Effect of Wind Loads on the Performance of Free-Fall Lifeboats

2014 ◽  
Author(s):  
Thomas Sauder ◽  
Eloise Croonenborghs ◽  
Sebastien Fouques ◽  
Nabila Berchiche ◽  
Svein-Arne Reinholdtsen
Keyword(s):  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Free Fall ◽  
Offshore Structures ◽  
Water Entry ◽  
Forward Speed ◽  
Cfd Simulations ◽  
Six Degrees Of Freedom ◽  
Complete Set ◽  
Water Exit

The paper presents a model describing the launch of free-fall lifeboats from offshore structures in strong environmental wind. Six-degrees-of-freedom numerical simulations of the lifeboat launch are performed using the free-fall lifeboat simulator VARUNA with a complete set of wind coefficients for the lifeboat. Those wind coefficients are obtained by CFD simulations validated against wind tunnel tests. The lifeboat launch simulations are then verified against time-domain CFD simulations of the whole launch in air until water entry. It is shown by means of numerical simulations that wind-induced loads on the lifeboat have a strong influence on its kinematics until water entry, and subsequently on the acceleration loads experienced by the occupants, on the structural loads on the lifeboat, and on its forward speed after water exit. It is concluded that the effect of wind-induced loads on the lifeboat performances should in general be investigated when establishing the operational limits for a given offshore installation.

scholarly journals Prediction of Ship Unsteady Maneuvering in Calm Water by a Fully Nonlinear Ship Motion Model

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
Ray-Qing Lin ◽  
Tim Smith ◽  
Michael Hughes
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Ship Motion ◽  
Ship Motions ◽  
Motion Model ◽  
Forward Speed ◽  
Fully Nonlinear ◽  
Six Degrees Of Freedom ◽  
Calm Water

This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL). In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water. During the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge, sway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage, respectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions and their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering, a universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces and moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an Experimental Hull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL and experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder, which is included using a flow acceleration factor.

Influence of Wave-Induced Skid Motions on the Launch of Free-Fall Skid Lifeboats From Floating Hosts: Experimental and Numerical Investigations

2014 ◽  
Author(s):  
Neil Luxcey ◽  
Svein-Arne Reinholdtsen ◽  
Thomas Sauder ◽  
Sébastien Fouques ◽  
Jingzhe Jin ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Model Test ◽  
Degrees Of Freedom ◽  
Free Fall ◽  
Weather Conditions ◽  
Norwegian Sea ◽  
Six Degrees Of Freedom ◽  
Offshore Installations ◽  
Storm Condition ◽  
Wave Induced

The evacuation of personnel from offshore installations in severe weather conditions is generally ensured by free-fall lifeboats. Their performance can be assessed by means of numerical simulations to estimate accelerations loads on occupants, structural loads on the lifeboat hull, as well as forward speed after water-exit. These parameters strongly depend on the water entry conditions of the lifeboat, which in turn are very sensitive to the previous phases of the launch that starts on the skid. On floating production, storage and offloading (FPSO) vessels in the Norwegian Sea, lifeboats are often installed on skids at the bow so that waves may induce large skid motions with typical extreme vertical amplitude of fifteen to twenty meters in a 100-year storm condition. Moreover, wave-induced motions may also cause trim and list of the skid, which initiates more complex six degrees-of-freedom trajectories during free-fall. In such conditions, a proper modelling of the lifeboat trajectory on the moving skid is necessary in order to assess the performance of the lifeboat with numerical simulations. This paper investigates the effects of the wave-induced skid motion on the launch of free-fall lifeboats from floating hosts. The first part of the paper describes the six-degrees-of-freedom numerical skid model used in MARINTEK’s lifeboat launch simulator VARUNA. The second part presents two model test campaigns aimed at validating the numerical skid model. The model test results are compared to those obtained from the numerical simulations. Finally, the importance of the skid motion on the lifeboat trajectory is discussed.

Investigation of the flight behavior of a flare-stabilized projectile using 6DoF simulations coupled with CFD

2019 ◽  
Vol 30 (9) ◽  
pp. 4185-4201
Author(s):  
Daniel Klatt ◽  
Michael Proff ◽  
Robert Hruschka
Keyword(s):  
Degrees Of Freedom ◽  
Rigid Body Dynamics ◽  
Flight Behavior ◽  
Free Flight ◽  
Aerodynamic Coefficients ◽  
Cfd Simulations ◽  
Time Resolved ◽  
Content Type ◽  
Six Degrees Of Freedom ◽  
Computational Fluid Dynamics Cfd

