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Karl-ulrich Evers - One of the best experts on this subject based on the ideXlab platform.

  • floe size distributions in laboratory ice broken by waves
    The Cryosphere, 2017
    Co-Authors: Agnieszka Herman, Karl-ulrich Evers, Nils Reimer
    Abstract:

    Abstract. This paper presents the analysis of floe-size distribution (FSD) data obtained in laboratory experiments of ice breaking by waves. The experiments, performed at the Large Ice Model Basin (LIMB) of the Hamburg Ship Model Basin (Hamburgische Schiffbau-Versuchsanstalt, HSVA), consisted of a number of tests in which an initially continuous, uniform ice sheet was broken by regular waves with prescribed characteristics. The floes' characteristics (surface area; minor and major axis, and orientation of equivalent ellipse) were obtained from digital images of the ice sheets after five tests. The analysis shows that although the floe sizes cover a wide range of values (up to 5 orders of magnitude in the case of floe surface area), their probability density functions (PDFs) do not have heavy tails, but exhibit a clear cut-off at large floe sizes. Moreover, the PDFs have a maximum that can be attributed to wave-induced flexural strain, producing preferred floe sizes. It is demonstrated that the observed FSD data can be described by theoretical PDFs expressed as a weighted sum of two components, a tapered power law and a Gaussian, reflecting multiple fracture mechanisms contributing to the FSD as it evolves in time. The results are discussed in the context of theoretical and numerical research on fragmentation of sea ice and other brittle materials.

  • Rubble Ice Transport on Arctic Offshore Structures (RITAS), part I: Scale-Model Investigations of Level Ice Action Mechanisms
    2013
    Co-Authors: Nicolas Serré, Basile Bonnemaire, Knut Vilhelm Høyland, Trine Lundamo, Karl-ulrich Evers, Arne Gürtner
    Abstract:

    A Model scale experiment on the interaction between level ice and an arctic offshore structure with a downward bending hull was conducted in April 2012 in the large ice tank of HSVA (Hamburg Ship Model Basin). The experiment investigated the different mechanical processes contributing to the ice action. The present paper is completed by a companion paper “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part II: 2D scale-Model study of the level ice action”. Detailed investigations on special aspects of the level ice action mechanisms are presented in “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part III: Analysis of scale-Model rubble ice stability” and “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part IV: Tactile sensor measurement of the level ice load on inclined plate”. The structure is inclined at the waterline and promotes a downward bending failure of the level ice. Several parameters are varied: structure width, ice incidence, ice thickness, ice elastic modulus, ice density, ice velocity. The structure front is vertically divided in three sections allowing independent measurement of the load at the waterline and the load from the accumulated ice rubble. The experimental results show that the level ice load is affected by the ice rubble accumulation up to a certain ice rubble amount. A lower ice density increases the ice load due to the increased ice rubble buoyancy. For the selected aspect ratios, a doubling of the structure width increased the rubble load but not the waterline load.

  • Rubble Ice Transport on Arctic Offshore Structures (RITAS), part II: 2D Scale-Model Study of the Level Ice Action
    2013
    Co-Authors: Nicolas Serré, Basile Bonnemaire, Knut Vilhelm Høyland, Juliane Borge, Karl-ulrich Evers
    Abstract:

    A Model scale experiment on the interaction between level ice and an arctic offshore structure with a downward bending hull was conducted in April 2012 in the large ice tank of HSVA (Hamburg Ship Model Basin). The experiments investigate the different mechanical processes contributing to the ice action. The present paper is completed by a companion paper “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part I: Model scale investigation of level ice action mechanisms”. Detailed investigations on special aspects of the level ice action mechanisms are presented in “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part III: Analysis of scale Model rubble ice stability” and “Rubble Ice Transport on Arctic Offshore Structures (RITAS), part IV Tactile sensor measurement of the level ice load on inclined plate.” The structure, a so called buoyancy box, is inclined at the waterline and promotes a downward bending failure of the level ice. Two-dimensionality is introduced by limiting the panel width to 1 meter with two transparent Lexan plates allowing monitoring of the ice breaking and accumulation process. Several parameters are varied: ice thickness, ice density, ice velocity. A tactile sensor is installed on the ice breaking area of the structure to monitor the local waterline ice loads. During each interaction tests, the volume and buoyancy of the rubble accumulated on the structure are measured for derivation of the rubble porosity. The waterline ice load is oscillating. The experimental results show that the magnitude of the load peaks increases. The rubble is subjected to a rotating motion and to a series of collapse events. Increased buoyancy forces reduce the rubble porosity.

