Influence of added mass on ice impacts

1988 ◽  
Vol 15 (4) ◽  
pp. 698-708 ◽  
Author(s):  
Michael Isaacson ◽  
Kwok Fai Cheung
Keyword(s):  
Contact Point ◽  
Added Mass ◽  
Offshore Structures ◽  
Impact Model ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Proposed Model ◽  
Impact Problems ◽  
Ice Impacts ◽  
The Impact

The present paper applies potential theory to describe the variation of the added mass of an iceberg and its coupling effects on an offshore structure for various separation distances up to the point of contact. The strengths and weaknesses of the proposed model are discussed together with its practical application in ice mass impact problems. An impact model based on dynamic analysis is developed to calculate the impact force and response of a structure for head-on collisions. Both the contact-point added mass estimated in the present study and the traditionally assumed far-field added mass are used in the impact model separately. The results are compared and the crucial roles played by the ambient fluid during impact are discussed. Key words: added mass, hydrodynamics, ice impact, ocean engineering, offshore structures.

Experimental Investigation of Ice Mass Hydrodynamic Interaction With Offshore Structure in Close Proximity

2015 ◽  
Author(s):  
Tanvir Mehedi Sayeed ◽  
Bruce Colbourne ◽  
Heather Peng ◽  
Benjamin Colbourne ◽  
Don Spencer
Keyword(s):  
Hydrodynamic Interaction ◽  
Impact Load ◽  
Numerical Study ◽  
Numerical Models ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Area Of Interest ◽  
Close Proximity ◽  
The Impact

Iceberg/bergy bit impact load with fixed and floating offshore structures and supply ships is an important design consideration in ice-prone regions. Studies tend to divide the iceberg impact problem into phases from far field to contact. This results in a tendency to over simplify the final crucial stage where the structure is impacted. The authors have identified knowledge gaps and their influence on the analysis and prediction of iceberg impact velocities and loads (Sayeed et. al (2014)). The experimental and numerical study of viscous dominated very near field region is the main area of interest. This paper reports preliminary results of physical model tests conducted at Ocean Engineering Research Center (OERC) to investigate hydrodynamic interaction between ice masses and fixed offshore structure in close proximity. The objective was to perform a systematic study from simple to complex phenomena which will be a support base for the development of subsequent numerical models. The results demonstrated that hydrodynamic proximity and wave reflection effects do significantly influence the impact velocities at which ice masses approach to large structures. The effect is more pronounced for smaller ice masses.

Improved Model for Impact of Viscoplastic Bodies

2016 ◽  
Vol 715 ◽  
pp. 180-185 ◽  
Author(s):  
Masniezam Ahmad ◽  
Khairul Azwan Ismail ◽  
Fauziah Mat ◽  
William James Stronge
Keyword(s):  
Plastic Deformation ◽  
Wave Propagation ◽  
High Impact ◽  
Impact Response ◽  
Stress Wave Propagation ◽  
Impact Model ◽  
Direct Impact ◽  
Proposed Model ◽  
Improved Model ◽  
The Impact

This study proposes an improved viscoplastic impact model that calculates impact response for direct impact between two compact bodies. The proposed model employs spring and viscous elements that represent the energy loss due to plastic deformation and stress wave propagation, respectively. The impact response is calculated by solving differential equations through analytical and numerical methods. This model can accurately predict impact response for low, moderate and high impact speeds.

Wave–current effects on large offshore structures

1989 ◽  
Vol 16 (4) ◽  
pp. 543-551 ◽  
Author(s):  
Michael Isaacson ◽  
John Baldwin
Keyword(s):  
Potential Flow ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Viscous Effects ◽  
Offshore Structure ◽  
Time Stepping ◽  
Waves And Currents ◽  
Flow Effects ◽  
Interaction Problem

The various effects that influence loads acting on a large offshore structure due to the combination of waves and currents are reviewed. These may be broadly associated with potential flow effects and viscous effects. The potential flow effects are nonlinear and may generally be investigated by perturbation or time-stepping methods. Viscous effects include the onset of flow separation, which affects the validity of the assumed potential flow, as well as steady and oscillatory forces. The fluid mechanics of the complete wave–current–structure interaction problem are not yet well understood and areas in need of additional research are identified. Key words: currents, drag, drift forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Experimental Study of Air Gap Response and Wave Impact Forces of a Semi-Submersible Drilling Unit

2006 ◽  
Author(s):  
Saeid Kazemi ◽  
Atilla Incecik
Keyword(s):  
Experimental Study ◽  
Offshore Structures ◽  
Model Tests ◽  
Air Gap ◽  
Scale Model ◽  
Offshore Structure ◽  
The Caspian Sea ◽  
Wave Impact ◽  
Impact Forces ◽  
The Impact

