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.

Results From Model Testing of Ice Protection Piles in Shallow Water

2006 ◽  
Author(s):  
Arne Gu¨rtner ◽  
Joachim Berger
Keyword(s):  
Model Test ◽  
Oil And Gas ◽  
Offshore Structures ◽  
Full Scale ◽  
Offshore Structure ◽  
Oil And Gas Fields ◽  
Ice Loads ◽  
Drifting Ice ◽  
Ice Model Test ◽  
Gas Fields

The development of oil and gas fields in shallow icy waters, for instance in the Northern Caspian Sea, have increased the awareness of protecting offshore structures by means of ice barriers from the impacts of drifting ice. Protection could be provided by Ice Protection Piles (IPPs), installed in close vicinity to the offshore structure to be protected. Piles then take the main loads from the drifting ice by pre-fracturing the advancing ice sheet. Hence, the partly shielded offshore structure could be designed according to significant lower global design ice loads. In this regard, various configurations of pile arrangements have been model tested during the MATRA-OSE research project in the Ice Model Test Basin of the Hamburg Sip Model Basin (HSVA). The main objective was to analyse the behaviour of ice interactions with the protection piles together with the establishment of design ice loads on an individual pile within the pile arrangement. The pile to pile distances within each arrangement were varied from 2 to 8 times the pile diameter for both, vertical and inclined (30° to the horizontal) pile arrangements. Two test runs with 0.1 m and 0.5 m thick ice (full scale values) were conducted respectively. The full scale water depth was 4 m. Based on the model test observations, it was found that the rubble generation increases with decreasing pile to pile distances. Inclined piles were capable to produce more rubble than vertical piles and considerable lower ice loads were measured on inclined arrangements compared to vertical arrangements. As initial rubble has formed in front of the arrangements, the rubble effect accelerated considerable. Subsequent to the build-up of rubble accumulations, no effect of the pile inclination on the exerted ice loads could be observed. If piles are used as ice barriers, the distance between the piles should be less than 4D for inclined piles and 6D for vertical piles to allow sufficient rubble generation. Larger distances only generated significant ice rubble after initial grounding of the ice had occurred.

Numerical simulation of ice-induced vibrations of steady-state type

2019 ◽  
Vol 22 (12) ◽  
pp. 2635-2647
Author(s):  
Wenliang Qiu ◽  
Tianyu Wu
Keyword(s):  
Numerical Simulation ◽  
Steady State ◽  
Model Test ◽  
Simulation Method ◽  
Offshore Structures ◽  
Structural Safety ◽  
Simulation Methodology ◽  
State Type ◽  
Ice Floes ◽  
Ice Pressure

Ice force is one kind of nonnegligible external loads that nature exerts on structures. The action of drifting ice floes may induce strong vibrations of offshore structures, and further reduce the structural safety and serviceability. The aim of this article is to develop a method to simulate the most dangerous situation during the interaction between ice and structure, that is, the ice-induced vibrations of steady-state type. A simulation methodology to realize structural steady-state vibration is proposed; it can simulate a special phenomenon of negative damping. The calculation of effective ice pressure is accomplished by an empirical formula which considers the dependence of the crushing strength on the ice velocity. The most important contribution of the simulation method is to capture the steady-state vibration phenomenon. The presented simulation methodology is conducted on the same model test introduced in a referenced study to verify the efficacy. Calculational examples show good agreements with the results of the model test, and the frequency contents of the generations coincide well with the targets. They directly prove the validity of the proposed simulation method. In addition, the numerical simulation method can be used in connection with finite element programs to perform a steady-state vibration analysis of 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.

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.

On the Safety of Fixed Offshore Structures, Failure Paths and Barriers

2002 ◽  
Author(s):  
Gerhard Ersdal
Keyword(s):  
Risk Assessment ◽  
Risk Analysis ◽  
Steel Structure ◽  
Offshore Structures ◽  
Point Of View ◽  
Structural Safety ◽  
General Level ◽  
Structural Failure ◽  
Offshore Structure ◽  
Protection Strategies

In order to ensure the safety of an offshore structure it is important to identify and maintain the barriers preventing hazardous events. Also, when monitoring the safety, the monitoring should be regarding how well these barriers are functioning, and utilise these to reassess the safety of the structure over time. The purpose of this paper is to apply a well-known method in risk assessment, Haddon’s energy and barrier model, to a new area; structural safety. The purposes of this exercise are to look at the structural safety from a risk assessment point of view, and to use this to identify and give an overview of the existing barriers. Furthermore, the purposes are to evaluate the efficiency and redundancy of these barriers, and to use this to evaluate the safety of offshore structures. This paper will analyse the safety of a fixed offshore structure through a qualitative approach. A possible event chart for a fixed offshore installation during operation in storms is established and analysed. Some of the root causes for potential structural failure are identified. These root-causes are kept on a general level, but considered in more detail than often seen in risk analysis. Hazards that are normally included in risk analysis, like boat collisions, fire, explosions, and dropped objects are not evaluated. Hazards that are evaluated are structural failure due to wave loading, fatigue damage, aging, and gross errors in design, fabrication, installation and operation. In order to identify the barriers (hazard reduction strategies, physical barriers and vulnerable target protection strategies), the different failure paths in the event chart are then analysed using Haddon’s ten preventive strategies for reducing damage from hazards. As an example a fixed offshore steel structure is used. A list of proposed barriers that influence the safety of such a fixed offshore installation are presented, and methods to measure these barriers are discussed.