Purpose The present work aims to investigate the capabilities of accurately predicting the six-degrees-of-freedom (6DoF) trajectory and the flight behavior of a flare-stabilized projectile using computational fluid dynamics (CFD) and rigid body dynamics (RBD) methods. Design/methodology/approach Two different approaches are compared for calculating the trajectory. First, the complete matrix of static and dynamic aerodynamic coefficients for the projectile is determined using static and dynamic CFD methods. This discrete database and the data extracted from free-flight experiments are used to simulate flight trajectories with an in-house developed 6DoF solver. Second, the trajectories are simulated solving the 6DoF motion equations directly coupled with time resolved CFD methods. Findings Virtual fly-out simulations using RBD/CFD coupled simulation methods well reproduce the motion behavior shown by the experimental free-flight data. However, using the discrete database of aerodynamic coefficients derived from CFD simulations shows a slightly different flight behavior. Originality/value A discrepancy between CFD 6DoF/RBD simulations and results obtained by the MATLAB 6DoF-solver based on discrete CFD data matrices is shown. It is assumed that not all dynamic effects on the aerodynamics of the projectile are captured by the determination of the force and moment coefficients with CFD simulations based on the classical aerodynamic coefficient decomposition.

Determination of Hydrodynamic Parameters for Remotely Operated Vehicles

2016 ◽  
Author(s):  
Ole A. Eidsvik ◽  
Ingrid Schjølberg
Keyword(s):  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Analytical Data ◽  
Relative Difference ◽  
Accurate Estimate ◽  
Six Degrees Of Freedom ◽  
Hydrodynamic Parameters ◽  
Planar Motion Mechanism ◽  
Rotational Degrees Of Freedom

In this paper the hydrodynamic parameters that characterize the behavior of a typical unmanned underwater vehicle are evaluated. A complete method for identifying these parameters is described. The method is developed to give a brief and accurate estimate of these parameters in all six degrees of freedom using basic properties of the vehicle such as dimensions, mass and shape. The method is based on both empirical and analytical results for typical reference geometries (ellipsoids, cubes, etc.). The method is developed to be applicable for a wide variety of UUV designs as these typically varies substantially. The method is then applied to a small observation class ROV. The results are first verified using an experimental method in which the full scale ROV is towed using a planar motion mechanism. An additional verification is performed with numerical simulations using Computational Fluid Dynamics and a radiation/diffraction program. The method shows promising results for both damping and added mass for the tested case. The translational degrees of freedom are more accurate than the rotational degrees of freedom which are expected as most empirical and analytical data are for translational degrees of freedom. The case study also reveals that the relative difference between the numerical simulations and the experimental results are similar to the relative difference between the proposed method and the experiment.

Research of Trajectory Planning of a High-Altitude Long-Range Gliding Unmanned Underwater Vehicle

2014 ◽  
Vol 519-520 ◽  
pp. 1313-1320
Author(s):  
Guang Pan ◽  
Huan Huan Liu
Keyword(s):  
High Altitude ◽  
Long Range ◽  
Degrees Of Freedom ◽  
Underwater Vehicle ◽  
Water Entry ◽  
Dynamic Simulations ◽  
Six Degrees Of Freedom ◽  
Unmanned Underwater Vehicle ◽  
The One ◽  
Air Trajectory

The air trajectory planned studied of the high-altitude long-range gliding unmanned underwater vehicle (HALRG-UUV) based on segmented control strategy is proposed. The aim of this research is twofold. On the one hand, specifying an altitude penetration strategy at the end of the gliding stage was presented with the aim of improving the vehicle glide ratio and achieving penetration. On the other hand, a rocket deceleration strategy was applied to adjust the speed and attitude of the vehicle in order to meet the water entry requirement. Besides, six-degrees-of-freedom mathematical model of the HALRG-UUV was developed based on the Newton’s law. Dynamic simulations of the vehicle under various conditions were performed with the aid of the MATLAB/Simulink codes. The result shows that the vehicle has a glide ratio of 1/9 in the air trajectory and meets the water entry requirement above water. This study lays the foundation for the further research of maneuverability and water impact of the vehicle.

Free fall water entry of a cone in three degrees of freedom

2020 ◽  
Vol 101 ◽  
pp. 102273 ◽  
Author(s):  
Shi-Li Sun ◽  
Yong Cheng ◽  
Jie Cui ◽  
Shi-Yan Sun
Keyword(s):  
Degrees Of Freedom ◽  
Free Fall ◽  
Water Entry ◽  
Three Degrees Of Freedom

General Observations of the Time-Dependent Flow Field Around Flat Plates in Free Fall

2015 ◽  
Author(s):  
Jakob Hærvig ◽  
Anna Lyhne Jensen ◽  
Marie Cecilie Pedersen ◽  
Henrik Sørensen
Keyword(s):  
Degrees Of Freedom ◽  
Model Development ◽  
Digital Camera ◽  
Free Fall ◽  
Flat Plates ◽  
Time Step ◽  
Future Studies ◽  
Six Degrees Of Freedom ◽  
Dependent Flow

The free fall trajectories of flat plates are investigated in order to improve understanding of the forces acting on falling blunt objects. The long term goal is to develop a general applicable model to predict free fall trajectories. Numerically the free fall of a flat plate is investigated using a six degrees of freedom (6DOF) solver and a dynamic mesh. To validate the simulation, the trajectories of aluminium plates falling in water are recorded by digital camera recordings and compared to the simulation. The simulation is able to calculate the motion of the plate within each time step with high accuracy, and thereby allowing the whole trajectory to be predicted with fair accuracy. With the numerical model able to predict the free fall and the complex plate fluid interactions, fluids forces can be extracted for model development in future studies.

