53 research outputs found
Emerging trends in numerical predictive technologies in offshore and marine engineering
Both computational structural dynamics ~CSD! and computational fluid dynamics ~CFD! have come together to empower offshore structural engineers to forecast and enhance the performance of various structures designs. Equally important, they enable researchers and scientists to experiment with a wide range of ??what-if?? scenarios for risk assessments, accident scenario investigations, and fragility analyses. The true value of any computational model is determined by both the accuracy of the results of the simulations and our ability to interpret all of the significant information contained in those results. To a large extent, the accuracy of the results can be assured via verification and validation analyses ~V&V analyses!, also known as numerical uncertainty analyses. The ability to find out and understand the effects of the physical phenomena/parameters that control the overall behavior of an offshore system depends, to a large extent, on the visualization tools used to view the results. Without strong visualization tools, it might be difficult to recognize the existence of problems or inefficiencies within a given design.Peer reviewed: YesNRC publication: Ye
Ships in ice: solutions from an enhanced finite element methodology, part1: numerical development and modeling philosophy
NRC publication: Ye
A Visco-Elasto-Plastic Stress-Strain Model for Polycrystalline Materials at High Temperatures
This paper deals with the application of a constitutive model for ice collisions onto offshore structures and ships, through the use of numerical methods. Ice, in nature, exists at very high temperature states. Therefore, its behaviour is characterized by time dependent (visco) elasto-plastic behaviour. Also, upon loading, ice cracks (damage) and ice pieces break away from the original ice mass. This cracking activity includes both micro cracking and macro cracking. The constitutive model, presented in this paper, takes into account the micro cracking activity in ice (ice damage model). However, the macro cracking activity (large fractures in the ice mass) is considered via the numerical applications (through the death of elements, failure criterion). Validation of the model is demonstrated via comparisons of measured versus predicted behaviour,.NRC publication: Ye
Description of the Marine Dynamics Virtual Laboratory, MDVL
The Marine Dynamics Virtual Laboratory (MDVL) is a virtual replica of the physical towing tank facility at the Institute for Marine Dynamics of the National Research Council of Canada. It is intended that the MDVL will be used to duplicate, numerically, various experiments that have been conducted in the IMD towing tank over the last 15 years. In turn, the physical model data will be used to validate the results of MDVL. Through this physical-numerical validation process, an acceptable degree of confidence in the results of MDVL numerical testing will be achieved. Once the validation process is completed, MDVL will be used to simulate the behaviour and performance of full scale marine vehicles in various sea states.NRC publication: Ye
Multi-surface failure criterion for saline ice in the brittle regime
In this paper, the development of a 3-D failure criterion for saline ice is presented. The need for such general 3-D failure formulation stems from the fact that, during ice-ship interactions, ice undergoes a complex state of deformation and stress before it fails and breaks away, and the use of the uniaxial strength of ice to compute impact ice loads may lead to inaccurate load calculations and non-conclusive results. In recent years, with the availability of High Power Computers (HPC), numerical methods are being used more than ever before in marine and ice engineering problems. Numerical models based on computational techniques such as finite elements, boundary elements and discrete elements require 3-D constitutive models and failure criteria to represent the behavior of the materials involved (such as the behavior of the ship structure, ice, and water "fluid"). At high-speed mpacts (strain rates >10-3 s-1), ice behaves as a linear elastic material with a brittle mode of failure. Previously, Derradfi-Aouat [Derradji-Aouat, A., 2000. A unified failure envelope for isotropic freshwater ice and iceberg ice.ASME/OMAE-2000, Int. Conference on Offshore Mechanics and Arctic Engineering, Polar and Arctic section New Orleans, US, PDF file # OMAW-2000-P?A # 1002] developed a unified 3-D failure envelope for both fresh water isotropic ice and iceberg ice. In this paper, that formulation is extended to include failure of saline ice (in addition to fresth water ice and iceberg ice.) The results of a significant number of true triaxial tests using Laboratory Grown Ice (LGSI) were obtained from the open literature. The results of these tests formed a database that enables the existing failure model [Derradji-Aouat, A., 2000. A unified failure envelope for isotropic freshwater ice and iceberg ice. ASME/OMAE-2000, Int. Conference on Offshore Mechancis and Arctic Engineering, Polar and Arctic section, New