Computing Acceleration Loads on Free-Fall Lifeboat Occupants: Consequences of Including Nonlinearities in Water Waves and Mother Vessel Motions

2010 ◽  
Author(s):  
Neil Luxcey ◽  
Se´bastien Fouques ◽  
Thomas Sauder
Keyword(s):  
Water Waves ◽  
Three Dimensional ◽  
Free Fall ◽  
Momentum Conservation ◽  
Irregular Waves ◽  
Stokes Waves ◽  
Induced Motion ◽  
Wave Models ◽  
Wave Induced ◽  
The Impact

The safety of occupants in free-fall lifeboats (FFL) launched from a skid is addressed, and the focus is on numerical evaluation of acceleration loads during water impact. This paper investigates the required level of detail when modeling the physics of a lifeboat launch in waves. The first part emphasizes the importance of the non-linearity of the wave surface. Severity of impacts in linear (Airy) waves is compared to impacts in regular Stokes waves of the 5th order. Correspondingly, severity of impacts in irregular waves of the 2nd order is statistically compared to impacts in linear irregular waves. Theory of the two wave models are also briefly presented. The second part discusses the importance of a more detailed modeling of the launching system. This concerns especially cases for which damage to the mother vessel induces major lifeboat heel angles. A three-dimensional skid model is presented, along with validation against experimental measurements. In addition, the wave induced motion of the mother vessel is included. Consequences on the severity of the impact of the lifeboat in regular waves are discussed. This study is based on MARINTEK’s impact simulator for free-fall lifeboats, in which slamming loads are evaluated based on momentum conservation, a long wave approximation, and a von Karman type of approach. It is coupled here to the SIMO software, also developed at MARINTEK. Performance of this coupling is discussed.

Theoretical Study of the Water Entry of a Body in Waves: Application to Safety of Occupants in Free-Fall Lifeboats

2009 ◽  
Author(s):  
Thomas Sauder ◽  
Se´bastien Fouques
Keyword(s):  
Water Waves ◽  
Degrees Of Freedom ◽  
Mass Matrix ◽  
Free Fall ◽  
Theoretical Method ◽  
Emergency Evacuation ◽  
Momentum Conservation ◽  
The Body ◽  
Water Impact ◽  
The Impact

The safety of occupants in free-fall lifeboats (FFL) during water impact is addressed. The first part of the paper describes a theoretical method developed to predict the trajectory in six degrees of freedom of a body entering water waves. Slamming forces and moments are computed, based on momentum conservation, long wave approximation and a von Karman type of approach. The added mass matrix of the body is evaluated for impact conditions by a boundary element method. The second part of the paper focuses on the application of the method to free-fall lifeboats, which are used for emergency evacuation of oil platforms or ships. Acceleration loads on FFL occupants during water impact are dependent on numerous parameters, especially the hull shape, the mass distribution, the wave heading relative to the lifeboat, and the impact point on the wave surface. Assessing operational limits of FFL by means of model tests only has therefore been costly and time consuming. This issue is addressed here by applying the theoretical method described in the first part. The model has been validated for FFL through extensive model testing in calm water and regular waves, and statistical estimates of acceleration levels for lifeboat occupants, as well as acceleration time series were obtained that can be used as inputs to numerical human response models.

scholarly journals Water waves, nonlinear Schrödinger equations and their solutions

1983 ◽  
Vol 25 (1) ◽  
pp. 16-43 ◽  
Author(s):  
D. H. Peregrine
Keyword(s):  
Water Waves ◽  
Rational Solution ◽  
Three Dimensional ◽  
Length Scale ◽  
Nls Equation ◽  
Nonlinear Water Waves ◽  
Weakly Nonlinear ◽  
Nonlinear Schrödinger ◽  
Wave Induced ◽  
Modulation Length

