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Sören Ehlers - One of the best experts on this subject based on the ideXlab platform.
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On the Scalability of Model-Scale Ice Experiments
Journal of Offshore Mechanics and Arctic Engineering, 2015Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Ice Model tests are a frequently used mean to assess and predict the performance of ships and structures in ice. The Model ice composition is adjusted to comply with Froude and Cauchy similitude. Recent research indicates that the internal mechanics of Aalto Model-Scale ice and sea ice differ significantly. This consequently limits the scalability and challenges state-of-the-art scaling procedures. This paper presents a qualitative assessment on selected topics to assess the differences between Model-Scale ice and sea ice and the influence of related experiments on determined mechanical properties. Furthermore, existing scaling approaches are discussed in context of recent research findings.
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On the Scalability of Model-Scale Ice Experiments
Volume 10: Polar and Arctic Science and Technology, 2014Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Ice Model-Scale tests are a frequently used mean to assess and predict the performance of ships and structures in ice. However, ice Model-Scale tests may not be treated as a black-box where any full-Scale scenario can be tested and a Froude-scalable result is obtained. Prior to scaling a thorough analysis of the physical processes is required and whether they can be transferred to full-Scale. Model-Scale ice is an empirically developed compound-material, consisting of frozen water, voids of air and other artificial dopants. The Model ice manufacturing process and dopant amounts have been adjusted to achieve Froude-scalability for the ice thickness and certain force response levels, i.e. ice resistance tests of ships breaking ice in the bending mode.However, not much is known about the internal mechanical processes of Model-Scale ice and how the Scaled force levels are reached. This may add uncertainty to ice Model tests and their application on new fields. Recent research indicated that the internal mechanics of Model-Scale ice and natural sea ice are different, which is also challenging some of the existing scaling approaches.Mechanical specimen tests in full-Scale and Model-Scale are usually compared by stresses, i.e. relating the failure load to the cross-sectional properties. However, depending on the tests different stress combinations might lead to failure, such as different geometries and dimensions may cause qualitatively different stress distribution, which ultimately limits the comparability of the tests.Subsequently, this paper presents a qualitative assessment on selected topics to assess the differences of Model-Scale ice and natural ice and the influence of the specimen geometry. Furthermore, existing scaling approaches are discussed in context with recent research findings.Copyright © 2014 by ASME
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Model Scale ice — Part B: Numerical Model
Cold Regions Science and Technology, 2013Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Abstract The Model-Scale ice of the Aalto University ice tank is fine-grained ice, which is used in experimental research on Arctic marine structures. However, the behavior of Model-Scale ice is not much explored and a deeper understanding of the Model-Scale ice mechanics is required to appraise the validity of full-Scale and Model-Scale ice property tests. Therefore, this paper presents a numerical Model that accounts for the Model-Scale ice micro-structure and a variety of the physical effects under load. The numerical Model accounts for the non-homogeneity of the Model-Scale ice and is based on damage mechanics. The basic mechanical properties, i.e. grain size, elastic strain-modulus, Poisson's ratio, compressive strength and tensile strength, are determined experimentally, and the free parameters of the damage Model are determined based on experimental evidence and by reverse engineering until the compliance of the numerical and experimental response is achieved. Furthermore, the response sensitivity on variations of the Poisson's ratio and the non-homogeneities is analyzed. Ultimately, the failure stresses of the numerical Model are compared with the experimentally-determined strength values. As a result, an experimentally-calibrated numerical Model of the Model-Scale ice is obtained. In the future, this numerical Model can be used to evaluate marine designs prior to testing, thus allowing for inexpensive simulation-based design of arctic marine structures.
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Model-Scale ice — Part A: Experiments
Cold Regions Science and Technology, 2013Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören Ehlers, Pentti KujalaAbstract:Abstract This paper is presenting novel Model-Scale ice property measurements for grain size, elastic strain-modulus, compressive and tensile specimen tests. The testing and analyzing procedure is targeted to define the basic material behavior accurately to understand the material behavior for the future development of a numerical material Model. Additionally, the Model-Scale ice thickness and the bending strength (following ITTC) are determined to classify the ice properties. The experiments consist of systematic in-situ tests to identify the Model-Scale ice properties in a format suitable for numerical simulations. The elastic strain-modulus is determined on the intact level ice sheet based on the load displacement relationship of the infinite plate deflection. All specimens are cut with a template to minimize dimensional variations. The specimens are loaded with a linear drive at constant speed while displacement and force are recorded. The resulting load–displacement curves indicate good repeatability. The experiments are conducted over a time of 4 h–5 h in the keeping phase , where the cooling system is adjusted to maintain the mechanical ice properties, and the obtained results do not show a dependency on the time of testing. A linear-elastic finite element Model is used to reproduce the plate bending measurements for the elastic strain-modulus determination. Therewith, it is found that the actual elastic strain-modulus is 27% larger than in plain stress theory due to stresses in thickness direction. Additionally, the approximate yield strength of the Model-Scale ice is investigated and is found to be significantly lower than the determined maximum stresses in compression, tension and bending. Consequently, this paper contributes to a deeper understanding of the mechanics of Model-Scale ice, and a procedure is shown how the mechanical parameters can be determined by systematic experiments and analyses.
