The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous f... more The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous foundation is not trivial. We apply a recently proposed iterative nonlinear procedure to the analysis. Mathematical models of the elastic foundation are incorporated into the governing nonlinear fourth-order differential equation of the system and then, the differential equation is transformed into an equivalent nonlinear integral equation using Green's functions. Numerical solutions of the integral equation clearly demonstrate herein that our nonlinear iterative numerical method is simple and 2 straightforward for approximate solutions of the static deflection of an infinite beam on a nonlinear elastic foundation. Iterative numerical solutions converge fast to corresponding analytic solutions. However, numerical errors are observed in a narrow neighborhood of material discontinuities of foundations.
WIT transactions on modelling and simulation, Aug 27, 2009
This paper presents recent accomplishments of the development of the Boundary Element Method (BEM... more This paper presents recent accomplishments of the development of the Boundary Element Method (BEM) for nonlinear waves around offshore structures and resulting wave forces. In order to investigate the capability of the present method, the nonlinear diffraction problem of a truncated circular cylinder is simulated. It is found that the present method is fairly accurate for wave forces and run-ups when compared with experimental results and also with other numerical results.
Journal of Ocean Engineering and Technology, Aug 31, 2019
The magnitude of the roll motion of a floating structure depends on the roll damping acting on th... more The magnitude of the roll motion of a floating structure depends on the roll damping acting on the body. In other words, the roll damping of a floating structure must be accurately obtained in order to precisely evaluate the roll motion. Various methods are used to evaluate the roll damping of a floating structure, such as the linear potential theory, computational fluid dynamics (CFD), and model tests. However, it is difficult to evaluate the roll motion of a floating structure with appendages such as a bilge keel and riser slot due to the limitation of ignoring the viscous effects in the linear potential theory. Among these methods, a model test based on a free decay test and harmonic excited roll motion (HERM) is known to be the most reliable method to estimate the roll damping of the floating structures. In this study, model tests using free decay and HERM techniques were performed in the Ocean Engineering Basin (OEB) of KRISO with various types of midship sections. The roll damping results were estimated based on post-processing methods using both techniques, and the roll damping results were compared.
Journal of Ocean Engineering and Technology, Oct 31, 2014
In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water... more In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with 3 × 4 complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effective line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.
Journal of the Computational Structural Engineering Institute of Korea
A Leg Mating Unit (LMU) is a device utilized during the float-over installation of offshore struc... more A Leg Mating Unit (LMU) is a device utilized during the float-over installation of offshore structures that include hyperelastic pads and mating part. The hyperelastic pads absorb the loads, whereas the mating part works as guidance between topside and supporting structures during the mating sequence of float-over installation. In this study, the design optimization of an LMU for the float-over installation of floating-type offshore structures is conducted to enhance the performance and to satisfy the requirements defined by classification society regulations. The initial dimensions of the LMU are referred to the dimensions of those used in fixed-type float-over installation because only the location and the number of LMUs are known. The two-parameter Mooney-Rivlin model is adopted to describe the hyperelastic pads under given material parameters. Geometric variables, such as the thickness, height, and width of members, as well as configuration variables, such as the angle and number of members, are defined as design variables and are parameterized. A sampling-based design sensitivity analysis based on latin hypercube sampling method is performed to filter the important design variables. The design optimization problem is formulated to minimize the total mass of the LMU under maximum von Mises stress and reaction force constraints.
International Journal of Offshore and Polar Engineering, 2020
The floating LNG bunkering terminal (FLBT) is a newly emerging offshore platform that can be rega... more The floating LNG bunkering terminal (FLBT) is a newly emerging offshore platform that can be regarded as a liquefied natural gas (LNG) station at sea. It has its own station-keeping system, and it is additionally moored to other vessels during LNG loading or unloading processes. The ship-to-ship mooring system is composed of a number of mooring ropes and fenders. The relative motion responses between loading arms and corresponding manifolds are crucial for the LNG transfer process, because they have their specified allowable displacement criteria. To investigate the multibody interactions, model tests were performed previously. Some hydrodynamic coefficients obtained from the model test were utilized in numerical simulations. The eigenvalue analysis on multibodies with the ship-to-ship mooring system was also conducted. The natural modes and periods induced by the mooring ropes and fenders were identified. A series of numerical simulations with various incident wave headings and configurations were conducted with the commercial program AQWA. Finally, we judged the operable incident wave heading range under allowable displacement criteria.
