Experimental and Numerical Studies on Ship Motion Responses Coupled with Sloshing in Waves

2009 ◽  
Vol 53 (02) ◽  
pp. 68-82 ◽  
Author(s):  
Bo-Woo Nam ◽  
Yonghwan Kim ◽  
Dae-Woong Kim ◽  
Yong-Soo Kim
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Impulse Response Function ◽  
Ship Motion ◽  
Computational Results ◽  
Floating Bodies ◽  
Motion Responses ◽  
Significant Difference ◽  
Response Amplitude Operators ◽  
Liquid Natural Gas

This study considers the motion responses of floating bodies in waves coupled with sloshing-induced internal forces and their effects on sloshing-induced impact loads. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite difference method. The considered models are a liquid natural gas floating production, storage, and offloading unit (LNG FPSO) with two partially filled tanks and a modified S175 hull with an antirolling tank. In the case of the LNG FPSO model, both numerical and experimental studies are carried out. Three degree-of-freedom motion responses are allowed in the presence of regular waves, and the measured response amplitude operators (RAOs) are compared with computational results. For the modified S175 hull, the computational results are compared with other existing computational results. It is observed that the present method provides a fair agreement with experimental and other numerical results, showing significant coupling effects on both motion responses and sloshing flows. The numerical study extends to the observation of pressure field inside the tanks, and a significant difference in internal pressure is also shown.

Numerical Study on Ship Motion Fully Coupled with LNG Tank Sloshing in CFD Method

2019 ◽  
Vol 16 (06) ◽  
pp. 1840022 ◽  
Author(s):  
Yuan Zhuang ◽  
Decheng Wan
Keyword(s):  
Incident Wave ◽  
Numerical Study ◽  
Three Dimensional ◽  
Ship Motion ◽  
Wave Flow ◽  
Motion Responses ◽  
Lng Tank ◽  
Cfd Method ◽  
Tank Sloshing ◽  
Fully Coupled

In this paper, numerical simulations of ship motion coupled with LNG tank sloshing in waves are considered. The fully coupled problems are performed by our in-house RANS/DES solver, naoe-FOAM-SJTU. The internal tank sloshing and external wave flow are solved simultaneously. The considered model is a three-dimensional simplified LNG FPSO with two prismatic tanks. The ship motion responses are carried out in beam waves to compare with existing experimental data to validate this solver. The coupling effects between ship motion and sloshing tanks are observed. The anti-rolling characteristics are found, and this kind of characteristic is obvious in low-filling conditions. Different incident wave amplitudes and frequencies are considered. When the incident wave frequency is close to ship motion natural frequency, the ship motion response is strong and an overturning behavior in sloshing tanks is observed. Meanwhile, impact pressures on bulkhead are also discussed. The pressure signal explains the phenomenon in tanks we discussed before.

Analysis of Sea Shock Encountered by a Ship in North East Japan

2014 ◽  
Author(s):  
Shigeaki Shiotani ◽  
Kenji Sasa
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Ship Motion ◽  
High Frequency Oscillation ◽  
Floating Bodies ◽  
Sea Floor ◽  
North East ◽  
Earthquake Motion ◽  
Vertical Ground Motion ◽  
Vertical Ground

In general, earthquake motion experienced by a navigable vessel is called a sea shock (or seaquake). Sea shock is assumed that the vertical ground motion of the sea floor propagates as a compressional (longitudinal) wave in water. Seaquakes are sudden, unexpected phenomena that are induced by undersea earthquakes. There are almost no examples of their systematic measurement and the phenomenon of seaquakes is said to not be thoroughly understood. The effect of seaquakes was studied theoretically during the 1990s, during research on the wave response of structures for the construction of VLFS. However, There are a few experimental studies on the effect of seaquakes on floating bodies because of the problem of reproducibility. We measured ship motion caused by sea shocks by examining seabed oscillation. Such measurements provided very valuable data. The conclusions obtained in the present study are that ship motion caused by sea shocks has high-frequency oscillation. In particular, the acceleration in the z direction is remarkable.

scholarly journals Time-Domain Simulation of Multibody Floating Systems Based on State-Space Modeling Technology

2011 ◽  
Author(s):  
Xiaochuan Yu ◽  
Jeffrey M. Falzarano
Keyword(s):  
State Space ◽  
Time Domain ◽  
Numerical Study ◽  
Equations Of Motion ◽  
Impulse Response Function ◽  
Linear Quadratic Regulator ◽  
Linear Quadratic ◽  
Motion Responses ◽  
Space Modeling ◽  
Floating System