An experimental study for predicting the air gap and potential deck impact of a floating offshore structure is the main topic of this research. Numerical modeling for air gap prediction is particularly complicated in the case of floating offshore structures because of their large volume, and the resulting effects of wave diffraction and radiation. Therefore, for new floating platforms, the model tests are often performed as part of their design process. This paper summarizes physical model tests conducted on a semi-submersible model, representing a 1-to-100 scale model of a GVA4000 class, “IRAN-ALBORZ”, the largest semi-submersible platform in the Caspian Sea, under construction in North of Iran, to evaluate the platform’s air gap at different locations of its deck and also measure the impact forces in case of having negative air gap. The model was tested in regular waves in the wave tank of Newcastle University. The paper discusses the experimental setup, test conditions, and the resulting measurements of the air gap and the wave impact forces by using eight wave probes and three load cells located at different points of the lower deck of the platform.

Hydrodynamic coefficients of a vertical circular cylinder

1990 ◽  
Vol 17 (3) ◽  
pp. 302-310 ◽  
Author(s):  
Michael Isaacson ◽  
Thomas Mathai ◽  
Carol Mihelcic
Keyword(s):  
Circular Cylinder ◽  
High Frequency ◽  
Closed Form Solution ◽  
Added Mass ◽  
Offshore Structures ◽  
Form Solution ◽  
Ocean Engineering ◽  
Radiation Problem ◽  
The Vertical Distribution ◽  
Linear Radiation

The added mass and the damping coefficient of a large surface-piercing circular cylinder extending to the seabed and undergoing horizontal oscillations are described. A closed-form solution to the corresponding linear radiation problem is obtained by the use of eigenfunction expansions. Attention is given to the vertical distribution of these coefficients and to their high-frequency asymptotic behaviour. Comparisons are made with experimental measurements. The application to typical offshore structures is discussed. Key words: added mass, cylinders, damping, hydrodynamics, ocean engineering.

Iceberg Impact Simulation on Offshore Structures

2017 ◽  
Author(s):  
Marc Cahay ◽  
Brian A. Roberts ◽  
Kenton Pike ◽  
Pierre-Antoine Béal ◽  
Cyril Septseault ◽  
...  
Keyword(s):  
Impact Load ◽  
Development Program ◽  
Offshore Structures ◽  
Separation Distance ◽  
Offshore Structure ◽  
Pressure Area ◽  
Common Framework ◽  
Multi Agent ◽  
Crushing Behavior ◽  
The Impact

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches. This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). The current development phase consists of the determination of the forces generated by an iceberg during an impact on an offshore structure. This paper will provide an overview of the latest Ice-MAS development. It will introduce the main functionalities of the simulation tool and the different options for modelling an offshore structure. It will then focus on the modelling approach used for an iceberg, the calculation of the different hydrodynamic coefficients and their variability according to the separation distance from the structure. The model used to compute the impact load will be detailed, including the local crushing behavior which is simulated by a pressure-area correlation.

Influence of hydrodynamic effects on iceberg collisions

1990 ◽  
Vol 17 (3) ◽  
pp. 329-337 ◽  
Author(s):  
Michael Isaacson ◽  
Kevin McTaggart
Keyword(s):  
Added Mass ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Iceberg Drift ◽  
Added Masses ◽  
Waves And Currents ◽  
Fixed Structure ◽  
Wave Induced ◽  
Hydrodynamic Effects ◽  
Selection Of

This paper examines various hydrodynamic effects which should be considered when analyzing iceberg collisions with a fixed structure. Iceberg added mass is among the hydrodynamic parameters that must be known to evaluate collision severity. Effective added mass is shown to vary with collision duration and recommendations are made for the selection of added masses to be used in iceberg collision design. Iceberg impact velocities are influenced by waves and currents, which can both be significantly influenced by the presence of a large structure. Wave-driven iceberg drift motions are shown to be more sensitive than current-driven motions to the presence of a structure. The contribution of wave-induced oscillatory motions to impact velocity is also discussed. Key words: added mass, hydrodynamics, ice impact, icebergs, ocean engineering, offshore structures.

scholarly journals A Dynamic Ice-structure Interaction Model for Prediction of Ice-induced Vibration

2019 ◽  
Author(s):  
Tianyu Wu ◽  
Wenliang Qiu
Keyword(s):  
Sea Ice ◽  
Model Test ◽  
Interaction Model ◽  
Simulation Method ◽  
Offshore Structures ◽  
Full Scale ◽  
Structural Safety ◽  
Offshore Structure ◽  
The Impact ◽  
Ice Induced Vibration