AbstractEquations governing modulations of weakly nonlinear water waves are described. The modulations are coupled with wave-induced mean flows except in the case of water deeper than the modulation length scale. Equations suitable for water depths of the order the modulation length scale are deduced from those derived by Davey and Stewartson [5] and Dysthe [6]. A number of ases in which these equations reduce to a one dimensional nonlinear Schrödinger (NLS) equation are enumerated.Several analytical solutions of NLS equations are presented, with discussion of some of their implications for describing the propagation of water waves. Some of the solutions have not been presented in detail, or in convenient form before. One is new, a “rational” solution describing an “amplitude peak” which is isolated in space-time. Ma's [13] soli ton is particularly relevant to the recurrence of uniform wave trains in the experiment of Lake et al.[10].In further discussion it is pointed out that although water waves are unstable to three-dimensional disturbances, an effective description of weakly nonlinear two-dimensional waves would be a useful step towards describing ocean wave propagation.

scholarly journals Three-dimensional surface gravity waves of a broad bandwidth on deep water

2021 ◽  
Vol 926 ◽  
Author(s):  
Yan Li
Keyword(s):  
Deep Water ◽  
Water Waves ◽  
Order Approximation ◽  
Three Dimensional ◽  
Finite Depth ◽  
Second Order ◽  
Leading Order ◽  
Broad Bandwidth ◽  
Stokes Waves ◽  
Deep Water Waves

A new nonlinear Schrödinger equation (NLSE) is presented for ocean surface waves. Earlier derivations of NLSEs that describe the evolution of deep-water waves have been limited to a narrow bandwidth, for which the bound waves at second order in wave steepness are described in leading-order approximations. This work generalizes these earlier works to allow for deep-water waves of a broad bandwidth with large directional spreading. The new NLSE permits simple numerical implementations and can be extended in a straightforward manner in order to account for waves on water of finite depth. For the description of second-order waves, this paper proposes a semianalytical approach that can provide accurate and computationally efficient predictions. With a leading-order approximation to the new NLSE, the instability region and energy growth rate of Stokes waves are investigated. Compared with the exact results based on McLean (J. Fluid Mech., vol. 511, 1982, p. 135), predictions by the new NLSE show better agreement than by Trulsen et al. (Phys. Fluids, vol. 12, 2000, pp. 2432–2437). With numerical implementations of the new NLSE, the effects of wave directionality are investigated by examining the evolution of a directionally spread focused wave group. A downward shift of the spectral peak is observed, owing to the asymmetry in the change rate of energy in a more complex manner than that for uniform Stokes waves. Rapid oblique energy transfers near the group at linear focus are observed, likely arising from the instability of uniform Stokes waves appearing in a narrow spectrum subject to oblique sideband disturbances.

scholarly journals Assessing the Impact of the Tropopause on Mountain Waves and Orographic Precipitation Using Linear Theory and Numerical Simulations

2015 ◽  
Vol 72 (2) ◽  
pp. 803-820 ◽  
Author(s):  
Nicholas Siler ◽  
Dale Durran
Keyword(s):  
Numerical Simulations ◽  
Linear Theory ◽  
Three Dimensional ◽  
Orographic Precipitation ◽  
Two Dimensional ◽  
Tropopause Height ◽  
Atmospheric Conditions ◽  
Mountain Waves ◽  
Wave Induced ◽  
The Impact

Abstract The partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms, but its impact on orographic precipitation has not been addressed. Here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and, in turn, orographic precipitation. Relative to the no-tropopause case, wave-induced ascent above the windward slope of a two-dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves—defined here as the “nondimensional tropopause height” . In idealized simulations of flow over both two-dimensional and three-dimensional ridges, variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions. The sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and strength of leeside descent, with significant impacts on the distribution of precipitation across the range (i.e., the rain-shadow effect). Using a modified version of Smith and Barstad’s orographic precipitation model, variations in are found to produce significant rain-shadow variability in the Washington Cascades, perhaps explaining some of the variability in rain-shadow strength observed among Cascade storms.

