Results are presented of a benchmark and uncertainty assessment study organised by the MARSTRUCT ... more Results are presented of a benchmark and uncertainty assessment study organised by the MARSTRUCT Virtual Institute on global linear wave loads on damaged ship. The study has two aims: to acquire valuable information regarding damage modelling in seakeeping analysis of damaged ships and to contribute to a rational approach for definition of the model uncertainty of linear seakeeping tools. Eight institutes participated in the benchmark, with six codes, representative of important linear seakeeping theories in use nowadays. The benchmark ship is the DTMB 5415 hull, with well documented and accessible data to perform seakeeping analysis and experimental results for motion and global wave loads. The uncertainty analysis is performed using the Frequency Independent Model Error as the uncertainty measure. The analysis is performed for vertical motions, vertical and horizontal global wave load components, and for torsional moments. Uncertainty measures of individual motion and load predictions are presented and compared. In addition, a comparative analysis of linear seakeeping theories is performed and the accuracy of the simplified methods used for the prediction of seakeeping of a damaged ship is assessed. Finally, recommendations are provided for efforts to improve modelling uncertainties in transfer functions of wave loads on damaged ships.
A decision support system with damage stability analysis has been recognized as an important tool... more A decision support system with damage stability analysis has been recognized as an important tool for passenger ships. Various software applications have been developed and taken into use over the years, without a direct link to any compelling requirement, set forth in the international regulatory framework. After the Costa Concordia accident, new regulations have been established, setting minimum requirements for a decision support system, as an extension to a loading computer. Yet, more advanced systems have been developed recently, aiming at providing valuable additional information on the predicted development of the stability of the damaged ship. This paper presents these alternative decision support systems with damage stability analysis methods for flooding emergencies on passenger ships. The technical background, usability, and usefulness of the various approaches are compared and discussed, taking into account the important statutory approval point of view. In addition, pra...
The water in a swimming pool on the top deck of a large passenger ship can be excited to a resona... more The water in a swimming pool on the top deck of a large passenger ship can be excited to a resonant motion, even in a moderate sea state. The motion of the water in the pool is mainly caused by longitudinal acceleration, resulting from the ship's pitch and surge motions. At resonance, there can be high waves in the pool and splashing of water. In this study the behavior of the Solarium Pool of the Freedom of the Seas was examined in various sea states and operating conditions. The motions of the pool were calculated on the basis of a linear seakeeping method, and the behavior of the water in the pool was studied with experimental model tests. A large-scale model of the pool was constructed and fitted to a purpose-built test bench that could be axially moved by a computer-controlled hydraulic cylinder. Water elevation in the pool was measured, and all tests were video recorded. Different modifications of the pool were tested to improve the behavior of the pool. A strong correlati...
ABSTRACT full text available until August 26, 2015 through this link: http://authors.elsevier.com... more ABSTRACT full text available until August 26, 2015 through this link: http://authors.elsevier.com/a/1RK6T3AMrSoKZU Numerical non-linear time domain simulation method for damaged ship motions is presented. Floodwater motion modelling is based on the lumped mass method with a moving free surface. The ship and floodwater motions are fully coupled. The variation of the floodwater mass is accounted for. A model to account for the flooding ingress transporting the momentum is presented. The experiments of abrupt flooding have shown that the ship may experience the first large roll towards the undamaged side, especially when a large undivided compartment is flooded. The presented time domain model is validated against the experimental data on the roll damping of the flooded ship and transient flooding. Two different initial stability conditions and two different compartment layouts are studied. Viscous dissipation of the floodwater motions is modelled with an equivalent friction coefficient. The impact of the viscous damping is studied. Transient flooding tests show that the inflow momentum has to be accounted for when the undivided compartment is flooded. The simulation model is capable of capturing the impact of the inflooding jet and the first roll on the opposite side of the damage is reproduced.
