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.

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 MEASUREMENTS OF FORCES ON DOLOS ARMOR UNITS AT PROTOTYPE SCALE

1988 ◽  
Vol 1 (21) ◽  
pp. 174 ◽  
Author(s):  
Gary L. Howell
Keyword(s):  
Degrees Of Freedom ◽  
Bottom Layer ◽  
Core Material ◽  
Crescent City ◽  
Side Scan Sonar ◽  
Six Degrees Of Freedom ◽  
Wave Measurements ◽  
A Site ◽  
Wave Induced

In-situ measurements of the structural bending moments and torque about the shank-fluke interface of the dolos armor unit have been made for 42-ton (36-metric tonne) dolosse at Crescent City, California jetty. The measurements include the static loads on the dolosse as well as wave induced forces. The data were obtained from internal strain gages cast into the dolos during construction along with a special data acquisition system. The measurement system was also capable of capturing impact forces caused by dolos rocking or movement. Measurements were made during the winter storm seasons from January 1987 through May 1988. Coincident with the structural measurements, wave height and period were measured at several water depths approaching the breakwater, including a site directly in front of the dolos test section. The Crescent City jetty is a shallow water breakwater with depth limited waves in about 10 meters of water depth. The structural measurements were made from 14 dolos units arranged in a rectangular section on the top layer of the trunk portion of the jetty. Four of these dolosse are also instrumented with an accelerometer platform to measure motion with six degrees of freedom. In addition, there are three instrumented dolosse on the bottom layer of the breakwater. These dolosse measure the static stress due to the units placed on top of them, as well as pulsating forces. The structural and wave measurements, reported here, are supplemented with hydrostatic pore pressure measurements in the core material of the breakwater, and by aerial photogrammetric motion analysis (Kendall, 1988), land based surveys, boudary condition surveys, hydrographic surveys, and side scan sonar surveys.

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.

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.

The Analysis of Motions of Semisubmersible Drilling Vessels in Waves

1970 ◽  
Vol 10 (03) ◽  
pp. 311-320 ◽  
Author(s):  
Ben G. Burke
Keyword(s):  
Mathematical Model ◽  
Test Data ◽  
Model Test ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Basic Principles ◽  
Six Degrees Of Freedom ◽  
Drilling Equipment ◽  
Wave Response ◽  
The Mathematical Model

Abstract A mathematical model was developed to compute the motions of semisubmersible drilling vessels in waves for a wide variety of semisubmersible configurations. The model was derived from a linear representation of motions, ocean waves, and forces. The semisubmersible is represented as a rigid space frame composed of a number of cylindrical members with arbitrary diameters, lengths and orientations. Forces on the semisubmersible are derived from anchorline properties, and hydrostatic hydrodynamic principles. A solution is obtained for motions in six degrees of freedom for a sinusoidal wave train of arbitrary height, period, direction and water depth. Results from the analysis of three semisubmersibles are compared with results from available model test data to verily the mathematical model. Introduction An accurate and complete representation of the response of a drilling vessel to waves is a valuable engineering tool for predicting vessel performance and designing drilling equipment. The performance and designing drilling equipment. The wave response for a floating vessel may be obtained to various degrees of accuracy from model tests or analytical means, as described by Barkley and Korvin-Kroukovsky and as applied by Bain. A review of the works cited shows that the evaluation of the wave response for a particular vessel requires considerable time and effort, either in model construction and testing or in computer programming and calculations. In order to reduce programming and calculations. In order to reduce the amount of time and effort required to evaluate a particular vessel, means were investigated to generalize and automate, on a digital computer, methods for evaluating wave response for vessels of arbitrary configuration. The mathematical model described in this paper is the result of such an investigation for semisubmersible-type drilling vessels. The paper presents a general description of the mathematical model and the basic principles and assumptions from which it was derived. The validity of the model is evaluated by comparing results of the analysis of three semisubmersibles with available model test data. MATHEMATICAL MODEL The mathematical model for calculating the motions of a semisubmersible in waves is derived from basic principles and empirical relationships in classical mechanics. All equations are derived for "small amplitude" waves and motions. The nonlinear equations that appear in the problem are replaced by "equivalent" linear equations in order to conform to the linear analysis method used in obtaining a solution. The model is implemented in a computer program that computes vessel response in all six degrees of freedom for a broad range of semisubmersible configurations and wave parameters. The basic elements in the theoretical model are outlined, with a more detailed discussion of the principles and derivations used to obtain the model principles and derivations used to obtain the model presented in the Appendix. presented in the Appendix. SEMISUBMERSIBLE DESCRIPTION AND EQUATIONS OF MOTION The semisubmersible is characterized as a space-frame of cylindrical members and is described geometrically by specifying end-coordinates and diameters for all of the members. Specification of the mass, moments of inertia, center of gravity and floating position are required to complete the description. The six equations of motion for the semisubmersible derive from Newton's second law for a rigid body. These differential equations, when written in matrix form, equate the product of the six-component acceleration vector, {x}, and the inertia matrix, I, to a six-component, force-moment vector, {FT}. SPEJ P. 311

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.