The motions and drift forces of side-by-side (SbS) moored FSRU and LNGC including sloshing effect... more The motions and drift forces of side-by-side (SbS) moored FSRU and LNGC including sloshing effect are studied by experiments. FSRU and LNGC have LNG cargo tanks and sloshing of LNG can affect the motions and drift forces of structures due to the coupling between sloshing and floating body motion. The effect of coupling can vary by filling level of LNG and the effect of filling level is investigated. The coupling effect is most strong at low filling level in beam sea. The effect of gap flow and sloshing is also investigated in the present study as well. The horizontal motions and drift forces are analyzed and it is confirmed that the gap flow is affected by the sloshing. The sway motion, sway drift force and gap flow are influenced by the sloshing in head sea although the sloshing is weak.
In order to evaluate the feasibility of semi-submersible platform to operate in Mexican oil field... more In order to evaluate the feasibility of semi-submersible platform to operate in Mexican oil fields in Gulf of Mexico, the motions and mooring line tensions are analyzed by numerical calculations and model tests. The same semi-submersible platform was considered to operate in two different sites under extreme environmental conditions. Model tests were conducted in ocean engineering basin to measure and analyze the dynamic behavior of semi-submersible in ultra-deepwater. Environmental conditions under consideration are individual cases of regular and irregular waves for hurricane conditions. This work shows selected results, from which we can make assessment for feasibility of the proposed design of the Semisubmersible with the given conditions.
The present work identifies the nonlinear restoring characteristics and excitation force of ship ... more The present work identifies the nonlinear restoring characteristics and excitation force of ship roll motion in regular beam waves. The steady-state roll response data measured from a numerical simulation is utilized for the experiments of the applied method. Using the approach proposed by Jang (2014), the J-function and its one of zero-crossing times play a crucial role in the identification. The J-function is defined to be the sum of inertia force and nonlinear damping. For the zero-crossing time to be measured, system responses of angular displacement, velocity and acceleration need to be known and so does the numerical interpolation. Numerical simulations using the ship models are conducted to show the workability and validity of the methodology. These numerical simulations show that Jang’s scheme is an effective and very simple method for the identification of the characteristics of ship roll motion and produces relatively reasonable solutions.
The motion of ocean-going ship with constant forward speed is considered in time domain. The doub... more The motion of ocean-going ship with constant forward speed is considered in time domain. The double-body linearization is adopted for ship motion calculations. The finite element method (FEM) based on variational principle is applied to solve the linearized boundary value problem. Time integration of free-surface boundary condition is carried out by 4 order Adams-Bashforth-Moultn method. In order to remove reflected waves at the truncated boundary, numerical damping zone is utilized. At every few steps, five-point Chebyshev filtering scheme is applied to smooth out unwanted saw-tooth waves. To include body nonlinear effect, nonlinear restoring and Froude-Kylov forces are additionaly calculated by considering incident wave elevation and relative ship position. For the validation of developed code, responses of three different ship models, wigley III, series60 and s175 container, are compared with existing experimental results or other computations. Nonlinear effects on motion RAO and...
Since 2012, the Baltic sea and some parts of American Sea have been set as Emission Control Areas... more Since 2012, the Baltic sea and some parts of American Sea have been set as Emission Control Areas(ECAs) by International Maritime Organization(IMO). ECAs are being spread rapidly as the result of tightening environmental regulations. Accordingly, the demand for LNG powered ships has been increased. As a result of this, discussions on LNG bunkering have been opened in Singapore, China and Europe. Korean government has recently initiated a research program for development of a Floating LNG Bunkering Terminal (FLBT). In this paper, a concept of a multiple docking aid system for FLBT operation is introduced. The proposed multiple docking aid system has ability to monitor a LNG Carrier(LNGC) and a LNG Bunkering Shuttle (LNGBS) simultaneously .
This paper presents a comparative study of FPSO model tests and numerical analyses that have been... more This paper presents a comparative study of FPSO model tests and numerical analyses that have been carried out for a joint project between KIOST and IMP. With a proposed design of FPSO for Mexican GoM (Gulf of Mexico), IMP and KIOST have been collaborating with each other. IMP proposes a FPSO which is aimed for environmental conditions of Mexican GoM. For evaluation of global performance of the FPSO, IMP carries out numerical analysis while KIOST does the model testing. The first part of the project is focused upon the hydrodynamic performance of the vessel motion and coupled analysis of mooring system with body motion. Environmental conditions under consideration are individual cases of wind, waves and current for both operational and extreme sea states (hurricane conditions). This work shows selected results, from which we can make assessment for feasibility of the proposed design of the FPSO with the given conditions.