Rüdiger U. Franz Von Bock Und Polach - One of the best experts on this subject based on the ideXlab platform.
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On the Scalability of Model-Scale Ice Experiments
Journal of Offshore Mechanics and Arctic Engineering, 2015Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Ice Model tests are a frequently used mean to assess and predict the performance of ships and structures in ice. The Model ice composition is adjusted to comply with Froude and Cauchy similitude. Recent research indicates that the internal mechanics of Aalto Model-Scale ice and sea ice differ significantly. This consequently limits the scalability and challenges state-of-the-art scaling procedures. This paper presents a qualitative assessment on selected topics to assess the differences between Model-Scale ice and sea ice and the influence of related experiments on determined mechanical properties. Furthermore, existing scaling approaches are discussed in context of recent research findings.
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Numerical analysis of the bending strength of Model-Scale ice
Cold Regions Science and Technology, 2015Co-Authors: Rüdiger U. Franz Von Bock Und PolachAbstract:Abstract Performance simulation tools are of high significance for the design and especially the optimization of ships and offshore structures. However, for ice covered waters such tools are hardly available and are either costly as ice Model tests or have a limited range of validity, such as semi-empirical formulas. This arises from the complexity of ice as material and insufficient knowledge on its mechanics. This paper presents a numerical analysis for Model-Scale ice in which material parameters are developed that can represent: tension, compression and in-situ downward bending. Those parameters are incorporated into a material Model following the Lemaitre damage law. The developed material characteristics for Model-Scale ice are intended to support the design process of ships and offshore structures. The key phenomenon joining the deformation processes in bending together with those in compression and tension, proved to be the through thickness dependency of properties. This analysis and development is a continuation of previously presented parameters for compression and tension and is developed in agreement with experimental evidence.
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On the Scalability of Model-Scale Ice Experiments
Volume 10: Polar and Arctic Science and Technology, 2014Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Ice Model-Scale tests are a frequently used mean to assess and predict the performance of ships and structures in ice. However, ice Model-Scale tests may not be treated as a black-box where any full-Scale scenario can be tested and a Froude-scalable result is obtained. Prior to scaling a thorough analysis of the physical processes is required and whether they can be transferred to full-Scale. Model-Scale ice is an empirically developed compound-material, consisting of frozen water, voids of air and other artificial dopants. The Model ice manufacturing process and dopant amounts have been adjusted to achieve Froude-scalability for the ice thickness and certain force response levels, i.e. ice resistance tests of ships breaking ice in the bending mode.However, not much is known about the internal mechanical processes of Model-Scale ice and how the Scaled force levels are reached. This may add uncertainty to ice Model tests and their application on new fields. Recent research indicated that the internal mechanics of Model-Scale ice and natural sea ice are different, which is also challenging some of the existing scaling approaches.Mechanical specimen tests in full-Scale and Model-Scale are usually compared by stresses, i.e. relating the failure load to the cross-sectional properties. However, depending on the tests different stress combinations might lead to failure, such as different geometries and dimensions may cause qualitatively different stress distribution, which ultimately limits the comparability of the tests.Subsequently, this paper presents a qualitative assessment on selected topics to assess the differences of Model-Scale ice and natural ice and the influence of the specimen geometry. Furthermore, existing scaling approaches are discussed in context with recent research findings.Copyright © 2014 by ASME
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Model Scale ice — Part B: Numerical Model
Cold Regions Science and Technology, 2013Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören EhlersAbstract:Abstract The Model-Scale ice of the Aalto University ice tank is fine-grained ice, which is used in experimental research on Arctic marine structures. However, the behavior of Model-Scale ice is not much explored and a deeper understanding of the Model-Scale ice mechanics is required to appraise the validity of full-Scale and Model-Scale ice property tests. Therefore, this paper presents a numerical Model that accounts for the Model-Scale ice micro-structure and a variety of the physical effects under load. The numerical Model accounts for the non-homogeneity of the Model-Scale ice and is based on damage mechanics. The basic mechanical properties, i.e. grain size, elastic strain-modulus, Poisson's ratio, compressive strength and tensile strength, are determined experimentally, and the free parameters of the damage Model are determined based on experimental evidence and by reverse engineering until the compliance of the numerical and experimental response is achieved. Furthermore, the response sensitivity on variations of the Poisson's ratio and the non-homogeneities is analyzed. Ultimately, the failure stresses of the numerical Model are compared with the experimentally-determined strength values. As a result, an experimentally-calibrated numerical Model of the Model-Scale ice is obtained. In the future, this numerical Model can be used to evaluate marine designs prior to testing, thus allowing for inexpensive simulation-based design of arctic marine structures.