It is important to study MULTIBODY dynamics when analyzing the transfer of cargo between ships and platforms at sea. The hydrodynamic interactions between multiple bodies in close proximity are expected to be significant and complex. In this paper, two levels of approximation of hydrodynamic coefficients are considered, i.e., the constant coefficient method (CCM) and the impulse response function (IRF). The equations of motion are written in standard state-space format, in which the convolution terms are computed using the trapezoidal rule. Initially, this newly proposed numerical scheme is successfully applied to calculate motion responses of a two-body floating system. The time-domain responses of this multibody floating system in both regular waves and random sea are further verified numerically. In addition, an ideal case of the motion mitigation of this system using Dynamic Positioning (DP) system is also given and discussed. The mean drift force is considered using Newman’s approximation. Numerical study shows that the optimal Linear Quadratic Regulator (LQR) method can help to mitigate the motion responses of this two-body floating system at sea. Finally, this scheme is extended to a three-body floating system, with the relative motions in random seas determined.

scholarly journals Vortex Shedding From Hulls in Close Proximity With Relative Motion

2018 ◽  
Author(s):  
Ian A. Milne ◽  
J. Michael R. Graham
Keyword(s):  
Vortex Shedding ◽  
Significant Contribution ◽  
Pressure Field ◽  
Computational Results ◽  
Floating Bodies ◽  
Damping Coefficients ◽  
Close Proximity ◽  
Forced Roll ◽  
Offshore Industry ◽  
Liquid Natural Gas

The safe and efficient offloading of liquid natural gas (LNG) in a side-by-side configuration has emphasised the need to accurately quantify the hydrodynamic responses of floating bodies when located in very close proximity. A new series of computational results are presented for the forced roll of a hull in the presence of a second body representative of a floating FLNG facility. The vortex shedding phenomenon which provides a significant contribution to the damping of an isolated hull, is demonstrated to be modified by the presence of the second body. The total damping coefficients were found to be significantly reduced by approximately 50 percent for the very small gap widths considered. It is shown that in addition to the modification of the local shedding dynamics, the variation in the pressure field owing to the presence of the second body also contributes significantly to the reduction in the damping. The findings will be of particular interest to the offshore industry for improving and optimising offloading practices.

Improvement Of Curvilinear Diagrams Of Concrete Deformation

2019 ◽  
pp. 99-104
Keyword(s):  
Reinforced Concrete ◽  
Peak Load ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Deformation Model ◽  
Reinforced Concrete Structures ◽  
Significant Difference ◽  
Deformation Diagrams

Problems when calculating reinforced concrete structures based on the concrete deformation under compression diagram, which is presented both in Russian and foreign regulatory documents on the design of concrete and reinforced concrete structures are considered. The correctness of their compliance for all classes of concrete remains very approximate, especially a significant difference occurs when using Euronorm due to the different shape and sizes of the samples. At present, there are no methodical recommendations for determining the ultimate relative deformations of concrete under axial compression and the construction of curvilinear deformation diagrams, which leads to limited experimental data and, as a result, does not make it possible to enter more detailed ultimate strain values into domestic standards. The results of experimental studies to determine the ultimate relative deformations of concrete under compression for different classes of concrete, which allowed to make analytical dependences for the evaluation of the ultimate relative deformations and description of curvilinear deformation diagrams, are presented. The article discusses various options for using the deformation model to assess the stress-strain state of the structure, it is concluded that it is necessary to use not only the finite values of the ultimate deformations, but also their intermediate values. This requires reliable diagrams "s–e” for all classes of concrete. The difficulties of measuring deformations in concrete subjected to peak load, corresponding to the prismatic strength, as well as main cracks that appeared under conditions of long-term step loading are highlighted. Variants of more accurate measurements are proposed. Development and implementation of the new standard GOST "Concretes. Methods for determination of complete diagrams" on the basis of the developed method for obtaining complete diagrams of concrete deformation under compression for the evaluation of ultimate deformability of concrete under compression are necessary.

A Relativistic Newtonian Mechanics Predicts with Precision the Results of Recent Neutrino-Velocity Experiments

2014 ◽  
Vol 6 (1) ◽  
pp. 1032-1035 ◽  
Author(s):  
Ramzi Suleiman
Keyword(s):  
Null Hypothesis ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Newtonian Mechanics ◽  
Speed Of Light ◽  
Symmetry Principle ◽  
Proposed Model ◽  
Significant Difference ◽  
The One ◽  
Complete Collapse