The motions and mooring loads of turret moored FSRU (Floating Storage & Regasification Unit) and ... more The motions and mooring loads of turret moored FSRU (Floating Storage & Regasification Unit) and LNGC (Liquefied Natural Gas Carrier) including sloshing are studied by experiments. Turret moored FSRU weathervanes on a turret and side-by-side (SbS) LNGC moves and interacts with FSRU. FSRU and LNGC have LNG cargo tanks and sloshing affects the motions and loads due to the coupling between sloshing and floating body motions. The performance of FSRU and LNGC offloading system is investigated through the assessment of global motions, accelerations, mooring loads and Ship-To-Ship (STS) loads. It is noted that although the direction of head moves to bow quartering, the sloshing occurs in longitudinal mode and affect the surge motion and mooring load. STS mooring affects the sway and roll motion of LNGC and interacts with LNGC sloshing.
This paper is concerned with the determination of nonlinear roll damping moments of ships includi... more This paper is concerned with the determination of nonlinear roll damping moments of ships including similar floating structures. Using the measured motion response data of ship's roll motion, an inverse problem is formulated for the determination. The problem of damping determination is mathematically involved in a Volterra integral equation of the "first" kind between the roll responses and unknown nonlinear roll damping. This first kind integral equation results in numerical instability, that is, solutions lack stability property. A regularization method is applied in order to suppress the instability. Any priori information is not required on the model of the nonlinear damping. The applicability of the present study is demonstrated through the numerical investigations using the given nonlinear roll equations from the tests.
Journal of the Society of Naval Architects of Korea, 2013
This study is constructed to investigate the sloshing effect on the motions of a two-dimensional ... more This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different methods are relatively in good agreement with the experiments, and these two results are similar in most wave frequency range. However, the discrepancies are apparent where the fluid motion is not governed by a single mode. But both of numerical methods over-predict the motion at the vicinity of the sloshing natural frequency. In order to correct the discrepancy, the modal damping needs to be investigated more precisely. Furthermore, another multi-modal approach, such as the Boussinesq-type method, seems to be required in the region of the intermediate liquid.
The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous f... more The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous foundation is not trivial. We apply a recently proposed iterative nonlinear procedure to the analysis. Mathematical models of the elastic foundation are incorporated into the governing nonlinear fourth-order differential equation of the system and then, the differential equation is transformed into an equivalent nonlinear integral equation using Green's functions. Numerical solutions of the integral equation clearly demonstrate herein that our nonlinear iterative numerical method is simple and 2 straightforward for approximate solutions of the static deflection of an infinite beam on a nonlinear elastic foundation. Iterative numerical solutions converge fast to corresponding analytic solutions. However, numerical errors are observed in a narrow neighborhood of material discontinuities of foundations.
Journal of Advanced Research in Ocean Engineering, 2015
The present work was an attempt to investigate the applicability of truncated mooring systems to ... more The present work was an attempt to investigate the applicability of truncated mooring systems to KRISO's deep ocean engineering basin (DOEB) with ratios of 1:100, 1:60, and 1:50. The depth of the DOEB is 15 m. Therefore, the corresponding truncated depths for this study were equal to 1500 m, 900 m, and 750 m. The investigation focused on both the static and dynamic characteristics of the mooring system. It was shown, in a static pull-out test, that the restoring force of a FPSO vessel could be modified to a good level of agreement for all three truncation cases. However, when the radius of the mooring site was reduced according to the truncation factor, the surge motion response during a free-decay test showed a significant difference from the full-depth model. However, the reduction of this discrepancy was achieved by increasing the radius up to its maximum possible value while considering the size of the DOEB. Especially, in terms of the time period, the difference was reduced from 24.0 to 5.3 s for a truncation ratio of 1:100, 54.1 to 8.6 s for a truncation ratio of 1:60, and 31.7 to 3.9 s for a truncation ratio of 1:50. As a result, the study verified the applicability of the truncated mooring system to the DOEB, and therefore it could represent the full-depth mooring system relatively well in terms of the static and dynamic conditions.