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Model-Scale ice — Part A: Experiments
Cold Regions Science and Technology, 2013Co-Authors: Rüdiger U. Franz Von Bock Und Polach, Sören Ehlers, Pentti KujalaAbstract:Abstract This paper is presenting novel Model-Scale ice property measurements for grain size, elastic strain-modulus, compressive and tensile specimen tests. The testing and analyzing procedure is targeted to define the basic material behavior accurately to understand the material behavior for the future development of a numerical material Model. Additionally, the Model-Scale ice thickness and the bending strength (following ITTC) are determined to classify the ice properties. The experiments consist of systematic in-situ tests to identify the Model-Scale ice properties in a format suitable for numerical simulations. The elastic strain-modulus is determined on the intact level ice sheet based on the load displacement relationship of the infinite plate deflection. All specimens are cut with a template to minimize dimensional variations. The specimens are loaded with a linear drive at constant speed while displacement and force are recorded. The resulting load–displacement curves indicate good repeatability. The experiments are conducted over a time of 4 h–5 h in the keeping phase , where the cooling system is adjusted to maintain the mechanical ice properties, and the obtained results do not show a dependency on the time of testing. A linear-elastic finite element Model is used to reproduce the plate bending measurements for the elastic strain-modulus determination. Therewith, it is found that the actual elastic strain-modulus is 27% larger than in plain stress theory due to stresses in thickness direction. Additionally, the approximate yield strength of the Model-Scale ice is investigated and is found to be significantly lower than the determined maximum stresses in compression, tension and bending. Consequently, this paper contributes to a deeper understanding of the mechanics of Model-Scale ice, and a procedure is shown how the mechanical parameters can be determined by systematic experiments and analyses.
Haukur Ingason - One of the best experts on this subject based on the ideXlab platform.
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Model Scale tests of a ro-ro space fire ventilation
2019Co-Authors: Anna Olofsson, Pierrick Mindykowski, Lei Jiang, Alen Rakovic, Haukur IngasonAbstract:The report contains results from a parametric study using Model Scale tests with natural and mechanical ventilation on ro-ro ship. Two types of fuels were used, heptane liquid fire and wood cribs. ...
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Model Scale tunnel fire tests with automatic sprinkler
Fire Safety Journal, 2013Co-Authors: Haukur IngasonAbstract:Abstract The study focuses on the performance of an automatic sprinkler system in a Model Scale tunnel with longitudinal ventilation. A total of 28 tests were carried out in a 1:15 Model Scale tunnel using an automatic sprinkler system with glass bulbs. The maximum heat release rate, energy content and failure of the automatic sprinkler system were analysed. The results show that high ventilation rates and low water flow rates result in a failure of the automatic sprinkler system in a longitudinal ventilated tunnel fire. The main reason for the failure under the tested water flow rates was the effect of the longitudinal flow on the fire development and the hot gas flow close to the sprinklers. The fire development and the activation heat release rate of the first activated bulb are intimately related to the ventilation velocity. The fire spread to the neighbouring wood crib was investigated and a presentation of tests conducted using a deluge system are given.
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Model Scale tunnel fire tests with point extraction ventilation
Journal of Fire Protection Engineering, 2011Co-Authors: Haukur Ingason, Ying Zhen LiAbstract:Experimental results are presented from a series of tests in a Model Scale tunnel (1 : 23). This study focuses on single and two-point extraction ventilation systems to complement a previous study with the same apparatus using longitudinal ventilation only. The point extraction ventilation system in this test series was operated under different fire loads and flow conditions of either forced longitudinal ventilation or natural ventilation. Wood crib piles were used to simulate the fire source, which was designed to correspond to a ‘heavy goods vehicle’ fire load at full Scale. The parameters varied were the number of wood cribs, the longitudinal ventilation velocity, and the arrangement of the extraction vent openings and their exhaust capacity. Measurement data were obtained for maximum heat release rates, fire growth rates, maximum excess temperatures beneath the ceiling, and heat fluxes. Fire spread between wood cribs with a separation distance corresponding to 15 m at full Scale was also investigated. These data are reproduced well by empirical correlations that were established as part of the study. It is concluded that fire and smoke flows upstream and downstream of the fire source can be fully controlled if the ventilation velocities upstream and downstream are above about 2.9 and 3.8 m/s, respectively, at full Scale for a single-point extraction ventilation system and greater than about 2.9 m/s on both sides at full Scale for a two-point system.