The research on quasi-luminal neutrinos has sparked several experimental studies for testing the "speed of light limit" hypothesis. Until today, the overall evidence favors the "null" hypothesis, stating that there is no significant difference between the observed velocities of light and neutrinos. Despite numerous theoretical models proposed to explain the neutrinos behavior, no attempt has been undertaken to predict the experimentally produced results. This paper presents a simple novel extension of Newton's mechanics to the domain of relativistic velocities. For a typical neutrino-velocity experiment, the proposed model is utilized to derive a general expression for . Comparison of the model's prediction with results of six neutrino-velocity experiments, conducted by five collaborations, reveals that the model predicts all the reported results with striking accuracy. Because in the proposed model, the direction of the neutrino flight matters, the model's impressive success in accounting for all the tested data, indicates a complete collapse of the Lorentz symmetry principle in situation involving quasi-luminal particles, moving in two opposite directions. This conclusion is support by previous findings, showing that an identical Sagnac effect to the one documented for radial motion, occurs also in linear motion.

scholarly journals Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

2021 ◽  
Author(s):  
Alexander Vakhrushev ◽  
Abdellah Kharicha ◽  
Ebrahim Karimi-Sibaki ◽  
Menghuai Wu ◽  
Andreas Ludwig ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lorentz Force ◽  
Applied Magnetic Field ◽  
Numerical Study ◽  
Flow Direction ◽  
Experimental Studies ◽  
Submerged Entry Nozzle ◽  
Mean Flow ◽  
Slab Caster ◽  
The Mean

AbstractA numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

A numerical study of vortex interaction

1984 ◽  
Vol 146 ◽  
pp. 331-345 ◽  
Author(s):  
I. G. Bromilow ◽  
R. R. Clements
Keyword(s):  
Flow Visualization ◽  
Numerical Study ◽  
Experimental Studies ◽  
Shear Layers ◽  
Controlled Study ◽  
Vortex Interaction ◽  
Flow Conditions ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Discrete Vortex Model

Flow visualization has shown that the interaction of line vortices is a combination of tearing, elongation and rotation, the extent of each depending upon the flow conditions. A discrete-vortex model is used to study the interaction of two and three growing line vortices of different strengths and to assess the suitability of the method for such simulation.Many of the features observed in experimental studies of shear layers are reproduced. The controlled study shows the importance and rapidity of the tearing process under certain conditions.

Vortex-Induced Vibrations of a Cylinder at Subcritical Reynolds Number

2011 ◽  
Author(s):  
Yoann Jus ◽  
Elisabeth Longatte ◽  
Jean-Camille Chassaing ◽  
Pierre Sagaut
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Damping Ratio ◽  
Experimental Studies ◽  
Cross Flow ◽  
Physical Analysis ◽  
Arbitrary Lagrangian Eulerian ◽  
Vortex Induced Vibrations ◽  
Low Mass

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.

Numerical study of sheared mobile polydisperse sediment beds with a coupled lattice Boltzmann - discrete element method

2021 ◽  
Author(s):  
Christoph Rettinger ◽  
Sebastian Eibl ◽  
Ulrich Rüde ◽  
Bernhard Vowinckel
Keyword(s):  
Discrete Element Method ◽  
Lattice Boltzmann ◽  
Numerical Study ◽  
Experimental Studies ◽  
Discrete Element ◽  
Parallel Execution ◽  
Coupling Mechanism ◽  
Size Segregation ◽  
Minimum Diameter ◽  
Element Method

<p>With the increasing computational power of today's supercomputers, geometrically fully resolved simulations of particle-laden flows are becoming a viable alternative to laboratory experiments. Such simulations enable detailed investigations of transport phenomena in various multiphysics scenarios, such as the coupled interaction of sediment beds with a shearing fluid flow. There, the majority of available simulations as well as experimental studies focuses on setups of monodisperse particles. In reality, however, polydisperse configurations are much more common and feature unique effects like vertical size segregation.</p><p>In this talk, we will present numerical studies of mobile polydisperse sediment beds in a laminar shear flow, with a ratio of maximum to minimum diameter up to 10. The lattice Boltzmann method is applied to represent the fluid dynamics through and above the sediment bed efficiently. We model particle interactions by a discrete element method and explicitly account for lubrication forces. The fluid-particle coupling mechanism is based on the geometrically fully resolved momentum transfer between the fluid and the particulate phase. We will highlight algorithmic aspects and communication schemes essential for massively parallel execution.</p><p>Utilizing these capabilities allows us to achieve large-scale simulations with more than 26.000 densely-packed polydisperse particles interacting with the fluid. With this, we are able to reproduce effects like size segregation and to study the rheological behavior of such systems in great detail. We will evaluate and discuss the influence of polydispersity on these processes. These insights will be used to improve and extend existing macroscopic models.</p>

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