This paper compares simplified and finite element method (FEM) models for tower and blade in dyna... more This paper compares simplified and finite element method (FEM) models for tower and blade in dynamic coupled analysis of floating wind turbine. A SPAR type wind turbine with catenary mooring lines is considered in numerical analysis. Floating body equation is derived using boundary element method (BEM) and convolution. Equations for mooring line, tower and blade are formulated with theories of catenary, elastic beam and aerodynamic rotating beam, respectively and FEM is applied in the formulation. By combining the equations, coupled solutions are calculated. Tower or blade may be assumed rigid or lumped body for simplicity in modeling. By comparing floating body motions, mooring line tensions and tower stresses with the simple model and original FEM model, the effect of including or neglecting elastic, rotating and aerodynamic behavior of tower and blade is discussed.
In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water... more In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with 3 × 4 complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effective line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.
This paper presents numerical simulations of a diffracted wave around a bottom-mounted circular c... more This paper presents numerical simulations of a diffracted wave around a bottom-mounted circular cylinder using the volume-of-fluid (VOF) method. Unsteady incompressible Navier-Stokes equations are solved based on the finite volume method (FVM) with a collocated variable arrangement. The SIMPLE-type correction algorithm with the momentum interpolation method is applied to solve Poisson equations. Among the many variations of the VOF method is the CICSAM (Compressive Interface Capturing Scheme for Arbitrary Meshes) scheme. To verify the availability in 2-phase flow simulations of the developed numerical code, dam-breaking and sloshing problems are investigated. The simulation results show good agreement with existing experiments in both flow pattern and global force. Before the numerical simulation of 3D diffraction problems, the wave is tested in a numerical wave tank. In this study, we introduce a buffer zone for efficient wave-making and damping; in the buffer zone, the near-field solution is gradually changed to the known incident wave at the far field. Second-order Stokes waves are well simulated in this wave tank. Finally, a diffracted wave by vertical circular cylinders is numerically simulated. The wave-induced forces and run-ups around the cylinder are compared with potential flow solutions based on the finite element method (FEM). Agreement between the 2 numerical solutions is fairly good.
The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous f... more The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous foundation is not trivial. We apply a recently proposed iterative nonlinear procedure to the analysis. Mathematical models of the elastic foundation are incorporated into the governing nonlinear fourth-order differential equation of the system and then, the differential equation is transformed into an equivalent nonlinear integral equation using Green's functions. Numerical solutions of the integral equation clearly demonstrate herein that our nonlinear iterative numerical method is simple and 2 straightforward for approximate solutions of the static deflection of an infinite beam on a nonlinear elastic foundation. Iterative numerical solutions converge fast to corresponding analytic solutions. However, numerical errors are observed in a narrow neighborhood of material discontinuities of foundations.
WIT transactions on modelling and simulation, Aug 27, 2009
This paper presents recent accomplishments of the development of the Boundary Element Method (BEM... more This paper presents recent accomplishments of the development of the Boundary Element Method (BEM) for nonlinear waves around offshore structures and resulting wave forces. In order to investigate the capability of the present method, the nonlinear diffraction problem of a truncated circular cylinder is simulated. It is found that the present method is fairly accurate for wave forces and run-ups when compared with experimental results and also with other numerical results.
Journal of Ocean Engineering and Technology, Aug 31, 2019
The magnitude of the roll motion of a floating structure depends on the roll damping acting on th... more The magnitude of the roll motion of a floating structure depends on the roll damping acting on the body. In other words, the roll damping of a floating structure must be accurately obtained in order to precisely evaluate the roll motion. Various methods are used to evaluate the roll damping of a floating structure, such as the linear potential theory, computational fluid dynamics (CFD), and model tests. However, it is difficult to evaluate the roll motion of a floating structure with appendages such as a bilge keel and riser slot due to the limitation of ignoring the viscous effects in the linear potential theory. Among these methods, a model test based on a free decay test and harmonic excited roll motion (HERM) is known to be the most reliable method to estimate the roll damping of the floating structures. In this study, model tests using free decay and HERM techniques were performed in the Ocean Engineering Basin (OEB) of KRISO with various types of midship sections. The roll damping results were estimated based on post-processing methods using both techniques, and the roll damping results were compared.
Journal of Ocean Engineering and Technology, Oct 31, 2014
In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water... more In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with 3 × 4 complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effective line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.
