IOP Conference Series: Materials Science and Engineering
In this paper asymmetry in sagging and hogging of a hull progressing in regular waves is investig... more In this paper asymmetry in sagging and hogging of a hull progressing in regular waves is investigated by applying a weakly nonlinear potential flow theory. At first instance ship motions in waves are evaluated using a linear strip-theory yielding transfer functions of ship motions and sectional loads. Then, by assuming time-histories of ship motions the nonlinear part of the Froude-Krylov and restoring forces and moments are evaluated using a panel representation. Linear and weakly nonlinear predictions are compared against available model tests for a roll-on/off (Ro-Pax) ship hull. The results confirm that importance of nonlinearities of restoring and Froude-Krylov part of wave loading on asymmetry of sagging and hogging.
IOP Conference Series: Materials Science and Engineering
In recent years, Computational Fluid Dynamics (CFD) is increasingly becoming more attractive for ... more In recent years, Computational Fluid Dynamics (CFD) is increasingly becoming more attractive for the analysis of ship seakeeping. This is because of the increasing efficiency of computers and the accuracy of solvers (e.g. Reynold Navier Stokes Averaged – RANS) that may be more accurate in terms of idealizing nonlinear phenomena in comparison to potential flow methods. Notwithstanding this, RANS methods remain sensitive to accurate wave modelling across the fluid domain as well as the reflection of domain boundaries. This paper studies the effective absorption of the reflected waves from a structure heading back towards the inlet boundary with a relaxation zone method. This is achieved by applying the RANS CFD solver OpenFOAM-v2206 and wave generation toolbox waves2Foam. The modelled case is a 2D box in waves with different wave lengths. The distance of the relaxation zone and the distance after the relaxation zone until the box varies and their effect to excitation forces is studied...
Large floating offshore structures encounter wave induced motions and loads in real service condi... more Large floating offshore structures encounter wave induced motions and loads in real service conditions. This paper evaluates these motions and loads. Model tests and numerical calculations are performed to determine the hydrodynamic characteristics of two floating offshore structures. Theoretical and experimental results are compared to check the validity of the computer program.
When navigating in shallow or harbour water vessel may hit an underwater obstacle (rock, underwat... more When navigating in shallow or harbour water vessel may hit an underwater obstacle (rock, underwater structure etc.). As a consequence its hull may be damaged, a kind of penetration of the obstacle into initially undamaged hull surface occurs. This penetration produces certain force that, depending on its magnitude, changes vessel position and motion. Actually process of penetration and force formation are considered as a simple geometrical intrusion of a point into undisturbed ship hull. Model testing provides constitutive relation between penetration and resulting force.
Estimation of propeller-induced excitation forces is discussed and a comparison between computed ... more Estimation of propeller-induced excitation forces is discussed and a comparison between computed and measured propeller-induced pressure distributions for an 8000/12000 dwt ro/ro vessel are shown. Diagrams for axial wake of model and full-scale ship are also compared. Vibration calculations are described, and modelling aspects, and the effect of the surrounding water are dealt with. The measurement of vibrations using a measuring system developed in the Finnish VTT Ship Laboratory is explained. An exciter test system is used. Prediction of the vibration level and trouble-shooting vibration measurements are also dealt with.
The majority of ship vibration problems are associated with so-called local vibrations. These loc... more The majority of ship vibration problems are associated with so-called local vibrations. These local problems are rather easy to cure, if a vibration test is done before the ship is completely fitted. A combination of theoretical and experimental approaches leads in practice to the best result in predicting the vibration level. This combination is also needed in the interpretation of measurements. For example, the exciter test in the construction stage must be conducted in shallow water. Thus calculations are needed to take into account the change in added mass and in other relevant parameters. Some practically important features of both calculations and experiments are discussed in this paper.
This textbook is a result of the work started in 1996 when I joined a very interesting, newly for... more This textbook is a result of the work started in 1996 when I joined a very interesting, newly formed Specialist Committee working on Ship Stability within the International Towing Tank Conference (ITTC). Thanks to this group of international enthusiastic scholars in the field, it became clear for me that both the research and the rules’ development in the field of ship stability will proceed in the direction of including ship dynamics into account. Moreover, this development will require sophisticated mathematical models of ship dynamics based on the first principles and taking realistically into account the environmental, often very hostile, conditions. These models should be verified and thoroughly validated. I am very grateful to Professor Eero-Matti Salonen for his valuable comments and corrections he has made to the original manuscript. I want to thank my colleagues Messrs Teemu Manderbacka and Otto Puolakka, the assistants in the course on Ship Dynamics, for their valuable rem...
This paper presents the results in modelling of ship-generated waves around a modem tanker using ... more This paper presents the results in modelling of ship-generated waves around a modem tanker using the FINFLO-SHIP RANS solver developed at Helsinki University of Technology. Simulation for three-dimensional turbulent free-surface flows is performed in a numerical water tank. A cell-centred finite-volume (FV) scheme is implemented for the solution of the RANS equations with the artificial compressibility and the nonlinear free-surface boundary conditions. The convergence performance is improved with the multigrid ...