Numerical Simulations of OC3 Spar and OC4 Semi-Submersible Type Platforms Under Extreme Conditions in the East Sea, Korea

2019 ◽  
Author(s):  
Hyunkyoung Shin ◽  
Youngjae Yu ◽  
Thanh Dam Pham ◽  
Junbae Kim ◽  
Rupesh Kumar
Keyword(s):  
Renewable Energy ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Reanalysis Data ◽  
Environmental Data ◽  
Offshore Wind ◽  
East Sea ◽  
Mooring Line ◽  
Six Degrees Of Freedom ◽  
Floating Offshore Wind Turbines

Abstract Since the Paris Conference of the parties in 2015, interest in renewable energy around the world is higher than ever. Korea also has plans to increase the proportion of renewable energy to 20% by 2030 through the renewable energy 3020 policy. Of these, 16.5GW is filled with wind power, the installation area is expanding from land to sea. Among them, some of big plans are using floating offshore wind turbines based on the marine environments in Korea. In this study, numerical simulations of the NREL 5MW wind turbine were performed using NREL FAST V.8. A comparison was made between two types of floaters, spar and semi-submersible, installed 58km off the Ulsan Coast with 150m water depth in the East Sea, Korea. The environmental data were obtained from the Meteorological Administration’s measured data and NASA’s reanalysis data, MERRA-2. Design Load Cases were selected by referring to IEC 61400-3. Maximum moments at both blade root and tower base, six-degrees of freedom motions and three mooring line tensions were compared.

scholarly journals Machine Learning Based Moored Ship Movement Prediction

2021 ◽  
Vol 9 (8) ◽  
pp. 800
Author(s):  
Alberto Alvarellos ◽  
Andrés Figuero ◽  
Humberto Carro ◽  
Raquel Costas ◽  
José Sande ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Meteorological Data ◽  
Weather Conditions ◽  
Gradient Boosting ◽  
Management Decision ◽  
Sea State ◽  
Six Degrees Of Freedom ◽  
Port Authorities ◽  
Management Decision Making ◽  
Safe Working

Several port authorities are involved in the R+D+i projects for developing port management decision-making tools. We recorded the movements of 46 ships in the Outer Port of Punta Langosteira (A Coruña, Spain) from 2015 until 2020. Using this data, we created neural networks and gradient boosting models that predict the six degrees of freedom of a moored vessel from ocean-meteorological data and ship characteristics. The best models achieve, for the surge, sway, heave, roll, pitch and yaw movements, a 0.99, 0.99, 0.95, 0.99, 0.98 and 0.98 R2 in training and have a 0.10 m, 0.11 m, 0.09 m, 0.9°, 0.11° and 0.15° RMSE in testing, all below 10% of the corresponding movement range. Using these models with forecast data for the weather conditions and sea state and the ship characteristics and berthing location, we can predict the ship movements several days in advance. These results are good enough to reliably compare the models' predictions with the limiting motion criteria for safe working conditions of ship (un) loading operations, helping us decide the best location for operation and when to stop operations more precisely, thus minimizing the economic impact of cargo ships unable to operate.

Stepping Response During Constrained and Unconstrained Standing in Moving Environments

2014 ◽  
Vol 156 (A3) ◽  
Keyword(s):  
Degrees Of Freedom ◽  
Ecological Validity ◽  
Platform Motion ◽  
Six Degrees Of Freedom ◽  
Limited Experience ◽  
Wave Induced ◽  
Stepping Response ◽  
Platform Motions

The purpose of this study was to determine the differences in human stepping response reaction between constrained and unconstrained standing while being exposed to simulated wave-induced platform motions. Twenty subjects (10 male and 10 female), with limited experience recreating or working in motion-rich environments, performed a constrained and an unconstrained standing task on a six-degrees-of-freedom motion bed while being exposed to two different simulated platform motion conditions. Stepping occurrence was greater during unconstrained standing than constrained standing during all three motion conditions. However, no significant differences in platform kinematics were found between stepping cases. These results suggest that stepping occurs more frequently than originally hypothesized. As such, stepping should not be considered as a last resource when all fixed-support options have been exhausted. This should be taken into consideration to ensure ecological validity when developing models to predict stepping occurrence.

Design and analysis of a lightweight lower extremity exoskeleton with novel compliant ankle joints

2021 ◽  
pp. 1-14
Author(s):  
Yong He ◽  
Jingshuai Liu ◽  
Feng Li ◽  
Wujing Cao ◽  
Xinyu Wu
Keyword(s):  
Lower Extremity ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Theoretical Models ◽  
Six Degrees Of Freedom ◽  
Movement Performance ◽  
Ankle Joints ◽  
Design Values ◽  
Flexible Deformation ◽  
Limb Rehabilitation

BACKGROUND: The exoskeleton for lower limb rehabilitation is an uprising field of robot technology. However, since it is difficult to achieve all the optimal design values at the same time, each lower extremity exoskeleton has its own focus. OBJECTIVE: This study aims to develop a modular lightweight lower extremity exoskeleton (MOLLEE) with novel compliant ankle joints, and evaluate the movement performance through kinematics analysis. METHODS: The overall structure of the exoskeleton was proposed and the adjustable frames, active joint modules, and compliant ankle joints were designed. The forward and inverse kinematics models were established based on the geometric method. The theoretical models were validated by numerical simulations in ADAMS, and the kinematic performance was demonstrated through walking experiments. RESULTS: The proposed lower extremity offers six degrees of freedom (DoF). The exoskeleton frame was designed adjustable to fit wearers with a height between 1.55 m and 1.80 m, and waist width from 37 cm to 45 cm. The joint modules can provide maximum torque at 107 Nm for adequate knee and hip joint motion forces. The compliant ankle can bear large flexible deformation, and the relationship between its angular deformation and the contact force can be fitted with a quadratic polynomial function. The kinematics models were established and verified through numerical simulations, and the walking experiments in different action states have shown the expected kinematic characteristics of the designed exoskeleton. CONCLUSIONS: The proposed MOLLEE exoskeleton is adjustable, modular, and compliant. The designed adjustable frame and compliant ankle can ensure comfort and safety for different wearers. In addition, the kinematics characteristics of the exoskeleton can meet the needs of daily rehabilitation activities.

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