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Experimental and Numerical Investigation of Brittle Ice Crushing Loads

Experimental and Numerical Investigation of Brittle Ice Crushing Loads
Author: Hauke Herrnring
Publisher:
Total Pages: 0
Release: 2023
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ISBN:
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Ice loads pose a significant risk for ship operation in ice covered waters. At low strain rates, the ice behaves ductile, whereas at high strain rates it reacts in brittle manner. This thesis focuses on the brittle mode, which is the dominating mode for ship-ice interactions. A multitude of experimental data and numerical approaches for the simulation of ice can be found in the literature. Nevertheless, versatile and profound validated simulation techniques are currently missing to access the consequences of an iceberg collision or ice floe impact. Hence, in this thesis the new experimental set-up of the ice extrusion tests for the investigation of ice crushing loads is presented and a finite element model for the simulation of brittle ice-structure interaction problems is developed. During the comprehensive ice extrusion test campaign confined ice specimens were pushed against quasi rigid or full-scale ship structures. The obtained results reveal that the failure mode depends mainly on the test speed, while the confinement of ice mainly determines the load level. The core objective of the developed Mohr-Coulomb Nodal Split (MCNS) ice material model is to enable efficient physical based ice-structure interaction simulations. Unlike previously existing ice models, the MCNS model takes spalling and crushing into account, which significantly increases the versatility and reliability of the approach. The confinement effect on the crushing strength and the anisotropic failure behaviour of the ice is modelled by the Mohr-Coulomb material model. To preserve mass and energy as much as possible, the node splitting technique is applied in addition to the element erosion technique. To validate the findings of the model, the simulated maximum ice forces and contact pressures are compared with small- and large-scale ice extrusion experiments and double pendulum tests. During validation, the MCNS model shows a very good agreement with these experimental results. Finally, a procedure is proposed to simulate full-scale ship-ice collisions on basis of the given methodologies and experimental results.

Numerical Investigation of Fracture of Polycrystalline Ice Under Dynamic Loading

Numerical Investigation of Fracture of Polycrystalline Ice Under Dynamic Loading
Author: Igor Gribanov
Publisher:
Total Pages:
Release: 2020
Genre:
ISBN:
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Cohesive zone model is a promising technique for simulating fracture processes in brittle ice. In this work it is applied to investigate the fracture behavior of polycrystalline cylindrical samples under uniaxial loading conditions, four-point beam bending, and L-shaped beam bending. In each case, the simulation results are compared with the corresponding experimental data that was collected by other researchers. The model is based on the implicit finite element method combined with Park-Paulino-Roesler formulation for cohesive potential and includes an adaptive time stepping scheme, which takes into account the rate of damage and failure of cohesive zones. The benefit of the implicit scheme is that it allows larger time steps than explicit integration. Material properties and model parameters are calibrated using available experimental data for freshwater ice and sea ice samples. For polycrystalline ice, granular geometry is generated and cohesive zones are inserted between grains. Simulations are performed for samples with different grain sizes, and the resulting stress-strain and damage accumulation curves are recorded. Investigation of the dependency between the grain size and fracture strength shows a strengthening effect that is consistent with experimental results. The proposed framework is also applied to simulate the dynamic fracture processes in Lshaped beams of sea ice, in which case the cohesive zones are inserted between the elements of the mesh. Evolution of the stress distribution on the surface of the beam is modeled for the duration of the loading process, showing how it changes with progressive accumulation of damage in the material, as well as the development of cracks. An analytical formula is derived for estimating the breaking force based on the dimensions of the beam and the ice strength. Experimental data obtained from the 2014-2016 tests are re-evaluated with the aid of this new analysis. The computation is implemented efficiently with GPU acceleration, allowing to handle geometries with higher resolution than would be possible otherwise. Several technical contributions are described in detail including GPU-accelerated FEM implementation, an efficient way of creation of sparse matrix structure, and comparison of different unloading/reloading relations when using an implicit integration scheme. A mechanism for collision response allows modeling the interaction of fragmented material. To evaluate the collision forces, an algorithm for computing first and second point-triangle distance derivatives was developed. The source code is made available as open-source.