Numerical Investigation of Hydrodynamic Performance of a Light Buoy with Different Mooring Configurations in Regular Waves

2021 ◽  
pp. 1-26
Author(s):  
Xin Li ◽  
Yimei Chen ◽  
Lilei Mao ◽  
Huiyu Xia
Keyword(s):  
Experimental Data ◽  
Yangtze River ◽  
Coupled Model ◽  
Coupling Model ◽  
Numerical Approach ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Regular Waves ◽  
Induced Motion ◽  
Wave Induced

Abstract The single-moored light buoys employed in the lower reaches of the Yangtze River play an important role in indicating ship navigation and ensuring safety. To clarify the interaction between waves and floating buoys moored to the riverbed, this paper develops a numerical approach to investigate the wave-induced motion performance of a light buoy and reveal the effects of different mooring configurations to extend its service life. A new open-source SPH based numerical model named DualSPHysics coupled with MoorDyn is implemented. This coupled model is validated by simulating the motion of a moored rectangle buoy in regular waves, and compared with experimental data and the numerical results of REEF3D code, a new mesh-based CFD model. The validation results show that the coupled model reproduces experimental data well and has a smaller deviation in comparison with REEF3D. Then the coupling model is applied to simulate the hydrodynamic performance of the real-size light buoy employed in Yangtze River and investigate effects of encounter angle between wave propagation direction and mooring chain. The results demonstrate the capability of this coupled mooring model to simulate the motion of a moored buoy in regular waves, and this numerical approach will be extended to simulate the light buoy in more complex environments such as irregular waves, flow or extreme weather in further work.

A Method to Upgrade Iceberg Velocity Statistics to Include Wave-Induced Motion

1987 ◽  
Vol 109 (3) ◽  
pp. 278-286 ◽  
Author(s):  
J. H. Lever ◽  
D. Sen
Keyword(s):  
Three Dimensional ◽  
Interaction Model ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Grand Banks ◽  
Drilling Rig ◽  
Velocity Statistics ◽  
Impact Risk ◽  
Induced Motion ◽  
Wave Induced

Iceberg impact design loads for offshore structures can be estimated by incorporating an ice/structure interaction model in a probabilistic framework, or risk analysis. The relevant iceberg and environmental parameters are input in statistical form. Iceberg velocity statistics are usually compiled from drilling rig radar reports, and hence represent estimates of average hourly drift speeds. Yet it is the instantaneous ice velocity which is the relevant input to the simulation of the iceberg/structure collision process. Thus, risk analyses based on mean drift speed distributions will only yield valid results for the subset of conditions where wave-induced iceberg motion is negligible. This paper describes a method which, for the first time, systematically accounts for wave-induced motion in iceberg impact risk analyses. A linear three-dimensional potential flow model is utilized to upgrade iceberg velocity statistics to include the influence of Grand Banks sea-state conditions on instantaneous ice motion. The results clearly demonstrate the importance of including wave-induced motion in iceberg impact risk analyses.

scholarly journals Double-Diffusive Convection in a Stochastic Shear

2015 ◽  
Vol 45 (12) ◽  
pp. 3155-3167 ◽  
Author(s):  
Timour Radko ◽  
James Ball ◽  
John Colosi ◽  
Jason Flanagan
Keyword(s):  
Internal Waves ◽  
Phase Distribution ◽  
Three Dimensional ◽  
Vertical Shear ◽  
Two Dimensional ◽  
Salt Fingers ◽  
Diffusive Dynamics ◽  
Wave Induced ◽  
The Impact ◽  
Double Diffusive

AbstractAn attempt is made to quantify the impact of stochastic wave–induced shears on salt fingers associated with internal waves in the ocean. The wave environment is represented by the superposition of Fourier components conforming to the Garrett–Munk (GM) spectrum with random initial phase distribution. The resulting time series of vertical shear are incorporated into a finger-resolving numerical model, and the latter is used to evaluate the equilibrium diapycnal fluxes of heat and salt. The proposed procedure makes it possible to simulate salt fingers in shears that are representative of typical oceanic conditions. This study finds that the shear-induced modification of salt fingers is largely caused by near-inertial motions. These relatively slow waves act to align salt fingers in the direction of shear, thereby rendering the double-diffusive dynamics effectively two-dimensional. Internal waves reduce the equilibrium vertical fluxes of heat and salt by a factor of 2 relative to those in the unsheared three-dimensional environment, bringing them close to the values suggested by corresponding two-dimensional simulations.

scholarly journals A Three-Dimensional Numerical Model with an L-Type Wave-Maker System for Water Wave Simulations by the Moving Boundary Method