Journal of the Computational Structural Engineering Institute of Korea
A Leg Mating Unit (LMU) is a device utilized during the float-over installation of offshore struc... more A Leg Mating Unit (LMU) is a device utilized during the float-over installation of offshore structures that include hyperelastic pads and mating part. The hyperelastic pads absorb the loads, whereas the mating part works as guidance between topside and supporting structures during the mating sequence of float-over installation. In this study, the design optimization of an LMU for the float-over installation of floating-type offshore structures is conducted to enhance the performance and to satisfy the requirements defined by classification society regulations. The initial dimensions of the LMU are referred to the dimensions of those used in fixed-type float-over installation because only the location and the number of LMUs are known. The two-parameter Mooney-Rivlin model is adopted to describe the hyperelastic pads under given material parameters. Geometric variables, such as the thickness, height, and width of members, as well as configuration variables, such as the angle and number of members, are defined as design variables and are parameterized. A sampling-based design sensitivity analysis based on latin hypercube sampling method is performed to filter the important design variables. The design optimization problem is formulated to minimize the total mass of the LMU under maximum von Mises stress and reaction force constraints.
International Journal of Offshore and Polar Engineering, 2020
The floating LNG bunkering terminal (FLBT) is a newly emerging offshore platform that can be rega... more The floating LNG bunkering terminal (FLBT) is a newly emerging offshore platform that can be regarded as a liquefied natural gas (LNG) station at sea. It has its own station-keeping system, and it is additionally moored to other vessels during LNG loading or unloading processes. The ship-to-ship mooring system is composed of a number of mooring ropes and fenders. The relative motion responses between loading arms and corresponding manifolds are crucial for the LNG transfer process, because they have their specified allowable displacement criteria. To investigate the multibody interactions, model tests were performed previously. Some hydrodynamic coefficients obtained from the model test were utilized in numerical simulations. The eigenvalue analysis on multibodies with the ship-to-ship mooring system was also conducted. The natural modes and periods induced by the mooring ropes and fenders were identified. A series of numerical simulations with various incident wave headings and configurations were conducted with the commercial program AQWA. Finally, we judged the operable incident wave heading range under allowable displacement criteria.
The motions and drift forces of side-by-side (SbS) moored FSRU and LNGC including sloshing effect... more The motions and drift forces of side-by-side (SbS) moored FSRU and LNGC including sloshing effect are studied by experiments. FSRU and LNGC have LNG cargo tanks and sloshing of LNG can affect the motions and drift forces of structures due to the coupling between sloshing and floating body motion. The effect of coupling can vary by filling level of LNG and the effect of filling level is investigated. The coupling effect is most strong at low filling level in beam sea. The effect of gap flow and sloshing is also investigated in the present study as well. The horizontal motions and drift forces are analyzed and it is confirmed that the gap flow is affected by the sloshing. The sway motion, sway drift force and gap flow are influenced by the sloshing in head sea although the sloshing is weak.
In order to evaluate the feasibility of semi-submersible platform to operate in Mexican oil field... more In order to evaluate the feasibility of semi-submersible platform to operate in Mexican oil fields in Gulf of Mexico, the motions and mooring line tensions are analyzed by numerical calculations and model tests. The same semi-submersible platform was considered to operate in two different sites under extreme environmental conditions. Model tests were conducted in ocean engineering basin to measure and analyze the dynamic behavior of semi-submersible in ultra-deepwater. Environmental conditions under consideration are individual cases of regular and irregular waves for hurricane conditions. This work shows selected results, from which we can make assessment for feasibility of the proposed design of the Semisubmersible with the given conditions.
The present work identifies the nonlinear restoring characteristics and excitation force of ship ... more The present work identifies the nonlinear restoring characteristics and excitation force of ship roll motion in regular beam waves. The steady-state roll response data measured from a numerical simulation is utilized for the experiments of the applied method. Using the approach proposed by Jang (2014), the J-function and its one of zero-crossing times play a crucial role in the identification. The J-function is defined to be the sum of inertia force and nonlinear damping. For the zero-crossing time to be measured, system responses of angular displacement, velocity and acceleration need to be known and so does the numerical interpolation. Numerical simulations using the ship models are conducted to show the workability and validity of the methodology. These numerical simulations show that Jang’s scheme is an effective and very simple method for the identification of the characteristics of ship roll motion and produces relatively reasonable solutions.