Practical Airgap Prediction for Offshore Structures

2004 ◽  
Vol 126 (2) ◽  
pp. 147-155 ◽  
Author(s):  
Bert Sweetman
Keyword(s):  
Model Test ◽  
Offshore Structures ◽  
Value Theory ◽  
Second Order ◽  
New Method ◽  
Statistical Regression ◽  
Post Processing ◽  
Offshore Structure ◽  
First Order ◽  
Order Diffraction

Two new methods are proposed to predict airgap demand. Airgap demand is the maximum expected increase in the water surface elevation caused incident waves interacting with an offshore structure. The first new method enables inclusion of some second-order effects, though it is based on only first-order diffraction results. The method is simple enough to be practical for use as a hand-calculation in the early stages of design. Two existing methods of predicting airgap demand based on first-order diffraction are also briefly presented and results from the three methods are compared with model test results. All three methods yield results superior to those based on conventional post-processing of first-order diffraction results, and comparable to optimal post-processing of second-order diffraction results. A second new method is also presented; it combines extreme value theory with statistical regression to predict extreme airgap events using model test data. Estimates of extreme airgap events based on this method are found to be more reliable than estimates based on extreme observations from a single model test. This second new method is suitable for use in the final stages of design.

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.

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.

Research Studies on Modeling Soil Erosion Caused by External Factors Near Offshore Structures

2013 ◽  
Author(s):  
Leonid G. Shchemelinin ◽  
Kirill E. Sazonov ◽  
Valeriy I. Denisov
Keyword(s):  
Soil Erosion ◽  
Model Test ◽  
Offshore Structures ◽  
Bottom Current ◽  
Offshore Structure ◽  
Sandy Bottom ◽  
Towing Tank ◽  
Sea Bed ◽  
Sea Currents ◽  
Research Studies

For development of hydrocarbon deposits located in a shallow part of coastal shelf, offshore structures of gravitational type are widely used. The foundations of such structures are towed to sites where they are flooded and installed directly on sea bed. During operation of offshore structures the sea bed soil around and beneath the structure foundations are exposed to external effects such as sea currents, waves and also propeller streams generated by ships approaching the structures. As a result the soil is washed out from under the structure which may cause reduction of bearing surface area and even lead to loss of stability of the structure on seabed. The model studies on soil erosion process near foundations of gravitational-type offshore platforms have been conducted at Krylov’s shallow water towing tank since 2000. This towing tank was not originally intended for such experiments, and, therefore, special experimental equipment has been developed for this purpose. These include a sandy bottom, current generation arrangements in the model test zone, instrumentation for measuring the bottom profile. Also specific model test procedures and methods for research on soil scour near the test objects have been developed and verified. The paper gives a review of these research studies at the Krylov Centre, describe the test equipment, modeling techniques and test data scaling procedures as well as the experience learned from the experiments. The paper gives some results of research studies of soil erosion near the foundations of offshore structures as a result of influence from sea currents and waves with coincident directions, and also as a result of influence from propeller streams of moored tankers and supply vessels. The paper presents the model test results regarding the efficiency of a mobile system developed for soil erosion protection near the offshore structure intended for exploratory drilling in shallow waters of the Gulf of Ob in the Kara Sea. A review of the recent Krylov’s studies in this field of research is given.

On the Distribution of Wave Impact Loads on Offshore Structures

2017 ◽  
Author(s):  
Thomas B. Johannessen ◽  
Øystein Lande ◽  
Øistein Hagen
Keyword(s):  
Model Test ◽  
Load Distribution ◽  
Impact Load ◽  
Peak Load ◽  
Offshore Structures ◽  
Impact Loads ◽  
Test Results ◽  
Wave Impact ◽  
The Impact ◽  
Crest Height

For offshore structures in harsh environments, horizontal wave impact loads should be taken into account in design. Shafts on GBS structures, and columns on semisubmersibles and TLPs are exposed to impact loads. Furthermore, if the crest height exceeds the available freeboard, the deck may also be exposed to wave impact loads. Horizontal loads due to waves impacting on the structure are difficult to quantify. The loads are highly intermittent, difficult to reproduce in model tests, have a very short duration and can be very large. It is difficult to calculate these loads accurately and the statistical challenges associated with estimating a value with a prescribed annual probability of occurrence are formidable. Although the accurate calculation of crest elevation in front of the structure is a significant challenge, industry has considerable experience in handling this problem and the analysis results are usually in good agreement with model test results. The present paper presents a statistical model for the distribution of horizontal slamming pressures conditional on the incident crest height upwave of the structure. The impact load distribution is found empirically from a large database of model test results where the wave impact load was measured simultaneously at a large number of panels together with the incident crest elevation. The model test was carried out on a circular surface piercing column using long simulations of longcrested, irregular waves with a variety of seastate parameters. By analyzing the physics of the process and using the measured crest elevation and the seastate parameters, the impact load distribution model is made seastate independent. The impact model separates the wave impact problem in three parts: – Given an incident crest in a specified seastate, calculate the probability of the crest giving a wave impact load above a threshold. – Given a wave impact event above a threshold, calculate the distribution of the resulting peak load. – Given a peak load, calculate the distribution of slamming pressures at one spatial location. The development of the statistical model is described and it is shown that the model is appropriate for fixed and floating structures and for wave impact with both columns and the deck box.

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