Experimental Investigation of Water, Snow and Granular Ice Effects on Ice Failure Processes and Impact Loads

Experimental Investigation of Water, Snow and Granular Ice Effects on Ice Failure Processes and Impact Loads
Author: Regina Sopper
Publisher:
Total Pages:
Release: 2016
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ISBN:
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A large series of laboratory ice crushing experiments was performed to investigate the effects of external boundary condition and indenter contact geometry on ice load magnitude under crushing conditions. Four boundary conditions were considered: dry cases, submerged cases, and cases with the presence of snow and granular ice material on the indenter surface. Indenter geometries were a flat plate, wedge shaped indenter, (reverse) conical indenter, and spherical indenter. These were impacted with artificially produced ice specimens of conical shape with 20° and 30° cone angles. All indenter - ice combinations were tested in dry and submerged environments at 1 mm/s and 100 mm/s indentation rates. Additional tests with the flat indentation plate were conducted at 10 mm/s impact velocity and a subset of scenarios with snow and granular ice material was evaluated. The tests were performed using a material testing system (MTS) machine located inside a cold room at an ambient temperature of - 7°C. Data acquisition comprised time, vertical force, and displacement. In several tests with the flat plate and wedge shaped indenter, supplementary information on local pressure patterns and contact area were obtained using tactile pressure sensors. All tests were recorded with a high speed video camera and still photos were taken before and after each test. Thin sections were taken of some specimens as well. Ice loads were found to strongly depend on contact condition, interrelated with pre-existing confinement and indentation rate. Submergence yielded higher forces, especially at the high indentation rate. This was very evident for the flat indentation plate and spherical indenter, and with restrictions for the wedge shaped indenter. No indication was found for the conical indenter. For the conical indenter it was concluded that the structural restriction due to the indenter geometry was dominating. The working surface for the water to act was not sufficient to influence the failure processes and associated ice loads. The presence of snow and granular ice significantly increased the forces at the low indentation rate (with the flat indentation plate) that were higher compared to submerged cases and far above the dry contact condition. Contact area measurements revealed a correlation of higher forces with a concurrent increase in actual contact area that depended on the respective boundary condition. In submergence, ice debris constitution was changed; ice extrusion, as well as crack development and propagation were impeded. Snow and granular ice seemed to provide additional material sources for establishing larger contact areas. The dry contact condition generally had the smallest real contact area, as well as the lowest forces. The comparison of nominal and measured contact areas revealed distinct deviations. The incorporation of those differences in contact process pressures-area relationships indicated that the overall process pressure was not substantially affected by the increased loads.

Experimental and Numerical Hydrodynamic Study of Submerged Ice Collision

Experimental and Numerical Hydrodynamic Study of Submerged Ice Collision
Author: Subodh Chander
Publisher:
Total Pages:
Release: 2015
Genre:
ISBN:
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Most of the research done on ice-structure interaction to date deals with the ice at the sea surface. However the majority of ice strengthened regions of ships and offshore structures are well below the waterline. The aim of this research is to examine the mechanics of ice loads caused by submerged ice blocks colliding with the structure. The kinematics of this process is an essential determinant of the energy that is available to drive the ice crushing process during the collision. The present research aims to develop a model to represent the mechanics of such collisions and set a direction for future work. This study includes experimental and numerical components. Various physical experiments have been conducted using a submerged ice model moving solely due to its buoyancy. Using a high speed camera, the experiments are recorded and analysed to determine the kinematics of collision. These include location, velocity and acceleration of the model ice as a function of time. In parallel, numerical simulations have being conducted using FLOW3DTM software. The results of the experiments are used to validate the numerical model of the underwater collision.