Sea ice crashing against offshore structures can cause strong ice-induced vibration and have a major impact on offshore structural safety and serviceability. This paper describes a numerical method for the prediction of ice-induced vibration when a vertical offshore structure is subjected to the impact of sea ice. In this approach, negative damping theory and fracture length theory are combined and, along with ice strength-stress rate curve and ice failure length, are coupled to model the internal fluctuating nature of ice load. Considering the elastic deformation of ice and the effect of non-simultaneous crushing failure of local contact between ice and structures, the present ice-induced vibration model is established, and the general features of the interaction process are captured. To verify its efficacy, the presented simulation methodology is subjected to a model test and two full-scale measurements based on referenced studies. Example calculations show good agreement with the results of the model test and full-scale measurements, which directly indicates the validity of the proposed simulation method. In addition, the numerical simulation method can be used in connection with FE programs to perform ice-induced vibration analysis of offshore structures.

Experimental Study of Combined Wave and Ice Loads on a Fixed Offshore Structure

2021 ◽  
Author(s):  
Shafiul Mintu ◽  
David Molyneux
Keyword(s):  
Offshore Structures ◽  
Numerical Code ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Engineering Research ◽  
Combined Loads ◽  
Individual Wave ◽  
Ice Loads ◽  
Ice Floes ◽  
Memorial University Of Newfoundland

Abstract Ice floes in the marginal ice zone (MIZ) are exposed to wind, wave, and current forces which greatly influence the dynamics of the ice floes. ISO 19906 recommends considering combined wave and ice actions while designing offshore structures for arctic and cold regions. Few studies have focused on ice-structure interactions in waves. There are not many tools available to estimate these combined loads on structures. A numerical tool “SAMICE” has been developed to simulate the hydrodynamics of wave-ice interactions, but there exists a lack of data for a realistic MIZ under wave actions for validation studies of the numerical code. To address this gap and to investigate the hydrodynamics of ice floes under waves, a set of experiments was conducted at the wave tank of Ocean Engineering Research Center (OERC) of Memorial University of Newfoundland. A six-component dynamometer was used to measure the loads on a model scale aluminum cylindrical gravity-based offshore structure. Loads were measured for five regular waves of various steepness in combination with three current speeds. Two ice concentrations with various floe sizes of random shapes were prepared from polypropylene sheets to represent the MIZ. Most of the tests were repeated three times and a statistical approach was used to analyze the loads. The preliminary analysis shows that the average wave-ice loads may be determined by ISO guidelines, but the predictions of impulse loads from individual wave-driven ice floes are very uncertain.

scholarly journals Structural Integrity of Fixed Offshore Platforms by Incorporating Wave-in-Deck

2021 ◽  
Vol 9 (9) ◽  
pp. 1027
Author(s):  
Nurul Uyun Azman ◽  
Mohd Khairi Abu Husain ◽  
Noor Irza Mohd Zaki ◽  
Ezanizam Mat Soom ◽  
Nurul Azizah Mukhlas ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Limit State ◽  
Pushover Analysis ◽  
Offshore Structures ◽  
State Equation ◽  
Air Gap ◽  
Wave Crest ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
The Impact

The structural integrity of offshore platforms is affected by degradation issues such as subsidence. Subsidence involves large settlement areas, and it is one of the phenomena that may be experienced by offshore platforms throughout their lives. Compaction of the reservoir is caused by pressure reduction, which results in vertical movement of soils from the reservoir to the mud line. The impact of subsidence on platforms will lead to a gradually reduced wave crest to deck air gap (insufficient air gap) and cause wave-in-deck. The wave-in-deck load can cause significant damage to deck structures, and it may cause the collapse of the entire platform. This study aims to investigate the impact of wave-in-deck load on structure response for fixed offshore structure. The conventional run of pushover analysis only considers the 100-year design crest height for the ultimate collapse. The wave height at collapse is calculated using a limit state equation for the probabilistic model that may give a different result. It is crucial to ensure that the reserve strength ratio (RSR) is not overly estimated, hence giving a false impression of the value. This study is performed to quantify the wave-in-deck load effects based on the revised RSR. As part of the analysis, the Ultimate Strength for Offshore Structures (USFOS) software and wave-in-deck calculation recommended by the International Organization for Standardization (ISO) as practised in the industry is adopted to complete the study. As expected, the new revised RSR with the inclusion of wave-in-deck load is lower and, hence, increases the probability of failure (POF) of the platform. The accuracy and effectiveness of this method will assist the industry, especially operators, for decision making and, more specifically, in outlining the action items as part of their business risk management.

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