A comparative study on the behaviour of free-fall lifeboat launching from a skid and from a hook

2000 ◽  
Vol 214 (2) ◽  
pp. 359-370 ◽  
Author(s):  
M Reaz H Khondoker ◽  
M Arai
Keyword(s):  
Numerical Simulation ◽  
Dynamic Response ◽  
Comparative Study ◽  
Impact Force ◽  
Free Fall ◽  
Water Entry ◽  
Hydrodynamic Forces ◽  
Response Criteria ◽  
Risk Of Injury ◽  
Tremendous Impact

There are two commonly used launching methods of free-fall lifeboats: from a skid and from a hook. A free-fall lifeboat, whether it is released from a skid or from a hook, experiences tremendous impact when it enters the water. This impact force, together with other hydrostatic and hydrodynamic forces and moments, affects the motions and accelerations of the boat considerably. In this paper, a comparative study on the behaviours of the skid and hook launching of free-fall lifeboats has been presented. Numerical simulation for different launching methods has been used as a tool to obtain trajectories of the lifeboat for different launching conditions. Also polar diagrams of accelerations are drawn using the data computed for the same conditions. Dynamic response criteria have been used in order to evaluate the risk of injury to the occupants during water entry of the lifeboat.

scholarly journals Impact Force of Free-fall Lifeboats at Water Entry

1994 ◽  
Vol 90 (0) ◽  
pp. 165-173
Author(s):  
Kazuo HITOMI ◽  
Osamu MIYATA
Keyword(s):  
Impact Force ◽  
Free Fall ◽  
Water Entry

scholarly journals Parametric Study on the Free-Fall Water Entry of a Sphere by Using the RANS Method

2019 ◽  
Vol 7 (5) ◽  
pp. 122
Author(s):  
Pengyao Yu ◽  
Cong Shen ◽  
Chunbo Zhen ◽  
Haoyun Tang ◽  
Tianlin Wang
Keyword(s):  
Impact Velocity ◽  
Impact Force ◽  
Free Fall ◽  
Water Entry ◽  
Time Step ◽  
Measuring Device ◽  
Mesh Density ◽  
The Impact ◽  
Peak Value ◽  
Rans Method

Motivated by the application of water-entry problems in the air-drop deployment of a spherical oceanographic measuring device, the free-fall water entry of a sphere was numerically investigated by using the transient Reynolds-averaged Navier–Stokes (RANS) method. A convergence study was carried out, which accounts for the mesh density and time-step independence. The present model was validated by the comparison of non-dimensional impact force with previous experimental and numerical results. Effects of parameters, such as impact velocity, radius, and mass of the sphere on the impact force and the acceleration of the sphere, are discussed. It is found that the peak value of the non-dimensional impact force is independent of the impact velocity and the radius of the sphere, while it depends on the mass of the sphere. By fitting the relationship between the peak value of the non-dimensional impact force and the non-dimensional mass, simplified formulas for the prediction of peak values of the impact force and the acceleration were achieved, which will be useful in the design of the spherical oceanographic measuring device.

Reliable and Efficient Injury Assessment for Free-Fall Lifeboat Occupants During Water Entry: Correlation Study Between Lifeboat Acceleration Indicators and Simulated Human Injury Responses

2014 ◽  
Author(s):  
E. van Dam ◽  
J. Uittenbogaard ◽  
S. A. Reinholdtsen ◽  
S. Fouques ◽  
T. Sauder
Keyword(s):  
Injury Risk ◽  
Free Fall ◽  
Weather Conditions ◽  
Correlation Study ◽  
Water Entry ◽  
Severe Weather ◽  
Risk Of Injury ◽  
Alternative Methodology ◽  
Injury Assessment ◽  
Human Injury

The evacuation of personnel from an offshore installation in severe weather conditions is generally ensured by free-fall lifeboats. During the water entry phase of the launch, the lifeboat may be subject to large acceleration loads that may cause harmful acceleration-induced loads on the occupants. The present/common methodology for assessing the occupant safety of free-fall lifeboats uses one single characteristic launch to perform injury risk analysis for a given free-fall lifeboat launch condition that includes e.g. weather conditions, lifeboat and host installation loading conditions. This paper describes an alternative methodology to fully assess the risk of injury for lifeboat occupants during water entry by introducing a correlation model between acceleration load indicators and injury responses. The results are presented in terms of seating matrices showing critical seat rows, in which the probability of being injured exceeds a pre-defined threshold.