Ice Crushing Pressure on Non-planar Surface

Ice Crushing Pressure on Non-planar Surface
Author: Hyunwook Kim
Publisher:
Total Pages:
Release: 2014
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ISBN:
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The objective of this study is to investigate ice-structure interaction and develop a numerical model to predict the changes of ice loads and pressure during ice-structure interaction on non-planar surfaces. It is important to understand the sequential ice pressure and load development during ice-structure interaction. This is particularly true for non-planar surfaces as most ships and many offshore structures are composed of near-flat panels that may be dented as part of in-service loading leading to panels that are concave. An important question is whether these concave surfaces act as load-increasers for subsequent ice interaction. Most laboratory and field trial tests have been performed based on the assumption that the structural shape is flat. Therefore, little information is available for cases where the structure is concave due to plastic deformation, or specific areas with intentional structural concave shapes. In support of this objective, a series of laboratory-scale ice crushing tests were performed. Force, time and displacement data were measured. It was observed that ice crushing on concave shape indenters induced higher ice loads and pressure magnitudes compared to flat indenters. As part of the experimental program, techniques to use pressure measurement film were adopted to obtain ice-structure contact location, actual contact area, and changes of magnitude of pressure within the contact region. Following the experimental program a numerical model of ice crushing for concave surfaces was developed. In order to achieve valid numerical simulation results, a crushable foam model was modified by adding failure criteria. This followed the effect of indenter shape, level of confinement, test speed and cone angle to be evaluated in the numerical model and compared with the experimental results. The numerical model is shown to be valid for the flat indenter cases and the wedge and conical-shaped indenter cases. The findings from this study show that the shape of the indenting surfaces does influence ice forces and pressure and that generally, concave indentation surfaces lead to increases in pressure and force arising from ice crushing. These effects can be qualified globally and locally using the pressure measurement film, and the effects can be modeled numerically. This work demonstrates that the assumption of ice loads associated with flat or convex shapes may lead to under design for concave shapes or may lead to structural overload in cases where structures previously that have been indented.

Experimental and Numerical Study of Dynamic Crack Propagation in Ice Under Impact Loading

Experimental and Numerical Study of Dynamic Crack Propagation in Ice Under Impact Loading
Author: Lan Yao
Publisher:
Total Pages: 0
Release: 2016
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ISBN:
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The phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees.

Experimental and Numerical Study of Dynamic Crack Propagation in Ice Under Impact Loading

Experimental and Numerical Study of Dynamic Crack Propagation in Ice Under Impact Loading
Author: Lan Yao
Publisher:
Total Pages: 129
Release: 2019
Genre:
ISBN:
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The phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees.

Advances in the Analysis and Design of Marine Structures

Advances in the Analysis and Design of Marine Structures
Author: J. W. Ringsberg
Publisher: CRC Press
Total Pages: 921
Release: 2023-04-14
Genre: Technology & Engineering
ISBN: 1000913732
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Advances in the Analysis and Design of Marine Structures is a collection of papers presented at MARSTRUCT 2023, the 9th International Conference on Marine Structures, held in Gothenburg, Sweden, 3-5 April 2023. The conference was organised by the Division of Marine Technology, Department of Mechanics and Maritime Sciences at Chalmers University of Technology, in Gothenburg, Sweden. The MARSTRUCT Conference series deals with Ship and Offshore Structures, addressing topics in the fields of: Methods and tools for loads and load effects Methods and tools for strength assessment Experimental analysis of structures Materials and fabrication of structures Methods and tools for structural design and optimization Structural reliability, safety, and environmental protection The MARSTRUCT conferences series of started in Glasgow, UK in 2007, the second event of the series took place in Lisbon, Portugal in March 2009, the third in Hamburg, Germany in March 2011, the fourth in Espoo, Finland in March 2013, the fifth in Southampton, UK in March 2015, the sixth in Lisbon, Portugal in May 2017, the seventh in Dubrovnik, Croatia in May 2019, and the eighth event in Trondheim, Norway in June 2021. Advances in the Analysis and Design of Marine Structures is essential reading for academics, engineers and all professionals involved in the design of marine and offshore structures. The Proceedings in Marine Technology and Ocean Engineering series is devoted to the publication of proceedings of peer-reviewed international conferences dealing with various aspects of ‘Marine Technology and Ocean Engineering’. The Series includes the proceedings of the following conferences: the International Maritime Association of the Mediterranean (IMAM) Conferences, the Marine Structures (MARSTRUCT) Conferences, the Renewable Energies Offshore (RENEW) Conferences and the Maritime Technology (MARTECH) Conferences. The ‘Marine Technology and Ocean Engineering’ series is also open to new conferences that cover topics on the sustainable exploration and exploitation of marine resources in various fields, such as maritime transport and ports, usage of the ocean including coastal areas, nautical activities, the exploration and exploitation of mineral resources, the protection of the marine environment and its resources, and risk analysis, safety and reliability. The aim of the series is to stimulate advanced education and training through the wide dissemination of the results of scientific research.