The motion of ocean-going ship with constant forward speed is considered in time domain. The doub... more The motion of ocean-going ship with constant forward speed is considered in time domain. The double-body linearization is adopted for ship motion calculations. The finite element method (FEM) based on variational principle is applied to solve the linearized boundary value problem. Time integration of free-surface boundary condition is carried out by 4 order Adams-Bashforth-Moultn method. In order to remove reflected waves at the truncated boundary, numerical damping zone is utilized. At every few steps, five-point Chebyshev filtering scheme is applied to smooth out unwanted saw-tooth waves. To include body nonlinear effect, nonlinear restoring and Froude-Kylov forces are additionaly calculated by considering incident wave elevation and relative ship position. For the validation of developed code, responses of three different ship models, wigley III, series60 and s175 container, are compared with existing experimental results or other computations. Nonlinear effects on motion RAO and...
Since 2012, the Baltic sea and some parts of American Sea have been set as Emission Control Areas... more Since 2012, the Baltic sea and some parts of American Sea have been set as Emission Control Areas(ECAs) by International Maritime Organization(IMO). ECAs are being spread rapidly as the result of tightening environmental regulations. Accordingly, the demand for LNG powered ships has been increased. As a result of this, discussions on LNG bunkering have been opened in Singapore, China and Europe. Korean government has recently initiated a research program for development of a Floating LNG Bunkering Terminal (FLBT). In this paper, a concept of a multiple docking aid system for FLBT operation is introduced. The proposed multiple docking aid system has ability to monitor a LNG Carrier(LNGC) and a LNG Bunkering Shuttle (LNGBS) simultaneously .
This paper presents a comparative study of FPSO model tests and numerical analyses that have been... more This paper presents a comparative study of FPSO model tests and numerical analyses that have been carried out for a joint project between KIOST and IMP. With a proposed design of FPSO for Mexican GoM (Gulf of Mexico), IMP and KIOST have been collaborating with each other. IMP proposes a FPSO which is aimed for environmental conditions of Mexican GoM. For evaluation of global performance of the FPSO, IMP carries out numerical analysis while KIOST does the model testing. The first part of the project is focused upon the hydrodynamic performance of the vessel motion and coupled analysis of mooring system with body motion. Environmental conditions under consideration are individual cases of wind, waves and current for both operational and extreme sea states (hurricane conditions). This work shows selected results, from which we can make assessment for feasibility of the proposed design of the FPSO with the given conditions.
The motions and mooring loads of turret moored FSRU (Floating Storage & Regasification Unit) and ... more The motions and mooring loads of turret moored FSRU (Floating Storage & Regasification Unit) and LNGC (Liquefied Natural Gas Carrier) including sloshing are studied by experiments. Turret moored FSRU weathervanes on a turret and side-by-side (SbS) LNGC moves and interacts with FSRU. FSRU and LNGC have LNG cargo tanks and sloshing affects the motions and loads due to the coupling between sloshing and floating body motions. The performance of FSRU and LNGC offloading system is investigated through the assessment of global motions, accelerations, mooring loads and Ship-To-Ship (STS) loads. It is noted that although the direction of head moves to bow quartering, the sloshing occurs in longitudinal mode and affect the surge motion and mooring load. STS mooring affects the sway and roll motion of LNGC and interacts with LNGC sloshing.
This paper is concerned with the determination of nonlinear roll damping moments of ships includi... more This paper is concerned with the determination of nonlinear roll damping moments of ships including similar floating structures. Using the measured motion response data of ship's roll motion, an inverse problem is formulated for the determination. The problem of damping determination is mathematically involved in a Volterra integral equation of the "first" kind between the roll responses and unknown nonlinear roll damping. This first kind integral equation results in numerical instability, that is, solutions lack stability property. A regularization method is applied in order to suppress the instability. Any priori information is not required on the model of the nonlinear damping. The applicability of the present study is demonstrated through the numerical investigations using the given nonlinear roll equations from the tests.
Journal of the Society of Naval Architects of Korea, 2013
This study is constructed to investigate the sloshing effect on the motions of a two-dimensional ... more This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different methods are relatively in good agreement with the experiments, and these two results are similar in most wave frequency range. However, the discrepancies are apparent where the fluid motion is not governed by a single mode. But both of numerical methods over-predict the motion at the vicinity of the sloshing natural frequency. In order to correct the discrepancy, the modal damping needs to be investigated more precisely. Furthermore, another multi-modal approach, such as the Boussinesq-type method, seems to be required in the region of the intermediate liquid.