Analysis and Numerical Simulation on Dynamic Response of Buried Pipeline Caused by Rock Fall Impaction

2012 ◽  
Author(s):  
Hongyuan Jing ◽  
Qinglu Deng ◽  
Jianbin Hao ◽  
Bing Han ◽  
Liangliang Li
Keyword(s):  
Numerical Simulation ◽  
Dynamic Response ◽  
Cross Section ◽  
Impact Force ◽  
Equivalent Stress ◽  
Rock Fall ◽  
Major Influence ◽  
Buried Pipeline ◽  
Stress Concentration Region ◽  
The Impact

Theoretical analysis methods are discussed to estimate additional stresses of shallow buried oil and gas pipeline caused by rock fall impaction. The process of impaction is simulated using finite elements software, in the model a 1 m3 square shape falling hard rock impacts soil ground upright of pipe with a vertical velocity, and dynamic response of pipeline is analyzed. The impact force, soil additional stresses, pipe displacement and additional stresses in the impaction process are studied. The effect of pipeline buried depth and rock velocity to the impaction also discussed. Results show that the impaction process is very short and the duration is about 10−3∼10−2s. The maximum impact force has approximately direct ratio with the velocity of rock. The additional vertical stress in soil caused by impaction load has a stress concentration region near the surface of pipe, and its distribution has the similar pattern with that in static load, but has a faster attenuation from the impaction center to sidewall. The most dangerous pipe cross-section appears in the underside of impaction center, and the maximum additional equivalent stress appears in the top of the cross-section, and has an approximately direct ratio with the velocity of rock if other impaction conditions are confirmed. The buried depth of pipeline has major influence to impaction. Large thickness of soil cover has marked effect on improve the protection of pipeline. According the study, shallow buried pipeline has weak defense to rock fall. The additional internal force and stress of pipeline caused by impaction of rock fall can be approximately estimated using theoretical methods or numerical simulation.

Numerical Invertigation of Water Entry of a Subsea Module With Deflated Cavity Shells

2020 ◽  
Author(s):  
Yingfei Zan ◽  
Ruinan Guo ◽  
Lihao Yuan ◽  
Fuxiang Huang ◽  
Dongchun Kang
Keyword(s):  
Numerical Simulation ◽  
Free Surface ◽  
Flow Field ◽  
Stokes Equations ◽  
Water Entry ◽  
Hydrodynamic Forces ◽  
Operating Conditions ◽  
Frame Structure ◽  
Navier Stokes ◽  
Navier Stokes Equations

Abstract In subsea installation operations, the hydrodynamic forces on the subsea module are important considerations when designing the structure and choosing slings. In this paper, the hydrodynamic forces and flow field of a subsea module with deflated cavity shells during forced water entry operation were investigated numerically. The numerical simulation was carried out based on Reynolds-averaged Navier–Stokes equations, with a constant lowering velocity of the module. The results of the numerical simulation were validated by experimental data and they showed good agreement. The relationship between hydrodynamic forces and draft was presented. Furthermore, the slamming positions, free surface variation, pressure variation in deflated cavity shells, slamming coefficient and the influence of holes were studied based on flow field scenes. It was found that the hydrodynamic forces varied with draft non-linearly. Moreover, the change of draft altered the form of the free surface due to the complex steel frame structure of deflated cavity shells. The present study can be further extended to assess the operating conditions of lifting operations and to advise on the design of the subsea module.

Numerical simulation of the water entry of a structure in free fall motion

2014 ◽  
Vol 13 (2) ◽  
pp. 173-177 ◽  
Author(s):  
Qingtong Chen ◽  
Baoyu Ni ◽  
Shuping Chen ◽  
Jiangguang Tang
Keyword(s):  
Numerical Simulation ◽  
Free Fall ◽  
Water Entry

Effects of CG Location on the Launch Behavior of Free-Fall Lifeboats

1995 ◽  
Vol 117 (2) ◽  
pp. 133-136 ◽  
Author(s):  
J. K. Nelson ◽  
D. J. Fallon ◽  
T. J. Hirsch
Keyword(s):  
Mass Distribution ◽  
Quantitative Data ◽  
Free Fall ◽  
Water Entry ◽  
Offshore Platforms ◽  
Risk Of Injury

The free-fall lifeboat was developed to reduce the risk of injury during evacuation in a maritime emergency. It is a generally accepted concept for lifesaving appliances that currently is in use on many ships and offshore platforms. Three concerns during launch of these lifeboats are the attitude of the boat at water entry, the headway immediately after water entry, and the acceleration forces to which the occupants are subjected. Limited quantitative data is available about the behavior of the boats during launch and, in particular, on the effects of mass distribution on the launch behavior of free-fall lifeboats. The purpose of this paper is to discuss quantitatively the launch behavior of free-fall lifeboats, with particular emphasis on the effects of changes in the location of the CG.

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