Fish farms are being placed in more exposed locations than earlier, encouraged by the “developmen... more Fish farms are being placed in more exposed locations than earlier, encouraged by the “development licenses” that the Norwegian Directorate of Fisheries have introduced. Traditional design methods for estimating fatigue damage for fish farms are based on formulations given in the code NS - 9415 Marine fish farms. These methods are initially developed for sheltered areas and may not give an adequate level of safety in more exposed locations, where the dynamic response from waves is of greater importance. Accurate calculations using state of the art methods are very time consuming both with respect to man hours, but especially with regard to CPU consumption. Hence, for practical design, simplified procedures, such as combination of the design wave method with an assumed Weibull distribution, are often used to limit the complexity of the analysis as well as the costs. To the authors knowledge, the accuracy of such simplified methods is not well documented for exposed fish farms and wit...
One of the challenges in bridge design is to ensure bridge girder integrity under accidental coll... more One of the challenges in bridge design is to ensure bridge girder integrity under accidental collision loads induced by the superstructures of drifting ships. Such accidents can happen either during earthquakes or tsunami inundations when ships are drifted. Accidents may also occur due to human errors in ship manoeuvring or technical failures. The collision accident may induce girder damage and compromise the safety of the bridge. Severe collision-induced structural damage may also lead to the collapse of the whole bridge. Among all collision incidents with bridge girders, shipping containers collision have not been investigated before. In fact, the containers piled on the ship deck can impose considerable impact loads on bridge girders. Therefore, this study aims to numerically investigate shipping container impacts with bridge girders. The impact demand of a single shipping container is first obtained through rigid indenter impact simulations. The effect of the impact angle is als...
Fires and explosions are continuous threats on offshore oil installations. It is required that th... more Fires and explosions are continuous threats on offshore oil installations. It is required that the structures are able to withstand the actual fires for a certain time, for example the time needed to evacuate personnel, etc. (typically 1 to 2 hour). Specific requirements regarding strength and passive fire protection were introduced several decades ago, long before advanced computational tools were available. The guidelines and the practice therefore had to be based on simplified descriptions of the complex physical problems. The fires, the temperatures in the structure and the structural integrity were schematically and conservatively described. Over the past decades, the knowledge about fires, material behaviour and structural performance at elevated temperatures has increased substantially. In addition, specialized computer tools have become available, and direct computer costs have dropped to almost zero. The industrial practices and the guidelines/recommendations formed in the ...
Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the ... more Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the understanding of ice loads on larger ships are needed to achieve a better structural design with reduced steel weight. Published rules for the strength of ships are derived from semi-empirical methods and calibrated with limited full-scale measurements on small ships. In 2015, the Lloyd's Register pointed out that for independent navigation of larger ships in heavier ice conditions, steel weight increases exponentially with the ice thickness, which negatively affects the economy of ships' operations. Motivated by this statement, the objective of this paper is to address uncertainty in rule-derived ice loads using an ice mechanics point of view. The focus is on the local ice crushing loads and the vessel speeds in the Unified Requirements for Polar Class Ships of the International Association of Classification Societies (IACS). In this work, we attempt to relate the IACS speed-dep...
Ice/moored-structure collision tests and drop tests of ice blocks onto stiffened panels were carr... more Ice/moored-structure collision tests and drop tests of ice blocks onto stiffened panels were carried out at Aalto University, Finland. In the experiments, focus was placed on simultaneous inelastic deformations of ice and a steel structure. Laboratory-grown freshwater ice blocks were used. During testing, a steel structure was impacted with an approximately one-ton ice block shaped as a truncated cube. A total of 18 impact tests in water and two drop tests in air were conducted. The impact tests in water were performed at speeds of 1 and 2 m/s for structures of different rigidity. In the drop tests, initial impact velocities were 3 m/s and 8m/s. This paper provides main findings and lessons learned from the execution of these tests.
The Norwegian Public Roads Administration is running a project ‘Ferry free coastal route E39’ whi... more The Norwegian Public Roads Administration is running a project ‘Ferry free coastal route E39’ which includes replacing ferry crossings by bridges or tunnels across eight fjords in Western Norway. Since most of the fjords are wide and deep, traditional fixed links are not possible to be constructed. Therefore, floating bridge and tunnel concepts are proposed for the fjord-crossing project. Because floating bridges and tunnels have many structural components close to the water surface, a critical concern of accidental ship collision loads is then raised. Considering the large displacement and high speed of the passing ships, the interactions between the bridge structure and the ship bow can be significant should collision occurs. It is therefore important to carefully evaluate bridge response subjected to ship collision loads in the design process. This paper presents a case study of ship collision analysis of the floating bridge concept for Bjørnafjorden. Two possible collision scena...
IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment
The Norwegian Public Roads Administration is running a project “Ferry free coastal route E39” whi... more The Norwegian Public Roads Administration is running a project “Ferry free coastal route E39” which includes replacing ferry crossings by bridges or tunnels across fjords in Western Norway. A floating bridge concept was proposed in the fjord-crossing project for Bjørnefjorden. As there are regular cruise routes passing by the bridge, it raises the concern for the consequences of accidental ship collision with the bridge girder. During the collision, the interactions between the bridge girder and the ship structure can be significant. Thus, in the design of the proposed bridge it is vital to evaluate the safety of the ship and the bridge. In this paper, detailed finite element models of a cruise ship and a steel box girder are developed. The impact scenarios and structural damages are studied. The results show that the proposed bridge girder design is generally safe to resist normal accidental ship collision loads. Numerical model of the whole bridge is also developed for further stu...
Volume 11A: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering
To accurately predict the critical loads due to wind and wave is one of the common challenges in ... more To accurately predict the critical loads due to wind and wave is one of the common challenges in designing a floating offshore wind turbine (FOWT). The fully-coupled aero-hydrodynamic simulation of a floating offshore wind turbine, the NREL-5MW baseline wind turbine mounted on a semi-submersible floating platform, is conducted with two methods. Firstly, the in-house code naoe-FOAM-os-SJTU, which is developed on the open source platform OpenFOAM and coupled with the overset grid technique, is employed for the directly CFD computations. And another in-house code FOWT-UALM-SJTU developed by coupling the unsteady actuator line model (UALM) with naoe-FOAM-SJTU is also utilized for coupling simulations. In both models, the three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved with the turbulence model k-ω SST, and the Pressure-Implicit with Splitting of Operations (PISO) algorithm is applied to solve the pressure-velocity coupling equations. Both two solvers provid...
Fish farms are being placed in more exposed locations than earlier, encouraged by the “developmen... more Fish farms are being placed in more exposed locations than earlier, encouraged by the “development licenses” that the Norwegian Directorate of Fisheries have introduced. Traditional design methods for estimating fatigue damage for fish farms are based on formulations given in the code NS - 9415 Marine fish farms. These methods are initially developed for sheltered areas and may not give an adequate level of safety in more exposed locations, where the dynamic response from waves is of greater importance. Accurate calculations using state of the art methods are very time consuming both with respect to man hours, but especially with regard to CPU consumption. Hence, for practical design, simplified procedures, such as combination of the design wave method with an assumed Weibull distribution, are often used to limit the complexity of the analysis as well as the costs. To the authors knowledge, the accuracy of such simplified methods is not well documented for exposed fish farms and wit...
One of the challenges in bridge design is to ensure bridge girder integrity under accidental coll... more One of the challenges in bridge design is to ensure bridge girder integrity under accidental collision loads induced by the superstructures of drifting ships. Such accidents can happen either during earthquakes or tsunami inundations when ships are drifted. Accidents may also occur due to human errors in ship manoeuvring or technical failures. The collision accident may induce girder damage and compromise the safety of the bridge. Severe collision-induced structural damage may also lead to the collapse of the whole bridge. Among all collision incidents with bridge girders, shipping containers collision have not been investigated before. In fact, the containers piled on the ship deck can impose considerable impact loads on bridge girders. Therefore, this study aims to numerically investigate shipping container impacts with bridge girders. The impact demand of a single shipping container is first obtained through rigid indenter impact simulations. The effect of the impact angle is als...
Fires and explosions are continuous threats on offshore oil installations. It is required that th... more Fires and explosions are continuous threats on offshore oil installations. It is required that the structures are able to withstand the actual fires for a certain time, for example the time needed to evacuate personnel, etc. (typically 1 to 2 hour). Specific requirements regarding strength and passive fire protection were introduced several decades ago, long before advanced computational tools were available. The guidelines and the practice therefore had to be based on simplified descriptions of the complex physical problems. The fires, the temperatures in the structure and the structural integrity were schematically and conservatively described. Over the past decades, the knowledge about fires, material behaviour and structural performance at elevated temperatures has increased substantially. In addition, specialized computer tools have become available, and direct computer costs have dropped to almost zero. The industrial practices and the guidelines/recommendations formed in the ...
Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the ... more Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the understanding of ice loads on larger ships are needed to achieve a better structural design with reduced steel weight. Published rules for the strength of ships are derived from semi-empirical methods and calibrated with limited full-scale measurements on small ships. In 2015, the Lloyd's Register pointed out that for independent navigation of larger ships in heavier ice conditions, steel weight increases exponentially with the ice thickness, which negatively affects the economy of ships' operations. Motivated by this statement, the objective of this paper is to address uncertainty in rule-derived ice loads using an ice mechanics point of view. The focus is on the local ice crushing loads and the vessel speeds in the Unified Requirements for Polar Class Ships of the International Association of Classification Societies (IACS). In this work, we attempt to relate the IACS speed-dep...
Ice/moored-structure collision tests and drop tests of ice blocks onto stiffened panels were carr... more Ice/moored-structure collision tests and drop tests of ice blocks onto stiffened panels were carried out at Aalto University, Finland. In the experiments, focus was placed on simultaneous inelastic deformations of ice and a steel structure. Laboratory-grown freshwater ice blocks were used. During testing, a steel structure was impacted with an approximately one-ton ice block shaped as a truncated cube. A total of 18 impact tests in water and two drop tests in air were conducted. The impact tests in water were performed at speeds of 1 and 2 m/s for structures of different rigidity. In the drop tests, initial impact velocities were 3 m/s and 8m/s. This paper provides main findings and lessons learned from the execution of these tests.
The Norwegian Public Roads Administration is running a project ‘Ferry free coastal route E39’ whi... more The Norwegian Public Roads Administration is running a project ‘Ferry free coastal route E39’ which includes replacing ferry crossings by bridges or tunnels across eight fjords in Western Norway. Since most of the fjords are wide and deep, traditional fixed links are not possible to be constructed. Therefore, floating bridge and tunnel concepts are proposed for the fjord-crossing project. Because floating bridges and tunnels have many structural components close to the water surface, a critical concern of accidental ship collision loads is then raised. Considering the large displacement and high speed of the passing ships, the interactions between the bridge structure and the ship bow can be significant should collision occurs. It is therefore important to carefully evaluate bridge response subjected to ship collision loads in the design process. This paper presents a case study of ship collision analysis of the floating bridge concept for Bjørnafjorden. Two possible collision scena...
IABSE Congress, Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment
The Norwegian Public Roads Administration is running a project “Ferry free coastal route E39” whi... more The Norwegian Public Roads Administration is running a project “Ferry free coastal route E39” which includes replacing ferry crossings by bridges or tunnels across fjords in Western Norway. A floating bridge concept was proposed in the fjord-crossing project for Bjørnefjorden. As there are regular cruise routes passing by the bridge, it raises the concern for the consequences of accidental ship collision with the bridge girder. During the collision, the interactions between the bridge girder and the ship structure can be significant. Thus, in the design of the proposed bridge it is vital to evaluate the safety of the ship and the bridge. In this paper, detailed finite element models of a cruise ship and a steel box girder are developed. The impact scenarios and structural damages are studied. The results show that the proposed bridge girder design is generally safe to resist normal accidental ship collision loads. Numerical model of the whole bridge is also developed for further stu...
Volume 11A: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering
To accurately predict the critical loads due to wind and wave is one of the common challenges in ... more To accurately predict the critical loads due to wind and wave is one of the common challenges in designing a floating offshore wind turbine (FOWT). The fully-coupled aero-hydrodynamic simulation of a floating offshore wind turbine, the NREL-5MW baseline wind turbine mounted on a semi-submersible floating platform, is conducted with two methods. Firstly, the in-house code naoe-FOAM-os-SJTU, which is developed on the open source platform OpenFOAM and coupled with the overset grid technique, is employed for the directly CFD computations. And another in-house code FOWT-UALM-SJTU developed by coupling the unsteady actuator line model (UALM) with naoe-FOAM-SJTU is also utilized for coupling simulations. In both models, the three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved with the turbulence model k-ω SST, and the Pressure-Implicit with Splitting of Operations (PISO) algorithm is applied to solve the pressure-velocity coupling equations. Both two solvers provid...
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