  • rubble ice transport on arctic offshore structures ritas part iii analysis of Model scale rubble ice stability
    22nd International Conference on Port and Ocean Engineering under Arctic Conditions (POAC'13)Federation of Finnish Learned SocietiesABSEspoo City of F, 2013
    Co-Authors: Sergey Kulyakhtin, Knut Vilhelm Høyland, Oda S Astrup, Karl-ulrich Evers
    Abstract:

    A series of tests on Model ice rubble were conducted at the Hamburg Ship Model Basin (HSVA) in Hamburg, Germany. This paper is the third out of four papers from the RITAS experiments. The three others are “Rubble Ice transport on Arctic Offshore Structures (RITAS), Part I: Model scale investigation of level ice action mechanisms”, “Part II: 2D Model scale study of the level ice action”, and “Part IV: Tactile sensor measurement of the level ice load on inclined plate”. Ice rubble properties were investigated both in water and air. For submerged tests a box with 0.93×0.97×1.1 m dimensions of internal volume was filled with rubble material and tilted afterwards until failure occurred. For dry tests a rectangular board 2×1.3 m with support ledges along the long dimensions was used for rubble ice pile construction and subsequent tilting. During both procedures initial geometry of rubble piles and angles of inclination leading to failure were measured. Considering ice rubble as a bulk material which obeys Coulomb’s failure criterion and that the repose angle of the pile equals to the friction angle (initially zero cohesion is assumed) the cohesion component of shearing strength can be estimated.

  • experimental studies on shear failure of freeze bonds in saline ice part i set up failure mode and freeze bond strength
    Cold Regions Science and Technology, 2011
    Co-Authors: Ada H V Repettollamazares, Knut V Hoyland, Karl-ulrich Evers
    Abstract:

    Abstract The strength of freeze-bonds in thin saline ice has been investigated through two series (in 2008 and 2009) of experiments in the Hamburg Ship Model Basin (HSVA) as a function of the normal confinement ( σ ), the submersion time (Δ t ) and the initial ice temperature ( T i ). The freeze-bonds were mostly formed in a submerged state, but some were also formed in air. The experimental set-up was improved in the 2009 experiments. In 2008 a ductile-like failure mode dominated (78%), whereas in 2009 the brittle-like dominated (93%). We suggest that this is a combined ice and test set-up effect. The 2009 experimental procedures allowed for careful sample handling giving higher strength and it was softer. Both these things should provoke a more brittle-like force–time response. The average freeze-bond strength in brittle-like samples was around 9 kPa while in ductile-like samples was around 2 kPa. The maximum freeze-bonds strength were measured for short submersion times, from 1 to 20 min, and reached a maximum value of 30 kPa. A Mohr–Coulomb like failure Model was found appropriate to represent the freeze-bond shear strength as function of the normal confinement. Saline freeze-bonds in saline water had cohesion/friction angle around 4 and 1.4 kPa/25° for the brittle- and ductile-like samples respectively, which fitted well with previously published data. A bell-shape dependence for τ c vs. Δ t was found, which agreed with the predictions by Shafrova and Hoyland (2007). We suggest that this is essentially a freeze-bond porosity effect and propose three phases in time with subsequent cooling, heating and equilibrium to account for this trend. Qualitative experiments showed that the submersion time and the initial ice temperature were strongly coupled. To account for the connection between contact time, block dimensions and ice properties and the freeze-bond strength, dimensionless number were used. Fourier scaling was more appropriate than Froude scaling to scale freeze-bonds. The freeze-bonding made in air developed fast (in less than 30 s) when the ice was cold and dry, but no freeze-bonding occurred for the same contact times when the ice was warm and wet.

Knut V Hoyland - One of the best experts on this subject based on the ideXlab platform.