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Model Scale tunnel fire tests with longitudinal ventilation
Fire Safety Journal, 2010Co-Authors: Haukur Ingason, Ying Zhen LiAbstract:Results from a series of tests in a Model tunnel (1:23) are presented. Tests were carried out with longitudinal ventilation under different fire conditions. Wood cribs were used to simulate the fire source, which was designed to correspond to a Scaled-down HGV (Heavy Goods Vehicle) fire load. The parameters tested were: the number of wood cribs, type of wood cribs, the longitudinal ventilation rate and the ceiling height. The heat release rate, fire growth rate, maximum gas temperature beneath the ceiling, temperature distribution, total heat flux at floor level, flame length, and back-layering length were investigated. Correlations for these parameters were investigated and proposed for longitudinal flow in tunnels.
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Fire incidents during contruction work of tunnels - Model-Scale experiments
2010Co-Authors: Anders Lönnermark, Jonatan Hugosson, Haukur IngasonAbstract:The report describes a series of Model Scale tests (1:40 Scale) describing the situation before breakthrough in a tunnel during construction. In such a situation this means that there is only one a ...
Alev Dramal - One of the best experts on this subject based on the ideXlab platform.
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adaptation of champion s health belief Model Scale for turkish women and evaluation of the selected variables associated with breast self examination
Cancer Nursing, 2007Co-Authors: Ozgul Karayurt, Alev DramalAbstract:The purpose of this study was to adapt Champion's Revised Health Belief Model Scale for Turkish women and to examine selected sociodemographic variables associated with breast self-examination (BSE). Data were collected from a total of 430 females who were living in one of the Health Center areas located in Izmir, a city in the west of Turkey. Champion's revised Health Belief Model Scale was translated into Turkish, validated by professional judges, translated back into English, and then tested. Factor analysis yielded 7 factors: susceptibility, seriousness, barrier 1, barrier 2, confidence, benefits, and health motivation. Significant correlations were found between 2 barriers. Therefore, 2 barriers were considered one barrier subScale. All the items on each factor were from the same construct. Cronbach alpha coefficients ranged from .58 to .89, and test-retest reliability coefficients ranged from .89 to .99 for the subScales. Women who received low scores on barriers reported greater frequency of BSE practice. Likewise, women having high scores on confidence, benefits, health motivation, susceptibility, and seriousness reported a greater frequency of BSE in the last year. The frequency of BSE practice was higher in high school and university graduates, women with a family history of breast cancer, and women with breast cancer and BSE training. The Turkish version of Champion's Revised Health Belief Model Scale was found to be a valid and reliable tool for use with Turkish women. It could be used to evaluate health beliefs about breast cancer and BSE among Turkish women.
David G Tarboton - One of the best experts on this subject based on the ideXlab platform.
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a new method for determination of most likely landslide initiation points and the evaluation of digital terrain Model Scale in terrain stability mapping
Hydrology and Earth System Sciences, 2006Co-Authors: Paolo Tarolli, David G TarbotonAbstract:Abstract. This paper introduces a new approach for determining the most likely initiation points for landslides from potential instability mapped using a terrain stability Model. This approach identifies the location with critical stability index from a terrain stability Model on each downslope path from ridge to valley. Any measure of terrain stability may be used with this approach, which here is illustrated using results from SINMAP, and from simply taking slope as an index of potential instability. The relative density of most likely landslide initiation points within and outside mapped landslide scars provides a way to evaluate the effectiveness of a terrain stability measure, even when mapped landslide scars include run out zones, rather than just initiation locations. This relative density was used to evaluate the utility of high resolution terrain data derived from airborne laser altimetry (LIDAR) for a small basin located in the Northeastern Region of Italy. Digital Terrain Models were derived from the LIDAR data for a range of grid cell sizes (from 2 to 50 m). We found appreciable differences between the density of most likely landslide initiation points within and outside mapped landslides with ratios as large as three or more with the highest ratios for a digital terrain Model grid cell size of 10 m. This leads to two conclusions: (1) The relative density from a most likely landslide initiation point approach is useful for quantifying the effectiveness of a terrain stability map when mapped landslides do not or can not differentiate between initiation, runout, and depositional areas; and (2) in this study area, where landslides occurred in complexes that were sometimes more than 100 m wide, a digital terrain Model Scale of 10 m is optimal. Digital terrain Model Scales larger than 10 m result in loss of resolution that degrades the results, while for digital terrain Model Scales smaller than 10 m the physical processes responsible for triggering landslides are obscured by smaller Scale terrain variability.