Time-Domain Analysis of Floating Bodies with Forward Speed

2002 ◽  
Vol 124 (2) ◽  
pp. 66-73 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Katja Stutz
Keyword(s):  
Nonlinear Wave ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Wave Structure ◽  
Nonlinear Effects ◽  
Time Domain Analysis ◽  
Offshore Structures ◽  
Driving Mechanism ◽  
Forward Speed ◽  
Transient Wave

Broaching, surf-riding, and capsizing of ships and offshore structures are transient wave-structure interactions which imply high risks for crew, vessel and cargo. As nonlinear effects are of great importance, time-domain investigations are indispensable. For unveiling the associated driving mechanism of these critical motions, it is desirable to analyze the cause-reaction chains in detail: Depending on the transient wave elevation, we obtain an instationary pressure distribution on the wetted surface of the cruising vessel. Resulting forces and moments excite vessel motions in six degrees of freedom. Based on the linear panel-method program for transient wave-body interactions, TiMIT [Korsmeyer et al. (1999)], this paper investigates seakeeping characteristics of offshore structures with forward speed. Results are presented in frequency and time domain. The procedure allows to identify critical seaways, and to analyze cause-reaction chains in deterministic wave sequences where critical and steep wave packets are embedded in random seas. The detailed evaluation reveals that large roll and pitch motions are easily reduced by variation of course and speed. For investigating the mechanism of wave/structure interactions, this paper introduces the relevant time-domain methodology, and indicates how nonlinear wave characteristics can be introduced in the time-stepping analysis. In subsequent steps nonlinear wave/structure interactions will also be considered.

Marine Vessel Dynamics Using 6-DOF Simulations

2008 ◽  
Author(s):  
Craig J. Pregnalato ◽  
Kyong-Huhn Lee
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
High Amplitude ◽  
Cfd Simulations ◽  
Six Degrees Of Freedom ◽  
Interface Capturing ◽  
Surface Ship ◽  
Vessel Motion ◽  
Marine Vessels ◽  
Fully Coupled

The response of marine vessels to steady currents and unsteady wave motions is presented using six degrees-of-freedom CFD simulations. The equations governing the fluid flow are coupled with the rigid-body equations of motion to predict the response of surface ships when driven by high-amplitude waves. In addition, the maneuvering performance of a submarine is analysed for a constant heading and depth. Such fully coupled simulations allow the accurate prediction of the hydrodynamic forces acting on the vessel as well as the corresponding vessel motion and are becoming increasingly important from a design standpoint. In these simulations, a high-resolution interface-capturing scheme is used to efficiently capture the dynamics of breaking and overturning waves and to examine their impact on a surface ship. The dynamics of the vessel are investigated in detail with particular emphasis on its angular response (i.e. pitch, roll and yaw).

CFD Simulations of Lifeboat During Sailing Phase in Harsh Weather

2015 ◽  
Author(s):  
Vidar Tregde ◽  
Sverre Steen
Keyword(s):  
Degrees Of Freedom ◽  
Free Fall ◽  
Model Tests ◽  
Full Scale ◽  
Cfd Simulations ◽  
Thrust Coefficient ◽  
Cfd Models ◽  
Calm Water ◽  
Set Up ◽  
Full Scale Tests

A free fall lifeboat is going through several phases during a drop; sliding on the skid, rotation on skid, free fall, water entry, ventilation, maximum submergence, resurfacing and the sailing phase. In the sailing phase, the engine is running, providing propeller thrust, and the vessel is exposed to wind and waves while trying to run away from the host. CFD simulations of the lifeboat in the sailing phase have been run in regular Stokes 5th order waves, as well as simulations in irregular seas. The regular waves have been set up with different wave heights and wave periods. The set-up of waves have been done to fulfil the requirements in DNV-OS-E406, which is the DNV-GL offshore standard for design of free fall lifeboats. Validation of the CFD models are done with comparison to model tests from calm water tests as well as self-propelled model tests in waves. Results from full scale tests in calm water and in waves are also used in validation of CFD results. The hydrodynamic problem solved for 3 degrees-of-freedom (DOF) free running model in waves with thrust force from propeller is solved using the CFD software Star CCM+. A method for estimating thrust coefficient with a combination of full scale calm water results and results from CFD simulations is presented. The CFD simulations have shown to give acceptable accuracy for lifeboat in a seaway. Further, the CFD simulations have shown to be very useful for demonstrating fulfilment of requirements in the offshore standard for lifeboats in the sailing phase.

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