  • experimental studies on shear failure of freeze bonds in saline ice part i set up failure mode and freeze bond strength
    Cold Regions Science and Technology, 2011
    Co-Authors: Ada H V Repettollamazares, Knut V Hoyland, Karl-ulrich Evers
    Abstract:

    Abstract The strength of freeze-bonds in thin saline ice has been investigated through two series (in 2008 and 2009) of experiments in the Hamburg Ship Model Basin (HSVA) as a function of the normal confinement ( σ ), the submersion time (Δ t ) and the initial ice temperature ( T i ). The freeze-bonds were mostly formed in a submerged state, but some were also formed in air. The experimental set-up was improved in the 2009 experiments. In 2008 a ductile-like failure mode dominated (78%), whereas in 2009 the brittle-like dominated (93%). We suggest that this is a combined ice and test set-up effect. The 2009 experimental procedures allowed for careful sample handling giving higher strength and it was softer. Both these things should provoke a more brittle-like force–time response. The average freeze-bond strength in brittle-like samples was around 9 kPa while in ductile-like samples was around 2 kPa. The maximum freeze-bonds strength were measured for short submersion times, from 1 to 20 min, and reached a maximum value of 30 kPa. A Mohr–Coulomb like failure Model was found appropriate to represent the freeze-bond shear strength as function of the normal confinement. Saline freeze-bonds in saline water had cohesion/friction angle around 4 and 1.4 kPa/25° for the brittle- and ductile-like samples respectively, which fitted well with previously published data. A bell-shape dependence for τ c vs. Δ t was found, which agreed with the predictions by Shafrova and Hoyland (2007). We suggest that this is essentially a freeze-bond porosity effect and propose three phases in time with subsequent cooling, heating and equilibrium to account for this trend. Qualitative experiments showed that the submersion time and the initial ice temperature were strongly coupled. To account for the connection between contact time, block dimensions and ice properties and the freeze-bond strength, dimensionless number were used. Fourier scaling was more appropriate than Froude scaling to scale freeze-bonds. The freeze-bonding made in air developed fast (in less than 30 s) when the ice was cold and dry, but no freeze-bonding occurred for the same contact times when the ice was warm and wet.

  • shoulder ice barrier ice tank testing part ii estimation of breaking length and block size using image analysis
    ASME 2009 28th International Conference on Ocean Offshore and Arctic Engineering, 2009
    Co-Authors: Ada H V Repettollamazares, Ove T Gudmestad, Arne Gu Rtner, Knut V Hoyland
    Abstract:

    When studying ice interaction on sloped structures, a key parameter that is usually reported after experiments and observations either in Full Scale or Model Scale is the breaking length associated with the ice failure. Moreover, either for numerical Modeling or load calculations the size of the blocks generated during ice-structure interaction that accumulates rubble is of importance. In this paper, the technique of image analysis has been used to obtain values of the breaking length and the ice block sizes generated during Model tests of a Shoulder Ice Barrier (SIB)-ice interaction. The Model tests were performed in the Hamburg Ship Model Basin (HSVA) during July 2007. Since the SIB represents a new concept in ice barrier structures, Model tests were intended to evaluate its general performance. A brief description of the Model tests and the image analysis technique used to analyze the data is done. A total of five experiments where ice thickness, ice flexural strength and shoulder inclination were varied, are analyzed. Results of the breaking length analysis show that there is a characteristic change in the breaking length associated with the transition from ice interactions on the bare structure (Phase 1) and interaction onto accumulated rubble (Phase 2). Average values of the breaking length of both phases for each experiment are presented. Since the information regarding breaking length in structures that accumulate rubble is sparse, the experimental results of Phase 1, where the rubble accumulation is still small, are compared with the predictions from three different Models presented in the literature for sloped structures, under similar ice conditions, that do not accumulate rubble. The comparison allows concluding that the breaking phenomenon is being reasonably well Modeled in the experiments. The block sizes of the upper layer of the accumulated rubble were analyzed and the block length and width distributions were found for each experiment. A linear trend was found between block size and ice thickness. A linear fitting of the data was performed in order to obtain simple equations which give an upper limit of the length and width of the ice blocks generated during the SIB-ice interaction as function of the ice thickness. The results may apply for ice interaction on sloped structures in general as well.Copyright © 2009 by ASME

Di, Felice F. - One of the best experts on this subject based on the ideXlab platform.