The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous f... more The analysis of static deflections of an infinite beam resting on a nonlinear and discontinuous foundation is not trivial. We apply a recently proposed iterative nonlinear procedure to the analysis. Mathematical models of the elastic foundation are incorporated into the governing nonlinear fourth-order differential equation of the system and then, the differential equation is transformed into an equivalent nonlinear integral equation using Green's functions. Numerical solutions of the integral equation clearly demonstrate herein that our nonlinear iterative numerical method is simple and 2 straightforward for approximate solutions of the static deflection of an infinite beam on a nonlinear elastic foundation. Iterative numerical solutions converge fast to corresponding analytic solutions. However, numerical errors are observed in a narrow neighborhood of material discontinuities of foundations.
Journal of Advanced Research in Ocean Engineering, 2015
The present work was an attempt to investigate the applicability of truncated mooring systems to ... more The present work was an attempt to investigate the applicability of truncated mooring systems to KRISO's deep ocean engineering basin (DOEB) with ratios of 1:100, 1:60, and 1:50. The depth of the DOEB is 15 m. Therefore, the corresponding truncated depths for this study were equal to 1500 m, 900 m, and 750 m. The investigation focused on both the static and dynamic characteristics of the mooring system. It was shown, in a static pull-out test, that the restoring force of a FPSO vessel could be modified to a good level of agreement for all three truncation cases. However, when the radius of the mooring site was reduced according to the truncation factor, the surge motion response during a free-decay test showed a significant difference from the full-depth model. However, the reduction of this discrepancy was achieved by increasing the radius up to its maximum possible value while considering the size of the DOEB. Especially, in terms of the time period, the difference was reduced from 24.0 to 5.3 s for a truncation ratio of 1:100, 54.1 to 8.6 s for a truncation ratio of 1:60, and 31.7 to 3.9 s for a truncation ratio of 1:50. As a result, the study verified the applicability of the truncated mooring system to the DOEB, and therefore it could represent the full-depth mooring system relatively well in terms of the static and dynamic conditions.
This paper compares simplified and finite element method (FEM) models for tower and blade in dyna... more This paper compares simplified and finite element method (FEM) models for tower and blade in dynamic coupled analysis of floating wind turbine. A SPAR type wind turbine with catenary mooring lines is considered in numerical analysis. Floating body equation is derived using boundary element method (BEM) and convolution. Equations for mooring line, tower and blade are formulated with theories of catenary, elastic beam and aerodynamic rotating beam, respectively and FEM is applied in the formulation. By combining the equations, coupled solutions are calculated. Tower or blade may be assumed rigid or lumped body for simplicity in modeling. By comparing floating body motions, mooring line tensions and tower stresses with the simple model and original FEM model, the effect of including or neglecting elastic, rotating and aerodynamic behavior of tower and blade is discussed.
In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water... more In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with 3 × 4 complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effective line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.
This paper presents numerical simulations of a diffracted wave around a bottom-mounted circular c... more This paper presents numerical simulations of a diffracted wave around a bottom-mounted circular cylinder using the volume-of-fluid (VOF) method. Unsteady incompressible Navier-Stokes equations are solved based on the finite volume method (FVM) with a collocated variable arrangement. The SIMPLE-type correction algorithm with the momentum interpolation method is applied to solve Poisson equations. Among the many variations of the VOF method is the CICSAM (Compressive Interface Capturing Scheme for Arbitrary Meshes) scheme. To verify the availability in 2-phase flow simulations of the developed numerical code, dam-breaking and sloshing problems are investigated. The simulation results show good agreement with existing experiments in both flow pattern and global force. Before the numerical simulation of 3D diffraction problems, the wave is tested in a numerical wave tank. In this study, we introduce a buffer zone for efficient wave-making and damping; in the buffer zone, the near-field solution is gradually changed to the known incident wave at the far field. Second-order Stokes waves are well simulated in this wave tank. Finally, a diffracted wave by vertical circular cylinders is numerically simulated. The wave-induced forces and run-ups around the cylinder are compared with potential flow solutions based on the finite element method (FEM). Agreement between the 2 numerical solutions is fairly good.
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Papers by Hong Gun Sung