new calculation method for the steering forces of a pod propulsor is presented. This method is al... more new calculation method for the steering forces of a pod propulsor is presented. This method is also applied to a hybrid propulsion where a shaft-line-driven main propeller is located straight in front of a contra-rotating propeller, powered by an electric pod. In the calculations the pod unit is divided into four parts: a rotating propeller, a strut, a motor housing and a fin. The forces are calculated separately for each part. Interaction between these parts is estimated by using simplified methods. The required input data consists of the open water characteristics of both propellers and a simplified outline geometry of the pod unit. The method is developed to the first quadrant of the pod propeller and applies only to steering angles that are less than the stall angle of the pod unit. The calculation method has been validated by comparing its results with the results of an extensive model test program. Transverse and longitudinal forces are estimated rather accurately. The accurac...
ABSTRACT The principle idea of using pressure-correction method for time-domain flooding simulati... more ABSTRACT The principle idea of using pressure-correction method for time-domain flooding simulation is presented. Special attention is paid on the handling of large openings and relevant modifications to the equations. Practical examples of application are also discussed. First, progressive flooding in a complex system of rooms and openings of a passenger ship is presented. The study concentrates on the effect of input parameters for non-watertight structures. The second example demonstrates cross-flooding calculation with the air compressibility taken into account.
The application of the pressure-correction method for analysis of progressive flooding in a damag... more The application of the pressure-correction method for analysis of progressive flooding in a damaged large passenger ship is studied through a case study. The emphasis is on the efficient convergence of the pressure-correction iterations. In addition, a simple method for estimation of increased flooding due to waves and implementation of pumping and closing of open doors into the pressure-correction equation are presented.
ABSTRACT Time accurate simulation of progressive flooding inside a ship often requires a short ti... more ABSTRACT Time accurate simulation of progressive flooding inside a ship often requires a short time step. However, after the initial phases, as the flooding progresses to undamaged compartments, the flow rates decrease and much longer time step could be used. Yet the collapsing of non-watertight structures may cause additional phases of fast flooding, where a shorter time step is required. In this paper the use of an adaptive time step in flooding simulation is discussed, and a new approach to this problem is presented. The time step is automatically adjusted during the simulation on the basis of the maximum absolute velocity of the free surface levels in the flooded compartments. The method is tested with small case studies, presenting typical flooding conditions in passenger ships.
ABSTRACT full text available until August 29, 2015 through this link: http://authors.elsevier.com... more ABSTRACT full text available until August 29, 2015 through this link: http://authors.elsevier.com/a/1RL7A3AMrSoKZg Coupling of the flooded water and ship motions was studied experimentally. Roll decay tests for one flooded compartment and transient abrupt flooding tests were performed for the box shaped barge model. The tests were conducted to obtain information on the flooding process for the development of numerical tools and to provide validation data. Quantitative values on the effect of flooded water on the roll damping were obtained. Flooded water behaves in a different manner in undivided and divided compartments. Flooded water in divided compartment increases roll damping significantly. In undivided compartment roll damping was high at low amount of flooded water. For higher amounts damping was of the same order as for the intact model. Initial flooding is a complex process where the ship and flooded water motions are coupled. Propagation of the flooding water inside the compartment, at a dam-break type abrupt flooding, was studied by tracking the surface of the flooded water. An image processing algorithm was used to obtain the tracked surface. Flooded water volume and its center of gravity were estimated from the tracked surface. Different internal layouts of the flooded compartment can lead to a totally different roll response. The inflooding jet plays an important role in the response in case of the undivided compartment. While, for a divided compartment, asymmetric flooding due to the obstructions causes high heel angle on the damage side.
Progressive flooding inside a damaged ship can seriously endanger the stability. Level sensors ca... more Progressive flooding inside a damaged ship can seriously endanger the stability. Level sensors can be used to detect the flooding and based on this data the breach can be estimated. For decision support the prediction of flooding extent and intermediate phases is necessary. For this purpose a new simplified but still reasonable accurate flooding prediction method has been developed. Details of this algorithm and some test cases and comparisons to experimental data and time-accurate flooding simulation results are presented. The application of the developed prediction method in decision support is also discussed.