  • Experimental analysis of the near wake from a ducted thruster at true and near bollard pull conditions using stereo particle image velocimetry (SPIV)
    2005
    Co-Authors: El Lababidy S., Bose N., Liu P., Walker D., Di, Felice F.
    Abstract:

    Thrusters working at low advance coefficients are employed in a wide range of offshore and marine applications on Floating, Production, Storage, and Offloading (FPSO) systems; shuttle tankers; tug boats; and mobile offshore units. Therefore, an understanding of the flow around the thrusters is of great practical interest. Despite this interest, there is lack of knowledge in the description of the hydrodynamic characteristics of a ducted thruster's wake at bollard pull and low advance coefficient values. This work was aimed at providing detailed data about the hydrodynamic characteristics of a Dynamic Positioning (DP) thruster near wake flow at different low advance coefficient values. Wake measurements were made during cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, the DP thruster near wake velocity components at different downstream axial planes, up to 1.5 diameters downstream, were obtained using a Stereoscopic Particle Image Velocimetry (SPIV) system. These experiments were carried out at different advance coefficient (J) values [bollard pull (J=0), J=0.4 and J=0.45].Peer reviewed: YesNRC publication: Ye

  • Evaluation of a dynamic positioning thruster wake using stereoscopic particle image velocimetry
    2004
    Co-Authors: El Lababidy S., Bose N., Liu P., Di, Felice F.
    Abstract:

    Thrusters working at low advance coefficients are employed in a wide range of offshore and marine applications on Floating, Production, Storage and Offloading (FPSO) systems; shuttle tankers; tug boats; and mobile offshore units. Therefore, an understanding of the flow around the thrusters is of great practical interest. Despite this interest, there is lack of knowledge in the description of the hydrodynamic characteristics of thrusters wake at bollard pull and low advance coefficient values. This work was aimed at providing detailed data about the hydrodynamic characteristics of a Dynamic Positioning (DP) thruster wake flow at different low advance coefficient values. Wake measurements were made during cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, the DP thruster far wake velocity components at different downstream axial planes, up to 15 diameters downstream, were obtained using a Stereoscopic Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel. These experiments were carried out at two different advance coefficient (J) values [bollard pull (J = 0), and J = 0.4].NRC publication: Ye

  • Experimental analysis of the wake from a dynamic positioning thruster
    2004
    Co-Authors: El Lababidy S., Bose N., Liu P., Di, Felice F., Felli M.
    Abstract:

    The knowledge of the effects of the wakes from Dynamic Positioning (DP) thrusters and the practical need to describe and predict their impact is fundamental in the assessment of design loading on slipstream-submerged equipment associated with offshore floating systems. In particular, with the increasing importance and application of DP thrusters in the offshore industry, the designer as well as the operator must have more information about the momentum in the wake from the thruster. This paper presents wake measurements from cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, DP thruster wake velocity components at different downstream axial planes were obtained experimentally using a Stereo Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel, up to 15 diameters downstream. These experiments were carried out with and without the nozzle in the bollard pull condition. This paper presents the results from these tests and discusses their importance for structures placed in the slipstream.NRC publication: Ye

Andrew J Goupee - One of the best experts on this subject based on the ideXlab platform.

  • design and testing of scale Model wind turbines for use in wind wave Basin Model tests of floating offshore wind turbines
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Matthew J Fowler, Richard Kimball, Dale A Thomas, Andrew J Goupee
    Abstract:

    Model Basin testing is a standard practice in the design process for offshore floating structures and has recently been applied to floating offshore wind turbines. 1/50th scale Model tests performed by the DeepCwind Consortium at Maritime Research Institute Netherlands (MARIN) in 2011 on various platform types were able to capture the global dynamic behavior of commercial scale Model floating wind turbine systems; however, due to the severe mismatch in Reynolds number between full scale and Model scale, the strictly Froude-scaled, geometrically similar wind turbine underperformed greatly. This required significant modification of test wind speeds to match key wind turbine aerodynamic loads, such as thrust. To execute more representative floating wind turbine Model tests, it is desirable to have a Model wind turbine that more closely matches the performance of the full scale design.This work compares the wind tunnel performance, under Reynolds numbers corresponding to Model test Froude-scale conditions, of an alternative wind turbine designed to emulate the performance of the National Renewable Energy Laboratory (NREL) 5 MW turbine. Along with the test data, the design methodology for creating this wind turbine is presented including the blade element momentum theory design of the performance-matched turbine using the open-source tools WT_Perf and XFoil. In addition, a strictly Froude-scale NREL 5 MW wind turbine design is also tested to provide a basis of comparison for the improved designs. While the improved, performance-matched turbine was designed to more closely match the NREL 5 MW design in performance under low Model test Reynolds numbers, it did not maintain geometric similitude in the blade chord and thickness orientations. Other key Froude scaling parameters, such as blade lengths and rotor operational speed, were maintained for the improved designs. The results of this work support the development of protocols for properly designing scale Model wind turbines that emulate the full scale design for Froude-scale wind/wave Basin tests of floating offshore wind turbines.Copyright © 2013 by ASME

El Lababidy S. - One of the best experts on this subject based on the ideXlab platform.

  • Experimental analysis of the near wake from a ducted thruster at true and near bollard pull conditions using stereo particle image velocimetry (SPIV)
    2005
    Co-Authors: El Lababidy S., Bose N., Liu P., Walker D., Di, Felice F.
    Abstract:

    Thrusters working at low advance coefficients are employed in a wide range of offshore and marine applications on Floating, Production, Storage, and Offloading (FPSO) systems; shuttle tankers; tug boats; and mobile offshore units. Therefore, an understanding of the flow around the thrusters is of great practical interest. Despite this interest, there is lack of knowledge in the description of the hydrodynamic characteristics of a ducted thruster's wake at bollard pull and low advance coefficient values. This work was aimed at providing detailed data about the hydrodynamic characteristics of a Dynamic Positioning (DP) thruster near wake flow at different low advance coefficient values. Wake measurements were made during cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, the DP thruster near wake velocity components at different downstream axial planes, up to 1.5 diameters downstream, were obtained using a Stereoscopic Particle Image Velocimetry (SPIV) system. These experiments were carried out at different advance coefficient (J) values [bollard pull (J=0), J=0.4 and J=0.45].Peer reviewed: YesNRC publication: Ye

  • Evaluation of a dynamic positioning thruster wake using stereoscopic particle image velocimetry
    2004
    Co-Authors: El Lababidy S., Bose N., Liu P., Di, Felice F.
    Abstract:

    Thrusters working at low advance coefficients are employed in a wide range of offshore and marine applications on Floating, Production, Storage and Offloading (FPSO) systems; shuttle tankers; tug boats; and mobile offshore units. Therefore, an understanding of the flow around the thrusters is of great practical interest. Despite this interest, there is lack of knowledge in the description of the hydrodynamic characteristics of thrusters wake at bollard pull and low advance coefficient values. This work was aimed at providing detailed data about the hydrodynamic characteristics of a Dynamic Positioning (DP) thruster wake flow at different low advance coefficient values. Wake measurements were made during cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, the DP thruster far wake velocity components at different downstream axial planes, up to 15 diameters downstream, were obtained using a Stereoscopic Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel. These experiments were carried out at two different advance coefficient (J) values [bollard pull (J = 0), and J = 0.4].NRC publication: Ye

  • Experimental analysis of the wake from a dynamic positioning thruster
    2004
    Co-Authors: El Lababidy S., Bose N., Liu P., Di, Felice F., Felli M.
    Abstract:

    The knowledge of the effects of the wakes from Dynamic Positioning (DP) thrusters and the practical need to describe and predict their impact is fundamental in the assessment of design loading on slipstream-submerged equipment associated with offshore floating systems. In particular, with the increasing importance and application of DP thrusters in the offshore industry, the designer as well as the operator must have more information about the momentum in the wake from the thruster. This paper presents wake measurements from cavitation tunnel tests carried out on a ducted propeller Model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, DP thruster wake velocity components at different downstream axial planes were obtained experimentally using a Stereo Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel, up to 15 diameters downstream. These experiments were carried out with and without the nozzle in the bollard pull condition. This paper presents the results from these tests and discusses their importance for structures placed in the slipstream.NRC publication: Ye