Orleans, US, PDF file # OMAE-2000-P/A # 1002] to be extended from the isotropic fresh water ice and iceberg ice to columnar saline ice. Mroz's [J. Mech. Phys. Solids 15 (1967) 163] concept for the multi-surface failure theory is used in both studies (the present study, for saline ice, as well as in the previous study, for the fresh water isotropic ice and iceberg ice). It appears that the same set of the equations is applicable to the failure of all three types of ice. The possibility of the existence of a universal and general failure criterion for all types of ice is discussed. The validation of the present multi-surface failure criterion was discussed on the basis of comparisions between predicted failure curves and actual true triaxial test results. An overall discrepancy of predicted versus measured strength values of less than 20% was calculated.Peer reviewed: YesNRC publication: Ye
A failure envelope for saline ice in the brittle regime
Gratz and Schulson (1994) and Gratz (1996) published the results of a large set of true-triaxial (3-D) strength experiments using Laboratory Grown Saline Ice (LGSI). In this paper, their results were used to develop a 3-D failure criterion "failure envelope" for saline ice. The latter was formulated on the basis of the multi-surface failure theory using the same set of elliptical equations as those used for fresh water isotropic ice and iceberg ice (previously, developed by Derradji-Aouat, 2000). The comparisons between the predicted and measured strength values demonstrate that the multi-surface formulation is appropriate to model the 3-D failure of saline ice. A global analysis reveals that there may exist a unified failure criterion for all three types of ice (freshwater isotropic ice, iceberg ice, and saline ice). If the existence of such a general failure envelope is demonstrated, the present failure envelope becomes all inclusive failure formulation "a universal failure envelope for all types of ice".NRC publication: Ye
Ice Forces on Conical Piers - Numerical and Development of Design Equations
Over the years, Canadian design codes recommended various equations for the calculations of ice loads on conical structures. It is believed, however, that application of the design equations results in very conservative ice load estimations, and consequently there is room for less severe design regulations. In this paper, it is recognized that the complexities of ice-structure interaction problems dictate that the method of calculating ice loads on offshore structures should be numerical. A finite element study is conducted to examine the effect of ice flow, size, ice thickness, and tensile strength of ice on the magnitude of ice loads. The results are used to develop a design chart and design equations for quick estimations of ice loads on conical piers.NRC publication: Ye
New developments in numerical methods in offshore and marine engineering
Both Computational Structural Dynamics (CSD) and Computational Fluid Dynamics (CFD) have come together to empower offshore structural engineers to forecast and enhance the performance of various structures designs. Equally important, they enable researchers and scientists to experiment with a wide range of "what-if" scenarios for risk assessments, accident scenario investigations, and fragility analyses. The true value of any computational model is determined by both the accuracy of the results of the simulations and our ability to interpret all of the significant information contained in those results. To a large extent, the accuracy of the results can be assured via verification and validation analyses (V&V analyses, also known as numerical uncertainty analyses). Our ability to find out and understand the effects of the physical phenomena/parameters that control the overall behaviour of an offshore system depends, to a large extent, on the visualization tools used to view the results. Without strong visualization tools, it might be difficult to recognize the existence of problems or inefficiencies within a given design.NRC publication: Ye
Experimental uncertainty analysis for ice tank ship resistance experiments using a model for a Canadian Icebreaker "Terry Fox"
Experimental Uncertainty Analysis (EUA) was performed on the results of the Terry Fox resistance in ice tests. The experiments were documented in an IMD report TR-2002-01. In any given test, the "total uncertainty" is the sum of two components: A "bias uncertainty" and a "random uncertainty". Bias uncertainties are due to system set up, equipments and instrumentation used, calibrations, etc. Random uncertainties are associated with the degree of test results repeatability, accuracy of actual test set-up of the experiment, potential model misalignments (such as heading, trim), effects of the surrounding environment (such as change in temperature during testing), human factors, etc. The main objective of this work is to quantify the level of uncertainty (or level of confidence) in the measured test data.NRC publication: Ye
Numerical trends in offshore engineering - strategic/technical brief
NRC publication: Ye
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