Results are presented of a benchmark and uncertainty assessment study organised by the MARSTRUCT ... more Results are presented of a benchmark and uncertainty assessment study organised by the MARSTRUCT Virtual Institute on global linear wave loads on damaged ship. The study has two aims: to acquire valuable information regarding damage modelling in seakeeping analysis of damaged ships and to contribute to a rational approach for definition of the model uncertainty of linear seakeeping tools. Eight institutes participated in the benchmark, with six codes, representative of important linear seakeeping theories in use nowadays. The benchmark ship is the DTMB 5415 hull, with well documented and accessible data to perform seakeeping analysis and experimental results for motion and global wave loads. The uncertainty analysis is performed using the Frequency Independent Model Error as the uncertainty measure. The analysis is performed for vertical motions, vertical and horizontal global wave load components, and for torsional moments. Uncertainty measures of individual motion and load predictions are presented and compared. In addition, a comparative analysis of linear seakeeping theories is performed and the accuracy of the simplified methods used for the prediction of seakeeping of a damaged ship is assessed. Finally, recommendations are provided for efforts to improve modelling uncertainties in transfer functions of wave loads on damaged ships.
A decision support system with damage stability analysis has been recognized as an important tool... more A decision support system with damage stability analysis has been recognized as an important tool for passenger ships. Various software applications have been developed and taken into use over the years, without a direct link to any compelling requirement, set forth in the international regulatory framework. After the Costa Concordia accident, new regulations have been established, setting minimum requirements for a decision support system, as an extension to a loading computer. Yet, more advanced systems have been developed recently, aiming at providing valuable additional information on the predicted development of the stability of the damaged ship. This paper presents these alternative decision support systems with damage stability analysis methods for flooding emergencies on passenger ships. The technical background, usability, and usefulness of the various approaches are compared and discussed, taking into account the important statutory approval point of view. In addition, pra...
The water in a swimming pool on the top deck of a large passenger ship can be excited to a resona... more The water in a swimming pool on the top deck of a large passenger ship can be excited to a resonant motion, even in a moderate sea state. The motion of the water in the pool is mainly caused by longitudinal acceleration, resulting from the ship's pitch and surge motions. At resonance, there can be high waves in the pool and splashing of water. In this study the behavior of the Solarium Pool of the Freedom of the Seas was examined in various sea states and operating conditions. The motions of the pool were calculated on the basis of a linear seakeeping method, and the behavior of the water in the pool was studied with experimental model tests. A large-scale model of the pool was constructed and fitted to a purpose-built test bench that could be axially moved by a computer-controlled hydraulic cylinder. Water elevation in the pool was measured, and all tests were video recorded. Different modifications of the pool were tested to improve the behavior of the pool. A strong correlati...
ABSTRACT full text available until August 26, 2015 through this link: http://authors.elsevier.com... more ABSTRACT full text available until August 26, 2015 through this link: http://authors.elsevier.com/a/1RK6T3AMrSoKZU Numerical non-linear time domain simulation method for damaged ship motions is presented. Floodwater motion modelling is based on the lumped mass method with a moving free surface. The ship and floodwater motions are fully coupled. The variation of the floodwater mass is accounted for. A model to account for the flooding ingress transporting the momentum is presented. The experiments of abrupt flooding have shown that the ship may experience the first large roll towards the undamaged side, especially when a large undivided compartment is flooded. The presented time domain model is validated against the experimental data on the roll damping of the flooded ship and transient flooding. Two different initial stability conditions and two different compartment layouts are studied. Viscous dissipation of the floodwater motions is modelled with an equivalent friction coefficient. The impact of the viscous damping is studied. Transient flooding tests show that the inflow momentum has to be accounted for when the undivided compartment is flooded. The simulation model is capable of capturing the impact of the inflooding jet and the first roll on the opposite side of the damage is reproduced.