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 161 ◽  
Author(s):  
Wei Jia ◽  
Shuxue Liu ◽  
Jinxuan Li ◽  
Yuping Fan
Keyword(s):  
Numerical Model ◽  
Water Waves ◽  
Moving Boundary ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Irregular Waves ◽  
Wave Tank ◽  
Type Wave ◽  
Boundary Method ◽  
Wave Maker

A three-dimensional numerical wave tank was developed based on Reynolds averaged Navier–Stokes equations and the volume of fluid method. The moving boundary method is adopted in this model to generate water waves. Piston-type wave-makers are mimicked for the total replication of the physical wave tank conditions. Two-dimensional regular and irregular waves are simulated, with the capability to trigger the active wave absorption algorithm. The two-sided wave-maker system with L-type arrangement is adopted in this model to expand the effective wave areas for three-dimensional waves. Oblique regular waves and multidirectional random waves are simulated, yielding a good agreement with theoretical solutions. The results indicate that this numerical model is an effective tool to provide finer details or complement data unavailable due to the physical setting of a tank experiment.

scholarly journals TURBULENT OSCILLATORY FLOW OVER RIPPLES AT HIGH REYNOLDS NUMBERS FOR PETA-SCALE SIMULATIONS

2018 ◽  
pp. 95
Author(s):  
Guillermo Oyarzun ◽  
Athanassios Dimas
Keyword(s):  
Coastal Zone ◽  
High Performance ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Small Scale ◽  
Poisson Solver ◽  
Execution Model ◽  
High Reynolds ◽  
Wave Induced ◽  
The Impact

Surface waves in the coastal zone induce oscillatory flow motions in the vicinity of the seabed. These wave-induced coastal flows interact with the sandy seabed and modify the bed shape by generating coherent small-scale bed structures, which are generally known as ripples. The presence of ripples in oscillatory flows is important due to the impact they have on the seabed roughness and how they affect the near-bed boundary layer hydrodynamics. Simulations of higher and more real-scale Reynolds number (Re) require the use of supercomputers in order to obtain results in a reasonable amount of time. However, the constant evolution of the computing facilities makes the development of parallel algorithms a rather difficult task. The objective of the proposed research is to advance in the comprehension of coastal processes utilizing high performance computing (HPC) for the numerical simulation of the three-dimensional, turbulent flow, which is induced in the coastal zone by wave propagation. In particular, our CFD code (SimuCoast) has been developed using a hybrid MPI+OpenACC execution model that increases its scalability and allows it to engage the vast majority of high-end supercomputers. Special attention has been paid in the parallelization strategy of the Poisson solver that is the most computational demanding operation.

scholarly journals Ocean glider flight in the presence of surface waves

2021 ◽  
Author(s):  
Lucas M. Merckelbach ◽  
Jeffrey R. Carpenter
Keyword(s):  
Surface Waves ◽  
Water Waves ◽  
Wave Motion ◽  
Near Surface ◽  
Ocean Surface Waves ◽  
Induced Motion ◽  
Wave Induced ◽  
Pressure Perturbations ◽  
Measured Pressure ◽  
Effect Of Surface

AbstractAutonomous, buoyancy-driven ocean gliders are increasingly used as a platform for the measurement of turbulence microstructure. In the processing of such measurements, there is a sensitive (quartic) dependence of the turbulence dissipation rate, ϵ, on the speed of flow past the sensors, or alternatively, the speed of the glider through the ocean water column. The mechanics of glider flight is therefore examined by extending previous flight models to account for the effects of ocean surface waves. It is found that due to the relatively small buoyancy changes used to drive gliders, the surface wave-induced motion, superimposed onto the steady-state motion, follows to a good approximation the motion of the wave orbitals. Errors expected in measuring ϵ at the ocean near-surface due to wave-induced relative velocities are generally less than 10%. However, pressure perturbations associated with the wave motion can be significant when using the glider-measured pressure signal to infer the glider vertical velocity. This effect of surface waves is only present in the shallow water regime, and can also affect glider depth measurements. It arises from an incomplete cancellation of the wave-induced pressure perturbation with the hydrostatic component due to vertical glider displacements, whereas for deep-water waves this cancellation is complete.

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