IOP Conference Series: Materials Science and Engineering
In this paper asymmetry in sagging and hogging of a hull progressing in regular waves is investig... more In this paper asymmetry in sagging and hogging of a hull progressing in regular waves is investigated by applying a weakly nonlinear potential flow theory. At first instance ship motions in waves are evaluated using a linear strip-theory yielding transfer functions of ship motions and sectional loads. Then, by assuming time-histories of ship motions the nonlinear part of the Froude-Krylov and restoring forces and moments are evaluated using a panel representation. Linear and weakly nonlinear predictions are compared against available model tests for a roll-on/off (Ro-Pax) ship hull. The results confirm that importance of nonlinearities of restoring and Froude-Krylov part of wave loading on asymmetry of sagging and hogging.
IOP Conference Series: Materials Science and Engineering
In recent years, Computational Fluid Dynamics (CFD) is increasingly becoming more attractive for ... more In recent years, Computational Fluid Dynamics (CFD) is increasingly becoming more attractive for the analysis of ship seakeeping. This is because of the increasing efficiency of computers and the accuracy of solvers (e.g. Reynold Navier Stokes Averaged – RANS) that may be more accurate in terms of idealizing nonlinear phenomena in comparison to potential flow methods. Notwithstanding this, RANS methods remain sensitive to accurate wave modelling across the fluid domain as well as the reflection of domain boundaries. This paper studies the effective absorption of the reflected waves from a structure heading back towards the inlet boundary with a relaxation zone method. This is achieved by applying the RANS CFD solver OpenFOAM-v2206 and wave generation toolbox waves2Foam. The modelled case is a 2D box in waves with different wave lengths. The distance of the relaxation zone and the distance after the relaxation zone until the box varies and their effect to excitation forces is studied...
Large floating offshore structures encounter wave induced motions and loads in real service condi... more Large floating offshore structures encounter wave induced motions and loads in real service conditions. This paper evaluates these motions and loads. Model tests and numerical calculations are performed to determine the hydrodynamic characteristics of two floating offshore structures. Theoretical and experimental results are compared to check the validity of the computer program.
When navigating in shallow or harbour water vessel may hit an underwater obstacle (rock, underwat... more When navigating in shallow or harbour water vessel may hit an underwater obstacle (rock, underwater structure etc.). As a consequence its hull may be damaged, a kind of penetration of the obstacle into initially undamaged hull surface occurs. This penetration produces certain force that, depending on its magnitude, changes vessel position and motion. Actually process of penetration and force formation are considered as a simple geometrical intrusion of a point into undisturbed ship hull. Model testing provides constitutive relation between penetration and resulting force.
Estimation of propeller-induced excitation forces is discussed and a comparison between computed ... more Estimation of propeller-induced excitation forces is discussed and a comparison between computed and measured propeller-induced pressure distributions for an 8000/12000 dwt ro/ro vessel are shown. Diagrams for axial wake of model and full-scale ship are also compared. Vibration calculations are described, and modelling aspects, and the effect of the surrounding water are dealt with. The measurement of vibrations using a measuring system developed in the Finnish VTT Ship Laboratory is explained. An exciter test system is used. Prediction of the vibration level and trouble-shooting vibration measurements are also dealt with.
The majority of ship vibration problems are associated with so-called local vibrations. These loc... more The majority of ship vibration problems are associated with so-called local vibrations. These local problems are rather easy to cure, if a vibration test is done before the ship is completely fitted. A combination of theoretical and experimental approaches leads in practice to the best result in predicting the vibration level. This combination is also needed in the interpretation of measurements. For example, the exciter test in the construction stage must be conducted in shallow water. Thus calculations are needed to take into account the change in added mass and in other relevant parameters. Some practically important features of both calculations and experiments are discussed in this paper.
This textbook is a result of the work started in 1996 when I joined a very interesting, newly for... more This textbook is a result of the work started in 1996 when I joined a very interesting, newly formed Specialist Committee working on Ship Stability within the International Towing Tank Conference (ITTC). Thanks to this group of international enthusiastic scholars in the field, it became clear for me that both the research and the rules’ development in the field of ship stability will proceed in the direction of including ship dynamics into account. Moreover, this development will require sophisticated mathematical models of ship dynamics based on the first principles and taking realistically into account the environmental, often very hostile, conditions. These models should be verified and thoroughly validated. I am very grateful to Professor Eero-Matti Salonen for his valuable comments and corrections he has made to the original manuscript. I want to thank my colleagues Messrs Teemu Manderbacka and Otto Puolakka, the assistants in the course on Ship Dynamics, for their valuable rem...
This paper presents the results in modelling of ship-generated waves around a modem tanker using ... more This paper presents the results in modelling of ship-generated waves around a modem tanker using the FINFLO-SHIP RANS solver developed at Helsinki University of Technology. Simulation for three-dimensional turbulent free-surface flows is performed in a numerical water tank. A cell-centred finite-volume (FV) scheme is implemented for the solution of the RANS equations with the artificial compressibility and the nonlinear free-surface boundary conditions. The convergence performance is improved with the multigrid ...
Uploads
Papers