new calculation method for the steering forces of a pod propulsor is presented. This method is al... more new calculation method for the steering forces of a pod propulsor is presented. This method is also applied to a hybrid propulsion where a shaft-line-driven main propeller is located straight in front of a contra-rotating propeller, powered by an electric pod. In the calculations the pod unit is divided into four parts: a rotating propeller, a strut, a motor housing and a fin. The forces are calculated separately for each part. Interaction between these parts is estimated by using simplified methods. The required input data consists of the open water characteristics of both propellers and a simplified outline geometry of the pod unit. The method is developed to the first quadrant of the pod propeller and applies only to steering angles that are less than the stall angle of the pod unit. The calculation method has been validated by comparing its results with the results of an extensive model test program. Transverse and longitudinal forces are estimated rather accurately. The accurac...
ABSTRACT The principle idea of using pressure-correction method for time-domain flooding simulati... more ABSTRACT The principle idea of using pressure-correction method for time-domain flooding simulation is presented. Special attention is paid on the handling of large openings and relevant modifications to the equations. Practical examples of application are also discussed. First, progressive flooding in a complex system of rooms and openings of a passenger ship is presented. The study concentrates on the effect of input parameters for non-watertight structures. The second example demonstrates cross-flooding calculation with the air compressibility taken into account.
The application of the pressure-correction method for analysis of progressive flooding in a damag... more The application of the pressure-correction method for analysis of progressive flooding in a damaged large passenger ship is studied through a case study. The emphasis is on the efficient convergence of the pressure-correction iterations. In addition, a simple method for estimation of increased flooding due to waves and implementation of pumping and closing of open doors into the pressure-correction equation are presented.
ABSTRACT Time accurate simulation of progressive flooding inside a ship often requires a short ti... more ABSTRACT Time accurate simulation of progressive flooding inside a ship often requires a short time step. However, after the initial phases, as the flooding progresses to undamaged compartments, the flow rates decrease and much longer time step could be used. Yet the collapsing of non-watertight structures may cause additional phases of fast flooding, where a shorter time step is required. In this paper the use of an adaptive time step in flooding simulation is discussed, and a new approach to this problem is presented. The time step is automatically adjusted during the simulation on the basis of the maximum absolute velocity of the free surface levels in the flooded compartments. The method is tested with small case studies, presenting typical flooding conditions in passenger ships.
ABSTRACT full text available until August 29, 2015 through this link: http://authors.elsevier.com... more ABSTRACT full text available until August 29, 2015 through this link: http://authors.elsevier.com/a/1RL7A3AMrSoKZg Coupling of the flooded water and ship motions was studied experimentally. Roll decay tests for one flooded compartment and transient abrupt flooding tests were performed for the box shaped barge model. The tests were conducted to obtain information on the flooding process for the development of numerical tools and to provide validation data. Quantitative values on the effect of flooded water on the roll damping were obtained. Flooded water behaves in a different manner in undivided and divided compartments. Flooded water in divided compartment increases roll damping significantly. In undivided compartment roll damping was high at low amount of flooded water. For higher amounts damping was of the same order as for the intact model. Initial flooding is a complex process where the ship and flooded water motions are coupled. Propagation of the flooding water inside the compartment, at a dam-break type abrupt flooding, was studied by tracking the surface of the flooded water. An image processing algorithm was used to obtain the tracked surface. Flooded water volume and its center of gravity were estimated from the tracked surface. Different internal layouts of the flooded compartment can lead to a totally different roll response. The inflooding jet plays an important role in the response in case of the undivided compartment. While, for a divided compartment, asymmetric flooding due to the obstructions causes high heel angle on the damage side.
Progressive flooding inside a damaged ship can seriously endanger the stability. Level sensors ca... more Progressive flooding inside a damaged ship can seriously endanger the stability. Level sensors can be used to detect the flooding and based on this data the breach can be estimated. For decision support the prediction of flooding extent and intermediate phases is necessary. For this purpose a new simplified but still reasonable accurate flooding prediction method has been developed. Details of this algorithm and some test cases and comparisons to experimental data and time-accurate flooding simulation results are presented. The application of the developed prediction method in decision support is also discussed.
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