale experiment in broken ice. The numerical model
reproduces the average towing force magnitude measured in the experiment and the
motion of ice when the ice concentration is below 80%. In addition, the ice resistance
obtained numerically is compared to existing analytical estimates of ice resistance to
drifting icebergs. The estimates appear to give much lower ice resistance mainly due
to no mechanical confinement during the drift.
The numerical model can be further developed in a number of ways: ice floe failure in
different modes might be introduced, the model of iceberg in ice can be coupled with
a ship model, validation against full-scale trials can be performed after they happen,
etc. On the current stage, the model can be used as a numerical towing tank or as an
aid for planning the first towing operations in the broken ice
An experimental comparison of thermal-mechanical properties of freshwater and saline ice in Arctic environments
No full textTermisk istrykk er en av de åtte islastene som må vurderes for støttestrukturdesign av bunnfestede havvindmøller definert av internasjonal standard IEC 61400031. Temperaturendringer i is driver dens deformasjon og forårsaker strukturer som begrenser ekspansjonen til å oppleve belastning. Den effektive termisk ekspansjonskoeffisient (ECTE) kan brukes til å kvantifisere forskjellen i hav versus fersk is oppførsel under termisk påvirkning. Siden den termiske ekspansjonen av fersk is generelt er godt forstått, kan termiske ekspansjonseksperimenter med fersk is sammenlignes med sjøis, som har en mer kompleks struktur bestående av en fast ismatrise som inneholder væske og gass. Fiber Bragg Grating (FBG) tøynings- og temperatursensorer muliggjorde målinger av termisk ekspansjon i ferske og saltholdige isprøver under forskjellige grenseforhold i det kalde laboratoriet. Eksperimenter ble sammenlignet blant ferske og saltholdige isprøver for tre distinkte anvendte termiske handlinger: lufttemperaturendring, flyting i vann og oversvømmelse av isoverflaten. Feltarbeid på fersk- og havis under samme meteorologiske forhold ble utført for å sammenligne termiske spenninger. De termiske ekspansjonslufteksperimentene ga ingen signifikante forskjeller i ECTE-verdier for fersk, granulær og søyleformet saltholdig is. Imidlertid ble det observert under flyteeksperimentene med ubegrenset is at granulær saltholdig is resulterte i en større ECTE enn fersk is. Negative verdier for ECTE ble oppnådd for kolonneformede sjøislufttemperaturendringsforsøk og under granulære saltholdige isflyteeksperimenter, som begge skjedde under oppvarmingssykluser. Flomforsøk beskrev den termiske responsen av latent varmefrigjøring under vannfrysing på isoverflaten, og det ble observert at fersk is viste sterkere hysterese i resultater enn saltholdig is. Termiske spenninger overvåket i omtrent en måned om vinteren i Vallundensjøen havisen knyttet til Van Mijenfjorden og i en nærliggende ferskvannssjø viste høyere verdier for fersk is enn havisen og økte over dypet for begge isarkene som opplevde de samme meteorologiske forholdene.Thermal ice pressure is one of the eight ice loads to consider for the support structure design of bottom-fixed offshore wind turbines defined by international standard IEC 61400031. Temperature changes in ice drive its deformation and cause structures restricting expansion to experience loading. The effective coefficient of thermal expansion (ECTE) can be used to quantify the difference in sea versus fresh ice behavior under thermal action. Since the thermal expansion of fresh ice is generally well understood, fresh ice thermal expansion experiments can be compared to sea ice, which has a more complex structure consisting of a solid ice matrix containing liquid and gas. Fiber Bragg Grating (FBG) strain and temperature sensors enabled measurements of thermal expansion in fresh and saline ice samples under different boundary conditions in the cold laboratory. Experiments were compared amongst fresh and saline ice samples for three distinct applied thermal actions: air temperature change, floating in water, and flooding the ice surface. Fieldwork on fresh and sea ice under the same meteorological conditions was performed to compare thermal stresses. The thermal expansion air experiments yielded no significant differences in ECTE values for fresh, granular, and columnar saline ice. However, it was observed during the unconfined ice floating experiments that granular saline ice
resulted in a larger ECTE than fresh ice. Negative values for ECTE were obtained for columnar sea ice air temperature change experiments and during granular saline ice floating experiments, both occurring during heating cycles. Flooding experiments described the thermal response of latent heat release during water freezing on the ice surface, and it was observed that fresh ice showed stronger hysteresis in results than saline ice. Thermal stresses monitored for approximately one month during winter in the Vallunden lake sea ice attached to Van Mijenfjorden and in a nearby freshwater lake demonstrated higher values for fresh ice than sea ice and increased over the depth for both ice sheets which experienced the same meteorological conditions
An experimental comparison of thermal-mechanical properties of freshwater and saline ice in Arctic environments
No full textTermisk istrykk er en av de åtte islastene som må vurderes for støttestrukturdesign av bunnfestede havvindmøller definert av internasjonal standard IEC 61400031. Temperaturendringer i is driver dens deformasjon og forårsaker strukturer som begrenser ekspansjonen til å oppleve belastning. Den effektive termisk ekspansjonskoeffisient (ECTE) kan brukes til å kvantifisere forskjellen i hav versus fersk is oppførsel under termisk påvirkning. Siden den termiske ekspansjonen av fersk is generelt er godt forstått, kan termiske ekspansjonseksperimenter med fersk is sammenlignes med sjøis, som har en mer kompleks struktur bestående av en fast ismatrise som inneholder væske og gass. Fiber Bragg Grating (FBG) tøynings- og temperatursensorer muliggjorde målinger av termisk ekspansjon i ferske og saltholdige isprøver under forskjellige grenseforhold i det kalde laboratoriet. Eksperimenter ble sammenlignet blant ferske og saltholdige isprøver for tre distinkte anvendte termiske handlinger: lufttemperaturendring, flyting i vann og oversvømmelse av isoverflaten. Feltarbeid på fersk- og havis under samme meteorologiske forhold ble utført for å sammenligne termiske spenninger. De termiske ekspansjonslufteksperimentene ga ingen signifikante forskjeller i ECTE-verdier for fersk, granulær og søyleformet saltholdig is. Imidlertid ble det observert under flyteeksperimentene med ubegrenset is at granulær saltholdig is resulterte i en større ECTE enn fersk is. Negative verdier for ECTE ble oppnådd for kolonneformede sjøislufttemperaturendringsforsøk og under granulære saltholdige isflyteeksperimenter, som begge skjedde under oppvarmingssykluser. Flomforsøk beskrev den termiske responsen av latent varmefrigjøring under vannfrysing på isoverflaten, og det ble observert at fersk is viste sterkere hysterese i resultater enn saltholdig is. Termiske spenninger overvåket i omtrent en måned om vinteren i Vallundensjøen havisen knyttet til Van Mijenfjorden og i en nærliggende ferskvannssjø viste høyere verdier for fersk is enn havisen og økte over dypet for begge isarkene som opplevde de samme meteorologiske forholdene
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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